Field experiments on the varietal difference of sweet potato in susceptibility to the root-knot nematode, Meloidogyne incognita, were conducted at Asahi, Chiba, during from 1943 to 1953. Determination of the nematode infestation was made in seven ways including gall formation indices. The varietal differences in susceptibility are apparent among the varieties tested, and these differences appear to be consistent from year to year. All of the varieties tested are classified into five categories according to their susceptibility, and the result indicates similarity to the result reported by Shibuya (1952) and a slight difference from the one reported by Tomonaga et al.(1956).

View full abstract

The Mexican marigold was examined to determine their nematode controlling effect when nematodes were immersed into the liquid from macerated root, stems, or leaves of the plant, or when they were planted in pot with mulberry seedling. Hatching of eggs of Meloidogyne sp.(tentatively identified as M. thamesi) after 10 days was highly decreased in the liquid from either part of the plant up to 0-7%, while approximately 70% hatched in the liquid from the macerated mulberry root or in the distilled water. It was further found that all of the newly hatched larvae were dead within 2 days. Paratylenchus sp., Xiphinema sp. and some free living nematode species were similarly dead. There was a tendency that growth of mulberry seedling with the Mexican marigold for 3 months was inferior to those without the Mexican marigold. No significant differences were found in the number of root galls as well as nematode population level in the soil between mulberry seedlings with and without marigold.

View full abstract

An instance of dispersal of the white tip nematode, Aphelenchoides besseyi Christie, having occurred in a rice paddy of Nagoya in 1967 is reported. The rice paddy was 50 m wide and 200 m long, and consisting of three plots; eastward, middle, and westward plots, each of which belongs to different growers with different rice variety. The disease occurred first in the middle plot which is 50 m wide and 20 m long, and then examination was made on the spread of the white tip disease throughout the paddy. Nematode infestation of seeds was also checked after harvest. The disease extended to both of the adjacent plots each up to 20m long with a heavy infestation area up to 12 m long in the eastward plot and 3-4 m long in the westward plot. It is apparent that dispersal of the nematodes has been made during a short period after transplanting by the flow of irrigation water from the source of the disease occurrence in the middle plot.

View full abstract

Fungicidal effect of nematicides on the nematode trapping fungi was examined byfumigating in a glass cylinder (in vitro) at three dosages of chemicals at 25°C, for 24 hr. Another fumigation experiment was also conducted in a glass cylinder or in vinyl bag containing sandy loam soil infested with Meloidogyne incognita or volcanic ash soil infested with M. hapla respectively, at a dosage for conventional nematode control, at 25° for 4 days. Nematode population was determined by the Baermann funnel technique or cucumber gall index. Nematode trapping fungi were detected by flax trap method or soil disc method. Nematicidal effect of the chemicals tested wasrecognized in all treatments without significant differences in the effect among the chemicals. Fungicidal effect of fumigation increased in order of dibromochloropropane (DBCP), dibromoethane (EDB), methylbromide (MB) <dichloropropene-dichloropropane (D-D) <chloropicrin (CP), ammonium-Nmethylisothiocarbamate (NCS). Activity of the nematode trapping fungi after fumigation was evaluated by the decrease in the population density of M. incognita and M. hapla 8 days since reinoculation, which had been made 30 days after fumigation, with the results that the trapping fungi of the DBCP and EDB treatment have proved to be most activ_??_an those of other treatments.

View full abstract