5. Variation in combining ability of an inbred maintained at several locations.


Samples of the inbreds Ind. Wf9 and Ill. Hy. were collected from several stations and a few commercial sources. Variations in plant characteristics such as plant height, ear height, stalk, strength and maturity were striking, especially between the Hy lines. In order to test the effect, if any, of the variations on the combining ability of these Hy selections, crosses were made using pollen from a single ear to row planting of the Connecticut inbred C103. Six of the crosses involving lines originally obtained from Illinois (maintained several generations in Connecticut), U.S.D.A., Ohio A.E.S., Pioneer Seed Co., E.W. Doubet, and Illinois A.E.S., and showing greatest phenotypic differences in the Connecticut inbred nursery were grown in 6 x 6 Latin squares in two locations in 1950. The trial of F1 hybrids grown in Connecticut showed significant differences in plant heights, ear heights, per cent moisture at time of harvest, number of plants surviv­ing entire season (initially thinned to uniform stand), and yield corrected to 15.5% moisture content. The second trial, grown in Delaware, yielded similar results. Analysis of covariance eliminating the stand factor from the recorded yields removed significance in the case of the Connecticut test, but the Delaware yields remained significantly different at the 1% level. Variations revealed in these field trials show clearly the mutability of at least one so‑called inbred and indicate strongly that not only are phenotypic characteristics of the inbred altered but also the factors involved with heterosis of F1 hybrid combinations are changed. Practical demands of maintaining named inbreds, as well as plant breeding techniques which utilize the mutability of plant materials are directly affected by these data.