(go to KOMUGI Home) (go to WIS List) (go to NO.86 Contents)

F2 monosomic analysis:
Besides the disomic and monosomic plants, nullisomic plants existed in every F2 populations that derived from F1 monosomic plants. Among them,most of or all of the nullisomic plants died before flowering in some F2 populations. Some nullisomic plants could survive to harvest in some other R) populations. Nullisomic plants deleted a part of chromosomes, and were stunted and nonvigorous, consequently they showed less culms than the disomic plants in the same population. This was due to the nullisomic effect, and did not related to whether the corresponding chromosome carried gene for this character or not. So, nullisomics were excluded after determination by meiosis observation. Thus, the data of nullisomics was not involved in the means and variances of F2 populations in Table 1.

As 4A, 7A and 7B F2 populations surpassed the cheek F2 population in variance, they were grouped into disomic and monosomic subpopulations. The 4A, 7A and 7B F2 disomic subpopulations exhibited statistically similar culm number per plant to the check F2 population. This result means that chromosomes 4A, 7A and 7B could not be the location of gene coding for oligo-culms. Thus, the low culm numbers of 4A, 7A and 7B F2 monosomic subpopulations could be attributed to their hemizygous state of corresponding chromosome. This hemizygous effect was previously observed in Bersee monosomic series (Law et al. 1987).

In all the 21 F2 populations that derived from F1 monosomic plants, only the 2A F2 population showed a considerable and significant low culm number per plant with small variance among plants (Table 1). 2A F2 population was similar to "88F2185" in the mean value of culm number per plant. Therefore, the gene for oligo-culms of "88F2185" is on chromosome 2A.

In 2A F2 population, monosomic plants possessed only one dose of "88F2185"s' chromosome 2A, and the disomic ones possessed two doses of this chromosome. However, statistic analysis showed no correlation between the culm number per plant and the dosage of chromosome 2A. Thus, the gene on chromosome 2A is hemizygous effective and dosage-independent.

Considering that Rht7 gene on chromosome 2A had pleiotropic effect reducing culm number per plant (Worland et al. 1980), and "88F2185" was a semi-dwarfing line, to determine whether the gene for oligo-culms of "88F2185" was Rht7 or not, the final height of plants in 2A F2 population were investigated. The result (Table 2) showed that the height of disomic plants in 2A F2 population was similar to that of the check F2 population, indicating that chromosome 2A of "88F2185" did not carry any dwarfing gene. Thus, the gene on chromosome 2A of "88F2185" for oligo-culms could not be Rht7.

As we known, tiller number is often related to flowering date, earlier flowering genotypes having fewer fertile tillers. The low culm number of 2A F2 population could have been attributed to the presence of day length sensitivity gene, ppd3 which was located on chromosome 2A. However, heading date investigation indicated that 2A F2 disomic plants was similar to the cheek F2 population in the time to ear emergency (Table 2), indicating that "88F2185" is similar to CS in chromosome 2A's effect on heading date. So, the gene for oligo-culms on chromosome 2A of "88F2185" did not belong to Ppd3 gene locus.

At spaced condition, the productive culm number of "88F2185" (4.1 + or - 1.08) was little lower than its total tiller number (3.4 + or - 1.44) plus one (main stem). So, the oligo-culms character of "88F2185" observed at harvest was due to its restricted tillering capacity. Richards had located a recessive gene, tin (tiller inhibitor) on chromosomal arm 1AS, which inhibited tillering in a bread wheat uniculm line (quoted from McIntosh et al. 1993). But in this experiment, the 1A, 1B and 1D F2 populations showed similar culm number to the check F2 population, indicating that group 1 chromosomes did not contribute to the oligo-culms of "88F2185". Whereas, the gene which reduced significantly the tiller number of "88F2185" was on chromosome 2A. Thus it belongs to a new gene locus. So, it is suggested that the gene symbol, Tin2 is designated to denote the dominant gene on chromosome 2A of "88F2185".


Ackowledgments

The first author is very grateful to Prof. Y.L. Zheng for his helpful assistance in the preparation of this manuscript. The help of Miss X.F. He in investigating characters is acknowledged.

<--Back | -->Next

(go to KOMUGI Home) (go to WIS List) (go to NO.86 Contents)