Resistance to Melon necrotic spot virus in Cucumis melo L. ‘Doublon’ artificially inoculated by the fungus vector Olpidium bornovanus

Melon necrotic spot virus (MNSV) can cause significant economic losses in melon (C. melo L.). In C. melo ‘Doublon’ a resistance to systemic symptom expression of MNSV after cotyledon mechanical inoculation has been described. The work reported here assessed the response of C. melo ‘Doublon’ when plants were inoculated with MNSV by the fungus Olpidium bornovanus, which is the natural vector of the virus. Although both cotyledon mechanical inoculation and inoculation by O. bornovanus transmitted MNSV, vector transmission was the most efficient method measured as absorbance values in ELISA tests. In ‘Doublon’ the virus inoculated by O. bornovanus accumulated in the roots to a concentration comparable to that in susceptible plants, nevertheless it was unable to spread beyond the base of the hypocotyl. Moreover, the only MNSV symptoms developed in ‘Doublon’, necrosis on the basis of the hypocotyl and partial browning of the roots, did not affect fruit production. These observations confirm that the resistance previously described in ‘Doublon’ after cotyledon mechanical inoculation is also effective when MNSV is inoculated by the fungal vector. This resistance may be related to a restriction of the long-distance movement of virus within the host plant, whereby virus movement is restricted to the base of the hypocotyl and systemic hypersensitivity occurs.