Small Islands are not the only places where coconut germplasm can be maintained in reproductive isolation, for both conservation and production of hybrid seednuts.
In the mainland, any place can be used as far no coconut palm is planted all around at a 500 m distance. In this case, the total design will require a diameter of 600 to 700 m and a surface of 20 to 22 hectares for the conservation of only one Tall coconut variety. Such an area may be difficult to find for coconut conservation purposes. Anyway, it will depend on the geographical structure of the land. For instance, many small isolated valleys could fit this design in Fiji and French Polynesia. In the Dhofar region of the sultanate of Oman, some irrigated coconut plantations surrounded by a sandy desert zone can also fit this design.
In the mainland again, it is possible to use a 300 m wide zone planted all around the coconut palms with forest trees or another perennial crop. Such a buffer forest zone will be enough to maintain a reproductive isolation for the coconut palms. In this case, the total design will require a diameter of 400 to 500 m, and a surface of 12 to 16 hectares for the conservation of one Tall coconut variety only. Such an area may be difficult to find for conservation purposes. Anyway, this design is planned to be used in Côte d’Ivoire, inside the Oil Palm and Rubber plantations of the National Agronomic Research Centre.
In the mainland again, a smaller isolation distance can be used if the surrounding zone is all planted with the same coconut variety. If a given coconut palm is surrounded in all directions by a radial line of at least 10 palms from the same variety; then we estimate than the seednuts harvested on this given palm will be true to type at more than 97% in average. An isolation zone of about 100 m wide is then sufficient.
The following plate gives examples of possible planting designs, with less or more dwarf red palms and producing less or more hybrid seeds (click on the image to enlarge it). Seednuts from the Tall variety will be harvested only on the zone colored in light green. Seednuts from the Red Dwarfs will be harvested on all red and orange hexagons, except the wider one. In this case, the total design will require a diameter of 300 to 400 m and a surface of 8 to 10 hectares for both conservation of one Tall coconut variety and production of hybrid seednuts.
The zone colored in light green, where seednuts from the Tall variety will be harvested, initially counts 137 useful palms. Why to plant 137 palms when the standard procedure requires only 96 palms for conservation purposes? Most of the Tall coconut varieties collected nowadays is mix between traditional varieties. When the palms will began to fruit, it will be necessary to remove 10% to 30 % of these palms, those which are not true-to-type. Anyway, these removed palms could be replaced later.
The advantage of the hexagon design is that different units can easily be planted close the one to the other, as shown in the following plate (click to enlarge). This theoretical design could produce 6 tall varieties, 2 dwarf varieties and 18 hybrid varieties. Such an organization could be applied to the Olomanu seed garden.
By R. Bourdeix, V. Saena Tuia and Alofa Leuluaialii
This website returns the information collected during four scientific visits conducted in 2001, 2010, 2012 and 2017 on behalf the Ministry of Agriculture of Samoa, the International Coconut Genetic Resources Network, the Secretatiat of the South Pacific Community, the Global Crop Diversity Trust, Bioversity International and the French Centre for Agricultural Research and Development, Coconut Industry Development for the Pacific (CIDP project) and the Darwin Initiative "Saving Pacific Coconuts".