Foliage and fruit susceptibility of a pecan provenance collection to scab, caused by Venturia effusa

Authors: Bock, Clive; ALARCON, YANINA - Noble Research Institute; CONNER, PATRICK - University Of Georgia; YOUNG, CAROLYN - Noble Research Institute; Stokes, Unicka; RANDALL, JENNIFER - New Mexico State University; Pisani, Cristina; Grauke, Larry; Wang, Xinwang; MONTEROS, MARIA - Noble Research Institute

Submitted to: Center for Agriculture and Biosciences International (CABI) Invasive Species Compendium
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/2020
Publication Date: 11/23/2020
Citation: Bock, C.H., Alarcon, Y., Conner, P.J., Young, C.A., Randall, J.J., Pisani, C., Grauke, L.J., Wang, X., Monteros, M.J. 2020. Foliage and fruit susceptibility of a pecan provenance collection to scab, caused by Venturia effusa. Center for Agriculture and Biosciences International (CABI) Invasive Species Compendium. 1:19. https://doi.org/10.1186/s43170-020-00020-9.
DOI: https://doi.org/10.1186/s43170-020-00020-9

Interpretive Summary: Technical Abstract and Interpretive Summary: Provide electronically in Word. Technical Abstract Background: Pecan (Carya illinoinensis) is an important native nut crop in the southern USA. In the Southeast, scab (caused by Venturia effusa) is a major constraint to production, and can result in significant yield losses. The breadth of sources of resistance are poorly defined, and the genetics of resistance has not been established. The aim of this study was to assess the severity of pecan scab on foliage and fruit of the trees in a collection of 875 native pecan genotypes from families in 19 provenances in various states in the USA and Mexico. Methods: The scab responses on foliage and fruit on each pecan tree was visually assessed in 2018 and 2019. Both a most severe measure (most severely infected leaf or fruit), and an overall tree rating was taken. Scab severity data were analyzed using a mixed model with means separation to explore provenance and family within provenance scab susceptibilities. Results: Significant differences in scab susceptibility between provenances and among families within provenances were detected. Trees from provenances in IL, KS, KY, MO, MS, TN and TX showed the greatest resistance (based on mean scab severity) for both foliar and fruit scab. Assessments of scab on foliage and fruit gave similar results, as did the values for the most severe scab in the tree and the overall scab severity score. Of the 875 trees assessed, 201 trees had undetectable levels of scab observed on foliage or fruit for one or both years. An additional 116 trees were free of disease on foliage but did not produce fruit in either year. Those provenances, families within provenances and trees with greatest resistance to scab most often originated from provenance locations with higher rainfall and consequently would be under selection to adapt to scab. Conclusions: Identifying populations with most diverse resistance, and those most consistently resistant trees can serve as a resource to develop a better understanding of the scab resistance mechanisms. These natural sources of scab resistance coupled with modern molecular and genomics tools will contribute to the accelerated development of new pecan cultivars with durable resistance to scab. Interpretive Summary Pecan is an important native nut crop in the southern USA. In the Southeast, scab disease is a major constraint to production, and can result in significant yield losses. Sources of resistance to scab are poorly defined, and the genetics of resistance has not been established. The aim of this study was to assess susceptibility of pecan genotypes in a collection of 875 native pecan genotypes from families in 19 provenances collected from various states in the USA and Mexico. There were differences in scab susceptibility between provenances and among families within provenances. Trees from provenances in IL, KS, KY, MO, MS, TN and TX showed the greatest resistance (based on mean scab severity) for both foliar and fruit scab. Of the 875 trees assessed, 201 trees had undetectable levels of scab observed on foliage or fruit for one or both years. An additional 116 trees were free of disease on foliage but did not produce fruit in either year. Those provenances, families within provenances and trees with greatest resistance to scab most often originated from provenance locations with higher rainfall and consequently would be under selection to adapt to scab. Identifying populations with most diverse resistance, and those most consistently resistant trees can serve as a resource to develop a better understanding of the scab resistance mechanisms. These natural sources of scab resistance coupled with modern molecular and genomics tools will contribute to the accelerated development of new pecan cultivars with durable resistance to scab.

Technical Abstract: Background: Pecan (Carya illinoinensis) is an important native nut crop in the southern USA. In the Southeast, scab (caused by Venturia effusa) is a major constraint to production, and can result in significant yield losses. The breadth of sources of resistance are poorly defined, and the genetics of resistance has not been established. The aim of this study was to assess the severity of pecan scab on foliage and fruit of the trees in a collection of 875 native pecan genotypes from families in 19 provenances in various states in the USA and Mexico. Methods: The scab responses on foliage and fruit on each pecan tree was visually assessed in 2018 and 2019. Both a most severe measure (most severely infected leaf or fruit), and an overall tree rating was taken. Scab severity data were analyzed using a mixed model with means separation to explore provenance and family within provenance scab susceptibilities. Results: Significant differences in scab susceptibility between provenances and among families within provenances were detected. Trees from provenances in IL, KS, KY, MO, MS, TN and TX showed the greatest resistance (based on mean scab severity) for both foliar and fruit scab. Assessments of scab on foliage and fruit gave similar results, as did the values for the most severe scab in the tree and the overall scab severity score. Of the 875 trees assessed, 201 trees had undetectable levels of scab observed on foliage or fruit for one or both years. An additional 116 trees were free of disease on foliage but did not produce fruit in either year. Those provenances, families within provenances and trees with greatest resistance to scab most often originated from provenance locations with higher rainfall and consequently would be under selection to adapt to scab. Conclusions: Identifying populations with most diverse resistance, and those most consistently resistant trees can serve as a resource to develop a better understanding of the scab resistance mechanisms. These natural sources of scab resistance coupled with modern molecular and genomics tools will contribute to the accelerated development of new pecan cultivars with durable resistance to scab.