Flow-Cytometric Analysis of Nuclear DNA Content in Vanilla Germplasm and Interspecific Hybrids: Implications for Breeding and Conservation

Vanilla planifolia, the principal source of natural vanilla flavor, is an economically important aromatic and medicinal crop. Its genetic improvement is constrained by a narrow cultivated genetic base, extensive clonal propagation, the long juvenile period before plants reach reproductive maturity, and limited cytogenetic information for wild relatives and interspecific hybrids. This study estimated 2C nuclear DNA content in 91 Vanilla accessions maintained at the University of Florida Tropical Research and Education Center, including 56 V. planifolia accessions, 21 accessions representing nine additional taxa, and 14 recorded interspecific hybrids. Young apical node tissue was co-chopped with Oryza sativa ssp. japonica ‘Nipponbare’ (2C = 0.795 pg), stained with propidium iodide, and analyzed by flow cytometry. Vanilla planifolia ranged from 3.32 to 4.13 pg 2C (3.25–4.04 Gbp equivalents), with a mean of 3.78 pg 2C (3.52 Gbp). Among the other taxa, V. phaeantha averaged 3.60 pg 2C (3.52 Gbp), whereas V. barbellata averaged 6.30 pg 2C (6.16 Gbp). The eight V. pompona accessions ranged from 5.74 to 6.19 pg 2C (5.61–6.05 Gpb). Recorded interspecific hybrids ranged from 3.57 to 7.36 pg 2C (3.49–7.20 Gbp). Several hybrid-designated accessions fell outside simple expectations based on the observed parental-species ranges, but flow cytometry alone cannot distinguish ploidy, aneuploidy, parentage, or peak-assignment effects associated with endoreplication. These data provide a comparative baseline for germplasm curation and identify accessions that warrant chromosome counting, molecular identification, parentage verification, and reproductive evaluation before breeding interpretation.