| Cytogenetics of solid stem in common wheat: Monosomic
F2 analysis of the variety S-615 R. I. LARSON Science Service Laboratory, Department of Agriculture Lethbridge, Alberta, Canada Varieties of common wheat, Triticum aestivum L. emend Thell., with pithy culms are more resistant than those with hollow culms to the wheat stem sawfly, Cephus cinctus Nort. The two sawfly resistant varieties, Rescue and Chinook, licensed to be grown in Canada had as their resistant parent S-615, a Portuguese variety obtained by the Dominion Experimental Farm at Swift Current from Lincoln College, Christchurch, New Zealand. None of these so-called solid-stemmed varieties is immune to sawfly attack, and none has culms completely filled with pith. Although it has not been demonstrated that pith is the only factor that makes a wheat variety resistant to sawfly, those environmental field conditions that tend to make the culm hollow also tend to make the crop susceptible to the sawfly. Therefore an investigation of the genetics of solid stem in S-615 to identify the chromosomes bearing genes affecting pith production was initiated in the hope that this knowledge would improve opportunities of combining these genes with those from other sources. Four monosomic F2 lines, XIII, XIX, XX and XXI were more solid than the normal F2 population of Chinese Spring x S-615 in every test in which an adequate sample was examined. This shows that these chromosomes, at least in Chinese Spring, carry genes for hollow stem. The change from a tetrahybrid to a trihybrid ratio in mono-XIII shows that Chinese Spring XIII has one gene for hollow stem and S-615 has not. As the loss of the other chromosomes did not change the apparent number of segregating genes it is probable that also they tend to make the culm hollow in S-615. Monosomics I, VIII, IX, X and XI were less solid than the normal F2 population in 1948 but not in 1949, when conditions were less faborable for pith development. Generally, this appeared to be due to a change in dominance relations of the genes. Monosomic VIII fit a trihybrid ratio best in 1949, suggesting that Chinese Spring chromosome VIII has a gene for solid stem not possessed by S-615. The linkage between solid stem and hooding supports this view. Mono-XII was less solid than normal in both 1948 and 1949. There is some evidence that chromosomes affect pith distribution. Although the loss of the chromosomes of homoeologous group 2 was quantitatively different from chromosome to chromosome and from year to year, the pith pattern of the monosomics had similar relations to their normal checks. Monosomic XVIII, too, in hybrids with several varieties,es, showed a characteristic pith pattern, tending to be slightly more solid in the top internode and less solid in the lower internodes than the respective normal hybrid. |
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