Akira Ogoshi

Introduction — The Genus Rhizoctonia

The genus Rhizoctonia was described by DeCandolle in 1815. He designated R. crocorum (Pers.) DC. as the type species, while R. solani,the most important species of Rhizoctonia, was described by Kuhn in 1858. The history of R. solani is almost as long as the history of plant pathology. It was published around the time when the potato late blight broke out in Europe, which caused the noteworthy potato famine in Ireland. Since these initial reports, the pathology, taxonomy, ecology, and disease control of Rhizoctonia have been extensively studied.

Ultrastructural changes during the symbiotic development of Spiranthes sinensis (Orchidaceae) protocorms associated with binucleate Rhizoctonia anastomosis group C

The process of symbiotic development of Spiranthes sinensis seeds to protocorms with differentiated shoots associated with binucleate Rhizoctonia anastomosis group C was divided into 7 stages (I–VII) based on increase of embryo and protocorm width. Each stage was observed ultrastructurally. The embryo contained large amount of lipid, small amount of starch, and protein body-like structure in all its cells. The embryo began to swell (stage I) as soon as several hyphae invaded the basal cells. Hyphae penetrated into the inner cortical parenchyma (ICP) and subepidermal parenchyma (SEP) cells and formed pelotons. The meristematic region (MR) was not colonized. Hyphal cell walls (FCW) were surrounded by an encasement layer (EL) and by the host plasmalemma. Pelotons that formed in ICP had thin walls and were digested, whereas pelotons in SEP were not digested. In stage I, mitochondria, ribosomes, proplastids, microbodies, rough endoplasmic reticulum, dictyosomes and vacuoles were observed in the host cytoplasm. Signs of hyphal digestion was already apparent in this stage. In stage II, clumps of digested pelotons consisted only of layers of FCW and EL and were surrounded by host cytoplasm and vacuoles, and/or secondary infected hyphae. Hyphal digestion and the reinfection of host cells occurred repeatedly throughout all growth stages. Protein body-like structures rapidly disappeared before stage III. At stage V and subsequent stages, it was also seen that the dispersed contents of digested hyphae were surrounded by the host plasmalemma. When ICP cells contained pelotons, amyloplasts were not observed. However, proplastids usually existed in the cells, and amyloplasts were observed in all SEP cells and other uninfected cells. Lipid bodies were slowly degraded throughout embryo and protocorm growth.

Comparison of Chinese and Japanese A1 isolates of Phytophthora infestans

The mating type, glucose-6-phosphate isomerase (Gpi) and peptidase (Pep) genotypes, RG57 fingerprint, and mitochondrial DNA (mtDNA) haplotype of Chinese isolates of Phytophthora infestans collected in Hebei and Gansu in 1996 were compared with those of Japanese isolates collected during 1997–2000. The Chinese isolates were divided into four genotypes, one of which was identical to the dominant Japanese genotype, A1-A (mating type A1; Gpi 100/100; Pep 100/100; RG57 100010001100110100011001110: 1–25, 14a, and 24a; and mtDNA haplotype IIa). Comparison of the genotypes with reported data revealed that some completely and partially identical genotypes occur in Russia and parts of Europe. The other two A1 genotypes and one A2 genotype were also detected in Gansu (Gpi 100/100, Pep 100/100, and mtDNA haplotype Ia), which were regarded as unique to this region.

INFLUENCE OF THE SOYBEAN CYST NEMATODE (HETERODERA GLYCINES) ON THE INCIDENCE OF BROWN STEM ROT IN SOYBEAN AND ADZUKI BEAN

Summary-Experiments were carried out in pots to study the influence of the soybean cyst nematode (Heterodera g/y&es) on the incidence of brown stem rot (BSR) in soybeans (Glycine max) and adzuki beans (Vigna angularis) caused by the soilbome fungi, Phialophora gregata fsp. sojae and P. g. f.sp. adzukicola. The presence of H. glycines increased the incidence of BSR in susceptible soybean (cv. Nakate-Hikarikuro) and adzuki bean (cv. Erimoshozu) for both pathogens. The disease-enhancing effects of H. glycines were not shown in the soybean cultivar Peking, which is resistant to the nematode. In a soybean cultivar resistant to BSR (cv. BSR302), the incidence of BSR was low, even under the presence of H. glycines. In split-root experiments using the two BSR susceptible cultivars, the diseaseenhancing effects of H. glycines were not observed in either soybeans or adzuki beans, whose roots were inoculated separately with P. gregata and H. glycines. 0 1997 Elsevier Science Ltd

Morphological and physiological comparisons of Helicobasidium mompa and H. purpureum

Morphological and physiological comparisons were made of sevenHelicobasidium mompa isolates and fourH. purpureum isolates. Colonies of theH. mompa isolates were thin, dense, or hard and dense, and most were pale brown to brown or dark brown, while that of isolate 344c was pinkish. Colonies ofH. purpureum isolates were hard and dense, and their colonies were dark brown. Diameters of hyphae were similar forH. mompa andH. purpureum. Dimensions of conidia and morphology of conidiophores ofH. mompa isolate 344c were close to those ofH. purpureum reported previously.H. mompa isolates grew well at 23°C, 25°C or 27°C, while all isolates ofH. purpureum grew well at 23°C. Growth rates ofH. purpureum isolates was almost the same as those ofH. mompa isolates with slow growth. Polygaracturonase activity at pH 3 was variable among the isolates for bothH. mompa andH. purpureum. Itaconic acid was produced abundantly by three isolates ofH. mompa but not produced by isolate AH130, whereas all isoaltes ofH. purpureum produced a small amount of itaconic acid.

Characterization of the nuclear DNA of Phialophora gregata ff.sp, adzukicola and sojae

Phialophora gregata nuclear (n) DNA was characterized by physical methods. The nDNA of f.sp.adzukicola was shown to be larger than that of f.sp.sojae, 2.9 and 2.1 × 1010 Da, respectively. The amounts of repetitive sequence and AT-rich region in the nDNA were also larger in f.sp.adzukicola than f.sp.sojae. These results indicate that the nuclear genome organization of the two formae speciales is differentiated.

Gene mpl1, activated during mating in Phytophthora infestans : similar to genes encoding pectate lyases

Clones of genes activated in mating cultures of A1 and A2 mating-type strains of Phytophthora infestans were isolated using the cDNA-representational difference analysis subtraction method. Clone cET58 was selected based on its accumulation in mating cultures and then was used as a probe to isolate cDNA clone cET58L2 from a cDNA library that was constructed from mycelia grown under mating conditions. Sequence analysis revealed that cET58L2 was 1043 bp long and contained a complete open reading frame of 789 bp. The amino acid sequence of the putative protein was similar to a pectate lyase, PLD, of Fusarium solani f. sp. pisi. The central region of the predicted protein was highly similar to the sequence of other pectate lyases. The gene from which the cDNA clones were derived was designated mpl1. A probe corresponding to the protein-coding region of mpl1 was prepared (probe p58L) for Northern and Southern analyses. The maximum rate of oogonia increase and mpl1 transcript accumulation reached a maximum after 5 days in mating culture. More than 13 genes with sequences similar to that of mpl1 were found in the genome, revealing mpl1 to be a multicopy gene. The mpl1 may be a pectate lyase gene that is activated in P. infestans during mating.

Differential Growth Response of A1 and A2 Mating Types of Phytophthora infestons on Rye A and V-8 Juice Agar Media Supplemented with Rhizome Powder of Cyperus rotundus

A new medium for studies of diversity among populations of A1 and A2 mating types of Phytophthora infestons has been evolved. The rye A agar and V-8 juice agar media on which P. infestons grows well have been amended with rhizome powder of Cyperus rotundus. A total of 259 isolates of A1 and A2 mating types representing Japan, Korea, India, Taiwan, Indonesia, Thailand, China, Nepal, U.K. and Mexico were screened for their growth response on these two media. Most of the A1 isolates did not grow well on them except Thailand while growth of A2 mating types differed as some grew on it whereas others did not. It is quite likely that the populations of A2 mating types that did not grow well on rhizome-amended medium are of different clonal lineage. This suggests that this medium can be used for the study of diversification among the isolates of the same or both the mating types as well as to detect the newly introduced genetically different isolates of P. infestans in a locality where it was not reported earlier.

Aphanomyces euteiches Drechsler, a causal fungus of "Susogare" of garden pea in Tokushima Prefecture.

“Susogare” of garden pea in Tokushima prefecture is characterized by yellowing, withering of under leaves and root rot. Aphanomyces euteiches was isolated from diseased pea roots. Peas, inoculated with this fungus, showed same symptoms as observed in field. A. euteiches was detected in 93 of 122 fields tested. It is considered that A. euteiches causes the “Susogare”.