Hideo Hamaguchi

Effects of Water Table Control by Farm-Oriented Enhancing Aquatic System on Photosynthesis, Nodule Nitrogen Fixation, and Yield of Soybeans

Abstract We evaluated the effects of the water table controlled by a water table controlling system, farm-oriented enhancing aquatic system (FOEAS), on soybean productivity. FOEAS was constructed in a heavy soil paddy field; we made plots with watertables maintained at −32 (water table depth [WTD]32) and −20 cm (WTD20) from the soil surface and, as a control, an open-ditch drained plot (ODD). Soybean cultivar “Tachinagaha” and non-nodulating cultivar “En1282” were cultivated in 2006 and 2007. The moisture of the topsoil in the water table-controlled plots showed lessfluctuation owing to rainfall. The roots and nodules were distributed only in the upper soil layer in ODD, but more weredistributed in deeper soil layers in WTD32 and WTD20. In Tachinagaha, the SPAD value and stomatal conductance were higher inWTD32 and WTD20 than in ODD, resulting in a higher apparent photosynthetic rate. The aboveground total dry weight and nitrogen accumulation of Tachinagaha were higher in the water table-controlled plots than in ODD; in En1282, this difference was insignificant. The relative ureide value which is an index of nodule activity, in ODD was depressed by both excess and deficit soil moisture; however, that in WTD32 remained relatively high during the growing stage. Tachinagaha showed higheryield in FOEAS plots, especially in WTD32 than in ODD in both years. The results indicate that control of water table by FOEAS increases nitrogen fixation, photosynthesis, and yield of soybeans in upland fields converted from paddy fields.

Association of Pythium and Phytophthora with pre-emergence seedling damping-off of soybean grown in a field converted from a paddy field in Japan.

Abstract In Japan, soybean is usually cultivated in fields that have been converted from rice paddies, and poor seedling establishment due to pre-emergence seedling damping-off is often observed during the rainy season. In this study, the factors that cause the damping-off in flooded soil were investigated under high soil moisture conditions in a greenhouse and in agricultural fields. In sterilized soil sampled from a soybean field, seedlings emerged well under 48-hr flooded conditions. In unsterilized soil, soybean seeds treated with the fungicide, mancozeb+metalaxyl exhibited much higher emergence rates even under 48-hr flooded conditions than the seeds treated with oxytetracycline +streptomycin, benomyl, or flutolanil. Pythium, Phytophthora, Mucorales, Trichoderma, Geotrichum-like microorganisms, and some fungi producing conidia in a false head, were isolated from decayed seedlings. Of the isolated microorganisms, oomycete microorganisms, Pythium helicoides, other Pythium sp., and Phytophthora sp. were pathogenic to soybeans under flooded conditions. As the length of the flooding period increased, pre-emergence seedling rot also increased. However, the pathogenic oomycetes rarely caused pre-emergence seedling rot under conditions without flooding. Furthermore, under flooded conditions, the damage caused by these pathogens was reduced by treating the seeds with mancozeb+metalaxyl. These results indicate that oomycete microorganisms are involved in pre-emergence seedling damping-off under flooded soil conditions.

Major QTLs associated with green stem disorder insensitivity of soybean (Glycine max (L.) Merr.)

Green stem disorder (GSD) is one of the most serious syndromes affecting soybean (Glycine max) cultivation in Japan. In GSD, stems remain green even when pods mature. When soybean plants develop GSD, seed surfaces are soiled by tissue fluid and seed quality is deteriorated during machine harvesting. We performed quantitative trait locus (QTL) analyses for GSD insensitivity using recombinant inbred lines (RILs; n = 154) derived from a cross between an insensitive line (‘Touhoku 129’) and a sensitive leading cultivar (‘Tachinagaha’) during a 6-year evaluation. Three effective QTLs were detected. The influences of these QTLs were in the following order: qGSD1 (LG_H) > qGSD2 (LG_F) > qGSD3 (LG_L). At these three QTLs, ‘Touhoku 129’ genotypes exhibited more GSD insensitivity than ‘Tachinagaha’ genotypes. The lower incidence of GSD for ‘Touhoku129’ was attributable primarily to these three QTLs because RILs harboring a ‘Touhoku 129’ genotype at the three QTLs exhibited a GSD incidence similar to that of ‘Touhoku 129.’ Although a limitation of this study is that only one mapping population was evaluated, this QTL information and the flanking markers of these QTLs would be effective tools for resolving GSD in soybean breeding programs.