BELGRADE, ZEMUN, YUGOSLAVIA
Maize Research Institute (Zemun Polje)
White dent population from the Yugoslav variety collection carries the Ga gene
--Vancetovic, J, Vidakovic, M, Vidakovic, M, Rosulj, M
Since the discovery of the Ga genes of incompatibility in maize (Demerec, Zeits i Abst u Verer 50:281–291, 1929; Schwartz, Proc. Natl. Acad. Sci. USA 36:719–724, 1950) their importance in protecting specialty types of corn (popcorn, white corn, etc.) from the other predominant types has been recognized. A carrier of the Ga gene can pollinate any other corn, but can be pollinated only by a carrier of the same dominant allele. It should be noted that the allele Ga1-S shows partial dominance (Nelson, Genetics 37:101–124, 1952). Once introduced into a population, the Ga gene, being dominant, spreads very quickly and soon reaches homozygosity. Incorporating Ga genes into the specialty types of corn is a prerequisite for keeping their purity during mass production.
Here we report the discovery of a white dent population carrying the Ga gene in maize.
The accession number 1862 of the Yugoslav variety collection population Beli rani brzak, from Bela Crkva, Banat, was included in a search for the restorer cytoplasm (Vidakovic et al., p. 138 in XVIIth Conference on Maize and Sorghum EUCARPIA, 1996). In 1993, two plants from this population were crossed by hand pollination, as females, with the tester B73 Ms10/ms10. A very small amount of seed was recorded from this cross. The next year, in the isolation field, plants from those two crossed ears were backcrossed with the Ms10/ms10 tester as females. Again, the number of successfully crossed ears was small; for the original ear 5, and for the second 3, instead of about 20, as was usually obtained in the rest of the experiment. A mixture of approximately the same amount of seed from backcrossed ears was made, and in 1995 the test for the presence of the restoring cytoplasm of about 60 plants was planted. On average, 1/8 ms10/ms10 sterile plants was expected from this type of cross.
The test was 100% fertile, indicating restoring cytoplasm is present. But in the further stages of testing (selfing of individual plants and outcrossing them to the ms10/ms10 tester), this hypothesis was rejected.
What was noticed is that the test was very late in maturity (the latest of all), and above all that all ears in the open pollination were white kerneled. How was this possible, since the surrounding maize was mostly yellow kerneled, and both testers, for crossing and backcrossing, were all yellow kerneled?
We supposed that the population might contain one of the Ga genes, and that in the first cross, since only a small amount of seed was obtained, unintended selfing occurred instead of crossing, while in the backcross, as the population is very late, even one badly cut tassel could pollinate the rest of the plants.
To test this hypothesis, in 1996 we took the original seed from the accession, and made pedigree crosses (plant to plant) with yellow dent maize of BSSS and Lancaster origin. Where the population was used as a male, selfing of the particular plants was made. Results of crosses indicated the presence of the Ga gene. When population 1862 was used as a female, only a few seeds were obtained from all of the crosses, while when used as a male, a full seed set was obtained on the BSSS and Lancaster lines.
In 1997, an additional testing was made with the popcorn lines BP1 and BP2, known for carrying the Ga genes, as well as with the stocks provided by the courtesy of Dr. Marty Sachs, Urbana, Illinois, to find which of the Ga genes is in question. Reciprocal crosses were made with four selfed progenies (from 1996) of the original population, a small amount of seed obtained from the cross of the population as a female with yellow dent corn in 1996, yellow dent lines B-84 (BSSS) and MV2-4-2 (Lancaster), and the following US stocks: (Ga1-S Su1)self, (Ga1 su1)self, and (Ga1 M1 Su1)self. Success of the crosses is given in percentages in Table 1.
Based on the results shown in Table 1, it seems that our population contains the gene Ga1-S (Marty Sachs, personal communications).
A sample of this population was sent to Urbana, Illinois in 1996.
It should be noted that the population is not yet homozygous for the Ga gene. In 2000, we made a series of crosses of 12 selfed families from the population, as females, with the red kerneled line as a male. Among 12 families, only one exhibited a seed set of 285 yellow kernels. But, since once a Ga gene enters a population, it spreads to total homozygosity (Nelson, 1952), so probably after a few additional multiplications the gene in this population will be fixed.
From a breeding standpoint, this variety is a potential source for extracting medium-to-late white kerneled inbred lines, protected from the pollen of yellow-kerneled materials.
Table 1. Success of the reciprocal crosses with the investigated population and different sources of Ga genes. The seed set of the appropriate cross is given in %, except for the small quantities, where it is given in kernels (ker.).
|1||1 ker.||80||100||15 ker.||100||100||100|
*Genotypes are: 1-1862/1; 2-1862/2; 3-1862/3; 4-1862/4; 5-B-84; 6-MV2-4-2; 7-1862×Yellow; 8-(Ga1-S Su1)self, 9-(Ga1su1)self, 10-(Ga1M1Su1)self, 11-BP1, 12-BP2
1–4 are selfed progenies from the pop. 1862. 5 and 6 are yellow dent maize lines. 7 is from the few kernels obtained from the cross of pop. 1862 and yellow dent maize. 16 and 17 are the ZP popcorn lines.