A procedure is outlined for the separation, into six parameters, of gene effects affecting genetic variation of a quantitative trait. These parameters represent mean effects, additive and dominance gene effects, and the three types of digenic epistatic effects. Estimates of the parameters are obtained using the population means of two inbred lines, their cross, and descendants due to subsequent selfing and crossing. The relative importance of the different gene effects can be evaluated from the magnitude and significance of the estimates.Population means of six inbred lines of corn, and all possible F1, F2, P1F1, and P2F1 crosses among them, were used to obtain estimates of the various gene effects for yield of shelled corn. Mean yield performance of the populations was obtained from four experiments grown at two locations in each of 2 years.With regard to the 15 crosses, the estimates of gene effects indicate that the dominance gene effects were quite important in the inheritance of yield. Estimates of additive gene effects were of low magnitude and many were non-significant. Epistatic gene effects were considered to be more important than additive gene effects in the inheritance of yield in the crosses studied. The additive × additive and additive × dominance gene effects were relatively more important than the dominance × dominance effects.
Five short‐season maize (Zea mays L.) hybrids were grown in 91‐cm and 46‐cm rows at populations of 48,000, 62,000 and 72,000 plants per hectare. The five hybrids responded similarly to changes in population density and distribution. All hybrids increased in grain yield with each increase in population and gave small but significant yield increases to narrowing the row width. Leaf area index (LAI) increased with increasing plant population or decreasing row width. The LAI values, even at the highest population, were much lower than those usually reported as giving maximum grain yield. This suggests that for short‐season hybrids the plant densities presently being used under standard production practices are too low to give maximum grain yields or to detect hybrid by population interactions for yield.
A 2‐yr field experiment was conducted to determine if separation of soybean [Glycine max (L.) Merr.] seeds by size or density might be effective in improving seedling emergence, speed of emergence, or yield. Eighteen soybean seedlots were separated into four size classes using round—hole screens, and into two density classes by floating low density seeds on sucrose solutions. These seeds were planted in a Typic Hapludalf—grey brown podsolic soil type. Seeds of largest size and seeds of lowest density had the lowest percent emergence and speed of emergence, provided these seeds came from seedlots of intermediate vigor. Seed size and density effects were greater when seeds were subjected to greater field stresses of low temperature and wet or crusted soils. The stand differences due to seed size and density persisted until harvest maturity. If compared to the unseparated control, only the smallest seed size was superior in emergence and speed of emergence, and high density seed did not show any advantage. Seed size had no effect on yield in early or late plantings, but high density seeds outyielded low density seeds in the late plantings. High density seeds did not outyield the unseparated seeds. In general, the effects of seed size and seed density on percent emergence, speed of emergence, and yield indicate that the potential for large scale vigor improvement in soybean seedlots through processing or conditioning is limited.
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