The genus Rhynchostylis contains important commercial orchids in Thailand with high diversity, but limited information is available regarding the genetic diversity of these orchids. Rhynchostylis has a short blooming period, which makes more difficult to distinguish between variations based only on their appearances. This study evaluated the genetic variation among six accessions of Rhynchostylis, along with one Vanda and one Aerides accession collected from different locations in the northeast of Thailand using 16 polymorphic inter-simple sequence repeat (ISSR) markers. The ISSR markers comprised 83 alleles with sizes ranging from 208 to 1,223 bp. The average number of alleles per locus was 5.19, with a standard deviation of 3.49. The average percentage of polymorphic bands was 95.21%. Polymorphism information content (PIC) values ranged between 0.05 and 0.44, with a mean average of 0.21. The calculated genetic similarity coefficients ranged from 0.383 to 0.914, suggesting a high level of genetic diversity among all the samples. UPGMA dendrograms were created using genetic similarity coefficients and divided into three main clusters. Cluster I contained four closely related R. gigantea orchids. Cluster II comprised two accessions, R. gigantea var. vivaphandhul and V. coelestis, while Cluster III contained two accessions of R. retusa and A. houlettiana. Based on ISSR data, the genetic similarities among the 8 orchid accessions do not correlate with flower color phenotypes and sampling locations, except for Cluster I. The results suggest that ISSR markers can effectively assess the genetic information of both wild and cultivated orchid resources. This study provides useful information for further development of novel markers specific to orchid varieties and for assisting the success of orchid breeding programs through the selection of parent plants.

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• Phylogenetic relationship based on DNA barcodes and comparative analysis of phytochemical contents among Rhynchostylis orchids in Thailand
  Juthaporn Saengprajak, Jirapa Phetsom, Aphidech Sangdee, Arnusorn Saengprajak, Thanwanit Thanyasiriwat, Wuttipong Mahakham
  Scientific Reports.2026;[Epub]     CrossRef
• Development of ISSR-derived SCAR markers for precise identification and conservation of Rhynchostylis gigantea and its variety rubrum in Thailand
  Juthaporn Saengprajak, Thanwanit Thanyasiriwat, Arnusorn Saengprajak, Aphidech Sangdee
  South African Journal of Botany.2026; 189: 551.     CrossRef