Trichoderma harzianum Endochitinase Does Not Provide Resistance to Meloidogyne hapla in Transgenic Tobacco.
Eggs of Meloidogyne hapla contain chitin, a substrate for chitinase. Our goal was to determine if endochitinase from the biocontrol fungus T. harzianum expressed in transgenic tobacco increases resistance to this nematode. Endochitinase-transgenic T tobacco seedlings expressing increased endochitinase activity in leaves (11 to 125 times over control) and roots (2 to 15 times over control) were transferred to quartz sand:loam soil mix (4:1 ratio) and inoculated with 5,000 M. hapla eggs/pot. Tomato (cv. Rutgers), pepper (cv. California Dream), and non-transformed tobacco plants were used as susceptible controls. Two experiments were performed in the greenhouse with nine and ten transgenic tobacco lines, respectively. Roots were harvested 55 days after inoculation, and number of eggs, secondstage juveniles (J2), reproductive factor (Rf), and (eggs + nematodes [J2])/g of fresh root weight were determined. The reproduction factor for tobacco plants ranged from 1.06 to 3.40. Significant differences in number of J2 and egg counts were found between some transgenic lines and control tobacco; however, they were not consistent for lines tested in both experiments. No statistical differences were detected for (eggs + nematodes [J2])/g of fresh root weight in either experiment. We conclude that the elevated endochitinase activity did not provide protection against root-knot nematodes.
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