Isolation of Nectria galligena from Cankers on Sweet Birch.

Arthur H. Graves (3) was the first per-son to describe Nectria canker on sweetbirch (Betula lenta) in the United States.Writing in 1919, he said that G. P. Clinton,from The Connecticut Agricultural Ex-periment Station, had found cankered birchtrees in New Haven in 1906, and Gravesfound the disease in Orange in 1909 and inMilford, Connecticut in 1918, as well as inNew York City (3). In Kienholz and Bid-well’s 1938 survey of tree diseases in Con-necticut forests, they reported that, of 813plots where B. lenta was found, 314 of theplots had B. lenta with cankers. The aver-age percentage of cankered trees rangedfrom 2 to 53%, and there was an averageof 4.6 cankers per tree.Early workers found it difficult to isolatethe pathogen from canker tissue, and usu-ally used easily obtained ascospore iso-lates. Ashcroft (1) studied the pathology ofthis fungus using 28 isolates from perithe-cia but had only 1 (from Pyrus malus)from the wood of a canker. Plante andBernier (6) recently reported that GoldenDelicious apple fruit can be used as “host”for virulence tests with isolates of N. galli-gena. This reminded us that Crandall, Gra-vatt, and Ryan (2) had successfully isolatedPhytophthora cinnamomi from roots ofchestnut trees with Ink Disease using themethod of C. M. Tucker, in which sliversof wood and inner bark from infected tis-sue were forced into an apple.“Granny Smith” apples are availableyear-round in markets in Connecticut. Ap-ples were carried to the forest during sur-vey trips, and cankers from marked B.lenta trees were sampled. A pocket knifeblade was sterilized in 95% ethanol andused to scrape away the bark surface. Theknife blade and our fingers were dipped inethanol again and used to remove smallpieces of cankered bark. The pieces werestabbed into the apple flesh, and the appleskin was marked with the tree number(Fig. 1). Back in the laboratory, the appleswere placed in clear plastic boxes withlids, and incubated in the dark in a cabinetat room temperature. Dark discoloration ofthe apple tissue expanded very slowly fromthe bark chip (Fig. 2). After 10 to 15 days,pure cultures of N. galligena were recov-ered by pealing away the skin, carefullyremoving a bit of the discolored tissue witha scalpel, and placing it on a petri platecontaining potato dextrose agar (DifcoLaboratories, Detroit). Other organismsoccasionally grew out from the bark intothe apple tissue, causing rapidly spreading,water-soaked lesions. Isolations from suchareas usually yielded bacteria or rapidlygrowing fungi, including Pestalotiopsis.ABSTRACTAnagnostakis, S. L., and Ferrandino, F. J. 1998. Isolation of Nectria galligena from cankers onsweet birch. Plant Dis. 82:440-441.The fungus Nectria galligena infects many species of hardwood trees, causing “perennial can-ker,” “European canker,” or “target canker.” Cultures from ascospores produced in stromata onthe cankers have confirmed the pathogen species, but the fungus has rarely been successfullyisolated from inside the cankers. Concern for the sweet birch trees affected by this disease inConnecticut prompted us to try isolations, using a method successful in isolating chestnut treepathogens. Small pieces of cankered bark were stabbed into Granny Smith apples and, afterincubation in boxes in the laboratory, pure cultures of N. galligena were easily removed as thepathogen slowly grew out, unchallenged, into the tissue of the apples. This technique will nowbe used to sample the N. galligena population in the birch populations being studied.Additional keywords: Betula lenta, European canker, Nectria canker, perennial canker, targetcanker