Better Rooting Procedure to Enhance Survival Rate of Field Grown Malaysian Eksotika Papaya Transformed with 1-Aminocyclopropane-1-Carboxylic Acid Oxidase Gene

A high survival rate for transformed papaya plants when transferred to the field is useful in the quest for improving the commercial quality traits. We report in this paper an improved rooting method for the production of transformed Malaysian Eksotika papaya with high survival rate when transferred to the field. Shoots were regenerated from embryogenic calli transformed with antisense and RNAi constructs of 1-aminocyclopropane-1-carboxylic acid oxidase (ACO) genes using the Agrobacterium tumefaciens-mediated transformation method. Regenerated transformed shoots, each measuring approximately 3-4？cm in height, were cultured in liquid half-strength Murashige and Skoog (MS) medium or sterile distilled water, and with either perlite or vermiculite supplementation. All the culturing processes were conducted either under sterile or nonsterile condition. The results showed that rooting under sterile condition was better. Shoots cultured in half-strength MS medium supplemented with vermiculite exhibited a 92.5% rooting efficiency while perlite showed 77.5%. The survival rate of the vermiculite-grown transformed papaya plantlets after transfer into soil, contained in polybags, was 94%, and the rate after transfer into the ground was 92%. Morpho-histological analyses revealed that the tap roots were more compact, which might have contributed to the high survival rates of the plantlets. 1. Introduction The world production of papaya in 2008 was valued at 9.1 million tonnes [1], and Malaysia is listed as one of the top six major exporters. The most popularly grown cultivar and the main variety grown for export is Eksotika, which is a high yielding variety producing 50–70 tonnes per hectare over a two-year crop cycle [2]. The release of Eksotika papaya variety in 1987 had since resulted in an increase in its production areas in Malaysia. Due to its importance to Malaysian economy, some important traits in Eksotika papaya need to be further improved to increase the papaya production so as to meet and widen the market demand. Similar to other tropical fruits, Eksotika fruit has a very short shelf life. There is a need to extend its shelf life in order to reduce post-harvest losses and to increase its export potential to distant destinations. Throughout the years, attempts had been made through conventional breeding and manipulation of post-harvest approaches but all were unsuccessful in improving this trait. Increasing the shelf life of papaya fruit through genetic engineering is therefore a more promising option. The ability to delay the ripening process in the