Putting the Brrr! into Breeding Tropical Fruit

Cryopreservation provides a secure, economical and disease-free alternative to field gene banks for preserving the genetic diversity of tropical fruits

Tropical fruit is a mainstay of the local economy in several countries of Southeast Asia. As high-value crops, they are important sources of income for poor farmers and priorities for research in the Consultative Group on International Agricultural Research (CGIAR). And, as rich sources of nutrients, especially vitamins A and C, they help fight malnutrition. Fruit farmers would like to increase production and improve quality to compete better in markets. This requires breeding better varieties, which in turn requires ready access to genetic diversity. And there lies the rub.

Because they grow in humid environments, the seeds of tropical fruits do not survive drying, the most common way to store seeds in gene banks. Fruit diversity is often conserved by planting whole trees in field gene banks, but this poses new problems. Different varieties may be adapted to particular climates, and field gene banks are vulnerable to pests and diseases as well as to extreme weather. Field gene banks are also expensive.

An alternative is cryopreservation, or storing plant tissues at ultra-low temperatures, usually in liquid nitrogen. The International Plant Genetic Resources Institute (IPGRI), funded by the Australian Center for International Agricultural Research, worked with partners in Malaysia, Philippines, Thailand and Vietnam to improve cryopreservation methods for storing tropical fruit diversity. The target fruits were papaya, mango, citrus, longan, litchi and persimmon, as well as several fruits native to Australia. As a result, the vital genetic diversity of these economically important species will be conserved and made available to breeders and others.

One problem is that freezing can create ice crystals that damage plant cells. Various techniques exist for minimizing the damage, but they need fine-tuning for different species. Regeneration techniques to reconstitute whole plants from small pieces of frozen tissue also need to be optimized for each species. Thanks to this project, more species can now be cryopreserved and regenerated successfully, and the knowledge gained will facilitate modifying the techniques for even more species in the future.

Using tissue culture additionally offers the opportunity to eliminate diseases that have accumulated within field-grown stocks. In the Philippines, the project helped to develop disease-free material of several citrus varieties, which are being used to establish new nurseries.

Training and capacity development were central to the project. An international training workshop at Griffith University in Australia attracted participants from Malaysia, Philippines, Thailand and Vietnam who are now able to use cryopreservation in national programs. Australia does not currently have gene banks for tropical fruits, but its improved knowledge and expertise in cryopreservation will be useful in efforts to help other countries develop appropriate conservation technologies for tropical fruit species.

IPGRI’s collaborators on the project were Griffith University, Australia; Department of Agriculture, Thailand; Institute of Plant Breeding, Philippines; Center of Biodiversity and Biosafety, Vietnam; and University Kebangsaan Malaysia, Malaysia.