Effect of spring applications of paclobutrazol and uniconazole on 'Red Rosa' plum fruit development and storage quality

Plum (Prunus salicina cv. Red Rosa) trees in an orchard in northern Israel were treated for two consecutive growing seasons (1993, 1994) with soil applications of paclobutrazol or uniconazole in the spring, at two levels terms ''low'' and ''high''. The dose in the second year was, in each case, half that in the Brst year. Fruit development and storage were assessed in each season and also in 1995, when no growth regulators were applied. Treatments with the growth regulators increased fruit weight and size in all three seasons. Treated trees bloomed earlier the following year than untreated control trees. Fruits were harvested three times during the 1993 and 1994 seasons and once in 1995 and were stored at 0 degrees C under both regular air and controlled atmosphere conditions for six and ten weeks, respectively. In regular air storage, 'Red Rosa' plums from all treatments maintained good quality for up to six weeks, except for the late harvested fruit, which began to show signs of gel breakdown (1993) or internal browning (1994). In controlled atmosphere storage, similarly good quality was maintained for eight or ten weeks depending on the harvest time. The major physiological disorder which developed was internal browning. Paclobutrazol and uniconazole at the ''low'' dose did not affect the storability of the plums. However, the ''high'' doses of both regulators enhanced gel breakdown in fruit of one of the harvests in 1994, indicating a potential for deleterious effects when applied in excess.