Submitted to: Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 28, 2000
Publication Date: N/A
Interpretive Summary: Plant-parasitic nematodes are microscopic worms that feed on plant roots, causing crop losses of more than seven billion dollars each year in the U.S. Root-knot nematode is one of the most economically important members of this group because it attacks a number of host crops. The problem addressed by this study is to find new ways of managing this nematode. The bacterium Burkholderia cepacia and the fungus Trichoderma virens were investigated for ability to suppress activity and reproduction of the root-knot nematode Meloidogyne incognita. In culture, the fungus and the bacterium were found to produce compounds that inhibited egg hatch and mobility of hatched nematodes. When compounds from the fungus were applied to nematodes growing on tomato roots in lab dishes, nematode numbers were reduced. In greenhouse tests with tomato, living and nonliving treatments of each microbe were applied to seeds and seedlings. Treatment with nonliving B. cepacia suppressed total nematode numbers by 29% compared to water treatment. No other treatment affected overall nematode numbers. Neither organism was efficient as a nematode management agent under the conditions of the greenhouse study. The results are significant because both microbes have been investigated as biocontrol agents for various plant diseases, and this study indicated that they may not be useful to scientists developing novel control strategies for root-knot nematode problems on tomato.
Technical Abstract: The bacterium Burkholderia cepacia (strain Bc-2) and the fungus Trichoderma virens (strain Gl-3) were investigated for suppressive activity against the root-knot nematode Meloidogyne incognita. Culture filtrates from each organism contained extracellular factors that inhibited egg hatch and mobility of second-stage juveniles (J2). Inhibitory activity that suppressed egg hatching was detected in culture filtrates from Bc-2 in low-molecular weight (< 3 KDa) fractions. Culture filtrates from Bc-2 and Gl-3 did not contain detectable chitinase or protease activities, indicating that the inhibitory factor(s) associated with the microbes are probably non-enzymic in nature. Monoxenic tomato root explant cultures of M. incognita were treated with culture filtrate from T. virens grown on Weindling's medium plus glycerol. Numbers of eggs+J2 per gram of root were significantly lower than numbers in cultures treated with non-inoculated medium. In greenhouse tests with tomato, Bc-2 and Gl-3 (viable and nonviable treatments) were applied individually as seed coatings and later as root drenches to seedlings. Treatment with nonviable B. cepacia suppressed (P < 0.05) total nematode numbers by 29% compared with water controls; no other treatment affected overall egg+J2 numbers per gram of root. Neither organism was efficacious as a nematode management agent under the conditions of the greenhouse study.