Screening for resistance to Seiridium cardinale, S-cupressi, and S-unicorne isolates in glasshouse-grown seedlings of Cupressaceae

Young glasshouse grown seedlings, 18-months-old, of several species within the Cupressaceae were inoculated with the canker-causing pathogens Seiridium cardinale, S. cupressi and S. unicorne at two positions: position 1, 35-40 cm above the root colar and position 2, 1.5-2.0 cm a.r.c. In terms of the lengths of lesions caused on inoculated stems, S. cardinale proved more virulent than S. cupressi or S. unicorne on all Cupressus species. S. cupressi was more virulent than S. unicorne only on C. macrocarpa. C. macrocarpa was the most susceptible to S. cardinale (at position 1 and 2), C. sempervirens and C. torulosa were also susceptible whereas C. arizonica was moderately susceptible to this pathogen (position 1). In contrast, Chamaecyparis lawsoniana was highly resistant to S. cardinale (position I and 2) but was more damaged by S. cupressi at position 1 and S. unicorne at position 2.

Intraspecific variation in susceptibility to S. cardinale was found in C. sempervirens seedlings (inoculated at position 2) from four different seed sources which developed different canker lengths after 50 days, although this variation was lower than between species variation.

Cankers developed more rapidly when inoculations were made 35-40 cm above the root collar, where the periderm had formed recently, than when made 1.5-2.0 cm above the root collar, where rhytidome development had occurred, suggesting that older bark is more resistant than younger bark to growth of Seiridium.

Inoculation of seedlings of C. sempervirens (Krete provenance) with 8 different isolates of S. cardinale showed the relatively low variability in virulence within this pathogen species. Only single isolate caused lesions <10 mm in length around the inoculation points 30 days after inoculation, whereas the other 7 isolates caused lesions of approximately 30 mm in length in the same time period.

These results correlate well with those published from previous studies where inoculations were made on older trees and demonstrate the utility of this method in the early screening of Cupressus seedlings for resistance to Seiridium canker and testing the virulence of the three fungus species.