Akademik Veri Yönetim Sistemi
AUSTRALIAN JOURNAL OF CROP SCIENCE, cilt.5, sa.2, ss.132-137, 2011 (SCI-Expanded)
Leaf losses caused by different biotic and abiotic factors may considerably affect the yield and yield components of sunflower. A better understanding of the effects of defoliation on sunflower would improve the ability of farmers and crop insurance adjusters to evaluate the economic impact of leaf losses to sunflower. The objective of this study was to investigate the effects of defoliation applications on hybrid and open pollinated sunflower cultivars grown during the growing seasons of 2000 and 2001. The study assessed two sunflower cultivars (P64A52 and GK-70), three growth stages (R1, R3 and R5) and five defoliation levels (0, 25, 50, 75, and 100%). Significant differences among cultivars were observed for all characters except for days to maturity, with hybrid cultivar having greater sensitivity. Growth stages significantly affected days to maturity, seed filling percentage, the ratio of dehulled/hulled seed weight, and seed yield. When compared to cultivar and growth stages, the effect of defoliation applications was more pronounced. All agronomic characters were adversely influenced by increased levels of defoliation. Hundred percent defoliation reduced oil content by 26.3% and seed yield by 89% compared to the non-defoliated plots. Low levels of defoliation during the early reproductive growth stages (R1 and R3) did not result in a significant reduction in yield. The findings of the study showed that the extent of yield losses was related to the levels of defoliation.