The Studies of Plant Host Resistance to the Reniform Nematode in Upland Cotton and the Effects of Bacillus firmus GB-126 on Plant-Parasitic Nematodes
Type of Degreethesis
Entomology and Plant Pathology
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Germplasm lines LONREN-1 and LONREN-2 were released in 2007 for cotton breeders to incorporate reniform nematode resistance into breeding efforts with desirable cultivars to establish nematode resistant high yielding cultivars. Previous screenings for reniform resistance in the LONREN-1 X FM966 breeding lines developed at Auburn University have demonstrated that the reniform resistance is accompanied by severe stunting and limited plant growth followed by low yields. The objectives of this study were to evaluate the effects that applying nematicides to selected LONREN breeding lines have on reniform ¬nematode populations, early seedling plant stunting, yield, and fiber quality. Three resistant breeding lines from the LONREN-1xFM966 cross, one susceptible line from the LONREN-1xFM966 cross, and the susceptible cultivar DP393 were treated with nematicides and their performances evaluated. In the greenhouse, nematicides increased plant heights in the resistant lines. Nematicides further reduced reniform populations in the resistant lines 45 days after planting (DAP). Reniform populations were 50% lower in the resistant lines compared to the susceptible lines by the end of the growing period. In microplot and field trials, the phenotypic stunting response of the resistant lines was reduced by nematicides with increases in plant heights at 30 and 75 DAP. Increases in yields were also evident in the resistant breeding lines that were treated with nematicides. Bacillus firmus strain GB-126 was evaluated for the capacity to reduce mobility of juveniles, inhibit egg production, and induce systemic resistance when used as a control against Heterodera glycines and Meloidogyne incognita. Experiments were established in vitro to examine egg hatching and mobility and paralysis of J-2s in 96 well plates containing 100µl of GB-126 cells at 1X107 and 1X106 cfu/ml and cell-free extracts at 100%, 50%, and 25% concentrations. Split-root assays were established to evaluate induced systemic resistance. GB-126 cells at both concentrations significantly reduced mobility of H. glycines J2s compared to Tryptic Soy Broth (TSB) and sterilized tap water (STW) controls at 36 h after treatment. Cell-free extracts of GB-126 reduced mobility significantly at 12 h after treatment in both 100% and 50% concentrations compared to TSB and STW controls. GB-126 cells and cell-free extracts also significantly reduced egg hatching of H. glycines and M. incognita at 9 and 4 days after inoculation, respectively. Induced systemic resistance was evident in the H. glycines split-root assay but not in the M. incognita split-root assay. The results of these experiments indicate that both cells and cell-free extracts of GB-126 can have antagonistic effects on H. glycines and M. incognita.