Location: Fruit and Tree Nut ResearchTitle: Incidence-severity relationships for scab on foliage and fruit of pecan
Submitted to: American Phytopathological Society Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/17/2017
Publication Date: 12/1/2017
Citation: Bock, C.H. 2017. Incidence-severity relationships for scab on foliage and fruit of pecan. American Phytopathological Society Annual Meeting. 107:S5.45.
Technical Abstract: Venturia effusa is the causal agent of pecan scab, the most prevalent disease of pecan in the southeastern US. Venturia effusa is currently only known to reproduce asexually, yet the genetic diversity among populations of pecan scab suggest it is a sexually reproducing pathogen. Analysis of the mating type idiomorphs in a collection of 1203 isolates of V. effusa revealed a 1:1 equilibrium. Based on identification of the mating type idiomorphs, select isolates were crossed in pairwise combinations in triplicate on oatmeal agar and stored at 4C in the dark. After a four month cold treatment, immature sexual fruiting bodies were observed with pairings of opposite mating types. The pairings were subsequently incubated at 24C with a 12h photoperiod to monitor maturation of the fruiting bodies. Pseudothecia were randomly selected from the zone between opposite mating types to evaluate the maturity of the ascocarp. Squash mounts of pseudothecia were examined to determine ascospore maturity. Asci and ascospores were typically observed after two weeks under a 12h photoperiod at 24C following the four month cold treatment. This first report suggests that the fungus is capable of producing sexual spores in vitro, which emphasizes the need to revisit the disease cycle. Identification of the sexual stage in nature will provide improved understanding of the disease epidemiology, pathogen population genetics, and potentially provide insight into approaches to manage this disease.