Report of the Chugoku Branch of the Crop Science Society of Japan

Air temperature elevation in the next century by greenhouse effect has been predicted. However, the effect of the temperature increase on irrigation requirement of rice cultivation is not obvious. The objectives of this study were to estimate the evaporative demands and changes of evapotranspiration (ET) in rice in Shimane prefecture, in the cases when the daily mean air temperature increases by 1〜5℃ from the average of ordinary years. The changes of air humidity were empirically estimated from air temperature and precipitation of past decade, and ET were estimated from the Penman equation. The possibility of water shortage was the highest in August due to high evaporative demands and low precipitation. The ET was predicted to increase 3% by 1℃ increment of air temperature from average of ordinary years, 8% by 3℃ and 14% by 5℃, respectively. When the rice produce average yield (476g m^<-2>) of ordinary years in Shimane prefecture, the ET was estimated from the means of harvest index, water-use efficiency and estimated saturation deficit under warming climate. The ET under the mean air temperature of ordinary years, under 1℃ increment from mean air temperature, 3℃ and 5℃ were calculated as 413mm, 459mm (1.11×413mm), 555mm (1.34×) and 682mm (1.65×), respectively. It was suggested that the maintenance and development of water resources, particularly in mountainous area, will be important under temperature elevation.

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Efforts were made to highlight the role of growth parameters, yield and yield components with special reference to raceme order simultaneously, to provide the comprehensive system of soybean cultivar classification. Soybean cultivar classification of 11 cultivars governed by the cluster analysis based on the above mentioned characters revealed three clusters i. e. A, B and C. Close observation of the analysis showed that the cluster A contains further two sub clusters 1 and 2. Sub cluster 1 occupies Kitamijiro, Enrei and Tatinagaha, while sub cluster 2 occupies Koganesiro and Harosoy cultivars. Similarly sub cluster 3 in cluster B consists of Tatisuzunari and Bragg, while sub cluster 4 consists of Tamahomare, Tanbaguro and Hukuyutaka. Cluster C consists of only one cultivar Touzan 69. Growth characters i. e. growth duration, first flowering, no. of phytomers, stem length and stem weight are mainly responsible to separate the clusters A and B. Yield components i. e. no. of pods, 100 seed weight and weight of perfect seed (seed yield) clearly separate the sub clusters 1, 2 and 3, 4 within the clusters A and B respectively. Low order racemes play a pivotal role for cultivar classification by separating not only the clusters A, B and C but also by differentiating the sub clusters within the clusters. Secondary raceme with compound leaf opens a new chapter by separating all the clusters from each other along with the sub clusters falling in them respectively. The correlation studies revealed that soybean yield under low planting density conditions depends on 100 seed weight and not on the total no. of pods/plant, and also, that yield increase with longer growth duration among clusters is mainly dependent on the no. of pods and seed weight on 2nd order raceme with compound leaf.

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A recently released rice cultivar 'Meguriai' was suggested to have higher grain filling ability. To evaluate the grain filling characteristics of Meguriai, its filled grain percentage, grain filling process, and other related characters were examined under both control and defoliating plots. Meguriai showed higher filled grain percentage, higher grain-filling rate, and higher final grain weight, in the grain on secondary branches, compared with Norin 22, a parent from which Meguriai was developed. Norin 22 showed the re-accumulation of non-structural carbohydrates in leaf sheath and culm at the period from 20 to 30 days after heading. Meguriai, on the other hand, did not show this reaccumulation. It was suggested that the grain of Meguriai, particularly for the grain on secondary branches, had higher sink activity to attract photosynthates, and resulted in higher filled grain percentage of the grain on secondary branches.

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In order to examine the agricultural characteristics of colored-kernel rice varieties, which included red rice and purple-black rice, 45 strains collected from Japan and 7 other Asian countries, as well as 17 leading varieties (common rice) of Hiroshima Prefecture, were cultivated under 2 soil fertility levels. The red rice strains from Japan could be divided into a short-grain type or long-grain type by the width/length ratio of hulled rice. The two groups were also different in regard to other morphological traits. The red rice strains from foreign countries varied widely in width/legth ratio. Concerning purple-black rice, there was no short grain-type among the strains from foreign countries. The red rice and purple-black rice strains were, as a rule, taller in plant height, lower in panicle number and lower in paddy yield than the leading varieties. The red rice strains from foreign countries also showed wide variations in plant height, panicle number and paddy yield. Responses to different soil fertilities were similar for most traits among the strains. One notable exception, though, was harvest index which increased slightly with high soil fertility in the case of the leading varieties, while decreasing for the other strains under the same conditions. The kernel colors of red rice, purple-black rice and common rice could be distiguished through their L value (lightness) as determined from a color difference meter. Also, the red rice showed continous variation in its kernel colors.

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