. Recent research on foliage diseases : conference proceedings : Carlisle, Pennsylvania, May 29-June 2, 1989. Leaves Diseases and pests United States Congresses. Figure 3.—A - D = Lophodermium australe. All illustrations are from longitudinal sections. A) Collapsed mesophyll and non-functional transfusion/vascular tissue. Note lack of hyphae and empty appearence of affected mesophyll area (X75); B) Definitive separation of diseased and normal-ap- pearing tissues at symptom boundary (X75); C) Hyphae in transfusion/vascular tissue in sympto- matic area (X470); D) Bending and crushing of host tis
. Recent research on foliage diseases : conference proceedings : Carlisle, Pennsylvania, May 29-June 2, 1989. Leaves Diseases and pests United States Congresses. Figure 3.—A - D = Lophodermium australe. All illustrations are from longitudinal sections. A) Collapsed mesophyll and non-functional transfusion/vascular tissue. Note lack of hyphae and empty appearence of affected mesophyll area (X75); B) Definitive separation of diseased and normal-ap- pearing tissues at symptom boundary (X75); C) Hyphae in transfusion/vascular tissue in sympto- matic area (X470); D) Bending and crushing of host tissues under stroma (X75). c = collapsed mesophyll cell(s) h = hypha(e) n = non-collapsed mesophyll cell(s) s = stroma v = transfusion/vascular tissue p = hypodermis appearing mesophyll in green tissue adjacent to symp- tom boundaries. Stroma development resulted in disruption, bending or crushing of underlying hy- podermal, mesophyll, endodermal, and transfusion/ vascular tissues (fig. 3D). The potential of a toxin in the relationship of L. australe and its pine hosts requires investigation. Discussion In observations of the various host/pathogen rela- tionships, the one tissue abnormality common to all was the collapse of mesophyll tissue in affected areas of symptomatic needles. This collapse was, in most instances, complete throughout the symptom areas with the exception of P. hedgcockii. Also, with the exception of the latter, the mesophyll cell collapse was not associated with a profusion of hyphae of the individual pathogens. This was particularly true with P. palustris on which both P. hedgcockii and M. dearnessii were studied. The former produced profuse amounts of hyphae in affected mesophyll while hy- phae of the latter were absent or very difficult to observe. Lophodermium australe and P. lethale on P. taeda produced similar host effects, but differed in hyphal presence in affected tissues. Regardless of the abundance of hyphae of the needle pathogens exam- ined, th
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