Location: Temperate Tree Fruit and Vegetable Research
Project Number: 2092-22000-021-003-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Jun 1, 2014
End Date: May 31, 2019
Objective:
The overall objective is to determine whether Streptomyces isolates producing both chitinase and antibiotics can provide control of the Zebra Chip (ZC) psyllid vector Bactericera cockerelli and/or the ZC causing bacterium Candidatus Liberibacter solanacearum (Lso) by incubating the insects treated with selected Streptomyces strains and introducing them into growing potato plants.
1. Confirm production of chitinases and one or more antibiotics in 10-20 (nonpathogenic) Streptomyces isolates.
2. Devise methods of delivering Streptomyces to psyllids harboring Lso, introducing Streptomyces-treated psyllids to growing potato plants, and monitor reduction in ZC symptoms in potato in field cage experiments.
3. Assess effect of Streptomyces on survival of Lso-infected potato psyllids.
Approach:
We propose a strategy for controlling both psyllids and the ZC-causing bacteria (Lso) that they vector, based on vulnerability to chitinases and antibiotics produced and secreted by most Streptomyces species. Streptomyces produce chitinase that could degrade the insect exoskeleton and the insect peritrophic membrane required for insect digestion, both of which are made of chitin. Streptomyces species are also major sources of numerous antibiotics that could be bacteriostatic or bacteriocidal to Lso harbored in the insect’s digestive system. Our objective is to determine whether Streptomyces isolates producing both chitinase and antibiotics can provide control for Bactericera and/or Lso, and hence ZC, by incubating the insects treated with selected Streptomyces strains and introducing them into growing potato plants.
Objective 1 (Wanner). Spores of 3 Streptomyces isolates with high and 2 with modest chitinase activity that produce one or more antibiotics will be prepared in MD and shipped to Texas AgriLife in Weslaco, TX (Henne Lab). A different set of 5 Streptomyces isolates will be prepared and shipped to USDA-ARS Wapato in WA (Munyaneza lab) for use in Objectives 2 and 3.
Objective 2 (Munyaneza, Henne). A membrane feeding technique described by Abernathy (1991) will be used to introduce Streptomyces into potato psyllids; the field cage assays will be conducted at USDA-ARS Wapato and at Texas AgriLife Weslaco. Following Streptomyces acquisition, the Lso-infected psyllids will be transferred onto caged healthy potato plants (cultivar Atlantic), 3 psyllids/plant under field conditions will consist of caged plants exposed to psyllids from Lso-infected colonies without exposure to Streptomyces. Caged plants without psyllids will be used as negative controls. Each treatment will be replicated 3 times (cages). Psyllids will be introduced to plants at tuber initiation (ca. 4-5 weeks after sprouting). The plants in the cages will be monitored for aboveground ZC symptoms. At harvest, tubers will be collected from each plant, and ZC incidence and severity will be estimated (Munyaneza et al. 2007a, b). Tubers will also be tested by PCR to confirm Lso infection and titer, and to confirm presence of the Streptomyces strains.
Objective 3 (Munyaneza, Henne). To assess effects of Streptomyces on survival of potato psyllids, Lso-infected psyllids will be allowed to acquire Streptomyces as described above. Following acquisition, 50 psyllids will be individually transferred to potato cuttings/whole leaves inserted into water-filled vials. Fifty additional Lso-infected psyllids not exposed to Streptomyces but fed with 5% sucrose will be kept individually and used as controls. Psyllids will be maintained in the laboratory at 28°C, checked daily for mortality, with survival tabulated at harvest. Potato foliage will be replaced as needed.
Results will demonstrate the potential of Streptomyces as a biocontrol agent against ZC in caged field studies; this may provide a new and potentially sustainable method for mitigating Zebra Chip. If successful, larger scale experiments will be devised for field trials.
