Micronutrients Improve Growth and Development of HLB-Affected Citrus Trees in Florida

Abstract

Enhanced nutritional programs (ENPs) have improved citrus trees’ growth and development in the era of Huanglongbing (HLB). Studies conducted with variable rates of manganese (Mn) and Iron (Fe) on young HLB-affected citrus trees showed that applying double the standard recommendation increased growth and biomass accumulation. Since HLB is believed to cause deficiency symptoms of micronutrients in citrus trees, it is critical to ensure their optimal levels in the leaves. This could be achieved by soil application of either a Mn rate of 8.9 to 11.5 kg ha−1 as MnSO4 (31%) for young HLB-affected ‘Valencia’ (Citrus sinensis (L.) Osbeck) citrus trees or an Fe rate of 9.6 to 11.8 kg ha−1 as Ferrous sulfate heptahydrate (20%) for ‘Bingo’ (Citrus reticulata, Blanco) citrus trees. Maintaining optimal levels of these micronutrients may enable citrus trees to carry out photosynthetic activities to ensure growth and development. It may also help the tree in the regulation of various physiological processes as part of the antioxidant enzyme Mn-superoxidase dismutase (SOD). Micronutrient manipulation through variable rates of fertilizer application to influence nutrient availability is an important mitigating factor for HLB-affected citrus trees and an integral component of citrus production in Florida.

Nutritional Performance of Five Citrus Rootstocks under Different Fe Levels

“…In a recent review by Alfaro et al [ 17 ], it was concluded that citrus rootstocks influence the quality of citrus fruits; however, few studies have focused on the assimilation of nutrients by rootstocks or on the corresponding translocation of nutrients through the rootstock/cultivar union. More recently, the particular importance of Fe in citrus was demonstrated, since the application of Fe(II) could restore the growth of trees affected by citrus greening or Huanglongbing (HLB), one of the most serious citrus diseases in the world [ 18 ].…”