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Poster: Biology & Disease Mgmt: Genetics of Resistance


Scab susceptibility of a provenance collection of pecan
C. BOCK (1), L. Grauke (2), P. Conner (3), S. Burrell (1), M. Hotchkiss (1), D. Boykin (4), B. Wood (1) (1) USDA/ARS SE Fruit & Tree Nut Research Laboratory, U.S.A.; (2) USDA/ARS Pecan Breeding and Genetics, U.S.A.; (3) University of Georgia, U.S.A.; (4)

Scab (caused by Fusicladium effusum) is the most economically destructive disease of pecan in the Southeast US. Epidemics are favored by rainfall and high humidity. A provenance collection of ~950 pecan trees from 19 locations representing the native range of the species is located in Byron, Georgia, and was assessed for pecan scab severity in 1998, 2013 and 2014. Foliar scab severity was estimated visually. There were consistent significant differences among the 19 provenances (F = 5.6 to 62.5, P<0.0001), with those from wetter locations (generally north of Texas) with the greatest proportion of scab resistant trees, while those provenances from the drier southern areas (Texas and Mexico) tended to be the most susceptible. However, within each provenance there was a range in susceptibility of trees. An association of provenance susceptibility with precipitation at the provenance source location bore out the relationship (r=-0.625 to -0.823 (P<0.0001 to 0.004)). Estimates of heritability were not entirely consistent among years, but different methods were used to assess scab severity in 1998 (a 1-5 category scale) compared to 2013 and 2014 (the percent ratio scale). Despite using different methods, there was generally good agreement among years in regard to severity of disease on individual trees. In conclusion, trees from more northern populations (in areas with greater annual rainfall) are most likely to provide valuable and diverse sources of resistance to scab.