DAMPING-OFF DISEASE OF PINE-SEEDLINGS ON SOILS TREATED WITH SIMULATED ACIDIC RAIN

Damping-off during seed germination and early seedling growth of Pinus rigida Mill., Pinus echinata Mill., Pinus taeda L., and Pinus strobus L. were observed for 28 days on three New Jersey (U.S.A.) Pine Barrens soils (Atsion, Downer, Lakewood) treated with simulated acidic rain solutions of pH 4.2, 3.5, or 3.0 (SO42-:Cl-:NO3-, 2.2:1.4:1.0). The soils were sandy, highly acidic, and deficient in mineral nutrients. Treatment with rain solution was started 53 days before planting the pine seeds and continued during germination. Seedling emergence and seedling mortality were affected significantly by solution pH, soils, and species. Seedling emergence of all pine species on Atsion and Lakewood soils decreased with increasing solution acidity. On Downer soil seedling emergence was unaffected by solution acidity probably because the buffering action of the soil decreased the acidity of the rain solution. Seedling mortality of all species increased with increasing treatment acidity on all soils and was significantly higher on Atsion (100% at pH 3.0) than on the other soils. Although solution acidity significantly increased the concentration of Al in the soil solution, there was no evidence of Al toxicity. Two isolated fungal species, a Trichoderma. and a Penicillium, significantly reduced seedling emergence and increased seedling mortality of P. rigida in sterile, acid-washed quartz sand; however, neither seedling emergence nor seedling mortality was affected significantly by solution acidity.