Salinity Negatively Affects Pollen Tube Growth and Fruit Set in Grapevines and Is Not Mitigated by Silicon

Abstract

Soil salinity impairs viticultural production by reducing vegetative growth and yield parameters such as bud fruitfulness, bunch number per cane, bunch weight, and berry weight. However, the effects of salinity on flower fertility, berry set, and berry development, and the resulting impacts on fruit yield are not well understood. The ability of silicon (Si) to enhance salt tolerance and yield performance has been well documented for some crops. Here, we investigated whether Si could improve grapevine reproductive performance, particularly under saline conditions. One-year-old Shiraz (Vitis vinifera L.) cuttings were grown in controlled conditions and treated with salt (35 mM NaCl) and/or Si (1.5 mM K₂SiO₃) from budburst to veraison. Salt stress reduced fruit set by increasing flower abscission and interrupting normal berry development, which resulted in more live green ovaries and seedless berries per bunch. In vitro and in vivo studies confirmed that poor berry development due to impaired fertilization was correlated with poor pollen tube growth in the style; pollen viability and stigma receptivity were not affected by salinity. Significantly more sodium (Na⁺) and chloride (Cl⁻) were present in leaves and flowers of plants in the salt treatments compared to control plants. Silicon did not prevent the accumulation of Na⁺ and Cl⁻ in reproductive organs or ameliorate the deleterious effects of salinity on reproductive capacity. However, Si-treated vines showed better instantaneous water use efficiency than control vines. This study suggests that fertilization is sensitive to salt accumulation and that salt exposure should be avoided to minimize negative effects of salinity on fruit yield.