Analysis of the population structure of Sclerotinia sclerotiorum causing white mold on common bean Brazil

• Ano de defesa: 2015
• Autor(a) principal: Lehner, Miller da Silva
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Feijão - Melhoramento genético; Feijão - Doenças e pragas - Controle; Feijão - Resistência a doenças e pragas; Phaseolus vulgaris; Melhoramento Vegetal
• Link de acesso: http://www.locus.ufv.br/handle/123456789/6385

White mold caused by the fungus Sclerotinia sclerotiorum is a highly destructive disease to common beans in Brazil. The pathogen is widely dispersed in the production areas, which leads to extensive damage to common bean yields. White mold control is done by intensive use of fungicides, because resistant cultivars are not available in Brazil. To assist the development of resistant cultivars and extend the durability of any resistant materials proper understanding of the genetic structure of the pathogen population is required. Nevertheless, relatively little is known about the genetic structure of S. sclerotiorum affecting common bean in Brazil. Microsatellite (SSR) markers and mycelial compatibility groups (MCGs) were used to assess the genetic structure of the population of S. sclerotiorum. A total of 300 isolates were collected from the main producing areas of common bean in Brazil. The population is subdivided into MCGs, within which random mating takes place. However, when analyzed as a whole (all MCGs), the population has a clonal genetic structure. The aggressiveness of 20 S. sclerotiorum isolates from distinct SSR haplotypes and variable morphology was assessed using two inoculation methods and two common bean cultivars. The aggressiveness of the isolates was similar, except for a higher response of Ss-217 when inoculated on plants of the genotype A195. Aggressiveness was not correlated with MCGs, SSR haplotypes, mycelial pigmentation, growth rate or sclerotia production. A total of 282 isolates of S. sclerotiorum were screened for sensitivity to thiophanate- methyl (TM), fluazinam and procymidone, fungicides usually used for white mold control of common bean in Brazil. No isolate was resistant to fluazinam or procymidone. One isolate was resistant to TM. The resistant isolate had a L240F mutation in the β-tubulin gene, which had never been reported. The fitness of TM- resistant isolate was comparable to sensitive isolates. Therefore, resistance management practices should be implemented to delay the spread of TM-resistant genotypes.