STYLE ABSCISSION IN THE CITRON (CITRUS MEDICA L.) AND OTHER CITRUS SPECIES: MORPHOLOGY,PHYSIOLOGY, AND CHEMICAL CONTROL WITH PICLORAM

Style abscission was studied in detail in citrons (Citrus medica L.) and other citrus varieties. The course of style abscission was followed under orchard conditions and also in an “explant” system consisting of pistils implanted in an agar-sucrose medium and maintained at 25 C in a humid chamber. Morphological and anatomical observations carried out with the explant system revealed a prominent swelling of cell layers proximal to the separation layer prior to abscission. Tests with explants from flowers of different developmental stages showed that before the end of anthesis only the ovaries are capable of performing abscission while style abscission is possible only at a later stage, presumably after fertilization had occurred. Ethylene was able to induce ovary abscission at later stages but could not induce earlier style abscission. Picloram (4, amino-3,5,6-trichloropicolinic acid) increased the percentage of style persistence in citron varieties which naturally tend to retain their styles. Picloram also induced style persistence in Valencia oranges and Eureka lemons, which naturally show 100 % style abscission. Hormonal determinations showed that the style had higher levels of auxin than the ovary but also higher levels of inhibitors, which increased towards the time of style abscission.