Periodic Reporting for period 3 - TROPICSAFE (Insect-borne prokaryote-associated diseases in tropical and subtropical perennial crops)
Reporting period: 2020-05-01 to 2022-04-30
The project addressed three insect-borne prokaryote-associated diseases of perennial crops (palm, citrus and grapevine) grown in tropical and subtropical areas due to ‘Candidatus Phytoplasma’ species associated with “lethal yellowing” (LY) in palms and “yellows” in grapevine (GY), and ‘Ca. Liberibacter’ species associated with “huanglongbing” (HLB) in citrus. The focus was on Africa (Ghana, South Africa), America (Mexico, Chile, Guadeloupe, Jamaica, Cuba), and Europe (Spain and Italy). Innovative tools and new solutions were provided to manage and reduce the impact of these diseases affecting and threatening these and other tropical and subtropical agricultural relevant crop species with socio-economic benefits in all the situations studied.
Pathogen identification. In Ghana ‘Candidatus Phytoplasma palmicola’strains were identified in coconut palms, in three alternative plant host species and in three putative insect vectors. In Jamaica ‘Ca. P. palmae’ was detected in coconut palms, in two alternative host species and Oecleus mackaspringii was described as new insect species potential vector in infected areas. In Mexico the 16SrIV-A, -B, and –D phytoplasmas were detected in coconut palms and in five alternative plant host species and transmission with adults of H. crudus to palms was achieved. In Cuba 16SrIV-A and other ribosomal groups of phytoplasmas were identified; the 16SrIV group was also detected in citrus species, in Pritchardia pacifica and in two insect species. Phytoplasmas detected in grapevine were: ‘Ca. P. solani’ (Italy, Chile, Spain, South Africa); ‘Ca. P. fraxini’, (Italy, Chile); ‘Ca. P. asteris’ (Italy, Chile, South Africa); “flavescence dorée” (Italy, Spain); ‘Ca. P. pruni’-related (16SrIII-J) (Chile). In South Africa ‘Ca. P. asteris’ was detected in grapevine, Mesembryanthemum crystallinum, and in two putative insect vectors. In Chile eight alternative host plant species and six insect vectors or potential vector for the 16SrIII-J phytoplasma were determined. In Italy samples from 13 plant species and from 11 insect vectors or putative vectors were determined as infected by the phytoplasmas detected also in grapevine. Surveys in citrus confirmed the presence of ‘Candidatus Liberibacter africanus’ in South Africa and ‘Ca. L. asiaticus’ in Guadeloupe and Cuba; these pathogens were not detected in Chile and in Spain. Only the known vectors Diaphorina citri in Cuba, and Guadeloupe and Trioza erytreae in South Africa and in Spain, were identified. Management. In Ghana and Mexico coconut varieties showing promising LY resistance were evaluated, and in Mexico resistant germplasm was transferred as in vitro plants to Cuba and Jamaica. Tamarixia dryi from South Africa was introduced in Spain where it showed good dispersion and parasitism efficacy against T. erytreae. Predictive models to estimate the invasion risk of T. erytreae in Europe demonstrates that the psyllid would probably establish in all the citrus growing regions. In Cuba the elimination of symptomatic trees at a regional scale resulted in the best HLB management strategy, and the efficacy of kaolin against D. citri kept the infestation level low. In Guadeloupe, despite the relatively low abundance of D. citri in some orchards under an integrated pest management program, the HLB levels and mortality of the trees were very high. In South Africa a management plan for ‘Ca. P. asteris’ and its vector Mgenia fuscovaria (showing several peaks in the year) has been developed. In Italy an experimental vineyard obtained with the F1 crossing population between genotypes with different GY susceptibility was infected using insect vectors. Its genotyping showed approximately 20% of the progeny as self-crossed and 188 samples were selected for the promising genetic features. Detection tools. LAMP diagnostic systems were developed for detecting LY phytoplasmas in plants and insects, and a specific quantitative PCR (qPCR) assay resulted able to differentiate among the LY-associated phytoplasma subgroups in Mexico. A ‘Ca. L. africanus’ specific PCR was developed. LAMP and qPCR assays for the specific detection of the South African ‘Ca. P asteris’ strain were developed and applied. “Flavescence dorée” phytoplasma detection was obtained in grapevine and in other plant and insect species following the new ELISA protocol specifically designed and ‘Ca. P. asteris’ presence was detected in infected periwinkles and colonies with an IFAS (immunoflourescence assay) protocol with the antiserum produced from phytoplasma colonies.
Thirteen main results with exploitation potential were identified. The use of biological control agents (entomopathogenic fungi) to reduce lethal yellowing spreading was identified as a potential methodology for pest disease control. The implementation of new fast and on-site pathogen kit detection based in LAMP, qPCR, ELISA and IFAS for both lethal yellowing and grapevine yellows also are exploitable results. A new chemical control strategy, use of alternative biological control agents, new forecasting models to predict vector infestations and a new PCR were obtained for “huanglongbing”. Finally for grapevine yellows a new method to identify disease resistance gene(s) and application thereof, and antimicrobial peptides were tested for their suitability to improve the disease management.
Thirteen main results with exploitation potential were identified. The use of biological control agents (entomopathogenic fungi) to reduce lethal yellowing spreading was identified as a potential methodology for pest disease control. The implementation of new fast and on-site pathogen kit detection based in LAMP, qPCR, ELISA and IFAS for both lethal yellowing and grapevine yellows also are exploitable results. A new chemical control strategy, use of alternative biological control agents, new forecasting models to predict vector infestations and a new PCR were obtained for “huanglongbing”. Finally for grapevine yellows a new method to identify disease resistance gene(s) and application thereof, and antimicrobial peptides were tested for their suitability to improve the disease management.
The obtained results will directly help farmers and research organisations by transferring the innovations to professionals to enable improved performance and sustainability in disease management, will help policy makers’ decisions, increase knowledge about the diseases dynamics and allow reduction of insecticide treatments.
All the information about the project results is available on the website until 2031 in English, Spanish, French and Italian. In there the final handbook of the project can be consulted and downloaded. It is also relevant to visit the project’s YouTube channel, which contains the project video and the recordings of the final conference and training sessions, among others.
The results achieved filled a lot of gaps in both knowledge and technology and contributed to:
• the identification and molecular characterization of pathogen strains, alternative host plant species and insect hosts associated to the selected diseases and crops
• new knowledge regarding epidemiological cycles and forecasting models to predict vector infestation
• find new varieties and cultivars tolerant to the selected diseases
• increase the knowledge about alternative biological and chemical control methodologies
• well-trained end-users in several countries thanks to the dissemination actions
• improve the economic impact on the agro-food chains
• increase the visibility of pest management alternative methodologies
• replicate the overall TROPICSAFE project methodology at international level in similar agronomical situations.
The research should be continued in order to fill gaps still existing for insect vector of lethal yellowing in Africa and all the other information that are evolving with the modification of environment due to the climate change.
All the information about the project results is available on the website until 2031 in English, Spanish, French and Italian. In there the final handbook of the project can be consulted and downloaded. It is also relevant to visit the project’s YouTube channel, which contains the project video and the recordings of the final conference and training sessions, among others.
The results achieved filled a lot of gaps in both knowledge and technology and contributed to:
• the identification and molecular characterization of pathogen strains, alternative host plant species and insect hosts associated to the selected diseases and crops
• new knowledge regarding epidemiological cycles and forecasting models to predict vector infestation
• find new varieties and cultivars tolerant to the selected diseases
• increase the knowledge about alternative biological and chemical control methodologies
• well-trained end-users in several countries thanks to the dissemination actions
• improve the economic impact on the agro-food chains
• increase the visibility of pest management alternative methodologies
• replicate the overall TROPICSAFE project methodology at international level in similar agronomical situations.
The research should be continued in order to fill gaps still existing for insect vector of lethal yellowing in Africa and all the other information that are evolving with the modification of environment due to the climate change.