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 side-by-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.
Highlights
Sclerotinia sclerotiorum (Lib.) de Bary, causal agent of white mold on dry bean (Phaseolus vulgaris L.), is among the most devastating and promiscuous necrotrophic fungal plant pathogens, having a diverse host range, including weed species and causes yield losses in many important agronomic crops (BOLTON et al, 2006).To establish management strategies it is important to understand the variation nature of that pathogen in population and aspects of epidemiology
Microsatellite markers have been very informative in studying genetic diversity and population biology of S. sclerotiorum due to the high mutation rates that are multiallelic in nature, which makes them useful in phylogenetic inference (SIRJUSINGH; KOHN, 2001)
The 25 S. sclerotiorum isolates from Brazil were grouped into clusters using a distance-based analysis of the data obtained from 8 microsatellite markers producing different base pair sizes
Summary
Sclerotinia sclerotiorum (Lib.) de Bary, causal agent of white mold on dry bean (Phaseolus vulgaris L.), is among the most devastating and promiscuous necrotrophic fungal plant pathogens, having a diverse host range, including weed species and causes yield losses in many important agronomic crops (BOLTON et al, 2006).To establish management strategies it is important to understand the variation nature of that pathogen in population and aspects of epidemiology. Sclerotinia sclerotiorum has a haploid somatic phase in which clonality is the result of both asexual reproduction by means of sclerotia and sexual reproduction by selffertilization (KOHN 1995) with the expectation that intraclonal variation is due to mutation (CARBONE et al 1999; CARBONE; KOHN 2001; HAMBLETON et al, 2002). Microsatellite alleles are often closely associated with mycelial compatibility, an independent marker used to genotype isolates and thought to be under multigenic regulation (SCHAFER; KOHN, 2006; CLARKSON et al, 2013). Microsatellite markers have been very informative in studying genetic diversity and population biology of S. sclerotiorum due to the high mutation rates that are multiallelic in nature, which makes them useful in phylogenetic inference (SIRJUSINGH; KOHN, 2001). In previous studies on S. sclerotiorum variation, mycelial compatibility groupings (MCGs) were used to measure population diversity among pathogen isolates
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