Early Seedling Growth Characteristics Relate to the Staygreen Trait and Dhurrin Levels in Sorghum

Abstract

Dhurrin content in leaves of the mature sorghum [Sorghum bicolor (L.) Moench] plant is a quantitative measure of the level of pre‐ and postflowering drought tolerance, with high dhurrin contents expressed in postflowering drought‐tolerant lines. Postflowering drought tolerance in sorghum has been linked to the staygreen trait and associated with increased grain yield during postanthesis stress. Seasonal variability in postflowering drought occurrences makes selection for the staygreen trait unpredictable and the efficiency and reliability of screening for the trait using only conventional breeding low. Differences in dhurrin content between high and low dhurrin levels lines is only markedly favored to the high dhurrin level lines in the upper leaves of matured field‐grown plants. Here we report a screening method using early seedling growth characteristics of sorghum lines of known dhurrin level grown in sand with no inorganic nutrients supply. The method was evaluated under cold and warm temperatures. Seedling growth characteristics and contents of dhurrin and high‐performance liquid chromatography‐detected sugars were determined at 5, 10, 17, and 23 d after emergence. High dhurrin level lines had larger increases in shoot fresh weight, dried weight, and length than did lines with low dhurrin levels at 10 d after emergence under both temperatures. Similar trends were observed when separating lines into high and low dhurrin levels using fresh shoot mass and length at 10 d after emergence. Dhurrin content decreased with seedling age, was statistically similar between dhurrin levels, and negatively correlated to concentrations of sugar. Thus, selecting for postflowering drought tolerance can be timely, reliably, and inexpensively done using early seedling growth characteristics.