Diversity of Pummelos (Citrus maxima (Burm.) Merr.) and Grapefruits (Citrus x aurantium var. paradisi) Inferred by Genetic Markers, Essential Oils Composition, and Phenotypical Fruit Traits

Pummelo (<i>Citrus maxima</i>) is an ancestral species that has given rise to several major citrus varieties, such as sweet orange (<i>C. x aurantium</i> var. <i>sinensis</i>) and grapefruit (<i>C. x aurantium</i> var. <i>paradisi</i>). This species is also cultivated and its fruit consumed, particularly in Asia. Over the course of evolution, the allogamous reproduction of pummelos and the absence of asexual multiplication have contributed to its diversification. To assess its phenotypic diversity and the chemical composition of leaf and peel essential oils, genetic analysis using DNA markers is an essential prerequisite to ensure the identity and if varieties belong to this species. Fifty-eight accessions classified as grapefruits or pummelos were analyzed using 42 SSRs, 4 Indels, and 36 SNP markers. Based on the allelic composition of these markers, 20 cultivars were detected belonging to pummelos, 18 cultivars to grapefruits, and 11 were interspecific hybrids. The grapefruit inter-cultivar SSR diversity is null. The genetic origin of five interspecific hybrids is elucidated. The level of phenotypic diversity and of essential oil composition corroborate the modes of diversification, with high levels for those resulting from crosses and very low levels for the group of grapefruit mutants. Only the characteristics of breeding selection (pulp color, acidity and aspermia) are variable in grapefruits. In the composition of leaf essential oils (LEOs), nine profiles were detected in grapefruits based on variations in six compounds (neral, geranial, β-phellandrene, γ-terpinene, (E)-β-ocimene, and β-pinene). The seven interspecific hybrids involving pummelo as one parent show particular LEO profiles but without specific compounds, with the exception of p-cymenene which is present only in Wheeny. The diversity of peel essential oils in pummelos is lower, but variations in γ-terpinene, β-pinene, limonene, and myrcene make it possible to define seven profiles. With genetic verification the chemical and phenotypic diversity of the two species, pummelo and grapefruit, revealed in this study can be used as a reference for behavior in a specific environment.