Characterization and pre‐breeding of diverse alfalfa wild relatives originating from drought‐stressed environments

Abstract

Changing climates and associated increased variability pose risks to alfalfa (Medicago sativa L.) cultivation, with the requirement to establish, survive, and maintain production under water stress. Crop wild relatives (CWR) of alfalfa include populations that have evolved to survive in a number of different, extreme environments, but until recently have had limited use in breeding programs. Here we report on the phenotypic diversity of alfalfa crop wild relatives that were selected to represent extremes in drought tolerance (by sourcing germplasm from environments with extremes in low rainfall, high temperature, shallow soils, and winter freezing) with the aim of providing germplasm with drought tolerance and improved forage yield traits for breeding programs in both warm and cool dry temperate environments. Newly formed hybrids created between M. sativa, M. arborea L. (a woody shrub), and M. truncatula Gaertn. (an annual species from the Mediterranean region) were developed or acquired to introduce new genetic diversity from the tertiary genepool. Preliminary characterization and evaluation was used for taxonomic classification, and to identify wild accessions and pre‐bred (hybrid) lines that offer new diversity for growth habit, seed size, fall dormancy, and forage yield. The accessions and pre‐breeding lines described have been donated to the Australian Pastures Genebank for conservation and distribution.

Phenotypic Diversity and Productivity of Medicago sativa Subspecies from Drought-Prone Environments in Mediterranean Type Climates

“…There is evidence that the genetic diversity of Medicago sativa has been reduced during the domestication process; indeed, cultivated alfalfa has lost about 30% of its genetic diversity compared to wild populations [ 9 ]. It has been proposed that landraces and wild relatives of alfalfa encompass greater genotypic and phenotypic diversity than commercial cultivars, as well as adaptive traits to survive in extreme drought stress conditions [ 10 , 11 , 12 , 13 ].…”

“…These subspecies represent the primary gene pool for alfalfa improvement [ 10 , 11 , 14 ]. Recently, Humphries et al [ 10 ] pointed out that primary gene pool offers great potential for alfalfa drought tolerance improvement. Indeed, most of the subspecies are originally from arid zones or drought-prone environments of Eurasia.…”

“…Many (by no means all) populations of subsp. falcata and varia occur in arid areas, and are potential sources of drought-resistant germplasm [ 10 ]. Some wild M. sativa subsp.…”

“…Recently, researchers have attempted the introgression of favorable traits from M. arborea genome to M. sativa subsp. sativa such as drought tolerance [ 10 , 17 , 18 ]. Hybrids between M. sativa subsp.…”

Crop Science special issue: Adapting agriculture to climate change: A walk on the wild side

“…The next step in the pre-breeding process is to characterize and evaluate CWR populations and CWR-derived lines. A set of papers focuses on improving drought, heat or salinity stress-related traits and includes Humphries et al (2021), "Characterization and pre-breeding of diverse alfalfa wild relatives originating from drought-stressed environments," who report that newly developed alfalfa hybrids between Medicago sativa x M. arborea and M. sativa x M. truncatula from the tertiary genepool offer new diversity useful to improve growth habit, seed size, fall dormancy and forage yield. Simon et al (2021), in "Wild carrot diversity for new sources of abiotic stress tolerance to strengthen vegetable breeding in Bangladesh and Pakistan," describe new sources of heat and drought tolerance in two wild Daucus species (also see the podcast about their paper: https://fieldlabearth.libsyn.…”