Agronomy and Crop Science

The beet leafhopper Circulifer tenellus is an important pest of agricultural crops in the United States, where it transmits beet curly top virus, beet leafhopper-transmitted virescence agent phytoplasma, and Spiroplasma citri to numerous crops, affecting yield and quality. Each of these pathogens have been linked to serious disease outbreaks within Washington State in the past century. To mitigate the risk of disease, growers target the beet leafhopper in their insect pest management programs. Knowledge of pathogen prevalence in beet leafhopper populations could help growers make better management decisions, but timely diagnostics is required. Four new assays were developed for the rapid detection of the beet leafhopper-associated pathogens. These include two assays that detect Beet leafhopper transmitted virescence agent (a PCR and a real-time PCR SYBR green assay), a duplex PCR assay that simultaneously detects beet curly top virus and Spiroplasma citri, and a multiplex real-time PCR assay for the simultaneous detection of all three pathogens. The screening of dilution series generated from plant total nucleic acid extracts with these new assays typically led to detection at levels 10- to 100-fold more sensitive than the conventional PCR assays currently used. These new tools will allow the rapid detection of beet leafhopper-associated pathogens in both plant and insect specimens and will have the potential to be used in diagnostic laboratories seeking to disseminate fast and accurate results to growers for implementation in their insect pest monitoring programs.

AbstractDuring the past two decades, a high mortality of coconut palms was observed in the coastal areas of Equatorial Guinea. Reportedly, the palm population has been reduced by 60%–70%, and coconut production has decreased accordingly. To identify the cause of the mortality, a survey was carried out in April 2021 in various localities of the coconut belt. Molecular analyses carried out on 16S rRNA and secA genes detected phytoplasma presence in the majority of the samples. Sequencing and BLAST search of the 16S rRNA gene sequences showed >99% identity of the detected phytoplasmas to ‘Candidatus Phytoplasma palmicola’. The RFLP analyses of 16S ribosomal gene using Tru1I and TaqI enzymes led to assign these phytoplasmas to subgroup 16SrXXII‐A. In all samples that tested positive, including one from a hybrid coconut palm and two from oil palm the same phytoplasma was identified. The phylogenetic analyses of 16S rRNA and secA genes confirmed respectively 99.98%–100% and 97.94%–100% identity to ‘Ca. P. palmicola’. RFLP analyses using MboII enzyme on the secA gene amplicon differentiated the phytoplasma found in Equatorial Guinea from those present in Ghana and Ivory Coast. The Equatorial Guinean phytoplasma strain resulted to be identical to the strains from Mozambique, confirming the presence of a geographic differentiation among phytoplasma strains in the coastal areas of Western and Central Africa. The identified phytoplasma is different from the ‘Ca. P. palmicola’ strains found in Ghana and Ivory Coast and represents the first identification a 16SrXXII‐A strain in Equatorial Guinea and in Central Africa. Strict monitoring and surveillance procedures for early detection of the pathogen are strongly recommended to reduce its impact and further spread in the country and permit the recovery of coconut plantations.

AbstractRecent outbreaks of ‘Candidatus Phytoplasma solani’ resulted in severe losses in potatoes, vegetable crops and grapevines in certain regions of Austria and constituted a major challenge for seed potato production. Therefore, the effects of various insecticides and insect deterrents on pathogen spread were studied both in laboratory and field experiments from 2018 to 2021. In laboratory transmission experiments, field captured Hyalesthes obsoletus were caged on differently treated Catharanthus roseus for five days. The insecticides lambda-cyhalothrin, deltamethrin, esfenvalerate, acetamiprid and chlorpyriphos showed the most rapid impact on insect survival and fully prevented phytoplasma transmission. The particle film forming products kaolin and diatomaceous earth had some effect. A transfer of the promising laboratory results to potato fields, however, was achieved to a limited extent only. Treatments with pyrethroids and acetamiprid every 8–10 days over the flight period of H. obsoletus roughly halved the number of symptomatic plants and tubers in case of moderately susceptible varieties and moderate infection pressure. In the event of susceptible varieties and high disease pressure, treatment effects were hardy discernible. In practical terms, the experiments indicate that insecticide applications alone are not sufficient to mitigate the disease. Spraying of diatomaceous earth and mineral oil did not affect disease incidence in the field.