Interaction of light and sterol on sporangium and chlamydospore production by Phytophthora lateralis.

ENGLANDER, L. , and L. F. ROTH. 1980. Interaction of light and sterol on sporangium and chlamydospore production by Phytophthora lateralis. Phytopathology 70:650-654. Chlamydospore production by Phytophthora lateralis was most greatly reduced by continuous or 12 hr of light daily. Chlamydospore abundant in V8 broth with 20 Ag/ml B3-sitosterol, and maximum production was suppressed by all light intensities tested (85, 170, 340, 680 sporangium production occurred with 10 gg/ ml. Growth (dry weight) was AW cm-) compared with production in the dark. Few chlamydospores not enhanced by sterol concentrations ranging from 1 to 200 ttg/ ml. formed in cultures on media without sterol, whether incubated in the light Cultures grown on V8 sterol agar or broth, and illuminated (680 MW cm-, or dark. Growth (dry weight or colony size) was not affected by combined Blacklight Blue and Cool White fluorescent lamps) either illumination. None of numerous regimes of diurnal temperature cycles continuously or 12 hr daily, produced at least four times as many sporangia enhanced sporulation more than constant temperatures. Optimal as were produced by cultures in the dark on sterol media, or in the light or sporangium production requires incubation on media with sterol at 14-16 C dark on media not amended with sterol. Chlamydospores were produced in the light; optimal chlamydospore production requires incubation at most abundantly in the dark on V8 sterol agar or broth, with production 24-25 C in the dark on media with sterol. Additional key words: soil fungi, sporulation, reproduction. Phytophthora lateralis Tucker and Milbrath is the causal agent Media. V8 broth and agar were prepared with commercial V-8 of a root rot disease affecting native stands of Chamaecyparis juice (Campbell Soup Co., Camden, NJ 08101) and clarified by lawsoniana (Murr.) Parl. along the Pacific coast of Oregon and centrifugation (1,000 g for 10 min) and filtration through Whatman California and numerous horticultural cultivars of Chamaecyparis GF/A glass-fibre paper (Whatman, Inc., Clifton, NJ 07014). V8 distributed by the ornamental plant industry (8,10). In the agar and broth contained clarified V-8 juice, 100 ml; CaCO 3, 0.1 g; spectrum of growth rates characteristic of the various Difco agar, 17 g (deleted in broth); and distilled water, 900 ml. V8 Phytophthora spp. , that of P. lateralis may be classified among the sterol agar and broth were prepared as above, except with only 890 slowest (14). Host resistance and fungal survival studies, which ml distilled water and, unless otherwise indicated, 0.02 g /3-sitosterol require quantities of inoculum, have been impeded by the time (Sigma Chemical Co., St. Louis, MO 63178) dissolved in 10 ml hot consuming process of inoculum production. 95% ethanol. Control media in some experiments contained Sterols play an important role in the development and ethanol (95%, 10 ml/ L) without sterol. Media were autoclaved 20 reproduction of several pythiaceous fungi. The literature on this min at 121 C, and 7-ml aliquots were pipetted into 6-cm-diameter subject is abundant (4). The reproduction of numerous plastic petri dishes. Phytophthora spp. is influenced by light (7,15,17) Fungus culture. Petri dishes with agar medium were seeded by The relationship of light and sterol on sporulation of inverting a 5-mm-diameter disk of corn meal agar cut from the Phytophthora spp. was investigated. Hendrix (3) studied periphery of a 7to 12-day-old colony of P. lateralis. Broth cultures sporulation by two Phytophthora spp. and found that sporangium were seeded by adding a homogeneous suspension of P. lateralis production on a medium with sterol was higher in illuminated than (prepared from 9to 15-day-old colonies grown on V8 broth and in unilluminated cultures. Merz and Vickers (6) reported partial comminuted in a Servall Omnimixer [Sorvall Instruments, reversal of the inhibitory effect of light on oospore formation by Newtown, CT 06470]) to autoclaved, cooled medium prior to four Phytophthora spp. when sterol was added to the culture dispensing it to petri dishes. medium; at any of the concentrations of sterol tested, production of Measurement of growth and sporulation. Dry weights of oospores was never as great in the light as in the dark. Englander colonies in liquid medium were determined by vacuum filtration on and Turbitt (1) found that near-ultraviolet light stimulated tared Whatman No. 1 filter papers, flushing unassimilated production of chlamydospores by P. cinnamorni only when the nutrients with measured amounts of water, and drying the filters to culture medium contained sterol. None of the concentrations of a constant weight at 75 C. Growth as increase in colony area was sterol tested (1-200 mg/ ml) enhanced chlamyd0opore production in determined on agar cultures by periodically marking the the dark. peripheries of the colonies on the bottoms of the petri dishes and In view of the significant effects of light'and sterols on other later tracing these outlines with a planimeter. pythiaceous species, their effects on P. lateralis were examined. Production of chlamydospores and sporangia was determined directly on cultures grown in agar or from samples of comminuted MATERIALS AND METHODS colonies when cultures were in liquid medium. After the prescribed incubation period, cultures were killed and fixed by flooding with a Isolates. P. lateralis isolate PL 11 was used in all experiments thin layer of FAA (formaldehyde, 48 ml; acetic acid, 40 ml, 95% reported here. Three other isolates, PL 12, 14, and 17, also were ethanol, 352 ml; and distilled water, 360 ml;. In each agar culture included in the final experiment. All P. lateralis isolates were from spores were counted in 20 microscope fields, delineated by an diseased, native C. lawsoniana, and their pathogenicity was ocular counting grid (each field 0.5 mm ), spaced uniformly along confirmed by inoculating rooted C. lawsoniana cuttings in the radii drawn below each colony, so that no preference was given to greenhouse. hyphae of a particular age. Colonies from broth cultures were transferred to an 8-ml-capacity Servall Omnimixer cannister 0031-949X/80/07065005/$03.00/0 containing 5 ml of water and comminuted for 30 sec at 70% @1980 The American Phytopathological Society (rheostat-controlled) line voltage. The resultant suspension was