Journal of Weed Science and Technology

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In order to obtain fundamental knowledge of habitat management for the in-situ conservation of wild and weed azuki beans as genetic resources, we investigated their growth including plant architecture change, dry weight, and seed production under three shading conditions (50%, 70%, and 100% in relative light intensity). Under the strong shading condition, the leaf size, total stem length, number of branches on the main stem, main stem circumference, dry weight, and total number of seeds all decreased in the wild and weed azuki beans, however, the inter-node length of the main stem increased. The strong shading slightly decreased the main stem length in wild azuki, however, it lengthened the main stem length or futile in weed azuki. This phenotypic plasticity is assumed to enhance a plant's success in gaining access to the top of vegetation crown when it is shaded by other plants during the seedling stage. The wild azuki bean had a high ability compared to the weed azuki bean in the expansion of the main stem under the light-limiting condition, suggesting that the wild azuki bean is better adapted to competitive environments. The reduced seed productivity in both the wild and weed azuki beans under the shaded conditions implies that they require much more light intensity at least during the late growing stage.

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The eighteen kinds of paddy rice herbicides concentration in water samples at Sakura R. and L. Kasumigaura were monitored from 2001 to 2005. The highest concentrations of the rice herbicides were observed at Sakura R. during middle May to early June and these concentration levels at the midstream of Sakura R. were 0.12-8.8 μ g · l-1. The residual rice herbicides observed in Sakura R. water was rapidly diluted and dispersed in L. Kasumigaura and the dilution magnification from downstream of Sakura R. to Tsuchiura bay of L. Kasumigaura was 3 to 17 times. The annual trends of the detected rice herbicides concentration at midstream of Sakura R. were almost correlated with the annual trend of sales amounts of these rice herbicides in Ibaraki prefecture.
The levels of the rice herbicides at L. Kasumigaura did not exceed EC₅₀ for fresh water algae. However the results of some rice herbicides' detected levels at Sakura R. exceeded EC₅₀ for fresh water algae.

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