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ARS Home » Southeast Area » Byron, Georgia » Fruit and Tree Nut Research » Research » Publications at this Location » Publication #326341
Title: Scab susceptibility of a provenance collection of pecan in three different seasons in the Southeastern USA

Author
item Bock, Clive
item Grauke, Larry
item CONNER, PATRICK - University Of Georgia
item Burrell, Sue
item Hotchkiss, Michael - Mike
item Boykin, Deborah
item Wood, Bruce

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/29/2016
Publication Date: 9/1/2016
Citation: Bock, C.H., Grauke, L.J., Conner, P., Burrell, S.L., Hotchkiss, M.W., Boykin, D.L., Wood, B.W. 2016. Scab susceptibility of a provenance collection of pecan in three different seasons in the Southeastern USA. Plant Disease. 100(9):1937-1945.

Interpretive Summary: Pecan scab is the most economically destructive disease of pecan in the Southeast US. It is spread in rain and is widespread in the Southeast where conditions are 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 with those from wetter locations (generally north of Texas) having a greater 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 born out by correlation analysis. 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 areas with greater annual rainfall (generally more norther locations) 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.

Technical Abstract: Pecan scab (caused by Fusicladium effusum) is the most economically destructive disease of pecan in the Southeast US. 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 born 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 1-5 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. The provenance collection contains a range of scab-resistant genotypes from diverse locations that can contribute to genetic improvement regarding scab resistance.