Isolation and Characterization of a Rhizobacterial Antagonist of Root-Knot Nematodes

<div><p>The rhizobacterial strain Jdm2 was isolated from the rhizosphere of the traditional Chinese medicinal herb <i>Trichosanthes kirilowii</i> in Jiangsu province, China, and was identified as <i>Bacillus subtilis</i>. Exposure of cell-free filtrate of the strain to the root-knot nematode <i>Meloidogyne incognita</i> under <i>in vitro</i> conditions caused substantial mortality of the second stage juvenile (J2) and significantly reduced egg hatchability. A greenhouse trial demonstrated that 56 days after treatment with Jdm2, the number of galls associated with <i>M. incognita</i> infection in the tomato (<i>Solanum lycopersicum</i>) roots was significantly reduced compared to controls, and the disease severity of infected plants was lower in treated plants (36%) compared to water control (75%). Consistently, in the field trial, the biocontrol efficacy of Jdm2 reached 69%, 51% and 48% after 30, 60 and 90 days post-transplantation, respectively. As indicated by PCR-DGGE analysis, inoculation with Jdm2 strain had an effect on the bacterial community of the tomato rhizosphere at the first stage, but was not able to imperil the bacterial community stability for long time. The novel bacterial strain Jdm2 enhances plant growth and inhibits nematode activity, and has the potential to be a safe and effective microbial pesticide.</p></div

Morphological and Physiological Characteristics of Strain Jdm2.

<p>+, positive reaction; -, negative reaction.</p

Biocontrol efficacy of Jdm2 against <i>M. incognita</i> and their biomass changes of tomato plants in the greenhouse tests.

1<p>Plant inoculated with antagonist suspensions at a concentration of 10⁹ CFU/mL with a water control. Each plant was inoculated with 10 egg masses.</p>2<p>Standard deviation of means.</p>3<p>Numbers followed by different letters in the same columns are significantly different from each other at 5% probability level. Data is mean of three replicates.</p

Dendrograms based on similarity matrices determined from the clusters analysis using the Pearson coefficient indices by means of unweighted pair group method using arithmetic averages (UPGMA) at 15, 30, and 60 days (A, B and C) post-inoculation.

<p>Scaling stands for similarity. ‘‘B1 –B4’’ was on behalf of the treatments amended with Jdm2, ‘‘A1–A4’’ was on behalf of the controls amended with Avermectins, and ‘‘C1–C4’’ was on behalf of the controls amended with water.</p

Field tests of antagonistic strains Jdm2.

1<p>Plants were treated with antagonist suspensions at a concentration of 10⁵ CFU/mL (500 mL for one seedling) or with the insecticide Avermectins, while control was a treatment with water.</p>2<p>Standard deviation of means.</p>3<p>Numbers followed by different letters in the same columns are significantly different from each other at 5% probability level. Data is mean of four replicates.</p