Increased endosperm hardness of grain in maize (Zea mays L.) is desirable for dry milling, storage, and expert purposes. This study was conducted to evaluate changes in endosperm hardness resulting from four cycles of visual recurrent selection for increased hardness in two dent corn synthetics representative of U.S. Corn Belt germplasm, and to determine associated responses in other agronomic traits. Testcrosses of random S1 lines from each cycle of selection were grown in replicated trials at four locations in each of 2 yr for determination of grain hardness and evaluation of agronomic traits. Evaluation of grain hardness was through measurement of average kernel density and the Stenvert hardness test. Significant increase in endosperm hardness was limited to the first cycle of selection in both synthetics. No significant changes corresponding to altered endosperm hardness were detected for any of five agronomic traits measured in testcross hybrids from S1 lines representing each cycle of selection. Estimated genetic correlation coefficients indicated a negative, nonsignificant trend between grain yield and grain hardness. These results indicate increases in grain hardness can be achieved through selection in dent corn germplasm common to the U.S. Corn Belt. However, continual progress in recurrent selection may require quantification of hardness by measurements such as kernel density and the Stenvert hardness test, rather than simple visual judgment of relative hardness. Genetic correlation coefficients indicate selection progress can be simultaneously made for both grain yield and grain quality.
A natural white grub infestation in a corn/soybean rotation near Boyd, MN, provided the opportunity to evaluate soil insecticide performance. The site, typical of severe P. implicita infestations, was associated with a sandy loam soil near a windbreak of populars. Insecticides were applied at planting on 4 May using planter-mounted Noble granular applicators calibrated to deliver the desired rates at 6.4 km/ha. Treatments were arranged in a randomized complete block design with 4 replications. Plots measured 4 rows × 180 m. Surviving stand was evaluated 27 Jun by counting all live plants; wilting, severely stunted, or “dead heart” plants were excluded. Yield, adjusted to 15.5% moisture, was measured on 23 Oct.
A natural white grub infestation in a corn/soybean rotation near Boyd, MN, provided the opportunity to evaluate soil insecticide performance. The site, typical of severe P. implicita infestations, was associated with a sandy loam soil near a windbreak of poplars. Insecticides were applied at planting on 4 May using planter-mounted Noble granular applicators calibrated to deliver the desired rates at 6.4 km/ha. Treatments were arranged in a randomized complete block design with 6 replications. Plots measured 1 row × 60 m. Surviving stand was evaluated 14 Jun by counting all live plants; wilting, severely stunted, or “dead heart” plants were excluded. Final stand, ear number and yield, adjusted to 15.5% moisture, were measured at harvest on 23 Oct. Because a thrown chain caused insecticide misapplication on some plots, a GLM was used and least-square means were calculated.
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