The relation between compositional nutrient diagnosis indices and susceptibility of Valencia orange to citrus decline

Abstract

The citrus decline is a major threat to citrus production in the southern region of Iran. This study aimed to determine the relationship between the leaf nutrient indices and the citrus decline severity index in Valencia orange (Citrus sinensis L. Osbeck) orchards. The multivariate compositional nutrient diagnosis (CND) was considered to evaluate the relation between nutrient indices and susceptibility of 235 commercial Valencia orange to citrus decline severity index. The CND reference norms for d = 11 leaf nutrients in a low-citrus decline severity subpopulation of ‘Valencia’ orange was determined as V*N = 2.967 ± 0.127, V*P = 0.288 ± 0.156, V*K = 2.795 ± 0.125, V*Ca = 2.600 ± 0.269, V*Mg = 1.331 ± 0.095, V*S = 0.930 ± 0.226, V*Fe = −1.459 ± 0.292, V*Mn = −3.695 ± 0.285, V*Zn = −4.035 ± 0.249, V*Cu = −5.111 ± 0.220, V*B = −3.219 ± 0.177, and V*Rd = 6.609 ± 0.116. These norms were used to determine the nutrient indices in the high-citrus decline severity subpopulation of ‘Valencia’ orange orchards. According to the principal component analysis and nutrient indices, the deficiency of leaf Ca, B, S, and Mg concentration and excess of P, N, Mn, K, and Cu had a significant correlation with the increment of citrus decline severity index. The balanced nutrition management based on these CND norms could reduce the severity of the citrus decline in Valencia orange orchards.