Two cycles of recurrent selection for hydroxamate concentration
Cyclic hydroxamic acids have been implicated in the resistance of maize to several insects and fungi. The objective of this study was to perform two cycles of simple recurrent selection to increase hydroxamate concentration in maize.
Five inbred lines Bx Bx, B49, C131A, Oh45, and W22 were chosen for use from an original source population of 13 inbred lines varying widely in hydroxamate content. These five lines possessed the highest hydroxamate content according to an analysis by the rapid procedure (Long et al., Crop Sci. 14:601, 1974).
The selected lines were grown in the greenhouse for inter-pollination in the spring of 1974. Pollen was collected from each of these inbreds, mixed in approximately equal proportions and placed on silks of the same inbred lines. Seed was then harvested from the intercross population and bulked, and a random sample was planted in the field the following summer. Approximately 300 plants were self-pollinated and the bulked seed was saved.
A portion of this seed was planted in the greenhouse in the Fall of 1975. Two hundred and sixty-three plants 36 to 40 cm tall were analyzed non-destructively for hydroxamate concentration using the rapid procedure, and the fifteen plants having the highest concentration were selected to make up the next intercross population. At maturity these plants were intercrossed by hand in all combinations. Selfed seed was also obtained from a number of these high hydroxamate plants. The procedure thus far constituted one cycle of simple recurrent selection. An additional cycle was performed in the summer and fall of 1976.
Heritability estimates were obtained according to the equation h2 = (Xo - X)/(Xp - X), where Xo = the mean of the selected population and X = the mean of the original source population.
One cycle of recurrent selection increased the original population mean from 0.54 mg to 0.79 mg hydroxamates/g fresh weight, and an additional cycle of recurrent selection increased this mean to 0.93 mg hydroxamates/g fresh weight. Heritability estimates for the two populations were calculated as h2 = 0.66 and h2 = 0.54, respectively.
B. J. Long, G. M. Dunn and D. G. Routley
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