Search

Sugarcane yellow mite, Oligonychus sacchari (Prostigmata: Tetranychidae), is one of the main detrimental pests in sugarcane growing areas in Iran. The early populations of mites colonize on the lower surfaces of sugarcane leaves. Because of high reproductive potential, multi-generation are produced per year under warm and humid temperature during sugarcane growing season. This pest imposes economic damage to sugar industries. Field trials were conducted on evaluation of varietal resistance of five sugarcane varieties against yellow mite during two successive seasons 2014–2015 and 2015–2016 in sugarcane fields at Salman Farsi Agro-industry unit in Ahwaz, Iran. After initiation of O. sacchari activity in fields, in each plot, fifteen leaves were selected at random and number of living mites was recorded. The results showed that there were significant differences among tested varieties. The variety IRC99-02 was the most susceptible in tested years by CP57-614 in the total number of living mites and dry-leaf even though CP69-1062 was the most resistant variety.

BGPI : équipe 2 / 5; International audience; Efficient strategies for limiting the impact of pathogens on crops require a good understanding of the factors underlying the evolution of compatibility range for the pathogens and host plants, i.e., the set of host genotypes that a particular pathogen genotype can infect and the set of pathogen genotypes that can infect a particular host genotype. Until now, little is known about the evolutionary and ecological factors driving compatibility ranges in systems implicating crop plants. We studied the evolution of host and pathogen compatibility ranges for rice blast disease, which is caused by the ascomycete Magnaporthe oryzae. We challenged 61 rice varieties from three rice subspecies with 31 strains of M. oryzae collected worldwide from all major known genetic groups. We determined the compatibility range of each plant variety and pathogen genotype and the severity of each plant pathogen interaction. Compatibility ranges differed between rice subspecies, with the most resistant subspecies selecting for pathogens with broader compatibility ranges and the least resistant subspecies selecting for pathogens with narrower compatibility ranges. These results are consistent with a nested distribution of R genes between rice subspecies.

We hypothesized that inducing systemic resistances can contribute to the control of the nematode Rotylenchulus reniformis in pineapple. In greenhouse experiments conducted in Martinique, the pineapple cultivars Smooth Cayenne and MD-2 were treated with methyljasmonate (JAME) and salicylic acid (SA), elicitors of induced systemic resistance (ISR) and systemic acquired resistance (SAR). The efficacy of the elicitors was tested by inoculating plantlets grown in individual pots with a monospecific population of R. reniformis reared on Vigna unguiculata . The final nematode populations, 45 days after inoculation on MD-2 treated with JAME were reduced by 67.0% ( p = 0.006). Nematode populations on MD-2 plants treated with SA were reduced by 55.8% ( p = 0.016). Nematode populations on SC were not reduced by the elicitors. In a second experiment, using split-root systems, JAME was applied to MD-2 plantlets and enzymatic activities involved in plant defense and stress responses were monitored for 14 h after treatment. Additional pots were inoculated with nematodes 24 h after JAME treatment and examined ten days later. Transient stress was observed along with an increase in enzymatic response after inoculation with nematodes. These results showed that the MD-2 was primed through an ISR by JAME. The question now arises whether ISR can be specifically induced only in certain pineapple cultivars. Results are discussed from the perspective of introducing new strategies to manage pineapple nematodes.

Corn (Zea mays) is widely cultivated for human food and animal feed and also provides an ecosystem service as a trap crop for the corn earworm Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) in tomato cropping systems. To be able to use corn as a trap crop for H. zea and to prevent it turning into a source of infestation, varieties are needed that are both attractive and resistant to H. zea. The main objective of this study was to compare the attractiveness to oviposition by H. zea and the resistance to H. zea of 10 sweet corn varieties in field conditions. We found Java, Garrison, Nova and Shinerock varieties that were both attractive to H. zea with a similar or higher number of eggs laid on silks than in the susceptible corn varieties, and resistant to H. zea, with fewer larvea per ear than in susceptible corn varieties. These varieties provide favorable habitats for generalist predators, ants, spiders, minute pirate bugs and lady beetles, which may account for their “dead-end” properties. Tropical farmers now have sweet corn varieties that can serve both as cash crops and as trap crops for H. zea.

This study focuses on the resistance of sugarcane, Saccharum spec. (Poaceae), to the sugarcane aphid, Melanaphis sacchari (Zehntner) (Hemiptera: Aphididae), which vectors Sugarcane yellow leaf virus (SCYLV). Resistance was characterized in cultivar R 365, using a 3-year field trial and laboratory experiments on potted plantlets and excised leaves. R 365 reduced aphid populations in the field by antixenosis and antibiosis. Using the electrical penetration graph technique, we detected delayed aphid salivation in phloem and inhibition of passive phloem sap uptake in R 365. The resistance factors also proved to be effective against the corn leaf aphid, Rhopalosiphum maidis (Fitch) (Hemiptera: Aphididae), another vector of SCYLV. (Resume d'auteur)

Applied silicon (Si) can improve resistance of plants to insect attack. We investigated the interactions between soil applied Si, sugarcane cultivar, and three documented feeding/penetration sites (internode, leaf bud, and root primordia), each at three heights (top, middle, and base) on the stalk and their effects on stem borer, Eldana saccharina Walker (Lepidoptera: Pyralidae) performance and the stalk damage it inflicts. Four sugarcane cultivars, treated (Si+) and untreated (Si-) with calcium silicate, were artificially infested with E. saccharina and the larvae were examined 21 days later. Silicon treatment significantly increased stalk Si content in all sugarcane cultivars and, overall, significantly reduced borer growth rate and also reduced stalk damage, particularly at the internode. Borer survival and growth rate and stalk damage were lowest at the internode, particularly in Si+ resistant cultivars. Although the internode had the hardest rind, hardness at each site was not significantly increased by Si+.

International audience; The objective of this study was to analyse the genotypic variability of sugarcane resistance to the main aphid vector of the Sugarcane yellow leaf virus (ScYLV) (Polerovirus, Luteoviridae), Melanaphis sacchari. We assessed the incidence of aphids in a field trial comparing 181 sugarcane cultivars. Based on the percentage of infested leaves, aphid incidence was scored every two weeks during three cropping seasons. Analysis of variance revealed highly significant genotype, and genotype 9 year variance, and high broad sense heritability. Using semivariograms, we showed that the alpha lattice design used in the field trial was able to cope with spatial correlation issues caused by the patchy nature of aphid infestations. Twenty-two aphid resistant cultivars were identified. A laboratory study of the development of M. sacchari on four of these 22 resistant cultivars confirmed the resistant status of three of them. We observed modest positive phenotypic and genetic correlations between the aphid incidence and the incidence of ScYLV. The 22 cultivars resistant to M. sacchari showed twofold lower mean virus incidence than the remaining 159 cultivars. (Résumé d'auteur)

Lors de la realisation d'un programme d'hybridation pour la creation de varietes resistantes a la fusariose, les segregations pour la resistance, ainsi que pour le type et la couleur de la feuille ont ete observees dans les descendances de croisements impliquant les varietes 'Perolera', 'Primavera', 'Roxo de Tefe', 'Guiana, 'Cayenne lisse', 'Perola', 'Puerto Rico' et Ananas bracteatus 'Sao Bento'. Les varietes 'Perolera' et 'Primavera' transmettent leur resistance a la fusariose a l'ensemble de leur descendance et la mortalite des semenceaux infectes artificiellement y est normalement faible. Les croisements entre les varietes susceptibles 'Cayenne lisse' et 'Perola' produisent des descendances entierement susceptibles presentant de tres faibles taux de survie a la fin du test. Ces resultats suggerent un mecanisme genetique simple, probablement un seul gene avec dominance. Les rapports de segregation pour le type de feuille concordent avec les frequences attendues sur base du modele bigenique de Collins et Kerns. Les segregations pour la couleur de la feuille obtenues dans les descendances de la vatiete rouge 'Roxo de Tefe' montrent une heredite monogenique dominante du type feuilles rouge fonce. (Resume d'auteur)

Tropical crop infestation by soil borne parasites (pineapple : Rotylenchulus reniformis and banana : Pratylenchus coffea e ) cann ot be controlled anymore by pes ticides in French Antillas under the new European regulations . Therefore, we investigated the possible contribution of induced systemic resistances ( ISR ) to biocontrol pests and to develop more environmentally friendly agrosystems. In Martinique ( Campus Agro - environnemental Caraïbe ), we are presently testing a strategy based on current knowledge on ISR through interaction between plants and beneficial microorganisms. The investigations are based on four main hypotheses: 1) The inoculum of soil borne parasites can be reduced introducing non - host rotation plants. Cover crops were selected on the basis of several functional traits (non - host status, high biomass), for their contribution to a balanced microfauna in the rhizos phere, and for their positive effect on soil mycorhization potential. 2) The selection of pineapple and banana varieties able to develop ISR AND adapt their metabolism to environmental changes is essential. We found differential responses against nematodes to an ISR inducer (methyljasmonate, 10 - 4 M) in several pineapple and banana varieties and we are now searching for a relation with markers of plant adaptability to environmental changes (genes for cysteine - proteases and their inhibitors phyto - cystatins). 3 ) The successful development of ISR responses is dependent on the capacity of a plant to tolerate abiotic stresses (drought, temperature, salinity...) in addition to the pathogens. As ISR may also be part of the global adaptability of plant metabolism to tol erate abiotic stresses from their habitat, we investigate the possible links between stress level and a plant's capacity to induce efficient ISR against soil - borne parasites ( ongoing ). 4) Pineapple and banana root systems bear diazotrophic bacteria (endoph ytic) that can be used as ISR inducers in the field. Seventy - five and ninety - one diazotrophic bacteria strains (endophytic) respectively for pineapple and banana were isolated from their root systems in different sites in Martinique including organic and i ntensive cropping systems. They are currently being identified (MIDI - FAME and ADNr16S sequencing) and tested as ISR inducers. Our research aims at validating the hypothesis that efficient and consistent systemic resistances to pathogens can be achieved i n the field by using selected varieties tolerant to abiotic stresses.

Plant expression of the entomopathogenic bacteria Bacillus thuringiensis cry gene has reduced the damage created by insect pests in several economically important cultures. For this study, we have conducted genetic transformation of the indica rice 'IRGA 424,' via Agrobacterium tumefaciens, using the B. thuringiensis cry1Aa and cry1B genes, with the objective of obtaining rice plants resistant to the insect pests from this culture. The gene constructions harbor the promoters maize proteinase inhibitor and ubiquitin. The results showed that high concentration of the hormone 2,4-dichlorophenoxyacetic acid and agarose as the gelling agent helped the production of embryogenic calli for the analyzed cultivar. More than 80% of the obtained transformed plants revealed the integration, using polymerase chain reaction, of the cry1Aa and cry1B genes. Analysis of the expression of the heterologous protein by Western blotting revealed the expression of the Cry1B ?elta-endotoxin in IRGA 424 plants transformed with the ubiquitin promoter. Data showed the production and dissemination of a high number of embryogenic calli in addition to obtaining plants transformed with the cry1Aa and cry1B genes until the reproductive phase. The feed bioassays with the transformed plants and Spodoptera frugiperda (JE Smith) larvae indicated high rates of mortality to the insect target. The highest corrected mortality rate achieved under laboratory conditions with Bt-rice plants transformed with the cry1B and cry1Aa genes was 94 and 84%, respectively. Thus, our results demonstrated the great potential of transformed Bt-rice plants in controlling the damage caused by these insect pests in rice paddy fields.

En France, le riz est principalement cultivé en zone méditerranéenne, en Camargue. La riziculture irriguée, avec semis direct, y est majoritairement contrainte par l'occurrence de périodes froides et le risque de salinisation des sols. S'y ajoutent des périodes de vent du nord, froid et sec, qui peuvent intervenir tout au long du cycle cultural (avril-mai à septembre-octobre). Depuis 1988, le Centre de coopération internationale en recherche agronomique pour le développement (Cirad) et le Centre français du riz (CFR), conduisent en Camargue un programme d'amélioration variétale. Il vise à créer des cultivars satisfaisant les producteurs (niveau et régularité de la production), les riziers (rendement industriel et transformation) et les consommateurs (qualités de cuisson et de goût). Les riz cultivés en Camargue appartiennent à la sous-espèce japonica d' Oryza sativa. L'hybridation constitue la base de création de variabilité. Les descendances sont sélectionnées selon la méthode généalogique associée ou non à l'haplodiploïdisation appliquée à la première génération. La sélection assistée par marqueurs a été récemment introduite afin d'améliorer l'efficacité de la sélection vis-à-vis de contraintes comme les maladies cryptogamiques dont l'occurrence, en rapport avec le climat, est erratique. Vingt-cinq (25) variétés ont été inscrites au Catalogue officiel, parmi lesquelles 5 ont connu un succès certain auprès des producteurs. Les avancées obtenues pour l'aptitude à la levée en conditions anaérobies, la tolérance à la pyrale, le format et le caractère aromatique du grain sont discutées. Les perspectives en lien avec l'évolution des objectifs, tels que le contrôle des adventices ou l'adaptation au changement climatique, sont exposées.

Plus de 80 % de la production de café arabica provient d'Amérique latine alors que l'espèce est originaire d'Afrique. La base génétique du caféier Arabica introduite en Amérique latine au XIX e siècle se limite à deux populations peu différentes (Bourbon et Typica). Malgré le handicap d'une base génétique étroite, les chercheurs ont créé dans les années 1950 à 1980 des variétés lignées très bien adaptées à l'intensification de la culture et présentant une qualité considérée comme un standard. Avec l'arrivée de la rouille orangée, des gènes de résistance de l'espèce diploïde C. canephora ont été transférés dans ces variétés améliorées. Des lignées combinant des résistances à plusieurs maladies et présentant une qualité à la tasse équivalente ou inférieure au standard ont été développées dans les années 1980 à 2000. À partir de 1990, face aux nouvelles exigences du marché, de nouvelles variétés hybrides F1 ont été sélectionnées pour l'adaptation à une agriculture écologiquement intensive basée sur l'agroforesterie. Après une vingtaine d'années d'expérimentations en milieux contrôlés ou chez les producteurs, il apparaît que les hybrides F1 produisent 30-60 % de plus que les meilleures lignées en systèmes agroforestiers, sans apport supplémentaire d'engrais. Aujourd'hui, le progrès génétique ainsi créé est plutôt mal diffusé. Dans de nombreux pays, les variétés sont propagées sans aucun contrôle de leur pureté variétale. Aucun catalogue variétal n'existe et les informations qui parviennent aux producteurs sont largement insuffisantes pour qu'ils puissent raisonner leur choix variétal en fonction de leur système de culture ou des exigences du marché. Pour une culture industrielle d'une telle importance économique, la faiblesse des recherches en amélioration génétique pour une filière semencière dynamique est frappante. La raison en est que la production de semences améliorées n'est pas rentable pour le secteur privé. Là où l'État s'est désengagé, il faut donner la possibilité à ce secteur d'investir dans la recherche et dans la production de semences de qualité.

La maladie de la feuille jaune peut entraîner d'importantes pertes de rendement chez la canne à sucre. Elle est causée par le Sugarcane yellow leaf virus (SCYLV, genre : Polerovirus, famille : Luteoviridae), qui est principalement transmis par le puceron Melanaphis sacchari (Zehntner) (Hemiptera : Aphididae). La résistance variétale étant le principal moyen de lutte contre les maladies virales, la caractérisation de sources de résistances efficaces et durables à la maladie de la feuille jaune est un enjeu majeur pour l'amélioration variétale de la canne à sucre. Au cours de cette thèse, la caractérisation la résistance à la maladie de la feuille jaune a été entreprise sous trois angles : i/ l'identification de marqueurs moléculaires associés à la résistance au SCYLV et à Melanaphis sacchari au sein du germplasm cultivé ii/ la caractérisation fine des mécanismes de résistance à M. sacchari chez le cultivar R 365 et iii/ l'évaluation de la diversité génétique des populations de Melanaphis spp. présentes sur la canne à sucre et sur Sorghum spp. L'identification de marqueurs associés à la résistance à la maladie de la feuille jaune a été réalisée par une approche d'association mapping menée sur deux panels de cultivars à la Réunion et en Guadeloupe. Ces deux panels ont été génotypés en utilisant les technologies AFLP et DArT. Leur phénotypage a été réalisé en conditions d'infestation naturelles. Ces travaux ont permis d'identifier 45 haplotypes significativement associés à la résistance à la maladie de la feuille jaune ou à son vecteur. Cinq des haplotypes associés à la réduction de l'incidence du virus ont été co-détectés dans les deux panels de cultivars. Trois haplotypes regroupent des marqueurs associés à la fois à l'incidence du vecteur et à celle du virus. La caractérisation de la résistance à Melanaphis sacchari chez le cultivar R 365 nous a permis de mettre en évidence un effet d'antixénose et un effet d'antibiose. L'étude du comportement alimentaire du puceron par EPG a montré que la résistance agissait à deux niveaux : elle augmente le temps nécessaire à l'établissement dans le phloème, puis empêche l'ingestion passive de sève élaborée durant les huit premières heures. La résistance du cultivar R 365 affecte également Rhopalosiphum maidis (Fitch) (Hemiptera: Aphididae) un autre puceron vecteur du SCYLV. L'étude de la diversité génétique a été basée sur une collecte mondiale de pucerons du genre Melanaphis collectés sur canne à sucre et Sorghum spp. Une étude morphométrique a mis en évidence plusieurs groupes de populations morphologiquement distincts, correspondant aux espèces M. sacchari et M. sorghi. Cependant, le séquençage du locus COI n'a pas permis de discriminer de façon claire les deux espèces. Nous avons développé une banque de microsatellites spécifiques de Melanaphis sacchari, qui a permis de mener l'étude de la diversité génétique des populations en utilisant 10 loci microsatellites polymorphes. La diversité a été étudiée à deux échelles. A une échelle mondiale les populations sont apparues strictement clonales, avec une faible diversité génétique intra zone géographique et une forte structuration par leur localisation géographique. A l'échelle de la Réunion, nous avons mis en évidence une structuration par l'hôte, certains génotypes se trouvant préférentiellement sur canne à sucre ou sur Sorghum verticilliflorum.

The 2010 Beltwide Cotton Conferences provided a new vision of the consequences of about 15 years of widespread and uncoordinated cropping of transgenic cotton in the United States. Insect-resistant and/or herbicide-tolerant cotton varieties modified parasite complexes, namely those of insects and weeds damaging cotton crops. The Conferences have revealed that the adaptation solutions so far proposed make illusory the expectations at the launch of transgenic cotton, in terms of effective pest control, cost reduction, and antagonism between chemical and biotech methods. The USA case points out that the technical and economic sustainability of transgenic varieties must lie in a systemic and coordinated approach.

Les conférences 2010 du Beltwide cotton ont apporté une vision nouvelle sur les conséquences de 15 années d'utilisation massive des variétés de coton transgénique aux Etats-Unis. L'observation des changements dans les complexes d'ennemis des cultures de cotonnier et les solutions recherche´es pour y faire face montrent que les effets positifs proclame´s de l'utilisation de ces varie´te´s se sont évanouies en termes d'efficacité du contrôle des ennemis des cultures, de réduction du coût et d'antagonisme entre voie chimique et voie biotechnologique de ce contrôle. La durabilité technique et économique des variétés transgéniques de´pend de l'approche systémique et coordonnée de leur utilisation.

International audience; The sustainability of Bt-cotton in China, at least along Yellow River Valley, has been questioned, so this paper examines its effectiveness along Yangtze River Valley, where Bt-cotton is also widely sown, to determine what might be the factors beneath the limited or reduced effectiveness being observed. The analysis is based on the data collected for several years from many locations in the Yangtze River Valley Varietal Experiment Network to provide information on the varieties and their agronomic performance, on the control of their GM characteristic, on the expression of the Bt-gene and on chemical control practices against cotton pests.All varieties declared to be Bt-cotton were confirmed to have the Bt-gene, the expression of which was assessed in three ways: through the analysis of Bt-protein production and through indoor and outdoor bioassays. Gene expression varied substantially between varieties and between years for the few varieties which were tested in two subsequent years.The Bt-cotton varieties being sown cannot control bollworms totally even early in the growing season, so surviving larvae could inevitably be observed, and this led farmers (or professionals in charge of supplying technical assistance to farmers) to spray chemicals regardless of the real infestation level. This demonstrates behaviour aimed at eradication of the pests as bollworms seem to be treated chemically more often than is required and far earlier than necessary on the first two generations of H. armigera. The chemical control of the Bt-cotton in Yangtze River Valley hence is not optimal, thus farmers are paying high prices for varieties which are not totally resistant to bollworms and pest control costs are not reduced to the extent that they might expect, lowering the profitability of cotton production. Also chemical protection costs are not decreasing as those pests unaffected by the Bt-gene, mainly but not exclusively sucking ones are requiring more control. This is illustrative of a phenomenon of pest complex shift which deserves more attention in following up the Bt-cotton use.

We conducted an assessment of the stalk damage of the spotted borer, #Chilo sacchariphagus# (Bojer), on 65 cultivars and elite clones under natural infestation conditions in Réunion Island, with the objectives (i) of comparing seven damage measures on the basis of their quantitative genetic parameters and (ii) of studying the relationships between borer resistance and sugarcane yield components. The heritabilities of the damage measures related to counts of borer exit holes were low, whereas the heritabilities of the damage measures related to bored stalks or internodes were high and similar amongst them. The percentage of bored stalks exhibited high phenotypic and genotypic correlations with the other damage measures, and appeared as the best cost effective damage measure. Genetic correlations revealed a negative relationship between resistance to borer and cane yield, due to a relationship of stalk damage with stalk length and (in a lesser extent) with stalk number. No significant genetic relationship between resistance and sugar content parameters was observed.

Silicon (Si) can improve resistance of plants to insect attack and may also enhance tolerance of water stress. This study tested if Si-mediated host plant resistance to insect attack was augmented by water stress. Four sugarcane cultivars, two resistant (N21, N33) and two susceptible (N26, N11) to Eldana saccharina Walker were grown in a pot trial in Si-deficient river sand, with (Si+) and without (Si−) calcium silicate. To induce water stress, irrigation to half the trial was reduced after 8.5 months. The trial was artificially infested with E. saccharina eggs after water reduction and harvested 66 days later. Silicon treated, stressed and non-stressed plants of the same cultivar did not differ appreciably in Si content. Decreases in numbers of borers recovered and stalk damage were not associated with comparable increases in rind hardness in Si+ cane, particularly in water-stressed susceptible cultivars. Overall, Si+ plants displayed increased resistance to E. saccharina attack compared with Si− plants. Borer recoveries were significantly lower in stressed Si+ cane compared with either stressed Si− or non-stressed Si− and Si+ cane. Generally, fewer borers were recovered from resistant cultivars than susceptible cultivars. Stalk damage was significantly lower in Si+ cane than in Si− cane, for N21, N11 and N26. Stalk damage was significantly less in Si+ combined susceptible cultivars than in Si− combined susceptible cultivars under non-stressed and especially stressed conditions. In general, the reduction in borer numbers and stalk damage in Si+ plants was greater for water-stressed cane than non-stressed cane, particularly for susceptible sugarcane cultivars. The hypothesis that Si affords greater protection against E. saccharina borer attack in water-stressed sugarcane than in non-stressed cane and that this benefit is greatly enhanced in susceptible cultivars is supported. A possible active role for soluble Si in defence against E. saccharina is proposed.

Após a liberação comercial dos dois primeiros cultivares transgênicos de algodoeiros, NuOpal e DP 90B, uma comparação a grande escala foi efetuada na safra 2006-2007, na fazenda Canaã, localizada a 35 km de Primavera do Leste-MT, com o objetivo de observar as pragas não-alvo da toxina Cry 1 Ac e determinar o manejo delas. O plantio foi realizada no dia 20 de dezembro de 2006, com 4 blocos de 1 ha de cada cultivar transgênico e os cultivares quase isogênicos ACALA 90 e DeltaOpal. Ataques das pragas não-alvo seguintes foram detectadas nos dois tipos de cultivares (Bt ou não-Bt): Spodoptera eridania e Pseudoplusia includens (identificação desta espécie a bem confirmar). O manejo dessas lagartas precisou de aplicações especificas como também o manejo dos ácaros rajados, além dos pulgões e moscas brancas. O uso de produtos específicos contra as pragas não-alvo da tecnologia Bt provocou um aumento dos custos de proteção. O número de aplicações, nas cultivares Bt, não foi reduzido, mas o número de produtos usado sim, em particular as formulações destinadas a controlar as lagartas. O balanço final foi feito com a análise de custo/beneficio. A estimativa de produtividade de algodão em caroço deu os resultados seguintes: 276.8, 293.7, 264.6, 310.3 @/ha para as cultivares ACALA 90, DP90B, NuOpal e DeltaOpal, respectivamente. Considerando os custos dos insumos e as porcentagens de fibra obtida por cultivar (descaroçamento a rolo) as margens estimadas foram as seguintes, na mesma ordem: 1054, 1194, 835 e 1465 US $/ha. Dessas margens retirar os outros custos: operacionais (maquinaria e mão de obra), administrativos e serviços. A escolha dos produtos vai ter uma importância relativa para melhorar o lucro final. Os fertilizantes, como os inseticidas nesta experimentação, tiveram uma proporção de quase 33% dos custos dos insumos. Os résultados paralelos obtidos nesta comparação alertam sobre os problemas metodológicos encontrados, tanto na estimativa da produtividade como da escolha dos inseticidas para o controle das pragas não-alvo da tecnologia Bt. Análises de várias situações de comparação, ao nível geral do país, ou pelo menos das regiões que plantam os algodoeiros Bt, deveriam fornecer uma melhor apreciação das condições de uso benéfico da tecnologia (plantas com o gene crylAc) para os produtores.

Silicon (Si) improves plant resistance to insect attack and may also enhance tolerance of water stress. The objective of this study was to evaluate whether Si-mediated resistance of sugarcane to the borer Eldana saccharina Walker (Lepidoptera: Pyralidae) is enhanced by water stress. Sugarcane cultivars, two resistant to E. saccharina (N21, N33) and two susceptible (N26, N11) were grown in a pot trial, in Si deficient river sand with (Si+) and without (Si-) calcium silicate. To induce water stress, irrigation to half of the trial was reduced prior to inoculation with E. saccharina eggs, and harvested 66 days later. Stressed and non-stressed plants of the same cultivar did not differ significantly in Si content. However, Si+ plants exhibited increased resistance to E. saccharina attack. In Si+ cane, E. saccharina larval survival and biomass was lower than in Si- cane, significantly so for stressed, susceptible cultivars N26 and N11, and for larval mass in non-stressed N26. Stalk damage was reduced in Si+ cane, significantly so for the stressed, susceptible cultivars N26 and N11, and non-stressed N26. This study showed that Si provides greater protection against E. saccharina attack in susceptible, water-stressed sugarcane than in non-stressed cane and/or resistant cultivars.

Após a liberação comercial do evento de transformação do algodoeiro 531 da empresa Monsanto no Brasil e uma primeira safra de avaliação a campo no Mato Grosso (safra 2006-2007), foram detectados problemas de controle de algumas lagartas não-alvo, tais como Spodoptera eridania e Pseudoplusia includens. Outras pragas (moscas brancas, ácaros rajados, bicudo) são presentes e, devido à diminuição do uso dos inseticidas utilizados contra as pragas-alvo, danos de percevejos foram observados nas maçãs verdes. O problema da escolha dos inseticidas a serem aplicados contra todas essas pragas ainda persiste. O uso de produtos muito seletivos das pragas não-alvo aumenta o custo da proteção reduzindo assim o lucro esperado pelos produtores. Deste modo, torna-se imprescindível estudar ainda numa segunda safra a evolução das pragas não-alvo e insetos secundários, e uma estratégia econômica no uso dos produtos visando os insetos ou ácaros não controlados pela tecnologia "Bt". O objetivo do projeto é comparar em grandes parcelas representativas o manejo de dois tipos de cultivares: NuOpal (com o gene crylAc) e DeltaOpal ("near-isogenic" ou "iso linhagem"), com repetições para evitar as dificuldades de interpretação dos resultados. Os resultados esperados são uma definição do manejo fitossanitário de uma cultivar "Bt" (NuOpal) além de uma comparação das planilhas econômicas de custos de produção entre as cultivares Bt e convencional e o desenvolvimento de metodologias experimentais.

Cultivar CD 409 derives from a breeding program by Coodetec/Cirad in Palotina, in the state of Paraná, and was obtained through the pedigree selection method. The CD 98-32 line, obtained from an Australian and South American genetic pool, was tested during growing periods 1999-2000, 2003-2004 in the experimental network of the states of Bahia, Goiás, Mato Grosso, and Minas Gerais. Over 40 trials were conducted. CD 409 is tall and growth regulator is consistently used. It has medium, jagged leaves and average pilosity. The fruiting habit of this material is similar to that of CNPA ITA 90; its differential lies in its capacity to retain top bolls, which allows for significant recovery after shedding of first fruiting positions under adverse conditions. It is resistant to bacteriosis and moderately resistant b the Blue Disease. Against "ramulose" and cotton rust ramularia, its resistance is similar to that of all other varieties used in the cerrado area. It has a good tolerance level to nematodes and this was demonstrated in several locations heavily infested with Meloidogyne incógnita. CD 409 is a useful choice for cotton growers with a medium and high level of technical capabilities and skills in his Brazilian cerrado, especially in areas affected by nematodes.

This report highlights the main points of relevance to SASEX. The main ones being: Studies on the taxonomy of moth pests of sugar cane including eldana and #Chilo sacchariphagus# using DNA methods, development of a method to apply soil treatments in a horizontal band against sugar pests, research into genetically transformed cane for enhanced resistance to sugarcane white grubs [extracted from the authors' executive summary]

Two common cultivars of sugarcane in Réunion (R570 and R579) were tested for their resistance to the stem borer Chilo sacchariphagus Bojer, a key pest in Southeast Asia, Indian Ocean islands and Mozambique. The laboratory and field trials showed important differences in varietal response to the borer damage only when the larvae started penetrating into the internodes. All the results confirmed the great susceptibility of cultivar R579 on the basis of speed of penetration, survival rates and damage patterns. The delay of penetration observed on R570 led to higher mortality of young larvae and consequently less damage. Resistance mechanisms were also noticed in the stem where larval tunnels were found much narrower than on R579. Different methods and devices were set up and developed to investigate the mechanical resistance of R570. Penetrometry studies indicated that penetration of an R570 internode required 15-50% more energy than that of R579, depending on the penetration site. On this cultivar the internal induration zone was also characterised and this may also account for the difficulty of larvae feeding on these tissues. An overview of results obtained from various methods is presented and further investigations to better understand these resistance mechanisms are discussed. (Autors' abstract)

Visando a atender a exigência do mercado da região centrosul do Brasil e o plantio em áreas com nematóide, a Coodetec/Cirad lançou no mercado na safra 00/01 a variedade CD 405, material obtido no programa de melhoramento genético da Coodetec/Cirad através do método de seleção pedigree. A linha CD 95-621 foi obtida de um cruzamento entre variedades de fundo genético Africano e sul americano, testado primeiramente em Palotina-PR na safra 96/97 e nas safras 97/98, 98/99 e 99/00 na rede experimental multilocal do Paraná e São Paulo. A variedade CD 405 é um material que pode ser classificado na categoria das variedades indeterminadas ("Full season"), tardia, de alta produtividade, pouco exigente em fertilidade, mas muito exigente em regulador de crescimento, sendo tolerante as deficiências hídricas e adaptada a colheita manual. Sua resistência é voltada à bacteriose e doença azul, é moderadamente resistente ao nematóide, fusariose e alternariose, porém é susceptível a ramulariose e ramulose. O rendimento e qualidade da fibra foram classificados como médios.

Les départements de la Guadeloupe et de la Martinique sont dominés par deux cultures pivots principales: le bananier et la canne à sucre. Alors que la pression parasitaire sur la canne à sucre est relativement faible, le bananier est soumis à de fortes pressions parasitaires qui nécessitent le recours à une lutte chimique dont l'impact sur l'environnement n'est pas négligeable. Afin de réduire l'usage des pesticides, les orientations prises actuellement, dans une logique d'agriculture raisonnée, intègrent fortement des pratiques de rotations culturales et de combinaisons variétales. On assiste donc à une transition d'un système monocultural à des systèmes de cultures associées qui modifieraient à la fois les systèmes d'exploitation agricole, le paysage, la biodiversité naturelle et cultivée avec des effets extrêmement bénéfiques sur l'environnement et la durabilité des systèmes de culture. Deux composantes majeures marquent cette évolution. En premier lieu, la pratique de rotations culturales associée à l'utilisation d'un matériel de plantation sain permet de contrôler efficacement les populations de nématodes dans le sol et ainsi de réduire considérablement les traitements nématicides polluants et coûteux. La canne à sucre, l'ananas, les plantes fourragères constituent des rotations à la fois efficaces, valorisables économiquement et bénéfiques au plan environnemental. En deuxième lieu, des menaces importantes liées à l'extension importante de la Maladie des Raies Noires (#Mycosphaerella figiensis#) dans tout l'arc Caraïbes incitent à rechercher des techniques alternatives à la seule lutte chimique actuellement utilisée contre l'espèce #Mycosphaerella musicola# (Cercosporiose jaune), seule présente aux Antilles. Le recours à des variétés tolérantes, issues des programmes d'amélioration génétique en cours, constitue une des voies les plus prometteuses, qui devra s'appuyer sur une combinaison judicieuse des variétés sensibles et plus ou moins résistantes, au niveau de la parcelle, de l'exploitation ou du bassin versant. (Texte intégral)

Depuis le début des années 90 une maladie à Begomovirus, causée par le PYMV, ravage les cultures de tomates des Antilles françaises. L'utilisation d'insecticides spécifiques n'a pas permis d'en contrôler efficacement le vecteur Bemisia tabaci; les pertes de production sont évaluées entre 30 et 50%. La création de variétés résistantes à la maladie, composante d'une opération plus large de lutte intégrée, a été retenue comme une des solutions possibles. Dès 1995 nous avons mis en place un programme de création variétale visant à associer à la résistance au Begomovirus PYMV, une très bonne résistance à Ralstonia solanacearum et une très bonne adaptation aux conditions climatiques de ces régions: hautes températures et pluies de l'hivernage. Les résistances à Ralstonia solanacearum utilisées proviennent soit de CRA 66 soit de H 7996 et H 7997, elles ont été introduites, dans le cadre d'un programme de double sélection récurrente, dans les meilleures sources de tolérances au PYMV que nous ayons pu identifier après évaluation au champ de plus de 80 géniteurs "résistants" au TYLCV méditerranéen provenant des travaux de M. Laterrot. Dans un premier temps, à cause de la liaison en répulsion sur le chromosome 6 entre Rs et Ty-1, nous avons obtenus des familles possédant un très haut niveau de résistance à Ralstonia solanacearum ou des familles possédant un bon niveau de résistance partielle au PYMV; ce matériel est en cours de diffusion. Après rupture de la liaison, les familles associant les deux résistances, sont en phase de contrôle avant sortie. Une résistance forte au PYMV est en cours de construction dans le cadre d'une collaboration tripartite avec l'Université de Floride et le Centre VOLCANI en Israël. Cette résistance permettra de conserver la plantation sans aucun symptôme durant toute la durée de la culture. L'évaluation de ces résistances vis à vis d'autres Begomovirus dans la zone intertropicale est envisagée.

Le programme d'amélioration génétique du bananier développé par le CIRAD a pour objectif l'obtention de nouvelles variétés conjuguant des caractères de résistance aux maladies -notamment cryptogamiques- et aux ravageurs à une amélioration des qualités agronomiques de la plante et des qualités gustatives des fruits. De telles variétés ont été obtenues par croisement de parents #Musa acuminata# et #M. balbisiana#. Cependant, ces hybrides inter-spécifiques présentent un risque d'activation de séquences génomiques du virus de la mosaïque en tiret du bananier (Banana streak badnavirus, BSV) intégrées dans le génome du parent #M. balbisiana#, et donc de dissémination du virus. En application stricte du principe de gestion du risque, la diffusion de ces nouvelles variétés a dont été suspendue jusqu'à l'obtention de données objectives sur les risques encourus. Les travaux actuels menés au Cirad visent à comprendre les mécanismes d'activation de la séquence intégrée et à caractériser le risque viral lié au BSV. Par ailleurs, une contrainte importante pour la diffusion des variétés de bananier réside dans l'infection des têtes de clones par le virus de la mosaïque atténuée du bananier (Banana mild mosaic virus, BanMMV). Un test générique par immunocapture- RT-nested PCR pour la détection polyvalente des tricho-, capillo- et foveavirus a été adapté et developpé pour la détection du BanMMV. Cet outil est nécessaire pour améliorer la qualité sanitaire des plants.

Transgenic cotton plants were amongst the first genetically modified (GM) plants to be released on the market in 1995/1996. Since then, the acreage devoted to GM cotton worldwide has increased dramatically, reaching 5.3 million hectares in the year 2000. This figure represents 16% of the world cotton acreage. In the United States of America, GM cotton represents more than 70% of the national cotton acreage, whereas in continental China, the proportion of transgenic cotton is approximately 10%. Other countries, such as Australia, Argentina, Mexico, and South Africa have already adopted this technology, while others are awaiting a proper legislation (or modifications thereof) to introduce these plants. Many more countries are in the process of evaluating GM cotton in the field. The rapid growth in the acreage devoted to GM cotton (from 700-800 000 ha in 1996 to more than 5 million ha in 2000) seems to indicate than farmers adopting this technology must somehow benefit from its use. The fact that these varieties have been grown on a large scale for 5 years allows a preliminary analysis of their financial and ecological impact. Despite important variations from year to year and from place to place, adopters of the GM technology seem to have benefited financially from transgenic varieties. The issue of GM plants is in the midst of a passionate debate in particular in Europe (but also in other countries), and various points regarding this technology have been raised. These include, but are not restricted to, public health, the impact on the environment (the development of toxin-resistant insects, (trans) gene flow...), as well as socio-economical issues. It is probable that the areas devoted to GM cotton will grow within the next few years through the opening of new markets, as well as through a more divers offer. Indeed, a number of companies and institutions are presently testing new transgenic cotton plants whose agronomic or technological properties have been modified through genetic engineering. Even though some of these products may never reach the market, it is probable that others will in the more or less near future.

As for any other crop, the integrated pest management on banana is based on genetic, biological, and chemical methods and on some cultural practices. The exported monospecific banana production mainly relies on very intensive cultural practices and the banana agro-industrial plantations offer very favorable conditions for the development of various pests and diseases. Among the nematode species, the burrowing nematode #Radopholus similis# is a root lesion nematode strictly linked with the worlwide "Cavendish" #Musa# variety and accordingly to environmental factors. The #Radopholus similis# populations seem diversified in term of aggressiveness. Hopefully the #Musa# germplasm complex is also diversified. If only few banana clones are widely cultivated in the world, different sources of resistance to diseases and pests have been identified among the wild and related #Musa# species and the few breeding programs that exist in the world are using these sources of resistances to create banana hybrids. Therefore, more information is urgently needed on these different natural banana sources of resistance growing in various environmental conditions to increase the variability which should exist among the commercialized bananas. Only the combination of improved resistant varieties cultivated with appropriate cultural practices will offer to future consumers (domestic and export) a large range of tasty and safe bananas. (Texte intégral)

Stenodiplosis sorghicola is one of the most damaging and widely distributed of all sorghum pests. In Africa, cultivation of midge resistant sorghum varieties is the best option for subsistence farmers. Techniques were set up in view of identifying resistance in sorghum cultivars, either under natural or artificial midge infestation. Farako-ba and Kouaré (Burkina Faso) and Longorola (Mali) are research stations that can be used at “hot-spots” for resistance screening under natural midge infestation. Midge pressure on test cultivars can be augmented by manipulating sowing dates, planting infestor rows, spreading midge-infested sorghum panicles containing diapausing larvae, increasing relative humidity by sprinkler irrigation, or controlling midge predators and parasitoids using selective insecticides. Artificial infestation allows an evaluation under high and uniform pest pressure, and under nochoice conditions. Twenty or 40 adult female midges are confined with sorghum panicles at anthesis, under wire-framed muslin cloth cages. Infestation is assessed by squeezing on a white sheet of paper, using an empty glass bottle, a random sample of 500 spikelets per cultivar. Orange stains are then counted, giving the percentage of midge-damaged florets. At crop maturity, midge damage is visually scored on a 1-9 scale, where 1 = < 10%, and 9 = > 80% midge-damaged spikelets.

Results obtained from several field experiments carried out on sugar estates on Réunion Island have provided valuable information on the ecology of the pyralid moth #Chilo sacchariphagus# and have elucidated the main factors regulating populations. These results indicate that predation, varietal resistance and biological control are important factors to consider when using integrated pest control. The value of these factors, whose use involves some changes in cultural practices, is discussed within the wider context of the environment and farm economics.

La sélection variétale, en matière de lutte contre les ravageurs, peut faire appel soit à des critères physiques, l'insecte étant incapable, pour des raisons morphologiques d'attaquer la plante, soit à des critères biochimiques, la présence de substances rendant la plante peu appétante voire repoussante ou peu propice à la consommation par le ravageur. Des cas sont étudiés comme : l'acarien et la larve mineuse chez le palmier à huile, l'acarien #Eriophyes guerreronis# chez le cocotier, la chenille mineuse des feuilles du caféier et les nématodes, le miride du cacaoyer, la sensibilité variétale du phytopte des agrumes, la sensibilité du #Leucaena# au psylle

Cotton production in Thailand has been decreased by nearly 50% over the last fifteen years. The cotton bollworm, #Helicoverpa armigera# Hubner is the key pest in Thai cotton cropping system. One strategy to circumvent this problem is to transfer to cotton plants genes encoding for #Bacillus thuringiensis# endotoxins which have been identified as very toxic towards this insect. Techniques were developed for embryogeni callus induction, transformation and regeneration of Sri Somrong 60, a Thai cotton variety. Somatic embryogenesis was obtained by culturing hypocotyl explants on to zeatin and NAA containing MS medium and subculturing on to hormone free medium. This method yielded 23-50% embryogenic callus induction. Transformation of Sri Somrong 60 with synthetic crylA(b) gene was accomplished by using #Agrobacterium tumefaciens# strain C 58: pG2260. The selection of resistant calli which were obtained at frequencies varying from 3 to 50%, was accomplished on kanamycin containing medium. The molecular analysis of recovered plants showed the integration of the transferred gene. Bioassays conducted with leaves of different transgenic plant lines showed different level of resistance towards #Helicoverpa armigera# first instar larvae. The association of B.t genes with other tolerance characters existing in the cotton germplasm is in progress using conventional breeding techniques.

De nouvelles variétés sélectionnées de sorgho, essentiellement de type guinea, ont été évaluées chez des paysans de la zone CMDT. Ainsi, durant deux ans (1995 et 1996), 60 tests variétaux ont été organisés dans la zone soudanienne. Deux variétés testées a été appréciées par les paysans : la MIKSOR 86-30-41 en zone nord et la IS 15401 en zone sud. Ces deux variétés ont été résistantes au striga (surtout la variété IS 15401) et productives avec des rendements souvent supérieurs à ceux des variétés locales. Elles ont eu également une bonne qualité de grain et de bonnes aptitudes culinaires. La variété IS 15401 diffuse spontanément auprès des paysans. Cependant, sa photopériodicité incite à préconiser son utilisation en zone sud en milieu ou bas de toposéquence sur des terres non inondables mais accumulant des réserves en eau. D'autres variétés ont présenté de l'intérêt dans certaines terroirs plus limités. Une enquête auprès des paysans a montré que de nombreux caractères interviennent dans leurs choix variétaux.