Lodging susceptibility index is associated with impaired source-sink relationship and sucrose allocation in oat varieties

Lodging impairs source-sink relationship by affecting the photosynthetic ability, transport of carbohydrates, dry matter accumulation and hence causes alterations in starch accumulation in grain. The characteristics of sucrose metabolism enzymes and related products were determined in basal second internode, flag leaf and grains of ten recently released oat varieties under both non-lodged and lodged conditions to elucidate the underlying mechanism of lodging resistance. Analysis of variance depicted significant variability for all studied parameters under both non-lodged and lodged conditions. The principal component biplot analysis showed that RO-11–1 and OL-1896 were in completely opposite quadrants with JHO-822 and OL-15 under both non-lodged and lodged conditions. Among all the varieties, lodging susceptibility index was lowest in RO-11–1, and maximum was observed in OL-15. The variation could be attributed due to differential sucrose metabolic profile in these two varieties under non-lodged conditions. The tolerant variety RO-11–1 showed better synchronization between source and sink tissues as the activities of sucrose metabolic enzymes in particular sucrose phosphate synthase and sucrose synthase (synthesis direction) were higher compared to sensitive OL-15. The increased synthesis of sugar and starch contributes toward plant fitness to tolerate wind gusts and regain upright position. Downregulation in acid invertase, neutral invertase and sucrose synthase (cleavage direction) activities resulted in decrease in soluble sugar content in both OL-15 and RO-11–1 with lodging. In grain, RO-11–1 recorded higher soluble sugars and starch content than OL-15 indicating better carbon partitioning to perform better under lodged conditions.