Lucerne growth and components of seed yield as influenced by plant growth regulators

Effects of 0.3, 0.5, and 0.7% chlormequat, 0.15 and 0.35% ethephon, and 0.12 and 0.22% paclobutrazol on lucerne growth and components of seed yield were investigated in Gansu province, China. The paclobutrazol application decreased above- and below-ground biomass by 25-48 and 44% at concentrations of 0.12-0.22%, and increased seed yield by 31-47%. Applications of ethephon and chlormequat did not affect lucerne biomass, but reduced seed yield in the first year. Plant growth regulators also affected yield components very differently, with paclobutrazol having the greatest effect. The 0.22% paclobutrazol application increased the number of racemes per shoot by 38%, the number of pods per raceme by 392% and the number of seeds per pod by 115%. Although ethephon and chlormequat reduced seed yield in the first year and gave no response in the second, these plant growth regulators had some positive affects on some seed yield components. The 0.15% ethephon application increased the number of racemes per shoot by 35% and the number of pods per raceme by 225%. The 0.3% chlormequat application increased the number of fertile shoots per unit area by 24% and number of pods per raceme by 178%. None of the plant growth regulators had ill effects on lucerne seed quality (1000-seed weight and seed germination). Among yield components, the number of pods per raceme and number of seeds per pod were the most important factors to determine lucerne seed yield and yield potential can be estimated with the use of the two factors as a selection criterion. Results from this study will be used to recommend further evaluation of paclobutrazol at multiple sites and to guide lucerne seed production in the north-west region of China.