Descriptors 213
usually possible until fruit production. Papaya germplasm shows considerable phe-
notypic variation for many horticultural traits (Ocampo et al. 2006). The different
criteria, which are used to estimate genetic diversity, include pedigree records, mor-
phological traits and molecular markers. Plant taxonomy is traditionally dependent
upon the comparative external morphological characters (Baxy 2009). However,
these are environmental and developmental stage dependent. Therefore, molecular
markers are preferred choice for plant identification as they are detectable in all
tissues and independent of environmental changes (Tapia et al. 2005). For the devel-
opment of papaya hybrids, pure lines are needed in order to avoid F 1 segregation.
Classical improvement procedures to obtain papaya lines are based on the inbreed-
ing of segregating populations and of germplasm accessions of Carica papaya L.
This strategy results in the selection of pure lines through progeny testing, which
can take up to five to six inbreeding generations (average 12 years), depending on
the genetic diversity of the background. The pure lines are then identified among the
progenies whose phenotypical segregation is considered to be null. Notwithstanding,
this methodology is expensive, laborious, time- and space-consuming, and influ-
enced by negative conditions in the environment.
Genetic diversity was determined using several molecular markers namely, ran-
dom amplified polymorphic DNA (RAPD), inter-simple sequence repeat (ISSR),
amplified fragment length polymorphism (AFLP), simple sequence repeat (SSR)
markers, and so on, have been used for analysis of genetic diversity, relationships
and germplasm identification of papaya (Jesus de et al. 2012), computing allelic
richness and frequency, expected heterozygosity and cluster analysis. Among the
molecular markers, RAPD and ISSR markers have been extensively used to study
genetic diversity and relationships in papaya germplasm (Rodriguez et al. 2010;
Sudha et al. 2012; Saran et al. 2015). Among these molecular markers, ISSRs and
SSRs are considered to be useful and have been extensively used for the identifica-
tion of species or germplasm in a wide range of plants (Ahmad et al. 2010). ISSR
amplifies inter-microsatellite sequences at multiple loci throughout the genome (Li
and Xia 2005) and permits the detection of polymorphism in microsatellites and
inter-microsatellite loci without previous knowledge of DNA sequences. These
markers can detect polymorphism in a single reaction with a good repeatability and
reproducibility (Saran et al. 2015). Knowledge of genetic variability is very use-
ful for identifying the best combinations between germplasm lines with the poten-
tial to maximise the genetic gains attained by hybridisation (Bertan et al. 2009).
Although the level of genetic diversity revealed by SSR markers is sufficient to
distinguish between breeding lines for varietal protection, the rather narrow genetic
diversity demonstrated indicates the need to introduce new germplasm or use other
techniques such as mutation and genetic engineering to provide breeding materials
for the future improvement. Genetic diversity was determined using seven simple
sequence repeat (SSR) markers. Although the level of genetic diversity revealed by
SSR markers in this study is sufficient to distinguish between breeding lines for
varietal protection, the rather narrow genetic diversity demonstrated indicates the
need to introduce new germplasm or use other techniques such as mutation and
genetic engineering to provide breeding materials for the future improvement of
papaya (Asudi et al. 2013).