Acclimatization, Rooting and Field Establishment of Micropropagated Papaya Plants

Export markets for papaya Maradol require elongated fruits that come from hermaphrodite flowers rather than rounded fruits from female flowers. That forces growers to try to have plantations with 100% hermaphrodite plants. Currently commercial growers use seeds that show only 75% hermaphroditism or lower. For this reason, they transfer 3 plants/pot to the field, water and fertilize them for further 2 months, only do then eliminate 2 of the 3 plants after flower sex examination. By comparison our micropropagated plants have 100% hermaphrodite flowers and 100% of their fruits are elongated in shape, and therefore the grower can directly transfer 1 plant/pot, reducing the need for plants from 6000/ha to only 2000 plants/ha. Our protocol includes rooting medium with efficient root production in vitro. However, the survival rates can be improve by inducing rooting in vitro and root development ex vitro, using commercial rooting products. The ventilation of the vessel has shown to be important to increase plant survival ex vitro. The best rooting, ex vitro performance and plant survival were achieve using ventilated vessels in vitro and rooting ex vitro with Radix 1500. In a commercial-scale field-trial, for 4 consecutive years, micropropagated plants conserved their 100% hermaphroditism in their flowers and consistently 100% of their fruits were elongated in shape while the control plants derived from seeds showed only 75% hermaphrodite flowers and therefore 25% of the less commercial rounded fruits. In addition, no differences were found in plant performance between the micropropagated plants and plants originated by seeds. As far as the physiology, photosynthetic rates and chlorophyll fluorescence they were very similar in both types of plants. In terms of plant height, micropropagated plants were slightly shorter but this is advantageous for harvesting. Fruit size and yields were also comparable and in terms of fruit appearance and quality, fruits from both plant types were equivalent.