Wed, Aug 04, 2021:On Demand
Background/Question/Methods
The effects of abiotic and biotic stressors on the carbohydrate dynamics of trees has become a subject of major focus in the study of tree mortality. The American chestnut (Castanea dentata) and the hybrid chestnuts developed by The American Chestnut Foundation are at particular risk of combined drought and pathogen stress. The disease chestnut blight, causal agent Cryphonectria parasitica, still poses a risk to the hybrid trees, even though the hybrid trees have been bred for blight resistance. Here we predict that changes in carbohydrate allocation will help explain changes in disease severity and mortality when trees are face with combined stressors.
To study how co-occurring pathogen and drought stress influence the allocation of carbohydrates in American, Chinese, and hybrid chestnuts, we grew 7 varieties of chestnuts from seed in a common garden and challenged the trees with a factorial treatment application of blight inoculation and artificial drought. The chestnuts were grown for one year before being harvested in the Fall. Nonstructural carbohydrate concentrations (NSCs) were quantified in the roots, branch tips, and canker margins. Canker size, stem mortality, and infection severity were also quantified on infected stems.
Results/Conclusions As expected, we found that American chestnuts had greater rates of disease severity and mortality within the infected treatments. We also found that combined drought and pathogen treatments significantly increased mortality across all chestnut varieties (p < 0.001) compared to the control as well as the single stress treatments. We did not find a significant increase in canker size due to co-occurring drought stress. Percent nonstructural carbohydrate concentration significantly varied by tissue type (p < 0.001) with roots having the highest starch concentrations (p < 0.001) and branch tips having the highest soluble sugar concentrations (p > 0.05). Breaking data up by tissue, we found that the drought and pathogen treatment showed significantly lower percent NSC concentration (p < 0.05) in all tissue types and across all varieties. Starch concentration were the drivers of this difference. Chestnuts that died had significantly lower NSC concentrations (p < 0.001), but interestingly this seemed to be due more to the drought effects than the pathogen. Thus, we find that co-occurring drought and pathogen infection does increase mortality across chestnut varieties and does differentially deplete NSC reserves compared to each stressor individually. Related to chestnut restoration efforts, our findings indicate the importance of mitigating drought risk for reintroduced chestnut trees moving into the future.
Results/Conclusions As expected, we found that American chestnuts had greater rates of disease severity and mortality within the infected treatments. We also found that combined drought and pathogen treatments significantly increased mortality across all chestnut varieties (p < 0.001) compared to the control as well as the single stress treatments. We did not find a significant increase in canker size due to co-occurring drought stress. Percent nonstructural carbohydrate concentration significantly varied by tissue type (p < 0.001) with roots having the highest starch concentrations (p < 0.001) and branch tips having the highest soluble sugar concentrations (p > 0.05). Breaking data up by tissue, we found that the drought and pathogen treatment showed significantly lower percent NSC concentration (p < 0.05) in all tissue types and across all varieties. Starch concentration were the drivers of this difference. Chestnuts that died had significantly lower NSC concentrations (p < 0.001), but interestingly this seemed to be due more to the drought effects than the pathogen. Thus, we find that co-occurring drought and pathogen infection does increase mortality across chestnut varieties and does differentially deplete NSC reserves compared to each stressor individually. Related to chestnut restoration efforts, our findings indicate the importance of mitigating drought risk for reintroduced chestnut trees moving into the future.