PROHEXADIONE-CALCIUM AFFECTS SHOOT GROWTH AND YIELD OF LEMON, ORANGE AND AVOCADO DIFFERENTLY

摘要

Lemon (Citrus limon L.) and navel orange (C. sinensis L.) trees were pruned in May and prohexadione-calcium (P-Ca) was applied to the canopy 24 h later. Prohexadione-calcium (250 mg L"1) delayed lemon shoot regrowth by ~2 weeks, but had no effect on the final amount of regrowth or on the 2-year average number of fruit per tree. P-Ca (500 mg L"1) had no effect on lemon shoot regrowth but reduced the 2-year average number of large fruit (> 6.1 cm transverse diameter) per tree, reducing 2-year average total fruit number per tree relative to untreated control trees (P < 0.05). P-Ca (250 and 500 mg L~(-1)) had no significant effect on navel orange shoot regrowth, but P-Ca (500 mg L"1) consistently stimulated navel orange shoot regrowth during the 2 yearsof research. Both P-Ca concentrations significantly reduced the 2-year average number of small fruit per tree (< 68.9 mm transverse diameter) to significantly reduce 2-year average total number of fruit per tree relative to untreated control trees. Three foliar applications of P-Ca (250 mg L"1) to 'Hass' avocado {Persea americana Mill.) trees during bloom (March, April, May) reduced vegetative shoot length in April and May compared to the untreated control when averaged across the 2 years of the study(P < 0.05). P-Ca (125 mg L~(-1)) applied in March and April increased the 2-year average number of large fruit (> 270 g per fruit) per tree compared to untreated control trees (P < 0.09). The varied responses to P-Ca among lemon, orange and avocado are of physiological interest.