| Location of gene(s) for branched spike character in
a selection of bread wheat DALMlR SINGH Genetics Division. Indian Agricultural Research Institute. New Delhi-110012. India Branched spike character in T. aestivum has been reported by Sharman (1944), Tsitsin (1963), Swaminathan et al. (1966), Koric (1967, 1971, 1974 and 1978) and Singh and Joshi (1983). Recently cytological studies made by Singh and Joshi (1983) has revealed that branched spikes in bread wheat were trisomics (2n = 43). It was suggested that branching of spike in bread wheat (T. aestivum) may be the result of triplication of a particular gene(s) involved in spike formation. In the present study an attempt was made to locate the gene(s) on specific chromosome in the branched material developed by Singh and Joshi (1983). For this purpose tetrasomic plants (2n = 44) with branched spikes (isolated by Singh and Joshi, 1983) were usbd as pollen parent and monosomic plants of var. Chinese Spring as female parents. The F1 hybrids of these crosses were analysed cytologically and 2n = 43 (trisomic) 2n = 42 (disomic) plants were identified in all the lines. Observations were made on the spike character on all the cytologically identified hybrid plants (Table - 1). It was observed that (disomic, 2n = 42 as well as trisomic, 2n = 43) all these F1 hybrid plants produced first few spikes with branched character (with low expression) and rest of the spikes as normal except line 5A in which branched spikes were produced only by trisomic (2n = 43) plants while disomic (2n = 42) plants produced only normal (unbranched) spikes. F1 hybrids of monosomic 5A produced both types of plants, ie plants with branched spike and with unbranched spikes. Branched spikes were produced only by trisomic (2n = 43) plants where chromosome 5A was in three dosage while disomic (2n = 42) plants where 5A was present in two dosage produced only unbranched and spelta type of spikes. These observations clearly demonstrated that chromosome 5A may be involved in controlling the branched spike character in this selection of bread wheat. Occurrence of spelta spikes on disomic (2n = 42) plants also show that branched selection possesses Q locus in recessive from because it produces spelta spike in combination with Chinese Spring (where Q locus is present in dominant condition). Low expressivity of branched character in the F1 hybrids in present study could be the suppressive effect of Q locus (which is also located on chromosome 5A) which is present (although in hemizygous condition) in all these crosses except the F1 disomic (2n = 42) hybrid plants. Similar suppressive effects were observed by Sharman (1944) in a F1 hybrid of T. vulgare (normal) and T.turgidum (branched) and Swaminathan et al. (1966) in a F1 hybrid of T. aestivum (var. Sonora 63) and branched mutant. Present investigation and the finding and of Sharman (1944) and Swaminathan et al. (1966) suggest that branched character can not be exploited in the presence of a gene (Q locus) which does not allow the full expression of branched character (even if Q is present in hemizygous condition). In the light of these observations it is suggested that the gene(s) for branched spike (located on chromosome 5A) present in the selection isolated by Singh and Joshi (1983) can serve as a useful source for transferring stable branched character in bread wheat provided the receipient variety carries Q locus in recessive form. Work towards this direction is in progress. |
| --> Next |