David H. Griffin

Screening for Resistance to Hypoxylon Mammatum in Populus Tremuloides Callus and Micropropagated Plantlets

Two in vitro procedures are being tested for screening trembling aspen for resistance to Hypoxylon canker: (1) tissue culture response to fungal culture metabolites and (2) ascospore inoculation of moisture stressed plantlets. In the first procedure, the sensitivity of five clones to the acidic ethyl acetate (AEA) fraction of partially purified culture filtrate was determined by comparing callus growth on ACM medium containing the AEA fraction with that of a control containing non-inoculated culture filtrate. Treatments of 0.1x and 1.0x AEA concentrations were inhibitory compared with controls. The clones varied considerably in callus growth and callus inhibition, with the inhibition relative to growth of the control directly related to that growth. Correlations of the resistance responses of 10 year old ramets to artificial inoculations with mycelial-infested grain show a moderate positive correlation of both callus growth of the control and callus inhibition with canker length and with incidence of branch death.

Hypoxylon canker incidence and mortality in naturally occurring aspen clones

Cankers low on the bole were associated with mortality. Small stems had more cankers below the lowest living branch. The frequency of cankers above the lowest living branch increased with tree size, suggesting that the infection court occurs on branches. With increasing tree size, cankers on branches originate farther away from the bole and fewer cankers cause mortality. Considerable variation existed in disease incidence and mortality among the clones and four sample locations

Resistance in Aspen to Hypoxylon Canker

Hypoxylon canker of aspen has many of the features of an ideal system for studying woody plant defense mechanisms against fungi. The primary hosts, trembling and European aspens (Populus tremuloides and P. tremula) occur over broad geographic areas of the northern hemisphere, providing an immense array of genetic and environmental diversity for the development of this system. Less commonly affected hosts such as P. grandidentata, P. trichocarpa, P. balsamifera, P. alba, and others provide a foundation of plant materials with different levels of resistance and susceptibility. The capacity to generate hybrids among these and other nonhost poplars further expands the foundations of test plant materials.