RECIPROCAL TRANSLOCATIONS IN SORGHUM VULGARE

Abstract

Endrizzi and hilorgan ( 1955) reported the occurrence of reciprocal translocations in Sorghz~77jl m ~ l g a r e but did not examine pachynema configurations. The present study deals with cytological observations at prophase of meiosis, including pachynema, of three reciprocal translocations obtained by Haensel (1960) after gamma irradiation of the reactive grain sorghum variety Experimental 3 . Seedlings of this genotype are transformed, after colchicine treatment under certain conditions (Franzlte et al., 1960), into either true breeding or segregating mutants. Materials and Methods At preanthesis stage, panicles of S. wz~ lgnre , variety Experimental 3 a true breeding dwarf grain type sorghum, whose origin has been previously described (Franzlte and Ross, 1952), were subjected to irradiation with cobalt 60 under different dosages by Haensel (1960). Three reciprocal translocations, designated as T165, T23 1 and T396, were identified in semi-sterile plants of progenies from these panicles. Pollen was examined by dissecting individual anthers in a lacto-phenol-acid fuchsin stain conlposed of 20 cc. of phenol, 20 cc. of lactic acid, 40 cc. of glycerin, 20 cc. of water and 8 cc. of I % acid fuchsin. This stain was observed to give the same results as IKI. About 500 pollen grains from each plant were examined in randomly selected microscope fields. Under greenhouse conditions, tlle percentage of viable pollen of normal Experimental 3 varied from 80-97%. T o identify plants l~omozygous for the translocation within the progeny of a heterozygous plant, those having 80% or more viable pollen were hand enlasculated and crossed to normal Experimental 3. Examination of the percentage of pollen abortion of tlle plants growing from these seeds identified plants hoinozygous for the translocation. Plants which showed about 50% ~ o l l e n abortion \vere classified as heterozv~ous for the translocation and were I J U transplanted to the field in the spring for study of meiosis. Heads talten fro111 these materials grown in the field were fixed in 3 ethyl alcohol: 1 glacial acid and stored in 70% ethyl alco1~ol. Chromosomes were stained with propionic carmine. hl~easureineks of chromosomes in translocation confi~u;ations at '3 pacl~ynenla kvere made from enlarged photographs. Results Cytological exan~inations of translocation configurations of the homozygous normal and homozygous reciprocal translocation lines at pachynema, dialtinesis, and metaphase I stages showed no irregularities. Differing proportions of rings and chain configurations in plants heterozygous for the translocations were observed, as shown in Table I. T396 followed by T231 have the largest proportions of chain configurations. The nucleolus cl~romoson~e was found to be involved in translocation T396. Per cent pollen viability is shown in Table I1 for plants obtained by selfing the translocation heterozygotes. The fertile plants showed some pollen abortion while the semisterile plants, l~eterozygous for the translocations, had means of 42.7% to 49.4% viable pollen.