# Genome-wide variation in and between two closely related underutilised horsegram species (Macrotyloma axillare and M. uniflorum, Fabaceae)

## TL;DR

This study explores genetic and morphological variation in two drought-tolerant legumes, horsegram and perennial horsegram, revealing significant genetic diversity, especially in African wild samples.

## Contribution

The study provides new insights into genetic and morphological differentiation and variation in two underutilized legume species, highlighting potential for crop improvement.

## Key findings

- M. axillare has 2.5 times more genetic diversity than M. uniflorum.
- African horsegram accessions are genetically distinct from South Asian ones.
- Four geographic clusters were identified within M. axillare.

## Abstract

The assessment of the degree and partitioning of genetic variation in crop populations and species is crucial to understand their adaptive evolution and provides vital knowledge to assist in the development of crops to combat food insecurity. Underutilised crops are understudied but are often drought-/heat-tolerant or nutritionally diverse; hence, as food security becomes more pressing, their investigations are increasing. Here, we focus on horsegram (Macrotyloma uniflorum (Lam.) Verdc.) and perennial horsegram (M. axillare (Meyer) Verdcourt), two closely related drought- and heat-tolerant underutilised legumes. Forty-two accessions were studied through phylogenetic and population genetic analysis and by measuring their seed and plant morphologies to assess genetic and morphological variation within and between the species. The species were distinct at the genetic level, with genetic diversity about 2.5 times greater in M. axillare than in M. uniflorum. Previously unsampled horsegram accessions from Africa were distinct from South Asia and therefore could contain novel genetic variation. Genetic variation suggested four clusters within perennial horsegram, which were largely structured by geography. Seed length is significantly greater in horsegram, and the two species differ in their dominant seed and stem colours, which could assist in-field identification. This work provides new insight into these species specifically and underutilised legumes more generally. Future investigations focused on identifying adaptive genetic variation are warranted to further reveal the potential of these crops in being optimized for promotion and commercialization, especially in countries which need more sustainable and reliable agricultural varieties to mitigate climate change.

Understanding the extent and partitioning of morphological and genetic variation in crops and their close wild relatives helps to identify novel variation that could be used in crop improvement. In our work we investigated two closely related underutilised legume crops called horsegram and perennial horsegram. We show that the species are morphologically similar, but a suite of characters can be used to differentiate them. Genetically the species are distinct; cultivated samples are closely related to each other, but wild samples of each are genetically variable. Wild samples from Africa in particular are the most variable, and novel adaptive variation may be present in these.