Discovery of Variegated Leaf Mutants in Oats (Avena sativa L.)
Solomon Kibite
Agriculture and Agri-Food Canada, Lacombe Research Centre, 6000 C & E Trail, Lacombe, Alberta T0C 1S0, Canada
In a mutation induction study at Agriculture and Agri-Food Canada (AAFC), Lacombe Research Centre, certified or breeder seed of five oat cultivars (AC Belmont, Boudrias, Murphy, CDC Bell and Bullion) were irradiated with 4 doses of gamma (100, 200, 300 and 400 Gy) and one dose of fast neutron (4 Gy) radiation. The M1 generation of the irradiated seeds and untreated seeds of each of the 5 cultivars were grown in a spaced plant nursery at Lacombe, Alberta, during the summer of 1999. The nursery was arranged in a completely randomized design with 5 replications and was established on a Penhold silt-loam (coarse loamy, mixed, frigid, Typic Haplustall) soil. Plots were 5 m long and consisted of 4 rows. The rows were spaced 22.5 cm apart. Plots were seeded using a plot seeder at the rate of approximately 56 kernels m-2 (250 kernels/plot). The seeding rate was not adjusted for germination. The land use for the nursery was fallowed the previous year and was fertilized in the spring according to soil test recommendations. Data were recorded on number of seedlings/plot and seedling height at 4-weeks after emergence. Each plot was carefully examined for the presence of mutants. Plants showing phenotypic abnormalities such as reduced plant height, short peduncle, large leaves, or extreme earliness or lateness (relative to the untreated control) were tagged and harvested individually. In addition each plot was harvested in bulk and after cleaning the seed, a balanced composite sample was prepared for each treatment (cultivar-radiation dose) combination. An aliquot of the balanced composite sample was used to grow the M2 generation in 2000. The M2 generation was grown using the same protocol and experimental design as used in the M1 generation.
Fig 1. Leaves from a variegated leaf mutant and a normal oat plant.
One of the obvious abnormalities observed in both the M1 and M2 generations was the variegated leaf trait (Fig. 1). This mutation was observed in only one of the five cultivars used in the study (cv. CDC Bell) and it was observed only in the high (300 and 400 Gy) radiation treatments. In the M1 generation of CDC Bell, this mutation was observed at frequencies of 0.0075 and 0.0051 in the 300 and 400 Gy radiation treatments, respectively. The mutation frequency in the M2 generation could not be calculated because the progeny of the variegated leaf mutants were not included in the M2 generation as they were harvested and threshed separately in the M1 generation.
The mutant plants were similar to normal plants of CDC Bell in terms of panicle characteristics, leaf size and number of leaves, but were slightly later in maturity, shorter in height (presumably because of slightly shorter internode lengths) and the leaves were variegated (i.e. have distinctly white and green stripes on the same leaf). The mutants are typified by a distinct variegated foliage that displays alternating and asymmetric stripes of white and green sectors that extend longitudinally from the leaf margin to the midrib. Leaves on the same plant may show differences in variegation pattern. The lower leaves are usually more variegated (have more white sectors) than the upper leaves. Variegated leaf mutants may also display variegated stems and panicles or may be sectorial (i.e. produce albino, variegated and normal tillers on the same plant).
Self-pollinating the variegated leaf mutants produced inconsistent sectorial segregation. Kernels produced on white florets produced mostly albino or variegated leaf plants, although sometimes these florets also produced plants with normal foliage. Kernels produced on green florets always produced normal plants. Self-pollination of panicles produced by normal tillers produces only normal plants, while self-pollination of variegated tillers may produce albino, variegated or normal seedlings. Albino tillers normally do not produce seed (are non-seed bearing), but if seeds were produced on these tillers the progeny would most like albinos. Thus, each variegated leaf mutant has the potential to produced three phenotypes: albinos, variegated and green plants through sectorial segregation of either the panicle or the tillers. None of the variegated leaf mutants that we have examined so far were true breeding (i.e. produced progeny that were exclusively variegated).
Variegated leaf mutants can be used to produce albino plants at will. Albino plants can be invaluable subjects in certain types of genetic, morphological, cytological and physiological research, but so far their usefulness was limited by the absence of a known and reliable source of large numbers of seedlings. In the past, albinos were used in research only when they were found by chance in natural populations.
Variegated leaf mutants have been previously reported in oats, and the Oat Gene Nomenclature Committee of the American Oat Workers Conference (2) has assigned symbols Cds-1, Cds-2 and Cds-3 to three genes discovered by Coffman (1). It is very unlikely that any of these genes was responsible for the expression variegation in the mutants described in this paper. It is not clear if seeds of genetic stocks carrying the Cds-1, Cds-2 and Cds-3 have been deposited for long-term storage and preservation at any of the international gene banks or working collections. We plan to study the inheritance of leaf variegation in the new mutants, the allelic or linkage relationships of the mutant genes to Cds-1, Cds-2 and Cds-3 (if these genes are still available) and the effects of G x E interaction on the expression of leaf variegation.
References
Coffman, F.A. 1964. Inheritance of morphological characters in Avena. USDA Tech. Bull. 1308, 100 pp.
Simons, M.D., J.W. Martens, R.I.H. McKenzie, I. Nishiyama, K. Sadanaga, J. Sebesta and H. Thomas. 1978. Oats: A standardized system of nomenclature for genes and chromosomes and catalog of genes governing characters. USDA-SEA Agric. Handb. 509. U.S.Gov. Print. Office, Washington DC.