Grapefruit Root and Rhizosphere Responses to Varying Planting Densities, Fertilizer Concentrations and Application Methods

Abstract

Huanglongbing (HLB) disease has caused a severe decline in citrus production globally over the past decade. There is a need for improved nutrient regimens to better manage the productivity of HLB-affected trees, as current guidelines are based on healthy trees. The aim of this study was to evaluate the effects of different fertilizer application methods and rates with different planting densities on HLB-affected citrus root and soil health. Plant material consisted of ‘Ray Ruby’ (Citrus × paradisi) grapefruit trees grafted on ‘Kuharske’ citrange (Citrus × sinensis × Citrus trifoliata). The study consisted of 4 foliar fertilizer treatments, which included 0×, 1.5×, 3× and 6× the University of Florida Institute of Food and Agriculture (UF/IFAS) recommended guidelines for B, Mn and Zn. Additionally, 2 ground-applied fertilizer treatments were used, specifically controlled-release fertilizer (CRF1): 12−3−14 + B, Fe, Mn and Zn micronutrients at 1× UF/IFAS recommendation, and (CRF2): 12−3−14 + 2× Mg + 3× B, Fe, Mn and Zn micronutrients, with micronutrients applied as sulfur-coated products. The planting densities implemented were low (300 trees ha−1), medium (440 trees ha−1) and high (975 trees ha−1). The CRF fertilizer resulted in greater soil nutrient concentrations through all of the time sampling points, with significant differences in soil Zn and Mn. Grapefruit treated with ground-applied CRF2 and 3× foliar fertilizers resulted in the greatest bacterial alpha and beta diversity in the rhizosphere. Significantly greater abundances of Rhizobiales and Vicinamibacterales were found in the grapefruit rhizosphere of trees treated with 0× UF/IFAS foliar fertilizer compared to higher doses of foliar fertilizers.

Possible economic losses on the oranges production chain of Peru due to introduction of Huanglongbing (HLB): Simulation of prospective scenarios to 2045

“…It is transmitted by the psyllid insect Diaphorina citri (Aubert, 1987;Garnier & Bové, 1996;Li et al, 2022;Liu et al, 2022;Pan et al, 2023). This psyllid primarily prefers grapefruit trees (Citrus paradisi) (Phuyal et al, 2020;Santiago et al, 2023) and the curry leaf tree (Murraya paniculata) (Hernández-Landa et al, 2018;Kalile et al, 2023;Meng et al, 2022;SENASICA, 2017) as hosts. Psyllid adults are not strong fliers, and their dispersion occurs through wind or human movement (Aidoo et al, 2023;Chen et al, 2022;Kalile et al, 2023).…”