Morphological and genetic variations in "Balady" Mandarin induced by gamma irradiation

Abstract

Induced mutagenesis using gamma ray has been proven applicable to improve varieties of many genotypes of crop species. The present investigation was carried out to study genetic variability induced by gamma rays in Balady mandarin. Bud woods were irradiated with doses of 0, 2, 4, 6 and 8 kr along with control and budded onto volkamer lemon rootstock. Bud survival percentage decreased with increasing dose of gamma radiation. Doses of 6 and 8 Kr were lethal where the LD50 was achieved at 2.1 Kr. Shoot length, leaf number per plant, leaf area per plant and stomata width decreased significantly by increasing the gamma dose from 0 to 4 Kr. Whereas, stomata number per unit area increased significantly compared to control. Molecular analysis of some induced mutants using ISSR and RAPD markers revealed that, the polymorphism percentage ranged from 50% to 80% when the ISSR primers were used and from73.33% to 100% for RAPD primers. The 4 Kr treatment caused the highest polymorphism percentage (69.05% and 85.32%), whereas the 2 Kr treatment had 62.5% and 74.23% for the ISSR and RAPD primers respectively. Gamma irradiation treatments included alteration in protein bands intensity, appearance of new bands and disappearance of other bands. The most visible changes in protein patterns were the appearance of new bands with molecular sizes of 264, 196 and 139 KDa in some selections of 4 Kr treatment, and bands of 87, 86, 82, 51, 45, 30 and 9 KDa in selections of 2 and 4 Kr treatments. The 4 Kr treatment achieved more genetic variation than the 2 Kr treatment.