Anther color in BSSS-101 inbred line
--Zhang, XH and Hallauer, AR
BSSS-101 line was derived by single-seed descent from the Iowa Stiff Stalk Synthetic (BSSS) population after 10 generations of self-pollination. BSSS-101 was regarded as a homogeneous line for breeding purposes. Purple and green anther colored plants were observed within BSSS-101 in the breeding nursery in 1992. In 1992, plants with purple and green anthers were crossed to produce the F1 generation. The F2 generation was produced in the 1992-1993 winter nursery by self pollination. The backcrosses of F2 generation plants with purple and green anthers to the parents with purple and green anthers were produced in 1993. Purple and green anther plants within the F2 generation also were selfed in 1993 to produce the F3 generation. Purple and green anther color parents and the F1 and F2 generations were grown in the 1993 breeding nursery. Purple and green anther color parents, and F1, F2, F3, and backcross generations were grown in the 1994 breeding nursery. In each season, individual plants were classified for purple and green anther color. Plants that had slightly blotched anther color upon emergence from stamens were also recorded. The classification of plants with different anther color was recorded in each generation at the time of pollen shed.
When two plants of different anther color were crossed within the BSSS-101 line of maize in 1992, the F1 generation exhibited a 3:1 ratio of plants with purple and green colored anthers in 1993: 53 plants had purple anthers and 17 plants had green anthers. The F2 generation also exhibited a 3:1 ratio: 157 plants with purple anthers and 52 plants with green anther (Table 1). In 1994, the 3:1 ratio also was observed in F1 and F2 generations: F1 generation had 15 plants with purple anthers and 5 plants with green anthers, and F2 generation had 287 plants with purple anthers and 93 plants with green anthers. An 8:1 ratio was observed in the F3 generation upon selfing F2 plants with purple anthers (160 plants with purple anthers and 20 plants with green anthers). For plants having green anthers, however, anther color did not segregate either in crosses made between plants with green anthers or in selfs of F2 plants with green anthers (Table 1). The backcrosses of F2 generation plants with purple anther color to the parent with purple anthers had only purple anthers. A 1:1 ratio was found in the backcrosses of F2 generation plants with purple anther color to the green anther color parent. When F2 generation green anther plants were crossed to the green anther parent, progeny of this backcross all had green anther color (Table 2). It was observed that plants with purple anthers had light-red silks, light purple color at base of stem, colorless aleurone, and red cobs. Plants with green anthers had green silks, green color at base of stem, colorless aleurone, and red cobs. Daily examination of the field plants indicated that the purple anthers were affected by sunlight. In general, if the anthers were slightly blotched purple upon emergence, the anthers later became completely purple after exposure to sunlight.
Table 1. Data for anther color obtained from crosses and selfs of BSSS-101
line in 1992, 1993, and 1994.
|Year||Generation||Purple anther (no. plants)||Green anther (no. plants)||Total||Ratio|
|1993||Parent (purple in 1992)||73||0||73||---|
|Parent (green in 1992)||0||74||74||---|
|F1 (purple x green cross in 1992)||53||17||70||3:1|
|F2 (self of cross in 1992-93)||157||52||209||3:1|
|1994||Parent (purple in 1993)||48||0||48||---|
|Parent (green in 1993)||0||30||30||---|
|F1 (purple x green cross in 1993)||15||5||20||3:1|
|F2 (self of cross in 1993)||287||93||89||3:1|
|F3 (purple anther F2 self)||160||20||80||8:1|
|F3 (green anther F2 self)||0||96||96||---|
Table 2. Data obtained for anther color of backcrosses of BSSS-101 line
|Crossa||Purple anther (no. plants)||Green anther (no. plants)||Total||Ratio|
|P x P||93||0||93||---|
|P x G||54||50||104||1:1|
|G x G||0||83||83||---|
Anthocyanin pigment is synthesized in the aleurone layer of the maize endosperm, in the embryo, and in many vegetative plant organs, including leaf, stem, anthers, glumes of the cob, tassel, and coleoptiles (Coe et al., Corn and Corn Improvement pp. 81-258, ASA, 1988). Genes that affected different plant tissues were determined and given gene designation. The a1 allele causes colorless aleurone, green or brown plant, and brown pericarp with p1-RP. The a2 allele is similar to al, but a2 gene has red pericarp with p1-RP. The a3 allele is a recessive intensifier of expression of R1 and B1 in plant tissues. Some genes affect aleurone and embryo color; beta determines aleurone and plant color and red pericarp; bz1 modifies purple aleurone and plant color to either pale or reddish brown, and anther color is yellow-fluorescent; bz2 is like bz1, but has anthers that are not fluorescent; the C1 gene determines colored aleurone, c1 colorless, C1-I dominant colorless, c1-p pigment inducible by light; the c2 gene has colorless aleurone, reduced plant color, and reduced chalcone synthase, and c2- Idf is a dominant inhibitor; the p1 gene confers red pigment in cob and pericarp; sm1, salmon silk color with P1-RR, and brown with P1-ww; and the r1 gene regulates the anthocyanin pathway, dominant R1 (S element) confers function in aleurone; dominant represented by R1-r or r1-r (P element) confers function in anthers, leaf tip, and brace roots (Coe et al. ibid; Coe, MNL 68:157-184, 1994).
In this study, the F1 generation had a 3:1 ratio for purple and green anthers. Anther color could be due to one pair of allelic genes and a modifier gene. The allele that controls purple anthers is completely dominant to the allele that controls green anthers. The modifier gene plays a role in the heterozygous condition only, based on the data of the backcrosses and on effect of anthers under sunlight.
The purple anther color genotypes may be of three kinds; c1-n, c1-p, and r-r, according to phenotype of plants, in which it had purple anthers, yellow pollen, light red silks, colorless aleurone, and red cob. The green anther genotypes can be just one kind, r-g, according to effects on colorless aleurone, red cobs, yellow pollen, and green silks of plant (Coe et al., ibid). The gene controlling anther color could be at the R locus or in the R region. The four basic types, R-r, R-g, r-r, r-g, designated by Emerson (Cornell Univ. Agric. Exp. Stn. Mem. 39. 1921), are symbolized according to effect on aleurone color (R vs. r) and on anther color (r, red vs. g, green). Hence, we conclude that the purple anther genotypes could be r-r.
The purple anthers became darker after exposure to sunlight, based on the blotched purple anthers that emerged from the stamens. A modifier gene of anther pigment may be pl-Bh, which leads to variegated pigment in virtually all tissues of the plant, including the kernel, an organ not pigmented by other pl alleles (Cocciolone and Cone, Genet. 135:575-588, 1993). The color at the base of the stem and silks of plants could be a linkage effect with anther color in the BSSS-101 line.
One pair of alleles should have the same anther color in the F1 generation of the cross of homozygous plants. The F1 generation, however, had a 3:1 ratio for plants with purple and green anthers. Anther color did not segregate when the purple anther parent was selfed. This suggested that some traits related to anthocyanin pigment were not homozygous or were partially homozygous in some plants and that there was a modifier gene that had an interaction in the case of heterozygotes. Because of segregation within the F1 generation, larger population sizes will be needed.
Based on these ambiguous results, we will increase the population size of the F1 and the F2 generations and control the environment in the crossing and selfing of plants. The genotypes of each generation will be tested with appropriate genetic tester stocks and by using isolation to determine which genes controlled the anther color of BSSS-101 plants.
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