Identity and sources of a sugary enhancer gene significant for sweet corn quality

Tests with sweet corns from two different sources have led to the identification of a gene, new to the maize list, that is of special interest because of a favorable effect on table quality. One source of the gene was two commercial hybrids, Tendertreat E. H. and Kandy Korn E. H. (E. H. = Everlasting Heritage), and the other was the Illinois sweet corn inbred line 677a. The gene is termed sugary enhancer and is tentatively symbolized se.

Outcrosses of the above three sugary (su) stocks were made to three dent corn inbred lines (182E, W22, W23), three popcorn inbred lines (Sg 18, 120, 153) and the flint variety, Canada Longfellow. Selfs and testcrosses to Ill.677a and also light yellow endosperm derivatives of Tendertreat E. H. (TT) and Kandy Korn E. H. (KK) of the resulting hybrids showed that Tendertreat E. H. and Kandy Korn E. H. were heterozygous and Ill. 677a was homozygous for the se gene. An overt phenotypic effect of se in homozygous condition is dilution of yellow pigmentation in the endosperm. The gene when homozygous does not change kernel form, but preliminary estimates indicate that it reduces kernel size about 10%. The diluting action of se on yellow-endosperm varies considerably according to the genetic background. The kernels on segregating ears derived from crosses of TT, KK, or Ill.677a to one or another of the popcorn strains Sg18, I28, and I53 were distributed between two fairly well defined classes, dark and light yellow endosperm. These matings regularly gave the results expected if the light yellow phenotype was homozygous for a recessive gene (se) that assorts independently of the sugary (su) factor. It was noteworthy that the results from se/+ heterozygotes involving the Ill.677a line as a parent in the outcrosses paralleled those from se/+ plants derived from the corresponding matings of the popcorns with TT and KK.

Three examples of the seed distributions observed following Su Se/su se x su se matings are:


The dark and light yellow kernel classes in populations resulting from outcrosses of TT, KK, and Ill.677a to the three dent inbred strains used, and also to Canada Longfellow, rather than to the popcorns, often were weakly defined or overlapping. Thus, the se gene frequently does not give an easily perceived phenotypic effect.

Light yellow endosperm derivatives from selfed TT or KK plants regularly gave only light yellow offspring when crossed with each other and also when outcrossed to the Ill.677a line. These matings provide confirmatory evidence that the Tendertreat E. H. and Kandy Korn E. H. commercial hybrids and the Ill.677a inbred strain carry the se gene in common.

Circumstantial evidence might suggest that the mutant gene here termed sugary enhancer (se) falls in one or another of the already established "soft" endosperm categories, such as floury or opaque. The se gene, for instance, dilutes yellow endosperm pigmentation, like floury-1, floury-2, and the several opaque factors. Furthermore, J. W. Gonzalez, A. M. Rhodes and D. B. Dickinson (Plant Physiol. 58:28-32) report that one of the three stocks in the near ancestry of Ill.677a which, as noted above, is homozygous se, was Bolivia 1035, a Carioco floury corn. The present writer's tests show, however, that Ill.677a, TT, and KK do not carry a gene which, in the absence of sugary, gives either a floury or an opaque phenotype.

TT, KK, and Ill.677a were pollinated with pollen from a floury-1 line. The endosperms of the resulting kernels regularly were translucent, i.e., non-floury. Non-floury and floury seeds were present in equal numbers in the F2 offspring of these hybrids as expected from floury heterozygotes. In contrast, the F2 populations derived from crosses between light yellow derivatives of TT, KK or Ill.677a and the popcorn inbred lines Sg 18, I28, or I53, although segregating for dark and light yellow endosperm, were non-floury throughout. These observations show that TT, KK, and Ill.677a do not carry floury-1, nor any other floury (or opaque) gene that regularly conditions soft endosperm. The evidence does not exclude the possibility, however, that in certain uncommon genetic environments, such as that of Bolivia 1035, for example, the se gene might yield a recognizable floury phenotype. Decisive evidence on the question whether se represents a new locus or is a novel type of allele at an already known locus must await the results of chromosomal site studies. The floury-2 (fl2) locus cannot be the se site because se assorts independently of su, whereas fl2 and su are linked with about 8% recombination between them. Provisional application of the symbol se to the sugary enhancer assumes that the gene resides at a previously unmarked locus.

Gonzalez, et al. (loc. cit.) found that Ill.677a kernels have an exceptionally high sucrose content at 18 days after pollination. The sucrose level was comparable to that in shrunken-2 (Supersweet) at this developmental stage. Unlike the effect of the sh2 gene, however, the high sucrose content was not associated with a large reduction in water soluble polysaccharides (phytoglycogen). We have observed that a high level of sweetness is characteristic of light yellow endosperm derivatives of Tendertreat E. H. and Kandy Korn E. H. also, but not of the dark yellow derivatives, of these se/+ plants at 20-25 days post-pollination. Thus increased sweetness appears to be a characteristic effect of the sugary enhancer gene in sugary kernels.

Hybrids between Ill.677a and light yellow derivatives of TT or KK (which produce only light yellow kernels) were found to be outstanding in table quality. Palatability of these se se homozygotes substantially exceeded that of Tendertreat E. H. and Kandy Korn E. H. (se/+ heterozygotes) in the judgment of several persons. The superiority is associated not only with greater sweetness but also with a certain "crispness" of endosperm texture not characteristic of currently grown sweet corns.

I am indebted to Bruce Ashman, Robert I. Brawn, W. C. Feyerabend, and Stuart Smith for seed used in this study.

R. A. Brink

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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