Abstract
Seven defoliation treatments were applied at three leaf growth stages_ It was found that yield response to defoliation increased as the defoliation treatments were applied closer to the critical pollination period. Defoliation at 8 and 10-leaf stages greatly affected the yield and yield components. The greatest reduction was produced by 100% full leaf defoliation for 100-grain weight. ear length, ear diameter and grain yield. Minimum reduction was noted b the application of 25% half leaf defoliation in most of the characters under study.
INTRODUCTION MATERIALS AND METHODS
Defoliation of maize at any stage of de-velopment has generally decreased final grain yield per plant (Allison et of,. 1 975: Cloninger et al., 1974). Defoliation during silking resulted in greater yield reduction with little or no yield reduction following leaf removal at very early or very late growth stage. Johnson (1978) found after defoliating full season and early maize hybrids that defoliation generally reduced aver-age yield regardless of the maturation period. Pinter (1980) reported that reduction in yield was attributable primarily to decrease in length of grain-covered portion of the car followed in order 11'. fewer grain rows and reduced L 00-grain weight. Jones and Simmons (198 I) re-ported defoliation reduced weight per grain. Barnett (1982) reported that defoliation de-creased ear and grain weight. VasiIas and Sief (1985) reported that defoliation reduced grain yield because ofreduced kernel size. car number, and kernels per ear_ The present studies were planned to evaluate the genotypic response of corn single crosses to defoliation and the effects of various degrees of defoliation at different leaf stages for grain yield and other characters.
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The studies reported were conducted in the Department of Plant Breeding and Genetics, University of Agriculture. Faisalabad during 1989. the treatments to study the effect of vari-ous degrees of defoliation were made on two single cross hybrids from four local and exotic inbred lines of lea L. The parental inbred lines, [man 54. JR. GPI) 25 and Wl87R-5 were grown in the field during spring 1989 to obtain two single crosses (Iman-54 x GPD25 and JR N W187R-5). Single crosses were sown during August 1989 follo•-ing randomized complete block design. in a split-split-plot arrangement with single crosses as main plots. growth stages as sub-plots and treatments as sub-sub plots, Each entry con-sisted of two 76cm apart rows of 4.5 meter length with row to row distance of 23cm. Seven defoliation treatments were applied at three growth stages i.e., 1) Control; no leaf removed, 2) 25% full leaf defoliation: every third full leaf blade was removed_ 3) 50% full leaf defoliation: every other full leaf blade was removed. 4) 100% full leaf defoliation; all full leaf blades were removed. 5) 25% hair leaf defoliation: every
