The pattern of distribution of the allele Bg-3449 in inbred Zpl 2077/54-14
--Vladimir V. Koterniak

Earlier (MNL 67:90-91) Bg-3449, a new allele of the regulatory element Bg, was reported. This allele was found in a selfed generation of the hybrid between the normal line, Zpl 2077/54-14, and opaque line Sp168o2. Inbred Zpl 2077-54-14, unlike Sp168o2, when crossed with plants possessing receptive alleles of o2, gave in selfed generations variegated kernels, i.e. kernels with flint and opaque sectors. This indicates that the somatic instability observed earlier in 3449o2 is contributed by inbred Zpl 2077/54-14. For determining the pattern of distribution of Bg-3449 in Zpl 2077/54-14, 53 plants of this line were crossed (as male parents) with an o2-m(r) no-Bg tester. All tested plants of inbred Zpl 2077/54-14 were obtained from a mixture of 13 selfed ears of the second generation of ear 83-864-1. This generation was obtained from the mixture of 6 selfed ears of the first generation of the same ear. F1 hybrids were selfed (3-5 ears on each cross). On selfed ears normal, variegated and opaque kernels were scored and the ratio of the sum of normal and variegated kernels to opaque ones was calculated. Evaluation of the significance of the difference between observed and theoretical frequencies was determined by the chi-square method.

All 177 selfed ears of testcrosses possessed normal, variegated and opaque kernels, which indicates homozygosity of all analyzed plants for Bg-3449. The presence of an active regulatory element in all plants tested occurs very rarely (Peterson and Salamini, Maydica 31:163-172, 1986; Peterson, MNL 64:8), though Peterson described the homozygous state of En in all 9 plants studied of the line 4Co63.

The major part of selfed ears (progenies of 38 plants out of 53) showed a ratio of normal and variegated to opaque kernels which did not differ significantly from 15:1. This suggests the presence of one regulatory element not linked to the o2 locus. A ratio close to 63:1 that shows the presence of two independently assorting copies of Bg-3449 was observed in the descendants of 21 plants of Zpl 2077/54-14. In progenies of 6 of them were ears with a ratio of 63:1 and ears with a ratio of 15:1.

In the selfed progenies no 3:1 ratio of normal and variegated kernels to opaque was observed. However, the results of kernel segregation on a set of ears suggest partial linkage between the Bg-3449 allele and the o2 locus in some cases. Thus, on 14 selfed ears, the progeny of 12 plants, the observed ratios differed from all theoretical ones studied. One part of these ears (5 ears belonging to descendants of 5 plants of inbred Zpl 2077/54-14) had a ratio of the sum of normal and variegated kernels to opaque that was intermediate between 3:1 and 15:1 (Table 1). The observed ratios of another part of the ears indicated (9 ears belonging to descendants of 8 plants) were intermediate between 15:1 and 63:1. Testcross progenies of the plant 92-5276p305 were from both parts. It is possible to consider the former part of the ears as descendants of plants possessing the regulatory element Bg-3449 partially linked to the o2 locus. The percentage of recombination between them was in the limits of 28.9-40.9 (Table 1). Accordingly, in the latter part it is possible to assume the presence of two copies of Bg-3449 at least one of which is linked either to the o2 locus or to another copy of the regulatory element.

Table 1. Recombination value between Bg-3449 and the o2 locus in ears where the ratio of the sum of normal and variegated kernels to those opaque is intermediate between the theoretical ratios 3:1 and 15:1 and is significantly different from both of them.
 

		Phenotype of kernels
Plant no. of inbred Zpl 2077/54-14	No. of analyzed ears of testcrosses	n*	v	o	Ratio (n+v)/o	% recombination between Bg-3449 and o2 locus**
91-5276p305	92-5895-1	322	65	38	10.2	40.2
91-5280p301	92-5945-1	294	51	33	10.5	40.9
91-5281p297	92-5961-2	352	66	40	10.5	40.9
91-5682p71	92-5971-1	228	35	38	6.9	28.9
91-5682p74	92-5977-2	249	45	31	9.5	38.2

*n, v, o - normal, variegated and opaque kernels, respectively
**calculation was made using equation r2-2r+1-4c=0, where r is recombination fraction and c is the ratio of opaque kernels to the total number of kernels from ear

In some tested plants, it also may be suggested that there is the presence of 3 copies of Bg-3449, at least one of which is linked either to the o2 locus or to another copy. This assumption may be made proceeding from segregation on 13 ears (belonging to descendants of 10 plants) on which the ratio of the sum of normal and variegated kernels to opaque ones did not differ significantly from both 255:1 and from 63:1, and was in the limits of 100.3-166.0. It is necessary to mention that all the ratios which did not differ significantly from 255:1 also did not deviate significantly from 63:1.

It was established that the mutation of Bg-3449 to the inactive state occurs very rarely (unpublished data), likewise the inactivation of the standard Bg allele (Salamini et al., Heredity 49:111-115, 1982). Approximate evaluation showed that the gametic frequency of this event is no more than 9x10-3. Therefore the diversity observed in inbred Zpl 2077/54-14 in the number of copies of Bg-3449, and its linkage strength with the o2 locus, is possibly the consequence of the transposition ability of this allele. 

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