The introduction of dwarfing genes in wheat and rice enabled significant yield improvements and was later termed the “Green-Revolution”. Dwarfing genes in sorghum have not been accompanied by such increases in grain production. On the contrary, some of the commercially employed dwarfing genes in sorghum have been associated with negative effects on grain yield. A positive correlation between plant height and grain yield was also observed in trial data for a diverse range of hybrids tested within the Queensland Department of Primary Industries and Fisheries Sorghum Breeding Program in north-eastern Australia. No attempts have previously been made to examine the physiological basis of the relationship between plant height and grain yield in sorghum. The dwarfing genes that are commercially used in wheat, Rht-B1 and Rht-D1 (formerly known as Rht1 and Rht2, respectively), on the other hand, have been studied extensively. They have been shown to have substantial and positive effects on grain number and harvest index, while not considerably reducing plant biomass, increasing grain yield. Our objective in this study was to examine the effect of height on the physiological and genetic determinants of growth and yield in sorghum to determine whether there was scope to improve yield by increasing the height of sorghum. A positive correlation between plant height and yield was observed in a population that was fixed for the major dwarfing genes, but showed variation in peduncle and panicle length, which are under control of minor dwarfing genes. To study the effects of a single major dwarfing gene (dw3) on biomass production and grain yield, 2- and 3-dwarf isogenic contrasts were developed in three different genetic backgrounds (R931945-2-2, R955343-1, R955637). In some cases, dw3 led to a significant reduction in plant biomass, which was not sufficiently offset by increase in harvest index to avoid yield reduction. This is contrary to the situation in wheat. The observed reductions in plant biomass in sorghum were associated with reduced tiller number and a reduction in radiation use efficiency (RUE) in the short types. Subsequent experiments suggested that an increase in allocation of biomass to the roots, rather than differences in photosynthetic capacity or respiration, was the main cause for the apparent reduction in RUE. However, due to plant-to-plant variability and the difficulty in accurately measuring root-total biomass ratio, studies with greater replication are required to confirm this hypothesis. It was also found that interactions with genetic background (and environment) moderated the effects of dw3, resulting in smaller height, biomass and grain yield reductions in some isogenic pairs. The effects of dwarfing genes on grain yield therefore need to be assessed separately for different genetic backgrounds. As lodging may be controlled by means other than height reduction (e.g. stay-green), we suggest that yield of standard sorghum types used in industrialised countries may benefit from moderate increases in plant height.
| Identifer | oai:union.ndltd.org:ADTP/254077 |
| Creators | Barbara George-Jaeggli |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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