GROWTH AND DEVELOPMENT OF CONTRASTING SORGOS IN VIGOR AND EARLYNESS

Abstract

Four sorghum varieties were subjected to a growth and developmental analyses at Zacatepec, Morelos, México. Despite the marked differences in total leaf number (TLN) and leaf initiation rate (LIR) as well as in plant size, vigor, and earliness, the four varieties showed the same leaf expansion rate. This suggests that the panicle initiation (PI) of sorghum depends both on TLN and LIR. Additionally, an inverse relationship was observed between the reproductive and the vegetative developmental rates, since the late-flowering varieties showed faster LIR ´'s than the early-flowering ones.

These varieties were also contrasting in Net Assimilation Rate (NAR), corresponding the higher NAR 's to the smaller. earlier varieties and the lower NAR 's to the late and vigorous varieties; therefore, there were little differences among sorghum cultivars in their rate of dry matter accumulation in the shoot. On the other hand, since the Relative Growth Rate (RGR) was identical in the four sorghum
varieties, it is postulated that the RGR represents the proportion of meristematic tissue in the whole plant, rather than the amount of dry matter produced per unit of biomass in the plant. lt was observed also that at PI the tillers started to grow rapidly, and the stem suffered a heavy, but temporal reduction in its dry matter accumulation. Apparently, the stem provided assimilates to the tillers while these organs were initiating their own leaves and could not be self-sufficient in photosynthates.