A field experiments were conducted at Horticulture Research Station, El-Kanater El-Khiria, Horticulture Research Institute, Agriculture Research Centre, Egypt during 2016 and 2017 seasons to investigate the effect of different irrigation water levels i.e.,100, 75 and 50% of the crop evapotranspiration (ETc) and foliar application with some stimulant substances i.e., proline at 150 mgl-1, potassium silicate at 2500 mgl-1 and putrescine at 10 mgl-1 as well as mulching treatments i.e., black polyethylene plastic, rice straw and sawdust mulches individually or in combination of treatments on vegetative growth characteristics, some bioconstituents, total yield and its components of taro plant under drip irrigation system and results interpreted. The results showed that that increasing water stress level from 75% to 50% of Etc decreased gradually all studied growth characteristics of taro plant (plant height, leaves number plant-1, lamina dry weight plant-1 and leaf area (cm2) plant-1 in the two seasons. In addition, increasing irrigation water stress resulted in decreasing of photosynthetic pigments (chlorophyll a, b and carotenoids) content in taro leaves. Moreover, the increase in water shortage is regularly increased the proline content and antioxidant enzymes activity i.e., superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in taro leaves compared to the full irrigation level (100% of ETc). Furthermore, different estimated yield characteristics of taro plant i.e., main corm length (cm), main corm diameter (cm), corms number plant-1, corms fresh weight (kg) plant-1, main corm fresh weight (g), corms fresh weight (kg) plot-1, corms fresh yield (ton) fed.-1 and corm dry matter % as well as taro corm bioconstituents of N, P, K, crude protein and starch contents decreased by reducing irrigation water levels. In this respect, water stress level at 50% of ETc recorded the highest reductions in different estimated characteristics compared to 75% of ETc level and unstressed plant (100% of ETc).
Regarding, the effect of foliar application with stimulant substances and mulching treatments, proline at 150 mgl-1 followed by potassium silicate at 2500 mgl-1 and putrescine at 10 mgl-1 as well as black polyethylene plastic mulch were the most effective treatments, respectively.
As for the effect of interaction, the results showed that all the interactions between irrigation water levels and foliar spray with the stimulant materials as well as mulching treatments increased different estimated traits of taro plant i.e., vegetative growth characteristics, bioconstituents, yield and its components as well as water use efficiency compared to the control. In this respect, foliar spray with proline at 150 mgl-1 was the most superior treatment followed by putrescine at 10 mgl-1 and potassium silicate at 2500 mgl-1 under water stress levels i.e., 75 and 50% of ETc when compared with the untreated plants during 2016 and 2017 seasons.
In general, it could be noticed that the applied stimulant substances i.e., proline, putrescine, potassium silicate and black plastic mulch treatments could partially reduce the harmful effects of drought stress on growth, bioconstituents, corms yield and its quality of taro plant.
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