Co-Authors:
Blum, A., Institute of Field and Garden Crops, Volcani Centre, PO Box 6, Bet Dagan, Israel
Golan, G., Institute of Field and Garden Crops, Volcani Centre, PO Box 6, Bet Dagan, Israel
Mayer, J., Institute of Field and Garden Crops, Volcani Centre, PO Box 6, Bet Dagan, Israel
Sinmena, B., Institute of Field and Garden Crops, Volcani Centre, PO Box 6, Bet Dagan, Israel
Abstract:
Stem reserves are increasingly recognized as an important source for grain filling when current photosynthesis is inhibited by stress. However, information in this respect for sorghum is seriously lacking. This study was designed to test the hypothesis that tall (1-dwarf) sorghum has greater stem reserve storage than shorter (3-dwarf; 'combine height') sorghum and that under conditions of environmental stress during grain filling this storage becomes an important source for grain filling. Tall (SA1170) and short (SM100) isogenic lines of milo sorghum (Sorghum bicolor (L.) Moench.) were tested in the field for 3 years under 3 treatments: (a) full irrigation (control); (b) drought stress which intensified towards grain filling; and (c) chemical desiccation of the leaf canopy at 12 days after anthesis, which eliminated the main photosynthetic source during grain filling. Data were collected on grain dry matter, stem dry matter and stem water soluble carbohydrates (WSC) changes with time. The tail genotype was about 2 m and the short genotype was about 1 m tall, under non-stress conditions. It was found that grain weight per panicle was reduced by drought stress only in the short genotype. Both kernel number and kernel weight and their interaction were responsible for this reduction. Chemical desiccation was a more aggressive treatment than drought stress. It reduced kernel weight and grain weight per panicle much more in the short than in the tall genotype. Changes in stem dry matter reflected well the changes in stem WSC content. Maximum stem weight at the onset of grain filling and stem dry matter loss during grain filling were always greater in the tail than the short genotype. Stem weight loss was markedly promoted by drought and chemical desiccation only in the tall genotype or in the short genotype only in a year when it developed heavy stems. Stem weight loss as percent of grain weight per panicle under drought and chemical desiccation was always greater in the tall than in the short genotype. Since stem weight loss was promoted by stress, it could not have been fully accounted for by maintenance respiration. Irrespective of year, treatment and genotype, plants with greater stem weight at the onset of grain filling lost more reserves from the stems during grain filling (r = 0.89, p < 0.0001; n = 18). Consequently, stem weight loss as percent of grain weight per panicle increased with larger stem weight (r = 0.73, p = 0.0006; n = 18). It is concluded that large stem reserve storage at the onset of grain filling ascribe stable grain filling under any stress which depresses the photosynthetic source during grain filling.
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