Patrick J. Conner

Pecan Varietal Differences in Hemipteran Kernel Damage

Pecan, Carya illinoensis Wangenh. (K. Koch), is susceptible to feeding by leaffooted bugs (Hemiptera: Coriedae) and stink bugs (Hemiptera: Pentatomidae) from fruit set to post harvest. These hemipterans are difficult to control with insecticide sprays. We found that 33 pecan varieties had consistent and significant differences in the incidence of hemipteran kernel damage indicating that host plant resistance may help solve this problem. The rank of varieties for average incidence of damage over 4 yrs, from highest to lowest was: ‘USDA 53-11-139’, ‘USDA 57-7-22’, ‘Shawnee’, ‘Moreland’, ‘USDA 40-9-266’, ‘USDA 49-20-112’, ‘Linberger’, ‘Cape Fear’, ‘Robinson’, ‘Shoshoni’, ‘USDA 64-11-17’, ‘USDA 55-12-17’, ‘Caddo’, ‘USDA 62-5-8’, ‘Sioux’, ‘Melrose’, ‘Tejas’, ‘Pawnee’, ‘Forkert’, ‘Kiowa’, ‘Owens’, ‘Candy’, ‘Gloria Grande’, ‘USDA 49-1-182’, ‘Western Schley’, ‘Creek’, ‘USDA 53-3-36’, ‘USDA 41-19-20’, ‘Maramec’, ‘Sumner’, ‘GraBohls’, ‘Kanza’, and ‘USDA 53-9-1’. Many of the more tolerant varieties have desirable ke...

Scab Susceptibility of a Provenance Collection of Pecan in Three Different Seasons in the Southeastern United States

Pecan scab (caused by Fusicladium effusum) is the most economically destructive disease of pecan in the Southeast United States. Wet, humid conditions typical of the Southeast are known to provide conditions conducive to epidemics. A provenance collection of pecan from 19 locations representing the native range of the tree is located in Byron, Georgia, and was assessed for pecan scab severity in 1998, 2013, and 2014. There were significant differences among the 19 provenances (F = 5.6 to 62.5, P < 0.0001). Provenances from wetter locations (generally north of Texas) had the greatest proportion of scab resistant trees, while provenances from the drier southern areas (Texas and Mexico) tended to be the most susceptible to scab. The association with rainfall was borne out by correlation analysis (r = -0.625 to -0.823 [P < 0.0001 to 0.004]). Other factors consistently associated with scab severity included leaflet tilt and droop angle (r = -0.533 to -0.883 [P < 0.0001 to 0.02]). Multiple regression analysis demonstrated that leaflet droop angle was a particularly good predictor of provenance susceptibility. Leaflet characteristics vary with provenance location, and whether there is a direct relationship between scab severity and leaflet characteristics is not established. Estimates of heritability were not entirely consistent among years, but different methods were used to assess scab severity in 1998 (a 1 to 5 category scale) compared with 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. The provenance collection contains a range of scab-resistant genotypes from diverse locations that can contribute to genetic improvement regarding scab resistance.