Comparison of Infection Caused by Pythium Debaryanum, Phytophthora Palmivora and Erwinia Caricae on Transgenic and Non-Transgenic Papaya Ringspot Virus Resistant Plants

Abstract

The study was conducted to determine the reaction of transgenic papaya ringspot virus (PRSV) - resistant papaya to some major fungal and bacterial diseases of papaya. Four lines of trans- genic papaya developed by the Institute of Plant Breeding (IPB) and non-transgenic 'Davao solo' were used in the screening. Plants were artificially inoculated with the most aggressive isolates in a contained greenhouse. Inoculation was done by incorporating Pythium debaryanum and Phytophthora palmivora - colonized wheat seeds into the base of the plant and by pricking the base of leaf petiole with a needle dipped in suspension of Erwinia caricae. Four transgenic papaya lines and 'Davao Solo' were susceptible to P. debaryanum and P. palmivora under greenhouse conditions. No significant differ- ences in per cent wilted seedlings caused by P. palmivora among transgenic four lines and 'Davao Solo' were observed (p = 0.05). Similarly, no differences in root rot severity (%) among the same test plants due to P. palmivora were noted. The three transgenic papaya lines were initially more susceptible than 'Davao Solo' to E. caricae seven days after inoculation but the same degree of infection was attained 14 days after inoculation. The transgenic and the non-transgenic papaya exhibited susceptible reactions to P. debaryanum in the greenhouse. No significant difference was observed in one transgenic line and 'Davao Solo' in terms of pre and post germination damping-off incidence in inoculated soil (p = 0.05).