Influence of prohexadione-calcium, trinexapac-ethyl and hexaconazole on lodging characteristic and gibberellin biosynthesis of rice (Oryza sativa L.)

We investigated the influence of prohexadione-calcium (Pro-Ca), trinexapac-ethyl (TNE) and hexaconazole (HX) on lodging and gibberellin (GA) biosynthesis pathway of rice cultivar, Hwayeongbyeo. It was observed that these novel synthetic growth retardants suppressed lodging of rice under field conditions through blocking GA biosynthesis pathway. These growth retarding chemicals were applied at basic (20 uM) and elevated (40 uM) rates either 10 days before heading (10 DBH) or 5 days before heading (5 DBH). We found that Pro-Ca, TNE and their combined application (Pro-Ca + TNE) were most effective in decreasing rice length and lodging index, when applied at 10 DBH. Similarly, the endogenous bioactive GA ₁ contents of rice significantly declined with application of Pro-Ca, TNE and Pro-Ca + TNE, while they were less effected by basic and elevated rates of HX as compared to the control. The growth retardants were more effective in decreasing rice lodging and blocking GA biosynthesis when applied in elevated rates. The levels of the endogenous gibberellins in rice shoots were measured by GC/MS-SIM using ²H ₂-labeled gibberellins as internal standards. Effect of these synthetic chemicals on growth and GA inhibition were stronger initially but eroded rapidly under field conditions. It was thus concluded that Pro-Ca and TNE were most effective in reducing plant length and suppressing lodging of rice crop under field conditions, where lodging is a major constraint to higher productivity.