A Comparison of Zinc, Phosphorous and Potassium Levels in Leaves and Fruit Pulp of Healthy and Huanglongbing Affected Citrus Cultivars

Mineral nutrition plays an important role in the growth and development of plants and is a significant factor in plant disease defense. In order to determine whether the distribution pattern of mineral nutrients is correlated with the Huanglongbing (HLB) disease status, leaf and pulp samples were collected from fifteen healthy and HLB-affected cultivars of citrus from the Sargodha district of Pakistan. Samples were removed from the field-grown trees and their HLB status determined by quantitative PCR. The levels of zinc (Zn), phosphorous (P), and potassium (K) were measured by inductively-coupled plasma mass spectrometry. Pulp tissues contained lower levels of all three minerals regardless of the infection status. No significant change (t-test) was found in K levels associated with the HLB-affected leaves (p=0.7843) or pulp (p=0.0997). Phosphorous decreased 9% (p=0.0437) in leaves and increased 29% (p=0.0120) in pulp in HLB-affected samples compared to healthy. Zn showed a 31% (p<0.0001) decrease in infected leaves but no change in the pulp tissue (p=0.6728). These results indicate that the partitioning of Zn and P between leaves and fruit was differently affected by the HLB-infection status of the tree. However, no relationship between HLB infection status and K was observed.