Scanning electron microscope observations of internal symptoms of white elm following Ceratocystis ulmi infection and cerato-ulmin treatment

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Abstract
Internal vascular symptoms induced by Ceratocystis ulmi infection and cerato-ulmin (CU) in white elm (Ulmus americana) were observed under a scanning electron microscope. Symptoms caused by CU were indistinguishable from those caused by C. ulmi. The main symptoms observed were (i) edemalike surface wall alteration, (ii) granular deposit, (iii) pit membrane heaving, (iv) smooth coating, (v) bubble and (or) tylose formation, (vi) rough coating, (vii) droplet formation, and (viii) vessel plugging with calluslike material. Internal symptoms appeared earlier in CU treated elms (as early as 2 h after treatment) than in C. ulmi infected elms (10 h after infection).