Drought tolerance in Malawian soybean (Glycine Max L.) germplasm
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Date
2020-01
Authors
Chiipanthenga, Margaret Kondowe
Journal Title
Journal ISSN
Volume Title
Publisher
University of the Free State
Abstract
Water-limited stress (WLS) is associated with adverse changes at morphological, physiological, biochemical and molecular levels among genotypes, which consequently affects crop growth and productivity. These changes are useful indicators in breeding of drought tolerant genotypes. This study was, therefore, carried out to identify genotypes that are good performing under WLS conditions and to determine traits’ response to WLS using a combination of morphological traits, physiological traits, water use efficiency and grain yield. In addition, interrelationships among morphological traits, physiological traits and water use efficiency were determined in order to identify traits that contribute to grain yield under WLS conditions. The study also elucidated the association between drought tolerance indices and grain yield under WLS conditions in separating tolerant genotypes from sensitive genotypes. It further looked at the impact of drought on grain yield of soybean with change in environment and season. The study also tried to understand the mode of gene action considering that the majority of the characteristics of importance in a crop are inherited quantitatively. Genotypes showed significant variability in tolerance levels to WLS. Genotypes with a high drought tolerance level generally exhibited a higher grain yield, 100-seed weight, plant height, number of pods per plant, minimal grain yield reduction, maintained a higher relative chlorophyll content, quantum yield of efficiency for photosystem II and water use efficiency under severe WLS compared to genotypes with a low drought tolerance level. Among the physiological traits, relative chlorophyll content was most significantly associated with genotype, while quantum yield of efficiency for photosystem II, photoprotective nonphotochemical quenching and non-photochemical quenching basal dissipation of light energy for other unregulated process were more frequently and significantly associated with WLS. Plant height, number of nodes per plant, 100-seed weight, water use efficiency and relative chlorophyll content were less affected by change in WLS levels. Results showed that selection criteria would differ across different WLS regimes. Morphological traits 100-seed weight, number of pods per plant, and bomass per plant significant directly contributed to grain yield under non-WL and moderate (50%) WLS. Water use efficiency showed the highest direct contribution to the variation in grain yield across WLS regimes of all the traits. Both significant positive and negative correlations were observed between morphological and physiological traits. The physiological trait relative chlorophyll content was strongly positively associated with morphological traits and contributed directly to grain yield variation under WLS. This showed that chlorophyll content can be used as physiological marker for identifying drought tolerant genotypes under WLS conditions. It was also observed that the tolerance indices mean productivity, geometric mean productivity, harmonic mean, drought resistance index and yield index correlated positively with both grain yield under non-WL (Yp) and WLS (Ys) conditions. This proved that these indices can be useful in screening for WLS tolerance in soybean. The WLS negatively impacted on grain yield of soybean with change in environment and season but the extent varied from one growth stage to the other. Grain yield was most sensitive to environment, followed by environment by season interaction effects. Effects of WLS were severe at flowering, indicating that the most critical growth stage to soil WLS is between flowering and pod-filling stages when plants partition assimilates for seed formation. Results further displayed the role of both additive and dominance gene effects in expression of tolerance to drought in soybean using grain yield and yield components such as number of pods per plant, number of seeds per plant per plant, and 100-seed weight. However, nonadditive gene effects were more important for WLS for the studied traits than additive gene effects in a current study.
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Keywords
Thesis (Ph.D. (Plant Sciences))--University of the Free State, 2020, Soybean, Morphological traits, Physiological traits, Grain yield, Water-limited stress