Tropical/subtropical germplasm resources have been reduced in their natural habitats by indiscriminated human activity, pressure from emerging pests, diseases and viruses and by weather-related causes. The loss of genetic diversity can be effectively reduced with the establishment and proper maintenance of ex-situ collections in the field and in-vitro culture. The establishment of field collections safeguard against germplasm losses due to natural disasters, facilitates long-term preservation and access ibility of domestic and foreign germplasm, offer an opportunity for the characterization and evaluation of clones and/or cultivars, and serve as genetic stock centers to readily meet the needs of current and future improvement program. In-vitro preservation reduces the risk of virus, pest and disease dissemination that may occur during germplasm exchange and distribution, accelerates the multiplication and distribution of valuable germplasm, and reduces the space needed for germplasm conservation and ma intenance costs. Characterization and evaluation assist in maintaining the genetic integrity of plant materials after an extended period of continuous propagation, and help germplasm users to recognize clones with desirable traits for later use in crop improvement programs. This research involves the introduction, evaluation, characterization and distribution of virus-free tropical/subtropical germplasm, and its preservation for long-term accessibility.
Materials and Methods
Primary field collections of plantain and banana (Musa spp.), and Annona spp. have been established in replicated plots and under intensive management for proper characterization and evaluation. Some of the Musa clones possess resistance to black Sigatok a, and were introduced from active breeding programs sponsored by the International Network for the Improvement of Banana and Plantain (INIBAP). We are in the process of establishing additional primary collections of mamey sapote (Pouteria sapota, Jacq.) and sapodilla (Manilkara sapota L., v. Rogen). Highly discriminating morphological descriptors and molecular markers will be used during the characterization and identification process. When appropriate, the plant descriptors developed by the Internati onal Plant Genetic Resources Institute (IPGRI) will be adopted. Random Amplified Polymorphic DNA (RAPD) or any other polymerase chain reaction (PCR) based markers that uses random primers to generate DNA fragments will be used in the genetic characteriza tion of the germplasm. We will attempt to successfully multiply and preserve in-vitro all the germplasm assembled in the primary collections. Standard tissue culture techniques mainly recommended for fruit crops will be adopted or modified and tested. From time to time, the regenerated germplasm will be field tested to ensure its genetic integrity. The program also maintains a collection of bamboos, and back-up collections of avocado (Persea americana, Mill.) and mango (Mangifera indica L.) to support similar ARS programs at Georgia and Florida.