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ARS Home » Southeast Area » Byron, Georgia » Fruit and Tree Nut Research » Research » Publications at this Location » Publication #346980
Title: Evidence for sexual reproduction: identification, frequency and spatial distribution of Venturia effusa (pecan scab) mating type idiomorphs

Author
item YOUNG, CAROLYN - Samuel Roberts Noble Foundation, Inc
item Bock, Clive
item CHARLTON, NIKKI - Samuel Roberts Noble Foundation, Inc
item CHAKRADHAR, MATTUPALLI - Samuel Roberts Noble Foundation, Inc
item KROM, NICK - Samuel Roberts Noble Foundation, Inc
item BOWEN, JOANNA - New Zealand Institute Of Plant & Food Research
item TEMPLETON, MATTHEW - New Zealand Institute Of Plant & Food Research
item PLUMMER, KIM - University Of Auckland
item WOOD, BRUCE - Retired ARS Employee

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2018
Publication Date: 7/1/2018
Citation: Young, C.A., Bock, C.H., Charlton, N.D., Chakradhar, M., Krom, N., Bowen, J.K., Templeton, M., Plummer, K.M., Wood, B.W. 2018. Evidence for sexual reproduction: identification, frequency and spatial distribution of Venturia effusa (pecan scab) mating type idiomorphs. Phytopathology. 108: 837-846.

Interpretive Summary: The most destructive disease of pecan (Carya illinoinensis) in the southeastern U.S.A. is pecan scab (caused by Venturia effusa, Pecan scab can result in catastrophic yield loss when conditions are favorable for an epidemic. Venturia effusa is currently known only by its asexual (conidial) stage. However, the chrateristics of genetic diversity observed within populations of V. effusa are typical of a sexually reproducing fungal pathogen. We identified a single mating-type gene, MAT1-1-1 in a draft genome of V. effusa. The MAT1-1-1 locus is flanked by two conserved genes encoding a DNA lyase (APN2) and a hypothetical protein. The mating type locus spanning the flanking genes was amplified and sequenced from a subset of 14 isolates, of which seven contained MAT1-1-1 and the remaining samples contained MAT1-2-1 (with an HMG-box). A multiplex PCR screen was developed and used to screen 784 mono-conidial isolates of V. effusa collected from 11 populations of pecan across the southeastern U.S.A. Analysis of this collection revealed the frequency of the mating type idiomorphs is in a 1:1 equilibrium of MAT1-1:MAT1-2, highly indicative of sexual recombination. The apparent equilibrium of the mating type idiomorphs provides impetus for a renewed effort to search for the sexual stage of V. effusa. Identification of a sexual stage will provide better understanding of the disease epidemiology and pathogen population genetics, and eventually a basis for better management of existing resistance genes in pecan.

Technical Abstract: Venturia effusa, (syn. Fusicladium effusum), is the causal agent of pecan scab, the most prevalent disease of pecan (Carya illinoinensis) in the southeastern U.S.A. Infection by the pathogen can result in serious and even catastrophic yield loss when conditions are favorable for an epidemic. Venturia effusa is currently known only by its asexual (conidial) stage. However, the degree and distribution of genetic diversity observed within and among populations of V. effusa are typical of a sexually reproducing fungal pathogen, and comparable to other Dothideomycetes with a known sexual stage, including the closely related apple scab pathogen, V. inaequalis. Using the mating type idiomorphs from V. inaequalis we identified a single mating-type gene, MAT1-1-1 (containing an alpha-box), in a draft genome of V. effusa. The MAT1-1-1 locus is flanked by two conserved genes encoding a DNA lyase (APN2) and a hypothetical protein. The mating type locus spanning the flanking genes was amplified and sequenced from a subset of 14 isolates, of which seven contained MAT1-1-1 and the remaining samples contained MAT1-2-1 (with an HMG-box). A multiplex PCR screen was developed to amplify MAT1-1-1, MAT1-2-1, and a conserved reference gene (TUB2), and used to screen 784 mono-conidial isolates of V. effusa collected from 11 populations of pecan across the southeastern U.S.A. A hierarchical sampling protocol representing region, orchard and tree allowed for analysis of mating type structure at different spatial scales. Analysis of this collection revealed the frequency of the mating type idiomorphs is in a 1:1 equilibrium of MAT1-1:MAT1-2. The apparent equilibrium of the mating type idiomorphs provides impetus for a renewed effort to search for the sexual stage of V. effusa. Identification of a sexual stage will provide better understanding of the disease epidemiology and pathogen population genetics, and eventually a basis for better management of existing resistance genes in pecan.