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Defoliation Effects and Seed Yield Components in Pearl Millet x Elephantgrass Hybrids

Dep. of Agronomy, 2183 McCarty Hall, Univ. of Florida, Gainseville, FL 32611

^* Corresponding author (Email: grassbr{at}gnv.ifas.ufl.edu).

Prior to widespread use of seeded hybrids of pearl millet x elephantgrass [Pennisetum glaucum (L.) R. Br. Pennisetum purpureum Schumach.], management to permit mechanical seed harvesting must be developed. Extreme panicle height and high biomass complicate this procedure. Defoliation management is a potential solution. This field study was conducted on a Mulat sand (sandy, siliceous, thermic Arenic Ochraquults) to (i) evaluate the effects of three defoliation treatments on height of phnicles, days to flowering, seed yield components, seed yield, seed germination, and plant survival in four hybrid genotypes and (ii) evaluate the associations among seed yield components under these defoliation treatments through the use of path-coefficient analysis. In the defoliation treatments, plants were cut zero, two, and three times per year at a 30-cm stubble height, both in 1991 and 1992. Linear effects of defoliation accounted for 18 to 90% (1991) or 18 to 96% (1992) of the total variation in the characteristics studied. Genotype x treatment x year interactions were common. Panicle height and plant biomass were drastically reduced with two and three cuts per year. Defoliation delayed flowering. Two cuts per year (mid-June and early August) did not decrease seed yield and seed quality significantly, nor did they affect plant survival Three cuts per year (the last in mid-September) drastically reduced seed production and seed quality. Path-coefficient analyses gave significant defoliation treatment and year effects in all traits. Seeds per panicle was always highly correlated to seed yield per plant, due to high positive direct effects and relatively low indirect effects through the other components. Defoliation altered the correlational structure among seed yield components and the compensatory mechanisms among them, but adequate seed production was maintained with two cuts per year.

Received for publication February 12, 1994.