Journal of Biology, Agriculture and Healthcare www.iiste.org ISSN 2224-3208 (Paper) ISSN 2225-093X (Online) DOI: 10.7176/JBAH Vol.9, No.1, 2019 34 Response of Haricot Bean (Phaseolus Vulgaris L.) Varieties to Drought Stress at Different Growth Stages Awoke Wasae 1 Berehanu Abate 2 Walelign Worku 2 1.Plant Science Department, Debark University, Ethiopia 2. School of Plant and Horticultural Sciences, Hawassa University, Ethiopia Abstract Drought is considered as the single most devastating environmental factor, which decreases crop yield more than the collective effect of other environmental factors. Varieties also differ in their reaction to drought stress, when they exposed to drought stress at different growth stages. Pot experiment was conducted at Hawassa College of Agriculture, southern Ethiopia, with objectives of identifying relatively drought tolerant haricot bean varieties and yield correlated traits under drought stress at different growth stages. Ten improved haricot bean varieties were subjected to drought stress by withholding water for 15 days at vegetative, flowering and pod-setting stages. The analysis of variance showed that phenology, growth and yield components were affected by both drought stress and varieties. However, their interaction effect was significant only for number of seeds plant -1 , seed yield and pod harvest index. Drought intensity indices at vegetative, flowering and pod setting stages were 0.046, 0.335 and 0.249 respectively. Drought at vegetative, flowering and pod setting stages reduces seed yield by 2.91, 33.53 and 25.11% respectively as compared to full irrigation. Plant height, branches, pods and seeds plant -1 and 100 seed weight were reduced most by the stress induced at flowering followed by pod setting stages. However, there was no statistical difference between the effects of drought stress at vegetative stage and full irrigation on all measured parameters. Varieties with higher yields under flowering stress were H/dumme (21.96g plant -1 ), Wajo(21.38g plant -1 ) and Nasir(17.45g plant -1 ) on the other hand Wajo (30.57g plant -1 ), H/dumme(22.6g plant -1 ) and Ibbado(30.45g plant -1 ) had better yield performance under full irrigtaion. Seed yield had significant and positive correlation with pod harvest index, days to maturity, number of pods on the main stem, seed plant -1 , 100 seed weight and plant height, which can be used as a selection index to screen drought tolerant haricot bean varieties. To achieve high yield, drought must be avoided during flowering and pod-setting stages, and varieties H/dumme, Wajo and Nasir can be recommended for drought prone areas. Keywords: Drought stress, drought tolerance, Phaseolus vulgaris L. DOI: 10.7176/JBAH/9-1-05 INTRODUCTION Haricot bean (Phaseolus vulgaris L.) is an important legume crop grown worldwide. It was most likely introduced to Ethiopia by the Portuguese in the 16 th century (Fisseha, 2015). Haricot bean is grown in central, southern, eastern, western lowlands and mid altitudes (1400-2000 m.a.s.l) of Ethiopia as a food and cash crop and produced predominantly by smallholder producers (Karanja et al., 2011; CSA, 2016). It is a food-secure crop as it contains protein, carbohydrate, fat and minerals substituting the animal products which are not affordable to buy by the majority of poor farmers (Schwartz et al., 1996). Haricot bean is cultivated as a sole crop in rotation with cereals (Wortmann, 2006) and intercropped under row planted crops like maize and sorghum. The national average yield of haricot bean in Ethiopia is 1.69t/ha (CSA, 2016), which is low as compared to the yield (2.5-3.6 t/ha) achieved at research centers (MoANR, 2016). There are many natural and agronomic factors hindering exploitation of the yield potential of this crop. Drought stress at different growth stages and growing of local and old varieties were the major production constraints. Drought is considered as the single most devastating environmental stress, which decreases crop productivity more than the combined effect of other environmental factors (Lambers et al., 2008; Shao et al., 2009). Even if there is an adequate average annual rainfall in Ethiopia, the production of sustainable and reliable food supply is becoming very difficult due to temporal and spatial imbalance in the distribution of rainfall and recurrent shortage of water at the required period. Most of haricot bean growing regions in Ethiopia have erratic rainfall distribution and sandy soil with low moisture holding capacity (Simane and Slruik, 1993). Drought is the most important factor limiting the productivity of rain fed production of different pulse crops in southern Ethiopia where this study was conducted (Saxena et al., 1993). Often crop failure occurs because of unavailability of water at some critical growth stages (Benjamin et al., 2003; Demirevska et al., 2009). However, there were controversial evidences on the effect of drought stress at different growth stages. Some scholars reported that drought stress at vegetative stage is good (Sangakkara, 1994; Nautiyal et al., 2002; Jaleel et al., 2008). However, other scholars argue that drought stress at vegetative stage is sever than that of flowering and pod setting stress (Bolanos and Edmeas, 1993; Mustapha, 2014). Most of the researchers reported and agreed that flowering and pod setting stresses are the most sensitive, while vegetative