Effects of foliar application of boron and calcium on perfect flower rate and fruit setting rate in olive

Abstract:【Objective】Boron and calcium are the essential microelements in the reproductive stage of ol-ive. Both of them may affect the development of flower primordium, pollen germination. Therefore the foli-ar fertilization of boron and calcium plays crucial role on flowering and fruit setting of olive. In this studywe examined the effect of foliage fertilization of boron and calcium with varied concentrations and the re-ciprocal action between them on perfect flower and fruit setting of olive. In addition, how pollen germina-tion influence fruit setting was also studied.【Methods】Foliar fertilization of boron (H₃BO₃) and calcium[Ca (HCO₃) ₂] with different concentrations was applied to olive branches through spraying during the wholeperiod of anthesis. A utterly orthogonal test was designed between H₃BO₃ (5 concentration levels of 0.20%, 0.15%, 0.10%, 0.05%, 0.00%) and Ca (HCO₃) ₂ (calculated by Ca O, 5 concentration levels of 1.50%, 1.00%, 0.50%, 0.25%, 0.00%) in three olive cultivars (‘EZ-8', ‘Leccino', ‘CG-32') which with thesame anthesis period of time in Longnan city of Gansu province. All trees chosen in the same olive or-chard have similar cultivation conditions (15 years old, 3 trees per cultivar) . Twenty five standard branch-es were selected randomly in middle to upper part of each tree without interplay among them. Foliar fertil-ization were carried out separately in pre-anthesis (3^th May) , anthesis (9thMay) and post-anthesis (21^th May) in 2013. Each branch is around 20 cm of length and 0.5-1.5 cm of diameter on which has about 1000 flowers growing on over 10 inflorescences. The microscopic observation-medium method was used tostudy pollen germination of olive (pollen germination rate and length of pollen tube) under different con-centrations of boron and calcium. A test of medium is agar (0.5%) + sucrose (10%) + H₃BO₃ (0, 25, 50, 75 or 100 mg·L^-1) , B test of medium is agar (0.5%) + sucrose (10%) + H₃BO₃ (50 mg·L^-1) + Ca (HCO₃) ₂ (0, 100, 200, 300 or 400 mg·L^-1) . The pollen germination rate and length after cultivating for 4 h, 24 h, 48 hunder 25 ℃ and 3 000 lx was observed.【Results】Foliar fertilization of boron-calcium had no significantinteractive influence on perfect flower rate and fruit setting rate in different olive cultivars. The possiblereason for is high calcium or calcium-boron could significantly inhibit pollen germination of olive. Themedium with boric acid of 50 to 75 mg·L^-1significantly increased olive pollen germination, while highercalcium and calcium-boron interaction inhibit pollen germination. The antagonism between boron and cal-cium might be negative to pollen germination, thus foliar fertilization of higher calcium (>0.25%) hadsomewhat negative effect on flower fertilization and fruit setting of olive. The perfect flower rate of‘EZ-8'and‘CG-32'increased significantly with the increase of boron concentration (calculate to H₃BO₃) fromnone to 0.10%, after that it decreased with the increasing of boron concentrations. Perfect flower rate of0.10% level was increased by 8.9% (‘EZ-8') and 11.5% (‘CG-32') higher than that of control. The fruitsetting rate of‘CG-32'was significantly higher than CK by 154.2% at the boron concentration of 0.05%.The fruit setting rate of‘EZ-8'and‘CG-32'remained significantly higher levels on control and 0.25%levels than that of higher calcium, while high calcium displayed significant inhibiting effect on fruit set-ting rate. But‘Leccino'response less sensitive to Ca levels.【Conclusion】Different cultivars had differentresponds to foliar fertilization of boron and calcium. The suitable concentrations of boron showed benefitto blossom and fruiting of olive. B at levels of 0.50% to 1.00% enhanced perfect flower rate, fruit settingrate as well as pollen germination rate, whereas B-Ca or only Ca shower negative effects on flowering, fruit-setting and pollen germination. Higher concentrations of boron and calcium were actually significantnegative to flowering and fruit setting. So, in the period of anthesis application of exogenous calcium andhigh concentration of boron should be avoided. Our results have some coincident conclusions with a fewanalogous studies, whereas the best spraying concentration and boron-calcium effects of this studyshowed some different with others, some reasons might be related to different sensitivities of cultivars onboron and calcium, inner boron-calcium contents of the trees before treated, surrounding conditions, therate of boron-calcium ions absorbed and transferred to inflorescence. More mechanism studies on the in-teraction of boron and calcium for flowering-fruit setting need to be carried out in the future, especiallysome reasons why high calcium is possible to inhibit fruit setting of olive.