A novel technique for treating seeds with biocontrol agents for the sustainable management of bacterial fruit blotch of watermelon

A novel technique for treating seeds with biocontrol agents for the sustainable management of bacterial fruit blotch of watermelon

Summary

Utilization of a non-pathogenic strain of A. citrulli, AAC00-1ΔhrcC as a biocontrol seed treatment can reduce seed to seedling transmission of bacterial fruit blotch (BFB). This strategy can easily be implemented into vegetable seed production. We are currently optimizing the concentration of biocontrol inoculum required for watermelon flower treatment under field conditions.

Objectives/Performance Targets

The main objective of this study is to optimize a flower inoculation technique for efficiently delivering biocontrol agents into watermelon seeds. The specific objectives include:

1. 1. To optimize the concentration of flower stigma inoculum required to maximize seed inoculation with AAC00-1ΔhrcC . 

2. 2. To determine the efficacy of flower inoculation with AAC00-1ΔhrcC in reducing seed-to-seedling transmission of BFB.

Accomplishments/Milestones

To date four experiments have been conducted to generate watermelon seeds under greenhouse conditions. In each experiment, at anthesis watermelon flowers were inoculated with AAC00-1ΔhrcC concentrations ranging from 10⁷ to 10⁹ CFU/flower. Flowers inoculated with sterile water served as negative controls. The four experiments yielded approximately 100 seed lots. To date 47 seed lots have been tested to determine the proportion of seeds that are contaminated per seed lot and concentration of AAC00-1ΔhrcC per seed in each lot. To date we have found that the optimal concentration for flower inoculation is 10^7 CFU/flower. Out of 29 seedlots from flowers treated with 10^7 AAC00-1ΔhrcC /flower, 55% were positive for the biocontrol agent.

We are in the process of testing the remaining seedlots and determining the inoculum load per seed for each positive lot. Additionally, seedling grow out assays are being performed on each lot to determine the effect of flower treatment on germination percentage. Based on our greenhouse studies, we are preparing to conduct trials under field conditions with 10⁷ CFU/flower as our inoculum concentration

Impacts and Contributions/Outcomes

Seeds are important for vegetable production, and seed treatments can be critical for plant disease management. Effective strategies for applying biological control seed treatments will provide an environmentally friendly and sustainable approach for managing seed borne bacterial diseases. Flower inoculation provides an advantage over other biocontrol seed treatment approaches because it can result in the deposition of the beneficial bacteria deep within the seeds. There the bacterium is protected from desiccation and can theoretically survive as long as the seed is viable. This technique can be easily incorporated into existing commercial seed production systems by inoculating female watermelon flowers during hand pollination. At present, labor-intensive hand pollination is routinely employed in hybrid watermelon seed production. This would reduce BFB seed-to-seedling transmission and ultimately reduce the frequency of BFB outbreaks.

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