Genotypic Variations in Response of Lateral Root Development to Fluctuating Soil Moisture in Rice

Abstract

Developmental plasticity in lateral roots may be one of the key traits for the growth of rice plants under soil moisture fluctuations. We aimed to examine responses in seminal root system development to changing soil moisture for diverse rice cultivars. Special attention was paid to the two different types of lateral roots ; the generally long, thick L type capable of branching into higher orders, and the non-branching S type. Plants were grown in half-split polyvinyl chloride tubes fixed with transparent acrylic plate for root observation under glasshouse conditions. When plants were grown first under drought conditions, then rewatered, the seminal root system development in terms of dry weight and total length was promoted as compared with plants grown under continuously well-watered conditions in IR AT 109 and Dular, drought tolerant cultivars. Promoted production of L type lateral roots mainly contributed to the development of the longer seminal root system. Plants exposed to soil submergence before they were grown under drought conditions did not show such promoted responses in these two cultivars. However, in KDML 105, a drought tolerant cultivar, the production of especially L type laterals was substantially promoted under drought and rewatered conditions. Honenwase was characterized by the shallow root system and great reduction in root system length when soil moisture becomes limited. These facts show that genotypic variations exist in the plastic response of rice seminal root system and that the L type lateral root plays a key role in manifestation of this plasticity.     

水稻广亲和恢复系WCR1的表现及其利用

ＷＣＲ１是从广亲和系ＳＭＲ中的早熟变异株中系选而成。是一个较好的偏籼广亲和恢复系（广亲恢系），与粳型三系或两系不育系配组，产量优势潜力较大，能筛选出偏粳型的强优势组合；又是一个籼型软米，可作软米直接利用，对于改善籼稻品质，是一个有价值的中间材料。     

A Varietal Difference in Coleoptile Growth is Correlated with Seedling Establishment of Direct Seeded Rice in Submerged Field under Low-Temperature Conditions

Abstract

To elucidate the physiological characteristics relating to better seedling establishment in submerged field under low-temperature conditions, we compared the time required to reach various growth stages after seed imbibition among rice {Oryza sativa L.) varieties differing in the performance of seedling establishment. Two experiments were conducted. In the field experiment, the percentage of seedlings with expanded second leaf at 30 days after sowing (PSSL) was measured and regarded as the index of establishment rate for each variety. In agar-bed experiment, the number of germinated seeds, the seedlings with the coleoptile elongated to the medium surface, and the seedlings with the 1st leaf apparent were counted daily under a 16°G condition. A sigmoid model was applied to the above values to evaluate the time requirements. There was a significant correlation between the duration from 50% germination to 50% emergence in the agar-bed experiment and PSSL in the field experiments. However, the duration from imbibition to 50% germination, and that from 50% emergence to 50% appearance of the first leaf were not significantly correlated with PSSL. We found that fast growth of the coleoptile is an important characteristic for the varieties that can provide stable and excellent seedling establishment at low temperature.     

Geostatistical Analysis of Yield,Soil Properties and Crop Management Practices in Paddy Rice Fields

Abstract

We examined the possible benefit of rational site-specific crop management practices in 17 paddy fields located in an area of 2.0 ha for the prevalence of precision agriculture methods on a cooperatively managed large-scale farm in Sakurai, Nara Japan. Data on grain yield, soil physicochemical properties and farmer's crop management practices were collected in each paddy field. Unhulled rice yield was estimated at a resolution of 5m ? 5m in an area of 1.2 ha using a yield-monitoring combine. The spatial distribution of the variations for the collected data was characterized using geostatistical procedures. The kriged map of the unhulled rice yield drawn from the results of geostatistical analysis indicated the potential value of rational site-specific crop management using the yield-monitoring combine. The ratio of spatially structured variation to the total variation of brown rice yield, that is, the controllable proportion to total variation, was 75.4%. Each yield component i.e., the number of spikelets per square meter, filled-spikelet percentage and 1000-grain weight contributed 33.7%, 54.7% and 11.6%, respectively, to brown rice yield. These three yield components combined contributed to 96.5% of the brown rice yield variation. The agronomic factors (soil fertility factor, early growth factor, N dressing and uptake factor) contributed 79.7%, 52.1% and 41.8%, respectively, to the variation of these three yield components. Therefore these agronomic factors accounted for 58.1% of the total variation of the brown rice yield and 77.1% (i.e. 58.1% out of 75.4%) of the spatially structured variation of the brown rice yield. This controllable proportion may be a criterion for the prevalence of site-specific crop management in large-scale farm management in general, although only one case study was conducted.     

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.