Effects of Ozone on Sporulation, Spore Germination, and Growth ofFomes annosus

Abstract

James, R. L., Cobb, F. W .. Jr., and Parmeter, J. R., Jr. 1982. Effects of ozone on sporulation, spore germination, and growth of Fornes annosus. Phytopathology 72: 1205-1208. Effects of ozone (OJ) on certain cultural characteristics of Fornes annosus were investigated in exposure chamber studies. Growth rates of F. annosus decreased and conidial germ tubes were shorter and had fewer branches as OJ dosages increased. F. annosus conidial production was very sensitive to OJ: very few conidia were produced when cultures were exposed to relatively low dosages (2.400 /ig'mJ-hr). Conidial germination was decreased at the higher OJ dosages. but spore germination was apparently stimulated at low dosages (184 /igl m'-hr). Colonization of wood disks exposed to OJ dosages of 16.870 ug. mJ-hr and greater was significantly less than that of nonexposed disks. However. OJ dosages that can be expected under field conditions appear to have little potential effect upon those aspects of pathogen biology that would substa ntially affect epidemiology of annosus root rot. Indirect effects of air pollution on the productivity of forest ecosystems may be as important as direct effects upon tree physiology and growth. For example, pollutants may influence the population dynamics of tree pests in ways that could cause dramatic increases in disease incidence. In the San Bernardino Mountains of southern California, oxidants apparently predispose pines to bark beetles (2). James et al (10, II) found that photochemical air pollution injury increases the susceptibility of ponderosa (Pinus ponderosa Laws.) and Jeffrey (Pinus jeffreyi Grev. and Balf.) pines to Fornes annosus (Fr.) Cke., an important root pathogen of conifers in California (I). Such increased susceptibility could lead to dramatic increases in disease incidence. On the other hand. pollutants may have direct effects upon the pathogen: reduced sporulation, spore germination, or growth. Ozone (0). a major phytotoxic component of photochemical air pollution (16), directly affects pathogenicity of some fungi. Effects on growth (5.6), spore production (3,14,18), spore germination (4.7), and hyphal morphology (17) have been reported. Most of the previous work has involved foliar pathogens that were exposed to ambient pollutants directly. The objective of this research was to investigate the effects of 03 exposure under controlled conditions on the root pathogen F. annosus. Studies were made to determine effects on linear growth, conidial production. conidial germination. and colonization of freshly cut pine disks.