Reduced Seedling Vigor and Interveinal Chlorosis Associated with ALS Mutation in Sorghum Are Affected by Background Genotype.

Resistance to Acetolactate Synthase (ALS) inhibitor herbicides in sorghum is poised to provide viable post-emergence weed control option for the crop, especially against grass weeds. However, introgression of the resistance gene in to adapted backgrounds has challenges related to adaptation and agronomic potential. Many of the resistant segregates tend to have reduced early season seedling vigor and variable degree of inter-venial chlorosis. Although, plants effectively grow out of these symptoms in later stages, such early season stress may have a enduring impact on adult plant performance. This study was conducted to quantify the effects of the ALS mutation on seedling vigor, extent of chlorosis and associated physiological functions; and to examine the interaction between the mutation and background genotype in affecting these traits. Large set herbicide resistant families comprising diverse genetic backgrounds were evaluated for early season seedling vigor, leaf chlorophyll content (SPAD), both before and after treatments with herbicides. Early season seedling vigor and the extent of chlorosis were significantly different between backgrounds and the variation disappeared as plant growth was advanced. Such variation did not have visible impact on day to flowering, maturity and on panicle and seed weights indicating that the early shock caused by mutation do not have lasting effect on yield.