Enhanced aerenchyma development in rice under transient drought-to-waterlogged (TD-W) stress promotes root system development by promoting lateral root production. This study analyzed the quantitative trait loci (QTLs) associated with the plasticity in aerenchyma development under TD-W stress. A mapping population of 60 F₂ genotypes of chromosome segment substituted lines (CSSL) derived from CSSL47 and Nipponbare crosses were grown in rootboxes and evaluated for shoot and root growth, and aerenchyma development (expressed as root porosity). The TD-W stress was imposed starting with water saturated soil condition at sowing and then to progressive drought from 0 to 21 days after sowing (DAS) prior to exposure to sudden waterlogging for another 17 days (21 to 38 DAS). We performed simple and composite interval mapping to identify QTLs for aerenchyma development. QTL associated with aerenchyma development was mapped on the short-arm of chromosome 12 and designated as qAER-12. The effect of qAER-12 on the plasticity in aerenchyma development under TD-W was significantly associated with the increase in lateral root elongation and branching. This resulted in greater root system development as expressed in total root length and consequently contributed to higher dry matter production. This qAER-12 is probably the first reported QTL associated with aerenchyma development in rice under TD-W and is a useful trait for the improvement of the adaptive capability under fluctuating soil moisture conditions.

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Genetic variation in the growth response to temperature is a basis for developing adaptation measures to global warming, but evaluation of cultivars for the temperature responses may depend on other environmental factors such as light. In this study, we tested the growth responses of 18 diverse rice cultivars to constant day/night temperature of 25, 28, 31 and 34ºC in artificially-lit growth chambers (ALC) in Wagga Wagga (7.8 MJ m^-2 d^-1), and in naturally-lit chambers (NLC) in Yanco (25 and 28ºC and 13.4 MJ m^-2 d^-1; 31 and 34ºC and 11.5 MJ m^-2 d^-1), both in NSW, Australia. There was a significant interaction between temperature and chamber type for total shoot and panicle biomass; total shoot biomass was largest at 31ºC in ALC, and at 25 and 28ºC in NLC. From the average of all temperatures, the total shoot biomass declined by 29.5% in plants grown in ALC compared with those grown in NLC. Importantly, cultivar performance in ALC was similar to that in NLC at these temperatures, as evidenced by the highly significant correlation in total shoot biomass between ALC and NLC. Among 18 cultivars, IR64, IR72, N22, Vandana, Takanari and Koshihikari commonly produced a larger total shoot biomass under higher temperature conditions. Leaf area at earlier measurement date was highly correlated with the final total shoot biomass at the higher temperature more than specific leaf area.

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Growth, yield and quality of sunflower (Helianthus annuus L.) in a rotational paddy field were compared with those in an upland field. In the rotational paddy field the growth was significantly suppressed and the seed and oil yields were significantly lower than those in the upland field. In the maturing period, oil accumulated in seeds until about 25 d after flowering (DAF) in both fields, but less in the rotational paddy field than in the upland field. Differences in oil contents (per seed) between the fields were seen from about 25 DAF onward. The fatty acid in seeds changed with maturing of plants. In mid-oleic hybrids, oleic acid increased remarkably until about 25 DAF and then decreased slightly; linoleic acid content decreased until about 14 DAF and then tended to increase. In linoleic acid hybrids, oleic acid increased until about 14 DAF and then decreased; the linoleic acid content tended to be low until about 14 DAF and then increased. Although the temporal patterns of fatty acid compositions during seed maturation were similar in both fields, the oleic acid content tended to be lower in the rotational paddy field even under the same climatic conditions and ripening periods. The differences between the fields were seen clearly from around 25 DAF. We discuss our findings with regard to physiological changes in developing seeds and the effects of high or changeable soil moisture content on sunflower growth and quality.

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In order to enhance rice productivity under water-deficient conditions, it is essential to improve nitrogen (N) uptake ability or its use efficiency. The objectives of the present study were to examine the genotypic variation in N uptake ability and physiological N use efficiency (PNUE) among 70 rice cultivars, and to clarify its association with biomass production and water uptake ability. Plants were grown under three soil moisture regimes: flooded and two non-flooded (−0.10 and −0.52 MPa soil water potential) conditions. A substantial genotypic variation in the amount of aboveground N uptake was observed, and the amount bore a positive correlation with aboveground biomass production regardless of soil moisture regime, whereas PNUE showed a negative if any correlation with biomass production depending on soil moisture regime. A significant interactive effect on the amount of aboveground N uptake between cultivars and soil moisture regimes was observed; there existed cultivars that exhibited superior N uptake only under non-flooded conditions. N uptake ability was closely correlated with water uptake ability, while a substantial genotypic variation in N uptake per unit water uptake was found in the two non-flooded regimes. These results indicate that a substantial genotypic variation in N uptake ability under water deficient conditions exists among diverse rice genetic resources, and that the variation is associated with water uptake ability and biomass production under the water-limited conditions at the early growth stage.

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Photoperiodic sensitivity is one of the most important factors determining whether a crop can adapt to and be cultivated under a broad range of conditions. In common buckwheat (Fagopyrum esculentum Moench), flowering time (flowering of the first flower) is a complex trait influenced by photoperiod, light quality, and temperature, which change daily under natural conditions, and their interaction. Common buckwheat shows a large genetic variation because of the outcrossing reproductive strategy of this species. Thus, flowering time variation within a population reflects both environmental and genotypic variations, and accurate evaluation of photoperiodic sensitivity in common buckwheat requires cultivation under controlled environmental conditions. Here, we investigated photoperiodic sensitivity and its genetic diversity in two buckwheat cultivars, the autumn ecotype Miyazakizairai and the summer ecotype Botansoba, by controlling photoperiod during cultivation under the same temperature regime. Our results showed that (1) the summer ecotype consisted of early-flowering genotypes, including genotypes not found in the autumn ecotype; (2) the autumn ecotype consisted of various genotypes, including early-flowering genotypes and a large number of late-flowering genotypes not found in the summer ecotype; (3) the autumn ecotype showed larger genetic diversity than the summer ecotype in long-day treatments; and (4) genetic diversity first became evident in the 14.5-hr photoperiod in the autumn ecotype, and in the 15.0-hr photoperiod in the summer ecotype. These results support the hypothesis based on previous studies that common buckwheat summer ecotypes were derived from autumn ecotypes by adaptation to climate in northern Japan.

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Alfalfa suppresses mugwort growth in the field. In the present study, the allelopathic effect of alfalfa on mugwort was examined using the above-ground (AGAB) and under-ground alfalfa biomasses (UGAB), and their water extracts. The sprouting of mugwort rhizomes or seed germination, growth of seedlings and leaf color changes in mugwort seedlings were evaluated in pot experiments. AGAB mixed into soil highly inhibited sprouting of mugwort rhizome fragments and growth of seedlings. The inhibitory effect was increased, and gradual leaf discoloration (yellowing) was observed in response to a higher dose of AGAB. However, UGAB affected neither sprouting of mugwort rhizome fragments nor growth of seedlings. The growth of mugwort seedlings was not significantly affected by water extracts of either AGAB or UGAB applied after emergence. The seed germination and seedling growth were significantly reduced by water extracts of AGAB and UGAB in the petri dishes experiments. These results indicated that the allelopathic effect of alfalfa along with the competitive ability and harvesting regime may play an important role in suppressing mugwort growth.

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Young seedlings of 22 Sorghum cultivars including sorghum, sudangrass and sorghum-sudangrass hybrids, were examined for their growth characteristics and sodium ion accumulation in different plant parts, under salt treatment. The salt treatment was started with 100 mM NaCl and increased to 150 mM during the experiment. The plant dry weight decreased under NaCl treatment in all cultivars, and especially the dry weight of leaf blade decreased markedly. The cultivar difference in the plant dry weight under salt stress was affected by that in relative growth rate which was mainly changed by net assimilation rate (NAR). Cultivars that maintained higher NAR under salt stress had a smaller specific leaf area and higher nitrogen content per unit leaf area. Sorghum plants under salt stress retained Na⁺ mainly in roots preventing the distribution of excess amount of Na⁺ to leaves, but the root dry weight was increased by salt stress. It was therefore considered that thicker leaf blades and apparent increases in root dry weight were the main contributors to the maintenance of dry matter yield and enhanced the growth of Sorghum cultivars under NaCl treatment.

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Although direct seeding is expected to be a labor-saving method in rice cultivation, poor seedling establishment is a major obstacle to widespread use of this practice. I previously reported that the seedling establishment of rice sown on sulfate-applied submerged soil was improved by the application of potassium molybdate to the soil. In this study, I investigated the effects of seed coating with poorly soluble molybdenum compounds on the seedling establishment to reduce the necessary amount of molybdenum (Mo). Seed coating with poorly soluble Mo compounds improved the seedling establishment in sulfate-applied submerged soil. Especially, ammonium phosphomolybdate and potassium phosphomolybdate were more effective and difficult to impair the seedling establishment even by seed coating of excessive amounts. Mo trioxide, which is a cheapest Mo compound, was also effective. Accordingly, seed coating with these Mo compounds would have the potential to improve rice seedling establishment in sulfur-rich submerged soil.

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Direct-seeding has been proposed as a water- and labor-saving method to grow irrigated rice. Our objective was to compare the effects of flooded and aerobic conditions on the yield stability of direct-seeded rice. We set up four trials in the field: aerobic, near-saturated and flooded soils with direct seeding, and flooded soil with transplanting. Grain yield of direct-seeded rice was comparable to that of transplanted under flooded conditions. However, the yield of direct-seeded rice under aerobic conditions was up to 21% lower than that under flooded conditions. This poor performance was associated with reduced leaf growth during the vegetative stage. Our results indicate that the yield stability of direct-seeded rice could be lowered by the water-saving irrigation, compared with the conventional flooded culture. In order to save irrigation water, physiological research on direct-seeded rice should target the vulnerability of rice to aerobic soils or to soil moisture fluctuations.

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A fiber reinforced plastic (FRP) pot, equipped with a slanted pipe through which water is supplied, has been used for assessment of rice herbicides. This pot may also be useful for controlling water table in upland conditions. In this experiment, early growths of soybean and morning glory grown under waterlogging and excess soil water conditions were evaluated. The waterlogging condition was attained by adjusting the top of the slanted pipe to soil surface level, and excess soil water condition (0.2 m³ m⁻³) by adjusting to 15 cm below the soil surface. The water content of the soil did not fluctuate during the treatment. Shoot growths of soybean and morning glory were poorer under waterlogging than excess soil water condition. The present experimental procedures using a FRP pot could be available for evaluation of wet damage of field crops grown under ill-drained field.

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