The leguminous strain of cucumber mosaic virus (CMV-L) systemically infects cowpea (Vigna unguiculata (L.) Walp.), whereas many other strains of CMV induce necrotic local lesions on inoculated leaves and do not spread systemically. The cDNAs of genomic RNAs of CMV-L were synthesized and nucleotide sequences were determined. RNA 1 was 3359 nucleotides (nt) long, and had one large open reading frame (ORF) that coded for a protein of Mr 111, 491, the la protein. RNA 2 consisted of 3047 nt and was able to encode the 2a protein of Mr 96, 720. RNA 3 was composed of 2213 nt and had two cistrons for the 3a protein and coat protein (CP). The 3a protein was encoded in the 5' proximal ORF and predicted to be a protein of Mr 30, 478. The CP gene was on the 3' proximal and coded for a protein of Mr 24, 191. Similarities in the nucleotide and amino acid sequences of RNAs 1 to 3 between CMV-L and Y strain of CMV (CMV-Y) were above 94%. In particular, the 3a protein of CMV-L showed no sequence divergence from that of CMV-Y. The infectious in vitro transcripts derived from full-length cDNA clones of CMV-Y and-L were reassorted between two viruses and used to inoculate cowpea. RNA 2 was solely necessary for the determination of infection types on cowpea, whereas RNA 3 of CMV-Y could modify the symptoms. Alignment analysis of the 2a proteins of several strains of CMV, including MB-8 that infects cowpea systemically, revealed several specific amino acid changes found in the leguminous strains or isolates.
The wild plant Lonicera japonica, commonly found associated with tomato crops in Japan has been found to be infected with tobacco leaf curl virus (TLCV). Several novel species of virus-specific single-and double-stranded DNA (ss and dsDNA) were detected from infected plants showing yellow vein mosaic symptoms. Mung bean nuclease studies revealed the presence of unit-genome length duplexes of closed circular, relaxed circular and linear forms of viral DNA. In addition, a subgenomic DNA was also detected. Geminivirus-specific degenerate primers which anneal within the AC1 ORF (replicase gene) and the AV1 ORF (coat protein gene) amplified a fragment of 1.1 kbp, which was cloned and sequenced. Alignment of this sequence with that of TLCV showed complete homology in the intercistronic region, replicase and coat protein genes, indicating the presence of the same TLCV strain as detected from infected tomato. The geminivirus isolated from the common perennial Eupatorium makinoi from Saga Prefecture, Japan, showed 89.2% sequence homology in the AC1 ORF region with the TLCV strain detected in L. japonica. Infected wild plants therefore possess at least two distinct strains of TLCV which may serve as a natural reservoir for infecting crop species.
We demonstrated that there were suppressive soils to bacterial wilt in tobacco fields in Japan. Two hundred sixteen soil samples from tobacco fields in Japan were screened for suppression against bacterial wilt of tobacco caused by Pseudomonas solanacearum by planting tobacco seedlings in these soils and inoculating them with P. solanacearum in a greenhouse. Disease incidence in nine soils was significantly lower than that in conducive soils. Five of these soils were sedimentary soils and four were volcanic soils. Eight of the nine soils were classified as loamy soils, the other was classified as sandy. When P. solanacearum was added to these soils, the population in the eight suppressive loamy soils decreased slightly, whereas the population in the suppressive sandy soil decreased drastically. The results indicate that suppressiveness is found in a wide variety of soils and that the suppressive soils in Japan can be divided into two groups based on the survival of the pathogen.
Life cycle, pathogenicity, conditions for conidial germination and mycelial growth and taxonomic classification of Cercospora pyracanthae Katsuki causing brown spot of Pyracantha spp. were examined. Among Pyracantha species plants, P. angustifolia (Franchet) Schneider was highly susceptible. Conidia of the causal fungus, produced on overwintered and diseased leaves on trees, acted as the source of primary infection of newly sprouted leaves in May and June. Then the overwintered and diseased leaves gradually defoliated. Conidia germinated in vitro within 12 hr. They could germinate from 5 to 35°C with an optimum temperature at 25°C, and from pH 3 to 9 with an optimum between pH 4 and 9. Mycelia grew well on various natural and chemically defined agar media. They grew well at 25°C within the range of 5 to 35°C, and at pH 4 to 9 with the range from 3 to 9. Germination of conidia was strongly suppressed by CuSO4⋅5H2O, maneb and thiophanatemethyl. Sporulation experiments on agar media were successful. After detailed examination under light and scanning electron microscopes, the causal fungus was placed in the genus Pseudocercospora Speg. emend. Deighton (1976) and renamed under a new combination, P. pyracanthae (Katsuki) Nakashima et Kobayashi.
Three hundred eight isolates of Magnaporthe grisea were collected from rice plants in 14 counties of Yunnan Province, China in 1988-89. Each isolate was tested for mating type and fertility with Mat1-1 and Mat1-2 female fertile tester strains. Three percent of these isolates consisted of Mat1-1, and 23% of Mat1-2. The remaining 74% isolates did not produce perithecia in crosses with both Mat1-1 and Mat1-2 fertile testers. The percentage of fertile isolates in each county ranged from 90% in Lincang to 0% in Lijiang, Dali, and Honghe. Almost all the isolates were differentiated into races based on the reaction of Japanese differential cultivars. Sixteen races were identified within the fertile isolates. Isolates of both mating types were found in two counties, Qujing and Xishuangbanna, and those in Xishuangbanna were slightly interfertile. In contrast, crosses between the hermaphroditic isolate CHNOS37-1-1 from Xishuangbanna and three male isolates from other counties led to the successful production of large numbers of perithecia containing viable ascospores. The crosses were fertile enough to permit the isolation of germinating ascospores. The southwestern area where fertile blast fungi were isolated with a considerable frequency, coincided with the area with a high diversity of rice cultivars.
Plant debris floating on the water surface after puddling was collected and applied in a sclerotia-free experimental field to confirm that mycelia in plant debris act as primary inocula for rice sheath blight in the Philippines. As we were able to isolate sheath blight fungus from plant debris, the mycelium apparently survived in debris until the following growing season. The percentage of diseased hills in plots without plant debris reached 3.9% by one month after heading, whereas in plots containing plant debris at a rate of 2kg and 4kg per 35m2, the values were 11% and 18%, respectively. Inoculum potential of sclerotia was about three times as much as that of plant debris. These results suggest that mycelium in plant debris may play a role as primary inoculum of the disease in the Philippines.
A virus, designated NC, isolated from gentian plants (Gentiana spp.) with severe necrosis in Fukushima Prefecture, was characterized and compared with other isolates of clover yellow vein virus (ClYVV). When 26 species of plants from 13 families were mechanically inoculated with the NC isolate, 19 species in 10 families were infected, thus being similar to ClYVV in host range and symptomatology. The virus was serologically identical to ClYVV in SDS agar double-diffusion tests, but was different from bean yellow mosaic virus (BYMV). The nucleotide sequence of the 3' terminal region of the NC isolate RNAs was compared with that of ClYVV-NFU, an isolate from bean (Phaseolus vulgaris) in Fukushima Prefecture. The 3' non-coding regions of both isolates were identical. They also had higher nucleotide sequence homologies with other ClYVV isolates (93.3-99.4%) than with BYMV isolates (73.7-77.1%). In the coat protein gene, the amino acid sequence of the NC isolate also showed higher homology with ClYVV isolates (91.6-98.2%), especially with ClYVV-NFU, than with BYMV isolates (72.9-76.5%). Based on these results, the NC isolate which caused gentian necrotic dwarf was identified as ClYVV.
One tree each of Tilia japonica (Japanese linden) and Acer palmatum (Japanese red maple) with wilt disease symptoms has been found in Hirosaki, Aomori pref., since 1993. Leaves turned yellow to brown, withered in early summer and finally fell. Defoliated twigs and small branches of affected tree also withered and fell. Occassionally, cupping of the leaves was found on affected trees. The xylem in affected branches of both trees exhibited vascular discoloration on one side, from which a species of Verticillium was isolated. Colonies of the fungus on PDA plates were at first white, then gradually turned black. The basal cell of the conidiophore remained hyaline. In old cultures, microsclerotia formed by budding of mycelial cells. The fungus developed mycelial colonies on PDA plates at a temperature range of 4-32°C, with an optimum at 20-25°C. From these and other cultural and morphological characteristics, the fungus was identified as Verticillium dahliae Klebahn. Isolates of V. dahliae from both trees reproduced the disease on small potted plants of T. japonica and A. palmatum in inoculation experiments. The fungus was also pathogenic to various vegetable and ornamental plants, including Brassica campestris, Cosmos bipinnatus, Lilium medeoloides, Lycopersicon esculentum, Platycodon glaucum, Raphanus sativus, Solanum melongena and others.
Leaf smut caused by Doassansia horiana P. Hennings occurs widely in paddy fields of cultivated Chinese arrowhead (Sagittaria trifolia L. var. edulis Sieb.). The cultivars ‘Aokuwai’, ‘Shirokuwai’ and ‘Suitakuwai’ of Chinese arrowhead, wild arrowhead (S. trifolia L.) and the wild species S. aginashi Makino were cultivated in a paddy field in Kadoma City, Osaka Prefecture in 1994 and 1995. Leaf smut spots formed on leaf blades of the three cultivars and wild arrowhead in July and August. The spots did not form on leaves of S. aginashi. Most spots formed from late July to early August, when the average temperature was more than 27°C. More spots formed on the three cultivars than on wild arrowhead. Blister smut was also observed on petioles of the cultivars during this period. No spots or blisters were observed on the corms of either the cultivars or wild arrowhead. Scanning electron microscopy showed spore balls in the immature spots on the leaf blade. Spore-like bodies were observed in immature spore balls. Many spore balls were found in mature spots on leaf blades and mature blisters on petioles. Spore balls in mature spots were larger than those in the immature spots. The surface of the spore balls was covered with mycelia. The immature spore balls in the wild arrowhead morphologically resembled those in Chinese arrowhead.