II. 5. Attempts to establish a balanced male sterile-semidominant chloroplast mutant linkage for hybrid barley.
C. A. Foster and D. A. Dawi*, Welsh Plant Breeding Station, Plas Gogerddan, Aberystwyth, Dyfed, SY23 3EB, Wales, U.K. *Present address: Agricultural Botany Department, Faculty of Agriculture, Shambat, Sudan. "R"
A semi-dominant chloroplast mutant and a system of utilizing this in hybrid barley production have been reported (Foster, 1979a,b). This mutant (Cb 3369) segregates on selfing into normal green dominant homozygotes, lighter green (or viridis) heterozygotes and albino recessive homozygotes, in the ratio of 1:2:1. The viridis plants are conditional lethal, failing to reproduce under field conditions in this climate, but surviving and yielding up to 75% of normal green plants under certain conditions. The temperature and light responses of this mutant have been studied by Dawi (1981). If a close repulsion linkage could be established between this gene and a gene for male sterility the selfed progeny of the viridis heterozygotes, having been produced in a high temperature/high light environment, could be sown in the field to provide normal green plants that would all be male steriles. These could serve as the female parents of an F1 hybrid, no further roguing being required.
Crosses have been made between this mutant and a range of male sterile genes or stocks containing 13 of the numbered gene series and 18 new male sterile stocks. The latter have not been fully tested for allelism, but recent tests have shown that 3 of them are allelic with 3 of the numbered genes also used. Crosses were made by pollinating a male sterile plant of each stock with a Cb 3369 viridis plant. The F1 plants were grown in the glasshouse and all segregated 1 green:l viridis, as expected. F2 progenies of the viridis F1 plants were grown in the field. With no linkage a 3 fertile:l male sterile ratio would be expected in the surviving normal green plants. With complete linkage all normal green plants would be male sterile. The results (Table 1) show that none of the male sterile genes was closely linked to the chloroplast mutant locus. Only the 9:9 segregation for the cross with msg7 deviated significantly from the non-linkage expectation. This segregation also deviated significantly from the complete linkage expectation. Both deviations were significant at the 5% level of probability. Thus, although there is some evidence that Cb 3369 vir and msg7 are on the same chromosome, the linkage is not sufficient to be of interest for the purpose intended.
Unfortunately, msg7 has not been located on or associated with a chromosome. Of the 13 numbered genes used only msg2 has been located on a chromosome (Tsuchiya, 1982), although msg1, msg5, msg23 and msg24 have also been assigned to chromosomes but not definitely located. Previous reports have also associated msg4 and msg16 with chromosomes. The remaining genes used, msg7, msg1l, msg13, msg18, msg27 and msg28, have not been reported as being definitely associated with a particular chromosome. Of the new male sterile stocks used, 8 are known to be non-allelic with 8 of the 13 numbered genes used (Dawi and Foster, 1983).
It is proposed to cross Cb 3369 viridis next with those numbered genes that have not yet been used and which are known to be on different arms of the chromosome already tested, i.e. msg3, msg6 and msg1O, and then with other male sterility genes known to be associated with but not located on a particular chromosome.
References:
Dawi, D. A. 1981. Genetic systems for hybrid barley (Hordeum vulgare L.) breeding. Ph.D. Thesis, University of Wales, Aberystwyth.
Dawi, D. A. and C. A. Foster. 1983. Allelism studies of new genetic male sterile stocks in the WPBS Collection. BGN 13:9-11.
Foster, C. A. 1979a. Two incomplete or semi-dominant mutants in barley. BGN 9:23-24.
Foster, C. A. 1979b. A balanced male sterile-chloroplast mutant scheme for hybrid barley. BGN 9:22-23.
Tsuchiya, T. 1982. Linkage maps of barley. BGN 12:100-104.
