Maize
Genetics Cooperation Newsletter 80. 2006.
A cross was made of a C1/C1-I y1 derivative of stock 6 times a haploid-inducing stock carrying C1 and Y1. In this cross, the colorless kernels have no anthocyanin expression in the endosperm or embryo, and subtle differences in endosperm color will be recognizable, not only because the female parent contributes no yellowness but because its kernels are smoothly rounded and somewhat flattened. In addition, the embryo is well-exposed and is of generous size in this stock, which allows some evaluation of variations in the size and form of the scutellum portion of the embryo. From six ears, 298 yellow, anthocyaninless kernels were screened for darker vs. lighter yellow vs. the remnant (i.e., neither darker nor lighter) without reference to the embryo. After color selection, all of the kernels were viewed for any altered embryo form, e.g. pointed or distorted scutella. The seeds were planted in a flat and the seedlings were classified for normal vs. the morphology characteristic of haploids (typically haploids are smaller, more stiff-leaved, somewhat streaked, and narrower-leaved). The results, from 283 seedlings that could be clearly classified, suggest that lighter endosperm color and altered embryos may be indicative of haploidy, but that neither criterion is definitive. This applies to the cross between these two specific germplasms, and may or may not be generalizable. Some additional observations are described below.
|
|
Darker yellow |
Darker, embryo form altered |
Lighter yellow |
Remnant, embryo form altered |
Remnant |
|
Normal |
20 |
2 |
14 |
9 |
193 |
|
Putative haploids |
2 |
1 |
10 |
4 |
28 |
The above results contrast with our report in the 2005 MNL that endosperms associated with haploid embryos are darker yellow. That report was based primarily on crosses onto yellow, hybrid materials. Our 2005 note refers to earlier evidence against 4n endosperms being associated with haploid embryos because 4n endosperms are substantially reduced in size. In a related study of crosses of C1 x C1-I, Sarkar and Coe (Genetics 54:453, 1966) found that the rate of loss events for C1-I was the same in endosperms associated with haploid embryos as in ones associated with diploid embryos, i.e., that C1-I dosage was the same.
Some additional experiments suggest that darker yellow endosperm is an inconsistent phenomenon. The haploid-inducing stock was crossed in the summer of 2005 onto about 40 ears each of B73, B55, Oh43, Mo17, and W22 inbred lines. In each cross the endosperm colors were uniform, showing no discriminative differences in yellowness. Crosses onto yellow hybrids also were inconsistent in 2005. Considering that this autumn led to fast drying and maturation, it is possible that seasonal influences on physiological conditions affect endosperm color development in kernels with haploid embryos. It is also the case that genes influencing yellowness differ among strains, including alleles at Y1 and at an array of other loci, and dominant diluting alleles like Wc1.
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