Submitted to: Compendium on Alfalfa Diseases
Publication Type: Book / Chapter
Publication Acceptance Date: December 5, 2012
Publication Date: N/A
Technical Abstract: Corky root rot (corchosis) was first reported in Argentina in 1985, but the disease was presumably present long before that. The disease occurs in most alfalfa-growing areas of Argentina but is more common in older stands. In space-planted alfalfa trials scored for root problems, corky root rot was one of the most prevalent diseases. The disease is characterized by thinning stands and lack of recovery after cutting. The causal agent first destroys the lateral roots and then produces a dry, brown, sunken canker on the taproot. The canker increases in size until it surrounds the main root and separates from healthy tissue under the lesion. The fungus eventually invades the entire root, and the plant dies. The root maintains its original shape but is much lighter in weight and corky, with patches of white mycelium mixed with darker areas. The fungus also can penetrate the root from the crown to form a dry rot. A typical isolate of the fungus was identified as a species of Xylaria at the Commonwealth Mycological Institute and registered under IMI 281351. Colonies on potato dextrose agar are white when young and change to dark olive gray to black as they age. The fungus forms spathulate stromata having hyaline, unicellular, ovoid conidia that measure 6.9 X 2.3 um.