II.6 Lethal chloroplast mutations linked to the msg2 locus.
C. A. Foster. Welsh Plant Breeding Station, Plas Gogerddan, Aberystwyth, Dyfed, SY23 3EB, Wales, United Kingdom.
The development of balanced tertiary trisomic stocks for F1 hybrid production on a field scale has required the incorporation of lethal chloroplast mutations to facilitate the multiplication of the B.T.T. stock prior to male sterile production (Wiebe and Ramage, 1971). While backcrossing Ramage's original B.T.T. stock (63-J-18-17, based on T2-7d and msg2) to adapted European varieties a search has been made for lethal chloroplast mutations suitable for incorporation into this material. Crosses between 45 such mutants, induced in several European varieties by diethyl sulphate, and male sterile plants from 63-J-18-17 were made in 1971. Small F2 progenies were grown in 1972 and F3 progenies of crosses involving 23 of the mutants that showed preliminary evidence of linkage to the msg2 locus were grown in 1973. These F3 progenies were precision seeded at 6 in. x 2 in. spacing, up to 50 F3 families of 23 plants each being tested per mutant.
Five of the mutants showed evidence of close linkage to the msg2 locus. In order to identify any F3 recombinant individuals in which the mutant and msg2 alleles were linked in coupling, as required for incorporation into B.T.T.'s, a single ear of each fertile F3 plant was harvested. Over 2300 F3 ears, to give F4 progenies, were grown in 1974 by sowing unthreshed ears 6 in. apart in drills. Germination and establishment were excellent. The ear/clumps that were segregating for seedling lethals were checked at ear emergence for segregation for male sterility. With complete linkage in repulsion all F4 progenies that segregated for the seedling lethality should also segregate for male sterility. Families not segregating for ms were identified and test crossed to msg2/msg2 plants in the field. These test cross progenies are being grown in the glasshouse in the winter of 1974/75 to distinguish between the two possible recombinant genotypes, i.e. Msg2A/Msg2a and Msg2A/msg2a. If the latter is found, the relevant reserve selfed F4 progeny will be crossed on to adapted B.T.T. lines balanced only for msg2, and lines balanced for msg2a will be derived. Some F3 and F4 data for the five mutants most closely linked to the msg2 locus are shown in Table 1.
Tests for allelism between these mutants and with an albino mutant (369-a) linked to msg2, isolated by Ramage following mutagenesis of a homozygous male sterile stock (Ramage, Wiebe, Eslick and Thompson, 1972), are being made.
References:
Wiebe, G. A. and R. T. Ramage. 1971. Hybrid barley. Barley Genetics II, 287-291.
Ramage, R. T., G. A. Wiebe, R. F. Eslick and R. K. Thompson. 1972. Use of mutagenic agents in hybrid barley breeding. B. N. 15, 73-78.
