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Oral: Pathogen Ecology


Evidence for sexual reproduction in Fusicladium effusum
N. CHARLTON (1), C. Mattupalli (2), B. Wood (3), C. Bock (3), C. Young (2) (1) The Samuel Roberts Noble Foundation, U.S.A.; (2) The Samuel Roberts Noble Foundation, U.S.A.; (3) USDA-ARS-SEFTNRL, U.S.A.

Fusicladium effusum is the causal agent of pecan scab, the most prevalent and often catastrophic disease of pecan in the southeastern USA. Despite earlier efforts to determine a sexual stage, reproduction in F. effusum has been observed only by asexually produced conidia. However, the degree and distribution of genetic diversity observed within and among populations of F. effusum are typical of a sexually reproducing fungus. The mating type locus was identified in a draft genome of F. effusum and was amplified and sequenced in 14 isolates collected from different geographic locations and cultivars, revealing that 50% of the samples contained the mtAA idiomorph and are considered mating type A (MTA). The remaining samples contained mtBA and are mating type B (MTB). A multiplex PCR screen was developed to amplify mtAA, mtBA and tubB, and used to screen 1203 isolates of F. effusum from 13 pecan populations across the southeastern USA. Analysis of this collection revealed the frequency of the mating type idiomorphs is in a 1:1 equilibrium. Select isolates were crossed in pairwise combinations on oatmeal agar and after six months, organs typical of immature sexual fruiting bodies were observed, indicating existence of a putative sexual stage. Identification of a sexual stage will provide improved understanding of the disease epidemiology and pathogen population genetics, and potentially provide insight into novel approaches to manage this damaging disease.