Evaluating Water-stress as Flowering and Fruiting Stimulus to Sweet Orange (Citrus sinensis. L) in Tropical Conditions

Abstract

This study aimed to find out the optimum water stress period to induce rest as stimulus after which irrigation should be resumed to obtain flowering and best fruit yield for sweet orange. The experiment was conducted at Kitayab, AlRaw and Central Zeidab Schemes in River Nile State, Sudan during 2014/15 and 2015/16 seasons. Mature orange trees (local Sinnari cultivar) grafted on sour orange root stock from farms where basin irrigation and different irrigation stopping periods after harvest were practiced. Nine trees spaced at 7×7 m. and with at least 10 years’ age, were randomly selected for experimentation in four sites. The soil at the experimental sites is mostly homogenous representing Nile fluvent sediments of entisols with loamy to clay loam texture. The experimental design was randomized complete block design (RCBD) with three replicates. The periods for irrigation stress after harvest and before the new flowering season were 2, 3, 4, 5, 6, 7, 8 and 9 weeks. All intervals ending at the onset of winter season. Parameters taken were: time of flowering, number of flowers/ squire meter, number of fruits/tree, number of dry branches/tree, difference in maturity/tree as percentage of mature fruits over others. Results obtained indicated that early flowering noticed after 9 weeks of irrigation stress compared to short periods. Number of flowers per a square meter increased in both seasons by increasing irrigation-stress period. Irrigation stress period affected significantly number of fruits per tree in both seasons, but not following the same trend of number of flowers per square meter. In both seasons, the highest number of fruits was registered by 3-week dry period treatment. Increasing irrigation-stress period increased dry branches per tree and differences in fruit maturity.