Phenolic metabolites of Ceratocystis minor from laboratory cultures and their effects on transpiration in loblolly pine seedlings

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Abstract
Several low molecular weight phenolic metabolites of Ceratocystis minor (Hedgcock) Hunt, a blue-stain fungus of loblolly pine, were isolated from cultures grown on 2.5% malt-extract liquid medium. The most abundant compounds were 6,8-dihydroxy-3-hydroxymethylisocoumarin and 6,8-dihydroxy-3-methylisocoumarin. Two unknown phenolic compounds were also isolated. Solutions of these fungal metabolites stimulated transpiration in loblolly pine seedlings when administered through the cut stem. Rates of water loss were doubled within 24 h after treatment with isocoumarin solutions. Administration of raw or sterile fungal culture (in liquid medium) on the other hand produced a small but significant inhibition of water loss shortly after treatment. Reduction in transpiration after treatment with fungal culture probably is the result of partial tracheid blockage by as yet unidentified fungal products. Effects of metabolites of C. minor on the water relations of loblolly pine are discussed in terms of a possible mutualistic association between C. minor and the southern pine beetle, Dendroctonus frontalis Zimmermann.