Summary. Allelic relationships of genes for naked caryopsis character of barley in three different hulless mutant lines of hulled variety 'HBL 110' and a hulless variety 'Dolmal were investigated.

Through F₁, F₂ and F₂ studies of the mutants and variety 'Dolma', the character was found to have two non-allelic genes. The genotype of parent variety "HBL 110' (hulled) was found to be n₁ n₁ n₂ n₂ and that of 'Dolma' (hulless) as n₁ n₁ n₂ n₂. The most relevant probabilities of arising hulless mutants from hulled variety were in either of two ways (considering locus n₁ and I and n₂ as II), (i) by dominant mutation at locus I only (n₁ n₁ n₂ n₂ -> n₁ n₁ n₂ n₂ and (ii) by recessive mutation at locus II only (n₁ n₁ n₂ n₂ -> n₁ n₁ n₂ n₂).

Introduction. Naked caryopsis (hulless) mutants in barley are characterized by complete detachability of the hulls (lemma and palea) on threshing, whereas in covered (hulled) barleys hull remains completely attached with the grain on threshing.

In previous studies, Wang (1936), Robertson (1937), Robertson et al. (1947), Scholaz (1955), Shaheen et al. (1961), Jain and Upadhyay (1963), Brückner (1974) and Gymer (1977) reported single recessive gene inheritance for naked caryopsis.

This report summarizes data obtained in the study of three different naked caryopsis mutants and a hulless variety 'Dolma'. The objectives of the study were: (a) to ascertain the allelic relationships of the mutated genes and (b) to ascertain the number of genes controlling expression of the mutant phenotype.

Materials and Methods. The four naked caryopsis lines and source of each are given in Table 1. The lines designated f 'mt₁', 'mt₂' and 'mt₃' are hulless mutants derived from hulled variety 'HBL 110' by Ethylmethane sulphonate (EMS) and combination of Ethylmethane sulphonate and Sodium azide (NaN3) and were obtained from the Department of Plant Breeding, H. P. Krishi Vishva Vidyalaya, Palampur, India. The hulless variety 'Dolma' is a yellow rust resistant selection from 'USA 115'.

The crosses between the hulless mutants and 'Dolma' were studied to ascertain inheritance of the character. Information regarding allelic relationships of genes for the character was obtained from F₁ phenotypic study and F₂ segregation pattern and for ascertaining number of genes the observed counts were compared with the expected in F₂ generation. Breeding behavior of the expected F₂ genotypes was confirmed in the F₃ generation.

For the sake of convenience the already assigned gene symbol N/n has been used for covered vs. naked caryopsis. The number assigned to the gene symbol are tentative for want of their allelic relationships with the known markers.

Results. The F, populations obtained from mutants in crosses 'mt₁' x 'mt₃', 'mt₂' x 'mt₁' and 'mt₂' X 'Dolma' had hulless plants. the F₁ population provided no confirmatory information about the allelic relationships of hulless genes since segregation for hulless and hulled plants was obtained in the F₂ and F₃ generations.

The F₂ population of the cross 'mt₂' x 'Dolma' consisted of 61 hulless and 19 hulled plants. A fit for 13: 3 ratio (X² = 1.31, P = 0.20 - 0.30) for this cross suggested that 'mt₂' and 'Dolma' had non-allelic genes and the character was conditioned by a two-factor control displaying dominant and recessive gene interaction (Table 2). Support for this ratio was obtained from the F₃ study in which the hulless and hulled plants of F₂ generation segregated for hulless and hulled plants with proportions of 2/5 and 4/6 as expected from the F₂ genotype (6/13 and 2/3). The genotype of the mutants and their F₁ and F₂ are presented in Figure 1.

Discussion. Further evidence is required to justify similar hypothesis for other characters. This situation appears to be a not uncommon situation in barley, when it is considered that such characters as blue aleurone (Smith, 1951), long weak basal internode (Kasha and Walker, 1961) and possibly accordion rachis (Enns, 1961) are under this form of control.

The study also suggested that genotype of the parent hulled variety 'HBL 110' is n₁ n₁ n₂ n₂ and the mutants 'mt₁', 'mt₂' and 'mt₃' from it might have arisen in either of three ways (considering locus n₁ as I and n₂ as II), (i) by dominant mutation at locus I only (n₁ n₁ n₂ n₂ -> n₁ n₁ n₂ n₂), (ii) by dominant at locus I and recessive at II (n₁ n₁ n₂ n₂ -> n₁ n₁ n₂ n₂) and (iii) by recessive mutation at locus II only n₁ n₁ n₂ n₂ n₁ n₁ n₂ n₂). The probability of the possibility (ii) is very low on account of the variety of simultaneous mutation at different loci for the same trait. Thus, the possibilities (i) and (iii) appear to be relevant.

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