BGN 10: A shrunken endosperm (sex 1), male sterile (msg 6) stock to facilitate crossing in barley BARLEY GENETICS NEWSLETTER, VOL. 10, III. GENETIC AND CYTOLOGICAL TECHNIQUES
Falk and Kasha, pp. 81-83

III. 1. A shrunken endosperm (sex 1), male sterile (msg 6) stock to facilitate crossing in barley.

D.E. Falk and K.J. Kasha, Crop Science Department, University of Guelph, Guelph, Ontario, Canada, N1G 2W1. "R"

The use of genetic male sterility has, as foreseen by Suneson (1940), become a widely used tool in barley breeding. In conventional crossing programs, it is being used to eliminate hand emasculation in producing F1 seed. Male sterile genes are also included in populations in order to increase and maintain out-crossing and continued recombination. Examples are the Evolutionary Method of breeding and in recurrent selection schemes. Genetic male steriles in combination with tertiary trisomics have been used to produce hybrid barley (Ramage, 1975). Eslick (1969) suggested that male sterile genes be linked with the recessive alleles of dominant, preflowering genes in order to identify the male sterile plants and rogue any fertile plants prior to pollen shedding.

On barley chromosome 6 the msg 6 gene has been found to be closely linked (< 1% recombination) to the shrunken endosperm gene sex 1 (Falk, Swartz and Kasha, 1980). We have recently obtained a recombination between these genes to establish the recessive alleles in the coupling linkage phase. Because sex 1 expresses xenia, plants heterozygous for this gene will produce 75% plump and 25% shrunken endosperm seeds. When the stock containing msg 6 and sex 1 is crossed with a cultivar dominant for these genes, the selfed seed on the F1 plants will be approximately 25% shrunken and 75% plump seeds. Over 99% of the shrunken seed should give rise to male sterile plants. These shrunken seeds can be separated mechanically or by hand with fairly good precision so that they will provide rows, plots or populations of male sterile plants when sown. In a breeding program, the male steriles can be removed from a population by selecting F2 plants producing only plump seeds. To retain male steriles and develop populations, allowing the fertile plants to sib-pollinate the male sterile plants will produce a ratio of 2 plump to 1 shrunken endosperm seed and, therefore, 2 fertile plants (Sex 1, Msg 6/sex 1 msg 6) to 1 male sterile plant (Fig. 1). A second cycle of sib-pollination in this population will give 1 plump to 1 shrunken endosperm seed and a 1:1 ratio of fertile to male sterile plants. Thus, the coupling of sex 1 to msg 6 permits the breeder to retain, increase or discard male steriles from the breeding populations.

Since the breeder can identify the male sterile plants before planting the seeds, he could grow rows of male steriles in his crossing field or grow individual male sterile plants for crossing indoors. This would conserve space and facilitate machine harvesting of rows or plots in the field. One could expect the occasional male fertile plant among the male sterile rows, resulting from either misclassification of sex 1, the rare cross-over, or possible field contamination. These would require some roguing.

Figure 1. Segregation of sex1 and msg6 linked in the coupling phase in advancing generations of a breeding population.

The sex l ; msg 6 stocks could be valuable for male sterile facilitated recurrent selection programs. Since the male steriles could be identified before planting, they could be placed in separate rows and used for crossing among the chosen lines. Selection pressure could be applied differentially to the male sterile and male fertile populations.

One drawback of the sex l ; msg 6 stock may be in the production of hybrid barley. The seed from the F1 plants would be 25% shrunken endosperm and this may reduce the yield somewhat. On the other hand, the sexl seeds contain elevated levels of lysine (Ullrich and Eslick, 1978) and may prove to be better from the feeding and nutrition aspects of livestock feed.

The sex l ; msg 6 stock has been produced from crosses with Heines Hanna (msg 6) and Compana (sex 1) as well as Betzes (orange lemma). Both 2-rowed and 6-rowed stocks of this mutant combination are being developed at Guelph and limited seed supplies should be available for distribution by September 1980. The background can be readily changed by using a backcrossing scheme. Stocks with these two genes in the repulsion phase are also being synthesized.

References:

Eslick, R.F. 1969. Balanced male steriles and dominant pre-flowering selective genes for use in hybrid seed production. Proc. 2nd Int. Barley Genet. Symp., Pullman, WA, U.S.A. Ed. R.A. Nilan. pg. 292-297.

Falk, D.E., M.J. Swartz and K.J. Kasha. 1980. Linkage data with genes near the centromere of barley chromosome 6. BGN 10:

Ramage, R.T. 1975. Hybrid barley. Proc. 3rd Int. Barley Genetic Symp., Garching, FRG. Ed. H. Gaul. pg. 761-770.

Suneson, C.A. 1940. A male sterile character in barley. J. of Hered. 31(5):213-214.

Ullrich, S.E. and R.F. Eslick. 1978. Allelism evidence for barley high lysine, shrunken endosperm xenia (sex 1) mutants. BGN 8:109-112.

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