Molecular analysis of intracultivar polymorphism in 'Peddarasam' mango (Mangifera indica L.) using microsatellite markers

Genetic heterogeneity within clones in various clonally propagated fruit crops is assumed to be very limited. 'Peddarasam' mango is one of the choicest, juicy cultivars of mango (Mangifera indica L.) in the Indian state of Andhra Pradesh for which genetic homogeneity has never been demonstrated. Fruit and leaf samples of 25 accessions of 'Peddarasam' (PR Acc-l to PR Acc-25) covering the three eco-geographical regions (Telangana, Rayalaseema and Coastal Andhra) of the state were collected through an exploration survey during the summer of 2009. Morphological descriptors and microsatellite markers were used to determine the intravarietal polymorphism. Of the 109 mango-specific microsatellites validated, 56 primers amplified 144 polymorphic bands ranging from 100 - 300 bp. The polymorphic information content ranged from 0.03 to 0.82 with an average of 0.50. Jaccard's similarity coefficient ranged between 0.36 and 1.00 signifying wide amplitude (64%) of intracultivar polymorphism, which is the probable reason for heterogeneity in production and quality of this cultivar across the state. Occasional seed propagation, occurrence of bud sports and de novo variation at the SSR loci are likely to be responsible of the intravarietal polymorphism. Microsatellite analysis revealed high intracultivar polymorphism attesting that 'Peddarasam', which is cultivated throughout Andhra Pradesh state, is not a pure clone, a fact which allows the genetic breeding of this cultivar by means of mass selection. SSR-82, SSR-15 and MngSSR-24 produced unique solitary alleles of 130 bp, 245 bp and 150 bp for PR Acc-10, PR Acc-12 and PRAcc-15, respectively, which will enable better identification of accessions from now onwards. Microsatellite markers were proven to be useful in assessing intracultivar polymorphism and identifying accessions of 'Peddarasam'. These results provide evidence that genetic variation among 25 accessions of 'Peddarasam' is present and can be further utilized in breeding programs.