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Effect of deficit irrigation on number of seeds per plant
The number of seeds per plant was significantly affected by deficit irrigation at P≤ 0.001. The control (S1) resulted in the highest number of seeds per plant (85.9) while plants stressed from 60 DAP until physiological maturity (S3) had the lowest number of seeds per plant (46.7) (Figure 5.2). The introduction of deficit irrigation S2, S3 and S4 resulted in 36%, 46% and 12 % reduction in number of seeds per plant, respectively. The results revealed that dry bean is very sensitive to the introduction of deficit irrigation at around 60 DAP (S3), which is during flowering to pod filling stage, as compared to stressing the plants during the flowering stage only (S4). The reduction in number of seeds per plant in S3 was due to flower and pods sescence during deficit irrigation (Figure 5.3). The higher seed yield in S1 may be due to greater photosynthesis and therefore more photosynthates available for translocation to the pods (Nandan & Prasad, 1998; Sarkar & Kar, 1995). Several studies have confirmed that water stress during reproduction stage resulted in reduced number of seeds per plant (Dubetz & Mahalle, 1969; Nielsen & Nelson, 1998; Panda et al., 2003; Zhang et al., 2004; Karam et al., 2007 & Gohari, 2013). The reduction in number of seeds per plant might have been caused by abscission of flowers (Figure 5.3), increased number of barren plants and incomplete seed setting due to water shortage, as was reported by Teran and Singh (2002).
Effect of deficit irrigation on number of pods per plant
The number of pods per plant is one of the most important yield components in determining grain yield (Fageria & Santos, 2008). Deficit irrigation significantly affected the number of pods per plant. The highest number of pods per plant resulted from the control plants (S1), with 22.60 pods per plant, and the lowest number of pods per plant resulted from treatment S2 (Figure 5.4). The results from the two treatments stressed from 41 (S2) and 60 DAP (S3) gave statistically similar results, while the plants stressed during flowering only (S4) performed far better. The introduction of deficit irrigation at S2, S3 and S4 resulted in a 41, 40 and 11 % decrease in the number of pods per plant, respectively. The number of pods at S2 and S3 were not significantly different because they went through deficit irrigation during flowering and pod development leading to senescence of flowers and young pods. The introduction of deficit irrigation is highly dependent on crop the growth stage and the extent of deficit irrigation.When water stress is imposed at flowering and post flowering it results in a reduction in the number of pods due to abortion of the embryo (Gardner et al., 1985), which can also lead to the pod abortion (Manjeru et al., 2007). Pandey et al. (1984) reported that water stress reduced flower production in maize. Wakrim et al. (2005) reported a reduction in the number of pods per plant due to deficit irrigation occurring during flowering stage in common bean and Bourgault et al. (2010) reported a reduction in the number of pods per plant due to deficit irrigation occurring during flowering stage in common bean and mungbean.
Effect of deficit irrigation on grain yield
There was a significant difference (P≤0.05) in grain yield due to deficit irrigation. The control (S1) (3.30 t ha-1) had a significantly higher yield than S2 (2.13 t ha-1), S3 (1.55 t ha-1) and S4 (1.83 t ha-1) (Figure 5.7). Similar results have been reported by several authors (Singh, 1995; Board & Harville, 1998 & Manjeru et al., 2007). Compared to the Control, grain yields of deficit irrigation treatments S2, S3 and S4 were reduced by 35%, 53% and 44%, respectively.
Webber et al. (2006) and Bourgault et al. (2013) reported non- significant yield differences between water stressed and well-watered treatments in common bean. However, several other researchers confirmed a reduction in yield due to water stress (Calvache et al., 1997; Nielsen & Nelson, 1998; Dapaah et al.., 2000; Karam et al., 2007; Bourgault et al., 2010; Istanbulluoglu et al., 2010; Bourgault et al., 2013). Moderate water stress was reported to reduce yield by 41% (Foster et al., 1995) and severe water stress reduced yield by up to 92% (Castellanos et al., 1996). Generally, water stress interferes with the normal metabolism of the plant during flowering and grain filling as these stages are crucial for yield production.
The reduction in yield was caused mainly by the reduction in the number of pods per plant and number of seeds per plant (Figure 5.4). The results revealed that 53 % of the variation in grain yield was due to the number of seeds per plant (Figure 5.8), while 47% of the variation was due to number of pods per plant (Figure 5.9). The reduction in yield due to number of pods per plant and number of seeds per plant under stress have been reported previously (Dubetz & Mahalle, 1969; Wallace et al., 1972; Stoker, 1974; Acosta-Gallegos & Shibata, 1989; Acosta-Gallegos & Adams, 1991; Castellanos et al., 1996, Nielson & Nelson 1998; Boutraa & Sanders, 2001a). Bennet et al. (1977) reported that among the yield components, number of pods per plant has been recommended as an indirect selection criterion for increasing yield due to its consistent correlation with yield. Unfortunately for the current trial the correlation was relatively low.
CHAPTER 1: GENERAL INTRODUCTION
1.1 Introduction
1.2 Background of the study
1.3 Problem statement
1.4 Aims and objectives of the study
1.5 Format of the study
CHAPTER 2: LITERATURE REVIEW
2.1 Genotype x environment interaction (GEI)
2.2 Plant population density
2.3 Moisture stress
2.4 Crop modelling
CHAPTER 3: EVALUATION OF VARIETY X ENVIRONMENT INTERACTION USING GGE-BIPLOT ON DRY BEAN (Phaseolus vulgaris L.).
3.1 Introduction
3.2 Materials and methods
3.3 Results and discussion
3.4 Conclusions
CHAPTER 4: EFFECT OF PLANT POPULATION ON GRAIN YIELD OF DRY BEAN (Phaseolus vulgaris L.).
4.1 Introduction
4.2 Materials and methods
4.3 Results and discussion
4.4 Conclusions
CHAPTER 5: DEFICIT IRRIGATION EFFECTS ON YIELD, YIELD COMPONENTS AND WATER USE EFFICIENCY OF DRY BEANS (Phaseolus vulgaris L.)
5.1 Introduction
5.2 Materials and methods
5.3 Results and discussion
5.4 Conclusions
CHAPTER 6: THE EFFECTS OF DROUGHT STRESS ON GROWTH AND YIELD OF DRY BEAN (Phaseolus vulgaris L.)
6.1 Introduction
6.2 Materials and methods
6.4 Conclusions
CHAPTER 7: THE EFFECTS OF DROUGHT STRESS ON THE PHYSIOLOGY OF DRY BEAN (PHASEOLUS VULAGARIS L.) PLANTS
7.1 Introduction
7.2 Materials and methods
7.3 Results and discussion
7.4 Conclusion
CHAPTER 8: CALIBRATION AND VALIDATION OF THE SWB MODEL FOR DRY BEAN (Phaseolus vulgaris L.) FOR DIFFERENT DROUGHT STRESS LEVELS
8.1 Introduction
8.2 Model description
8.3 Materials and methods
8.4 Results and discussion
8.5 Conclusion
CHAPTER 9: SUMMARY, CONCLUSIONS AND RECOMMENDATIONS
9.1 Summary and Conclusions
9.2 Recommendations
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