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Poster: Biology & Disease Mgmt: Genetics of Resistance


Differential effects of stalk rot diseases on photosystem II photochemical efficiency among resistant and susceptible sorghum lines.
A. BANDARA (1), D. Weerasooriya (1), T. Tesso (1), C. Little (1) (1) Kansas State University, U.S.A.

Stalk rots are among the most injurious sorghum diseases worldwide. Understanding the plant physiological changes that occur during these diseases will help to uncover potential resistance mechanisms. The objective of this study was to test the effect of stalk rots on sorghum (Sorghum bicolor (L.) Moench) leaf chlorophyll content and photosystem II photochemical efficiency (Fv/Fm). Two resistant (SC599, SC35) and susceptible (Tx7000, BTx3042) lines were field evaluated in 2014 and 2015. Plants were inoculated with Fusarium thapsinum (Fusarium stalk rot), Macrophomina phaseolina (charcoal rot), and phosphate-buffered saline (control) at 14 d after flowering. Flag leaf chlorophyll and Fv/Fm were measured at soft-dough, hard-dough, and physiological maturity using a Soil and Plant Analytical Development meter (SPAD) and a chlorophyll fluorometer, respectively. ANOVA was performed with appropriate modeling for repeated measures. Compared to control, both pathogens significantly reduced SPAD (P < 0.0001) across genotypes and growth stages and the reduction was greater in 2014. Across years and growth stages, both pathogens significantly reduced the Fv/Fm (P < 0.016) of susceptible lines while no such effect was evident for the resistant lines. Despite the apparent chlorophyll reduction during disease development, the ability to maintain higher photosynthetic activity at the tested growth stages appeared to contribute to physiological resistance against stalk rot diseases