Читать книгу Biotechnology of Fruit and Nut Crops - Группа авторов - Страница 111

From the early 1980s to the mid-1990s, characterization of coconut germplasm diversity involved isozymes and polyphenols as biochemical markers (Carpio, 1982; Jay et al., 1989; Fernando et al., 1997). In the late 1990s, there was a major shift towards using molecular markers to examine the genetic diversity of coconut. A wide range of molecular marker approaches have been employed, including; (i) inverse sequence-tagged repeat (ISTR) (Rohde et al., 1995; Duran et al., 1997); (ii) randomly amplified polymorphic DNA (RAPD) (Ashburner et al., 1997; Duran et al., 1997; Rodriguez et al., 1997; Wadt et al., 1999); (iii) restriction fragment length polymorphism (RFLP) (Lebrun et al., 1998); (iv) amplified fragment length polymorphism (AFLP) (Perera et al., 1998); and (v) microsatellites or simple sequence repeat (SSR) (Karp, 1999; Perera et al., 1999; Teulat et al., 2000). These studies have laid the foundation for the construction of a linkage map estimating the physical position of genes of interest or loci QTL on the chromosomes.

In particular, one study (Herrán et al., 2000) constructed linkage maps for two parents of the cross ‘Malayan Yellow Dwarf × Laguna Tall’, showing six QTL links with some important plant traits such as early flowering and higher yield. Further analysis using the same mapping population revealed a number of QTLs related to other characteristics, namely leaf production and trunk girth (Ritter et al., 2000). By analysing the linkage map constructed for Rennell Island Tall in the Solomon Islands, another study (Lebrun et al., 2001) identified QTLs which were linked to bunch and fruit number. Apart from yield-related traits, MAS has been used to improve lethal yellowing disease resistance. Several hybrids including Dwarf × Tall, Tall × Dwarf and Tall × Tall have been characterized by RAPD analysis to identify markers associated with resistance to that phytoplasma disease (Cardeña et al., 1999).

Diversity and genetic relationships in coconut populations from different geographic regions have been evaluated using microsatellite markers (Xiao et al., 2013; Loiola et al., 2016). The technique has also been applied to characterize a wide range of coconut varieties in India (Rasam et al., 2016). This study also uncovered variation between varieties and suggested the need for artificial pollination within each population to maintain seed purity.