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ARS Home » Research » Publications at this Location » Publication #129377


item Oneill, Nichole
item Bauchan, Gary

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/2002
Publication Date: N/A
Citation: N/A

Interpretive Summary: Spring black stem and leaf spot is a major disease of alfalfa (Medicago sativa), the major high quality forage crop for cattle and horses in North America. The disease is caused by the fungus Phoma medicaginis, and there are no alfalfa cultivars with good resistance to this fungus. The disease causes millions of dollars in crop losses a year. In a search for sources of genes for resistance to the disease, we evaluated other species of Medicago for their reaction to the fungus. The annual Medicago species core collection, consisting of 201 lines representing 33 Medicago species was evaluated for resistance to the disease. This core collection is a small subset of the total collection. Plants of each line were sprayed with spores of the fungus and evaluated for disease severity. Most of the annual species and lines were susceptible to the disease. However, lines from 10 species exhibited high disease resistance. The identification of disease resistant lines among annual Medicago species offers the potential for utilizing resistance genes through breeding or genetic engineering methods, for the improvement of alfalfa. In addition the resistance found in these annual Medicago species will enhance their utilization as a forage crop. Alfalfa growers will benefit by being able to grow high quality, high yielding alfalfa.

Technical Abstract: The annual Medicago core collection, consisting of 201 accessions, represents the genetic diversity inherent in 3159 accessions from 36 annual Medicago species. This germplasm was evaluated for resistance to spring black stem and leaf spot caused by Phoma medicaginis. Spring black stem and leaf spot is a major destructive disease in perennial alfalfa (Medicago sativa) grown in North America, Europe, and other temperate regions. Disease control is based principally on the use of varieties with moderate levels of resistance. The degree of resistance found among accessions within species was variable, however most annual species and accessions were susceptible. Most accessions from 10 species exhibited high disease resistance. These included accessions of M. constricta, M. doliata, M. heyniana, M. laciniata, M. lesinsii, M. murex, M. orbicularis, M. praecox, M. soleirolii, and M. tenoreana. Most of the accessions within M. arabica, M. minima, M. lanigera, M. rotata, M. rugosa, M. sauvagei, and M. scutellata were highly susceptible. Disease reactions among some accessions within species were highly variable. On a 0-5 disease severity scale, rating ranged from 0.67 to 4.29 within accessions of M. polymorpha. Most of the M. truncatula and M. turbinata accessions exhibited significantly more susceptibility than accessions of other species.