Masahiro Morokuma

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.

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.

Phytotoxic Substances in Bangladeshi Allelopathic Rice BR 17

Abstract Aqueous methanol extracts of Bangladeshi rice (Oryza sativa L.) cultivar BR 17 inhibited the growth of roots and coleoptile of Echinochloa crus-galli extract-concentration dependently. The extracts were then purified by several chromatographic runs, and a phytotoxic active substance was isolated and identified by spectral analysis as (–)-3-hydroxy-β-ionone. The concentration of (–)-3-hydroxy-β-ionone in BR 17 was higher than that of two other phytotoxic substances, 9-hydroxy-4-megastigmen-3-one and 3-oxo-α-ionol, found in BR 17. The novel isolated (–)-3-hydroxy-β-ionone inhibited the growth of E. crus-galli at concentrations higher than 10 μM. Those phytotoxic substances may contribute to the allelopathic effect of BR 17. Therefore, the rice cultivar BR 17 may be potentially useful for weed management as a weed suppressing agent when incorporated into the soil or included in a rice-based cropping system.