The diversity of pathogenicity of Xanthomonas campestris pv. poae, the causal agent of bacterial wilt in the genus Poa, was studied. Strains of X. c. pv. poae were distinguishable into three groups, according to differences in their pathogenicity against Poa species. Group 1, represented by strain JT-P192, caused mild wilt and a pale yellow appearance in leaves of annual bluegrass and supina bluegrass. Group 2, represented by strain JT-P482, was pathogenic to annual bluegrass, rough bluegrass and supina bluegrass, but caused only wilt symptoms. Group 3 included the type strain of X. c. pv. poae, which caused only a wilt in annual bluegrass, rough bluegrass, supina bluegrass and big bluegrass. Compatible and incompatible relationships were evaluated from the symptoms on infected plants and from bacterial multiplication in the lowest part of the culm after leaf clipping-inoculation.
Fusarium oxysporum, a soilborne phytopathogenic fungus, produces endo polygalacturonase (PG) which has been suggested to be related to disease development. A polyclonal antibody (PAb) APG1 was prepared against purified PG from F. oxysporum f. sp. lycopersici race 2. By direct tissue-blotted immunobinding assay (DT-IBA) with the antibody, PG production by the pathogen in the stem of the host plant was confirmed. Degenerate primers were designed based on partial amino acid residue information for the PG protein from the fungus: part of the PG-encoding gene was obtained by PCR. Using TAIL-PCR, the complete gene encoding PG was cloned and sequenced. The structural gene comprises 1318 bp coding for 371 amino acids with a putative signal peptide of 22 amino acids, and the open reading frame is interrupted by four introns of 47, 51, 50, and 54bp. The deduced amino acid sequence of the mature protein showed 82.9, 29.0, 27.6, 14.2, and 26.9% homology with those of F. moniliforme PG, Cochliobolus carbonum PGNI, Aspergillus niger PG, A. oryzae PG, and Sclerotinia sclerotiorum PGI, respectively.
Resistance-inducing compounds, 4-hydroxybenzoic hydrazide (4HBHZ), salicylic hydrazide (SHZ) and 2-furoic acid (2FA) inhibited tomato cell wall-bound peroxidase and horse radish peroxidase (HRP) activities. However, salicylic acid (SA), a non-inducer of resistance against Fusarium wilt did not inhibit peroxidase activity. HRP was allosterically regulated by the substrate. These resistance-inducing compounds acted as inhibitory effectors of HRP. On the contrary, 4-coumaric acid (4CA) and salicylhy-droxamic acid (SHAM) acted as stimulatory effectors. Among these compounds, 4HBHZ and SHZ were bound to compound III, an inactive intermediate of peroxidase. Furthermore, 4HBHZ weakly activated compound III and acted as a cofactor of the NADH-dependent peroxidase reaction as did 4CA and SHAM.
To compare biological and serological reactions of 28 bean yellow mosaic virus (BYMV) isolates collected from different hosts and locations in Japan, 15 different bean (Phaseolus vulgaris) cultivars were inoculated with the 28 isolates. Four biological variations (pathotypes I-IV) were observed among the 28 BYMV isolates. Pathotype I systemically infected only one bean cultivar, Honkintoki, out of the 15 cultivars studied. Pathotype II infected systemically Honkintoki, Kentucky Wonder and four other cultivars. Pathotype III infected systemically Honkintoki, Kentucky Wonder, Master Piece and four other cultivars. Pathotype IV infected systemically all 15 bean cultivars. Pathotype II also showed higher seed-transmissibility in broad bean (Vicia faba) than other pathotypes. The 28 BYMV isolates also varied serologically in their reactions in TAS-ELISA to 16 monoclonal antibodies (MAbs) produced against a BYMV isolate and two clover yellow vein virus (ClYVV) isolates. These reactions corresponded, to some degree, to biological variability. MAb-1F3 reacted with pathotypes I, II and III, and with one ClYVV isolate. MAb-2C4 reacted only with pathotype II. MAb-5F2 reacted with all BYMV and ClYVV isolates. MAb-2B4, -2C5, -3F9, -3F11, -4G8 and -4H9 reacted with all BYMV isolates in pathotypes II and III, and with some BYMV isolates in pathotypes I and IV. MAb-1A2 and -2H8 reacted strongly with pathotype III and with two ClYVV isolates. On the other hand, the differences in reactivity of six polyclonal antisera against four BYMV isolates and two ClYVV isolates in DAS-ELISA were not observed clearly. Our results indicate that the BYMV population in Japan is biologically and serologically variable and can be grouped into four pathotypes.
Etiological and biological studies were carried out on the causal fungus of black leaf blight of Welsh onion, causing severe damage on Welsh onion, which is cropped continuously using home-grown seeds. The disease was observed in the fields of Shimonita-cho, Gunma prefecture, as well as in the northern part of the Kanto District including Shimonita-cho, the Tohoku District and Hokkaido, but is scarcely observed in southern part of Kanto District and western Japan. Symptoms appearing on Welsh onion inoculated with a mycelial mat of the fungus or with naturally matured ascospores were similar to those developed under natural infection. On all diseased lesions originating from both natural infection and artificial inoculation, only the perfect state was observed. The optimum temperature for growth of the fungus on PDA was about 20°C, and 20-25°C for the maturation of asci and germination of ascospores. The pH range for fungal growth was from 4 to 9, with the optimum from 6 to 9.
Silver-coated cloth or silver oxide (Ag2O) markedly inhibited root rot diseases of cucumber and Japanese hornwort (Cryptotaenia japonica Hassk.) caused by Pythium spp. Silver oxide (Ag2O) at 30ppb in hydroponic nutrient solution inhibited zoospore motility of Pythium aphanidermatum and Pythium sp. type F. Germination was also inhibited by 10 percent over that of the control which was unexposed to silver oxide. Germination of zoospores was also inhibited completely by 50ppb silver oxide. When the concentration of silver ion eluted from silver-coated cloth into the hydroponic solution was about 40ppb, zoospores of Pythium spp. lost their ability to swim and germinate. After using silver-coated cloth in hydroponic culture of cucumber plants for more than 40 days, the residual amount of silver ion in cucumber fruits was less than the limit of Ag detection by atomic absorption spectrophotometer.
Detailed observations and cultural studies led to the conclusions that the causal fungus of black leaf blight of Allium fistulosum does not have any anamorph, and that the hitherto described anamorphs belonging to the causal fungus in Japan were incorrect. These anamorphs were different fungi, causing other diseases of welsh onion, or often occurring together with black leaf blight. Through comparative morphological studies, the causal fungus of Allium black leaf blight disease was identified as Mycosphaerella allicina (Fries: Fries) Vestergren having no anamorph. M. schoenoprasi (Auerswald) Schröter, which had long been known as the causal fungus in Japan, was treated as a synonym of M. allicina.