Genetic and phylogenetic comparisons of the fast-growing species in genus Neolamarckia for breeding and industrial exploitation

The Neolamarckia Bosser genus consists of two species: Neolamarckia cadamba (Roxb.) Bosser and Neolamarckia macrophylla (Roxb.) Bosser, which are highly valued for industrial and medicinal applications in South Asian countries. The two species are sympatric and share several important characteristics in growth, wood quality, phytochemicals, and secondary meta-bolites. N. cadamba has been extensively utilized while N. macrophylla is rarely exploited. This article provides an overview of these two species from various aspects, specifically emphasizing their genetic relationships. Based on the organelle genomes, a single gene linked to cellulose synthesis, and molecular markers, the interspecific variation was initially analyzed, revealing a close genetic relationship between the two species. These results highlight the potential for cross-species research and pave the way for further exploration. Their evolutionary divergence and taxonomic positions within the Rubiaceae family require further clarification through nuclear genomes. Both species exhibited a moderate level of genetic diversity within populations in terms of nucleotide diversity per site with nrDNA ITS markers (π=0.1185±0.0242) for N. cadamba or heterozygosity with SSR markers (0.05~0.29) for N. macrophylla. While population genetic structure assayed with molecular markers was generally low in N. cadamba (Fst≈3 % in China), it could be high in N. macrophylla (Φ_st≈ 55 % in Indonesia). Quantitative genetic differentiation in wood traits was small among provenances of N. cadamba but remains to be investigated in N. macrophylla. The two species potentially have similar wood properties and low heritability of wood traits. Molecular studies on wood traits in both species are limited, emphasizing the significance and urgency of future research on genetic improvement of wood traits for industrial purposes, prompting action and making progress in this area.