Genetic and aggressiveness variation among Sclerotinia sclerotiorum dry bean isolates from Brazil fields

Abstract

Sclerotinia sclerotiorum, infection of bean fields, has increased in Brazil. Fungicides application is the control strategy used due to lack of cultivars with complete disease resistance. To guide the use of isolates in resistance screening 25 S. sclerotiorum isolates from Brazilian dry bean fields were characterized using microsatellite markers, mycelial compatibility groups (MCGs) and aggressiveness. Microsatellite primer pairs were used to identify polymorphisms among the S. sclerotiorum isolates and MCGs were determined from interaction of all isolates grown sideby-side. Aggressiveness was derived from a straw test where fungal mycelium was placed over a cut bean stem and rated for disease progress. Data from microsatellite profiles grouped the 25 isolates into four clusters and seven MCGs were identified. No association among host cultivar and cluster or MCG of isolates was observed. For MCGs, 57% contained isolates sampled frequently over multiple locations and 43% contained isolates unique to locations. There were significant differences among isolates in aggressiveness within and between MCGs. The most aggressive isolates in resistance screening will be helpful in the identification of higher levels of resistance in bean germplasm/lines.

Reaction of brazilian cotton genotypes to white mold depends on pathogen aggressiveness and incubation conditions

“…The greater aggressiveness of strain ScC was evident in the growth chamber, in comparison with strain ScS, even though this had been described as highly aggressive to soybeans (GARCIA; JULIATTI, 2012). Variability in S. sclerotiorum aggressiveness, reported in common beans, sunflower and soybeans (PRICE;CALHOUN, 1975;IRANI et al, 2011;ZANCAN et al, 2015), is commonly observed among strains isolated from different hosts or from distant geographical regions (KULL et al, 2004;DAVAR et al, 2011) due to variation in effector production (CASTRO et al, 2016). Such variability is relevant since, in breeding programs, the use of more aggressive strains is recommended in order to identify greater resistance levels in the germplasm collection (ZANCAN et al, 2015).…”

“…Variability in S. sclerotiorum aggressiveness, reported in common beans, sunflower and soybeans (PRICE;CALHOUN, 1975;IRANI et al, 2011;ZANCAN et al, 2015), is commonly observed among strains isolated from different hosts or from distant geographical regions (KULL et al, 2004;DAVAR et al, 2011) due to variation in effector production (CASTRO et al, 2016). Such variability is relevant since, in breeding programs, the use of more aggressive strains is recommended in order to identify greater resistance levels in the germplasm collection (ZANCAN et al, 2015). The result obtained in this study suggests a possible physiological specialization of S. sclerotiorum to its host, previously suggested (DAVAR et al, 2011) but still awaiting for omics studies about the interaction Sclerotinia-cotton to be confirmed.…”

“…Nevertheless, it was possible to observe considerable variability for partial resistance among the genotypes, including commercial ones, such as FM944 GL, which expressed the smallest lesion size and disease severity, contrasting with FM975 WS. Research with lineages of common beans, canola and soybeans, resistant to this pathogen has been studied; however, no sources of complete resistance have been identified, but only variability for partial resistance (ARAHANA et al, 2001;AHMADIFAR;DALIL 2013;JULIATTI et al, 2013;ZANCAN et al, 2015).…”

An overview of the Sclerotinia sclerotiorum pathosystem in soybean: impact, fungal biology, and current management strategies

“…These findings suggest that soybean genotypes should be selected for resistance using appropriately representative isolates. In Brazil, the importance of characterizing S. sclerotiorum isolate diversity has been investigated for dry bean resistance evaluations; however, little or no regional variation in aggressiveness was found and/or no interaction between isolate diversity and cultivars was observed (Koga et al 2014;Lehner et al 2016a, b;Zancan et al 2015). As such, resistance evaluations, should account for the regional variation within a pathogen population to ensure the development and release of a durable SSR-resistant varieties.…”

Are Sclerotinia sclerotiorum populations from the tropics more variable than those from subtropical and temperate zones?

“…In this study, the genotypic diversity varied from 0.64 to 0.71, which led the authors to speculate on the occurrence of outcrossing, but no specific analyses were performed to test this hypothesis. Recently, three papers addressing variability of S. sclerotiorum from dry bean fields in Brazil were published (Abreu and Souza 2015;Lehner et al 2015;Zancan et al 2015). All studies used SSR markers and MCGs to estimate the variability, but the conclusions were different.…”