The effect of root-knot nematodes and Ethrel on Fusarium wilt of tomatoes

The reaction of two tomato varieties, 'Moneymaker' (susceptible to Fusarium) and 'Fortos' (resistant to Fusarium) to inoculation with Meloidogyne javanica, M. incognita and Fusarium oxysporum f. sp. lycopersici race 1 as well as to application of Ethrel (2 chloroethane phosphonic acid)-an ethylene releasing compound-was studied. With 'Moneymaker', Ethrel reduced wilt symptoms drastically and this was correlated with a reduction in the number of infected vascular bundles in the stem. Height of the stems was increased. Both nematode species counteracted the therapeutic effect of Ethrel by increasing the number of infected vascular bundles. 'Fortos' remained resistant to Fusarium in the presence of nematodes and/or Ethrel. Only, a slight tendency toward resistance-breaking by the nematode was observed. In this variety enhancement of the pathogenic effects of the nematodes by Ethrel was evidenced by increased gall size. Histological studies indicated no difference in xylem structure among the various treatments. These results support the evidence that plant growth regulators play a role in the pathogenicity of root-knot nematodes, the Fusarium resistance of the plants, and the effect of nematodes on the severity of Fusarium wilt.