Physiological responses of common bean(Phaseolus vulgaris L.)genotypes to water stress
Date
2014-07-17
Authors
Kalima, Salyula Philip
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Abstract
Common bean (Phaseolus vulgaris L.) is highly constrained by water deficit especially occurring during the reproductive development which significantly reduces the grain yield. A late planted crop, is likely to experience water stress. The purpose of the study was to determine the association of the morphophysiological traits with water stress and how they relate to grain yield in common beans. A field experiment involving eight common bean genotypes (CAR-ZAR, KE 3, ZM 4488, KE 4, SER 76, SER 180, GADRA, and SER 89) and three water regimes (50 %, 75 %, & 100 % of crop evapotranspiration) was conducted at National Irrigation Research Station (NIRS) in Mazabuka district during the 2012 growing season. A 3 x 8 split plot design with four replications was used; with water stress as the main plot factor and genotype as the subplot factor. Water stress was imposed at pre-flowering stage and was discontinued after 43 days when the crop was in its late reproductive stage. The results showed that significant differences were found among genotypes for relative injury percentage, chlorophyll a, chlorophyll b, total chlorophyll, relative water content, grain yield, number of pods per plant, hundred seed weight, number of seeds per pod and days to fifty percent flowering for the three water regimes. Grain yield in normally irrigated treatment (2.19 ton ha-1) was 60 % higher than in 50 % water stress treatment (0.87 ton ha-1), while in the 75 % water stress treatment (1.08 ton ha-1), the reduction in grain yield was 50.8 %. There was significant genotype by environment (GXE) interactions. These interactions were observed in relative injury percentage, chlorophyll a, chlorophyll b, total chlorophyll, relative water content, grain yield, number of pods per plant, hundred seed weight, number of seeds per pod and days to fifty percent flowering in the high water stress condition. The genotypes GADRA, KE 4, ZM 4488, and SER 180 were identified as water stress tolerant while the genotypes SER 89, CAR-ZAR, KE 3 and SER 76 were identified as water stress sensitive genotypes based on GM, DSI and PR. It was postulated that positive association between yield reduction (PR) and drought susceptibility index (DSI) renders either trait useful in selecting water stress tolerant genotypes. All the traits measured were positively and significantly correlated to grain yield apart from chlorophyll b which had a negative correlation (r=-0.41**). A strong positive correlation was recorded for hundred- seed- weight (r = 0.41**), chlorophyll a content (r = 0.57**) and number of pods per plant (r = 0.36*). A stepwise multiple regression showed that hundred- seed- weight, chlorophyll a, chlorophyll b and number of pods per plant contributed significantly to the total variation of grain yield. These results suggest that a selection method based on hundred seed weight, chlorophyll a,
chlorophyll b and number of pods per plant can be used in breeding for bean genotypes to water stress.
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Keywords
Crops and water stress