The objective of the present study was to establish the effect of genome zones marked by mutant and morphological loci on grain yield. Two F2 populations were developed as source material for this investigation by self-pollinating the F1 hybrids Ku123 x 2-9m and UIT757 x 2-9m. The multimarked line 2-9m carries the following mutant loci (chromosomes and co-ordinates of loci are indicated in brackets): ws3 (2-0), lg1 (2-11), gl2 (2-30), y1 (6-17), sh1 (9-29), wx1 (9-56). The lines Ku123 and UIT757 have a red cob, 2-9m has a white cob. We suppose that this trait is conditioned by the gene P1 (1-26). The parental forms within each pair are divergent in three non-located factors controlling the anthocyanin contents (dominant trait) in different parts of plant: factor 1 - in aleurone, factor 2 - in anthers, factor 3 - in seedlings. The line 2-9m carries the dominant allele of factor 1 and the recessive alleles of factors 2 and 3. These factors are linked to each other; factors 1 and 2 are especially tightly linked in repulsion. Their classification is difficult in some cases, and we can't exclude the possibility that these factors correspond to the gene R1 (10-64).

According to chi-square test the F2 segregation of all the markers does not differ from the monogenic 3:1 and 1:2:1 ratios at P<0.01. The F2 plants were selfed and supplementary pollinated to provide ears with normal grain yield. The homozygous plants retain their genotype in F3, and the heterozygotes segregate. So, we can identify the F2 plant genotype and separate the dominant homozygotes from the heterozygotes for most of the loci. This was carried out for all the markers except P1 and factor 2. The F2 segregation for y1, factor 1, and factor 3 is represented by three genotypic classes: the dominant homozygotes (+/+), the heterozygotes (+/-) and the recessive homozygotes (-/-); and for gl2, lg1, ws3, sh1, wx1 by two: +/+ and +/- (the recessive homozygotes -/- were excluded from further analysis because they may decrease the grain yield of the plants). The F2 segregation for P1 and factor 2 was determined by the phenotype in two classes: the dominant homozygotes and the heterozygotes (+/ ) and the recessive homozygotes (-/-). In each of the investigated classes the grain yield was studied for the following parameters: mean and variance.

In both of the F2 hybrids (Ku123 x 2-9m and UIT757 x 2-9m) statistically significant differences (P<0.05) were observed for the wx1 marker (Table 1). The grain yield of the heterozygous plants (+/-) was higher by 15% than that of the homozygotes (+/+). Such a phenomenon may be related to the formation of the compensation gene complex (CGC), extinguishing destructive effects of semilethals due to breeding for viability (Strunnikov, J. Com. Biol. 35: 666-677, 1974). When the selected CGC line is crossed with unselected lines, the resulting hybrids have one CGC dose with additive effects and one dose of recessive semilethals without depression action in the heterozygote. Such gene combination appears to increase the heterosis effect. Since the multimarked line 2-9m carries some mutations, the CGC foundation may be conditioned by minimizing the negative mutation action during the breeding and reproduction of this line. Therefore the results suggest that in the line 2-9m the chromosome 9 segment marked by the wx1 locus affects the grain yield due to CGC (or its component) factor.

This chromosome 9 segment is also marked by the sh1 locus. According to Table 1 the difference of the grain yield in relation to the sh1 locus had the same sign as that of the wx1 locus, but wasn't as great or as statistically significant. Probably the grain yield factor is linked more tightly to the wx1 than the sh1 locus.

In the F2 hybrid UIT757 x 2-9m (Table 1) statistically significant differences in grain yield were observed for factor 2 between the classes +/ and -/- (P<0.01), and for factor 3 between classes +/+ and -/- (P<0.001); and, +/- and -/- (P<0.05). The highest grain yield was found for factor 2 in the class +/ and for factor 3 in the class +/+. Since the line UIT757 has the dominant genotype +/+ for both factors, the grain yield factors appear to be located in the line UIT757 in the chromosome zones marked by factors 1 and 2. As these factors are linked, probably there is only one high yield factor in the marked zones.

Table 1. The effect of marked genome zones on grain yield (gm per plant).
 

Marker Alleles		n	mean	error	variance	n	mean	error	variance
ws3	+/-	100	140.0?	4.4	1892	-	-	-	-
	+/+	53	153.8?	6.4	2157	-	-	-	-
lg1	+/-	101	144.9?	4.4	1938	98	138.9?	4.8	2237
	+/+	52	144.6?	6.5	2204	30	137.8?	8.9	2391
gl2	+/-	110	143.7?	4.4	2168	86	142.0?	5.0	2107
	+/+	43	147.5?	6.2	1669	42	131.9?	7.7	2550
y1	-/-	36	152.8?	8.1	2344	31	144.5?	6.9	1489
	+/-	89	146.4?	4.6	1867	64	140.3?	6.5	2735*
	+/+	31	133.4?	7.8	1867	33	130.0?	7.9	2061
sh1	+/-	99	147.7?	4.6	2095	80	141.4?	5.5	2440
	+/+	57	141.2?	5.7	1832	48	134.2?	8.4	1962
wx1	+/-	98	151.9?	4.6	2083	74	147.2*	5.8	2470
	+/+	58	134.2?	5.4	1679	54	121.1?	5.7	1772
P1	-/-	50	143.1?	6.9	2353	35	142.9?	7.4	1936
	+/	106	146.3?	4.2	1843	93	137.1?	5.1	2391
factor 1	-/-	35	139.7?	7.6	2016	33	140.2?	7.9	2070
	+/1	86	146.0?	4.7	1860	65	143.9?	6.1	2430
	+/+	35	149.2?	8.3	2382	30	125.7?	8.1	1989
factor 2	-/-	41	149.1?	7.7	2425	23	119.1?	7.2	1204
	+/	112	145.1?	4.1	1837	105	143.0**	4.8	2401
factor 3	-/-	-	-	-	-	22	119.6?	8.4	1544
	+/-	-	-	-	-	82	139.7*?	5.6	2601*
	+/+	-	-	-	-	24	152.8***	7.5	1347
Total		156	145.3	3.6	1988	128	138.7?	4.2	2256

*, **, *** The differences from the minimum value in the group are significant at P<0.05, 0.01, 0.001, respectively.

In the same F2 hybrid (Table 1) for the locus y1, F-test for factors 2 and 3 has shown significant differences (P<0.05) for grain yield variances between the classes. The highest variances were found in the classes +/- for factor 2 in the class +/.

The results suggest that the marked genome zones affect the grain yield and its variance. Future research is needed to ascertain the nature of the effects observed. 

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