Morphogenetic Characterization of Mutants and Polyploids of Grapefruit

Abstract

Gamma irradiation application is widely used by breeders for improving crops, and searching new traits which enhance both quality and quantity of crop. In present studies, bud woods of three white fleshed varieties i.e. Foster, Frost Fresh, Reed and three pink fleshed varieties of grapefruit i.e. Shamber, Red Mexican Foster and Red Blush were irradiated with gamma rays on different levels i.e. 0, 20Gy, 50Gy, 80Gy, 110Gy and 140Gy. These budwood were grafted on rough lemon in nursery. Morphological characterization i.e. Survival percentage, number of leaves, leaf length and width, shoot length and number of branches were carried out. These morphological parameters decreased with increased dose of gamma radiation. 80% decline in survival percentage was observed at 140Gy of gamma radiation. Similarly 86.31% in number of leaves, 72.88% in leaf length 82.58% in width, 86.65 % in shoot length and 72.63% number of branches were reduced. In second experiment, genetic characterization with the help of SSR markers was done to identify the mutation induced by the gamma radiation. Total 18 SSR markers were used but one primer did not show any polymorphism even in control as well as in treated budwoods. Variation among gamma irradiated bud woods and non-treated (control) budwoods were observed during PAGE due to higher resolving power of PCR amplificates. Polymorphic Information Content (PIC) was found in range of 77.85-39.78. Allele frequency, allele length, genetic diversity, heterozygosity as a result of amplification of DNA were obtained. In third experiment, colchicine was applied by In Vivo and In Vitro methods. In Vivo colchicine application, ten young branches were treated with colchicine to induce polyploidy. Morphological analysis i.e. branch length, number of branches, number of leaves, leaf length and width were checked. In Vitro method, seeds were exposed to 4 hour in colchicine solution at different concentrations i.e. control, 0.05, 0.08, 0.1, 0.2, 0.3 and 0.5 mg L-1 . Morphological and cytological analysis were carried out. Higher colchicine concentrations increased the leaf length, width and area but reduced number of leaves. Cytological analysis i.e. stomatal density, size, length and width, area and aperture were observed with Nikon microscope. At maximum concentration of colchicine, number of stomata were reduced but their length, width, area and aperture were higher as compared to control or lower concentrations of colchicine.