We investigated concentrations of mycotoxins during the growth of four cultivars of forage maize (Zea mays L.) in Nasushiobara, Tochigi prefecture, and their distribution in ears of maize grown in ...Morioka, Iwate prefecture, Japan. In experiment 1, we measured concentrations of naturally occurring fumonisin, nivalenol, deoxynivalenol and zearalenone at progressive crop growth stages. Concentrations of fumonisin in stems + leaves remained very low or not detectable, but those in ears became detectable at 40 days after heading and increased rapidly after 50 days after heading (DAH) (fumonisin B₁+ B₂<3260 μg/kg; mean value at 50–74 days after heading). Concentrations varied widely within cultivars on the same day. Concentrations of nivalenol, deoxynivalenol and zearalenone in stems + leaves and in ears were low or not detectable throughout the experiment. In experiment 2, we collected three ears of each cultivar at the late yellow-ripe stage that showed extreme symptoms of Fusarium ear rot. Concentrations of fumonisin were extremely high in the upper half of ears in all cultivars (fumonisin B₁+ B₂18,000–25,900 μg/kg) but low in the lower half and bracts. Concentrations of nivalenol, deoxynivalenol and zearalenone were extremely low or not detectable. These results show that fumonisin concentrations in ears increased rapidly after 50 DAH, they were extremely high in ears of all cultivars with symptoms of Fusarium ear rot, and fumonisin was the most common contaminant. These results will help reduce mycotoxin contamination.
Guinea grass (Panicum maximum Jacq.) is an important C-4 perennial herbage in the southern part of Japan. In February 2002, a blast disease was found on the grass cultivated on the Okinawa Islands, ...the southern most region of Japan. Early symptoms appeared as small, round or ellipsoid lesions on leaves. Lesions later expanded to 2 to 5 x 1 to 2 mm and were spindle shaped and grayish white in the central area with dark brown margins. We obtained three single-conidia isolates of a Pyricularia-like fungus from the lesions and deposited them in the NIAS Genebank, Japan as MAFF306662, 306671, and 306672. The isolates were grown under near-UV light on V8 juice agar for 7 days to produce conidia, and guinea grass plants of the seven- to eight-leaf stage grown from seeds in a green house, five plants for each isolate, were inoculated by atomizing them with the conidial suspension of 10⁵ conidia/ml. The same number of plants sprayed with sterilized distilled water served as the control. The experiments were repeated twice. All plants were covered with plastic bags for 24 h at 25°C to maintain high relative humidity. After 7 days, all inoculated plants showed symptoms identical to those observed in the field. Controls remained symptom free. The Pyricularia-like fungus was reisolated from lesions on inoculated leaves. The morphologies of the isolates were observed and described from the colonies grown under the condition described above. Conidiophores were pale brown, emerging singly or in small groups, straight or flexuous, geniculate toward the apex, and 36 to 197 x 2 to 5 μm. Conidia were obpyriform, straight, colorless to pale brown, smooth, and 19 to 30 x 5 to 10 μm with two to three septa. The morphologies were the same as those of the description of the genus Pyricularia. Previously, all Pyricularia isolates from Gramineae had been identified as P. grisea, except for those from rice (3,4). However, a new taxonomy of Pyricularia spp. based on DNA analyses was proposed by Couch and Kohn (1). Only the isolates from Digitaria were classified as P. grisea and those from C-3 grasses classified as P. oryzae. However, the species names for the isolates from the other C-4 grasses were not described. We analyzed the sequences of the rDNA-ITS region (ITS1-5.8s-ITS2) and β-tubulin gene of the isolates from guinea grass following Couch and Kohn (1). The sequences of rDNA-ITS (GenBank Accession No. AB512785) and β-tubulin (AB512786) of the isolate MAFF306672 matched the sequences of those of the Pyricularia sp. LS-group (AB274426 and AB274458, respectively) isolated from Leersia oryzoides. Hirata et al. (2) reclassified Pyricularia isolates from Gramineae by multilocus phylogenetic analysis and showed that non-P. oryzae and non-P. grisea isolates could be classified into two groups of the Pyricularia sp., a LS- and a CE-group, corresponding to those isolated from Leersia spp. and Setaria spp. or Cenchrus spp. of grasses, respectively. Since no Magnaporthe teleomorph was produced by the crossing tests using the isolates, we identified the isolates from guinea grass as the Pyricularia sp. LS-group on the basis of their morphology and the molecular phylogenetic analysis. To our knowledge, this is the first report of blast on guinea grass in Japan.
The anthracnose fungus Colletotrichum acutatum was detected in symptomless blueberry bushes (Vaccinium spp.) in a Japanese blueberry field. Naturally diseased bushes and their apparently healthy ...neighbours were selected, and C. acutatum was isolated from the symptomless tissues of each bush from February 2000 to January 2002. Analysis of the diseased bushes during the dormant period revealed that the fungus was able to survive on symptomless tissues, such as shoot bark and bud scales. Furthermore, C. acutatum was consistently isolated from symptomless leaves and shoots of several surrounding symptomless bushes. Arbitrarily primed PCR (ap-PCR) analyses of the fungal isolates obtained from the diseased and symptomless bushes revealed that most C. acutatum isolates were genotypically identical, regardless of their origins. Inoculation tests using leaves of various blueberry cultivars suggested that the presence or absence of symptoms on each bush can not always be explained by differences in cultivar susceptibility, and other factors may be associated with the appearance of symptoms.
We have demonstrated the phylogenetic diversity and antagonistic activities of three genera of dominant culturable bacteria (Bacillus, Pseudomonas and Pantoea) on tomato leaves. A total of 133 ...Bacillus isolates that were dominant on greenhouse plants and 109 Pseudomonas and 48 Pantoea isolates that were dominant on field-grown plants were analyzed based on their 16S rRNA gene sequences. Bacillus pumilus (38%), Pseudomonas monteilii (76%) and Pantoea agglomerans (90%) were the most predominant of their genera, respectively. In the genus Bacillus, effective biological control agents (BCAs) against tomato leaf mould were interspersed among its phylogenetic tree as minority groups, while the effective BCAs of Pseudomonas and Pantoea were in majority groups that showed consistent suppressive activities. The results suggest that isolating Pseudomonas and Pantoea species from field-grown tomato plants may be preferable for BCA-candidate screening than isolating species of Bacillus from greenhouse.
An omnivorous phytopathogenic fungus, Glomerella cingulata, was isolated from rice plants in Japan. We evaluated the effect of the fungus as an inoculum source for anthracnose to other plants. Leaf ...sheaths of rice plants were monitored in mid-June and mid-July for 2 years to evaluate the quantitative inhabitancy of G. cingulata in the fungal community. The pathogenicity of G. cingulata to 20 plant leaves was elucidated. A hygromycin B-resistant green fluorescent protein (GFP) mutant of the fungus was used to observe fungal infection and development processes on rice plants. Glomerella cingulata was detected on rice sheaths in mid-June at a low frequency, but was not detected in mid-July. The fungus has a broad pathogenic spectrum, whereas development of the GFP mutant in tissues of rice plants was limited. Thus, the effect of G. cingulata inhabiting rice plants as a source of inoculum for other crops is likely to be low, although the fungal potential to infect various plants was ascertained.
The pathogen of brown stripe in leaves of Cynodon dactylon (bermudagrass) and Zoysia japonica (Zoysia grass) in Japan is identical with Bipolaris heveae, a rubber tree pathogen, based on ...morphological and phylogenetic characteristics, following pathogenicity studies. Crossing isolates used in the study with each other, the obtained teleomorph is described as Cochliobolus heveicola sp. nov.
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