Inter-Veinal Chlorosis and Reduced Seedling Vigor Associated with ALS Mutation in Sorghum Have No Impact on Adult Plant Performance.

Resistance to Acetolactate synthase (ALS) inhibitor herbicides is poised to offer a rare post-emergence weed control option in sorghum. Introgression of the trait from the wild relative into cultivated sorghum resulted in the development of numerous ALS resistant parental lines and hybrids. Depending on genetic backgrounds, many of the resistant lines express various levels of inter-veinal chlorosis and reduced vigor at seedling stages. The objective of this study was to investigate the effects of such unusual phenotype on physiological and agronomic characteristics. Thirty-six ALS resistant lines expressing varying levels of inter-venal chlorosis and seedling vigor were grown in the field during the 2013 crop season. Data were collected on seedling growth parameters including height and chlorophyll content (CC) on day 14 and 34 and biomass on day 14 after planting. At later stages, additional data were recorded on days to flowering (DF), panicle weight (PW), 1000 kernel weight (TKW), adult plant CC, height and biomass. Results revealed significant variability for all traits measured except for TKW. Seedling CC was significantly and positively correlated with seedling height (r=0.74) and seedling biomass (r=0.71). This agrees with the marked difference in CC observed between green and yellow seedling backgrounds. The significant negative relationship between seedling CC and DF (r=-0.49) may be the result of reduced seedling growth in yellow backgrounds that appear to have caused delayed DF. Moreover, correlation between seedling CC and adult plant height, adult plant biomass and PW were negative and significant with r=-0.51, -0.29, and -0.35, respectively. But, correlation between these traits and adult plant CC were positive. The result indicates that early season yellowing and the associated low seedling vigor, though appear to delay flowering and perhaps maturity do not have negative effects on adult plant biomass and grain yield.