Effects of time of water stress on flowering, seed yield and seed quality of common onion (Allium cepa L.) under the arid tropical conditions of Sudan

Abstract

An experiment was conducted for two consecutive seasons to investigate the effect of water stress on seed yield and seed quality of onion (Allium cepa L.). Water stress was imposed on the plants at four stages of reproductive growth, namely, bolting, flowering, seed formation and seed maturation stage, respectively. Watering was withheld for an interval of 2 weeks only once for every treatment “growth stage” during the first season, while during the second season, the interval of watering was extended to 3 weeks. Numbers of leaves per plant, umbel diameter, number of florets per umbel, number of seeds per florets; number of seed stalks per plant, 1000 seed weight per plant and seed yield and seed quality were recorded. Water stress at any stage of reproductive growth significantly reduced seed yield and its effect was variable depending on plant growth stage. Based on 1000 seed weight per seed head, bolting followed by anthesis were the most sensitive growth stages during the first season. Water stress at the time of anthesis significantly decreased the diameter of seed head when compared to control. The average number of seeds per floret was significantly decreased by stressing at bolting compared to all treatments. In the second season, seed formation stage was the most critical only followed by anthesis stage. When seed yield per plant was measured, the most sensitive stage was bolting. Number of florets per umbel and umbel diameter were reduced by water stress. In the first season, 1000 seed weight was not affected, but in the second season, it was significantly reduced with water stress at seed formation stage. Seed germination and field emergence were not affected. However, water stress at bolting in the second season resulted in lower seed quality. Some stress treatments were observed to promote seed germination and seedling emergence.