Tsutomu Matsui

The Difference in Sterility due to High Temperatures during the Flowering Period among Japonica-Rice Varieties

Summary The objectives of this study are to compare the floret sterility induced by a high temperature given in the daytime during the flowering period among nine japonica rice varieties, and to clarify the mechanism of the high-temperature-induced sterility. Nine japonica rice varieties were subjected to 35.0, 37.5 or 40.0°C day- temperature conditions (1000-1600) for six consecutive days using sun-lit phytotrons, and the percentage of fertility, pollination and germinated pollen grains on the stigmas were examined. The temperature that caused 50% sterility varied with the variety, and a difference of approximately 3.0°C was observed between the most tolerant and susceptible varieties. Under the 37.5°C day-temperature condition, the percentage of florets with 10 or more germinated pollen grains was roughly coincident with the percent fertility, but under the 40° C day-temperature condition, it was higher than the percent fertility. Many of the florets with less than 10 germinated pollen grains had less than 20 total pollen grains on their stigmas under both temperature conditions. From these results, we concluded that sure pollination under high-temperature conditions is an important factor and that the high-temperature tolerance of the processes following pollen germination is also required for fertility under excessively high temperature conditions.

Effects of high temperature and CO2 concentration on spikelet sterility in indica rice

Abstract The effects of increasing temperature and CO 2 concentration on floral sterility were examined for rice (cv. IR 72) using open-top chambers located at the International Rice Research Institute in Los Banos, Philippines. The field-based open-top chamber system was used to simulate four different environments: ambient temperature and CO 2 concentration (control); ambient temperature, ambient +300 μ 1 1 −1 CO 2 ; ambient +4°C temperature, ambient CO 2 concentration; ambient +4°C temperature, ambient +300 μ 1 1 −1 CO 2 . High temperature during flowering resulted in increased pollen sterility with the degree of sterility exacerbated if rice was exposed to both high temperature and increased CO 2 concentration. The critical air temperature for spikelet sterility (as determined from the number of germinated pollen grains on the stigma) was reduced by ca 1°C at elevated concentrations of carbon dioxide. We speculate that this downward shift in critical temperature may be due to the observed increase in air temperature within the canopy at high CO 2 concentrations. This increase in air temperature, in turn, may be related to stomatal closure and reduced transpirational cooling in an elevated CO 2 environment. Data from this experiment indicate that increasing CO 2 concentration could limit rice yield if average air temperature increased simultaneously.

High Temperature at Flowering Inhibits Swelling of Pollen Grains, a Driving Force for Thecae Dehiscence in Rice(Oryza sativa L.)

Summary To clarify the mechanism of high temperature-induced floret sterility in rice (Oryza sativa L.), we studied the effects of high temperature at flowering on the ability of thecae to dehisce and on pollen-grain swelling which causes thecae dehiscence. Two japonica rice cultivars, grown in four L pots under submerged soil conditions were subjected to high (39°C) and moderate (34°C) temperatures from 10 : 00 to 16 : 00 for three consecutive days at the flowering stage. The percentage of the thecae dehisced in response to artificial opening of the florets by removing lemma and the mean diameter of the pollen grains measured during four minutes after the artificial opening were examined to determine the ability of the thecae to dehisce and that of the pollen grains to swell, respectively. The high temperature given on the day of flowering decreased both the percentage of the dehisced thecae and the diameter of the pollen grains but did not affect the relationship between them. The thecae of the plants which had been subjected to the high temperature for one or two days before flowering, however, showed a lower dehiscence percentage than those of the plant treated on the day of flowering against the same pollen-grain diameter. We concluded that high temperature given on the day of flowering decreased the ability of the pollen grains to swell resulting in poor thecae dehiscence, and that, besides this decrease, high temperature given just before the days of flowering lowered the function of thecae themselves to dehisce, causing poorer thecae dehiscence.

Stability of Rice Pollination in The Field Under Hot And Dry Conditions in The Riverina Region of New South Wales, Australia

Abstract Even Under Extremely Hot (40ºC) Conditions During Anthesis, Heat-induced Floret Sterility Does Not Appear To Be A Serious Issue For Australian Rice Growers. This Contradicts Previously Reported Temperature Thresholds For Floret Sterility. To Determine The Factors Associated With Stable Rice Production Under Hot and Dry Conditions in The Riverina Region of New South Wales (Australia), We Examined Rice (Cv. ‘Langi’) Pollination At Different Distances From The Windward Edge of A Paddy Field and Its Association With Canopy Microclimate. With An Air Temperature of 34.5ºC and A Relative Humidity of 20.7% During Anthesis, Poor Pollination of Florets Occurred At The Windward Edge, But Pollination Remained Stable Farther From The Edge. The Temperature Difference Between The Air and The Panicles in The Canopy Reached As High As 6.8ºC Under These Conditions Because of Low Humidity and Strong Transpirational Cooling. Moreover, The Length of The Dehiscence At The Base of The Thecae During Anthesis Was Long; This Is A Desirable Trait For Heat Tolerance. The Long Basal Dehiscence of The Thecae of This Cultivar and The Lower Panicle Temperatures Relative To The Ambient Temperature Caused By High Transpirational Cooling Appear To Be The Key Factors Responsible For Stable Pollination Under The Extremely High Temperatures of The Riverina Region.

Geostatistical analysis of soil chemical properties and rice yield in a paddy field and application to the analysis of yield-determining factors

Abstract To obtain basic information for rational site-specific soil management for rice production, spatial variability of soil chemical properties and grain yield of rice was evaluated in a 50 m × 100 m paddy field. One hundred surface soil samples were collected from each of the 5 m × 10 m plots before puddling to investigate the spatial variability of their chemical properties: pH, EC, total C content, total N content, C/N ratio, contents of mineralizable N, inorganic N, available P, exchangeable Ca, Mg, K, and Na. Grain yield was also measured at harvest for the corresponding 100 plots. Geostatistical analysis was carried out to examine their within-field spatial variability using semivariograms, and multivariate analysis was also carried out to evaluate yield-determining factors. Geostatistical analysis of the soil properties indicated a high to moderate spatial dependence for all the properties except for the inorganic N content. The ranges of spatial dependence were about 20–30 m for the pH, EC, total C content, total N content, content of exchangeable Na, about 40 m for the contents of available P, mineralizable N, exchangeable Ca and Mg, and about 50–60 m for the C/N ratio and content of exchangeable K. Grain yield showed a moderate spatial dependence with a range of about 50 m. The results of spatial dependence enabled to prepare kriged maps of the soil properties and yield to compare their spatial distribution in the field. Multivariate analysis further showed, in combination with geostatistics, that the soil chemical properties contributed significantly to the yield as yield-determining factors and explained as much as 65% of the spatially structured or non-random variation of the yield. In conclusion, the possible benefit of site-specific soil management or precision agriculture was demonstrated even in an almost flat paddy field.

Correlation between viability of pollination and length of basal dehiscence of the theca in rice under a hot-and-humid condition

Abstract Anticipated global warming may increase the floret sterility of rice (Oryza sativa L.). For selection of genotypes tolerant to high temperatures during the flowering period, it is important to identify morphological traits associated with tolerance to temperature stress. This study investigated the relationship between the length of dehiscence at the basal part of thecae and the viability of pollination in 18 cultivars of rice subjected to a hot-and-humid condition (37/25 ˚C, day/night, >90% relative humidity) for three days at flowering. Control plants were left under the ambient conditions in a semi-cylindrical house covered with cheesecloth (30% shading; temperature range: 24-35 ˚C). The length of basal dehiscence of thecae and the number of pollen grains on the stigmata were examined with a light microscope after flowering. The length strongly correlated with the percentage of florets having more than 80 pollen grains on the stigmata under the ambient condition (r = 0.72, P < 0.001), and with the percentage of florets having more than 20 pollen grains on the stigmata under the hot condition (r = 0.93, P < 0.001). In other words, the length correlated with pollination viability or reliability under both conditions. In addition, basal dehiscence was shorter in the non-japonica-type cultivars than in many of the japonica-type cultivars under both conditions. We concluded that the low pollination viability in the non-japonica-type cultivars is associated with their small basal dehiscence on the thecae, and the length of basal dehiscence can be used as a selection marker of high temperature tolerance.

Effects of Elevated CO2 and Global Climate Change on Rice Yield in Japan

Long-term CO2 x temperature experiments on rice using Temperature Gradient Chambers (TGCs) revealed that nearly doubled CO2 concentration in the atmosphere increases crop dry matter production by 24% through the enhancement of radiation conversion efficiency to biomass, but not through the promotion of radiation interception rate. Although temperature gave a negligibly small influence on the CO2 effect on biomass production, it significantly affected the grain yield through spikelet fertility. High temperatures were most damaging rice spikelets at the moment of their flowering and made them sterile. The temperature (Tmh) at which 50% spikelets are sterile was 38.2°C for a high temperature-tolerant genotype ‘Koshihikari’, and 36.6°C for a sensitive genotype ‘Akihikari’. Those findings from TGC experiments were parametrized and incorporated into rice growth simulation model SIMRIW.

Cumparsion between Anthers of two Rice (Oryza sativa L.) Cultivars with Tolerance to High Temperatures at Flowering or Susceptibility

Abstract Anthers of rice cultivar, cv. Nipponbare, which showed floret fertility even when the temperature at flowering was high(tolerant) and cv. Hinohikari, which showed floret sterility at high temperatures (susceptible) were compared. The anther of Nipponbare had better developed cavities for dehiscence and thicker locule walls than Hinohikari. The well-developed cavities enable easy rupture of the septa in response to swelling of the pollen grains. The thick locule walls promote the swelling of pollen grains by retaining water in the locules. Since the swelling of pollen grains is the driving force to open the theca and the septum rupture is an indispensable process for the theca dehiscence, the well-developed cavities and the thick locule walls may be responsible for the tolerance to high temperatures in Nipponbare.

Gas Exchange through the Slit between the Lemma and the Palea in the Rice (Oryza sativa L.) Floret before Anthesis

A rice floret emerges fi-om the sheath of the fl ag leaf just before anthesis and opens for about one hour in the morning. Before flower-opening, stamen and pistil are enclosed in a huil , probably to avoid d irect contact with water (Corbet, 1990; Fagri et aI., 1979) a nd protect them Ii-om damage by insects and diseases. Since the stomata on the outer surface of rice hull are vestigial (Hoshikawa, 1993), the slit between the lemma and palea is considered to be the primary pathway for passage of gas between the inside and outside of flo ret, although the edge of the lemma is hooked to the edge of the palea (I-Ioshikawa, 1993) a nd the slit looks tightly closed. The radical prepara tory process such as decomposition of starch in the pollen grains occurs in the rice Ooret just berore the a nthesis (Koike et a I. , 1987). Such a radical preparatory process may requ ire oxygen for respiration. Ir so, where does the oxygen for respiration d uring th is process come from ? The purpose of this report is to clari fy whether the preparatory process requ ires supply of oxygen from out side of the floret a nd the route of the oxygen su pply. For this purpose, we exam in ed the effect of sealing of the slit between lemma and palea on the preparatory processes for the a nthesis.

Correlation of Nitrogen Concentration with Dry-Matter Partitioning to Spikelets and Total Husk Volume on the Panicle in Japonica Rice

Summary A rice husk restricts the grain development physically. We examined the correlation of the total husk volume on a panicle, a parameter of yield capacity, with the nitrogen concentration (per dry weight) and the dry weight of the above-ground part of the plant, using single-stem-trained japonica rice (cv. Nipponbare) plants. The growth of rice plants was regulated by shading at two levels and nitrogen application at three levels from about 40 days before the heading (about 10 days before the panicle initiation). The number of spikelets per dry weight of the above-ground part of the plant at the end of the spikelet differentiation stage was linearly correlated with the nitrogen concentration at that time. The ratio of the spikelet dry weight at heading to the dry weight of the above-ground part of the plant at the end of the spikelet differentiation stage increased as the nitrogen concentration increased at a low nitrogen concentration, but the increase of the ratio slowed down at a nitrogen concentration of 2%. Decrease in dry weight of the spikelet resulted in a decrease of lemma size. Therefore, the ratio of the total husk volume on a panicle to the plant dry weight at the end of spikelet differentiation stage also increased as the nitrogen concentration increased at a low nitrogen concentration, but the increase stopped at a nitrogen concentration of 2% in contrast to the ratio of the spikelet number to the dry weight of the plant. These results suggest that, to increase the total husk volume on a panicle by nitrogen application, dry-matter production must be increased by the nitrogen application.