Alternate Bearing of the Olive (Olea europaea L.) as Related to Endogenous Hormonal Content

Reproductive characteristics as well as changes in endogenous abscisic acid (ABA), indole-3-acetic acid (IAA), gibberellins (GAs) and cytokinins were followed for two consecutive years in the lateral buds of alternate bearing, 15- years-old ‘Nabali Muhasan’ olive trees. Results indicated that free ABA and GAs concentration in the “On”-year (year of high crop load) trees was lower than in the “Off”-year (year of low crop load) trees during October to November. However, in the following year for the same period, free ABA in the “Off” year trees was higher than in the “On” year trees. While free GAs in the “Off” year was almost the same as free GAs in the “On”year during the same period suggesting GAs might not have the inhibitory effect for flower bud induction and initiation. Results of IAA concentration did not show any considerable differences in the “On” and in the “Off” year trees during the period September to November in both seasons. This suggests that IAA might not be involved in flower bud induction and initiation in olive. Cytokinins concentration in the “On’ year trees was significantly higher than in the “Off” year during September to November. However in the following year for the same period, no significant difference in cytokinin concentration was recorded. Suggesting a difficulty in establishing a relationship between flower bud induction and initiation and cytokinin concentration. Results indicate that ‘Nabali Muhasan’ is a prove to alternate bearing as yield in the “On” year trees was almost two folds higher than in the “Off” year trees. Which was accompanied by higher number of fruits per shoot in the two consecutive seasons and an increase in the percent of fruit set. A significant increase in shoot length by 95% was observed in the “Off”-year trees between May and October in the season 99/2000, as compared to 39% increase in the “On”-year trees. Higher average number of perfect flowers, lower average number of staminate flowers per inflorescence and higher average number of inflorescences per shoot was observed in the “On-Year” trees. Concluding that the relationship between endogenous plant hormones, vegetative and reproductive growth in the ‘Nabali Muhasan’ olive is complementary