MET maize - update

In order to improve the biological yields of modern maize hybrids, a different breeding approach has been attempted using land races with multiple tiller and ear habits (MNL 56:62; 58:85). Problems associated with the plants with multiple tiller and ear (MET) include the size of ear and kernel, ear height and lodging. Genetics of tillering and earing habits were also not clearly defined. Some well-established facts have accumulated concerning MET, and the aim of this article is to present information obtained.

Inheritance of tillers-An inbred line, IK, was developed from the MET population (Choe et al., SABRAO 19(2), 1987) and used as a female parent on six inbreds: A-type, Hi3l, C166, Hi26, A632 and B73. IK produces two to three tillers per plant under ordinary plant density and all the tillers bear a few harvestable ears. The male lines used were assumed to produce no tillers. Table 1 shows the plants segregating for tillers and less than one tiller in F2 populations. Assuming a 3 to 1 ratio for tillers to less than one tiller in F2 generations, all the families studied showed that the gene involved in tillering habits of MET is a single dominant gene. Chi-square values calculated for individual family, pooled and heterogeneity were all nonsignificant. The dominant effect of the gene was also confirmed in the F1 plants. However, it should be emphasized that the penetrance and expressivity for tillering was variable depending upon the genetic background of the parents. The variable penetrance and expressivity for the tiller phenotype may be explained by physiological aspects such as apical dominance of the main stem or heterosis revealed in the hybrid combination and by other genetic systems suppressing or enhancing the expression of the major dominant tiller gene. The variability in the penetrance and expressivity of tiller types didn't seem to be due to any obvious environmental effects.

Table 1. The Chi-square values assuming a 3:1 ratio for tiller to no-tiller plants in F2 generations.
  No. of plants/family    
Family More than two tillers Less than one tiller X2 values
IK x A-type 53 19 0.07 NS
IK x Hi31 24 4 1.71 NS
IK x C166 18 10 1.71 NS
IK x Hi26 17 6 0.01 NS
IK x A632 36 15 0.53 NS
IK x B73 30 9 0.08 NS
Homogeneity     4.12
Pooled 178 63 0.17 NS
Heterogeneity     3.96 NS

Kernel size-The original MET materials and released lines all had small kernel size (less than 15 grams/100 kernels). However, from two different studies we found that the kernel size is not related to the tillering habits of plants. The first evidence was obtained from the study conducted to improve the kernel size or weight by means of simple mass selection. In 1987, we found that kernels selected based on the weight of seed from our base populations, which are maintained by sibbing, did not show any discrepancies in the number of tillers. Namely, the kernels weighing over 25 grams/100 kernels also tillered as much as the kernels weighing less than 15 grams/100 kernels. More apparent evidence was obtained when we planted the F2 segregating populations with large kernels. F2 seeds from MET by U.S. lines were all large in kernel size and showed segregating plants for tillers. At the same time we found that the small kernels of the original MET materials were never recovered in the subsequent generations when they were crossed with large kernels of U.S. dent lines. But the tillering habits were retained regardless of the kernel size.

Ear height-The original MET materials all had high ear height. However, ear height of the F1 crosses between MET and a U.S. line with low ear height was very low (Table 2). The ear height of the MET type would be no problem for future breeding.

Table 2. Comparison of average ear height of IK and F1 plants between IK and a low eared U.S. dent line.
  No. of tillers/plant Plant height* (cm) Ear height* (cm)
IK 2.0 ± 1.1 195 ± 11.5  117 ± 10.5
(lK x LE)F1 1.8 ± 0.8 206 ± 21.4 84 ± 14.4

* Heights of main stem and tillers were measured and averaged.

Table 3. Fresh and dry weight of MET and uniculm hybrids.
  Fresh weight, ton/Ha Dry weight*, ton/Ha
MET hybrid** 120  12
FR29 x FR34*** 80  9

* oven dried, ** measured at the siiking stage and "** measured 10 days after pollination

Biological yields-Fresh and dry weight of F1 hybrids between the MET lines were compared with those of ordinary uniculm hybrids (Table 3). The fresh and dry weights of some of the F1 hybrids with multiple tillers and ears were much higher than those of common uniculm hybrids. However, the fresh weight as well as dry weight were very variable depending upon the time of harvesting.

Peroxidase activity-Quantitative and qualitative measurements of peroxidase activities in various parts of plants showed typical band patterns among the MET types, uniculm inbreds and their hybrids.

B. Choe, H. Lee, Y Seo, B. Kim and J. Park

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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