Читать книгу Biotechnology of Fruit and Nut Crops - Группа авторов - Страница 108

Farmers traditionally planted seedlings from their own best palms, but they could not avoid pollination from nearby unselected palms. The genetic gain from selection in a regime of open pollination is limited. Cross-pollination by hand between high yielding parent palms was first undertaken in 1926 in Fiji using red MD as the seed parent and Niu leka (an indigenous robust Fijian Dwarf) as the pollen parent. To produce hybrid fruit commercially, alternate rows of two or more varieties were inter-planted and selectively emasculated to produce F1 hybrids.

The CIRAD (French Agricultural Research and Development Organization) breeding programme in the Ivory Coast has used reciprocal recurring selection as a starting point, by exploiting ecotype combining ability, and basing phenotypic choices on inheritable characters (Gascon and de Nucé de Lamothe, 1978). Genetic improvement involving hybridization between populations from different environments resulted in a doubling of the number of hybrids produced within 20 years. Hybrids can be produced on a large scale, e.g. 1 ha of highly productive fruit-bearing trees can produce c.15,000 fruit per annum by assisted pollination (de Nucé de Lamothe and Wuidart, 1992). This method requires emasculation of the female parent and then manual or assisted pollination (Wuidart and Rognon, 1981). However, the cost of the resulting selected seed-nuts can be too expensive for smallholders (Verdeil et al., 1998). Dwarf × Tall F1 hybrids became available in commercial quantities in the 1970s, and a few seed gardens of these hybrids can still be found in several countries. The planting of these hybrids was promoted by national, bilateral and international agencies and private companies, and this has met with mixed success.

According to Baudouin (1999), the efficiency of breeding can be improved by: (i) combining genetically distant genotypes to increase heterosis; (ii) increasing selectable diversity in breeding populations; (iii) using molecular marker and quantitative trait loci (QTL) to increase selection efficiency using marker-assisted selection (MAS); and (iv) using in vitro propagation for rapid dissemination of the genetic gain (Verdeil et al., 1998). A constraint on these breeding approaches, however, arises from the invisible susceptibilities to biological hazards that are similar and different between geographically distant populations. For example, the Malaysian Tall was introduced into the Solomon Islands in the 1920s, where the indigenous leaf beetle Brontispa longissima inflicted severe damage, requiring expensive protection in the seed garden and nurseries (Levers Pacific Plantations, unpublished data).