International Journal of Horticulture, 2016, Vol.6, No.2, 1-10
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DNA banding pattern of each of the genotypes is expected to differ if they are genetically different. Even subtle
difference at genotypic level which other-wise some time could not be possible to differentiate by phenotyping,
can be confirmed by use of markers. The DNA markers could pave the way for success. Polymorphism
information content (PIC) ranged from 0.13(Primer OU-30) to as high as 0.86 (Primer OU-5). Thimmappaiah
(2011) reported a narrow range PIC from 0.147 to 0.354 with an average of 0.229 in 60 cashew nut accessions
using 20 RAPD markers In the present pursuit, PIC value of four RAPD primers e.g., OU 5, OU 16, OU 28 and
OU 34 were appreciably higher (>0.70) than the average PIC value of 0.568 over 15 primers and each such primer
had also revealed 100% polymorphism over the test genotypes. Thus, these RAPD primers may be considered
more informative in terms of the extent of polymorphism.
Rp (resolving power) value ranged from 3.64 (Primer OU-5) to as high as 15.36 (Primer OU-3) with a mean value
of 8.27. It is worth to note that the RAPD primer OU-34 revealed highest number of polymorphic bands (14) with
100% polymorphism as well as very high PIC and Rp values. Such a RAPD primer alone could discriminate all
28 cashew genotypes. Thus, this informative and discriminative primer is of immense value for study of genetic
diversity in a set of cashew genotypes. Similarly, Neto Silva et al. (1995) identified one of the 6 primers that
distinguished each of the 4 cashew clone seedlings. However, Ye Chunjiang
et al. (2005) proposed combination of
RAPD with ISSR primers for detection of new genomic loci for genome mapping, finger printing and gene
tagging.
A few of the RAPD markers were specific to test genotypes used. The cashew hybrids A 71 and E 16 revealed a
specific 2640 bp band amplified by Primer OU 3 (Figure 1a). In this context, band 280 bp and 210 bp produced by
Primer OU-34, were unique to D 19 and H 6 respectively (Figure 1c). Similarly, Primer OU 34 specifically
revealed three specific bands of fragment size 3250 bp, 1960 bp and 880 bp in VTH 711/4 and E 16; RP-2 and
Kalyanpur Bold Nut; and RP 1 and D 19 respectively. Further, it is worth to note that the polymorphic band of
fragment size 675 bp amplified by Primer OU 34 was unique to RP 1, RP 2 and Kalyanpur Bold Nut , but an
adjacent band of bit smaller amplicon size (530 bp) produced by the same primer was specifically absent in these
three parent varieties of cashew nut. Primer OU-28 produced a specific band of amplicon size 1340 bp in A 62 and
J 6; and another 485 bp amplicon in RP-1 and D 19 only. Neto Silva et al.
(1995) also detected cashew cultivars
using RAPD profiling. Tomar et al. (2014) scored 119 polymorphic amplicons and they reported presence of 34
unique bands specific to land races of mango.
The RAPD markers are dominant in nature and therefore, absence of a specific band could serve as valuable
information for varietal discrimination and assessment of genetic relationship. The 2160 bp and 680 bp
polymorphic bands produced by Primer OU-3 were specifically absent in J -20 and A 48; and E 16 and A 71
respectively. While 1320 bp band was amplified by RAPD primer OU-16 in all cashew test genotypes except G
8, H 6 and D 19 respectively. Similarly, OU-28 failed to reveal 1600 bp amplicon in A 62 and RP 1; and the
primer OU 34 also could not produce a 935 bp amplicon in cashew hybrid H 6 and D 19. Besides, the unique 1510
bp and 1120 bp band amplified by Primer OU 32 and Primer OU 34 were specifically absent in C 30 and H 6
respectively. The absence of characteristic bands in a few cashew test genotypes might be attributed to the fact
that these markers might be linked to negative traits. Thus, presence or absence of bands revealed by specific
primers could certainly serve as valuable markers for varietal identification (Samal, 2002) and more often could
serve as valuable markers for elimination of duplicates (Virk et al.
,
1995). Castiglione et al. (1993) used RAPD
markers to define all the commercial poplar clones including those which could not be distinguished with
morphological traits.
Similarity index value (S.I) between each pair of genotypes is likely to give a clear picture of the extent of
genomic homology in terms of gene content and nucleotide sequence. It ranged from 0.37 to as high as 0.71
between A 62 with J 6 with average S.I. value of 0.585. Thus, RAPD was found to be potent enough to sort out
divergent genotype combinations with similarity index value as low as 0.37. In this context, Thimmappaiah et al.
(2009) observed similarity co-efficient values varying from 0.43 to 0.94 between different pair of 100 cashew nut
