Acceptance of shrunken-2 (sh2) sweet corn (Zea mays L.) hybrids is limited by poor seed quality and seedling emergence, especially in cold soils. The conductivity of the electrolytes leached from imbibing seeds, a rapid measurement of seed quality, is highly correlated with field emergence among sweet corn hybrids. Our objective was to determine if conductivity is related to field emergence in a sh2 population that had undergone selection for improved field emergence for 10 cycles. The response of conductivity to indirect selection was linear, and the linear trend accounted for a large portion of the variation in conductivity (r2 = 0.70). Conductivity ranged from 82.0 dS·m–1 in cycle 0 to 35.3 dS·m–1 in cycle 8, with cycle 10 not differing from cycle 8. High conductivity indicates greater electrolyte leakage. At P ≤ 0.01, conductivity was negatively correlated with all seed performance ratings; field emergence (r = –0.82), plant height (r = –0.81), uniformity (r = –0.92), and relative emergence (r = –0.85).
Dimethyl sulfide (DMS) has been identified as the compound responsible for the characteristic aroma of cooked sweet corn (Zea mays L.) and, along with sugar and water-soluble polysaccharides, is one of the main flavor components in the kernels. Because of the close relationship between DMS and its amino acid precursor S-methylmethionine, the premise was formulated that it might be possible to improve sweet corn aroma and overall eating quality through enhanced production of DMS from increased application of N and S to the crop in the field. Studies were conducted on a Plainfield sand and a Flanagan silt loam to evaluate the effects of N and S fertilization on kernel DMS production in several commercial sh2 hybrids; in the process, the effect of N and S fertilization on various yield and yield component parameters was also determined. Hybrid was the main factor affecting kernel DMS production, although in both soils kernel DMS levels were influenced by significant interactions between hybrid and fertilizer treatments. Kernel DMS content, in response to increasing N fertilization rates, increased by an average of 85% in three of six hybrids in the Plainfield sand and by 60% in two of three hybrids in the Flanagan silt loam. The effect of S fertilization on kernel DMS production was small, with only one hybrid on the sandy soil showing a positive response (38%) to S application, and then in combination with high N rates. Irrespective of N-S fertilization regime, kernel DMS concentrations decreased at both locations by an average of ≈8.5% per day as kernel maturity increased. The results showed that kernel DMS production may be enhanced by N nutrition, independent of N fertilization effects on ear and kernel yields.
A set of 216 polymerase chain reaction-based molecular markers was screened for polymorphisms using two morphologically dissimilar broccoli (Brassica oleracea L. ssp. italica Plenck) lines, ‘VI-158’ and ‘‘Brocolette Neri E. Cespuglio’. Fifty-nine of these simple sequence repeat (SSR) and sequence-related amplified polymorphic (SRAP) primer pairs generated 69 polymorphisms that were used to construct a linkage map of broccoli from a population of 162 F2:3 families derived from the cross between these two lines. Ten linkage groups were generated that spanned a distance of 468 cM with an average interval width of 9.4 cM. The map was used to identify quantitative trait loci (QTL) associated with differences in harvest date maturity and head weight in the population grown in the same location over 2 years. Heritability estimates for days to maturity and head weight were 0.84 and 0.64, respectively. Four QTL for harvest maturity were identified that described 55.6% of the phenotypic variation in the first year with two of these QTL also detected in the second year of the experiment that described 29.2% of the phenotypic variation. Five QTL were identified as associated with head weight in 1999 and accounted for 71.8% of the phenotypic variability. Two of these QTL accounted for 24% of the phenotypic variability in head weight in 2000. To our knowledge, this is the first linkage map of broccoli and the first combined SSR and SRAP map of B. oleracea, which should provide a useful tool for the genetic analysis of traits specific to ssp. italica.
Supersweet corn has problems establishing a stand, a problem that is related to a damaged pericarp that allows leakage from seeds during imbibition. This study compared seed vigor and sugar leakage of sweet corn isolines with different endosperms. Isoline pairs (C68, IaS125, Ia453, Il442a, and Oh43) of sweet corn (Zea mays L. var. rugosa) with two endosperms (sul or sh2) were used. Seeds were germinated at 10, 15, or 20C. Seeds also were planted in Urbana, Ill., where seedling growth was measured. Seeds also were soaked in water for 24 h, and then leachate was analyzed for sugars (anthrone method) and for sucrose, fructose, and glucose (HPLC). No seeds germinated at 10C. At 15 and 20C, more sul seeds germinated than sh2 seeds in most cases. In fields, sul plants were more vigorous than sh2 plants based on emergence, plant height, leaf number, weight, and leaf area. More sugars leaked from sh2 than sul seeds. More sucrose leaked from sh2 than sul seeds in all but two isolines, where none leaked. More fructose leaked from sh2 than sul seeds in all but two isolines, where no differences occurred. More glucose leaked from sh2 than sul seeds only in Oh43.
Inbreds IL451b sugary1 (su1) and IL678a su1 isogenic for the sugary enhancer1 (se1) gene mutation were used to analyze the relationship between se1 gene dosage and endosperm sugar content. Each line was self-pollinated and reciprocal crosses were made between the isolines of each genotype to produce se1 gene dosages of 0, 1, 2, and 3 in the triploid endosperm. Ears were harvested at 15, 18, 21, 24, 27, and 45 days after pollination (DAP). Whole kernels were freeze-dried, ground into powder, and stored at –80°C until subsequent chemical analyses. Sucrose, glucose and fructose were analyzed using high-pressure liquid chromatography (HPLC), the results of which indicated a significant increase in kernel sugar content when the se1 allele is homozygous.
Sucrose content at 21 DAP (typical maturity for harvesting) was observed to increase in the IL451b and IL678a backgrounds from zero to three doses of se1 by 65% and 18% respectively, indicating that this mutation varies in its expression in different genetic backgrounds. Associations between kernel phytoglycogen and starch content and se1 gene dosage are presented. The biochemical lesion associated with the se1 gene product is discussed.
Genotype-by-environment interaction (G×E) is a fundamental concern in plant breeding since it hinders developing genotypes with wide geographical usefulness. Analysis of variance (ANOVA) has been widely used to interpret G×E, but it does not elucidate the nature and causes of the interaction. Stability analysis provides a summary of the response patterns of genotypes to different growing environments. Two classes of phytochemicals with putative health promoting activity are carotenoids and tocopherols that are relatively abundant in broccoli. Growing clinical and epidemiological evidence suggests that vegetables with enhanced levels of these phytochemicals can reduce the risk of cancer, cardiovascular, and eye diseases. The objective of this study is to have better understanding of the genetic, environmental and G×E interaction effects of these phytochemicals in broccoli to determine the feasibility of the genetic enhancement. The ANOVA and Shukla's stability test were applied to a set of data generated by the HPLC analysis of different carotenoid and tocopherol forms for six broccoli accessions grown over three environments. The ANOVA results show a significant G×E for both phytochemicals that ranged from 22.6% of the total phenotypic variation for beta-carotene to 54.0% for delta-tocopherol while the environmental effects were nonsignificant. The genotypic effects ranged from as low as 1% for alpha-tocopherol to 31.5% and 36.0% for beta-carotene and gamma-tocopherol, respectively. Stability analysis illustrated that the most stable genotype for all phytochemicals is Brigadier. The results suggest that feasibility of the genetic enhancement for major carotenoids and tocopherols. A second experiment that includes a larger set of genotypes and environments was conducted to confirm the results of this study.
Extensive variability was found among 24 currently available commercial sh2 hybrids of sweet corn (Zea mays L.) for yield and yield components, and for the chemical components of eating quality. The primary source of variation was explained by genotypic differences, with the environmental effects due to planting locations having a minor influence. Kernel sugar concentrations, however, had a highly significant level of genotype by environment interaction. The extensive genotypic variability among the sh2 hybrids indicated that allelic variation at other loci is profoundly influencing sucrose and total sugar levels in freshly harvested sweet corn. In each case, the kernel chemical components of quality decreased from 20 to 29 days after pollination (DAP). Mean performance of sh2 hybrids for yield, yield components, and kernel quality parameters was in all cases equal or better than the hybrids homozygous for the su1 endosperm mutation. In addition, there were no strong negative relationships between yield and some of the important chemical components of kernel quality, suggesting that it may be feasible to develop superior sh2 hybrids with acceptable yield potential and improved eating quality targeted for the different sweet corn markets.
Ten cycles of simple mass selection for increased field emergence and kernel weight in a population of shrunken2 (sh2) maize affected various kernel and seedling traits. Ten of 29 variables measured were intercorrelated and were included in the first principal factor of a principal component, factor analysis. The eight variables in factor 1 that increased with cycles of selection were: emergence and kernel weight (the two selection criteria) plant height 41 days after planting (a measure of seedling vigor), uniformity of stand, total starch content per kernel total carbohydrate content per kernel, concentration of starch, and starch content per kernel. The two variables in factor 1 that decreased were: conductivity of electrolytes that leached from imbibing seeds and symptomatic infection of kernels by fungi. Factor 1 was a “seed and seedling quality” factor. The other 19 variables formed five principal factors that primarily were “sugar,” “pericarp,” and “asymptomatic fungal infection” factors. These five factors and the variables from which they were formed, were not affected by selection. These results suggest that seed and seedling quality factors can be improved by selection in a sh2 population without affecting sweetness or tenderness. These results also suggest that although selection for increased emergence and kernel weight lowered the incidence of symptomatic infection by fungi, the population was not improved specifically for resistance to Fusarium moniliforme Sheldon.