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International audience; Hybridizations between Musa species and subspecies, enabled by their transport via human migration, were proposed to have played an important role in banana domestication. We exploited sequencing data of 226 Musaceae accessions, including wild and cultivated accessions, to characterize the inter(sub)specific hybridization pattern that gave rise to cultivated bananas. We identified 11 genetic pools that contributed to cultivars, including two contributors of unknown origin. Informative alleles for each of these genetic pools were pinpointed and used to obtain genome ancestry mosaics of accessions. Diploid and triploid cultivars had genome mosaics involving three up to possibly seven contributors. The simplest mosaics were found for some diploid cultivars from New Guinea, combining three contributors, i.e., banksii and zebrina representing Musa acuminata subspecies and, more unexpectedly, the New Guinean species Musa schizocarpa. Breakpoints of M. schizocarpa introgressions were found to be conserved between New Guinea cultivars and the other analyzed diploid and triploid cultivars. This suggests that plants bearing these M. schizocarpa introgressions were transported from New Guinea and gave rise to currently cultivated bananas. Many cultivars showed contrasted mosaics with predominant ancestry from their geographical origin across Southeast Asia to New Guinea. This revealed that further diversification occurred in different Southeast Asian regions through hybridization with other Musa (sub)species, including two unknown ancestors that we propose to be M. acuminata ssp. halabanensis and a yet to be characterized M. acuminata subspecies. These results highlighted a dynamic crop formation process that was initiated in New Guinea, with subsequent diversification throughout Southeast Asia.

International audience; Fruit quality traits are directly linked to consumer acceptability, and thus key targets for banana breeding programs. We explored the genetic control of three major organoleptic and ripening-related traits, namely pulp acidity (pH), firmness (PF) and dry matter content (DMC), over a 7-day ripening period and three production cycles in a banana segregating population genotyped by sequencing. Significant broad-sense heritabilities were estimated with 0.77, 0.46 and 0.81 values for pH, PF and DMC, respectively. QTL detection was first performed on the whole dataset to analyze their dynamics. In a second approach, per-cycle data were considered to evaluate the stability across production cycles. Finally, a meta-analysis was performed. Various QTLs were detected, as well as many QTL colocalizations, while 12 of these QTLs were more prominent as they were detected in several approaches and/or explained over 15.0% of the phenotypic variation. Candidate genes were proposed for 10 of these QTLs. The QTL with the largest contribution to pulp acidity (R-2 = 19.3-50.6%) was located on LG1_7 on the genetic map of Pisang Madu, i.e. a parent that is closely related to Cavendish, the world's most cultivated dessert banana cultivar group. This QTL is located on a chromosome derived from a reciprocal translocation that does not recombine in Pisang Madu, which is a favorable context for molecular marker monitoring. These first results will provide a relevant basis for marker-assisted selection in banana improvement programs.

Banana cultivars (Musa ssp.) are diploid, triploid and tetraploid hybrids derived from Musa acuminata and Musa balbisiana. We presented a high-quality draft genome assembly of M. balbisiana with 430 Mb (87%) assembled into 11 chromosomes. We identified that the recent divergence of M. acuminata (A-genome) and M. balbisiana (B-genome) occurred after lineage-specific whole-genome duplication, and that the B-genome may be more sensitive to the fractionation process compared to the A-genome. Homoeologous exchanges occurred frequently between A- and B-subgenomes in allopolyploids. Genomic variation within progenitors resulted in functional divergence of subgenomes. Global homoeologue expression dominance occurred between subgenomes of the allotriploid. Gene families related to ethylene biosynthesis and starch metabolism exhibited significant expansion at the pathway level and wide homoeologue expression dominance in the B-subgenome of the allotriploid. The independent origin of 1-aminocyclopropane-1-carboxylic acid oxidase (ACO) homoeologue gene pairs and tandem duplication-driven expansion of ACO genes in the B-subgenome contributed to rapid and major ethylene production post-harvest in allotriploid banana fruits. The findings of this study provide greater context for understanding fruit biology, and aid the development of tools for breeding optimal banana cultivars., A high-quality draft genome assembly of Musa balbisiana (the banana B-genome) is reported. Comparative genomic and gene functional analyses provide insights into the subgenome evolution and functional divergence between the A- and B-subgenomes.

BACKGROUND: The effect of temperature on chilling injury during fruit growth was studied in a new banana hybrid CIRAD925 in which seasonal variability in chilling susceptibility was observed when fruits were stored at 13 ∘ C. RESULTS: The relationship between the response to chilling (presence/absence) and the temperature during banana fruit growth was examined with a logistic regression model. An explanatory variable X N,P was defined as the mean temperature during a period, expressed in weeks, which began N week(s) after flowering and lasted P week(s). The model was calibrated with 143 bunches with a green life of 30 ± 5 days and validated with 156 bunches grown in six plots under different growing conditions. Chilling injury was best predicted by the mean temperature during the period beginning 1 week after flowering and lasting 5 weeks (X 1,5 ). Above a mean temperature of 24.1 ∘ C in the period concerned, banana fruits had a 95% probability of chilling injury at 13 ∘ C. Below a temperature of 23.4 ∘ C, banana fruits only had a 5% probability of chilling injury. CONCLUSION: The results provide a tool to predict chilling susceptibility in banana fruit whatever the thermal conditions in tropical regions. (Resume d'auteur)

The management of banana postharvest conditions is a pre-requisite for adapting the storage, shipping and gassing conditions to the specific physiology of individual hybrid bananas. The cultivar 'CIRAD 925', developed by CIRAD, is a good case study for adapting banana food chain conditions to accommodate the specificities of this hybrid. Indeed, the storage and ripening conditions should be adapted to this cultivar which is tolerant to the black leaf streak disease. The management of temperature and relative humidity during the maturation step is therefore a key challenge to avoid peel splitting and browning. These physiological disorders are exposed here, and associated biochemical factors are described and discussed. The cuticular wax behaviour during ripening at different relative humidities and its impact on peel splitting and browning is associated with the intensity of these disorders.(Resume d'auteur)

International audience; The aim of this study was to understand the genotypic factors and post-climacteric storage conditions that affect bruise susceptibility of banana peel. Putative physicochemical indicators of bruise susceptibility, including peel electrolyte leakage (PEL), total polyphenolic content, hardness, water content, and peel thickness, were investigated. Bruise susceptibility is the lowest impact energy needed to produce visible bruising by an object dropped on post-climacteric banana fruit from a pre-determined height, converted into impact energy (20-200 mJ with a 20 mJ increment). The bananas were stored either at 18 degrees C throughout ripening or at 13 degrees C between the 2nd and 6th day after ethylene induction. Five cultivars with contrasting susceptibility to impact bruises were used. Neither Grande Naine nor hybrid Flhorban925 bruised at the maximum impact energy (200 mJ) during ripening whatever the storage conditions. A gradient in bruise susceptibility was observed among the other cultivars: French Come > Fougamou > hybrid Flhorban916. Bruise susceptibility increased during ripening and was higher in bananas stored at 18 degrees C. The lower ripening temperature resulted in a two-day delay to fruit maturity as well as in bruise susceptibility. Bruise susceptibility was positively correlated with PEL (R=0.78) and to a lesser extent negatively correlated with hardness (R=-0.45), and was not correlated with polyphenolic content. In conclusion, membrane permeability provides the first clue to understanding bruise susceptibility.

Past phylogenetic studies pointed to some Mlali clones (AAcv) as the 2N gamete donor parents of 'Cavendish' (AAA) and 'Gros Michel' (AAA) cultivars, thus revealing their significance to Musa breeding. Nevertheless, cultivated bananas are usually highly sterile at diploid and triploid level, which seriously hampers the production of new hybrids. Therefore, it is necessary to investigate the floral biology of these Mlali clones to evaluate their capacity of generating such progenies. Pollen fertility of both diploid and doubled-diploid Mlalis (as donor of diploid gametes) was assessed by different approaches. At anthesis, the Alexander staining technique has revealed that up to 35% of haploid and diploid pollen were viable. Pollen viability was confirmed in test crosses with wild Musa accessions presenting no fertility problems. The results were then correlated with post-meiotic observations at the tetrad stage: 70% were regular tetrads in the diploid and doubled-diploid clones whereas the remaining cells were aggregated under forms of pentads and hexads and, more rarely, heptads leading probably to aborted microspores. Detailed observations of the irregular tetrads suggested that meiotic errors occurred during both first and second mitosis of the meiosis. These preliminary results suggest that doubled-diploid Mlali clones (AAAAcv) might be useful male parents with high breeding potential for the development of new disease-resistant AAA export bananas. (Resume d'auteur)

All bananas cultivated for export are Cavendish cultivars and are considered to be very susceptible to both the burrowing nematode Radopholus similis and the lesion nematode Pratylenchus coffeae . Twelve cultivars of Musa spp. genome AAA cv. Grande Naine from mass field selections in Martinique and Guadeloupe were cloned and micro-propagated in tissue culture. Resistance of these sibling cultivars to nematodes was tested in two growth chamber trials and in one 2-year field trial in a former banana field heavily infested with nematodes and without control methods (no guying or nematicide applications). The field trial also included a new synthetic hybrid FB920 that has tolerance to yellow and black Sigatoka and partial resistance to nematodes. Trends were similar in growth chamber and field trials in that all Cavendish cultivars were susceptible to nematode species, although some differences in susceptibility were detected, and in particular roots of the selected cultivar MA13 contained fewer R. similis than the most susceptible cultivars of Cavendish (cvs. Petite naine, Poyo and L93). Cultivar MA13 was also less susceptible than most commercial cultivars to P. coffeae in the growth chamber trials, and a similar but insignificant trend was documented in the field trial. In the field trial, all cultivars experienced severe damage (lengthening of vegetative and reproductive stages, uprooting and reduced yield), which was attributed to the high level of nematode infestation. Although tolerance to nematodes in the field trial was greater for the synthetic new hybrid FB920 than for the Cavendish cultivars, FB920 produces small bunches and tall plants that will prevent its development as a banana for export (but will not prevent its production by small holders). In summary, this study shows that there is useful variation in tolerance to R. similis and P. coffeae among sibling Cavendish cultivars and that growth chamber trials with in vitro -cultivated plants are useful for screening for such susceptibility.

a b s t r a c t Varietal mixture is a cultural technique in which the genetic and functional diversities of varieties are used to manage pests and diseases. This strategy is commonly used on grass crops such as rice, barley, maize, and wheat to mitigate some windborne and soilborne pathogens. The effects of varietal mixtures on the number and community structure of pests, including plant-feeding nematodes (PFNs), however, have rarely been studied. In experiments conducted in Martinique, we evaluated the effect of varietal mixtures of bananas on PFN communities. A growth chamber experiment was used to measure the susceptibility of three banana cultivars dessert banana cv. 902 (Musa AAA, Cavendish subgroup); a new synthetic hybrid cv. FB924 (Musa AAA); and a plantain cv. Creole blanche (Musa AAB, French Horn) to the two major PFNs. The multiplication rates of Radopholus similis and Pratylenchus coffeae were substantially different on the three varieties; for example, the multiplication rate was up to 10 times greater on plantain cv. Creole blanche than on hybrid cv. FB924. In a field experiment, we planted the three varieties in pairs that included all six possible combinations. Banana varietal mixtures significantly affected both PFN densities and community composition. Differences in community composition among the pairs involved a shifting equilibrium among nematode species and an interspecific competition for food resources. The relative abundance of the spiral nematode Helicotylenchus multicinctus increased while that of the burrowing nematode R. similis, which is the most damaging species on bananas, decreased. The use of a varietal mixture in which one variety supports a low PFN multiplication rate appears to have practical relevance, especially in systems based on very susceptible cultivars such as plantains. The use of varietal mixtures should not create management problems, especially for plantations that produce bananas for local markets. © 2011 Elsevier B.V. All rights reserved.

International audience; The study of movements of individual organisms in heterogeneous environments is of primary importance for understanding the effect of habitat composition on population patterns. We developed a new experimental methodology to measure individual movements of walking insects, based on radiotracking. Our aims were to understand the link between habitat heterogeneity and moving patterns, and to characterize the movements with dynamic models of diffusion. We tracked individual movements of adults of Cosmopolites sordidus (Coleoptera: Curculionidae) with passive radio frequency identification (RFID) tags under different field management practices. Diffusion models based on recapture data indicated a subdiffusive movement of this species. Substantial variation was found between individual paths, but this variation was not sex dependent. Movement of released C. sordidus was affected by banana planting pattern and the presence/absence of crop residues but not by the presence of a cover crop between rows of bananas or by banana variety. These results show that the RFID technology is useful for evaluating the dispersal parameters of cryptic insects in heterogeneous environments.

Introduction. La duree de vie verte est une caracteristique post-recolte majeure des fruits ; elle definit leur capacite a se conserver au long de la chaine de distribution. Pour des fruits climacteriques comme l'est la banane, la duree de vie verte doit etre optimisee afin de satisfaire les exigences de transport et de commercialisation. Le calcium est connu pour renforcer les tissus des plantes ainsi que leur duree de vie verte. Materiel et methodes. Dans notre etude, nous avons teste l'effet de l'application de calcium avant et apres la recolte sur les caracteristiques post-recoltes de bananes de deux cultivars (Grande Naine et Flhorban920, Musa spp., group AAA, Cavendish). Resultats et discussion. L'ajout de calcium dans la fertilisation de la variete Flhorban920 n'a pas au d'effets significatifs sur la duree de vie verte (moyenne de 36 jours), ni sur la durete et l'epaisseur de la peau des fruits (respectivement 63.7 N et 3.94 mm). L'application de calcium au champ par pulverisation directe sur les fruits n'a pas modifie la composition chimique de la pulpe et de la peau. Pour les applications de calcium apres recoltes (par trempage), la duree de vie verte des fruits de Cavendish et de Flhorban920 n'a ete modifiee de maniere significative ni par la presence de calcium, ni par le type d'application (duree de vie verte de 45 et 26 jours pour les fruits des varietes Cavendish et Flhorban920, respectivement).

International audience; Farmers are inundated with advertisements about many innovations that are supposed to increase their yields or reduce environmental impact. However, the benefit of these innovations depends on the farming context. Here we present the ad hoc adaptation of the crop model SIMBA and a method to evaluate 16 innovations in six types of farms previously selected through a typology of the banana farming systems in Guadeloupe. The innovations include regulation of pesticide use, rotations and fallows, intercropping, conditional application of pesticides, resistant cultivars, and integrated systems. Our results show that, for a given innovation, the yield and pesticide reduction vary widely with different farm types. We show that environmentally friendly innovations often cause a greater decrease in yield in more productive farm types. Nevertheless, despite an apparent trade-off between yield and pesticide use, some innovations address both production and environmental issues, e.g., rotation with fallows improved with cover crops, regular fallows, and rotations with pineapples for the most intensive farm types. Our modelling study confirms the importance of innovation-farm type interactions and the usefulness of models for assessing large numbers of technological innovations among a wide range of biophysical and technical contexts.

Acceptability criteria in dessert banana were investigated to enable sensory qualities to be taken into account earlier in the assessment of new banana hybrids in a selection scheme. Twelve banana cultivars were characterized by sensory profiling and physical-chemical analyses at a defined eating stage. The 'right' levels of sourness, sweetness, firmness, mealiness, and banana aroma were evaluated by 214 consumers on the 'Just-About-Right' scale. Optimal acceptance of a banana means at the most 20% of consumers judged the banana to be e.g. 'too …' or 'not … enough'. The ideal banana received scores ranging between 6.1 and 6.7 for sweetness, between 2.8 and 3.3 for sourness, above 6.3 for banana aroma, between 3.7 and 4.7 for firmness and between 1.0 and 1.4 for mealiness on a discrete 0–9 scale, by titratable acidity of 5.5 meq 100 g−1, or a pH of 4.9, and a pulp puncture force between 1.9 and 2.4 N. Acceptability thresholds were calculated when a maximum of 33% of consumers judged bananas to be e.g. 'too …' or 'not … enough'. Screening new hybrids revealed the advantage of using an acceptability threshold of 33% of unsatisfied consumers as the first step, since after a hybrid has passed the acceptability threshold, crop management can be directed towards being as close as possible to the characteristics of the ideal banana. (Resume d'auteur)

Dessert banana production worldwide is based on just a few highly productive, easy to grow and international market compatible cultivars from the Cavendish sub-group (AAA genome). However, these cultivars are hampered by pests and diseases, which has led to extensive pesticide use. New pest and disease resistant varieties that are productive enough to meet international market demand are now needed to reduce pesticide use and thus the detrimental environmental impact. Hybrid bananas bred by the CIRAD banana breeding program are resistant to many diseases, particularly Sigatoka diseases, but exhibit morphological traits and yield components which differ markedly from those of Cavendish bananas. After an analysis of traits related to plant morphology and yield in 530 banana hybrids, the effects of modifying the level of competition between bunches and suckers through sucker pruning management practices were compared on the new hybrid CIRAD 925 and on a reference variety from the Cavendish sub-group ‘Grande Naine’. Hybrids from the CIRAD banana breeding program tend to have thin stems, small bunches and a short crop cycle. Total sucker pruning until mother plant harvest significantly increased the fruit diameter, first cycle bunch weight, second cycle duration and decreased the plant size. However, the effect on bunch weight was greater for Grande Naine, while the effects on second cycle duration and pseudostem girth were greater for CIRAD 925. The level of apical dominance of the central meristem on suckers seemed to explain the varietal differences in the effects of sucker pruning management. Our results showed that traits related to plant morphology and yield components could be modified by sucker pruning management and that a tailored management of mother-plant/sucker competition could be a way to improve the suitability of new hybrids for the banana industry.

The authors wish to thank Frédéric Bakry and Léonidas Féréol for providing some doubled haploid lines and Guillaume Fort for technical help.This paper is dedicated to the memory of Jacky Ganry.; Breeding new interspecific banana hybrid varieties relies on the use of Musa acuminata and M. balbisiana parents. Unfortunately, infectious alleles of endogenous Banana streak virus (eBSV) sequences are present in the genome of Musa balbisiana genitors. Upon activation by biotic and abiotic stresses, these infectious eBSVs lead to spontaneous infections by several species of Banana streak virus in interspecific hybrids harboring both Musa acuminata and M. balbisiana genomes. Here we provide evidence that seedy M. balbisiana diploids display diverse eBSV allelic combinations and that some eBSVs differ structurally from those previously reported. We also show that segregation of infectious and non-infectious eBSV alleles can be achieved in seedy M. balbisiana diploids through self-pollination or chromosome doubling of haploid lines. We report on the successful breeding of M. balbisiana diploid genitors devoid of all infectious eBSV alleles following self-pollination and on the potential of breeding additional M. balbisiana diploid genitors free of infectious eBSVs by crossing parents displaying complementary eBSV patterns. Our work paves the way to the safe use of M. balbisiana genitors for breeding banana interspecific hybrid varieties with no risk of activation of infectious eBSVs.

International audience; Peel splitting is a major physiological disorder affecting post-harvest banana quality. This phenomenon occurs only 3-6 days after ripening induction in specific cultivars such as cv. 925 when stored in saturating humidity conditions. In these conditions, Cavendish cultivars (Grande Naine, cv. GN) are not susceptible to splitting. Cvs. 925 and GN were thus investigated to detect possible determinants associated with splitting. Splitting intensity was tentatively found to be associated with an inverse water flux at high relative humidity (RH) through an osmotic peel to pulp water flux resulting from the higher sugar content in the pulp than in the peel. Rheological properties were measured, and although the peel resistance and elasticity in cv. 925 were surprisingly higher than in cv. GN, saturating humidity conditions (100 % RH) substantially reduced the peel resistance. However, the peel epicuticular wax in cv. 925 was clearly thinner than that in cv. GN, thus leading to limitation of peel hydration in cv. GN. Peel splitting in cv. 925 was also associated with a boost in respiration, an increase in oxidative stress markers (H2O2), resulting in an increase in cellular damage markers (MDA, PEL). Overall, our results suggest that peel splitting at high RH in cv. 925 is related to fast decrease peel water content and the induction of high oxidative stress damage.

The effect of temperature on chilling injury during fruit growth was studied in a new banana hybrid CIRAD925 in which seasonal variability in chilling susceptibility was observed when fruits were stored at 13 °C.The relationship between the response to chilling (presence/absence) and the temperature during banana fruit growth was examined with a logistic regression model. An explanatory variable XN , P was defined as the mean temperature during a period, expressed in weeks, which began N week(s) after flowering and lasted P week(s). The model was calibrated with 143 bunches with a green life of 30 ± 5 days and validated with 156 bunches grown in six plots under different growing conditions. Chilling injury was best predicted by the mean temperature during the period beginning 1 week after flowering and lasting 5 weeks (X1,5 ). Above a mean temperature of 24.1 °C in the period concerned, banana fruits had a 95% probability of chilling injury at 13 °C. Below a temperature of 23.4 °C, banana fruits only had a 5% probability of chilling injury.The results provide a tool to predict chilling susceptibility in banana fruit whatever the thermal conditions in tropical regions. © 2015 Society of Chemical Industry.

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; International audience; The ex ante assessment of innovative agro-ecological innovations is a key step in the development of more sustainable crop management systems. To this end, models are useful tools because they make it possible to rapidly assess numerous innovations in different contexts. Whereas many farm optimisation models focusing on the farmer’s strategic decision to adopt new crop management systems have been published, little attention has been given to the ex ante modelling of the dynamic operational impacts of innovation adoption at the farm level. BANAD, a mechanistic model for such applications,is proposed. It allows the ex ante assessment of innovative management systems including new agroecological techniques, while taking into account different farming contexts and policy and market conditions. It includes three components: (i) a crop management system model, (ii) a crop model (SIMBA) and (iii) a farming system model. Our results applied to the ex ante assessment of six innovative banana management systems for three contrasted farm types in Guadeloupe showed that the impacts of agroecological innovations, which include rotations, improved fallow, intercropping, pest-resistant cultivar, and an integrated organic system, can vary considerably according to (i) the farm type in which the innovation is integrated, (ii) the nature of the agro-ecological innovations, and (iii) the criteria considered and the temporal horizon of the assessment. Innovative intercropping systems that were effective at the field level in terms of the yield improvement and decreased pesticide use could be problematic at the farm level because they increased the workload and decreased income. The adoption of rotations or improved fallow seemed to be relevant for smallholders but could induce a critical period of 1.5–2.5 years during which income decreased drastically. Under certain conditions of markets and subsidies, very environmentally friendly innovations that are less productive can however be economically effective.

The context for the production of bananas for export is characterised by a wide range of transport-times between producer and importer countries, and by the use of a single cultivar of banana (Musa spp., AAA group, cv. Cavendish Grande Naine).We investigated the green-life of pink banana (Musa spp.,AAA group, Red sub-group, cv. Figue Rose Naine) for the different physiological ages of banana fruit, measured in degree-days (°Cd). We measured the temperature threshold of pink banana (19.8°C) and showed that the green-life of pink banana decreased linearly with the physiological age of the fruit. Thus, we confirm the validity of the relationship between accumulated heat units during fruit growth and green-life that was previously established for Cavendish banana.We searched for the optimum physiological age (°Cd) for harvest, in order to ensure a green-life that fulfilled the requirements for transport and that maximised fruit weight. For Martinique, the optimum flowering-to-harvest interval was found to be 548°Cd, to ensure 25 d of green-life, as required for transport, and to maximise fruit size.We showed that fruit weight was not a good indicator on which to select bananas for harvest in order to ensure a particular green-life. This is the first time that guidance has been proposed for the transport and export of a non-Cavendish banana. These results may assist other producer countries that wish to diversify their banana exports by growing pink banana. (Resume d'auteur).

Mycosphaerella leaf spot diseases of banana caused by Mycosphaerella musicola (Sigatoka leaf spot, SLS) and M. fijiensis (black leaf streak, BLS) are very destructive. The cultivation of resistant banana clones appears to be the most appropriate means to combat disease because genetic resistance is usually more durable than chemical control. Since pathogen populations maintain a high level of genetic diversity and single gene resistances, such as is suspected in total or hypersensitive resistance situations, are easily overcome, the phenomenon of "partial resistance", which may be multigenic and hence more durable, is used in CIRAD breeding programmes. New hybrids of banana developed by CIRAD are routinely selected for resistance against Mycosphaerella leaf spot diseases. There are four steps in the evaluation process. Firstly, the level of resistance to M. musicola is assessed under field conditions in Guadeloupe. Secondly, the most resistant hybrids are selected for detached-leaf resistance tests to M. musicola and M. fijiensis under controlled conditions. Thirdly, the efficacy of partial resistance of selected hybrids against M. musicola is confirmed in the field in the French West Indies and against M. fijiensis in the field in Mayotte. Finally, the durability of the hybrids' partial resistance is assessed by measuring disease severity in experimental plots for several years. This complete 4-steps process allows, through experimental approaches, to select banana cultivars with durable resistance against Mycosphaerella leaf spot diseases. (Resume d'auteur)

Bananas cultivated for export all belong to Cavendish cultivars and are all recognized as very susceptible to nematodes, particularly to the burrowing nematode Radopholus similis and the lesion nematode Pratylenchus coffeae. Even if there have been many changes in the management of banana nematodes in large commercial banana plantations, chemical control still remains most often the last resort method to manage the nematodes, although the number of registered products is definitely declining. Therefore, nematode control though genetic improvement is gaining new interest worldwide. In this study, 55 banana accessions mostly diploids from the Musa acuminata genome group (AA) but including some triploid accessions (AAA), some diploids of the Musa balbisiana genome group (BB) and some interspecific hybrids (AAB, AB) were evaluated for resistance to four nematode species R. similis, P. coffeae, Meloidogyne incognita and M. arenaria. These experiments were conducted in a growth chamber under controlled conditions. All banana accessions were susceptible to nematode species, although many different levels of susceptibility were detected. This study confirmed the good resistance status to R. similis of some cultivars from the Pisang jari buaya and Pisang batuau subgroups and the partial resistance of 17 diploid accessions significantly different from the susceptible reference cv. Grande Naine. This study also showed that 12 diploid accessions exhibited a partial resistance to P. coffeae, including some usual or potential genitors belonging to the wild diploids subspecies burmannica (cvs. Long Tavoy 1 and 2) and burmannicoides (cv. Calcutta 4). No source of resistance to Meloidogyne spp. was found. These screening results, combining for the first time four nematode species, are discussed within the scope of banana breeding in order to produce parental diploid lines with single or combined nematode resistances and further develop triploids that can substitute existing susceptible commercial cultivars.

The monoculture of banana can have a serious detrimental impact on the environment as pesticide treatments can lead to surface and groundwater pollution. Different approaches based on IPM (integrated pest management) have been developed in the French West Indies to reduce the use of the pesticides in banana cultivation. These methods have been developed using management techniques that prevent the build-up of banana pathogens and also eliminate them, non-chemical techniques, such as cultural practices and biological control, and resistant cultivars. As a result, new crop management systems have led to a 65% decrease of pesticide use over the last 10 years. Major results of the research already undertaken and future research that is being considered to reduce pesticide use in banana plantations are reviewed. (Resume d'auteur)

Banana hybrids with resistance to Yellow Sigatoka and Black Leaf Streak disease were evaluated for resistance to the burrowing nematode Radopholus similis and to the lesion nematode Pratylenchus coffeae in a growth chamber at 24–28°. Plants produced by tissue culture were acclimatised for 6 weeks prior to inoculation. Forty-five days after inoculation with nematodes, the root systems were processed and nematode numbers assessed. Two cultivars of Grande Naine (Musa AAA, Cavendish subgroup, ITC1256 and cv902) and one cultivar of Yangambi Km5 (Musa AAA, Ibota subgroup, ITC1123) were used respectively as susceptible and resistant controls. Results based on multiplication rates and root infestations showed that three of these hybrids (FB918, FB919 and FB924) were not significantly different from the resistant control Yangambi Km5 with a lower multiplication of R. similis. Similarly four of these hybrids (FB918, FB919, FB920, FB924) showed a lower multiplication of P. coffeae, not significantly different from the same resistant control. This is the first study that shows a partial resistance to both nematode species, R. similis and P. coffeae within synthetic hybrids of M. acuminata, adding an important extra value to these dessert banana hybrids formerly bred to resist to Mycosphaerella leaf spot diseases.

The synthetic banana hybrid FB920 (Musa spp., AAA group) has been designed to be resistant to Sigatoka and Black Leaf Streak Diseases, caused respectively by Mycosphaerella musicola and Mycosphaerella fijiensis. In addition to these features, the hybrids seem less susceptible to plant-parasitic nematodes, especially the burrowing nematodes (Radopholus similis) and the lesion nematode (Pratylenchus coffeae) than classic Cavendish cultivars, such as Williams, Grande Naine, or Poyo. This genetic modification drastically reduces pesticide use. Herein, we used the SIMBA model (a model to simulate phenology, growth, and plant-parasitic nematode/banana interactions) to examine the population dynamics of plant-parasitic nematodes in cropping systems with hybrid FB920 in various initial conditions. Results from field observations and simulations show that in the long-term, the spiral nematodes (Helicotylenchus multicinctus) can overtake the burrowing nematodes and that nematode populations are smaller than in Cavendish banana fields. This reduced capacity of FB920 to support multiplication of R. similis reduces the use of pesticides and thus re-creates favourable conditions for fauna, thereby increasing the global sustainability and resilience of banana agro-ecosystems.

Background The genetic basis of growth traits has been widely studied in forest trees. Quantitative trait locus (QTL) studies have highlighted the presence of both stable and unstable genomic regions accounting for biomass production with respect to tree age and genetic background, but results remain scarce regarding the interplay between QTLs and the environment. In this study, our main objective was to dissect the genetic architecture of the growth trajectory with emphasis on genotype x environment interaction by measuring primary and secondary growth covering intervals connected with environmental variations. Results Three different trials with the same family of Eucalyptus urophylla x E. grandis hybrids (with different genotypes) were planted in the Republic of Congo, corresponding to two QTL mapping experiments and one clonal test. Height and radial growths were monitored at regular intervals from the seedling stage to five years old. The correlation between growth increments and an aridity index revealed that growth before two years old (r = 0.5; 0.69) was more responsive to changes in water availability than late growth (r = 0.39; 0.42) for both height and circumference. We found a regular increase in heritability with time for cumulative growth for both height [0.06 - 0.33] and circumference [0.06 - 0.38]. Heritabilities for incremental growth were more heterogeneous over time even if ranges of variation were similar (height [0-0.31]; circumference [0.19 to 0.48]). Within the trials, QTL analysis revealed collocations between primary and secondary growth QTLs as well as between early growth increments and final growth QTLs. Between trials, few common QTLs were detected highlighting a strong environmental effect on the genetic architecture of growth, validated by significant QTL x E interactions. Conclusion These results suggest that early growth responses to water availability determine the genetic architecture of total growth at the mature stage and highlight the importance of considering growth as a composite trait (such as yields for annual plants) for a better understanding of its genetic bases.