Performing Department
Agricultural and Environmental Sciences
Non Technical Summary
One of the most destructive pathogens impacting diverse vegetable crops is a Phytophthora pathogen that impact roots, stems and fruits. A broad range of vegetable cropsare affected by this pathogen including pepper, tomato, cucumber, eggplant, squash, pumpkins, snap and lima beans. This pathogen survives in the soil for many years and it is therefore very difficult to control. Farmers rely on cultural strategies that are inadequate and effective chemicals cause toxicity hazards to farmworkers and the environment, affecting soil, water, aquatic life, and nontarget organisms including wildlife. Development of pathogen resistance to these fungicides is also a problem and new products are needed. This project will advance the evaluation effective bacteria for plant protection against P. capsici in sweet pepper as an alternative to conventional pesticides.
Animal Health Component
0%
Research Effort Categories
Basic
5%
Applied
85%
Developmental
10%
Goals / Objectives
The objectives of this project are to: (i) evaluate the effect of selected BCA on P. capsici disease severity in greenhouse and field environments, (ii) Compare the efficacy of the selected novel isolates with commercially available biocontrol agents in greenhouse and field environment, (iii) improve the biocontrol efficacy by using value added compost in greenhouse and field environment and, (iv) demonstrate project results on biocontrol technology to growers.
Project Methods
i) BCA inoculum preparation and application: Candidate BCAs, Bacillus subtilis (Prt), B. amyloliquefaciens (PsL) and B. thuringiensis (IMC8) selected for this study had superior performance in suppressing Phytophthora blight/root rot and promoting pepper plant growth in growth chambers and greenhouse experiments. Based on preliminary results, BCA inocula from 24 h-old nutrient broth cultures will be diluted to estimated bacterial concentration of 1 x 108 colony forming units (CFUs) per mL measured using previously standardized optical densitometry corresponding to108 cfu/mL. Candidate BCAs will be grown separately and mixed before inoculation using 1:1 (v/v) equal concentrations and volumes of BCAs. Pepper Seed treatment with BCAs will be by soaking for one hour, in a rotary shaker at 200 RPM to allow seeds to imbibe and become colonized by the BCAs before sowing in miracle grow soil in greenhouse nursery plugs. Based on previous data, individual BCAs are better than a mixture of two BCAs and a mixture of three BCAs was as good as fungicide metalaxyl (Ridomil®; Syngenta, Greensboro, NC. Thus, treatments will consist of three BCAs used individually and in a mixture of the 3 BCAs, and compared to two chemical fungicides (CF) [metalaxyl and a Copper-based fungicide], two commercial biofungicide (BF) and water control (WC) for a total of 9 treatments.ii)Evaluation of the effect of selected BCA on P. capsici disease severity. The BCA-inoculated nursery seedlings will be planted in 'Miracle Grow' soil mix in the greenhouse where the BCA colonized seedlings will be maintained for three weeks after germination before they are transplanted to the field and greenhouse experiments. Seeds of susceptible cultivar 'California Wonder' will be used. Detection of phytophthora inoculum will be used to confirm the presence of P. capsici pathogen in the selected test fields using the modified soil dilution plating assay and/or leaf baiting (French-Monar et al., 2007). Field planting will use standard production practices recommended for pepper (Hansen, 2019) with six replicates of single rows and a one-meter separation between treatments to avoid cross contamination between treatments. Raised beds and polyethylene or organic mulch will be used and irrigation will be provided by drip tape placed about 2.5 cm below the soil surface along the center of the raised beds. Each raised mulched bed will represent a main plot in which treatments will be randomized as sub-plots. To reinforce seed treatments, additional treatment with BCA spray applications will be initiated two weeks after planting and plants will be sprayed to run-off. In addition, value-added mulch that was previously inoculated with BCA will be applied on the base of each plant. This system allows treatment of the seed, the soil and the plant.Greenhouse experiments will be conducted at TSU where seedlings colonized with BCA as described above will be grown in Miracle Grow soil infested with P. capsici using 30 ml of inoculum/kg soil, that has been pre-determined and selected as best inoculum level for greenhouse studies (Bhusal and Mmbaga 2020). Reinforcement of seed treatments with BCAs will be as described in field studies. All plants will be monitored for disease development and evaluated for disease severity on a scale of 0-5, in which 0 = no visible symptoms; 1 = slightly wilted with brownish lesions beginning to appear on the stem; 2 = stem lesions extending to cotyledons and 30% of plant diseased; 3 = stem lesions extending to petioles and 50% of the plant diseased; 4 = petioles collapse, and 80% of the plant diseased; 5 = entire plant dead. (Irabor and Mmbaga, 2017). Crop yield in quantity and quality will be measured by number and weight of fruits per plot while quality will be evaluated by presence or absence of fruit blemishes. The three objectives (i)-(iii)will be addressed concurrently.iv) Demonstration of project results on biocontrol technology to growers will be carried out during the annual farm Expo when TSU research results show-casetheir research results to growers. Education program for farmers will use poster and oral presentationson research results. Special Invitations for the annual farm Expo will be sent to organic farmers who have supported this research.Data analysis for all studies will use the SAS linear model for analysis of variance (SAS 2010). Multiple comparisons between pairs of means will be performed using a series of t-tests according to SAS procedures in PROC. ANOVA (SAS/STAT. 2010).