Photosynthetic and storage limitations to yield in Sorghum bicolor (L. Moench)

Abstract

Under favourable growing conditions, the source-sink relationships in grain yield of sorghum were analysed in terms of capacities for net assimilation, of head storage, and of the transport system to move assimilates between source and sink. In four commercial hybrids (Dekalb E57, Pacific Goldfinger, Texas 610SR, and Texas 626) grown at three population densities (20.2, 40.4 and 80.8 plants m-1), the assimilates supply was varied by increasing or decreasing the radiation available per plant (by thinning or shading), the potential gram storage capacity was decreased by spikelet removal, and the transport system was reduced by incision of the culm, all manipulations being performed at anthesis. Decreasing the number of grains increased the size of those remaining in all cultivars at all population densities The degree of Increase was greatest for T626 and T610 and least for E57 Thinning increased the grain size In all cultivars, but only sufficiently to cause a significant increase In gram yield In T610 and T626 Reduction in the assimilate supply by shading decreased the gram size and yield in all cultivars. Reduction In the transport system had no significant effect on gram yield. These results showed that there was surplus capacity for storage and transport In all cultivars In T626, T6L0, and Goldfinger, all post-anthesis assimilate was stored as gram and grams could grow larger The yield was therefore completely source-limited In E57, however, not all port-anthesis assimilate was stored as gram, and these grams showed little capacity to grow larger, which suggests that the yield was partially limited by both source and sink.

Sucrose accumulation in sugarcane is influenced by temperature and genotype through the carbon source - sink balance

“…Studies where removal of sink components led to compensatory growth in remaining components supported the hypothesis that the source rather than the sink was limiting (Muchow and Wilson 1976;Yong-Zhan et al 1996). Compensatory growth of this nature was demonstrated in sugarcane by removal of 25, 50, or 75% of the plants in field plots, 4 months before harvesting, at which time biomass yields were reduced by only 4, 30, and 63%, respectively, because of increased dry mass of the remaining plants (Bell and Garside 2005).…”

Potential yield and water-use efficiency benefits in sorghum from limited maximum transpiration rate

“…However, this previous assumption is inconsistent with the observations that seed growth is arrested when the soil becomes very dry (Muchow 1989) and that decreased grain mass and final harvest index in cereals under post-anthesis drought stress is a consequence of a shorter grain filling duration, rather than a decreased grain growth rate (Bieler et al 1993;Frederick and Camberato 1995;Li et al 2000). Nevertheless, the capacity of sorghum to transfer stored reserves to the seeds (Muchow and Wilson 1976) assures that the final harvest index will achieve at least a minimum value. Hence, in a manner similar to that used in the sorghum model of Hammer and Muchow (1994), the linear increase in harvest index was maintained at the same daily rate, but the increase was stopped whenever the soil dried to a fraction of transpirable soil water equal to or less than 0.1 and a minimum harvest index of 0.2 had been reached (Kamoshita et al 1998).…”

Source capacity during flowering affects grain yield of amaranth (Amaranthus sp.)

“…Obviously the plants were able to compensate the sudden loss of sink capacity completely by subsequently producing new flowers and seeds. Muchow and Wilson (1976) suggested that sorghum spikelets that would abort under normal conditions remain viable when competition is reduced by spikelet removal. This could also apply in the present case of amaranth but was not studied.…”

“…In soybean (Liu et al 2006, Proulx andNaeve 2009), sunflower (Charlet and Miller 1993), and sorghum (Muchow and Wilson 1976), removal of flowers, pods or spikes resulted in increased grain size but yield reduction. Also in wheat and maize, individual grain mass could partly compensate for reduced grain numbers , Oveysi 2010) but did not always respond (Borras et al 2004).…”

“…Seed mass of wheat was only little responsive to changes in assimilate availability (Borras et al 2004, Cartelle et al 2006. The removal of spikelets of Sorghum bicolor increased the mass per seed, while shading reduced grain yield and seed size (Muchow andWilson 1976, Gambin andBorras 2007). In sunflower individual seed mass increased with percentage of floret removal but the increase could not compensate the overall yield loss (Charlet and Miller 1993).…”