Читать книгу Biotechnology of Fruit and Nut Crops - Группа авторов - Страница 35

The first step in a breeding programme is germplasm collection and characterization of parental candidates for producing hybrids. Polymerase chain reaction (PCR)-based marker technologies, i.e. random amplified polymorphic DNA (RAPD), simple sequence repeats (SSRs), inter-simple sequence repeats (ISSR), amplified fragment length polymorphism (AFLP) and probe-based studies such as restriction fragment length polymorphism (RFLP) along with morphological traits have been used in cashew. Silva Neto et al. (1995) used an RAPD marker (OPB-15) to identify dwarf cashew seedlings. Mneney et al. (1997) and Mneney and Mantell (2001) described RAPD-based germplasm characterization of 20 cashew accessions in Tanzania. Their study showed very high levels of similarity among cultivars, demonstrating the lack of cashew germplasm diversity in Tanzania. Croxford et al. (2005) generated SSR markers for multiplex PCR analysis in four Anacardium species: A. occidentale, A. microcarpum, A. pumilum and A. nanum for obtaining species-specific markers. Cavalcanti and Wilkinson (2007) produced the first linkage map of the species to investigate the genetic basis of the economically important dwarfing trait and other agronomic characteristics. The resulting 19 resolved groups in the female map and 23 in the male map confirmed the ambiguity of chromosome number. Cavalcanti et al. (2012) screened 71 F1 genotypes for identifications of QTLs (quantitative trait loci) for yield-related traits: nut weight, male and hermaphrodite flowers. Eleven QTLs were detected: three for nut weight, four for male and four for hermaphrodite flowers. Santos et al. (2010) studied 66 F1 plants for QTLs associated with traits including colour, size and weight of cashew apple.

Other studies have included utilization of RAPD markers to describe 90 accessions in the germplasm collection of the Directorate of Cashew Research, Puttur, Karnataka, India (Dhanaraj et al., 2002). A comparative study involving RAPD, ISSR and AFLP markers was undertaken for 19 cashew accessions (Archak et al., 2002). Among the markers tested, AFLP was most useful for correlating markers specific to phenotypic characteristics. It was considered most suitable for selection of desired parental traits in breeding programmes. Archak et al. (2002) used a combination of RAPD and ISSR markers to report low diversity among the 24 selections and 11 hybrids from major cashew breeding centres in India. Samal et al. (2003) characterized cashew using RAPDs for cultivars grown in Orissa. Syed et al. (2005) reported the use of sequence-specific amplification polymorphism (SSAP) based on the Ty-1 copia retrotransposon sequence in cashew. The polymorphism in this locus and its correlation with phenotypic traits are more accurate than AFLPs. Thus, SSAP can be used to develop QTLs for various phenotypic traits in cashew. Thimmappaiah et al. (2009) characterized 100 accessions which included interspecific hybrids of A. pumilum, A. microcarpum and Anacardium orthonianum with A. occidentale using RAPD, ISSR and SSR markers for assessing germplasm diversity in the cashew population. Molecular markers and marker-assisted selection in cashew has been reviewed by Thimmappaiah et al. (2011). A ‘core collection’ of 54 accessions that could represent most of the genetic diversity in the entire population of 172 accessions using RAPD and ISSR was conducted by Thimmappaiah et al. (2011). In this study, they reported that cluster analysis using data generated by RAPD, ISSR and SSR resulted in cluster aggregation of cultivars, irrespective of their geographical location or place of origin. This molecular marker study was able to identify a conserved subset in the germplasm repository at the Cashew Research Station, Puttur, India (Thimmappaiah et al., 2016). Jena et al. (2016) have used RAPDs to characterize genetic diversity of cashew cultivars in Orissa, India.