ARS | Publication request: Genotype × environment interactions in populations possessing Ga1-s and ga1 alleles for cross incompatibility in maize

Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 21, 2011
Publication Date: June 1, 2012
Citation: Gonzalez, M.D., Pollak, L.M., Goggi, A. 2012. Genotype × environment interactions in populations possessing Ga1-s and ga1 alleles for cross incompatibility in maize. Euphytica. 185(3):377-384.

Interpretive Summary: A genetic system called gametophytic incompatibility is used in popcorn seed to prevent contamination with dent corn pollen. Using the same system in organic corn would benefit organic farmers who now must take full responsibility for contamination of their crop by their neighbor's GMO pollen. Incorporation of the genetic system into organic cultivars is difficult and inefficient because it requires using a pollen-mix test resulting in visual kernel markers that are often inaccurate. Efficiency would be increased if the genetic system was better understood. We determined the dominance relationship of alleles of this gene by using several genotypes. We showed that when pollen containing different alleles compete on silks not fixed for the trait, pollen grains with the recessive allele are completely eliminated from fertilization. Our results confirm that organic cultivars with residual heterozygotes will unlikely be contaminated by foreign GMO pollen Because it is difficult to identify all the heterozygous plants when incorporating the genetic system, it is unlikely that those plants will allow contamination.

Technical Abstract: Pop corn (Zea mays L.) inbred lines with genotype Ga1S/Ga1S are normally cross incompatible to dent corn (Z. mays L.) pollen with genotype ga1/ga1 but the reciprocal cross is fully receptive resulting in full seed set. However, in previous studies the incompatibility reaction of heterozygous plants to ga1/ga1 pollen produced different results. It is suggested that only pollen grains with the Ga1S allele affect fertilization on Ga1S/ga1 silks with complete or almost complete elimination of pollen grains with the ga1 allele when mixed together. The objective of this study was to determine the dominance relationship of alleles Ga1S and ga1 on gametophyte factor 1 gene in maize. The inbred lines W22 (Ga1S/Ga1S) and A632 (ga1/ga1) as well as the F1 the cross A632 x W22 (Ga1S/ga1) were crossed to A632 as the male parent. BC3F1 and BC3F2 populations were created by back crossing the F1 of cross B114 (ga1/ga1) x Mo508W/Mo506W (Ga1S/Ga1S) with B114 three times. Individual progenies with the lowest number of purple seeds after pollination with a mixture of their own pollen and ga1/ga1 pollen that produces purple seeds were classified as heterozygous Ga1S/ga1. The BC3F2 population was grown from yellow seeds of a self-pollinated heterozygous plant. The inbred line W22 was completely sterile to A632 pollen, but the reciprocal cross was normal. The F1 of cross A632 x W22 (Ga1S/ga1) and the inbred line A632 (ga1/ga1) were equally receptive to ga1/ga1 pollen. The BC3F1 population segregated with a phenotypic ratio of 50% receptive: 50% non receptive. The number of purple seeds produced by non-receptive progeny in BC3F1 was significantly lower than the number of purple seeds produced by the receptive progeny. The BC3F2 population resulted in 100 % non-receptive progeny to ga1 pollen. Our results confirm that ga1 behaves as a dominant allele in the absence of competition with Ga1S pollen. However, when gametes with ga1 and Ga1S alleles compete on Ga1S/ga1 silks, pollen grains with the ga1 allele are completely eliminated from fertilization.