Field-grown Moringa oleifera response to boron fertilization: Yield component, chemical composition of seed-oil and physiology

Abstract

Boron is a trace element that is essential for the normal growth and development of plants. The present study is performed to evaluate the effects of boron fertilization on yield component, chemical composition of seed-oil and physiology of Moringa oleifera. Soil drenching (SD) (TS1, TS2, TS3: 0.5, 0.9 and 1.8 g plant−1) and foliar spray (FS) (TF1, TF2, TF3: 400, 800 and 1000 mg L−1) of boron (B) were performed for field-grown Moringa oleifera in southwest China. The results showed that all SD and FS treatments, to varying degrees, improved the chlorophyll and carotenoid contents, as well as the relative water content and nitrate reductase activity in the leaves. Except for TS3, all of the SD treatments significantly increased canopy diameter, whereas all FS treatments significantly increased the number of fruit settings and branches producing fruit. However, excessive SD with B (over 1.8 g plant−1) showed a negative effect on the vegetative and reproductive growth. All B treatments increased the number of seeds per fruit pod, the weight of seeds and fruit pods; the fruit pod length was also significantly increased. Except for TS3, all of the B treatments markedly improved the yield of fruit pods (from 15.40% to 21.70%), but only TF2 and TF3 treatments resulted in a significant increase in the yield of seeds (13.40% and 18.50%, respectively) compared with the control treatment. All of the B treatments increased crude protein content in seeds of M. oleifera, while only the TF2 and TF3 treatments significantly increased the oleic acid (C18:1) and eicosenoic acid (C20:1) contents and decreased the α-linen acid (C18:3) content of seed oil. These findings indicate that boron at an appropriate concentration could steadily improve the vitality and fertility of pollen and increase in the fruit-setting, but B foliar spraying showed a better effect on the reproductive growth and resulted in significantly higher yields of fruit pods and seeds than soil drenching with B. Our data suggested that the optimum dose of soil drench was 0.9 g plant−1, while the best dosage of foliar spray could be over 1000 mg L−1.