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  • Author or Editor: Rosa Ana Malvar x
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Pink stem borer (Sesamia nonagrioides Lef.) is one of the most important insect pests of corn (Zea mays L.) in southern Europe. The objectives of this work were to determine the level of resistance in different sweet corn inbreds and to identify sources of resistance to ear feeding by the pink stem borer. Twenty-eight sweet corn (su1 and su1se1 ) inbreds and four resistant field corn (Su1Se1 ) inbreds were evaluated for ear resistance at different sowing dates, under two methods of artificial infestation. There were significant differences between infestation methods for ears with damaged grain, husks, cobs, and shanks. The inbred×infestation method interaction was significant for general appearance of the ear. The most resistant inbreds were identified by using mean comparisons and principal component analysis of ear damage traits. All inbreds were damaged. Hence, resistance was incomplete and in need of improvement. EP59, H3, I5125, IL767b, and V7726 were the most resistant sweet corn inbreds, which did not differ significantly from A635, the most resistant field corn inbred. General appearance of the ear appears to be a good indicator of pink stem borer resistance and can be used in preliminary evaluation. Variability exists in the resistance of these sweet inbreds to the pink stem borer and the use of field corn inbreds may not be necessary in the improvement of resistance, although further research is needed to determine if the sources differ in the pertinent genes conferring resistance.

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The genes sugary1 (su1) and shrunken2 (sh2) are commonly used to produce sweet and super-sweet corn (Zea mays L.), respectively. In this work we compare corn borer [european corn borer (ECB) (Ostrinia nubilalis Hbn.) and pink stem borer (PSB) (Sesamia nonagrioides Lef.)] susceptibility in seven pairs of su1 and sh2 near-isogenic sweet corn inbreds (101t, C23, C40, C68, Ia453, Ia5125, and P39) and the relationship between corn borer resistance and vegetative phase transition. The seven pairs of near-isogenic inbreds were evaluated under corn borer infestation during 3 years in northwestern Spain. Differences among inbreds were significant for most of the traits, although resistance was partial. Ia5125su1 and C40su1 were the most resistant inbreds. Differences between a few pairs of near-isogenic su1 and sh2 strains were significant for some vegetative phase change and corn borer damage-related traits. Generally su1 strains flowered earlier, had a shorter juvenile phase, fewer PSB, and more ECB larvae than sh2 strains. However su1 and sh2 strains did not differ significantly for most traits related to phase transition and corn borer damage; notably ear damage was not significantly different between su1 and sh2 strains. These results suggest that theoretical and practical results of sweet corn (sugary1) breeding for corn borer resistance could be capitalized for super-sweet corn (shrunken2) breeding.

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Field corn (Zea mays L. var. mays) cultivar heterosis could improve sweet corn (Zea mays L. var. rugosa Bonaf) heterotic patterns. Two Spanish field corn (Su) and two sweet corn (su) heterotic patterns have been reported previously. The objective of this study was to determine which sweet × field corn crosses could be used to improve sweet corn heterotic groups. A diallel among three sweet corn cultivars (`Country Gentleman', `Golden Bantam', and `Stowell's Evergreen') that are representative of the variability among modern sweet corn cultivars, and three field corn synthetic cultivars [`EPS6(S)C3', `EPS7(S)C3', and `EPS10'] representing the heterotic patterns involving Spanish field corn, was evaluated for 2 years at two locations in northwestern Spain. Differences in heterosis effects (h jj') and average heterosis (h) were significant for all traits except grain moisture. Differences for cultivar heterosis (h j) and specific heterosis (s jj') were significant for grain yield, plant height, and kernel row number. `EPS6(S)C3' had lower s jj' for yield in crosses to `Golden Bantam' than to `Stowell's Evergreen', while `EPS7(S)C3' had higher s jj' in crosses to `Golden Bantam' than to `Stowell's Evergreen'. The best crosses to establish enhanced sweet corn heterotic patterns involving Spanish maize would be `Golden Bantam' × `EPS6(S)C3' and `Stowell's Evergreen' × `EPS7(S)C3'. New sugary 1 cultivars would require preliminary cycles of intrapopulational recurrent selection for agronomic performance and flavor prior initiating an interpopulational recurrent selection program to enhance heterosis.

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