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Rhizomania, one of the most devastating diseases in sugar beet production, is caused by Beet necrotic yellow vein virus ( BNYVV) and transmitted by Polymyxa betae. Previously, disease control was possible by cultivation of sugar beet hybrids carrying a major resistance gene Rz1, which restricts virus accumulation in taproots and suppresses symptom development. Over the last few years, BNYVV strains with four RNA components have arisen, which are able to overcome Rz1-mediated resistance. All strains described so far possess an A67V amino acid exchange within the RNA3-encoded P25 pathogenicity factor. In this study, BNYVV was isolated from Rz1 plants, collected in the United Kingdom, the Netherlands and Germany, displaying patches of strong rhizomania symptoms. Sequencing of the coat protein and P25 gene of three isolates showed 100% nucleotide sequence identity and detected AYPR as the P25 tetrad amino acid composition. The ability of this strain to accumulate to higher levels in young plants of Rz1 resistant but not in Rz1 + Rz2 resistant genotypes was initially demonstrated in a greenhouse assay in natural field soil from the Netherlands. This strain was loaded into a virus-free P. betae population and compared to reference strains. The AYPR strain retained its resistance-breaking ability in the Rz1 genotypes and displayed replication at a higher rate compared to the Rz1-resistance-breaking P type. The strain origin is unclear and it remains speculative whether the occurrence at different geographic locations is the result of independent selection or displacement of infested soil. [ABSTRACT FROM AUTHOR]

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The cucurbit powdery mildew (CPM) caused by different fungal species is a major concern for cucurbit crops around the world. In Argentina CPM constitutes the most common and damaging disease for cucurbits, especially for squash crops (Cucurbita moschata). The present study displays initial insights into the knowledge of the disease in western Argentina, including the determination of the prevalent species causing CPM, as well as the evaluation of the resistance of squash cultivars and breeding lines. Fungal colonies were isolated from samples collected in Mendoza province, Argentina. A field trial was also performed to assess the resistance of five squash accessions, including commercial cultivars and breeding lines. The severity of CPM was analyzed and epidemiological models were built based on empirical data. The morphological determinations and analysis with specific molecular markers confirmed Podosphaera xanthi as the prevalent causal agent of CPM in Mendoza. The results od the field trial showed differences in the resistance trait among the squash accessions. The advanced breeding line BL717/1 showed promising results as source of CPM resistance for the future development of open pollinated resistant cultivars, a crucial tool for an integrative control of the disease.

A number of plant species have adapted to parasitize other plants, and some parasitic species pose severe constraints to major crops. The role of strigolactones and other metabolites present in host root exudates as germination stimulants for weedy root parasitic weed seeds has been known for the last 40 years. Recently, the ecological and developmental roles of strigolactones have been clarified by the discovery that they are a new class of plant hormone that controls shoot branching and serve as host recognition signals for mycorrhizal fungi. Parasitic plants also recognize these chemicals and use them to coordinate their life cycle with that of their host. Here we review agronomic practices that use parasitic germination stimulant production as a target for manipulation to control parasitic weeds. [ABSTRACT FROM AUTHOR]

Abstract: Grain mould causes qualitative and quantitative loss to grain in sorghum. Grain mould resistance is a complex problem as grain mould is caused by complex of fungi and the resistance is governed by many traits. Breeding efforts during the last 3 decades to develop grain mould resistance in high yielding genotypes have not paid many dividends. We developed a strategy to breed for grain mould resistance in high yielding back ground. Twenty five crosses between elite lines and grain mould resistant genetic stocks (susceptible×resistant/moderately resistant and moderately resistant×resistant crosses) were evaluated in F1, and derivatives performing superiorly for grain mould resistance in F2–F4 at physiological maturity were advanced. The early generation material F2s (10) and F3s (125) in 6 locations (representing rainy-season-sorghum growing 6 states of India where grain mould is one of the major biotic stresses), and later generations F4s and F5s in 3 locations (one location, Parbhani is a hot spot for grain moulds and 2 locations, Hyderabad and Coimbatore in epiphytotic conditions) were evaluated. Only 25 selections out of 384 derivatives in F4 were superior over locations for grain mould resistance at physiological maturity and harvest maturity (Our simultaneous studies in RILs for grain mould resistance across years and locations have shown that the variation obtained for grain mould resistance at physiological maturity is genetically governed and the grain mould score further gets compounded at harvest maturity depending on rainfall received after physiological maturity). These superior lines were advanced and further evaluated in F5 and F6 for grain mould resistance and grain yield. During 2007, out of 25 F5 derivatives, 12 were on par (scored 3.1–4.4) with resistant check, B 58586 (3.2 score) where as susceptible check, 296 B registered a score of 7.5. GMN nos. 41, 52, 59, and 63 performed on par with resistant check, B 58586 for grain mould resistance over 9 environments. Since we selected for grain mould resistance in early generations at physiological maturity in multi-locations, we could identify superior lines for grain mould resistance. Most of these lines are high yielding and on par with elite check, C43 for grain yield. These lines are distinct for DUS testing traits from grain mould resistant check, B 58586. [Copyright &y& Elsevier]

Cucurbit downy mildew, caused by the oomycete Pseudoperonospora cubensis, is a devastating, worldwide-distributed disease of cucurbit crops in the open field and under cover. This review provides recent data on the taxonomy, biology, ecology, host range, geographic distribution and epidemiology of P. cubensis. Special attention is given to host-pathogen interactions between P. cubensis and its economically-important cucurbit hosts ( Cucumis sativus, C. melo, Cucurbita pepo, C. maxima, and Citrullus lanatus); pathogenic variability in P. cubensis at the species, genus, and population levels; and, differentiation of pathotypes and races. Genetics and variability of host resistance and cellular and molecular aspects of such resistance are considered. A focus is given to methods of crop protection, including prevention and agrotechnical aspects, breeding for resistance-classical and transgenic approaches, chemical control and fungicide resistance. Novel technologies in biological and integrated control are also discussed. This review also summarizes the most important topics for future research and international collaboration. [ABSTRACT FROM AUTHOR]

White rot is an important disease of sunflowers. Sunflower genotypic responses to S. sclerotiorum have to be evaluated with precision. White rot disease could be assessed by components of partial resistance and this would help to evaluate accurately genotypic responses. Here we wish to show which of variables or components of white rot are most suitable for describing sunflower performance during disease cycle. Twelve sunflower genotypes have been grown in an experiment and then inoculated. Disease incidence, relative incubation period, disease severity (observed at two moments), and the growth lesion rate were scored. All variables showed variability among the genotypes. The disease incidence and relative incubation period were confirmed as components of partial resistance. The results also indicated that the growth lesion rate during the intermediate and last phases of the disease seemed most appropriate to be used simultaneously with disease incidence and relative incubation period. If these three components were selected simultaneously, developed cultivars would have a more complex resistance and they would be less prone to the disease. [ABSTRACT FROM AUTHOR]

1. Plant virus diseases severely constrain agricultural production world-wide, especially in less developed countries. The use of resistant cultivars may put a selection pressure on the plant virus to evolve towards more aggressive types. We used a modelling approach to show the impact of resistance, expressed through different mechanisms, on selection for plant virus strains with a higher multiplication rate. Begomoviruses (Geminiviridae: Begomovirus) inducing leaf curl diseases on tomato were used as key examples. 2. A model for the epidemiology of the plant–virus–vector system was combined with a model for the within-plant dynamics of the virus. Four types of resistance were defined, each expressing resistance through one or more model parameters. The evolutionary stable strategy (ESS) approach was used to study the effect of resistance on the evolution of within-plant virus multiplication rate. 3. Resistance expressed through reduced virus acquisition by the vector, and resistance expressed through reduced inoculation of the plant, do not put a selection pressure on the virus to evolve towards a higher multiplication rate. 4. Resistance expressed through reducing within-plant virus titre and symptom reducing resistance do put a selection pressure on the virus to evolve towards a higher multiplication rate. 5. Synthesis and applications. We have shown how to disentangle different types of plant resistance. We have also shown that each type of resistance puts a different type of selection pressure on the virus. Virologists and plant breeders can use these results to develop methods to characterize the combination of resistance mechanisms in the cultivars they breed and, on the basis of this, determine whether the cultivar will put a selection pressure on the virus to evolve more harmful types. This new approach to plant resistance against virus diseases has been made possible by combining ecological insight in virus–vector–plant interactions with ESS calculations. [ABSTRACT FROM AUTHOR]

Abstract: Date palm (Phoenix dactylifera L.) is qualified as a ‘tree’ of great ecological and socio-economical importance in desert oases. Unfortunately, it is being decimated, especially in Morocco and Algeria, by a fusariosis wilt called bayoud and caused by Fusarium oxysporum f. sp. albedinis (Fao). Controlling this disease requires the implementation of an integrated management program. Breeding for resistance is one of the most promising component strategies of this program. Few naturally resistant cultivars with a mediocre fruit quality (dates) are known. Conventional and non-conventional methods are under development and have to use the simplest and easiest methods to screen for resistant individuals. The use of pathogen toxins as selective agents at the tissue culture step might be a source of variability that can lead to the selection of individuals with suitable levels of resistance to the toxin and/or to the pathogen among the genetic material available. Foa produces toxins such as fusaric, succinic, 3-phenyl lactic acids and their derivatives, marasmins and peptidic toxins. These toxins can be used bulked or separately as selective agents. The aim of this contribution was to give a brief overview on toxins and their use as a mean to select resistant lines and to initiate a discussion about the potential use of this approach for the date palm–Foa pathosystem. This review does not pretend to be comprehensive or exhaustive and was prepared mainly to highlight the potential use of Foa toxins for selecting date palm individuals with a suitable resistance level to bayoud using toxin-based selective media. To cite this article: A. El Hadrami et al., C. R. Biologies 328 (2005). [Copyright &y& Elsevier]

Verticillium wilt of olive (VWO), caused by the soil-borne pathogen Verticillium dahliae, is considered one of the most important diseases affecting this tree crop. One of the best VWO management measures is the use of tolerant cultivars. Remarkably, no information is available about olive functional traits and their potential relationship with tolerance to V. dahliae. Twenty-five selected functional traits (for leaf, stem, root and whole plant) were evaluated in six olive varieties differing in their VWO tolerance level to identify possible links between this phenotype and functional traits' variation. High intervarietal diversity was found among cultivars and several functional traits were related with VWO tolerance. Tolerant varieties showed higher leaf area, dry matter content (leaf, stem and plant) and mass fraction for stems, but lower for leaves. Significant differences were also detected for root functional traits, tolerant cultivars displaying larger fine root diameter and lignin content but smaller specific length and area of thick and fine roots. Correlations were found among functional traits both within varieties and between levels of tolerance/susceptibility to VWO. Associations were observed between biomass allocation, dry matter content and VWO tolerance. The most relevant difference between tolerant and susceptible cultivars was related to root system architecture. [ABSTRACT FROM AUTHOR]

In breeding for resistance to rhizomania, breeding material was routinely examined for resistance to the rhizomania virus over several years. This study was performed in order to investigate the value of virological examination of sugarbeet breeding material in breeding for resistance to the rhizomania virus. Tests were conducted with varieties susceptible or partially resistant to rhizomania, as well as with several new and more-resistant hybrids. A test on young plants showed that all genotypes contained beet necrotic yellow-vein virus (BNYVV), but that the virus content differed widely. Plants of two commercially used partially resistant varieties had, on average, only half the virus content of susceptible varieties in their roots, and plants of eight new hybrids still in the process of registration contained less than one third of that amount. There was a significant negative correlation between the quantity of BNYVV in young plant roots and final yield under disease conditions in the field. Opportunities for further improvement in the level of the resistance to BNYVV in sugarbeet by means of conventional breeding programmes are discussed. [ABSTRACT FROM AUTHOR]

The bean-pod weevil (BPW), Apion godmani Wagner, often causes heavy losses in crops of common bean ( Phaseolus vulgaris L.). Farmers need resistant bean cultivars to minimize losses, cut production costs, stabilize seed yield, and reduce pesticide use and consequent health hazards. To design effective breeding methods, breeders need new and better sources of resistance and increased knowledge of their modes of inheritance. We therefore: (1) compared sources of resistance to BPW, (2) studied the inheritance of resistance, and (3) determined whether the sources possess similar or different genes for BPW resistance. The following sources of resistance, originating from the Mexican highlands, were evaluated for 3 years at INIFAP-Santa Lucía de Prias, Texcoco, Mexico: 'Amarillo 153', 'Amarillo 169', 'Hidalgo 58', 'J 117', 'Pinto Texcoco', 'Pinto 168', and 'Puebla 36'. All except 'Puebla 36' were crossed with the susceptible cultivar 'Jamapa'. 'Amarillo 153' and 'Puebla 36' were crossed with another susceptible cultivar, 'Bayo Mex'. The parents, F hybrids, and F populations were evaluated for BPW damage in 1992. Backcrosses of the F of Jamapa/Pinto 168 to the respective susceptible and resistant parents were also evaluated in 1992. All seven resistant accessions were crossed in all possible combinations, excluding reciprocals. The resulting 21 F hybrids and 21 F populations were evaluated for BPW damage in 1994. 'J 117' had the highest level of resistance to BPW. 'Pinto Texcoco' and 'Puebla 36' had the highest mean damage score of all seven sources of resistance. The F hybrids between susceptible parents and resistant sources were generally intermediate. Two genes segregating independently controlled the BPW resistance in each accession. One gene, Agm, has no effect when present alone, whereas the other gene, Agr, alone conferred intermediate resistance. When both genes were present, resistance to BPW was higher. Based on mean BPW damage scores, all 21 F hybrids and their F populations, derived from crosses among seven resistant accessions, were resistant. However, data from individual plant damage scores in F populations of Amarillo 169/Pinto 168 and Pinto Texcoco/Pinto 168 suggested that at least one gene in each of the three accessions was non-allelic. Data also indicated that 'Amarillo 169' had a dominant gene that conferred high levels of BPW resistance, irrespective of the alleles at the other locus; and that 'Pinto Texcoco' and 'Pinto 168' possessed two different genes for intermediate resistance. [ABSTRACT FROM AUTHOR]

Diploid parents with some resistance to PLRV, were intercrossed to give 3 families with 191 clones which were evaluated for reaction to PLRV and yielding ability. After inoculation with PLRV the clones could be separated into those: 1) resistant, 2) susceptible, 3) intolerant, reacting with low virus concentration, 4) tolerant and 5) intermediate in reaction. Both the ELISA test and the evaluation of external disease symptoms were necessary to separate the clones. No correlation was found between resistance to PLRV and tuber yielding ability. [ABSTRACT FROM AUTHOR]

Verticillium (Verticillium dahliae Kleb.) wilt is one of the most devastating diseases affecting olive (Olea europaea L. subsp. europaea var. europaea) cultivation. Its effective control strongly relies on integrated management strategies. Olive cultivation systems are experiencing important changes (e.g., high-density orchards, etc.) aiming at improving productivity. The impact of these changes on soil biology and the incidence/severity of olive pests and diseases has not yet been sufficiently evaluated. A comprehensive understanding of the biology of the pathogen and its populations, the epidemiological factors contributing to exacerbating the disease, the underlying mechanisms of tolerance/resistance, and the involvement of the olive-associated microbiota in the tree's health is needed. This knowledge will be instrumental to developing more effective control measures to confront the disease in regions where the pathogen is present, or to exclude it from V. dahliae-free areas. This review compiles the most recent advances achieved to understand the olive–V. dahliae interaction as well as measures to control the disease. Aspects such as the molecular basis of the host–pathogen interaction, the identification of new biocontrol agents, the implementation of "-omics" approaches to unravel the basis of disease tolerance, and the utilization of remote sensing technology for the early detection of pathogen attacks are highlighted. [ABSTRACT FROM AUTHOR]

Fusarium head blight (FHB) and the accumulation of deoxynivalenol (DON) mycotoxin induced by Fusarium graminearum and other Fusarium fungi cause serious problems for oat production in the Nordic region (Scandinavia, Fennoscandia). Besides toxin accumulation, FHB causes reduction in grain yield and in germination capacity. Here, genomic approaches for accelerating breeding efforts against FHB and DON accumulation were studied. Resistance-related traits included DON content, F.graminearum DNA (relative to oat DNA) content (qFUSG) measured with real-time quantitative polymerase chain reaction (PCR), Fusarium-infected kernels (FIKs) and germination capacity (GC). Plant germplasm used in the study consisted of mostly breeding lines, and additionally, a few cultivars and exotic accessions. Genome-wide association study (GWAS) and genomic prediction, enabling genomic selection (GS) on the resistance-related and collected agronomic traits, were performed. Considerable genetic correlations between resistance-related traits were observed: DON content had a positive correlation (0.60) with qFUSG and a negative correlation (−0.63) with germination capacity. With the material in hand, we were not able to find any significant associations between markers and resistance-related traits. On the other hand, in genomic prediction, some resistance-related traits showed favorable accuracy in fivefold cross-validation (GC = 0.57). Genomic prediction is a promising method and genomic estimated breeding values (GEBVs) generated for germination capacity are applicable in oat breeding programs. [ABSTRACT FROM AUTHOR]