Poster: Root Biology

Abs # 536: Photoautotrophic rooting and growth of papayas in vitro.

Presenter:	Fitch, Maureen M.M, mfitch@pbarc.ars.usda.gov
Authors	Fitch, Maureen M.M (A)   Leong, Terryl  (B)   Saito, Nancy  (B)   Yamamoto, George  (B)   Dela Cruz, Amy  (B)   Yeh, Aileen W (B)   White, Susan  (B)   Maeda, Sharyn H. (A)   Ferreira, Stephen A. (C)   Moore, Paul H. (A)
Affiliations:	(A): Pacific Basin Agricultural Research Center (B): Hawaii Agriculture Research Center (C): University of Hawaii

Papaya plants micropropagated on Murashige and Skoog medium containing 3% sucrose, 1 ìM benzyladenine, and 1ìM naphthalene acetic acid, became contaminated by slow-growing bacteria. Shoot growth was not inhibited on the proliferation medium, but subsequent root development in half-strength MS medium devoid of growth regulators was repressed. The contaminant(s) were not identified. Cultures were treated with 500 mg/L carbenicillin and 200 mg/L cefotaxime and were decontaminated by the antibiotic treatment. Reappearance of the bacterial contamination, despite stringent aseptic technique, suggested that the media might be modified to maintain growth and reduce plant loss. Since sucrose might enhance bacterial growth, it was eliminated from the proliferation and root formation media. Growth of uncontaminated shoots was observed on the autotrophic media. Growth of shoots was reduced to less than 10% on the autotrophic proliferation medium, but was 80% on the autotrophic rooting medium compared to growth in sucrose-containing media. Subsequent root formation occurred 1-2 months later in the autotrophic medium compared to the sucrose-containing medium. Despite a 30% smaller root mass, canopy and stem growth were normal following root formation. Experiments are ongoing to improve root initiation and development rates in the absence of sucrose. The autotrophic rooting medium will facilitate high throughput micropropagation by eliminating the inhibitory effect of bacterial contamination.