Exogenous Brassinosteroids Regulate Mango Fruit Set through Inflorescence Development and Pollen Fertility

Abstract

Fruit set reduction is currently an important issue with regard to mango cultivation due to pollen infertility. Brassinosteroids (BRs) reportedly promote plant reproductive development, which is considered to be a strategy for reducing fertilization failures due to infertile pollen. In this study, 24-epibrassinolide (EBR), a natural brassinosteroid, and 7,8-dihydro-8α-20-hydroxyecdysone (DHECD), a brassinosteroid mimic, were applied to mango inflorescence to evaluate the effects of EBR and DHECD on inflorescence bud development and pollen fertility. Both BRs were sprayed at amounts of 0.01 or 0.1 µM when the inflorescence buds had developed to the ‘large bud swell’ stage. The results demonstrated that exogenous DHECD and EBR improved inflorescence bud development and reduced the percentage of malformed inflorescence. Application of the BRs increased the inflorescence length, the total number of flowers per inflorescence, the pollen viability, and the fruit set level. In addition, DHECD enhanced pollen germination in the pistil by elevating the pollen enzyme activities of α-amylase, Ca2+-ATPase, and polymethylesterase. The 0.1 µM DHECD application effectively improved both inflorescence bud development and pollen enzyme activity. A certain concentration of DHECD showed potential similar to EBR. It was concluded that EBR and DHECD can play effective roles in regulating fruit set through pollen fertility and can help with the problem of low fruit set outcomes in mango.