Submitted to: Nematropica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 5, 2001
Publication Date: N/A
Interpretive Summary: Plant-parasitic nematodes are microscopic worms that attack plants, causing seven billion dollars in annual crop losses in the U.S. The problem addressed by this study is to find new ways of reducing crop losses caused by root-knot nematode. Bell pepper seeds and seedlings were treated with three beneficial microbes. Individual treatments were live and dead formulations of the bacterium Burkholderia cepacia (strains Bc-F and Bc-2) and the fungus Trichoderma virens (strain Gl-3). Combined treatments were Bc-F/Gl-3, Bc-2/Gl-3, Bc-F/Bc-2, and Bc-F/Bc-2/Gl-3. Shoot height and fresh weight, fruit numbers, and fruit weight were not affected by treatment. Dry shoot weight was greatest with Bc-F treatment. Fresh root weight was lowest with two combination treatments. The nematode numbers per gram of root were lowest with individual microbe treatments. Dead fungus treatment increased nematode numbers compared with most treatments. The numbers recorded from combination treatments were not different from those on untreated plants. The results are significant because they suggest that strain combinations decrease biocontrol effectiveness relative to applications of individual microbes. Also, the microbes have been studied as biocontrol agents for soilborne plant diseases, and these strains are now demonstrated to act against nematodes. This research will be used by scientists developing environmentally safe methods for managing diseases caused by nematodes.
Technical Abstract: Pepper (Capsicum annuum L.) seeds and seedlings were treated with three beneficial microbes alone and in combination to determine their effects on root-knot nematode (Meloidogyne incognita) populations and on plant vigor. Individual treatments were viable and nonviable formulations of Burkholderia cepacia strains Bc-2 and Bc-F, and Trichoderma virens strain Gl-3 (applied as seed coatings and seedling drenches). Combination treatments were Bc-F/Gl-3, Bc-2/Gl-3, Bc-F/Bc-2, and Bc-F/Bc-2/Gl-3. At transplanting, seedlings were each inoculated with 10,000 M. incognita eggs or left uninoculated. Nonviable formulations were tested on inoculated plants only. The greenhouse-grown plants were harvested 10 weeks later. Shoot height and fresh weight, and fruit numbers and weight, were not affected by treatment. Bc-F application increased dry shoot weight (P < 0.05) compared to most treatments. Fresh root weight was less (P < 0.05) on nematode-inoculated plants with Bc-F/Gl-3 and Bc-F/Bc-2/Gl-3 treatments than on controls. Egg+second-stage juveniles (J2) numbers per gram root were suppressed (P < 0.05) with Bc-2, Bc-F, and Gl-3 treatments, compared with untreated controls, but increased with nonviable Gl-3 treatment. The egg+J2 numbers recorded from combination treatments were not significantly different from untreated controls. This suggests that strain combinations decreased biocontrol effectiveness relative to applications of individual microbes.