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Do carbohydrates influence the alternate bearing, tree growth, and scab resistance of pecans?

Kumari, Rashmi
Pecan (Carya illinoinensis (Wangenh.) K. Koch), is an economically important deciduous nut crop in the United States. Carbohydrates reserves play an important role in regulating growth, development, reproduction, and defense. This research analyzed how carbohydrate reserves impact alternate bearing patterns, bud development, tree growth and scab resistance in pecans. The first experiment focused on the impact of carbohydrate reserves on alternate bearing and budbreak timing in six pecan cultivars, comprising three commercial cultivars (‘Pawnee’, ‘Lakota’, and ‘Desirable’) and three breeding lines (1992-01-0603, 1992-09-0041, and 1992-09-0045). These trees are maintained in the USDA-ARS National Pecan Advanced Clonal Test System (NPACTS) orchard in Somerville, Texas. The fresh shoots, which contained first and second-season growth, were collected in the middle of each month from November 2021 to May 2022 and were shipped to Oklahoma State University overnight and separated immediately into bark and wood, dried and powdered. Sugar and starch contents were then measured using the anthrone test to quantify respective carbohydrate storage concentrations in each sample. Results highlighted significant variances in carbohydrate levels across different cultivars and breeding lines. Positive correlations were detected between nut yields and carbohydrate levels in late dormancy. For bud break timing, efficient starch mobilization in early months correlated with early bud break. The second segment of this study examined the difference in carbohydrate allocation between dwarfing (‘Cordele Dwarf’, SP-43-2, SP-43-2-4, and 2004-01-0027) and non-dwarfing (SP-43-1, SP-43-2-3, and 2004-01-0038) pecan phenotypes. The research identified significant differences in sugar concentrations in the bark tissues of dwarf trees compared to their non-dwarf counterparts. The final component of the study investigated the influence of carbohydrates on scab resistance in pecan trees. Pecan scab, caused by Fusicladium effusum, is a significant concern for pecan growers. By analyzing carbohydrate concentrations in both scab-resistant (‘Lakota’, 1992-01-0603, 1992-09-0041, and 1992-09-0045) and susceptible cultivars (‘Desirable’ and ‘Pawnee’), the study revealed that scab-resistant varieties tend to maintain more robust carbohydrate reserves, particularly during winter and early spring months. Overall, this research provides novel insights into the critical role of carbohydrate reserves in the physiological processes of pecan trees.