Assessing Suitability of Irrigation Scheduling Decision Support Systems for Lowland Rice Farmers in Sub-Saharan Africa—A Review

Irrigation in lowland rice production systems in Sub-Saharan Africa (SSA) is mainly based on traditional surface irrigation methods with continuous flooding practices. This irrigation method ends up using a lot more water that would have otherwise been used to open more land and be used in other water-requiring sectors. Various studies suggest Alternate Wetting and Drying (AWD) as an alternative practice for water management that reduces water use without significantly affecting yield. However, this practice has not been well adopted by the farmers despite its significant benefits of reduced total water use. Improving the adoption of AWD using irrigation Decision Support Systems (DSSs) helps the farmer on two fronts;to know “how much water to apply” and “when to irrigate”, which is very critical in maximizing productivity. This paper reviews the applicability of DSSs using AWD in lowland rice production systems in Sub-Saharan Africa.

The differenee in protein content,MDH,POD and COD isozymes during root different developmental stages in lowland rice and upland rice

The difference in protein content, MDH,POD and COD isozymes have been seenbetween lowland rice roots and upland rice roots during root growth and development. High pro-tein content has been examined in upland rice roots,but isozyme bands in lowland rice roots aremore than that in upland rice roots.Total area of POD isozyme bands at seedling and tilleringstages of upland rice is larger than that of lowland rice.The POD isozymes zymogram in the rootof upland rice is more stable compared with that of lowland rice.More COD isozyme numbershave been showed in roots of upland rice,but the relative activity of COD isozyme in roots of up-land rice at the seedling and tillering stages is lower than that of lowland rice.COD7 band can beshown in upland rice root at flowering stage,but it is absent in lowland rice.Therefore,COD7,band can be taken as an index for resistance of the upland rice to drought environment.

Integrated management of African rice gall midge (AfRGM) (<i>Orseolia oryzivora,</i>Harris and gagné), weeds and diseases of lowland rice

Studies were conducted during the 2001 and 2002 cropping years at Edozhigi and Sachi in the Southern Guinea Savannah of Nigeria to study the effect of following rice with another crop on the next rice crop. There were twelve treatments consisting of poor, good and excellent weed management and pesticidal applications against (AfRGM and diseases set up in a randomized complete block design, in twelve plots in 3 replicates. Results showed that rice treated with gramular isazofos at 0.75 kg a.i. ha–1 and benomyl at 1.0 kg/ha at 20 and 40 days after transplanting (DAT), with good weed management and a follow up crop after rice reduced AfRGM occurrence and disease incidence with a consequent increase in yield of the next rice crop. In 2001 infestation of rice by ARGM was more at Sachi than Edozhigi, while in 2002 there was low ARGM occurrence at the two locations. Brown leaf spot was high at the two locations in the two years of the trial while leaf blast was checked by the integrated control methods used in the study. Higher yields were (1.7 - 11.9 t·ha) from treated-well weeded plots that were cropped to cowpea after the 2001 rice harvest Ludwigia decurens, Sphanoclea geylanica Cyperus difformis and Lepllocidia chinensis were the widely occurring weed species at Edozhigi site while Cyperus difformis, Ipomea mvolucrata, F. awuata and Firnbristylis litoralis were weed species prevalent at Sachi site. The rice nematode, hirschmanniella sp. was recorded at the Sachi site along with other nematodes but was absent at the Edozhigi site. The net benefit farmers would derive for following this rice-dry-season crop sequence vary from US$ 172 - 427 and US$ 175 - 265 ha–1 at Sachi and Edozhigi respectively.

Genetic Diversity of Rice Landraces from Lowland and Upland Accessions of China

Genetic diversity of rice landraces from lowland and upland accessions of China was investigated using 66 polymorphic simple sequence repeat （SSR） markers. The total number of alleles detected from all 324 tested accessions was 555 with an average allele number （Na） of 8.409 per locus, the average effective number of alleles （Ne） of 3.574 and the average Shannon＇s information index （I） of 1.378. The genetic diversity was higher for the indica landraces compared to the japonica landraces, and the upland landraces were more genetically diverse than the lowland landraces. The SSR markers, RM72, RM232, RM219, RM241, RM224 and RM3 showed the highest rates of polymorphism and these SSR markers were suitable to assess the genetic diversity of rice germplasm resources. A dendrogram of 324 accessions of lowland and upland landraces showed that all rice accessions were mainly subdivided into two groups, japonica and indica, with some being intermediate. The distribution of lowland and upland landraces among the japonica and indica rice groups was distinct, with obvious differentiation between the lowland and upland landraces in japonica rice, but no such clear distinction in indica rice.

Comparative transcriptional profiling under drought stress between upland and lowland rice (Oryza sativa L.) using cDNA-AFLP

The continuous growth of lowland rice (LR) in paddy fields supplied with enough water over the years, and of upland rice (UR) in naturally rain-fed soils, has resulted in greater resistance to drought stress in UR compared to LR. To elucidate their differential regulation mechanisms of drought-resistance, genome-wide transcript regulation under drought stress in UR and LR was investigated using cDNA-AFLP. The results indicated that over 90% of gene expression was not affected by drought stress in the two rice genotypes, more than 8% was regulated by drought stress in both, and less than 1% was specifically expressed in UR or LR. Fifty-seven genes were specifically expressed in UR and thirty-eight specifically in LR. Genes specifically expressed in UR included cell rescue and defence genes functioning in drought-resistance, signal transduction molecules, nucleotides and amino acid biosynthesis genes required for plant growth, and the regulatory genes for growth and development. In LR, genes specifically expressed were related to protein and nucleotide degradation. Some genes were upregulated earlier in UR, and downregulated genes were inclined to be downregulated earlier in UR compared to LR, implying that more rapid regulation mechanisms caused earlier responses of UR to drought stress. Expression levels of upregulated genes in UR were higher than those in LR. The differences in gene expression between UR and LR could account for stronger regulation ability, more drought-resistance and superior growth of UR under drought stress compared to LR.

Germplasm Innovation of Heat Tolerance in Rice for Irrigated Lowland Conditions in the Philippines

Heat-tolerant varieties, such as N22 and Dular, which were used in this study, usually have low yield potential and undesirable plant characteristics but combining them with high yielding and improved rice varieties, new heat-tolerant rice genotypes with high yield potential can be achieved. In this study, phenotyping and selecting desirable materials from various crosses were performed under high temperature conditions during the reproductive stage. Screening was performed in the field and glasshouse to select individuals with heat tolerance and high yield potential. Several advanced breeding lines from Gayabyeo/N22 cross produced desirable individuals with heat tolerance, resistance to pests and diseases, and high yield potential. The genetic variation in percent sterility among the selected backcross populations grown in high temperature environments showed that large number of plants can be identified and selected with lower percent sterility.

Effects of puddling on percolation and rice yields in rainfed lowland paddy cultivation: Case study in Khammouane province, central Laos

We investigated the effects of puddling on percolation and rice yields in rainfed lowland paddy cultivation. We selected a study village in Khammouane province, central Laos, and set up non-puddling and puddling plots from high to low positions. Even when puddling was conducted carefully, the ponding water in the plots disappeared in the case of little rainfall. Further, percolatifons during the later periods of rice growth increased drastically. Therefore, it is difficult to overcome drought stresses only by conducting puddling. We also compared the water conditions in the non-puddling and puddling plots. In the puddling plots at high position and low position along a stream, the number of days without ponding water in the puddling plots was less than that in the non-puddling field in July, suggesting the possibility of a different transplanting date. We tried to estimate the effects of transplanting date on the rice yields and found that transplanting 15 days earlier leads to an increase of 0.5 t/ha in the rice yields. Moreover, the profits from the increased yields exceed the puddling costs considerably, leading to a definite increase in income. Because the transplanting date has no effects in the fields with high ground water, puddling is effective in paddy fields where ponding does not occur to a significant degree.

Impact of Smart Valley on Soil Moisture Content and Rice Yield in Some Lowlands in Burkina Faso

To reduce the impact of rainfall variability on lowland rice yields, Burkina Faso state develops lowlands for small rice farmers. However, the high cost of these infrastructures makes impossible to duplicate them to satisfy the needs which are enormous. The Smart-Valley technology which is actually popularized in certain coastal countries of West Africa would therefore be a boon to increase the productivity of the Sudanese lowlands if it well regulates runoff. The object of this study was therefore to know if smart valley technology could increase soil moisture in order to mitigate the impact of drought’s pockets on rice cultivation in the Sudanese lowlands. The experiment takes place in three lowlands during the rainy seasons 2018 and 2019. The climatic data comes from the meteorological stations in the study areas as well as those installed on the sites. The infiltration measurements were carried out using the double Muntz ring. The soil moisture measurement device consisted of a smart valley area of 5 ha and an undeveloped area of 5 ha per site. Sixteen tubes were installed per lowland allowing the humidity to be measured at a depth of 10, 20, 30, 40 cm using a probe. Four rice varieties, Orylux6, FKR62N, FKR19 and FKR64 were tested on plots of 0.25 ha per variety in the smart valley and undeveloped parts. The results showed that the humidity level was 12% higher in the smart-valley plots throughout the cycle compared to the unmanaged area. In addition, humidity decreases rapidly in unmanaged plots as rain becomes increasingly scarce. Finally, the smart-valley development allowed an average increase in rice yields of 21% compared to the average yield of undeveloped plots.

水稻双胚苗(Rice Twins)遗传研究

水稻双胚苗为隐性性状受一对主效基因控制,并存在若干修饰基因,使双胚苗率表现数量遗传特征;不同双胚苗品系遗传基础不同;水稻双胚苗同水稻的无融合生殖育着密切的联系。

Identification of QTLs for Blast, Bacterial Blight, and Planthopper Resistance Using SNP-Based Linkage Maps from Two Recombinant Inbred Rice Lines

Rice is the most significant global food security. Several biotic factors limit rice production, breeding biotic-resistant rice has, therefore, become an increasingly important goal. Two elite rice lines, IR71033-121-15 (IR71033) and IR57514-PMI-5-B-1-2 (IR57514), provide potential genes for biotic stress resistance traits. In this study, genotyping by sequencing (GBS) for single nucleotide polymorphism (SNP)-based linkage map construction was used to detect quantitative trait loci (QTLs) for blast (BL), bacterial blight (BB), whitebacked planthopper (WBPH), and brown planthopper (BPH) resistance. IR71033 was derived from Oryza minuta and carried BL, BB, WBPH, and BPH resistance QTLs. IR57514 is a well-adapted rainfed lowland line that carries BL and BB resistance QTLs. Two sets of recombinant inbred line (RIL) populations derived from crosses of KDML105 × IR71033 and KDML105 × IR57514 were used to dissect the genetic basis of disease and insect pest resistance. The RIL populations were evaluated for BL, BB, WBPH, and BPH resistance from 2016 to 2018 at four rice research centers in Thailand. From these, we identified a large number of SNPs through GBS and constructed high-resolution linkage maps. By combining phenotypic evaluation with the GBS data, a total of 24 QTLs on four chromosomes were detected that confered pest resistance and explained 7.3% - 61.4% of the phenotypic variance. These findings should facilitate identifying novel resistance genes and applying marker-assisted selection for resistance to the four major rice pests investigated here. These strategies will improve the resilience and reliability of rice varieties adapted to the low-yielding environment of rainfed lowland areas worldwide.

水稻和陆稻分化相关性状的QTL分析及水旱不同栽培条件下连续选择的影响

本研究以来自云南的地方品种Ch5-10和Ch6-11为亲本,后代用SSD方法而得到的RIL9群体为试验材料,对水、陆稻差异性状(始穗期、剑叶宽、株高等)进行了考察,并利用SSR分子标记构建遗传连锁图谱,进行了各性状的QTL定位;在自然和人工选择的过程中,栽培稻无论是形态上还是基因组上,都发生多种多样的变化。利用F 2群体(父、母本和前述的SSD群体相同)采用Bulk混合选择的方法,在F 4代开始进行水、旱田两种条件下种植,以模拟水陆稻的分化条件,经过5代的种植后繁殖成株系,分别得到CA、CB两个群体。对这两个群体的水陆稻差异性状(始穗期、最高分蘖数、有效分蘖数、剑叶宽、株高等)进行了考察。结果表明,利用SSD方法而得到的RIL9群体对始穗期、剑叶宽、株高等3个性状进行QTL分析,两年共检测到19个QTL,分别位于1,2,3,7,8,9,11号染色体上。其中株高qPH-1效应最大,贡献率为22%(2009年安徽),16%(2009年北京),16%(2010年北京),表现为来自亲本Ch5-10的等位基因增加株高;利用Bulk方法而得到的CA群体(经过水田筛选5代、289个株系)和CB群体(经过旱田筛选5代、332个株系),考察其最高分蘖数、有效分蘖数、始穗期、株高、剑叶宽等5个性状。2009年安徽和北京两地试验发现:两群体间除安徽始穗期和北京剑叶宽差异不显著外,其他性状差异均达到极显著水平。根据氯酸钾抗性和低温发芽力的QTL定位结果,选择qSLtr-2、qSLratio-2、qRL28-2-1和qRL28-4附近的标记RM166、RM5472、RI05751和RM5979,及未定位到QTL的标记RM259对CA群体和CB群体进行基因型分析,两群体间t测验结果表明,RM5472、RI05751和RM5979差异均达到极显著水平,RM259和RM166差异不显著。说明在人工模拟水、陆稻选择的条件下这2个群体有了明显的分化。

利用水、旱稻DH系定位产量性状的QTL及其环境互作分析

为研究水、旱栽培条件对水稻产量及其构成因素QTL表达的影响,以粳型陆稻IRAT109和粳型水稻越富杂交的116个株系的DH群体为材料,利用已构建的水稻分子连锁图(其中94个RFLP标记和71个SSR标记),在水田、旱田栽培条件下,定位了千粒重、结实率、有效穗数、穗粒数及单株产量等性状的QTL。结果表明,水田条件共检测到11个加性QTL和13对上位性QTL,旱田条件下检测到18个加性QTL和17对上位性QTL,其中控制千粒重的2个加性QTL和1对上位性QTL及控制有效穗数的1个加性QTL在水田、旱田条件下都检测到。检测到11个控制产量性状QTL区域存在一因多效或紧密连锁,其中3个区域也是控制根系性状QTL的热点区。发现8个加性QTL和8对上位性QTL对表型变异贡献率(以下简称贡献率)大于10%(其中4个加性QTL和5对上位性QTL为旱田条件下检测到),这些高贡献率QTL特别是旱田条件下的高贡献率QTL对旱稻产量性状分子育种具有一定的指导作用。

氢醌和双氰胺对种稻土壤N_2O和CH_4排放的影响

通过盆栽试验，研究了脲酶抑制剂氢醌（ＨＱ）、硝化抑制剂双氰胺（ＤＣＤ）及二者的组合（ＨＱ＋ＤＣＤ）对种稻土壤Ｎ２Ｏ和ＣＨ４排放的影响．结果表明，在未施麦秸粉时，所有施抑制剂的处理均较单施尿素的能显著减少水稻生长期供试土壤Ｎ２Ｏ和ＣＨ４的排放．特别是ＨＱ＋ＤＣＤ处理，其Ｎ２Ｏ和ＣＨ４排放总量分别约为对照的１／３和１／２．而在施麦秸粉后，该处理的Ｎ２Ｏ排放总量为对照的１／２，但ＣＨ４排放总量却较少差别．不论是Ｎ２Ｏ还是ＣＨ４的排放总量，施麦秸粉的都比未施的高出１倍和更多．因此，单从土壤源温室气体排放的角度看，将未腐熟的有机物料与尿素共施，并不是一种适宜的施肥制度．供试土壤的Ｎ２Ｏ排放通量，与水稻植株的ＮＯ－３Ｎ含量和土表水层中的矿质Ｎ量分别呈显著的指数正相关和线性正相关；ＣＨ４的排放通量则与水稻植株的生长量和土表水层中的矿质Ｎ量呈显著的线性负相关．在Ｎ２Ｏ与ＣＨ４的排放间，未施麦秸粉时存在着定量的相互消长关系；施麦秸粉后，虽同样存在所述关系，但难以定量化．

铵态氮和硝态氮营养对水、旱稻根系形态及水分吸收的影响

为研究不同形态氮素营养对水稻和旱稻根系生长及水分吸收的影响,采用水培供应不同形态氮素(铵态氮、硝态氮、铵态氮和硝态氮混合)的方法培养水稻和旱稻,并对水稻和旱稻的根系形态进行了扫描分析;同时,通过测定根系伤流液和采用HgCl2抑制水通道蛋白活性的方法,比较了水稻和旱稻根系对不同氮素形态响应的差异。铵态氮营养水稻(或旱稻)的根干质量明显低于硝态氮营养水稻(或旱稻),但单位根表面积的水分吸收与根系伤流液量比硝态氮营养高;3种形态氮素营养水稻(或旱稻)运输水分的主要方式均是水通道蛋白的跨膜运输途径,但铵态氮营养水稻(或旱稻)的根系通过水通道蛋白跨膜运输途径运输水分的能力明显高于硝态氮营养水稻(或旱稻);与水稻相比,旱稻对硝态氮营养具有较强的适应性。

水、陆稻在水田、旱地栽培的生态适应性研究——Ⅱ.稻株碳、氮代谢的生态适应性观察

旱种条件下,不论水稻还是陆稻,全糖、全氮含量均高于水种条件,醇溶糖占全糖的比例较高,碳/氮比低;陆稻的醇溶糖占全糖的比例远远高于水稻,这一特性很少随种植条件的改变而产生很大的变化,这可能是其对旱地适应性较强的生理原因之一。同时发现:贮藏性物质的增加是水稻旱种条件下的重要生理表现。

植物生长物质冠菌素诱导旱稻、水稻幼苗抗旱性的效应及生理机制

以旱稻297和水稻越富幼苗为材料,在20%PEG模拟干旱条件下,研究了植物生长物质冠菌素处理对叶片水分状况、质膜透性、渗透调节物质(脯氨酸、可溶性糖和可溶性蛋白)及内源激素(ABA、IAA和GA3)含量的影响。干旱胁迫下,冠菌素处理可以维持旱稻297(0.01μmol/L)和越富(0.1μmol/L)较高的叶片相对含水量,促进幼苗叶片中脯氨酸、可溶性糖和可溶性蛋白的积累,降低质膜透性,维持细胞质膜的完整性;同时,冠菌素(0.01和0.1μmol/L)处理明显促进旱稻297和越富幼苗叶片中ABA的积累,并改变了IAA和GA3的浓度及比例。冠菌素处理能改善旱稻和水稻幼苗耐干旱胁迫的能力,最适浓度分别为0.01μmol/L和0.1μmol/L。

水-氮联合限制条件下对水稻生产模型ORYZA2000的验证与评价

介绍了水稻生长模拟模型ORYZA2000,并应用2002年水肥耦合试验资料,在水氮联合限制条件下对水稻生产模型ORYZA2000进行了参数校正,对模拟效果进行了图解分析和回归分析,结果表明,在水分平衡和氮素平衡条件下,ORYZA2000模拟水稻生物量、产量、氮素平衡以及田间水分平衡是可行的。该模型在水稻节水灌溉领域有很大的应用价值,为我国水稻节水灌溉向数字化发展提供了有利工具。

水稻和陆稻品种抗旱性综合评价

从产量性状、外部形态和生理生化3个方面多个指标中选出11项有代表性的指标,采用其旱/水比相对值(划分评分标准)和权重计分法对4个水、陆稻品种(组合)进行了抗旱性综合评价,综合评分以TANGARA最高(4.06分)明显高于其他3个品种,IAPAR9(3.33分)次之,稍高于新香优80(3.21分),R80最低(2.59分)。表明TANGARA有较强的抗旱性,IAPAR9和新香优80抗旱性相差不大,R80较差,与生产实际表现基本一致。表明此项方法具有较强的客观性和准确性。

Cd Pb Cu Zn As复合污染对水稻的影响

应用田间试验和盆栽试验，研究Ｃｄ、Ｐｂ、Ｃｕ、Ｚｎ、Ａｓ复合污染在草甸棕壤上对水稻产量及元素含量的影响。结果表明，在接近土壤环境质量标准低浓度水平下，水稻发育正常，减产幅度＜１０％，但土壤Ｃｄ、Ｐｂ临界值下降，籽实中Ｃｄ、Ｐｂ、Ｚｎ吸收系数提高，Ｃｄ、Ｐｂ含量超标，低剂量时Ｃｄ超标３７．５％，高剂量时超标１００％，增加了对人体健康潜在危险。主要原因在于５元素间存在协同作用，Ｐｂ、Ｃｕ、Ｚｎ、Ａｓ的存在增加了Ｃｄ的活性与解吸率，使其易迁移，为防止土壤污染增加了困难。