Many kinds of plant diseases, insect pests and nematodes have frequently occurred on plants of crop fields, gardens and roadsides of Japan and caused damage to agricultural and horticultural crop fields, gardens plants and roadside trees. Plant disease and insect pest diagnosis, which are usually undertaken at agricultural experiment stations, plant protection offices and extension offices, are very important to food security, food production and keeping plants in the environment healthy. I have researched data bases on plant diagnosis of the Chiba Agricultural Experiment Station and Nara Prefectural Protection Office, and showed issues of plant diagnosis. I also prsent an outlook future plant clinical practices of Japan.
Southern blight of ginger [Zingiber officinale (Willd.) Roscoe] occurred on Hachijo Island of Tokyo Metropolis in 2012. A pathogen isolated from the diseased plants was identified as Sclerotium rolfsii Saccardo based on morphological characteristics as well as molecular analyses of the rDNA-ITS region. An inoculation test confirmed that the fungus was a causal agent of this disease. This is the first report of the disease in Japan.
True leaves of young lettuce plants (3 to 4 weeks old) were more susceptible than their cotyledons to isolates of Bremia lactucae (BL) collected from Ibaraki Prefecture. In the three commercial cultivars described as resistant ones in the seed company catalogs, cv. Haru P was consistently resistant to three isolates of BL, however, the other two showed susceptible reaction and rich conidial formation was observed on the inoculated true leaves of young lettuce plants.
We investigated the occurrence of wood-rotting fungi in a peach orchard in Yamanashi Prefecture where some peach trees died after gale damage and some other trees suffered with dieback of main or side branches. We found the fruit bodies of nine wood-rotting fungi on peach trees. Trametes versicolor, Ganoderma applanatum and Ganoderma lucidum have already been recorded as causing disease outbreaks on peach trees. The other five fungi, i.e., Fomitopsis sp., Trametes hirusuta, Oligoporus sp., Laetiporus cremeiporus and Perenniporia fraxinea are recorded for the first time on peach trees. Abortiporus biennis may not be a pathogen of peach trees. We would like to propose their disease names after further studies on pathogenicity to peach trees and other properties of those species.
Chiba Prefecture is the largest producer of calla lily (Zantedeschia rehmannii) in Japan. In 2011, root rot, leaf yellowing and stunted growth of calla lily occurred in Chiba Prefecture. A pathogen isolated from the diseased plants was identified as Pythium myriotylum based on cultural characteristics as well as molecular analysis of the nuclear ribosomal internal transcribed spacer (ITS) region. An inoculation test confirmed that the oomycete was the causal agent of the disease. This is the first report of the disease in Japan.
Gray mold of perennial pea (Lathyrus latifolius) and primrose (Primula malacoides) occurred in Ibaraki Prefecture on June 2009 and in Fukuoka Prefecture on September 2010, respectively. Both causal agents were identified as Botrytis cinerea. Perennial pea is added to hosts of‘gray mold of sweet pea’caused by B. cinerea in Japan. B. cinerea pathogenicity on primrose had not been confirmed. Hence, we analyzed pathogenicity and formally reported the disease‘gray mold of primrose’in Japan.
The seedlings and petals of russell prairie gentians that had been subjected to UV-B irradiation showed reduced anthracnose symptoms. This is possibly due to suppression of Colletotrichum fioriniae hyphal growth by UV-B irradiation. Furthermore, defense responses in the host plants are also possibly involved in reducing anthracnose symptoms.
Gray mold of Christmas bells (Sandersonia aurantiaca) and fairy bells (Disporum pullum) occurred on Hachijo Island of Tokyo Metropolis in 2011 and 2012 respectively. These pathogens isolated from the diseased plants were identified as Botrytis cinerea Persoon based on morphological characteristics as well as molecular analyses of the rDNA-ITS region. Inoculation tests confirmed that the fungus was a causal agent of the diseases. These are the first reports of the diseases in Japan.
The development of methods for efficiently capturing native parasitoids and their molecular identification has proved useful in basic and applied studies on parasitoids as biological control agents. In this study, we developed a method for capturing Cotesia vestalis, an important native parasitoid of the diamondback moth, Plutella xylostella, by periodically placing Komatsuna traps, consisting of potted Komatsuna (Brassica rapa) plants infested with P. xylostella larvae, in fields in Tsukuba, Ibaraki Prefecture, Japan from June to December in 2012. The traps were then transferred to our laboratory for collection of the parasitoids that later emerged from P. xylostella. We also developed specific PCR primers to identify C. vestalis. Our results reveal that a total of 62 parasitoids were captured using the traps during the experimental period, especially in June and July (n=58), and that all the parasitoids captured and then analyzed using the primers (n=58) were C. vestalis.
We investigated susceptibility to 12 insecticides in populations of the oriental tea tortrix, Homona magnanima Diakonoff, collected from tea fields in Shizuoka Prefecture from 2004 to 2008. In the Shimada- Yui populations, the corrected mortalities 8 days after treatment with each of three insect growth regulator (IGR) insecticides, i.e. tebufenozide, methoxyfenozide, and chromafenozide [diacylhydrazine (DAH) analogs], showed slightly lower mortality compared to the susceptible strain except for chromafenozide. The mortalities to methoxyfenozide showed a gradual decrease in five years. Resistance ratios based on LC50 of tebufenozide were 10.7 and 30.1; those of methoxyfenozide were 10.9 and 11.7 in 2005 and 2006, respectively. In the case of treatment with flufenoxuron and lufenuron [both benzoylurea (BU) analog], the susceptibilities from 2004 to 2008 did not change with a clear tendency, although the susceptibility to flufenoxuron was considerably lower than lufenuron in each year and population, the resistance ratio of flufenoxuron in 2005 was 305.7. Flubendiamide, profenofos, chlorpyrifos, emamectin benzoate, and spinosad showed high insecticidal effects. As for methomyl, its resistance was found in 1980s, the change of methomyl-susceptibility was not clear.
We investigated the flight height of adults of several species of minute insects, including the tea spiny whitefly, Aleurocanthus camelliae Kanmiya and Kasai, using yellow sticky traps set vertically in three tea fields during the end of Oct. to the end of Nov. in 2011. The traps were set at heights from 0.5 m to 3.5 m above ground with 0.5 m intervals; the numbers of target minute insects captured by the traps were counted by binocular microscope. The numbers of A. camelliae adults captured by each trap set vertically showed the max at 1.0 m height above ground: about same height as the tea canopy, although the numbers captured at traps higher than 1.5 m height were very few (one or two individuals). As for the other minute insects, adult males of Pseudaulacaspis pentagona and their parasitoid, Arrhenophagus albitibiae, showed the trend to be more numerous at lower traps, although more than a few individuals (30 - 59, and 5 - 23, respectively) were captured at the highest traps of 3.5 m. The numbers of Trichogramma dendrolimi: egg-parasitoid of Tortricidae, were about the same at each height.