Effects of Dry Matter Production,Translocation of Nonstructural Carbohydrates and Nitrogen Application on Grain Filling in Rice Cultivar Takanari,a Cultivar Bearing a Large Number of Spikelets

Abstract

The effects of dry matter production and the remobilization of nonstructural carbohydrates (NSC) on grain filling were investigated using the Indica-based Japonica crossed rice cultivar Takanari, which can bear a large sink. For three years,beginning in 1994, shade treatments were conducted with different nitrogen applications to develop large variations in plant growth. The percentage of ripened spikelets showed the greatest correlation with the total amount of carbohydrate supply per spikelet during 10 to 20 days after heading, calculated by adding the amount of dry matter increase to the amount ofNSC decrease in leaf sheaths and culms during the period. Between the two components, the dry matter increase was more important. The NSC reserve played a role in compensating for the shortage of carbohydrate supply from assimilates after heading and showed a tendency to increase the percentage of ripened spikelets when dry matter production after heading was limited. However, the maximum ratio of compensatory translocation from the NSC reserve was estimated to be only 48%, becauseofsmaller reservoir size compared with the demand. The NSC reserve at heading was not significantly increased by increasing the dry matter production before heading. It was concluded that to increase grain filling ability it is more effective to increase the dry matter production after heading than that before heading. Nitrogen application showed negative effectson the translocation of reserve NSC. It is important to optimize the nitrogen content to maximize the total source of carbohydrate supply.     

Analysis of the Dry Matter Production Process Related to Yield and Yield Components of Rice Plants Grown under the Practice of Nitrogen-Free Basal Dressing Accompanied with Sparse Planting Density

References

Experiments were carried out in 1999, 2000 and 2001 on the field of Iwate University, Japan to examine the effect of nitrogen-free basal dressing accompanied with sparse planting density (BNo) on the dry matter production (DMP) of 12 rice cultivars or lines belonging to the early, medium and late-maturing genotypes. During the period from transplanting to panicle initiation (PI), DMP was lower in BNo than in the conventional cultivation (CONT) in all 3 years. The DMP during the period from PI to full heading (FH) was also lower in BNo than in CONT, particularly in the high solar radiation year of 1999, because of the small leaf area index. During the ripening stage, leaf area index in BNo was smaller, but crop growth rate in BNo was similar to or higher than that in CONT due to the large net assimilation rate, which resulted from the largeflag leaf and 2nd leaf, and the heavy specific leaf weight in BNo. The DMP per panicle during the period from PI to FH positively and significantly correlated with the number of spikelets panicle-¹. The percentage of ripened grains (PRG) was also closely related with the amount of carbohydrates from stems (??S) and photosynthesis after FH (?W) contributed to a spikelet during the early ripening period (during 20 days after FH). The higher DMP per panicle in BNo compared with CONT during the period from PI to FH, therefore, resulted in a larger number of spikelets panicle-¹ in the former. On the other hand, the large amount of carbohydrate supply per spikelet during the early ripening period could also secure a high and stable PRG in BNo, especially under unfavorable weather conditions.     

Root Development,Water Uptake,and Shoot Dry Matter Production under Water Deficit Conditions in Two CSSLs of Rice: Functional Roles of Root Plasticity

Abstract

Root traits that can contribute to drought resistance have not been clearly indentified. We examined the role of root system development in enhancing water uptake and contribution to dry matter production by using the root box-pinboard method, with which quantitative assessment of root system development and the water uptake of root are possible. Chromosome segment substitution lines CSSL45 and CSSL50, and the recurrent parent Nipponbare were grown under continuously waterlogged conditions (control), and various intensities of water deficit in root boxes. There was no significant difference among the genotypes in shoot growth and root development, while CSSL45 and CSSL50 showed greater shoot dry weight than Nipponbare under water deficit conditions. This was due to their abilities to promote root system development as compared with Nipponbare, which facilitated greater water extraction than Nipponbare, especially under the mild water deficit condition of 20–25% w/w soil moisture contents. Furthermore, the increased root length density did not exceed the estimated critical value for water uptake, which indicates that plastic root system development was functionally effective and efficient for the enhancement of water uptake under mild water deficit conditions.