Cocktail Therapy of Fosthiazate and Cupric-Ammoniun Complex for Citrus Huanglongbing

Huanglongbing (HLB) is a destructive citrus bacterial disease caused by Candidatus Liberibacter asiaticus (Ca.Las) and cannot be cured by current pesticides. Root lesion and Tylenchulus semipenetrans juveniles were observed in HLB-affected citrus tree roots. We hypothesize that root treatment with fosthiazate (FOS) and Cupric-Ammonium Complex (CAC) will improve the root growth and inhibit HLB. CAC is a broad spectrum fungicide and can promote growth of crops. FOS kills Tylenchulus semipenetrans and protects roots from damage by harmful bacteria such as Ca.Las. After 90 days of combination treatment of FOS and CAC through root drenches, the citrus grew new roots and its leaves changed their color to green. The inhibition rate of Ca.Las reached more than 90%. During treatment process, the chlorophyll content and the root vitality increased 396 and 151%, respectively, and starch accumulation decreased by 88%. Transmission electron microscopy (TEM) and plant tissue dyeing experiments showed that more irregular swollen starch granules existed in the chloroplast thylakoid system of the HLB-infected leaves. This is due to the blocking of their secretory tissue by starch. TEM and flow cytometry experiments in vitro showed the synergistic effects of FOS and CAC. A transcriptome analysis revealed that the treatment induced the differential expression of the genes which involved 103 metabolic pathways. These results suggested that the cocktail treatment of FOS and CAC may effectively kill various pathogens including Ca.Las on citrus root and thus effectively control HLB.

The citrus microbiome: from structure and function to microbiome engineering and beyond

Individual microbes often have defined relationship with their hosts that include beneficial, commensal, and pathogenic interactions. However, at the community level, plant microbiomes are considered to play a beneficial role in protecting the plant from potential pathogens, acquiring nutrients, and improving growth and production. Citrus is a globally important perennial fruit crop and its production faces many challenges. There have been tremendous interests to explore the structure and function of citrus microbiome and engineer citrus microbiome to address various challenges. In this review, we summarized recent advances in understanding of citrus microbiome, including the composition and function of microbiome in the rhizosphere, rhizoplane, endorhiza, core members and their functional traits. We conducted comparisons of citrus root-associated microbiome with other plant root-associated microbiomes. We also present a perspective on how incoming pathogens interact with the resident microbial community and their outcomes. Despite the promising potential of the citrus microbiome to combat disease, harnessing the citrus microbiome for beneficial applications remains in its infancy. We envision that rapid development of high throughput sequencing and multi-omics technologies, artificial intelligence, consortia of microbes, genome editing technology, and high-throughput culturing present many exciting opportunities to citrus microbiome research and microbial engineering to improve citrus health and productivity.

Genome Resource for the Huanglongbing Causal Agent ‘Candidatus Liberibacter asiaticus’ Strain AHCA17 from Citrus Root Tissue in California, USA

‘Candidatus Liberibacter asiaticus’ is the unculturable causative agent of citrus huanglongbing disease. Here, we report the first citrus root metagenome sequence containing the draft genome of ‘Ca. L. asiaticus’ strain AHCA17, obtained from a pummelo tree in California. The assembled genome was 1.2 Mbp and resulted in 37 contigs (N50 = 158.7 kbp) containing 1,057 predicted open reading frames and 45 RNA-coding genes. This draft genome will provide a valuable resource in further study of ‘Ca. L. asiaticus’ genome diversity and pathogen epidemiology.

Field Diagnosis of Citrus Root Weevil Damage

Root weevils infest citrus groves throughout the citrus growing regions of Florida. Among the eight weevil species that have been identified in Florida citrus groves, five have some potential to cause economic problems for nurserymen and commercial growers. The most important weevil species are Diaprepes root weevil (Diaprepes abbreviatus), southern blue-green citrus root weevil (Pachnaeus litus), and the blue-green citrus root weevil (Pachnaeus opalus). The little leaf notcher (Artipus floridanus) and Fuller rose beetle (Asynonychus godmani) are of less concern, but may be locally important (Fig. 1). This paper will deal with Diaprepes and the blue-green root weevils because they are of major economic importance and frequently occur in citrus groves. This document is HS-1014, one of a series of the Horticultural Sciences Department, UF/IFAS Extension. Original publication date May 2005. HS-1014/HS260: Field Diagnosis of Citrus Root Weevil Damage (ufl.edu)

Diaprepes Root Weevil on Southern Highbush Blueberry in Florida

Citrus root weevil, Diaprepes abbreviatus (Linnaeus) is a destructive pest on citrus trees. It is now becoming a significant pest on blueberry in central Florida, at times causing major damage to blueberry bushes that are more than two years old. This 3-page fact sheet written by Douglas A. Phillips, Oscar E. Liburd, and Larry W. Duncan and published by the UF/IFAS Entomology and Nematology Department will educate blueberry growers on how to monitor, identify, and control citrus root weevil. http://edis.ifas.ufl.edu/in1241

Ability of Citrus Root System to Overcome a Strong Wax Layer

The present work aimed to investigate the effects of mechanical impedance of wax layer (wax discs were installed 0.1 m deep) on root system deepening of citrus seedlings growing in columns with sand and nutrient solution. Two planting systems were evaluated: direct seeding (DS) and planting of seedlings (PS) (plants obtained from seed germination in tubes). Two experiments were carried out in a sequence: first to investigate the wax layer resistance levels (0.14 to 2.7 MPa) on root system penetration and two planting systems (DS and PS). The second evaluated the root and plant development of the two planting systems and two resistance of wax layer to root penetration: control (0.14 MPa) and a strong wax layer (1.06 MPa). The experimental design was randomized blocks, the first experiment in a 2 × 4 factorial scheme with 4 replications and the second a 2 × 2 factorial scheme with 6 replications. Resistance level ≥ 1.52 MPa (60% hard wax and 40% soft wax) completely limited root penetration in the artificial strong layer. The presence of strong wax disc reduced the citrus root system in both planting systems. PS was associated with greater root and shoot vigor, indicating that, in soils with good physical structure and porosity or allowing root deepening beyond the cohesive layer, this planting system is fully adequate, despite the possible benefit of not cutting the pivoting root in direct sowing.