Variability of the Angular Leaf Spot pathogen in Argentina

APARICIO M; SPEDALETTI Y; STENGLEIN S; TABOADA G; ABAN C; MAMANÍ GONZÁLES S; VIZGARRA O; CUELLAR D; GALVÁN M

Skukuza

Workshop; Common Bean Disease Workshop on Angular Leaf Spot and Root Rots; 2015

ARS-USDA, Agricultural Research Council (South Africa)

Angular leaf spot (ALS) caused by the fungus Pseudocercospora griseola (Sacc.) Crous & U. Braun, has been reported to be one of the most destructive and widespread problems of common bean production in Argentina. The importance of the disease has increased in recent years, becoming one of the main causes of yield losses and seed quality decrease. The success of breading for resistance to ALS requires a thorough identification of the pathogen diversity. In the northwestern region of Argentina, which is the principal area of common bean production of the country, 13 races of the ALS pathogen have been identified based on a set of differential cultivars. The aims of this study were to analyze the genetic variability and population structure of P. griseola isolates collected in several bean fields in northwestern Argentina by means of URP-PCR and ITS-rDNA sequences. Based on the ITS sequences the isolates were identified as Andean (P. griseola f. griseola) or Middle American (P. griseola f. mesoamericana) and the haplotype structure of each group was inferred. A total of 135 bands were amplified using 12 URP primers. Principal coordinates analysis (PCoA) was performed to estimate genetic similarity between isolates. The Andean isolates showed a higher dispersion suggesting lower genetic similarity than the Middle American isolates. The AMOVA based on the URP data showed that the Andean isolates significantly differed from the Middle American once, with low levels of gene flow and 75% of the variation remaining among groups, supporting the idea of coevolution of the pathogen with its host. Some admixed genotypes evidenced in the structure analyses might be the result of parasexual reproduction. The URP approach was more efficient than other genome-wide multilocus techniques used in previous studies to characterize the P. griseola isolates since URP markers identified 37 unique multilocus haplotypes compared with 18 haplotypes defined with RAPD and ISSR markers. Our results demonstrate that this technique is a powerful tool to characterize intraspecific polymorphisms and detect diversity among P. griseola isolates. Increased knowledge of the population biology of the ALS pathogen would contribute to better management of the disease in agricultural ecosystems. Furthermore, the great variability reported herein should be considered when identifying genotypes with durable resistance to angular leaf spot.