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United States Department of Agriculture

Agricultural Research Service

Title: First Report of Phytophthora Megasperma F. Sp. Medicaginis Causing Phytophthora Root Rot on Annual Medicago Spp.

Authors
item Dehaan, Robert - UNIVERSITY OF MINNESOTA
item Sheaffer, Craig - UNIVERSITY OF MINNESOTA
item Samac, Deborah

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 12, 1996
Publication Date: N/A

Interpretive Summary: Annual medics are currently being tested for use as weed suppressing smother crops, cover plants in row crop production, and for short season forage crops. Use of annual medics has the potential of increasing soil fertility, decreasing use of herbicides and soil erosion. Annual medics are native to regions surrounding the Mediterranean Sea, and commercial varieties have been primarily selected in Australia. Therefore, most plan types have not been exposed to many of the diseases prevalent in the Midwestern US. Selection and use of disease resistant plants will be important for successful use of annual medics. Commercial varieties and plant introductions seeded into a Phytophthora root rot (PRR) disease nursery in St. Paul, MN, in 1992 and 1993 were evaluated for symptoms of PRR. Plants from all varieties and most plants from the plant introductions developed symptoms of PRR. Symptoms included death of seedlings, plant stunting, leaf yellowing, and root rotting. Plant mortality was 18 to 100% depending on the plant type. A greenhouse seedling test was used to show that the fungus causing PRR on alfalfa also causes PRR on annual medics. Resistant plants were identified in several plant introductions indicating that disease resistant varieties can be bred that will thrive in the Midwestern US.

Technical Abstract: Varieties and plant introductions of annual Medicago spp.(annual medics) seeded into a Phytophthora root rot (PRR) disease nursery in St. Paul, MN in 1992 and 1993 were evaluated for symptoms of PRR. Plants from all varieties and most plants from the plant introductions developed symptoms of PRR. Symptoms included damping off of seedlings, plant stunting, leaf yellowing, and root necrosis. Plant mortality was 18 to 100% depending on germplasm. The germplasm tested included Medicago littoralis cv. Harbinger AR, M. polymorpha cvs. Santiago and Serena, M. rugosa cv. Paraponto, M. scutellata cvs. Kelson and Sava, M. truncatula cvs. Caliph and Mogul, and plant introductions of M. polymorpha, M. tornata and M. truncatula. In a greenhouse assay, 7 day old seedlings of M. scutellata cv. Sava and two plant introductions of M. polymorpha (PI 368939, SA1327) were inoculated with two strains of P. m. medicaginis (M2019 and FD1206, C. Grau, Univ. Wisc.) pathogenic on alfalfa. Symptoms of PRR were rated 14 days later on a 0 to 5 scale. Both strains caused PRR symptoms on plants from the three germplasms and P. m. medicaginis was reisolated from diseased roots and hypocotyls. The percentage of resistant plants, rated 0 to 2, were: PI368939 67%, SA1227 31%, 'Sava' 0%. Use of annual medics in the Midwestern United States as weed suppressing smother crops, cover plants in row crop production, and for short season forage crops is currently being investigated. Annual medics are native to regions surrounding the Mediterranean Sea and commercial varieties have been primarily selected in Australia. Therefore, most germplasm has not been exposed to many of the diseases prevalent in the Midwest. Selection and use of disease resistant germplasm will be important for successful use of annual medics.

Last Modified: 8/21/2014
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