Molecular Characterization and Genetic Diversity of Yellow Passion Fruit Based on RAPD Markers

Molecular genetic variability studies are essential to complement the agronomic characterization of yellow passion fruit genotypes (Passiflora edulis Sims). Therefore, this study aimed at evaluating the genetic diversity of 24 genotypes of yellow passion fruit obtained from a research program developed by the University of Brasilia and Embrapa Cerrados, using RAPD molecular markers. RAPD markers were obtained from eight decamer primers and converted into a matrix of binary data, from which genetic dissimilarities among genotypes were estimated, and clustering analysis was performed. A total of 54 RAPD markers were obtained, with 6.8 bands per primer on average. From this total, 46 (85.2%) RAPD markers were polymorphic. The OPD10 primer presented the highest number of polymorphic bands. The high percentage of polymorphic markers evidenced the existence of genetic variability among genotypes. Nei’s genetic distance between genotypes ranged from 0.043 to 0.451. Clustering resulted in the formation of at least five groups of similarity.


Introduction
Passiflora is the numerically and economically most important genus of the Passifloraceae family.Its species are popularly known as passion fruit and have tropical and subtropical distribution.Among the 150 accepted species in Brazil (Bernacci et al., 2015), 70 produce edible fruits and, consequently, exhibit great economic importance for the Brazilian fruticulture (Cunha & Barbosa, 2002).Yellow passion fruit (Passiflora edulis Sims) is the species with the highest economic importance in the country due to its fruit quality, fruit yield, and industrial yield (Meletti & Brückner, 2001).
The Brazilian mean yield of yellow passion fruit is approximately 14.1 t ha -1 year -1 (Anuário Brasileiro da Fruticultura [ABF], 2018).Increased yields have been recently reported in the Brazilian savanna region.However, the national average is still considered as low based on the productive potential of the genetically improved cultivars grown under appropriate crop management practices (Neves, Jesus, Ledo, & Oliveira, 2013).Despite the low yields recorded, Brazil is the world's largest producer and consumer of passion fruit (ABF, 2018).
Breeding practices represent one of the most important strategies to increase yield, fruit quality, and disease resistance in passion fruit (Santos et al., 2011).As Passiflora is highly diverse, the characterization and utilization of this biological diversity may provide useful information for breeding programs with different results (Cerqueira-Silva, Jesus, Santos, Corrêa, & Souza, 2014).However, proper evaluation and quantification are required for efficient use of the genetic variability (Santos et al., 2011).
Studies into the genetic diversity of accessions generate important and useful information for germplasm collection, maintenance, and characterization (Faleiro et al., 2004).In this context, the use of DNA molecular markers and classical breeding procedures has been suggested as essential strategies to accelerate the production of new varieties that are adapted to different Brazilian regions (M.G. Pereira, T. N. S. Pereira, & Viana, 2005).
to demonstrate the existence of high genetic variability among Passiflora accessions (Bellon et al., 2005;Bellon, Faleiro, Junqueira, & Junqueira, 2007;F. G. Faleiro, A. S. G. Faleiro, Cordeiro, & Karia, 2003).As a result, RAPD markers have extensively contributed to the selection of parents and development of crossing plans in genetic breeding programs, as well as to the selection of improved plant materials (Bellon, Faleiro, Junqueira, & Fuhrmann, 2014;Fonseca, Faleiro, Junqueira, Barth, & Feldberg, 2017).Therefore, the objective of this study was to evaluate the genetic diversity of 24 genotypes of yellow passion fruit using RAPD molecular markers.
The reproducible RAPD markers were converted into a binary data matrix.The genetic distance among genotypes was estimated based on the complement of Nei and Li's similarity coefficient (1979), using Genes software (Cruz, 2013).The matrix of genetic distance was used for genotype clustering based on the unweighted pair group method with arithmetic mean (UPGMA).In addition, a graphical dispersion was generated based on the Multidimensional Scale (MDS) using the principal coordinates method.Analyses were performed using the statistical analysis system (SAS, 2004) and Statistica (Statsoft, 2000) software.

Results and Discussion
The eight primers generated a total of 54 RAPD markers.From this total, 46 (85.2%)RAPD markers were polymorphic.These results exhibit a polymorphism higher than the reported by Kososki (2014), who worked with P. edulis genotypes considered as promising sources of disease resistance (51.5%).The OPD10 primer presented the highest number of polymorphic bands whereas OPE16 exhibited the highest number of monomorphic bands (Table 1).The use of molecular markers is highly practical because it allows a fast study of the existing variability, with the attainment of a limitless number of genetic polymorphisms and no influence of the environment, in addition to allowing the detection of polymorphisms at any stage of plant development (Faleiro, 2007).In this study, the genetic variability among genotypes was confirmed by the high percentage of polymorphic markers.High polymorphism was reported by Bellon et al. ( 2014) when estimating the genetic variability in wild and commercial accessions of P. edulis.
Several authors have observed variability in yellow passion fruit.Bellon et al. ( 2007) recorded an average number of 14.4 bands per primer whereas Cerqueira-Silva et al. ( 2010) found 5.7 bands per primer.An average number of 6.8 bands per primer was observed in this study.Therefore, these data demonstrate considerable variability among genotypes, which can be exploited in future conservation and breeding researches.
Genetic variability among genotypes was expected to be detected since yellow passion fruit is a self-incompatible allogamous plant, which prevents self-fertilization and the crossing of different plants that contain the same incompatibility alleles (Santos et al., 2011).As a result, gene flow among genotypes is favored during cross-pollination.The high variability observed is also due to the broad genetic base observed in the passion fruit breeding programs of the University of Brasilia and Embrapa Cerrados, which is the result of crosses between accessions of different geographic origins at the base of the crossings (Bellon et al., 2005).
Genetic dissimilarities varied from 0.043 to 0.451 among genotypes.The highest genetic distance was verified between Rosa Intenso 3 and AP01 (Figure 1).As stated by Santos et al. (2011), the success of passion fruit breeding programs is closely related to the appropriate choice of divergent parents, which when crossed must result in wide genetic variability to be used for selection among segregating populations.Therefore, the identification of parents with high genetic variability has been a goal of many breeding programs that aim to explore the heterosis. jas.ccsenet.

Table 1 .
Primers used to obtain the RAPD markers and the respective numbers of polymorphic and monomorphic bands