To develop chemical control measures against lettuce (Lactuca sativa) big-vein disease (BV), 36 fungicides were tested for the effect on infectivity by Olpidium brassicae and the expression of lettuce big-vein symptom by drench treating. Thiophanatemethyl (TM) was effective with optimum conditions as follows: (i) the effective concentration of TM was more than 350ppm; (ii) soil around lettuce roots was saturated with ca. 50ml TM per 90ml pot; and (iii) treatment with TM on day of transplanting. The effects of TM persisted for ca. 1 month. No phytotoxicity were observed. From these results, TM application was effective during the initial growth period of lettuce for the control of lettuce big-vein disease.
Dieback has been found frequently on kiwifruit branches more than 10 years old in Kagawa Prefecture in recent years. The dieback often begins at large cut ends and sunburned parts of kiwifruit branches. It usually occurs on thick branches and lateral branches, but in serious cases, primary and secondary scaffold branches and trunks are also affected. Phomopsis sp., Fusicoccum aesculi and several other fungi were isolated from the diseased branches. Both isolates of Phomopsis sp. and F. aesculi were pathogenic to kiwifruit branches. The two isolates of Phomopsis sp. were also pathogenic to fruits of kiwifruit, satsuma mandarin and apple and to branches of peach and Jananese pear. The two isolates of F. aesculi were also pathogenic to fruits of kiwifruit. Based on morphological and cultural characterisitics, the causal pathogens were identified as Diaporthe sp. and Botryosphaeria dothidea, which are the same as kiwifruit soft rot fungi.
Fungal strains in the genus Fusarium and Trichoderma that were isolated from the rhizosphere of some plants were screened for inhibition of “Bakanae” disease (Giberrella fujikuroi) and bacterial seedling blight (Burkholderia plantarii) that are very serious diseases, caused by seedborne pathogens of rice (Oryza sativa) seedlings. Of the tested 350 Fusarium and 66 Tricho-derma strains, frequency of the strains that inhibited “Bakanae” disease was very high when the seeds were treated with conidi-al suspensions and/or cultural filtrated and sown in small pot. Among those strains with high inhibitory activity against “Bakanae” disease by treatments at comparatively low inoculum doses, many strains also had high inhibitory activity against bacterial seedling blight as well. Among those strains, Fusarium oxysporum SNF-356 and Trichoderma sp. SKT-1 isolated from the rhizosphere of tomato (Lycopersicon esculentum) and Japanese lawgrass (Zoysia japonica), respectively, were the most effective and had equivalent inhibiting activity as some chemicals, including ipconazole, copper flowable and oxolinic acid when seeds were soaked in 1.0×107 and 1.0×105 conidia/ml or higher suspensions. Particularly, the activity of SKT-1 against “Bakanae” disease was stable and not influenced by the degree of seed infection. The occurrence of “Bakanae” disease at the heading stage of rice plants that emerged from the seeds treated with either of the isolates and were transplanted and grown in paddy fields was significantly lower than that on untreated seeds.
Strain SKT-1 of Trichoderma sp., when rice seeds were soaked in a suspension of its conidia at 4×104-1×106 conidia/ml, gave high control of “Bakanae” (foolish seedlimg) disease, that was nearly equivalent to that of seed disinfection with ipconazol-copper flowable. At 2×105-1×106, it also gave high control of bacterial seedling blight, bacterial grain rot and bacterial brown stripe, nearly equivalent to those of seed disinfection with oxolinic acid wettable powder. At 1×107, it also gave control of blast and brown spot in the stage of seedling, nearly equivalent to that of ipconazol-copper flowable. Typical pathogenic symptons, such as damping-off, poor emergence and growth retardation, were not observed when rice seeds and seedling bed soil were treated with SKT-1. SKT-1 conidia and with those washed by centrifugation gave clear control against “Bakanae” disease and bacterial seedling blight was clearly seen, but neither SKT-1 conidia killed by autoclaving nor the supernatant solution from the centrifugation controlled disease. SKT-1 strain gave high control of “Bakanae” disease and bacterial seedling blight in treatments during soaking and germination. In post-seeding treatments of conidia at low concentrations, however, disease control of “Bakanae” disease decreased and bacterial seedling blight was not controlled by any SKT-1 concentration tested. Tests performed on the loss of disease control in combination with benomyl revealed that SKT-1 had lost its inhibitory effects against “Bakanae” disease by one day after seeding and against bacterial seedling blight by the time of seeding. In subsequent combined treatments, however, SKT-1 controlled both diseases.
Monoclonal antibodies (MAbs) specific to the 22-kDa coat protein (CP) of Broad bean wilt virus 2 (BBWV-2) were produced. The 22-kDa CP of the IA isolate expressed in E. coli was used to immunize mice and three independent hybridoma cell lines were screened. In western blot analyses, the MAbs (MAb3-9B, MAb5-12A and MAb6-2A) reacted to the bacterially expressed 22-kDa CP of the IA isolate and most BBWV-2 isolates, but not to some other BBWV-2 isolates and other plant viruses. In immuno-electron microscopy, MAb3-9B and MAb6-2A reacted with BBWV-2 particles to the 10-5 dilution.
In 2001, a new bacterial disease was observed on hydroponically cultured pak-choi [Brassica campestris L. (chinensis group)] in Fukushima Prefecture, Japan. Symptoms were expressed as water-soaked lesions that extended from the midrib to the tip of leaves. A causal bacterium was isolated not only from the infected tissues but also from the hydroponic solution. Stab inocula-tion of the midrib reproduced the original symptom. The symptom was also expressed after artificial inoculation of the roots, suggesting possible root infection from the bacterium in the hydroponic solution. The pathogen was identified as Xanthomonas campestris pv. campestris (Pammel 1895) Dowson 1939.
A rapid and simple procedure is described to detect the genomic RNA molecule of Cymbidium mosaic virus (CyMV). This method, named RT-LAMP, allows direct detection of RNA from infected plants without careful RNA extraction, rapid ther-mal cycling and gel electrophoresis. RT-LAMP was successfully used to detect CyMV from leaves of Phalaenopsis orchid in-fected with CyMV. A large amount of byproduct, pyrophospate ion, is produced, yielding a white precipitate of magnesium pyrophosphate in the reaction mixture. The presence or absence of this white precipitate allows easy detection of the amplifi-cation of CyMV genomic RNA without gel electrophoresis.
Mutants of Trichoderma sp. SKT-1 with tolerance to benomyl were easily induced with UV irradiation or nitrosoguanidine. Strain SKT-3 induced by UV irradiation possesses high tolerance to benomyl (MIC 1000μg/ml). Because it could be re-isolated on benomyl-containing culture media, activity of the strain could be tested in the environment, including soil and water systems. SKT-3 had suppressive activities against “Bakanae” disease and bacterial seedling blight comparable to its parent strain, SKT-1 and was compatible with benomyl-containing fungicides.
An outbreak of a new bacterial disease of flowering cabbage (Brassica oleracea var. acephala) was recorded in Hyogo (1999) and Shizuoka (2000) prefectures, which is characterized by dark brown leaf spots with gray center and yellow V-shaped lesions at the leaf margins. The pathogen was identified as Xanthomonas campestris pv. campestris (Pammel 1895) Dowson 1939. We propose the disease name as black rot of flowering cabbage.