Minoru Aragaki

Morphological distinctions between Phytophthora capsici and P. tropicalis sp. nov.

Phytophthora isolates with deciduous long- pedicellate sporangia can be separated into two groups by isozyme analyses, but an apparent overlap in morphological characteristics was previously deemed as sufficient justification for inclusion of both groups in P. capsici with an expanded descrip- tion of the species. However, the occurrence of two morphologic groups in a species is unsettling, prompting a reexamination of the taxon. Compara- tive morphological and cultural studies of 100 Phy- tophthora isolates with deciduous, long-pedicellate sporangia which have been referred to P capsici, re- vealed that they were separable into two taxa: Phyto- phthora capsici with broad sporangia, sporangial length to diameter ratio less than 1.8, predominately round sporangial bases, absence of chlamydospores, good growth at 35 C, and pathogenicity to Capsicum; and Phytophthora tropicalis sp. nov., distinguished from P capsici by narrow sporangia less than 26 ptm in diameter, sporangial length to diameter ratio of more than 1.8, predominately tapered sporangial ba- ses, production of chlamydospores by most isolates, poor or no growth at 35 C, and weak or no virulence to Capsicum.

A simplified method for sporangial production by Phytophthora cinnamomi.

Fischer, G. W., and C. S. Holton. 1957. Biology and control of the smut fungi. Ronald Press Co., New York. 622 p. Leach, J. G., and Mary A. Ryan. 1946. The cytology of Ustilago striiformis forma poae-pratensis in artificial culture. Phytopathology 36: 876-886. Raghunath, T. 1969. Nuclear behavior in the germinating teliospores of the smut Georgefischeria riveae. Caryologia 22: 223-228. Ward, E. W. B., and Kathleen W. Ciurysek. 1961. Somatic mitosis in a basidiomycete. Canad. J. Bot. 39: 1497-1503.

Photosporogenesis in Exserohilum rostratum : temperature effects on sporulation and spore morphology

The sporulation of Exserohilum (= Helminthosporium) rostratum occurred in the dark at temperatures from 28 to 34 C. Light induced sporulation at lower temperatures, enhanced sporulation at 28 and 31 C, but inhibited the terminal phase of sporulation at 34 C. In dark-grown cultures, spores were characteristically elliptical and spore length increased with temperature to 31 C. Under continuous light, characteristic rostrate spores were formed at all temperatures tested, spore size increasing with temperature to 24 C, and then decreasing slightly with further temperature increases to 31 C. At 24 C, length of spores formed under continuous fluorescent irradiation was more than three times those formed in the dark. Under alternating light and dark conditions, both elliptical and rostrate conidia were formed as well as an intermediate, cylindrical spore type. Sporulation and spore length increased with light intensity. Added glucose (up to 4%) in vegetable-juice agar tended to shorten spores in light-grown culture.

Sporangial germination of Phytophthora from papaya.

SUMMARYSporangia of Phytophthora parasitica require only water for indirect germination or production of zoospores. However, papaya fruit extracts induce formation of germ tubes from the sporangia....

Photosporogenesis in Exserohilum Rostratum: Influence of Temperature and Age of Conidiophores in the Terminal Phase

Conidium development of Exserohilum rostratumn was partially inhibited by light at 28 and 31 C, and completely inhibited at 34 C. Older conidiophores were very sensitive to inhibitory wavelength and readily dedifferentiated into vegetative aerial mycelia. Light was effective in stimulating spore elongation during the formation of conidiophores as well as during the development of conidia. Exposure to light during the formation of conidiophores in the inductive phase resulted in the formation of rostrate conidia in the subsequent dark-terminal phase. The effect was greatest in young conidiophores incubated below 24 C. The phenomenon was not evident when older conidiophores were exposed to light.

Effects of Monochromatic Radiation on Pycnidial Formation and Exudation of Conidia in Botryodiplodia Theobromae

Botryodiplodia theobromae Pat. is common and widespread in the tropics as a wound parasite on a wide range of host plants (Goos et al., 1961). In papaya (Carica papaya L.) it causes stem-end and surface rots of fruit characterized by bluish-black lesions with a wide border of water-soaked tissue (Hunter and Buddenhagen, 1972). Leonian (1924) and Fulkerson (1955) showed that light is an important factor in the fruiting of a number of species in the Sphaeropsidales. An absence of stromata and near complete suppression of pycnidial formation characterized cultures of B. theobromae grown in the dark, but stromatal development was good in those cultures exposed to daylight (Wardlaw, 1932). Ekundayo and Haskins (1969) reported that long-wave ultraviolet (shorter than 340 nm) was effective for

SPORANGIAL CADUCITY AND PEDICEL LENGTH OF PHYTOPHTHORA NICOTIANAE VARIETY PARASITICA

Seven-9% of the sporangia of Phytophthora nicotianae var. parasitica produced on clarified vegetable juice liquid medium were readily detached, but when produced on diseased Cordyline terminalis (ti) leaf surface, 21-27% were detachable. In contrast, P. palmivora, a species which is generally recognized to produce caducous sporangia, produced 76% detachable sporangia on clarified vegetable juice. Pedicels of detached sporangia of P. nicotianae var. parasitica produced on ti leaf were uniformly short, whereas those obtained from clarified vegetable juice were highly irregular in length. Despite the formation of moderate numbers of detachable sporangia with pedicels of uniform length, P. nicotianae var. parasitica is considered a species with non-deciduous sporangia, since special conditions are necessary for the production of caducous sporangia.

Stability of hilum protuberance in Exserohilum species.

Development of the protuberant conidial hilum, an important characteristic in the genus Exserohilum, is markedly affected by temperature. Temperatures higher than 28 and 34 C inhibited the formation of protuberant conidial hilum in E. turcicum and E. rostratun, respectively. In E. pedicellatum protuberant conidial hilum formation was partially inhibited at 34 C. These critical temperatures for inhibition of protuberant hilum coincided with those for inhibition of sporulation by light. Continuous light had no discernible effect on the development of hila, except for the stimulation of production of protuberant hila at 24 C in E. turcicum.