Pitch Canker Disease Research Articles

Inhibition of Fusarium moniliforme var. subglutinans, the causal agent of pine pitch canker, by the soil bacterium Arthrobacter sp.

A species of Arthrobacter was recovered during culture of the causal organism of pitch canker of southern pines. Fusarium moniliforme var. subglutinans (FMS). Arthrobacter is a relatively common soil bacterium and is lytic to several fungal pathogens in the soil. Soil samples from two seed orchards with pitch canker and one from a healthy pine plantation all yielded Arthrobacter. These isolates were evaluated for their ability to inhibit the growth of FMS isolates from pitch canker tissue and from soil in areas with high pitch canker disease incidence, and to several other species of Fusarium isolated from the same soil samples where Arthrobacter was recovered. Generally the pitch canker isolates were more sensitive to Arthrobacter than the soil fusaria. There was variation in the ability of the Arthrobacter isolates to inhibit the growth of the fusaria recovered from the soil at the three different test sites. Light and scanning electron microscope observations revealed that hyphae of FMS growing near an isolate of Arthrobacter were enlarged, producing many vesicularlike structures. The surface of these hyphae was warped and wrinkled in comparison with normal hyphae.

Shoot Dieback of Planted Sand Pine Caused byFusarium moniliformevar.subglutinans

BLAKESLEE, G. M., S. W. OAK, and S. H. KRATKA. 1980. Shoot dieback of planted sand pine caused by Fusarium moniliforme var. subglutinans. Plant Disease 64:703-704. Fusarium moniliforme var. subglutinans was identified as the cause of shoot dieback in plantationgrown Ocala and Choctawhatchee varieties of Pinus clausa in Florida. Isolates cultured from sand pine were pathogenic to seedlings of both slash and sand pine. Sand pine seedlings were also susceptible to isolates of F. moniliforme var. subglutinans obtained from pitch cankers on slash pine. Pitch canker disease, caused by Fusarium moniliforme Sheld. var. subglutinans Wollenw. and Reink., is widespread in southern pine plantations and seed orchards in the southeastern United States (2,6,9). Damage has been most severe in slash pine (Pinus elliottii Engelm. var. elliottii) plantations in the pine flatwoods regions of Florida, where the fungus causes branch cankers resulting in shoot dieback, reduced growth rates, stem deformity, and mortality (4,9,10). Although the known host range for F. moniliforme var. subglutinans is rather broad (1,2,5,7) and includes most of the economically important southern pines, neither the Ocala nor the Choctawhatchee varieties of sand pine (Pinus clausa (Chapm.) Vasey var. clausa Ward. and var. immuginata Ward., respectively) have been recognized as natural hosts. We report the isolation of F. moniliforme var. subglutinans from cankers on sand pine, describe the symptomatology of the naturally occurring infections, and establish proof of pathogenicity. MATERIALS AND METHODS In December 1978, we observed shoot dieback on numerous trees in a 6to 8-yrold plantation of Ocala sand pine in western Calhoun County, Florida. Similar symptoms were observed in December 1979 on several planted 5-yrold Choctawhatchee sand pines in Taylor County. In both instances, conspicuous, girdling cankers subtended symptomatic shoots, samples of which were collected for diagnostic evaluation and isolation. The pathogenicity of several isolates obtained from the diseased trees was Florida Agricultural Experiment Stations Journal