Date of Award

5-1979

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Mecley Mitcher

Second Advisor

Donald L. Ham

Third Advisor

Farrell B. Brown

Abstract

Fusarium moniliforme and F. moniliforme var. subglutinans were isolated from pitch cankered pines. Pathogenicity studies revealed that both fungi were capable of reproducing the disease; however, F. moniliformevar. subglutinane appears to be the primary casual agent of pitch canker in South Carolina. Considerable variation existed in virulence among isolates of the pitch canker fungus. No interaction existed between pine species and isolates of the pitch canker pathogen isolated from them. Histopathological and histochemical studies undertaken on developing cankers revealed that the pitch canker fungus invaded cells of all tissue types in stems of artificially inoculated seedlings. Hyphae grew intercellularly and also intracellularly through pits. The prolific resin production by cankered stems is due, apparently, to increased synthesis of the substance by existing, non-infected resin ducts. Resin also may be produced by non-infected parenchyma cells within diseased stems. Starch was degraded only in the tissues external to the vascular cambium, and remained unaltered in the xylem. Both cellulose and starch were degraded in advance of hyphal invasion, which suggested the production of extracellular enzymes by the pathogen. Lignin remained unchanged in all infected stems, while the fate of pectin is uncertain. Initial symptoms of loblolly pine top dieback were browning and twisting of the distal portion of the needles on the affected terminal which was followed by defoliation and death of the shoot. Distinct, resinous cankers seldom were present on affected terminals, and the pitch canker fungus was not isolated consistently from symptomatic tops. Although F. monilif orme var. aubglutinans did cause cankers on artificially inoculated terminals, dieback did not result from cankers girdling the stem. Host susceptibility to pitch canker was increased by nitrogen fertilization. Phosphorus and/or potassium had a compounding effect on increasing host susceptibility when applied with nitrogen. Slash pine seedlings subjected to water stress were less susceptible to pitch canker than watered, non-stressed seedlings. A low negative correlation existed between pitch canker severity and water stress. Other factors, possibly relating to the physiological state of growth of the seedling at the time stress was imposed, may exert a greater influence on host susceptibility than does water stress. Pitch canker developed on slash pines from artificial inoculations made during any season of the year. Remedial treatment of infected field-grown slash pine was unnecessary, since cankers on this species are primarily annual.

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