Drought is a major limitation to crop yields worldwide. Screening for soybean yield under water deficit is often a bottleneck in breeding programmes. We assessed the validity of a standardized drought tolerance screening method to predict water‐limited field performance of soybean in NW Argentina. First, to determine the phenological period when yield of glasshouse‐grown plants was more sensitive to water deficit, we applied treatments during 21 days in V7, R3 or R5 stages, being the period from R5 to R6 the most critical for yield. Afterwards, two glasshouse experiments were carried out to quantify the tolerance of either eight or four genotypes, respectively, by applying a controlled water deficit of constant intensity during the critical period. Finally, yield data obtained in field trials in Argentina across several locations and seasons classified according to rainfall were analysed. Drought Susceptibility Index was calculated for each experiment and for field data, and rankings of tolerance were similar in all cases. This standardized method, which can be automated for high‐throughput phenotyping, could represent a useful tool in breeding programmes for identifying soybean cultivars with improved performance under drought conditions.

Charcoal rot of soybean (Glycine max (L.) Merr.), caused by Macrophomina phaseolina (Tassi) Goid., is an economically important disease worldwide. In recent years, charcoal rot has become a concern for farmers in north-western Argentina. The present work aimed to (1) evaluate disease incidence of charcoal rot; (2) assess morphological and genetic characteristics of M. phaseolina isolates from soybean and other hosts collected in north-western Argentina; and (3) compare genetic diversity between soybean isolates of M. phaseolina from Argentina and the USA. Incidence of charcoal rot evaluated in 11 locations during five growing seasons (2008-2012) was 1%, 1%, 1%, 5-10% and 90%, respectively, indicating a gradual increase over the cropping seasons. Cluster analysis by AFLP of Argentinean isolates exhibited one main group, with isolate Mp56 separated at a genetic distance of 0.70. Four main groups were identified using SSR markers at the same genetic distance, with Mp56 and Mp53 separated from them. There was no clear association between AFLP, SSR profiles, morphological characteristics or host of origin within isolates from Argentina. However, using principal coordinate analysis of SSRs, 22 isolates of M. phaseolina from soybean from north-western Argentina were clearly distinguished from 11 isolates previously collected from two states in the USA. Our results confirmed the increasing importance of charcoal rot in north-western Argentina and identified characteristics of isolates that may be useful for breeding for disease resistance and developing integrated management programmes for charcoal rot in Argentina in the future.Keywords: charcoal rot, disease development, Macrophomina phaseolina, pathogen genetic diversity, SSR markers Résumé: La pourriture noire du soya (Glycine max (L.) Merr.), causée par Macrophomina phaseolina (Tassi) Goid., est une maladie économiquement importante dans le monde entier. Depuis les dernières années, elle préoccupe les producteurs du nord-ouest de l'Argentine. Ces travaux visaient à: (1) estimer l'incidence de la maladie; (2) évaluer les caractéristiques morphologiques et génétiques des isolats de M. phaseolina collectés sur le soya et d'autres hôtes du Nord-Ouest argentin; et (3) comparer la diversité génétique entre les isolats de M. phaseolina collectés sur le soya en Argentine et aux États-Unis. L'incidence de la pourriture noire évaluée à 11 endroits durant 5 saisons de croissance (de 2008 à 2012) était de 1%, 1%, 1%, 5-10% et 90%, respectivement, ce qui indique une progression graduelle d'une saison à l'autre. L'analyse typologique des données AFLP des isolats argentins a fait ressortir un groupe principal incluant l'isolat Mp56 séparé par une distance génétique de 0.70. Quatre groupes principaux ont été identifiés à l'aide de marqueurs SSR à la même distance génétique, Mp56 et Mp53 en étant séparés. Il n'y avait pas de corrélation nette entre les données AFLP, les profiles SSR, les caractéristiques morphologiques ou l'hôte d'origine parmi les isolats argentins. Tout...

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