Masanori Toyota

Effects of Reduction in Plant Height Induced by Chlormequat on Radiation Interception and Radiation-Use Efficiency in Wheat in Southwest Japan

Abstract The effects of reducing plant height by the growth retardant chlormequat on radiation interception and radiation-use efficiency in field-grown wheat were studied in southwest Japan. Chlormequat was applied to wheat cultivar Sanukinoyume 2000 at the beginning of jointing. The cumulative total solar radiation intercepted by the plant canopy (Si) was determined by continuous measurements of total solar radiation above the canopy with a dome pyranometer and below the canopy with tube solarimeters. Nondestructive measurement of leaf area index (LAI) and mean tip angle of the canopy (MTA) using a plant canopy analyzer was performed weekly. Chlormequat application shortened the culm length by 12.6% compared with the control, but did not affect the aboveground dry matter (AGDM), LAI, yield or yield components except for the harvestindex (HI). The extinction coefficient in canopy (K) was not affected by chlormequat, so that Si at heading and anthesis were not significantly different. Radiation-use efficiency (RUE) of chlormequat treated plants estimated from the slope ofalinearregression of Si vs AGDM was 1.34 g MJ-1 for the period up to heading and 1.57 g MJ-1 for theperiod up to anthesis. The RUE values were not significantly different between chlormequat-treated and control plants. Although the effect may be restricted to the duration from heading to the premature ripening stage, a higher MTA in chlormequat should provide a more even distribution of radiation within the canopy, which should increase the photosynthetic performance. These results suggested that shortening the culm length of this wheat cultivar by about 12% is beneficial in reducing the risk of lodging without affecting light interception characteristics or RUE.

Initiation and Development of Spikelets and Florets in Wheat as Influenced by Shading and Nitrogen Supply at the Spikelet Phase

Abstract The spike of the main culm in winter wheat was examined by scanning electron microscopy from the double ridge to 6 days after the terminal spikelet stage to quantitatively evaluate the effects of shading and nitrogen supply at the spikelet phase on the numbers of spikelets and floret primordia, and the development of florets. Positional differences on a spike in grain setting at maturity were also investigated. Nitrogen supply affected neither the rate nor duration of spikelet initiation, the number of spikelets remaining unchanged. Although nitrogen supply positively affected the initiation and development of florets, it slightly reduced the grain weight per spike at maturity due to a decrease in the number of grains per spike and the reduced grain weight. These results suggested that under the field condition, nitrogen supply at the double ridge stage is too late to have a significant effect on the spikelet number, and might induce competition for nitrogen between the main culm and tillers, or induce mutual shading between plants, resulting in lighter grain weight per spike. Shading decreased the rate of spikelet initiation, resulting in a significant decrease in spikelet number. The initiation and the development of florets were also decreased by shading. Lower non -structural carbohydrate content at the terminal spikelet stage suggested that the limited assimilate supply by shading was likely responsible for the decreases in the initiation and development of spikelets and florets.

Tillering responses to high red/far-red ratio of four Japanese wheat cultivars.

Abstract The effect of high red/ far-red ratio (R/FR) on tillering in wheat and its cultivar differences were investigated with a pot experiment. Four Japanese wheat cultivars with a different degree of winter habit: Abukumawase, Sanukinoyume 2000, Norin 61 and Iwainodaichi, were grown under the tunnels with different R/FR conditions: one tunnel covered with a light control film which attenuates irradiance in the far red range (high R/FR) and the other with a transparent polyethylene film with a white shading cloth (control). The high R/FR treatment increased R/FR by 25%, and slightly decreased air temperature. The low temperature in high R/FR had some effect on the time of the developmental stage; however, physiological responses to high R/FR and its cultivar differences were observed. Tillering dynamics was quantified and analyzed based on phyllochron, site-filling and the time of cessation of tillering. The high R/FR significantly delayed the time in calendar days of full expansion of flag leaf and anthesis, but the effect of treatment was not significant in growing degree days. The high R/FR had no significant effect on the phyllochron and the maximum number of leaves on the main stem. The maximum number of tillers per plant was significantly increased and the cessation of tillering was significantly delayed by the high R/FR in all cultivars. In conclusion, the increase in the number of tillers in the high R/FR was attributed mainly to the delay of the cessation of tiller emergence, along with the significant increase in rate of tillering in some cultivars.

A high seed yield and associated attributes of dry matter production achieved by recent Japanese soybean cultivars

Abstract Field experiments were carried out in 2014 and 2015 to characterize the associated attributes responsible for dry matter accumulation in high-yielding soybean. We attempted to create a high-yielding environment by introducing narrow-row planting at two planting densities, using a new cultivar ‘Hatsusayaka’ and a current leading cultivar ‘Sachiyutaka’ in an upland experimental field. Dry matter accumulation was assessed in terms of light interception and radiation use efficiency (RUE). Growth analysis was performed to evaluate the crop growth rate (CGR) and the contribution of the net assimilation rate (NAR) and mean leaf area index to CGR. Maximum soybean yields of 590 and 658 g m−2 were obtained for Hatsusayaka and Sachiyutaka, respectively, in 2015 at the high planting density, with the corresponding maximum aboveground dry matter equaling 1463 and 1331 g m−2 and maximum LAI equaling 8.5 and 7.6. Although cumulative intercepted solar radiation was lower than in previous studies, early canopy closure at around the beginning of the flowering stage and very high RUE (1.54 and 1.68 g MJ−2 for Hatsusayaka and Sachiyutaka, respectively) contributed to the high dry matter accumulation. In contrast to the high yield in 2015, continuous excess soil moisture in early August 2014 may have inhibited nodule nitrogen fixation and decreased the nitrogen content, resulting in an extremely high specific leaf area and low leaf greenness, which agrees well with the low NAR during the corresponding period.

Changes in radiation interception and R:FR over time and with canopy depth of two soybean cultivars with different branching characteristics

Abstract Because an outgrowth of auxiliary bud in plant is regulated by light quality detected by phytochrome, branching differences in various environment or cultivars in soybean would be the results of the responses to light environment. Therefore, we analyzed differences in the number of branches of two determinate soybean cultivars, ‘Hatsusayaka’ and ‘Sachiyutaka’, between low and high planting densities in relation to light quality within the canopy. We compared changes in the ratio of red to far red (R:FR) irradiance at the ground level over time and with canopy height with those in the fraction of intercepted photosynthetically active radiation (FIPAR) and leaf area index (LAI). Regardless of time or distance from the top of the canopy, the changes in R:FR were sigmoidal, and were symmetrical with those of FIPAR and LAI. The effects of density and cultivar on FIPAR, LAI, and R:FR could be modeled with a logistic function. The number of branches was greater at low density than at high density, and in Hatsusayaka than in Sachiyutaka. However, there were no notable differences in the dynamics of R:FR between planting densities or between cultivars. Close relationships between parameters of the dynamics of the changes in R:FR and of those in FIPAR and LAI suggest that FIPAR and LAI are major factors that regulate R:FR, regardless of time or canopy depth. We found no evidence of a causal relationship between the dynamics of R:FR within the canopy over time or with canopy depth and number of branches of either cultivar.