Effectiveness and concentration of foliar-application of potassium fertilizers on grapevine evaluated by expression of potassium uptake related genes

【Objectives】 Foliar application of potassium(K) fertilizer has been widely adopted in grape production as an effective K supplement measurement. In this study, four types of K compounds were sprayed in three different concentrations at full-blooming stage and berry expansion stage of grapes, to study the responses of the physiological traits and the expression variation of K uptake related genes, and to evaluate the effectiveness of these K fertilizers and concentrations for practical grape production. 【Methods】 Grapevine cv.‘Summer Black’ (hybrid of V. vinifera × V. labrusca) vines were used as experimental material, 0.2%, 0.5% and 0.8% solutions of K2SO4, K2CO3, K2SO4·2MgSO4 and KCl were sprayed at the full-bloom stage and berry expansion stage. The growth rate of leaves and shoots, fruit setting rate, leaf chlorophyll content, single berry weight and total soluble solid content were measured, and the expression variation of the four K uptake related genes, VvHAK13, VvKEA2, VvSIRK and VvSORK were analyzed using real-time quantitative PCR. 【Results】 All the foliar applications of K fertilizers are effective to improve the physiological indexes to different extents, and K2SO4·2MgSO4 shows the best result, following are K2SO4, K2CO3, KCl. The optimum spraying concentrations are 0.2%-0.5% at full blooming stage and 0.5%-0.8% at berry expansion stage. Relatively higher K fertilizer concentration is required at berry expansion stage than at full blooming stage. The four K uptake related genes show different expression responses to the treatments. In general, the expression of VvKEA2, VvSIRK and VvSORK are up-regulated, but that of VvHAK13 down-regulated. In berry expansion stage, the four K uptake related genes show more remarkable responses to spraying concentrations of 0.5%-0.8%, but do the same to spraying concentration of 0.2%-0.5% at full-bloom stage.【Conclusions】 Spraying K fertilizer is effective to up-regulate the expression of K-related genes, which are reflected by the increased physiological indexes. Among the four tested fertilizers, K2SO4·2MgSO4 shows the best result, following are K2SO4, K2CO3 and KCl. Spraying concentration of 0.2%-0.5% is recommended in full-bloom stage and 0.5%-0.8% in the berry expansion stage of grape.