Breeding and genetics of dry down and test weight in early maturing elite by elite maize hybrids

Field dry down after physiological maturity and test weight are important features for maize (Zea mays L.) hybrids. The objectives of this research are to better understand the genetic basis controlling the expression of both traits, and to identify elite inbred lines and hybrids with high test weight and fast field dry down. Three North Carolina II mating designs made of elite North Dakota State University (NDSU) and industry lines were used for F1 production. Experiments evaluating hybrids were arranged in 12 x 12 partially balanced lattice designs across four environments in 2007 and 2008. Ear moisture data were collected at four 7-day intervals with an electronic moisture meter BLD5604 starting 45 days after pollination. The area under the dry down curve (AUDDC) was proposed as a new method to evaluate dry down. AUDDC was calculated based on four rating dates to represent dry down rate. Results suggested that AUDDC can be a good index for fast dry down selection and using the meter BLD5604 can reliably assess this trait. For the sample studied, low average dominance levels were observed for dry down and test weight (0.11 and 0.55, respectively). General combining ability (GCA) variances were significant for these two traits but not for specific combining ability (SCA) variances, indicating additive genetic effects are more prevalent than dominant effects. Both narrow and broad sense heritability estimates for field dry down and test weight were relatively high (h 2=0.76 for both traits; H=0.84 and 0.75, respectively), indicating selection can be efficiently done with both traits. Based on means of NC II groups and heritability index selection, inbred lines which have potential for hybrid development were identified, as well as hybrids which were superior or equivalent to commercial checks used in this study. This study not only provided genetic information of field dry down and test weight to serve in a breeding program, but also identified superior inbred lines and hybrids for future germplasm improvement and/or hybrid development. The AUDDC method simplified the phenotyping of dry down and certain combinations can be used for molecular studies as a complement to classical quantitative genetics.