Seedling drought tolerance in upland cotton

Combining root morphological and plant physiological traits associated with drought tolerance should result in improved drought resistance in cotton (Gossypium hirsutum L.). This study was designed to evaluate the response of root growth of selected Converted Race Stocks (CRS), TAM94L-25, and 'Lankart 1421 (LK 142) under water stress and nonstressed conditions, and to compare their excised leaf water loss (ELWL). Two putative seedling drought tolerant and two putative nonseedling drought tolerant CRS lines, plus TAM94L-25 and LK 142, were grown with and without moisture stress in a greenhouse at College Station, TX, in 2002 and 2003. The robust rooting CRS, M-9044-0031-R and M-8744-0175-R, had longer tap root length (RL), higher lateral root number (LRN), greater total root dry weight (TRDW), greater root weight per unit length of tap root (W/L), and greater shoot dry weight (SDW) than the nonrobust CRS M-9044-0045-NR and M-9044-0057-NR, and LK 142 regardless of water regime. Two cycles of seedling drought resulted in an increase in LRN in M-9044-0057-NR, TAM94L-25, and LK 142. SDW and TRDW were highly correlated and SDW was associated with W/L. The excised leaf water loss (ELWL) tended to be greater in the NR CRS lines when measured at 30-m intervals for 8 h. Results suggested (i) that root parameters, initial water content (IWC), and ELWL, could be used as a reliable selection criteria for drought tolerance and (ii) that day-neutral CRS accessions could be used as a source of useful genetic variability for a cotton drought tolerance improvement program.