Effect of gamma ray irradiated pollen technique on fruit growth in Citrus

Citrus is one of the most economically important fruit crops in the world, greatly valued as table fruit as well as in the processing industry. Among the different citrus fruits, pummelo plays a major role in the processing industry. However, the presence of a large number of seeds in pummelo greatly hinders processing quality. Therefore, induction of seedlessness in pummelo is one of the major goals around the world. Currently, irradiated pollen technique emerges as a novel tool for induction of seedlessness in any fruit. However, reduction of fruit size is a great concern in irradiated pollen technique. Hence, an experiment was conducted to study the effect of gamma ray irradiated pollen technique on fruit growth in citrus using pummelo (C. grandis (L.) Osb.) as seed parent while sweet orange (Citrus sinensis (L.) Osb.) cv. ‘Mosambi’ and sweet lemon (C. limetta Risso) as pollen sources. Irradiation of pollen grains was performed at 50, 100, 200, 300 and 400 Gray (Gy) by using 60Co gamma ray and the experiment was laid out in complete randomized design with 5 replications. With the increased doses of irradiation, fruit growth in terms of length, diameter, weight and volume differed significantly throughout the period of observation starting from 35 days after pollination to till maturity. At maturity, maximum fruit length (387.70 mm), weight (590.27 g) and volume (885.27 cc) were recorded in C. grandis × C. limetta crosses at control while minimum fruit length (129.74 mm) and weight (211.54 g) were observed in C. grandis × C. sinensis crosses at 300 Gy. There was no fruit retention till maturity in either cross combination at 400 Gy. Among two different cross combinations, with the increased dose of irradiation, the rate of reduction in fruit growth in terms of length and weight as compared to respective control was much higher in C. grandis × C. sinensis crosses. However, for the production of marketable size fruits (not more than 300 g), irradiation of either pollen parent at 200-300 Gy was found to be the best while, doses below 200 Gy caused the production of fruits weighing more than 400 g, which do not have good market value.