Tissue culture and associated biotechnological interventions for the improvement of coconut (Cocos nucifera L.): a review.

MAIN CONCLUSION: The present review discusses not only advances in coconut tissue culture and associated biotechnological interventions but also future research directions toward the resilience of this important palm crop. Coconut (Cocos nucifera L.) is commonly known as the 'tree of life'. Every component of the palm can be used to produce items of value and many can be converted into industrial products. Coconut cultivation faces a number of acute problems that reduce its productivity and competitiveness. These problems include various biotic and abiotic challenges as well as an unstable market for its traditional oil-based products. Around 10 million small-holder farmers cultivate coconut palms worldwide on c. 12 million hectares of land, and many more people own a few coconut palms that contribute to their livelihoods. Inefficiency in the production of seedlings for replanting remains an issue; however, tissue culture and other biotechnological interventions are expected to provide pragmatic solutions. Over the past 60 years, much research has been directed towards developing and improving protocols for (i) embryo culture; (ii) clonal propagation via somatic embryogenesis; (iii) homozygote production via anther culture; (iv) germplasm conservation via cryopreservation; and (v) genetic transformation. Recently other advances have revealed possible new ways to improve these protocols. Although effective embryo culture and cryopreservation are now possible, the limited frequency of conversion of somatic embryos to ex vitro seedlings still prevents the large-scale clonal propagation of coconut. This review illustrates how our knowledge of tissue culture and associated biotechnological interventions in coconut has so far developed. Further improvement of protocols and their application to a wider range of germplasm will continue to open up new horizons for the collection, conservation, breeding and productivity of coconut.

Biology, propagation and utilization of elite coconut varieties (makapuno and aromatics).

Coconut farming is not only a vital agricultural industry for all tropical countries possessing humid coasts and lowlands, but is also a robust income provider for millions of smallholder farmers worldwide. However, due to its longevity, the security of production of this crop suffers significantly from episodes of natural disasters, including cyclone and tsunami, devastating pest and disease outbreaks, while also affected by price competition for the principal products, especially the oil. In order to reduce these pressures, high-value coconut varieties (makapuno and aromatics) have been introduced in some regions, on a limited scale, but with positive outcomes. Even though these two varieties produce fruit with delicious solid or flavoursome liquid endosperm, their distinct biochemical and cellular features unfortunately prevent their in situ germination. In fact, embryo rescue and culture have been developed historically to nurture the embryo under in vitro conditions, enabling effective propagation. In an attempt to provide a comprehensive review featuring these elite coconut varieties, this paper firstly introduces their food values and nutritional qualities, and then discusses the present knowledge of their biology and genetics. Further possibilities for coconut in general are also highlighted, through the use of advanced tissue culture techniques and efficient seedling management for sustainable production of these highly distinct and commercially attractive varieties of coconut.