Toshiro Kuroda

Effects of High Temperature on Growth, Yield and Dry-Matter Production of Rice Grown in the Paddy Field

Abstract The effect of high temperatures on growth, yield and dry-matter production of rice growing in the paddy field was examined during the whole growth period in a temperature gradient chamber (TGC) from 2002 to 2006. Experimental plots, TG1 (control), TG2, TG3 and TG4, were arranged along the temperature gradient (from low to high temperature) in TGC. The mean and maximum air-temperatures in TG4 were 2.0 –3.6ºC and 4.0º7.0ºC higher, respectively, than those in TG1. The plant height was taller and the maximum tillering stage was earlier in TG2, TG3 and TG4 than in TG1. Plant dry weight at maturity in TG2 and TG3 was 12.8−16.4% heavier than that in TG1. In TG4, the increase in the panicle dry weight during the ripening period was smallest and plant dry weight at maturity was 11–16% heavier than that in TG1. The increase in plant dry-matter during the ripening period was smallest in TG4. The decrease in the dry weight of stem and leaf during the ripening period, which represents the amount of assimilate translocation to the panicle, was also larger in TG2-4 than in TG1. The increase in the dry weight of stem in TG2-4 at maturity was also larger than that in TG1. The photosynthetic rate in TG2-4 was up to 35.6% lower than that in TG1 because of the acceleration of leaf senescence. Brown rice yield in TG4 was 6.6−39.1% lower than that in TG1. This yield decline was due to the decrease in the percentage of ripened grains and increase in the percentage of sterile spikelets. The relation between brown rice yield and mean air-temperature during 20 days after heading showed that the brown rice yield declined when mean air-temperature exceeded 28ºC.

Effects of Flag Leaves and Panicles on Light Interception and Canopy Photosynthesis in High-Yielding Rice Cultivars

Abstract The effects of flag leaves and panicles on canopy photosynthesis in a leading cultivar (Nipponbare) and two high-yielding rice cultivars (Takanari and Ghugoku 117) bred in Japan were compared. The total dry matter production was in the order of Takanari > Ghugoku 117 > Nipponbare. Canopy photosynthesis was highest in Takanari throughout the growth season, and was higher in Chugoku 117 than in Nipponbare during the ripening period. The photosynthetic rate in the flag leaf was in the order of Nipponbare > Takanari > Chugoku 117. The light extinction coefficient of canopy was higher in Takanari than in the others. At the middle ripening stage, canopy photosynthesis increased 35 and 17% in Nipponbare and Takanari, respectively, by the removal of panicles and decreased 37 and 48%, respectively, by the removal of flag leaves. In Chugoku 117, canopy photosynthesis was hardly influenced by these treatments. Clearly, the panicles intercept more radiation at the upper layer of the canopy in Nipponbare than in Takanari and flag leaves contribute more to canopy photosynthesis in Takanari than in Nipponbare. However, these effects were small in Chugoku 117. In conclusion, Takanari produces more dry matter than the others due to larger, wider, longer and more erect 1st (flag) and 2nd leaves above the panicles, which intercept more radiation. Chugoku 117 had erect panicles which allowed more radiation to penetrate into the deeper layer of the canopy, resulting in a high dry matter production. The lower panicle height relative to leaf layer and erect panicles are important characteristics for higher yield in rice.

Characteristics of Flowering and Pod Set in Wild and Cultivated Types of Soybean

Abstract Characteristics of flowering and pod set were compared between wild and cultivated types of soybean grown in pots (1/5000 a) in a vinyl house. The wild type had 10-fold more nodes than the cultivated type. The flowering habit of the wild type was similar to that of the indeterminate type. The wild type developed 10-fold more flowers than the cultivated type, but set relatively few pods. During the process of domestication from wild to cultivated type, i) the pole climbing characteristic disappeared and development of branches and racemes with compound leaves was repressed, resulting in a decreased number of nodes, ii) flower production decreased and the rate of pod set increased markedly, and iii) the number of pods decreased, but seed size became bigger.

Comparison of Leaf Photosynthesis between Wild and Cultivated Types of Soybean

The ancestor wild species of soybean is considered to be Glycine soja Sieb. et Zucc. (Hymowitz, 1970), which grows naturally in the north-eastern section of China, Korea and Japan. With the progress of cultivation, it lost the habit of pole climbing, production of hard seed and dormancy, and on the other hand acquired upright standing, pod-cracking resistance and large seed (Hardley et al., 1973). Saitoh et al. (2004) reported that during the process of domestication from wild type to cultivated type, i) development of branches and racemes with compound leaves was repressed, resulting in a decreased number of nodes, ii) fl ower production decreased and the rate of pod set increased markedly, iii) the number of pods decreased, but seed size increased. There are many studies on the leaf photosynthetic rate of wild and cultivated crop species, e.g., wheat (Evans et al., 1970), rice (Takano et al., 1971), barley (Chapin et al., 1989). Most investigators reported that the leaf photosynthetic rate of some wild relatives of crop species was higher than that of the cultivated species. Kokubun et al. (1988) compared the leaf photosynthetic rates among six species of subgenus Glycine and obtained the same differences as reported for other crop species, but limited studies have been reported on the leaf photosynthetic characteristics of Glycine soja. This study was conducted to clarify the changes in the leaf photosynthetic capacity during the domestication process of soybean.