Transfer of anthracnose resistance and pod coiling traits from Medicago arborea to M. sativa by sexual reproduction

Abstract

Five asymmetric hybrid plants were obtained between Medicago sativa (2n = 4x = 32) and Medicago arborea (2n = 4x = 32) through sexual reproduction and the use of a cytoplasmically male sterile M. sativa genotype. Over 2,000 pollinations were made to obtain these hybrids. Amplified fragment length polymorphism (AFLP) analysis showed that in the most studied hybrid (WA2273), 4% of the bands unique to the M. arborea parent were present, versus 72% for the unique M. sativa bands. This suggests that only a single M. arborea chromosome or chromosome parts has been transferred. WA2273 had 7% of AFLP bands which were not present in either parent, which is suggestive of chromosome rearrangements as would be expected if only chromosome parts or a single part had been transferred from M. arborea. Phenotypic evidence for hybridity was obtained for pod coiling (1.4 coils in WA2273 versus three coils in the M. sativa parent and its self and testcross populations, and one coil in M. arborea), and Colletotrichum trifolii race 2 resistance (transferred from the resistant M. arborea parent, as the M. sativa parent and the self populations were highly susceptible). The hybrids were self sterile, but were female fertile to a high level when crossed with 4x, but not 2x, M. sativa, indicating they were at or near 4x. Both the pod coiling trait and anthracnose resistance segregated in the progeny of testcrosses between WA2273 and M. sativa. The work demonstrates that agronomically useful traits can be introgressed into M. sativa from M. arborea by use of male sterile M. sativa and sexual reproduction.

The Hybridization Barrier between Herbaceous Medicago sativa and Woody M. arborea Is Weakened by Selection of Seed Parents

“…No differences as pollen parents in crosses with alfalfa have been detected. M. arborea plants used in Queensland traced to the accession SA30528 = CPI131489, collected in Spain [ 9 ].…”

“…Eventually, an alfalfa seed parent that produced progeny with hybrid traits was identified in 2003 [ 8 ]. Seed from this seed parent was sent to Australia, where the hybridization was repeated [ 9 ]. This was the first level of weakening the hybridization barrier.…”

“…The first hybrids from both programs have most of the alfalfa genome with introgression of parts of the M. arborea genome, based on DNA analysis [ 9 , 10 , 11 ], and contain much new variation for alfalfa breeding. Recently, anthracnose resistance was transferred from M. arborea to alfalfa [ 9 ], and alfalfa × M. arborea derivatives have been used in alfalfa breeding [ 10 ]. Also, traits, such as larger seed and vegetative organs, are currently being backcrossed into alfalfa.…”

Phylogeny and character evolution in Medicago (Leguminosae): Evidence from analyses of plastid trnK/matK and nuclear GA3ox1 sequences

“…sativa and M . arborea have been produced ( Bingham, 2005 ;Armour et al, 2008 ). (2) Section Lupularia, presently containing the two species M .…”

Evidence That 2n Eggs Explain Partial Hybrids between Medicago sativa and Medicago arborea

“…Herbaceous alfalfa, Medicago sativa (L.) and woody M. arborea (L.) were considered reproductively isolated until 2003, when an alfalfa seed parent was found in Wisconsin that produced hybrids [ 1 ]. The interspecific hybridization was repeated in Australia and chromosome counts indicated hybrids were 4x/near 4x [ 2 ]. Analysis of DNA indicated that hybrids contained mostly alfalfa DNA and traits, but also contained DNA and traits from M. arborea .…”