EFFECTS OF WATERLOGGING ON CHICKPEAS .2. POSSIBLE CAUSES OF DECREASEDTOLERANCE OF WATERLOGGING AT FLOWERING

Waterlogging tolerance of chickpeas was found, in earlier work, to dec rease sharply at flowering. Three experiments were performed to attemp t to explain the mechanisms involved in this response. In the first, a range of treatments was imposed to modify the plant's source/sink rel ationships, as carbohydrate supply and partitioning were considered po ssible determinants of waterlogging tolerance. Plants from which buds were removed showed the most rapid recovery after waterlogging. Defoli ation immediately before waterlogging reduced the rate of recovery. Ap plication of benzyladenine plus gibberellic acid prior to waterlogging delayed stomatal closure and leaf senescence, inhibited apical growth and stimulated axillary growth. The second experiment aimed to confir m the influence of bud removal and to determine whether waterlogging t olerance is correlated with carbohydrate supply. Treatments comprised two sowing times, ten days apart, and two bud treatments (retained and removed). Waterlogging was imposed when older plants had been floweri ng for seven days and younger plants were in bud. Waterlogging caused soluble sugars to accumulate in the lower stem, suggesting that a defi ciency of assimilates did not contribute to waterlogging injury. Simil arly, waterlogging increased nitrogen concentration in the stem, throu gh mobilisation from senescing leaves. Bud removal enhanced leaf survi val and reduced mortality rate after waterlogging; it also increased s tarch concentration in the lower stem, indicating that storage of assi milates decreased in flowering plants. However, across all treatments, starch concentration was not correlated with waterlogging tolerance. In the third experiment, the effect of the senescence-promoting factor ethylene on preflowering and flowering plants was assessed, using the ethylene-releasing agent ethephon. Ethephon reduced growth to a sligh tly greater extent when applied prior to flowering than at flowering. There was no evidence that inadequate supply of carbohydrates or nitro gen in the stem, or increased sensitivity to ethylene, contributed to waterlogging intolerance in flowering chickpea plants.