SCREENING PINUS-SYLVESTRIS FOR RESISTANCE TO SPHAEROPSIS-SAPINEA

Artificial inoculation was used to determine if It is feasible to scre en for resistance to Sphaeropsis sapinea (FR.) DYKO and SUTTON in 2-ye ar old seedlings of Pinus sylvestris L. Six varieties were exposed to 2 spore concentrations in outdoor mist chambers. Inoculations were rep eated on 4 dates in late spring to early summer. Varieties differed in infection incidence, indicating potential resistance. Phenological gr owth stage of seedlings was more important than date of inoculation; i nfection levels decreased after needles began to elongate. Therefore i noculations would be most effective during active shoot elongation pri or to needle elongation. At least 2 inoculations are recommended when screening for resistance with this method because the incidence of inf ection varied among growth stages, and varieties differed in growth pe riodicity. The Penn State XP-74 variety was found to be more resistant than the others, and the East Anglia variety was the mast susceptible after varietal infection rates were adjusted for variation due to sta ge of growth and health of seedlings. The evidence for resistance sugg ests that genetic improvements may he attained through this screening method.