Genotypic Variation in Response of Rainfed Lowland Rice to Prolonged Drought and Rewatering

Abstract

Duration of the drought period is important for plant response during drought and after rewatering. We hypothesized that, if drought duration is extended, (1) high seedling vigor and rapid development of a deep root system will not be advantageous, and (2) osmotic adjustment will be more important. Six diverse rice (Oryza sativa L.) genotypes were selected from rainfed lowland germplasms to examine the development of a deep root system and osmotic adjustment, and their relationship with biomass production during drought and after rewatering, under two different drought durations (shorter and prolonged) in the greenhouse. NSG19 and KDML105 had greater seedling vigor (larger seedling biomass), developed a deep root system earlier in response to drought, extracted soil water more quickly, and their pre-dawn leaf water potential declined more rapidly during the prolonged drought period. These two genotypes showed superior drought recovery even after a prolonged drought period in which they suffered a greater reduction in transpiration, water use efficiency, and biomass production. The superior recovery ability was associated with larger plant size by the end of the drought period rather than with plant water status during drought, such as osmotic adjustment or leaf water potential. Osmotic adjustment was greater during prolonged drought periods (ca. 0.7 MPa) than during shorter drought periods (ca. 0.5 MPa), and lower osmotic adjustment was mostly associated with a higher leaf water potential. Genotypic variation in osmotic adjustment was observed, but there was no clear relationship between osmotic adjustment and biomass production during drought periods. These patterns of response of rice seedlings to drought and rewatering in the greenhouse should help to explain the patterns of adaptation of rainfed lowland rice in the field. Selection for drought recovery ability should be an advantageous strategy for early season drought.     

Relay-Intercropping of Stylosanthes guianensis in Rainfed Lowland Rice Ecosystem in Northeast Thailand

We evaluated the usefulness of the Stylosanthes guianensis (stylo)- rice relay-intercropping system for increasing agricultural productivity in Northeast Thailand. Although large production variability was observed, the relay-intercropping system produced an average of 350 g m-² stylo dry matter during the dry season under non-irrigated and non-fertilized conditions in the experimental fields at the Ubon Rice Research Center. Utilization of the stylo production as green manure increased rice yield, but only slightly. The relay-intercropping also slightly improved soil chemical properties, but not significantly. The trial of the relay-intercropping in farmer’s fields produced a maximum of 367 g m-² stylo dry matter. Since the stylo production did not decrease the subsequent rice production, the rice-stylo relay-intercropping system is worth considering as one way to utilize the paddy fields during the dry season in Northeast Thailand.     

抗旱剂“ASA”在水稻生产上应用效果试验

采用拌种试验,并通过在同一时期施用不同数量"ASA"抗旱剂的小区对比试验,分析"ASA"抗旱剂对水稻生产的影响,结果表明:该药剂有促进水稻生长的作用,通过拌种可以增强水稻秧苗素质,对水稻有一定的增产作用,其中40 g/667 m2浓度的处理效果最好,较常规对照区增产1.6%～4.5%。     

Molecular Breeding for Rainfed Lowland Rice in the Mekong Region

Abstract

In the past 20 years, the rice-breeding program in Thailand had little success in developing new cultivars to replace Kao Dawk Mali 105 (KDML105) and Kao Khor 6 (RD6) for the rainfed lowland rice environments. The main reason for the poor adoption of new cultivars by farmers is the susceptibility to diseases and unacceptable grain qualities. The conventional breeding program also takes at least 15 years from initial crossing to the release of new cultivars. A new breeding strategy can be established to shorten the period for cultivar improvement by using marker-assisted selection (MAS), rapid generations advance (RGA), and early generation testing in multi-locations for grain yield and qualities. Four generation of MAS backcross breeding were conducted to transfer genes and QTL for bacterial blight resistance (BLB), submergence tolerance (SUB), brown plant hopper resistance (BPH) and blast resistance (BL) into KDML105. Selected backcross lines, introgressed with target gene/QTL, were tolerant to SUB and resistant to BLB, BPH and BL. The agronomic performance and grain quality of these lines were as good as or better than KDML105.     

Root Growth and Water Extraction Response of Doubled-Haploid Rice Lines to Drought and Rewatering during the Vegetative Stage

Abstract

Doubled haploid lines (DHLs) of rice (Oryza sativa L.) were used to examine responses to drought and rewatering in controlled rainfed lowland conditions, in order to determine whether confounding by unrelated traits would be less than has been reported previously for contrasting cultivars that differ in genetic background. IR62266 and four DHLs derived from the cross between IR62266 and CT9993 (DHL-32, -51, -54 and -79) were grown in pot experiments in the greenhouse during the 2000 dry and wet seasons at IRRI, Los Baños, Philippines. There were two water regimes (well-watered and drought). Estimated water extraction obtained by time domain reflectometry (TDR) was similar to cumulative transpiration estimated from pot weighing for each genotype. Genotypic variation was observed in root traits and water extraction, with extraction slower in DHL-32 and faster in DHL-79, especially in deeper soil layers. An upper bound relationship between water extraction from a soil layer and root length density (RLD) in that layer was readily apparent over DHLs and soil depths, suggesting a critical value of RLD for water extraction of 0.30 cm cm^?3 in these conditions. Because soils in the field would not be as homogenous as the puddled soils used in these greenhouse experiments, this critical RLD for water extraction from a soil layer is a reference for ideal conditions, and requires careful validation in the field. Use of DHLs permitted comparisons with reduced confounding by genetic background, with consequent improvements in precision.     

Estimating Percolation and Lateral Water Flow on Sloping Land in Rainfed Lowland Rice Ecosystem

Abstract

Quantifying water losses in paddy fields assists estimation of water availability in rainfed lowland rice ecosystem. Little information is available on water balance in different toposequence positions of sloped rainfed lowland. Therefore, the aim of this work was to quantify percolation and the lateral water flow with special reference to the toposequential variation. Data used for the analysis was collected in Laos and northeast Thailand. Percolation and water tables were measured on a daily basis using a steel cylindrical tube with a lid and perforated PVC tubes, respectively. Percolation rate was determined using linear regression analysis of cumulative percolation. Assuming that the total amount of evaporation and transpiration was equivalent to potential evapotranspiration, the lateral water flow was estimated using the water balance equation. Separate perched water and groundwater tables were observed in paddy fields on coarse-textured soils. The percolation rate varied between 0 and 3 mm/day across locations, and the maximum water loss by lateral movement was more than 20 mm/day. Our results are in agreement with the previously reported findings, and the methodology of estimating water balance components appears reasonably acceptable. With regard to the toposequential variation, the higher the position in the topoesquence, the greater potential for water loss because of higher percolation and lateral flow rates.     

水稻直播栽培高产机理研究初报

在前几年试验观察研究的基础上，1998－1999年设立水稻直播高产机理栽培试验。结果表明，直播比移栽对照增产，其增产机理在于：直播稻生育进程加快，分蘖早生快发，低节位分蘖成穗率高，易获得足够的穗数；群体结构协调，光合速率高，光合产物累积速度快；植株养分吸收能力、根系活力和抗倒能力增强。     

平铺镇水稻直播栽培技术的探讨

平铺镇是水稻种植大镇,水稻直播技术被越来越多的农民采用,但种植技术参差不齐,倒伏情况普遍存在,导致产量下滑,对此提出了在生产管理过程中的具体意见及应对措施.     

耐旱水稻种质资源的筛选初探

通过分析干旱胁迫灌水与浅水灌溉对照处理条件下水稻生育期、农艺性状及产量性状的变化,探讨了20份水稻种质资源的耐旱性。结果表明:干旱胁迫处理条件下水稻生育期延长,农艺性状及产量因子水平均低于对照处理条件下水平。从抗旱指数与理论产量综合评价,垦01-1387、垦稻12、绥粳3、松粳4、北稻4等品种(系)的抗旱能力相对较强。     

Toposequential Variation in Soil Fertility and Rice Productivity of Rainfed Lowland Paddy Fields in Mini-Watershed (Nong)in Northeast Thailand

Abstract

Mini-watersheds called Nongin Thai are geographical components of rainfed lowland rice culture in Northeast Thailand, and constitute distinct units in understanding environmental constraints for low and unstable rainfed rice production there. The toposequential variation of soil fertility and its relation to rice productivity within mini-watersheds, was examined by phytometry of sampled soils and field measurements of rice growth and yield. The phytometry experiment with irrigated potted rice using soils sampled from various rice fields within each mini-watershed, revealed that soil fertility as evaluated by rice dry matter production showed a 5 times difference among the fields at most. The difference in the soil fertility was ascribed primarily to that in nitrogen (N) supply capacity, which itself had a strong correlation with soil organic carbon (SOC) content. Accordingly, the biomass production of pot-grown rice was proportional to SOC. content, which suggested the usefulness of SOC as an index for soil fertility evaluation. The effect of clay on the soil fertility was much less than that of SOC. The actual rice yield in each field also showed quite large field-to-field variation, most of which was explained by the SOC content, rice growth duration and fertilizer application rate even though water availability also affected the yield. The yield positively correlated with growth duration and hence with earlier transplanting. Both SOC and clay contents of fields showed steep gradients with ascending field elevation within mini-watersheds, resulting in a marked toposequential distribution of rice yield. The toposequential distributions of SOC and clay contents imply that rice culture after deforestation accelerated soil erosion from upper to lower fields. The large toposequential gradient in soil fertility requires different resource and crop management for each toposequential position, in order to improve rice productivity of the mini-watershed as a whole.     

湖南发展双季稻生产的优势

论述了湖南双季稻生产的有利气候生态条件和生产技术基础。从气候生态条件来说,一是7月下旬到8月上、中旬的夜间高温和高温火南风天气,不利于一季中稻的开花和灌浆结实;二是8月和9月的台风或热带风暴．容易造成一季晚稻的倒伏和两迁害虫的危害;三是4月初到10月底≥10℃的活动积温和有效积温,均能满足双季稻生长发育的需要,尤其是在抽穗开花到灌浆结实阶段避免了不利气候的影响。从生产技术基础来说,首先是双季稻品种产量高,稳产性好,能满足早晚两季不同熟期搭配种植的需要;其次是双季稻的生产技术成熟,农民具有种植双季稻的习惯和经验;再就是双季稻的早晚两季互补性强,避免了单季稻由于自然灾害造成减产所引起的粮食安全风险。。     

Drought Resistance Improvement in Rice: An Integrated Genetic and Resource Management Strategy

Abstract

Drought is the major constraint to rice production in rainfed areas across Asia and sub-Saharan Africa. In the context of current and predicted water scarcity, increasing irrigation is generally not a viable option for alleviating drought problems in rainfed rice-growing systems. It is therefore critical that genetic management strategies for drought focus on maximum extraction of available soil moisture and its efficient use in crop establishment and growth to maximize biomass and yield. Extensive genetic variation for drought resistance exists in rice germplasm. However, the current challenge is to decipher the complexities of drought resistance in rice and exploit all available genetic resources to produce rice varieties combining drought adaptation with high yield potential, quality, and resistance to biotic stresses. The strategy described here aims at developing a pipeline for elite breeding lines and hybrids that can be integrated with efficient management practices and delivered to rice farmers. This involves the development of high-throughput, high-precision phenotyping systems to allow genes for yield components under stress to be efficiently mapped and their effects assessed on a range of drought-related traits, and then moving the most promising genes into widely grown rice mega-varieties, while scaling up gene detection and delivery for use in marker-aided breeding.     

Variation in root system architecture and drought response in rice (Oryza sativa): Phenotyping of the OryzaSNP panel in rainfed lowland fields

Root growth at soil depths below 30 cm may provide access to critical soil water reserves during drought in rainfed lowland rice. In this study, the OryzaSNP panel, a set of 20 lines representing genetic diversity in rice used for the discovery of DNA sequence polymorphisms, was evaluated for root characteristics in the field over three seasons varying in drought severity. Root length density (RLD) at a depth of 30–45 cm varied up to 74–92% among genotypes under drought stress (2008–2009 dry seasons), ranging from 0.024 to 0.23 cm cm⁻³ in 2008 and from 0.19 to 0.81 cm cm⁻³ in 2009. Real-time monitoring of soil moisture profiles revealed significant differences among genotypes, and these differences were correlated with RLD at those soil depths. Among the lines evaluated, the Aus isozyme group, particularly the genotype Dular, showed greater drought resistance associated with deep root growth and the highest drought response index (less reduction in yield by drought stress). Since the set of genotypes used in this study has been completely sequenced for SNP markers, the phenotypic information on root growth and drought avoidance responses presented here could be used in initial analysis of the genetic basis of dehydration avoidance traits and in facilitating improvement in drought resistance in rice.     

水稻抗旱性的研究进展

随着全球水资源的日益匮乏和旱灾的日趋严重,水资源短缺正成为制约我国农业发展的重要因素。培育抗旱栽培稻品种并实现水稻旱种,不但可较大程度地节约水资源,且有利于稳产增产、节约能源和减少环境污染,故栽培稻的抗旱性研究作为稻作科学研究的重要课题显得愈来愈重要。本文从水稻抗旱性鉴定形态指标、生理指标和分子标记研究三方面分别概述,并对今后水稻抗旱性方向进行了探讨。     

收获时期对水稻制种产量的影响

采用3个不同熟期的水稻品种(早熟品种:白粳1号、中熟品种:通88-7、中晚熟品种:通系929),分别在不同时期收获(出穗后30~80 d,每次间隔5 d),并对各收获时期的产量进行测定,总结分析了三个不同熟期水稻品种的最佳收获时期及其与种子产量的关系。结果表明,水稻种子产量从出穗后30~65 d,随着出穗天数的增加而增长,超过65 d因田间损失(尤其是遇到霜冻后)而下降。在试验区的气候条件下,水稻种子适宜收获期为出穗后50~60 d,最迟不超过65 d;早熟、中熟品种由于出穗期较早,适宜收获期可以延至出穗后55~60 d,初霜前收获;中晚熟品种为出穗后50~55 d,初霜期开始收获,初霜之后霜冻之前(9月末)收获结束,收获过早(≤50 d)种子产量降低,过晚不仅种子产量受到损失,而且种子质量下降。     

水稻应用膨化砂无土旱育苗技术试验效果初探

为解决水稻旱育秧取"客土"难题,我们采取膨化砂做育秧基质,开展水稻无土育秧试验研究,取得了良好效果。试验结果显示:水稻秧苗健壮,根系发达,盘根良好,适于机械插,插秧后返青快,分蘖早,优质高产,为解决水稻育秧取土难题开辟了有效途径。     

不同生物肥在水稻生产中的应用对比试验

为了探索生物肥在水稻生产中的增产效果,特选取三种生物肥进行对比试验。结果表明,三种生物肥均可使水稻增产,增产率在4.45%～6.69%、增效在40.12～55.80元/667 m2。其中,平安福生物肥增产效果较好,较对照增产6.69%。     

盘锦稻区水稻高产目标产量结构分析与探讨

以盘锦地区种植的水稻中晚熟组区试及科室育种后代材料为试材,比较了2010～2011两年上述材料产量性状及构成因素,探讨最适合盘锦地区的高产产量结构,结果表明:株高方面高产品种以107 cm左右为宜,产量结构方面,穗数、穗粒数、千粒重如能达到每穴15穗、成粒120粒、26 g将会达到一个较协调且高产的理想结构,其产量将达到750～850 kg/667 m2。