Submitted to: International Symposium on Tropical and Subtropical Fruits
Publication Type: Abstract Only
Publication Acceptance Date: 7/2/2004
Publication Date: 9/12/2004
Citation: Zhu, Y.J., Agbayani, R., Tang, C.S., Moore, P.H. 2004. Developing transgenic papaya to improve broad disease resistance against fungal pathogens [abstract]. Proc 3rd International Symposium on Tropical and Subtropical Fruits. p48:O-03.
Interpretive Summary: abstract only.
Technical Abstract: Papaya (Carica papaya L.), one of the more important fruit crops of the tropics, has limited resistance to a range of fungal pathogens that may kill the plants or, at a minimum, reduce productivity and quality of the fruit. Phytoalexins have been shown to be important natural components in the defense of plants against pathogen infection. Several fruit crops, including grapevine and peanut synthesize the stilbene-type phytoalexin, Resveratrol, (trans-3,4’, 5-trihydroxy-stilbene) when attacked by fungal pathogens such as, Botrytis cinerea or Plasmopara viticola (Blaich, 1980). The level of resistance to P. viticola was positively correlated with the capacity of Vitis spp. to synthesize stilbene (Dercks, 1989). We conducted in-vitro pathogen inhibition assays to show that Resveratrol inhibited fungal pathogens of tropical plant, papaya (Carica papaya L.). Resveratrol at 1.0 mM in V8 agar culture medium inhibited mycelia growth of Phytophthora palmivora up to 50% of control. The compound was active against P. palmivora as low as 100 'M. Resveratrol was not as effective against the anthracnose pathogen, Colletotrichum gloeosporiodes. Further, we transformed papaya embryogenic cultures with the stilbene synthase gene cloned from grapevine and driven by its own inducible promoter along with the hygromycin resistance or kanamycin resistance gene under the control of a CaMV35S promoter. The presence of transgenes was confirmed by PCR and Southern blot analysis. Transgenic papaya plants were challenged with P. palmivora in greenhouse condition. Data from greenhouse studies showed that disease level in transgenic plant was reduced to 35% of the disease level in non-transformed control plants. This result indicated that metabolic engineering Carica papaya with heterologous phytoalexins either under its own inducible promoter or a constitutive promoter can improve plant defenses against fungal pathogens.