II.25 Induction of mutations for seedling lethality on chromosome 2.
R. T. Ramage and Jerri Miller Jones. Department of Agronomy and Plant Genetics, University of Arizona, Tucson, Arizona 85721, USA.
All of the present commercial hybrid barleys use the male sterile gene, msg2, located on chromosome 2. If a normal chromosome 2 carrying a seedling lethal and the msg2 allele absolutely linked in coupling were available, it could be substituted into current breeding programs to produce trisomics balanced for both a seedling lethal and a male sterile gene. Such trisomics would greatly facilitate the production of hybrid barley. The objective of this study is to induce mutations for seedling lethality on a msg2-carrying chromosome.
Seed that were homozygous for the male sterile allele msg2 were produced by crossing a balanced tertiary trisomic as male onto male sterile diploids. As most of the functional pollen produced by the BTT carried the msg2 allele, the crossed seed were homozygous for msg2. These seed were treated with diethyl sulfate to induce mutations. A treatment of 6,000 ml of a 0.01 M solution per 5 pounds of seed was used. The treated seed were planted in the female rows of a standard isolated crossing block. The cultivar Arivat was planted in the male rows of the crossing block. Approximately 25 percent of the treated seed produced mature plants.
Crossed seed set on the treated male sterile plants were both M1 and F1 seed and were used to produce about 85,000 M1-F1 plants. One head per M1-F1 plant was harvested and planted in head-hills. Hills that were segregating for seedling lethality were marked with surveyors flags. About 35,000 hills were planted and of these, about 7,500 were marked as segregating for seedling lethality.
At flowering time, the hills that were segregating for seedling lethality were classified for male sterility. Of these, 832 hills were classified as not segregating for male sterility and were marked with surveyors ribbons. These hills included those that had a seedling lethal closely linked with msg2.
The selected 832 hills were harvested in bulk and used to plant hill-rows. The hill-rows were examined for seedling lethality and for male sterility and 200 were selected as segregating for a seedling lethal and not segregating for male sterility. Plants from these 200 rows were crossed as male onto normal msg2 dipolids. The crossed seed and selfed seed from the male parents were grown. Lines which had a selfed progeny segregating for seedling lethality and containing no male steriles and a crossed progeny consisting of male fertiles and male steriles in about a 1:1 ratio were selected as containing a chromosome 2 carrying a seedling lethal and the msg2 allele closely linked in coupling.
Of the 200 lines, 59 were selected as having good seedling lethals very closely linked in coupling with msg2. These are being allele tested by crossing plants from one line with plants from another line. Green plants from rows segregating for seedling lethality, which are either MA/MA or ma/MA, are crossed onto male sterile ma/mA plants from mA/mA X ma/MA crosses. Seedlings from the crosses and their male parents are grown and examined for seedling lethality. If a segregating male parent produces a segregating crossed progeny, the two lines are considered to be allelic. If a segregating male parent produces an all viable crossed progeny, the crossed progeny is grown to flowering and if it contains about 1 male fertile : 1 male sterile, the two lines are considered to be non-allelic. Also, 50 of the 59 lines have been allele tested with an albino gene obtained from R. F. Eslick that he has designated a65 and also alb,,e.
Of the 50 lines tested with Professor Eslick's a65 (alb,,e) gene, 10 were found to be allelic to it (77, 128, 369, 412, 482, 548, 632, 601, 776 and 801). At a different locus, 6 alleles have been found (15, 26, 88, 106, 140 and 226). Two other sets of alleles have been found (360 and 461, 583 and 603). Because the allele tests are incomplete, only 4 loci can be definitely identified (a65, 15, 40 and 58). The line 360 is non-allelic to a65 and 15 but has not been tested with 40 and 58. The line 583 is non-allelic to a65 but has not been tested with 15, 40, 58 and 360.
Three of the lines, a65 (369), 143 and 253, have been established in balanced tertiary trisomic form, i.e., trisomics that are balanced for both the seedling lethal and the msg2 alleles. These three lines have not yet been allele tested.
Allele tests and BTT establishment are being continued.