Ratio of rice reflectance for estimating leaf blast severity with a multispectral radiometer

 Rice reflectance was measured to determine the spectral regions most sensitive to leaf blast infection with a multispectral radiometer. As disease severity increased, reflectance also increased in the 400–500 nm (blue), 570–700 nm (red), and 900–2000 nm regions but decreased in the 500–570 nm and 700–900 nm regions. The increased reflectance in the blue and red regions may be attributed to decreased chlorophyll and carotenoid contents in response to the blast infection. The maximum and minimum reflectance differences occurred at 680 nm and 760 nm for the nondiseased and diseased rice, respectively. The spectral location of maximum sensitivity was 675 nm regardless of disease severity. Rice reflectance ratios were evaluated as indicators of leaf blast severity. Two ratios, R550/R675 (reflectance at 550 nm divided by reflectance at 675 nm), and R570/R675 quantified the significant disease severity. These wavelengths were selected based on the sensitivity minima and maxima. The ratios of nondiseased rice plants varied depending on growth stage. The variation in ratios must be considered when they are used to estimate leaf blast severity. Received: April 2, 2002 / Accepted: August 12, 2002     

Use of multispectral radiometry for assessment of rhizoctonia blight in creeping bentgrass

ABSTRACT The ability to identify diseases early and quantify severity accurately is crucial in plant disease assessment and management. This study was conducted to assess changes in the spectral reflectance of sunlight from plots of creeping bentgrass during infection by Rhizoctonia solani, the cause of Rhizoctonia blight, and to evaluate multispectral radiometry as a tool to quantify Rhizoctonia blight severity. After inoculation of 6-year-old creeping bentgrass turf with R. solani anastomosis group 2-2, reflectance of sunlight from the foliar canopy was measured at light wavelengths of 460 nm (blue) to 810 nm (near infrared [NIR]), at 50-nm intervals. Visual estimates of disease severity and percentage of canopy reflectance were made daily throughout each of three epidemics of Rhizoctonia blight from the onset of visible symptoms until maximum disease severity was reached. In each experiment, linear regression analysis revealed a significant reduction in the percentage of NIR (760 and 810 nm) reflectance as disease severity increased. However, in the majority of analyses, regression models explained <50% of the variability between components. Multispectrum radiometry appears to function best when used to assess differences in disease severity at discrete points in time rather than over an entire epidemic.     

基于高光谱的渭北旱塬区棉花冠层叶面积指数估算

以棉花冠层高光谱反射率与冠层叶片叶面积指数(LAI)为数据源,在分析LAI与原始高光谱反射率、一阶微分光谱反射率、光谱提取变量和植被指数相关性的基础上,采用一元线性与多元回归的方法构建了棉花LAI高光谱估算模型,并进行精度估算。结果显示,在可见光范围内随着生育期的推进及施氮量的增加冠层光谱反射率逐渐降低,在近红外范围内从苗期到花铃期随着施氮量增加反射率逐渐增加,花铃期到吐絮期反射率明显降低;各生育期冠层光谱的提取变量与LAI的相关性不强,全生育期各种光谱提取量及植被指数与LAI的相关性高于不同生育期;棉花冠层叶片LAI在反射光谱1 461 nm处相关系数达到最大值(r=-0.726);对于一阶微分光谱,LAI的敏感波段发生在742 nm处,r=0.744;以敏感波段742 nm一阶微分光谱反射率建立的逐步回归估算模型精度最高,RMSE=0.94,RE=26.27%,r=0.78。说明以全生育期为基础,采用一阶微分光谱敏感波段,并根据实际条件选择有效的估测模型,可以进行棉花LAI的预测。     

Effects of panicle development stage and temperature on rice panicle blast infection by Magnaporthe oryzae and visualization of its infection process

Panicle blast, caused by the fungus Magnaporthe oryzae (syn. Pyricularia oryzae), directly contributes to yield loss in the field. The effects of panicle development stage and temperature on panicle blast were studied and the infection process of M. oryzae in panicles was visualized. Rice panicles at different development stages from three rice cultivars were inoculated with a conidial suspension in vitro. The rice cultivar Lijiangxintuanheigu was highly susceptible to panicle blast at 5 days postinoculation (dpi) when the pulvinus distance was 15–20 cm. Nanjing 9108 was moderately susceptible to panicle blast when the pulvinus distance was 8–10 cm, but Yliangyou 800 was resistant. The effect of temperature on panicle blast was determined under 22–35 °C temperature treatments. Inoculated panicles placed at temperatures of 28 and 30 °C showed the highest lesion grade based on lesion length at 5 dpi. The infection process of M. oryzae in rice panicles was observed by confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM). M. oryzae initially formed the appressorium to invade through the epidermis of rice panicles at 24 hours postinoculation (hpi). As the disease progressed, the invasive hyphae formed dense mycelial networks in the inner parenchyma cells at 60 hpi. Our results will contribute to the understanding of panicle development stage and temperature effects on panicle blast and improve resistance evaluation methods. Additionally, visualization of the infection process by CLSM and TEM are valuable methods to observe M. oryzae invasive hyphae inside rice panicle cells.     

炭疽病胁迫下的茶树叶片高光谱特征分析

试验以茶树不同炭疽病受害程度的叶片及健康叶片为材料, 室内测定其光谱反射率。结果表明, 炭疽病危害后, 茶树叶片的光谱值随发病程度的增加表现出有规律的变化, 740～1 000 nm波段的光谱反射率随病情加重呈现下降趋势; 而1 370～2 500 nm波段却表现出相反趋势。在742～974 nm和1 374～2 500 nm, 炭疽病受害程度与光谱反射率呈极显著相关。对光谱一阶微分特征分析表明, 在680～780 nm范围内处理间变幅最大, 有2个波段的一阶微分值与受害程度表现出极显著相关性, 分别为715～763 nm和776～778 nm波段。建立的炭疽病严重度诊断模型, 均达到极显著水平, 其中利用植被指数(Rg - Rr)/( Rg+ Rr)建立的模型精确度最高。     

丙硫磷控制稻瘟病的作用方式及应用技术

经１９９３－１９９５年生物测定和田间多点试验示范发现；１．丙硫磷对稻瘟菌孢子萌发和附着胞形成有显著的抑制活性，ＥＣ５０为１０３．３ｍｈ／Ｌ，５００ｍｇ／Ｌ的抑菌率达９６．２％；２．丙硫磷１０００ｍｇ／Ｌ对水稻苗叶瘟和穗瘟的预防效果分别为７９．４％和９０．７％，治疗效果分别为３９．３％和４１．８％；３丙硫磷６００－９００ｇ／ｈｍ＾２防治双季稻和瓜后稻穗瘟病的田间小区效果分别为７０．８％－８０．２％和     

Geographic distribution of false smut disease of rice in India and efficacy of selected fungicides for its management

False smut disease of rice caused by the fungus Ustilaginoidea virens, has become a serious production constraint in various rice-growing regions of India. Analysis of rice false smut disease survey data of last 24 years revealed significant changes in the intensity of the disease in various rice-growing regions of India over the years. We evaluated three fungicide formulations viz., trifloxystrobin-tebuconazole (TT) combination (0.04%), kresoxim methyl (KM) (0.1%) and propiconazole (PC) (0.1%) for their effectiveness against false smut disease of rice. Under in vitro condition, TT and PC completely inhibited the fungal growth while KM inhibited the growth by 80%. We evaluated the efficacy of these chemicals in a multi-location trial in 3 hot spot locations, consecutively for three years. A single fungicide spray was given in 3 different crop stages (booting, 50% panicle emergence and 100% panicle emergence). The results indicated that all the treatments significantly reduced the percentage of both infected panicles and spikelets in all the three locations. Both TT and PC were most effective in reducing the disease intensity and increasing the yield when applied either in booting or in 50% panicle emergence stage.     

Effects of Low Doses of Glyphosate on Agronomic Traits of Upland Rice

Research has shown the occurrence of the hormesis effect in some upland rice cultures resulting from low-dose application of glyphosate. Glyphosate herbicide is widely used in Brazilian agriculture for controlling the large quantity of weeds. The aim of this work was to verify the effects of low-dose application of glyphosate herbicide on agronomic characteristics in upland rice. The experimental design used was randomized blocks comprising five low-dose applications of glyphosate herbicide (10, 20, 40, 70, and 100?g acid equivalent [a.e.] ha^?1) and the control, in two stages of development of the rice culture (tillering [V4] and floral differentiation [R1]) with four repetitions. The agronomic traits of upland rice were evaluated. Data were subjected to variance analysis, polynomial regression analysis for the quantitative factor, and Tukey’s test for the qualitative factor at p?<?0.05. The grain yield and the number of spikelets per panicle increased with the application of 10?g a.e. ha^?1 of glyphosate at the floral differentiation stage. Until the low dose of 75?g a.e. ha^?1, there was an increase in the number of panicles. Low doses between 70 and 100?g a.e. ha^?1 applied in R1 provided less spikelets per panicle, lower 100-grain weight, and lower grain yield. The leaf flavonoid content increased due to the increase in the low doses of glyphosate herbicide.

     

氮肥施用量和施用方法对超级杂交稻纹枯病发生的影响

 The experiments of resistance of different super hybrid rice (SHR) combinations to sheath blight (ShB) (Rhizoctonia solani Kühn) and effect of nitrogen fertilizer (NF) dosage and fertilization methods on ShB occurrence were conducted in Hangzhou during 2005-2006. The results indicated that the resistance level of different SHR combinations to ShB were significantly different. For the same combination, the severity of ShB depends on the seeding and transplanting period. The disease index showed a positive correlation with the nitrogen dosage, but depended on resistance level of combination. The ShB severity of susceptible combination showed high positive correlation with NF dosage. At the flowering stage, there were no effect of nitrogen fertilization method on the occurrence of ShB, but the fertilization method showed significantly effect at dough stage. The occurrence of ShB was significantly affected by the supply rate of nitrogen at different rice growing stage. When the total NF supply was 165 kg per hectare, the occurrence of ShB with high NF rate (80%) at early stage (as basal and tillering fertilizer) and low rate (20%) at late stage (as panicle fertilizer) was more serious than that of low NF rate (60%) in early and high NF rate (40%) as panicle fertilizer. The result was the reverse of conventional viewpoint about that high NF supply at rice late growing stage might lead to severe occurrence of ShB.     

谷蠹的趋光行为及部分影响因素研究

为探讨昆虫的趋光性和灯光诱捕技术在储粮害虫防治中的应用,在实验室条件下探究了光源波长、光强、虫龄、虫口密度和饥饿处理对谷蠹成虫趋光行为的影响。结果表明,在可见光区,谷蠹趋光性较强的波长范围在530nm和575nm,在紫外光区,谷蠹趋光性较强的波长为365、385和395nm。在一定的光强范围内,谷蠹的趋光性随光强度的增强而增大。随着日龄的增加,趋光性先增强后逐渐减弱,10~15日龄成虫的趋光性最强。随着成虫饥饿处理时间的延长,谷蠹的趋光性先增强后减弱,饥饿处理2d的趋光性最强。随着释放虫口密度的增加,谷蠹的趋光性增强。研究结果为谷蠹灯光诱捕技术的研究和应用提供了一些参考。     

稻曲病的接种技术研究

 探索在田间条件下进行稻曲病的人工接种技术。通过比较3种接种体发现,上年保存于-20℃的厚垣孢子不能引起发病;用PS液体培养获得的薄壁分生孢子可引起发病,孢子浓度越高引起病穗率越高;菌丝片段-分生孢子混合液接种发病最严重。病原菌的培养菌龄对接种效果有影响。在水稻的3个时期接种,以抽穗破口前6~9d的效果最好。在一天的3个时段接种,以下午4~6时的病情最重。在接种液里添加马铃薯煮汁可显著提高接种发病率。本文的接种技术能高效引发稻曲病,最高穗发病率100%,最大病情指数93.96,最多穗病粒数110粒。该接种技术可鉴别出品种抗病性的差异。     

Early assessment of the yield loss in rice due to the brown planthopper using a hyperspectral remote sensing method

The brown planthopper (BPH) is an important pest in rice. Rice losses due to BPH's damage are often more than 10% of yield. Assessments on loss rates from BPH are now basically dependent on experiential indices. However, early assessments on rice yield losses using hyperspectral data are still rare. In this study, reflectance from rice canopy was measured in net cages after different densities of BPH release. Results showed that reflectance in the near-infrared region (750–1000 nm) from milk grain stage, and in 400–531 nm and 567–705 nm from mature grain stage was closely related to BPH density. These spectral indices: red-edge parameters (λ_r, Dλ_r, Sλ_r), ratio of the maximal reflectance in green (490–560 nm) to minimal reflectance (640–740 nm) in red (R_GREEN/R_RED), ratio of the near-infrared peak (R_NIR) to R_RED, normalized difference vegetation index between R_NIR and R_RED and soil-adjusted vegetation index (SAVI) from both milk and mature grain stages, indicated BPH densities well. As expected, rate of loss in rice grain was higher with increasing BPH density. SAVI, Dλ_r, Sλ_r and reflectance at 760 nm (R₇₆₀) from milk grain stage were significantly correlated with rates of loss in panicle, and 1000-grain weight and multiple-linear regression models for detecting loss rate were established. The hyperspectral reflectance from rice at milk grain stage can be used to assess rice yield losses due to BPH and improve management policies.     

石羊河流域下游民勤荒漠植物光谱特征分析

选取石羊河流域下游民勤10种典型荒漠植物进行地面反射光谱测定,通过分析荒漠植物光谱特征、红边参数及对比荒漠植物与农作物光谱数据,提取荒漠植物识别的波段和所需波段光谱分辨率。结果表明:1)10种荒漠植物具有相似的光谱曲线形状,但是不同荒漠植物种由于叶子的组织结构、色素含量和含水量不同,使得反射率大小又具有各自的特点;5个波段区间光谱曲线差异显著,用于识别荒漠植物。2)荒漠植物红边位置都靠近长波方向;沙蒿的红边幅值最大,锦鸡儿最小;沙拐枣的红边面积最大,泡泡刺最小。3)荒漠植物光谱反射特征在680nm、970nm、1450nm和2190nm附近与农作物有较大差异,光谱分辨率在可见光和近红外波段需要30nm或更窄,在中红外波段需要50nm或更窄。     

Effects of Elevated Atmospheric CO(2) Concentration on the Infection of Rice Blast and Sheath Blight

ABSTRACT The effect of elevated atmospheric CO(2) concentration on rice blast and sheath blight disease severity was studied in the field in northern Japan for 3 years. With free-air CO(2) enrichment (FACE), rice plants were grown in ambient and elevated ( approximately 200 to 280 mumol mol(-1) above ambient) CO(2) concentrations, and were artificially inoculated with consist of Magnaporthe oryzae. Rice plants grown in an elevated CO(2) concentration were more susceptible to leaf blast than those in ambient CO(2) as indicated by the increased number of leaf blast lesions. Plants grown under elevated CO(2) concentration had lower leaf silicon content, which may have contributed to the increased susceptibility to leaf blast under elevated CO(2) concentrations. In contrast to leaf blast, panicle blast severity was unchanged by the CO(2) enrichment under artificial inoculation, whereas it was slightly but significantly higher under elevated CO(2) concentrations in a spontaneous rice blast epidemic. For naturally occurring epidemics of the sheath blight development in rice plants, the percentage of diseased plants was higher under elevated as opposed to ambient CO(2) concentrations. However, the average height of lesions above the soil surface was similar between the treatments. One hypothesis is that the higher number of tillers observed under elevated CO(2) concentrations may have increased the chance for fungal sclerotia to adhere to the leaf sheath at the water surface. Consequently, the potential risks for infection of leaf blast and epidemics of sheath blight would increase in rice grown under elevated CO(2) concentration.     

28%三环唑·嘧菌酯悬浮剂对水稻稻瘟病的防治效果

为科学合理地选择和使用田间控制稻瘟病的杀菌剂,本研究通过室内苗期测定和大田试验,评价复配剂28%三环唑·嘧菌酯SC对水稻稻瘟病的防治效果。结果表明,28%三环唑·嘧菌酯SC对水稻苗瘟及穗瘟均有很好的预防和治疗效果。在温室人工控制条件下,施药后接种的防效高于接种后施药的防效,最高防效分别为97.35%和92.70%。在田间对穗瘟的最高防效达到91.11%,与对照药剂75%三环唑WP和250 g/L嘧菌酯SC的平均防效相当,可以在生产上推广使用,推荐有效成分用量为252～420 g/hm~2。     

水稻稻曲病室内人工接种技术

为提高稻曲病人工接种的发病效果和稳定性,在温棚条件下采用水稻孕穗期注射接种法分别研究了稻曲病菌不同接种体、培养时间、接种浓度和接种时期的接种效果。采用病菌马铃薯蔗糖液体培养基（potato sucrose broth,PSB）作为接种体,其穗发病率为100%,明显好于病菌米糠培养液（23.33%）。病菌在PSB中培养5～7天接种效果较好,随病菌培养天数的延长,接种效果明显下降。接种的分生孢子浓度越低水稻病穗率和病粒数也越低。在水稻品种两优培九孕穗中后期,采用含分生孢子浓度为4×106个/mL的病菌PSB培养液注射接种,穗发病率达100%,平均病粒数35.1粒,最高达87粒。研究表明,温棚条件下建立的稻曲病人工接种技术能获得稳定的发病效果,并可区别水稻品种间的抗性差异。     

小麦条锈病单片病叶特征光谱的初步研究

以健康小麦植株叶片为对照,把小麦条锈病病叶按照严重度分成8个级别,应用高光谱遥感(Hyperspectral Remote Sensing)技术,采用ASD Field-Spec Pro FR 2500型光谱仪和LI-Cor1800-12外置积分球,测定各级别单片病叶上发病区域的反射光谱。结果表明,随着病害严重度的增加,反射率随之增强。在350～1 600 nm波段范围内反射率与严重度基本成正相关,535 nm以后反射率与严重度相关达显著水平。选择相关性最高的波段(670～690 nm),利用SAS软件进行逐步回归分析,建立了小麦条锈病严重度和光谱反射率之间的回归模型,即y=-0.576 8+0.7953R685-0.603 6R690。     

不同稻区稻瘟病菌致病型变异及基于MAS的品种对稻瘟病的抗性鉴定

稻瘟病是影响水稻生产的重要病害。监测田间稻瘟病菌菌群致病型的组成是有效推行利用抗病品种抗瘟策略的必须环节。本研究采集2015年湖北省10个稻作区的穗颈瘟标本,以单基因鉴别品系对分离得到的菌群进行致病型的测定,并分区进行品种的抗瘟性鉴定,结果表明,不同稻作区菌群致病型的组成存在差异,品种对不同稻作区菌群的抗性明显不同,单基因品系中9个抗性基因在湖北稻区受侵染程度也存在明显差异。     

Effect of rice growth stages and silicon on sheath blight development

ABSTRACT The objective of this study was to determine the effect of silicon (Si) and rice growth stages on tissue susceptibility to sheath blight (Rhizoctonia solani Kühn) under controlled conditions. Rice plants (cv. Rio Formoso) were grown in pots containing low-Si soil amended with Si at 0, 0.48, 0.96, 1.44, and 1.92 g pot(-1) and inoculated with R. solani at the following days after emergence: 45 (four-leaf stage), 65 (eight-leaf stage), 85 (tillering), 117 (booting), and 130 (panicle exsertion). For plants inoculated with R. solani at all growth stages, Si concentration in straw increased as rate of Si increased from 0 to 1.92 g pot(-1). Concentration of calcium in the straw did not differ among plant growth stages. Although incubation period was not affected by the amount of Si added to the soil, this variable was shorter at booting and panicle exsertion stages. As the rates of Si increased in the soil, the total number of sheath blight lesions on sheaths and total area under the relative lesion extension curve decreased at all plant growth stages. The severity of sheath blight was lower at booting and panicle exsertion stages as the rates of Si increased in the soil. In general, plants grown in Si-nonamended pots and inoculated with R. solani were more vulnerable to infection at all growth stages, but especially at 45 days after emergence. Plant dry weights for inoculated plants increased as the Si rates increased from 0 to 1.92 g pot(-1). The greatest dry weight increases occurred for plants inoculated at booting and panicle exsertion stages. Si fertilization is a promising method for controlling sheath blight in areas where soil is Si deficient and when cultivars that exhibit an acceptable level of resistance to sheath blight are not available for commercial use.     

植保无人飞机喷施30%苯甲·丙环唑微乳剂防治水稻主要病害

为了探究植保无人飞机喷施30%苯甲·丙环唑微乳剂对稻瘟病、纹枯病和稻曲病的田间防治效果,以及对水稻生长的影响,为植保无人飞机施药的推广提供科学依据,在水稻分蘖末期和破口期采用植保无人飞机进行药剂喷施防治水稻主要病害试验。结果表明:在减量25%的情况下,植保无人飞机喷施30%苯甲·丙环唑微乳剂对纹枯病病株和病情指数的防治效果分别为71.33%和82.72%,对稻瘟病病穗和病情指数的防治效果分别为76.36%和80.41%,对稻曲病病穗和病情指数的防治效果分别为71.11%和79.25%。该施药方式对水稻中后期主要病害防治效果均优于对照药剂和人工施药的防治效果。