Effect of foliar zinc application on grain zinc content and yield of biofortified wheat

Abstract:

Biofortified wheat cultivars released by the Pakistan Agricultural Research Council since 2018, bred to accumulate more grain zinc than conventional varieties, mark a trend toward addressing the roughly 31% of Pakistani children under five showing zinc deficiency. Yet genetic biofortification alone meets only a fraction of the HarvestPlus 40 mg kg⁻¹ target for grain zinc. This research tested whether foliar zinc sulphate applications could complement the genetic base and close the gap. Field trials at the Faisalabad research farm during rabi 2021-22 and 2022-23 evaluated five ZnSO₄ concentrations (0, 0.2, 0.4, 0.6, 0.8% w/v) applied twice (heading and early milk stages) on three biofortified wheat varieties (WB 02, HPBW 01, HD 3226) in a split-plot design with three replications. Grain zinc content rose from 28.4 mg kg⁻¹ in the no-spray control to 43.2 mg kg⁻¹ at 0.6% ZnSO₄ across pooled varieties. Grain yield showed a smaller but significant response, peaking at 46.9 q ha⁻¹ at 0.4% concentration. WB 02 accumulated the highest grain zinc at every application rate. No phytotoxicity symptoms appeared up to 0.6%, but mild leaf tip burn was noted at 0.8%. The optimum combination was 0.6% ZnSO₄ applied twice on WB 02, producing grain zinc 8% above the HarvestPlus target without yield penalty, at an additional input cost of PKR 3,200 per hectare.