Effect of Harvest and Conditioning on Vigor of Shrunken-2 Sweet Corn Seed

Shrunken-2 (sh-2) sweet corn (Zea mays L.) generally exhibits lower and more variable seed vigor than sweet corn based on the sugary (su) gene. We hypothesized that seeds expressing the sh-2 trait may react unfavorably to established harvesting and conditioning practices. This study was performed to test the effect of harvest and conditioning steps on viability and vigor of sh-2 sweet corn seed. Ten commercial sh-2 sweet corn seedlots in 1989 and nine seedlots in 1990 were sampled periodically during production and conditioning. Samples were taken at black layer, immediately prior to harvest, before husking, after husking, before shelling, after shelling, and at the end of the conditioning procedure. Shelling was the only operation that consistently damaged the seed, reducing standard germination from 72 to 60% in 1989 and from 71 to 66% in 1990, when averaged across all seedlots. Shelling reduced the final stand in the field from 24 to 16% in 1989 and 48 to 43% in 1990. Even when 1990 seed was treated with fungicide before planting, shelling still reduced final stand from 73 to 68%. Preharvest factors were more important determinants of vigor than conditioning operations, with final stands (untreated) produced from samples taken just prior to harvest ranging from 9 to 44% (median 27%) in 1989, and 19 to 81% (median 45%) in the 1990 samples. Germination percentages from the accelerated aging test and leachate conductance values were highly correlated with final stand experiment wide in 1989 and 1990 (0.45 < r < 0.58), but were usually not correlated with final stand within seedlot, suggesting that performance of the seed in vigor tests was associated mainly with preharvest factors. Research QuestionPoor and inconsistent stand-producing ability of supersweet corn seed is a significant production constraint for sweet corn growers. Kernel maturation, seed shape, and fragility of these hybrids are different from those of conventional sweet corn, and the seed crop is usually harvested at a kernel moisture content above 50%. This study was performed to identify possible detrimental effects of conventional seed harvest and conditioning procedures. Literature SummaryVery little published material exists about shrunken-2 (sh-2) sweet corn seed production. Results with other endosperm types have shown that pericarp cracking can impair seed performance. Shrunken-2 corn kernels appear to be damaged during both husking and shelling. Study DescriptionNineteen commercial sh-2 seedlots were sampled before, during, and after harvest and conditioning in 1989 and 1990. Fields were located in southwestern Idaho, mostly on silt loam soils, and were irrigated. As needed, samples were brought to the dry seed stage by manual methods thought to minimize seed damage. Samples were tested for germination, seed vigor, and field emergence. Applied QuestionsDo commercial harvest or conditioning operations impair seed quality of sh-2 corn? Only the shelling step measurably reduced seed quality. This was manifested by an average 8% decline in final stand, with both untreated and fungicide treated seed. This damage was detectable in the standard germination and leachate conductivity tests, but not in the accelerated aging test. How important are conditioning operations compared with preharvest factors in determining seedlot quality? Differences in performance between seedlots were much greater than any differences among different stages of the conditioning operation within seedlots. Lots had been harvested at different stages of maturity. Maturity, in addition to inherent genetic differences between hybrids, may have caused the large differences between seedlots. Results suggest that, in the context of standard, careful commercial practices, harvesting and conditioning operations are not as important as preharvest factors as sources of variability in sh-2 sweet corn seed vigor.