Factors influencing the phytotoxicity of cafenstrole (N, N-diethyl-3-mesitylsulfonyl-1H-1, 2, 4-triazole-1-carboxamide) to rice plants in paddy fields were investigated in a greenhouse. The phytotoxicity of cafenstrole (3-6g a. i./a) to the plants was not affected by the rice seedling properties (Fig. 1), rice seedling age (Fig. 2), temperature (Fig. 4), soil type (Fig. 5), flooding water depth in the range of 1-6cm (Fig. 6) or water leakage (Fig. 7). The phytotoxicity of cafenstrole, however, was enhanced when the transplanting depth was 1cm and all the roots of the rice seedlings were located on the soil surface (Fig. 3).
In conclusion, the transplanting depth of rice plants appears to be an important factor influencing the phytotoxicity of cafenstrole.

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Plants of Scirpus juncoides Roxb. var. ohwianus T. Koyama were sampled from eight sulfonylurea-resistant populations and six-susceptible populations in rice fields in the Hokkaido and Tohoku regions, in the northern part of Japan (Table 1). Germination tests were conducted under several germinant conditions using S. juncoides seeds from the fourteen populations in 1998 and those from four populations (3 resistant and 1 susceptible) in 1999 to investigate their germination performance at low temperature. The germination percentages of both biotypes were very high when the seeds germinated in glass tubes filled with tap water at 15°C, and the difference between the biotypes was not obvious (Table 2). However, the germination percentage of the resistant plants was significantly higher than that of the susceptible plants when the seeds germinated on submerged soil surface in petri dishes. The differences between the biotypes were more obvious at 15°C than at 30°C (Table 2). The germination rate of the resistant plants was also significantly higher than that of the susceptible plants at 15°C (Table 3). Similar results were obtained in 1998 and 1999, indicating that the difference between the biotypes was due to their genetic difference (Table 4, Table 5). In a rice field infested with resistant S. juncoides plants, weed seedlings were collected after rice transplanting and diagnosed as sulfonylurea-resistant orsusceptible plants. The results indicated that the resistant plants emerged earlier than the susceptible plants, namely 10 days after rice transplanting (Table 6). It was suggested that a higher control effect could be obtained by earlier application of herbicides in rice fields infested with resistant S. juncoides plants in Hokkaido where the air and water temperatures are very low during the weed emergence period after rice planting.

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We examined two hundred and twenty five specimens of naturalized Oxytripolium deposited in nine herbaria, TNS, TI, MAK, KPM, KYO, OSA, WAKAYAMA, KURA and RIB in Japan. We identified three taxa, 1) Aster subulatus Michx. var. subulatus, 2) Aster subulatus Michx. var. sandwicensis A. G. Jones, 3) Aster subulatus Michx. var. elongatus Bosserdet. (Japanese common name is Houkigiku, Hiroha-houkigiku, Oo-houkigiku, respectively). Chromosome number of Aster subulatus Michx. was 2n=20 (tetraploid), that of Aster subulatus Michx. var. sandwicensis A. G. Jones, 2n=10 (diploid), and that of Aster subulatus Michx. var. elongatus Bosserdet, 2n=20 (tetraploid). Basic chromosome number X=5 was different from that of other Japanese Aster species with X=9.
A natural hybrid between Aster subulatus Michx. and Aster subulatus Michx. var. sandwicensis A. G. Jones was detected in Okayama Prefecture, and it was designated as Murasaki-houkigiku (in Japanese). Hybrid plants between Aster subulatus Michx. and Aster subulatus Michx. var. sandwicensis A. G. Jones could be obtained. Their morphological characters were similar to those of the natural hybrid. The chromosome number of the hybrid was 2n=15. The hybrids produced infertile achenes because they were triploid.
A natural hybrid between Aster subulatus Michx. var. sandwicensis A. G. Jones and Aster subulatus Michx. var. elongatus Bosserdet was found in Chiba Prefecture, and it was designated as Osozaki-houkigiku (in Japanese). Hybrid plants between Aster subulatus Michx. var. sandwicensis A. G. Jones and Aster subulatus Michx. var. elongatus Bosserdet could be obtained. Their characters were similar to those of the natural hybrid.

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Arthraxon hispidus (Thunb.) Makino (Poaceae) is an annual weed in arable and ruderal sites in Japan. It is used for dying silk fabric, and has been brought into cultivation in Hachijo Island for this purpose. Three accessions from farmers'seed-stocks, 11 wild accessions collected in Hachijo Island and 5 wild accessions collected in the Kinki district (Table 1) were grown under uniform conditions, and 26 traits were compared.
A remarkably high variability was observed in the phenological and morphological traits among wild and cultivated accessions. The cultivated accessions showed a typical domestication characteristics such as synchronous branching and heading, larger leaves, enlarged spikes and spikelets and longer internodes, and uniform maturation compared with the wild accessions. Two wild accessions from Hachijo Island showed the same characteristics as those of the cultivated accessions (Fig. 1 and Table 2).
The first and second principal components, which were derived from 16 quantitative traits, illustrated the morphological and phenological differences among the cultivated accessions from Hachijo Island, wild accessions from Hachijo Island and wild accessions from the Kinki district (Fig. 2).
It is likely that the presence of the adaptive characteristics in the cultivated accessions was due to unconscious selection under cultivation and partly to conscious selection for higher yield or better quality of the dye.

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Experiments were carried out in order to obtain information on the practical control of tuber production of Eleocharis kuroguwai Ohwi, a perennial paddy weed. In the experiments, single planting of the weed alone and mixed planting with paddy rice were conducted in paddy fields. The plants were subjected to four levels of light intensity during the tuber formation period (Fig. 3, Table 1), to observe the changes in the dry matter and tuber production associated with the suppression of the radiation absorbed by the weed. Then, the quantitative relation between the shading intensity and tuber production was analyzed.
The growth of the stem, the assimilatory organ of the weed, was reduced in proportion to the reduction of the light intensity (Fig. 5). As the stem growth and light intensity decreased, the radiation absorbed during the tuber formation period markedly decreased, and the aboveground weight at the end of the tuber formation period was considerably reduced (Table 1, 2). Along with the reduction of the light intensity, the ratio of the tuber dry matter weight to total dry matter weight (aboveground and tuber dry matter weight) at the end of the tuber formation period (tuber-total dry matter ratio) was reduced (Table 2). Therefore, the total tuber weight was remarkably reduced with the decrease of the intercepted radiation (Fig. 6). However, the average weight of a tuber did not change, as the tuber number decreased in proportion to the reduction of the total tuber weight (Table 2).
The contribution rate of accumulated carbohydrates present in the vegetative parts at the tuber initiation stage to the carbohydrates of the tubers at the end of the tuber formation period was estimated to be very low and ranged from 3 to 5% (Fig. 6). It was confirmed that tuber production directly depended on the total dry matter production and the tuber-total dry matter ratio, as indicated in our previous study.
When the radiation absorbed during the tuber formation period was reduced to 20% of that in the non-shading control in the single planting of the weed or 40% in the mixed planting, the tuber production depended only on the amount of carbohydrates accumulated in the vegetative parts at the tuber initiation stage. It is concluded that the decrease of the radiation absorbed during the tuber formation period up to 20% of that in the non-shading control in the single planting or 40% in the mixed planting is an effective method of control to reduce tuber reproduction of the perennial weed.

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