Reduction in plant height is generally associated with an increase in lodging resistance, drought tolerance and grain yield of wheat worldwide. Historically, a significant increase in grain yield was observed through the introduction of semi-dwarf wheat varieties utilizing the gibberellic acid-insensitive Rht genes (Rht1 or Rht2). The gibberellic acid sensitive (GA-sensitive) reduced height (Rht) genes are available that are alternatives to gibberellic acid insensitive (GA-insensitive) Rht genes, having a neutral effect on coleoptile length seedling vigor suggesting their potential in using alone or in combination with GA-insensitive Rht genes to improve grain yield and drought tolerance in wheat. This study was conducted to evaluate parents and F1 crosses under drought stress. The crossing was done using line × tester mating design, comprising eight lines and five testers having different GA-sensitive and GA-insensitive Rht genes. Parents and F1 crosses were sown in the field under RCBD with three replications in normal and drought stress. Data were recorded for morpho-physiological traits. The mean comparison showed significant differences among parents and hybrids for most of the studies' traits. The general combining ability showed that line 1 is the good general combiner for days to heading, lodging (%), plant height, peduncle length, internodal length and days to maturity under normal conditions while L5 was the good general cobiner for chlorophyll contents and stomatal conductance both under normal and drought stress. The spcaicfic combing ability estimases showed that the cross L1 × T1 was best for days to heading, lodging (%), plant height and internodal length both under normal and drought stress. F1 hybrids showed a significant reduction in plant height (18-25%), peduncle length (20-28%) and increased grain yield (15-18%) under drought stress. Expression analysis showed upregulation of Rht13 at the middle part of the peduncle internode under drought stress. From the expression analysis, five crosses were selected, and their segregating population was raised and space-plated. Rht13 genes reduced plant height (-30 to -45%), peduncle length (-30 to -53%), peduncle internode length (-28% to -48%), increased spike length (+20% to +50%), number of grains per spike (+17 to +26%) and grain yield per plant (+29% to +50%) compared to Rht1 gene. These results suggested the possibility of using the GA-sensitive Rht13 gene for the development of high-yielding and drought-tolerant wheat varieties.
Keywords: comparative expression analysis; drought tolerance; dwarfing genes; line × tester; reduced height; wheat.