Project Number: WVA00293
CRIS Number: 0086478
Multi-State Project: NE-140
BIOLOGICAL IMPROVEMENT OF CHESTNUT AND MANAGEMENT OF THE CHESTNUT PATHOGENS AND PESTS
Investigators: MacDonald, W. L.
Performing Department: Plant & Soil Sciences -- 1825
Start Date: 10/01/1998
Termination Date: 09/30/2003
Reporting period: 01/01/2001 to 12/31/2001
Progress Report:
Two hypoviruses, introduced over a six-year period from 1992-97, are being evaluated for their ability to regulate chestnut blight in a 5,000 tree American chestnut stand in West Salem, WI. In 2001, the stand was subdivided into 12 plots representing various stages of disease development because of the increasing magnitude of the task to sample and culture isolates from cankers. Approximately 25% of the stems in the 12 plots are infected with 1,100 cankers. A European hypovirus CHV-1 [Euro 7] is the most commonly identified hypovirus and it has been associated with over 80% of the cankers that were treated with hypovirus between 1992-1997. Nontreated cankers on trees with treated cankers readily acquire hypovirus but cankers on previously uninfected trees that became infected since 1998 do not acquire hypovirus as rapidly. Subjective canker ratings indicate improvement in canker morphology in successive years. Additional vegetative compatibility types were discovered in 2001 but at very low frequencies. In another second field test, the periodic removal of competing vegetation on the survival of American chestnut is being evaluated with and without the introduction of hypoviruses. Over a 12-year period, the rate of tree mortality of the original sprouts has been similar among all treatments until 1996 when tree mortality in cleared plots slowed. In plots where a clearing regime was not maintained, little or no sprouting occurred and all stems now are dead. The number of cankers from which hypovirulent bark samples have been recovered always was greater from trees that received hypovirus inoculation. Further, hypovirus recovery increased with subsequent year samplings of the same cankers. A third field test has evaluated the influence of canker age and time of hypovirus introduction on the replication of hypoviruses in chestnut blight cankers. To accomplish this, sets of artificially established cankers were challenged over a one-year period in July, September, November, April, and July by introducing hypovirulent inoculum into the canker margin. A highly debilitating and a moderately debilitating hypovirus were compared. The highly debilitating hypovirus reduced canker growth regardless of the challenge date, with cankers treated in April showing the greatest reduction. The greatest recovery of hypoviruses also occurred in cankers treated in April regardless of the hypovirus employed.
Publications: (No publications.)
Impact:
The natural biological control of the chestnut blight fungus is known in several locations in North America and Europe. Our field and laboratory tests are to understand the mechanisms by which these hypoviruses become established and spread with the ultimate goal of employing them as biological control agents in eastern North America.