No abstract

In 1977 and 1978, all possible single‐cross hybrids between 12 maize (Zea mays L.) inbreds were evaluated for root‐pulling resistance and yield at plant densities of 38,500 and 55,300 plants per ha. Griffing's diallel analysis was used to determine the nature of genetic effects responsible for production of a large root system as estimated by root‐pulling resistance. Both additive and nonadditive genetic effects contributed significantly (P < 0.01) to the expression of root‐pulling resistance. General combining ability effects interacted significantly (P < 0.01) with environmental changes caused by plant densities and by years, in particular. These interactions may reduce effectiveness of selection for root size based on root‐pulling resistance. The correlation of root‐pulling resistance to grain yield was not significant in either year at either plant density, suggesting that selection for increased root size to gain increased corn rootworm tolerance would not result in decreased grain yield.

No abstract

To study root characteristics, as well as potential tolerance to corn rootworms (Diabrotica spp.) of northern‐adapted genotypes, 44 maize (Zea mays L.) inbreds were evaluated at two locations in both 1974 and 1975 for vertical‐pull resistance at the pretassel and kernel milk stages of plant growth and, for root dry weight and root spread at the later growth stage. The inbreds also were evaluated at one location in 1975 for root‐rot resistance at the kernel dent stage of growth to determine its effect on pull resistance. Highly significant differences existed among inbreds for all characters measured. Although interactions of inbreds with environments were evident, the magnitude of these interactions were relatively small when compared to the differences among inbreds. Highly significant positive rank correlations for inbreds between environments were found for vertical‐pull resistance at both pretassel and milk stages; root dry weight; and nodal root spread. A highly significant simple correlation (r = 0.61) was found between root rot and percent loss in vertical‐pull resistance at the dent stage. The root characteristics measured appear to be relatively stable over environments and effective selection for each should be possible.

Synopsis Plant production reached a maximum at 12,000 to 16,000 plants per acre in eastern South Dakota. Grain production reached a maximum at the same level and fell off drastically if population levels exceeded this optimum. Under conditions of drouth, maximum yields may be associated with very low population levels.