Studies on Nature and Periodicity of Pre-Harvest Fruit-Drop in Sweet Orange

Studies on the extent and periodicity of fruit-drop of different kinds were carried out during 1969–70 on 8-year old trees of six sweet orange cultivars viz., Musambi, Pineapple, Hamlin, Jaffa, Blood Red and Valencia. Of all, Blood Red recorded the highest fruit-drop of physiological nature (38.1 per cent), whereas Valencia had the lowest (30.0 per cent). Musambi recorded 34.8 per cent drop of this nature which was statistically at par with that of Pineapple, Jaffa and Hamlin. Musambi also had the heaviest fruit-drop of pathological nature (22.4 per cent), caused mostly by stem-end rot. Blood Red came next in order but its pathological drop was at par with similar drop recorded in Jaffa, Hamlin and Pineapple. All cultivars except Hamlin had a relatively higher incidence of stem-end rot as compared to styler-end rot. Lowest fruit-drop of pathological type (4.1 per cent) was encountered in Valencia. In terms of total fruit drop, Musambi and Blood Red recorded the highest of all and Valencia the lowest. Physiological fruit-drop was at its peak in August-September and afterwards it declined. On the contrary, pathological fruit-drop was negligible in August, increased slightly in September and thereafter it registered a steep rise in October. Subsequently, its rate continued on more or less, same scale, declining slightly in December. The total fruit-drop had its peak from September to November, whereas in December its rate fell down significantly.