| Results and Discussion With the exception of HW 178-A and HW 489, all the varieties of T. dicoccum when crossed to C 306 produced strong chlorotic F1 hybrids indicating that the varieties carry the Ch1 gene (Table 1). The F1 hybrid plants between Sonalika and four T. dicoccum varieties, namely, HW 43, HW 1018, HW 1046 and Khapli-53 Yellow expressed the symptoms of both necrosis and chlorosis simultaneously indicating that these varieties also carry the gene Ne1. The variety HW 178-A produced normal and necrotic F1 off-spring when crossed to C 306 and Sonalika respectively. Results indicate that the variety is non-carrier for chlorosis gene while it carries the gene Ne1. Normal hybrids were obtained in the crosses of HW 489 with both the testers indicating that this variety is non-carrier for both necrosis and chlorosis genes. The F1 hybrids between Sonalika, a Ne2 Ch2m - carrier (Kochumadhavan et al 1984), and three T. dicoccum varieties, viz., HW 1016, HW 1017 and Sangli 2-2, exhibited only chlorosis and it is likely that chlorosis may obscure the expression of necrosis. Consequently, this type of epistatic gene action caused difficulty in identifying the genotype of these varieties of T. dicoccum as to have Ne1 or ne1. When both the complementary gene systems for hybrid necrosis and hybrid chlorosis operate in F1 hybrids, the phenotypic expression of one hybrid weakness over the other or the simultaneous occurrence of both kinds of hybrid weakness depends on the relative strength of alleles existing at Ne- and Ch- loci. Therefore, the genes with respect to necrosis in the varieties: HW 1016, HW 1017 and Sangli 2-2 could not be determined for want of single-gene tester (ne1Ne2ch1ch2) for necrosis or a two-gene tester (ne1Ne1Ch1ch2) for necrosis and chlorosis with the authors. While the single-gene tester is extremely rare, the two-gene tester has not been established in polyploid wheats. Varieties of T. dicoccum, like other tetraploid species of wheat, are either Ne1 - carriers or noncarriers (Nishikawa 1967; Tsunewaki 1969b; Tomar et al 1987). Ne2 - carriers have not yet been reported in 4x wheats despite the location of this gene in B genome. Therefore, the Ne2 gene, found restricted to the western 6x wheats is presumed to have originated by mutatio at the hexaploid level in Europe (Tsunewaki and Kihara 1962). Hermsen (1966) reported that the Indian emmer wheat Khapli carried the Ch1 gene. The present study reveals a high prevalence of Ch1 -carriers in T. dicoccum varieties and this further corroborates the observation of Kochumadhavan et al (1984) that the gene Ch1 widely occur among the Indian varieties of T. dicoccum. References Hermsen JGTh (1966) Hybrid necrosis and red hybrid chlorosis. Proc. 2nd Int Wheat Genet Symp Lund, Hereditas Suppl 2: 439-452 Hermsen JGTh and Waninge J (1972) Attempts to localize the gene Ch1 for hybrid chlorosis in wheat. Euphytica 21: 204-208 Kochumadhavan M, Tomar SMS and Nambisam PNN (1984) Hybrid necrosis and hybrid chlorosis in Indian varieties of Triticum dicoccum Schubl. Euphytica 33: 1-6 Nishikawa K (1967) Identification and distribution of necrosis and chlorosis genes in tetraploid wheat. Seiken Ziho 19: 37-42 Tsunewaki K (1960) Monosomic and conventional analysis in common wheat. III. Lethality. Jap J Genet 35: 71-75 Tsunewaki K (1969) Origin and phylogenetic differentiation of common wheat revealed by comparative gene analysis. Proc 3rd Int Wheat Genet Symp pp 71-85 Tsunewaki K and Kihara H (1961) F1 monosomic analysis of Triticum macha. Wheat Inf Serv 12: 1-3 Tsunewaki K and Kihara H (1962) Comparative gene analysis of common wheat and its ancestral species. I. Necrosis. Jap J Genet 37: 474-484 |
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