The rice seed disinfectant, ipconazole, had antifungal in vitro activities against a wide range of plant pathogenic fungi from the Ascomycotina, Basidiomycotina, Deuteromycotina and Zygomycotina. Most of the EC50 values for the tested fungi did not exceed 0.5μg/ml. Seed treatments with wettable powder containing 6% ipconazole protected against the major rice seed-borne and soil-borne diseases, “Bakanae” disease, Helminthosporium leaf spot, blast and seedling blights caused by Rhizopus sp. and Trichoderma viride. High concentrations of residual ipconazole, which varied with the method of application, were detected by HPLC analysis on the outer portion of seeds. Regardless of the method, the residual ipconazole in the intact seeds remained nearly the same after a period of water soaking. The isolation frequencies of Fusarium moniliforme, the causal fungus of “Bakanae” disease, from infected, untreated rice seeds were 75%, 25% and 15% from hulls, endosperm and embryo, respectively. Ipconazole permeated into the seeds in a sufficient amount to be fungitoxic or fungistatic during treatment conditions and successive water soaking. In shake culture, mycelial growth of F. moniliforme was reduced by 50% and gibberellin production was totally inhibited by 0.1μM of ipconazole. The inhibition of gibberellin production at the fungistatic concentration may partially contribute to its activity against “Bakanae” disease. In a paddy field trial, ipconazole-treated seedlings showed no “Bakanae” symptom through harvest time. The protective action of ipconazole appears to consist of both fungicidal and fungistatic activities.
Electrophoretic analysis of total DNA extracted from Rhizoctonia solani Kühn AG-2-2 IV isolate PE-42, the causal fungus of large patch of zoysiagrass, revealed a 3.0-kb band in addition to the band of chromosomal DNA. Because the band was regarded as a double-stranded plasmid DNA based on restriction enzyme analyses, it was designated as a PE-42 plasmid fragment. The PE-42 plasmid DNA recovered from agarose gel hybridized to DNA of all 22 large patch isolates used, but not to DNA of other zoysiagrass pathogens. Southern hybridization analysis using the PE-42 plasmid DNA as a probe showed that the DNA could be used as a marker to distingush the large patch fungus from other intraspecific groups of Rhizoctonia solani. DNAs extracted from zoysiagrasses having various stages of large patch symptom and yellow patch symptom or having no symptoms (healthy) were subjected to Southern hybridization. The PE-42 plasmid DNA hybridized to the DNAs from zoysiagrass with large patch symptom, but not to DNAs from yellow patch and heathy plants. Thus, the PE-42 plasmid DNA was considered to be useful as a probe for molecular diagnosis of large patch of zoysiagrass.
Ampelomyces quisqualis produced pycnidia but not conidia on malt-yeast extract (MY) agar, while in MY broth the fungus formed both pycnidia and conidia in 7 days. Shaking the culture greatly increased the amount of conidia produced in MY broth. Among the vegetables tested, carrot broth was best for conidial formation under shaking conditions, followed by tomato broth and cucumber broth. The fungus failed to grow in potato broth. When A. quisqualis conidia produced in carrot broth were incubated together with Oidium euonymi-japonicae conidia on glass slides under moist conditions, parasitism of this mycoparasite on its powdery host was observed for the first time outside the host of the powdery mildew.
Three DNA regions in Xanthomonas campestris pv. citri which were homologous to the avrBs3 gene family commonly found in Xanthomonas spp. were cloned and their nucleotide sequences were determined. The sequences from 247bp upstream of the translational start to 111bp downstream from the termination site of the open reading frames in these regions were identical except in the tandem repeats of 102bp in the middle of their coding regions. Thus, they contain the same leucine zipper, nuclear localizing signals and inverted repeats as noted by De Feyter et al. Two of them enabled a nonpathogenic mutant missing one of these avrBs3 homologous regions to form a canker, but the remaining one did not even 30 days after inoculation. Comparison of the tandem repeats provided us more information on its organization required for canker formation.
A new method for analysing β-1, 3-glucanase activity was developed, to replace the somewhat complicated DNS method which is currently used to measure β-1, 3-glucanase activity. A new method, the pNPG4 degradation method, using p-nitrophenyl-β-D-laminaritetraoside (pNPG4) as a substrate was easier and more precise than the DNS method. We measured β-1, 3-glucanase activity on diseased eggplants with the pNPG4 degradation method. The enzyme activity of leaves in eggplants infected with Verticillium dahliae increased up to 1.5 times that in healthy plants, from 4 days before to 1 day after symptom appearance. The activity in naturally infected eggplants increased as well when the symptoms appeared in parts of the plants. Therefore, Verticillium wilt of eggplant can be diagnosed by measuring β-1, 3-glucanase activity using the pNPG4 degradation method.
Pathogenicity of 13 strains belonging to two species, including three subspecies, of phytopathogenic bacteria in the genus Acidovorax was tested on five plant species including rice. The pathogenicity of an individual strain to rice was compared with its ability to suppress lesion enlargement of bacterial brown stripe on rice sheath after inoculation with living cells or cell extracts (CEs) of each strain. On the basis of the pathogenicity tests, the two species and the three subspecies were clearly distinguishable on the plants. Three strains isolated from rice and strain MAFF 302183 from corn were pathogenic to rice and nine strains were not. Inoculation with A. avenae MAFF 301505 (a virulent strain on rice) mixed with living cells of an avirulent strain or the virulent strain MAFF 302183 which produced an anti-bacterial substance against MAFF 301505 suppressed lesion enlargement in comparison to a single inoculation with the virulent strain. Inoculation mixed with CEs, however, failed to suppress lesion enlargement unless the CEs contained the anti-bacterial substance. Pre-inoculation with living cells of each avirulent strain suppressed the enlargement of the lesion caused by a challenge inoculation with the virulent strain MAFF 301505 6 hours after pre-inoculation. On the other hand, pre-inoculation with CEs derived from all strains suppressed lesion enlargement, but the degree of suppression by nine avirulent strains was stronger than that of four virulent strains. The CEs of all strains failed to elicit the hypersensitive reaction (HR) in tobacco but living cells of all strains except for MAFF 301576 elicited the HR. These results suggest that the CEs may contain substances which induce the suppression of lesion enlargement on rice with no activity to elicit tobacco HR. The difference in the ability of the CEs from virulent and avirulent strains to induce suppression may be related to the virulence of the bacteria.
A symptomatic mutant with mild symptoms derived from a greenhouse-maintained isolate of onion yellows phytoplasma after using garland chrysanthemum and leafhopper vector, Macrosteles striifrons for about 10 years. From comparing characteristics of the wild type and symptomatic mutant, the symptomatic mutant was similar to the wild type in its host range, transmission pattern and incubation periods in the infected plants and insects, and differed only in the symptoms in diseased plants.
In autumun 1997 powdery mildew of perennial statice was found in Mie and Oita prefecture, Japan. Many white, powdery mycelial colonies appeared on leaves, stems and branches of the plants. The fungus successfully caused disease on perennial statice after artificial inoculation, but not on Limonium sinuatum. Conidia were cylindrical, (29-) 36-54 (-62)×14-20μm in size, formed singly on conidiophores straightly erected on the aerial mycelia. Lobed appressoria differentiated on the germ tubes from conidia. No cleistothecia were observed. On the basis of morphological characters of the conidial stage, the fungus was found to be an Oidium sp. of the Erysiphe polygoni type.