In hydroponically raised seedling method for long-mat type rice cultivation, influences of seed disinfectants on seedling growth were examined. Damage from the disinfectants appeared severely in the roots than in the upper part of rice seedlings, so the extension of roots was obstructed. On the other hand, the restraint of root extension in seedlings treated with pefurazoate or benomyl was lesser than in the seedlings treated with other disinfectants. These results suggest that pefurazoate and benomyl could be applied to hydroponically raised seedling method for long-mat type rice cultivation.
The control effect of chemicals on the root-rot caused by Pythium sp. in Cocoyam (Xanthosoma sagittifolium) was investigated in Sri Lanka. The effect was observed in two treatments: one was the treatment of metalaxyl (ridomil) solution applied to inoculated soil, and the other was the treatment of dipping inoculated sucker to metalaxyl solution in the field, the effect of metalaxyl solution was also investigated. Thirty-seven days after the application of metalaxyl solution, increase of leaf number and plant height was observed and showed well plant growth, and the infectivity index decreased. Treatments of dipping suckers and application of metalaxylto the soil were effective in controlling this disease.
Stem and root rots of perennial spiraea (Astilbe×arendsii) and Otacanthus caeruleus occurred in Tokyo Metropolis in 1998. A Rhizoctonia species isolated from the diseased plants was identified as Rhizoctonia solani Kühn. Inoculation tests showed that the fungus was the causal agent of these diseases. This is the first report on these diseases in Japan.
Sclerotinia rot of aster (Aster pilosus Willd.) and strawflower (Helichrysum bracteatum Willd.) occurred in Tokyo Metropolis in 1998. The causal fungus isolated from the diseasd plants was identified as Sclerotinia sclerotiorum (Libert) de Bary by morphological observations and inoculation tests. This is the first report on the disease in Japan.
Root rot of New Guinea Impatiens occurred in Saitama Prefecture in 1998. A fungus isolated from the diseased plants was identified as Pythium spinosum Sawada. The inoculation experiment showed that the fungus was the causal agent of the disease.
Experiments were conducted to assess whether two strains of the pupal parasitoid wasp Itoplectis naranyae could differ in offspring production and sex ratio. Galleria mellonella was used as a host. Galleria mellonella was highly suitable for the develpment of parasitoid offspring, and the percentages parasitoid emergence did not differ between the two strains, regardless of host size. Females of Kobe strain produced more female offspring than Tsukuba strain did. Factors that caused this sex-ratio difference were discussed.
Virulence of the brown planthopper Nilaparvata lugens that immigrated into Japan in 1991, 1992, 1995 and 1996 was examined on four indica rice varieties, IR26 (carrying a resistance gene Bph-1), Mudgo (Bph-1), ASD7 (bph-2) and Babawee (bph-4) and on two japonica rice lines, Saikai 190 (Bph-1) and Norin PL10 (Bph-3). The planthoppers were reared on a susceptible japonica rice variety Reiho, and the newly-emerging brachypterous females were released on 5-to 7-week-old test rice plants at tillering stage. I defined the females whose abdomina became swollen within five days after releasing or those which have survived for five days as virulent individuals. The 1995- and 1996-populations of N. lugens had higher proportions of virulent females on the Bph-1-carrying rice varieties, 54-79% on IR26, 39-66% on Mudgo and 95% on Saikai 190, than the 1991- and 1992-populations. However, all the tested populations had still low proportions of virulent females on the rice varieties carrying bph-2, Bph-3, or bph-4, especially those carrying Bph-3 or bph-4. These results show that virulence to Bph-1 in the N. lugens populations immigrating into Japan has become stronger after 1988-1990 in which change of the virulence was first found, and suggest that the resistance of Bph-1 has been broken down for this N. lugens population.
To evaluate the effects of Beauveria bassiana preparations (Botani Gard™) as control agents of whiteflies, two experiments were conducted on tomato. First, the tomatoes in a plastic house were sprayed with emulsifiable suspension formulation (ES) of the agent on May 19 and 26 and June 2 to control Trialeurodes vaporariorum. The temperature and relative humidity in the plastic house were moderate (daily average temperature: 19.6-21.7°C) and higher (daily average humidity: 78.1-84.7%), and the most effective control of the whitefly was obtained. Secondly, other tomatoes in a vinyl house were sprayed with wettable powder formulation (WP) on October 14, 21 and 28 to control Bemisia argentifolii that had been artificially introduced in the plants in advance. The whitefly was also effectively controlled in spite of the lower temperature and relative humidity. These results show that B. bassiana preparations are useful for the management of whiteflies attacking tomatoes.
A laboratory strain was established on the ragweed beetle, Ophraella communa LeSage, which has recently been introduced into Japan. The original population was collected in Tsukuba, Japan in September and October 1998. At 25°C of 16L-8D and 60% RH conditions, the durations of egg, hatching to adult emergence and preoviposition were about 6, 18 and 5 days, respectively, with the ragweed, Ambrosia artemisiifolia L. grown in a greenhouse as a host plant.
Leaf blight symptoms of Bouvardia×hibrida have broken out in two areas in Oshima Island, Tokyo Metropolis in 1998. The nematodes isolated from the diseased plants were identified as Apherenchoides fragariae by morphological observation and morphometrics. To confirm the virulence of the nematodes, 200 individuals extracted from the field Bouvardia were inoculated on the leaves of healthy Bouvardia sp., Primula sp., Begonia sp., Gerbera sp. and Eustoma sp. in pots with three replications. These tests were successful in reproducing the leaf blight symptom characteristic to the nematode and in establishing nematode colonies on all the plants tested. This is the first record on the leaf blight disease of Bouvardia caused by A. fragariae in Japan.