Graduate student University of Florida LAKE ALFRED, Florida
Body of Abstract: In vascular plants, phloem tissue is responsible for translocation of photoassimilates from source to sink, which can be exploited and disrupted by phloem-limited pathogens. These pathogens are of economic importance because they alter carbon availability in plants, negatively impacting plant growth and productivity. In addition to sugar transport, they impact the source-sink dynamics through feedback regulation. Huanglongbing (HLB), a phloem-limited disease caused by Candidatus Liberibacter asiaticus, is currently an existential threat to the Florida and Texas citrus industries. Because source-sink dynamics are mediated by phloem translocation, HLB is expected to interrupt translocation and the feedback signals that regulate carbon fixation. Citrus is grown mainly for its fruits so it’s important to understand how source-sink activity is regulated using fruits as the sink organ, to facilitate development of practices to improve citrus yield. The objective of the study is to understand how source-sink regulation of photosynthetic signaling is impacted by HLB and how sink demand responds to these different dynamics. We used 8-year-old HLB-affected and -unaffected ‘W. Murcott’ citrus scion trees grown under protective screens. The disease status will be confirmed using qPCR and the study will be carried out at stage I and II of fruit development. To assess the source-sink dynamics, branches of citrus trees will be girdled to separate them from alternate sinks, defoliated at 0%, 25%, 75% rate with a control treatment (no defoliation or girdling) per fruit. Maximum rate of carboxylation and electron transport rate in carbon fixation will be measured using gas exchange measurements. The fruit carbon demand will be assessed by the available non-structural carbohydrates in leaf samples, carbon utilized and accumulated (fruit dry mass increase, respiration, and photosynthesis). At the end of the study, we expect to have a better understanding of how phloem-limited pathogens impact source-sink dynamics and crop carbon demand.