Ratoon Stunting Disease (Leifsonia xyli subsp. xyli) affects source-sink relationship in sugarcane by decreasing sugar partitioning to tillers

Abstract

Ratoon Stunting Disease, caused by the bacterium Leifsonia xyli subsp. xyli (Lxx), decreases sugarcane yield by reducing culm growth and tillering, especially in plants with high Lxx titers when the symptoms are more severe. The role of Lxx titers in affecting sugar partitioning and sugarcane growing is still unclear. We hypothesized that high Lxx titers affect source-sink relationship by causing physiological changes in the sugarcane that reduces sugar partitioning to tillers. The study was carried out with susceptible sugarcane genotype CB49260, evaluating physiological traits and biomass production in plants with low (158 ± 28 Lxx cells per 100 ng of plant DNA) and high Lxx titers (2090 ± 385 Lxx cells per 100 ng of plant DNA). Overall, the level of bacterial titers affected sugarcane growth through changes in ethylene level, sugar and biomass partitioning. Plants with high Lxx titers presented a lower number and biomass allocation to tillers than low Lxx titers. Additionally, plants with high Lxx titers had higher biomass allocation to the main culm than low Lxx titers plants due to greater sucrose and starch contents in the main culm caused by the higher number of cell parenchyma, decreased soluble acid invertase activity, and low number of tillers. Changes in sugar and biomass partitioning in plants with high Lxx titers were associated with low release of ethylene in the leaf and culm. Sugarcane with high Lxx titers presented physiological changes that restricted sugar supply for tillering, resulting in a decrease in the number and biomass allocation to the tillers.