Physiological Basis And Regulation Of Floret Development In Wheat

Enhancing yield is one of the most important goals for wheat growers and, consequently, most wheat improvement programs. Among the yield components, grain number per spike is a key factor for increasing wheat yield. Studies on morphology of wheat kernel development had indicated that formation of wheat grains is the result of several sequential development stages: floret initiation, development, fertilization and grain fill. Fertile florets in the spike, which are mainly determined during pre-anthesis period, are significantly correlated to the grains harvested. This paper was focused on the physiology of floret development and degeneration, and the roles of plant hormones in regulation of floret development and grain set.Studies of 27 wheat (Triticum aestivum L.) genotypes differing in kernel number per spike showed significant differences in total spikelets, fertile spikelets, total florets, fertile florets per spike among various genotypes. There was highly significant correlation between kernel number per spike and fertile spikelets, total florets, fertile tlorets and grain set rate. There was significant correlation between floret differentiation rate and total florets, fertile florets, and kernel number per spike, whereas the duration of floret differentiation was not significantly related to total floret number and kernel number per spike. We concluded that improving the kernel number per spike should be focused on increasing the spikelet number, floret differentiation rate and grain set rate.From this analyses, three genotypes were selected for analyses the role of plant hormones and assimilate in floret development, which are: ?7J1攚ith the highest grain set and fertile florets per spike, 揌8679攚ith the least grain set and fertile florets per spike, and a medium,擸MI 58? Genotypes with more kernels per spike showed the higher floret differentiation rate, and 208 florets initiated per spike in genotype 97J I. The significant difference of floret development and grain set was laid on the upper florets in the spikelet, which had highest grain set in genotype 97J1 and lowest in H8679. During the high growth period of spike and97node before anthesis, assimilate partitioned into the spike was correlated to the spike size of the genotype.The analyses of dynamic of endogenous hormones during floret development showed the peak level of endogenous ABA appeared between stamen and pistil differentiation and antherlobe formation, and the timing delayed with the size of spike (earliest in H8679 and latest in 97J1). From antherlobe formation to meiosis, the levels of ABA and GA, +~ decreased sharply in the ears of 97J 1, while in the ears of H8679 there was only a slight decease in ABA, and even an increase in GA,+3. The ratio of iPA/ABA and IAAIABA in 97J1 ears increased sharply from antherlobe formation to meiosis, but changed only slightly in H8679 ears. The endogenous hormones showed the opposite changes between fertile and infertile florets in the spikelet. The fertile floret showed the steady decrease of ABA and GA,? levels and lower level of IAA with its development, as well as hormone balance. The infertile floret, however, showed the higher level of LAA and sharply decrease of IAA/ABA and GA/ABA and iPAIABA ratio at the beginning of its degeneration. and increase of ABA level with its degeneration process. These results indicated that the sharp decreases of ABA and GA, ~ in ears from antherlobe formation to meiosis and the lowest maintenance at meiosis might be favorable for development of fertile florets and grain set in wheat, and the higher level of IAA and sharply decrease of IAA/ABA and GA/ABA and iPA]ABA ratio might be the main physiological reason of floret degeneration.During the whole period of floret development, the solutions of IAA, GA3, zeatin and ABA were injected into the cavity around the young spike to study the regulating effects of exogenous hormones on floret development in the genotype YM 158. The results showed that zeatin promoted the floret...