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Gamma irradiation for management of post-harvest fruit rot of papaya caused by Phytophthora palmivora
M. A. DRAGICH (1), J. Uchida (1), L. Wong (2), C. Kadooka (1), K. Kamiya (3). (1) University of Hawaii at Manoa, Honolulu, HI, U.S.A.; (2) Pa'ina Hawaii LLC, Kunia, HI, U.S.A.; (3) Kamiya Gold Inc., Laie, HI, U.S.A.

<i>Phytophthora palmivora</i> is an Oomycete pathogen that causes fruit rot of papaya both in the field and during post-harvest. A post-harvest treatment that retains fruit qualities for looks, taste and texture that controls fruit rot would reduce post-harvest losses and risk at market. Two types of irradiation experiments were conducted: one measuring spore germination and mycelial growth in perti dishes, and another measuring pathogen growth on mature green papaya fruits. Doses of 400 gry, 500 gry, 700 gry, 1 kgry, and 4 kgry were used to treat <i>P. palmivora</i> in petri dishes. Doses of 400 gry and 700 gry were used to treat the pathogen on papaya fruit. The results for each treatment were compared to untreated controls. In petri dishes, 700 gry was shown to be the minimum dose which arrested spore germination and eliminated mycelial growth. This rate on papaya fruit also prevented lesion development. 400 gry doses on papaya fruit also drastically reduced development, and we were unable to re-isolate <i>P. palmivora</i> from fruit treated at 400 gry. For the purpose of extended shelf life, 400 gry treatments have eliminated lesion development for 6 days post treatment. Currently 400 gry is the appropriate dose for purposes of complete elimination of papaya fruit rot caused by <i>P. palmivora</i>, based on three repeated tests, with ten fruit per treatment.

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