Pre-Harvest Stem-End Rot In Citrus Cultivars due to Colletotrfchum gloeosporioides

摘要

Stem-end rot was previously considered as post-harvest disease of citrus fruits, but recently, it has been observed as a cause of pre-harvest fruit rot in citrus orchards of Punjab state of India. Pre-harvest stem-end rot causing agent, Colletotrichumgloeospo-rioides, was characterized and evaluated on different stages of citrus cultivar, 'Kinnow' beginning from floral buds to mature fruits. Two isolates of Colletotrichum, Cg-1 (slow growing with orange pigmentation in culture media) and Cg-2 (fastgrowing, without pigmentation in culture media) were isolated from infected fruits, and ascribed to species C. gloeosporio-ides. All stages of fruit growth, starting from petal-fall stage to 14-week old fruits were found susceptible to stem-end rot infection after artificial inoculations under in vitro and in vivo conditions. Older fruits developed stem-end rot more quickly as compared to younger fruits. The symptoms appeared as necrotic lesions on unopened and opened flowers, and persistent calyces (buttons) formed as a result of flower infection. The symptoms initiated as brown to reddish brown or black spots in all stages near the stem-end region, which became firm and dry and ultimately, the rind became softened and resulted in rotting in the advance stages. Isolate Cg-1 was pathogenic to all stages of citrus fruits and, incidence remained the same irrespective of stage of fruit under both in vitro and in vivo conditions. Isolate Cg-2 was ineffective at both petal-fall and button-sized fruit stage, but caused serious damage in mature fruits.