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Dep. of Agronomy, College of Agricultural and Life Sciences, Univ. of Wisconsin–Madison, Madison, WI 53706. Contribution from the Wisconsin Agric. Exp. Sta. Research supported by Hatch funds and the College of Agric. and Life Sciences, Univ. of Wisconsin-Madison
* Corresponding author (wftracy{at}wisc.edu).
In maize (Zea mays L.), some experiments have indicated that early vegetative phase transition is associated with increased resistance to disease, insects, and stalk lodging. The sweet corn population Minn11 was selected over three cycles of divergent recurrent selection for early-phase transition and late-phase transition. Objectives were to determine the effectiveness of divergent recurrent selection and if the divergent selection program was associated with resistance to common rust (Puccinia sorghi). Selection resulted in a significant linear response for last leaf with juvenile wax in both the early and late directions of selection. The third cycle in the late direction (C3L) had two more leaves with juvenile wax than cycle zero (C0). The third cycle in the early direction (C3E) had 1.5 fewer leaves with juvenile wax than C0. To determine the effects of divergent selection for vegetative phase change on response to common rust the populations were inoculated with rust at three developmental times, vegetative stage (v) 5, v10, and v15, and rust damage was rated on leaves 7 through 13 individually, resulting in 21 potential responses for each direction of selection. Among the 21 leaf by developmental stage combinations, there were 9 significant linear trends in the late direction of selection. Most of the linear trends were detected in leaves 7 through 9. Selection for early transition did not affect response to common rust. The amount of leaf area damaged by rust in C3E never differed from the amount in C0.
Abbreviations: C, Cycle • E, early • L, late
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Received for publication August 28, 2007.
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