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- Author or Editor: Dimuth Siritunga x
Native to Central America, papaya (Carica papaya) is one of the most cultivated fruit crops in the tropical areas of the world. Genetic diversity analyses are an important aspect of conservation of plant genetic resources. In the island of Puerto Rico, where papaya has been consumed for centuries, knowledge on the genetic diversity of papaya is lacking. Therefore, 162 papaya accessions were evaluated using 23 simple sequence repeat (SSR) markers. Of these accessions, 139 were farmer-held samples from Puerto Rico, 13 were U.S. Department of Agriculture (USDA) repository samples, and 10 were commercial varieties. A total of 214 alleles were identified with a mean observed heterozygosity (Ho) of 0.219. Inbreeding coefficient (F) was 0.565, and when evaluating the population structure of these accessions, 2 groups (k = 2) were identified. Unweighted pair group method with arithmetic mean (UPGMA) dendrogram showed no geographical organization within the unknown Puerto Rican samples. This assessment provides an extensive record of the genetic diversity of papaya in Puerto Rico which can contribute to breeding strategies and to the conservation of papaya genetic resources in the Caribbean.
Papaya ringspot virus (PRSV) devastates papaya production worldwide. In Puerto Rico, papaya fields can be completely infected with PRSV within a year of planting. Information about the diversity of the Puerto Rican PRSV (PR-PRSV) population is relevant to establish a control strategy in the island. The coat protein gene (cp) of PRSV was sequenced from 62 isolates from different regions in Puerto Rico. The viral population of PRSV in Puerto Rico has 4% nucleotide and 5% amino acid diversity. Analysis of the coat protein (CP) amino acid sequence showed a variable amino terminal (N-terminal) region with a conserved aphid transmission motif and a variable EK repeat region. The core and carboxyl terminal (C-terminal) region were conserved. In the phylogenetic analysis, Puerto Rican isolates grouped independently of their geographical origin, with the exception of southern isolates that formed two separate subgroups and were the most divergent. Sequences of the cp from the Puerto Rican isolates, when compared with sequences from other countries, showed least genetic distance with isolates from the United States and Australia, followed by other American and Caribbean isolates. The U.S. and Australian isolates are sister taxa to the Puerto Rican isolates in the phylogenetic tree. This suggests that PRSV from Puerto Rico and the isolates from the United States and Australia have a common origin thought to be from a Mexican population.
The Solanaceae family is one of the largest and well-distributed plant families in the world. It contains species of agricultural and economical importance, such as Solanum tuberosum, Solanum melongena, Solanum lycopersicum, Nicotiana tabacum, and Capsicum annuum. In Puerto Rico, there are ≈46 species of Solanaceae of which six are endemic: Brunfelsia densifolia, Brunfelsia lactea, Brunfelsia portoricensis, Goetzea elegans, Solanum ensifolium, and Solanum woodburyi. Our objective was to use DNA barcoding to identify the Solanaceae species in Puerto Rico, including the endemics, and to assess the species relationships between them. To accomplish our objective, two chloroplast regions (psbA-trnH and matK) and a nuclear region [internal transcribed spacer (ITS)] were assessed. Pairwise distance and phylogenetic analysis demonstrate that DNA barcoding can be used to discriminate at the species level among these taxa in Puerto Rico. For all three markers, the genus that showed the highest pairwise distance between represented species was Solanum, whereas the genus that displayed the least was Capsicum. Phylogenetic trees of single and concatenated regions were generated from sequences obtained in this study and from data downloaded from the National Center for Biotechnology Information database. Our results show that this technique can be used to identify species with one, two, or three combinations of DNA barcode markers depending on the taxon. In addition, this is the first study to include the endemic species S. woodburyi in a molecular phylogenetic analysis, and it was found to have a close relationship with S. ensifolium, also endemic to Puerto Rico, and to Solanum bahamense from the Bahamas and Greater Antilles. Therefore, we suggest that S. woodburyi might be part of the Bahamense clade.