干旱区玉米抽雄期叶绿素含量高光谱最佳模型选择

采用相关性、线性和非线性分析法,探讨了玉米抽雄期叶片叶绿素含量与多种高光谱参数之间的关系,并建立了叶绿素含量的定量监测模型。结果表明:(1)原始光谱反射率与叶绿素含量在713 nm处具有最大相关系数r=0.86,光谱反射率一阶微分在760 nm处与叶绿素含量具有最大相关性r=0.84。同时,最大一阶微分分别对应的波长(λr,λb,λy)、绿峰反射率(Rg)和其对应的波长λg、红边内最大一阶微分总和(SDr)、比值植被指数(SDr/SDb,SDr/SDy,(Rg-Ro)/(Rg+Ro))以及归一化植被指数(SDr-SDb)/(SDr+SDb)等10种参数分别与叶绿素含量的相关性达到极显著相关。(2)采用相关性达到极其显著的12种光谱参数进行建模,其中原始光谱、绿色反射峰以及光谱反射率一阶微分、基于红边面积与蓝边面积的比值植被指数和归一化植被指数所建立的10个模型R2都不小于0.72,前两者所建立的指数模型优于线性模型,而后三者所建立的线性模型则优于指数模型。(3)所选取的五个方程中,在760 nm处的光谱反射率一阶微分值所构建的线性模型:y叶绿素=6912x760nm+44.878因其具有最大决定系数和最小的RMSE,并且其模型表达式相对简单,因此是玉米抽雄期叶绿素含量的最佳预测模型,从模型决定系数R2来看,它比其他模型至少提高了11.4%。     

利用光谱特征参数估算病害胁迫下杉木叶绿素含量

为了探索建立炭疽病胁迫下杉木叶绿素含量的高光谱估算模型,促进遥感技术在森林病虫害监测中的应用,通过获取不同发病程度的杉木冠层光谱及相应的叶绿素含量,将冠层光谱数据、一阶微分数据与相应的叶绿素含量分别进行了相关分析。采用逐步回归、主成分回归及偏最小二乘回归方法构建叶绿素含量的估算模型。叶绿素含量与原始光谱在可见光(614～698nm)和近红外区(724nm之后)达到极显著相关,且在近红外区基本趋于稳定;与一阶微分光谱在424～486nm、514～532nm、552～682nm、698～755nm和762～772nm波段全部达到极显著相关;3种建模方法均消除了参数间多重共线性的影响,模型的决定系数全部达到极显著水平,其中逐步回归模型精度最高,相对误差和均方根误差分别为10.71%和0.194。研究表明受到不同程度炭疽病胁迫的杉木冠层光谱反射差异较大,可利用高光谱信息定量估算病害胁迫下的杉木叶绿素含量,且估算精度较高。     

马铃薯受马铃薯甲虫危害后冠层光谱特征的初步研究

使用美国ASD野外便携式光谱仪测量马铃薯受马铃薯甲虫危害后冠层光谱反射率,进行光谱微分、相关分析,得出结论：在750～975 nm范围内,受害后的马铃薯与健康的马铃薯相比冠层光谱反射率下降,红边斜率降低。选择了马铃薯受害后的敏感波段为736～920 nm。     

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。     

典型龟裂碱土光谱特征分析及碱化程度预测

以宁夏银北地区典型龟裂碱土为研究对象,表层土壤光谱反射率选择平滑、倒数等7种数据处理方式,采用全回归、逐步回归和偏最小二乘三种回归方法,分析龟裂碱土光谱特征,筛选对土壤pH值和ESP的敏感波段,建立龟裂碱土碱化信息的预测模型。结果表明：龟裂碱土的光谱反射曲线属于缓斜型;土壤表层反射率与土壤pH值和ESP在研究波段内均呈极显著正相关关系;反射率倒数对数的一阶微分和反射率的一阶微分在特征波段范围表现较好;反射率与土壤pH值的相关性优于与土壤ESP的相关性。从拟合度和选用敏感波段的多少整体考虑,采用偏最小二乘回归来拟合土壤pH值和ESP的方程最佳,拟合度分别达到0.93和0.8367。     

新疆北部不同类型土壤光谱特征及对有机质含量的预测

对北疆地区淡栗钙土、冷钙土、石灰性黑钙土、石膏灰棕漠土等4种土壤类型的反射光谱进行分析,研究土壤有机质含量与光谱反射率之间的关系。结果表明,石灰性黑钙土的反射率明显低于其它土壤类型。有机质含量高于14 g·kg^-1时光谱反射率与有机质含量呈负相关,有机质含量很低（<8 g·kg^-1）时,土壤的光谱反射率与有机质含量之间呈正相关。分别采用593.6 nm波段的原始光谱反射率、661 nm波段的反射率去除包络线和547.4 nm波段反射率的一阶微分与土壤有机质含量建立回归模型,经检验三种模型均能较好地预测有机质的含量,其中光谱的一阶微分预测精度相对较高,可较好地预测北疆主要类型土壤的有机质含量。     

小麦条锈病多时相冠层光谱与病情的相关性

通过田间接种诱发了不同等级的小麦条锈病,随着条锈病的传播,在不同的小区间形成病情梯度,利用ASD手持式地面非成像光谱仪(325～1075nm)测定不同生育期、不同病情指数的冬小麦冠层光谱反射率,并同步调查病情指数,进而对不同生育期、不同病情指数的小麦条锈病冠层光谱反射率进行相关分析。结果表明,不同病情指数的冬小麦植株在600～703、770～930nm波段的冠层光谱反射率存在显著差异,并在波段770～930nm间,病情指数(DI)与光谱反射率呈显著负相关,负相关系数达到极显著;而在600～703nm间,病情指数与光谱反射率呈显著正相关,相关系数达到极显著。构建了3个生育期病情指数与650和850nm波段处的光谱反射率的回归方程:拔节期,DI=13.03×R650nm-0.67×R850nm 10.22(R2=0.6570);灌浆期,DI=48.63×R650nm-2.41×R850nm-41.51(R2=0.8196);乳熟期,DI=24.42×R650nm-5.10×R850nm 67.77(R2=0.7336)。     

麦蚜对小麦冠层光谱特性的影响研究

通过对田间不同程度麦蚜危害的小麦冠层反射光谱测量,研究了各波段反射光谱的变异特征,并对光谱反射曲线进行微分分析。结果表明:在麦蚜危害的初期,近红外反射率明显降低,即陡坡效应受到明显的削弱,随着麦蚜危害程度加重,小麦冠层的反射率在不同波段有明显下降,尤其在近红外区下降更为显著。利用光谱微分技术,对受麦蚜不同程度危害的小麦冠层反射率求一阶导数,得到红边斜率。结果表明,麦蚜危害后小麦冠层的红边斜率在近红外波段发生剧烈的变化,且随着危害程度的加重其值逐步下降。将归一化植被指数(NDVI)分别和百株蚜量进行相关及回归分析,并对监测蚜虫敏感波段的选择做了初步的探讨。     

开都河流域下游绿洲盐渍化土壤高光谱特征

土壤光谱反射特性是土壤遥感的物理基础.通过野外调查采样、土壤盐分实验分析与土壤高光谱数据采集,对土壤高光谱数据一阶和二阶导数微分变换处理,分析土壤样品的光谱特征,建立土壤光谱和土壤盐分含量间的相关关系,对研究区盐渍化土壤含盐量进行定量反演.研究结果表明:1)从土壤光谱反射率的形态特征来看,土壤的光谱反射率曲线总体上变化较为平缓,光谱特征形态较为相似,且基本平行.2)研究区土壤光谱反射率曲线的形状大致可由300 ～ 600nm、600 ～ 800nm、800～1000nm、1000 ～ 1400nm、1400 ～1900nm、1900 ～ 2100nm、2100～ 2500nm七个折线段和560nm、900nm、1400nm、1900nm、2200nm五个特征吸收点来控制.3)利用光谱反射率一阶导数微分的盐渍化土壤含盐量多元线性回归预测模型的预测效果均优于利用反射率原型和反射率二阶导数微分,其中氯化物-硫酸盐型RMSE=0.33,硫酸盐型RMSE=0.31,硫酸盐-氯化物型RMSE=0.22.     

基于野外实测高光谱数据的干旱区耕作土壤含水量反演研究

利用2011年3月野外实地采集的不同含水量土壤的高光谱数据,研究了南疆地区耕作土壤草甸土含水量与高光谱反射率之间的定量关系,构建了一元线性回归与多元逐步回归的土壤含水量预测模型.结果表明,土壤含水量在380～ 1080 nm波段与反射率呈负相关关系;反射率经倒数(1/R)、对数(logR)、一阶微分(R’)变换后可提高其与含水量的相关性;以50个建模样本所建立模型的相关系数均达到极显著水平,所有模型通过对37验证样本进行预测,比较决定系数、均方根误差、相对误差后,表明多元逐步回归模型的预测能力要优于一元线性回归模型,从所有模型中优选出以698、702、703、746、747 nm波段反射率倒数(1/R)建立的多元逐步回归模型为最优模型,该模型实测值与预测值之间的R2为0.9199,RMSE为1.6026,RE为0.6517,可用于基于野外高光谱数据的土壤含水量的估测.     

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     

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。     

The effects of rust and anthracnose on the photosynthetic competence of diseased bean leaves

ABSTRACT The effects of rust (caused by Uromyces appendiculatus) and anthracnose (caused by Colletotrichum lindemuthianum) and their interaction on the photosynthetic rates of healthy and diseased bean (Phaseolus vulgaris) leaves were determined by gas-exchange analysis, in plants with each disease, grown under controlled conditions. The equation P(x)/P(0) = (1 - x)() was used to relate relative photosynthetic rate (P(x)/P(0)) to proportional disease severity (x), where beta represents the ratio between virtual and visual lesion. The beta values obtained for rust were near one, indicating that the effect of the pathogen on the remaining green leaf area was minimal. The high values of beta obtained for anthracnose (8.46 and 12.18) indicated that the photosynthesis in the green area beyond the necrotic symptoms of anthracnose was severely impaired. The impact of anthracnose on bean leaf photosynthesis should be considered in assessments of the proportion of healthy tissue in diseased leaves. The accurate assessment of the healthy portion of the leaf could improve the use of concepts such as healthy leaf area duration and healthy leaf area absorption, which are valuable predictors of crop yield. The equation used to analyze the interaction between rust and anthracnose on the same leaf was P(z) = P(0) (1 - x)(x) x (1 - y)(y), where P(z) is the relative photosynthetic rate of any given leaf, P(0) is the maximum relative photosynthetic rate, x is anthracnose severity, y is rust severity, betax is the beta value for anthracnose in the presence of rust, and betay is the beta value for rust in the presence of anthracnose. From the resulting response surface, no interaction of the two diseases was observed. Dark respiration rate increased on diseased leaves compared with control leaves. The remaining green leaf area of leaves with both diseases was not a good source to estimate net photosynthetic rate because the effect of anthracnose extended far beyond the visual lesions, whereas the effect of rust on photosynthesis was essentially limited to the pustule plus halo.     

Induction of systemic resistance to <Emphasis Type="Italic">Exobasidium vexans</Emphasis> in tea through SAR elicitors

The effect of two chemical elicitors (acibenzolar-S-methyl benzo-[1,2,3]- thiadiazole-7-carboxylic acid S-methyl ester [Boost 500SC]) and salicylic acid in inducing resistance in tea plants against blister blight disease caused by Exobasidium vexans Massee, was studied. Treatments with elicitors resulted in reduced severity of blister blight disease in nursery plants on challenge with the pathogen. There was a significant increase in the activities of defense enzymes like phenylalanine ammonia lyase, peroxidase and β-1,3-glucanase on elicitor treatments in tea leaves challenged with the pathogen than on unchallenged leaves. Acibenzolar-S-methyl (ASM) at 0.14% registered the lowest disease severity (25.2%), whereas treatments with salicylic acid were inferior. Under field conditions, the application of ASM at 0.14% resulted in disease protection of 25%. When ASM was applied in alternate rounds with a standard fungicide, the disease protection improved to 46.8%. The importance of incorporating ASM as a component in integrated disease management and also its importance in organic tea cultivation is discussed.     

Effect of foliar diseases of wheat on the physiological processes affecting yield under semi-arid conditions

The effects of Septoria leaf blotch (caused by Mycosphaerella graminicola) and leaf rust (caused by Puccinia recondita ) on the physiological processes affecting yield were studied under semi-arid conditions in Israel. In the absence of water stress, photosynthetic activity decreased as the rate of disease development increased. Transpirational activity was reduced in leaves infected by Septoria leaf blotch, but intensified in leaves with slight leaf rust infections (0.5-5% severity). When leaf rust seventy exceeded 5%, the transpirational water loss declined. Both diseases were associated with a decrease in the maximum rate of grain-weight accumulation, but did not affect the duration of weight accumulation. An inverse linear relationship between disease and final grain weight was observed. Under conditions of water stress, photosynthetic activity of leaves slightly infected by Septoria leaf blotch (1-5"., severity) was greater than that of uninfected leaves. Severely infected leaves (" 25% severity) photosynthesized the least. Both diseases were associated with a decrease in the maximum rate of grain weight accumulation, but the duration of accumulation was longer in tillers with a slow rate of disease development than in uninfected tillers. The relationship between disease and final grain weight in these cases was parabolic; yield was increased at low levels of infection. Theoretical explanations and practical implications of these phenomena are presented and discussed.     

亚洲玉米螟为害后玉米冠层光谱变化和产量损失研究

2006年在河北农林科学院植保所农场夏播高感亚洲玉米螟的玉米品种郑单958上,于大喇叭口期人工接种2龄玉米螟幼虫以造成不同梯度为害,利用便携式遥感光谱仪(ASD FieldSpec UV/VNIR)在玉米不同生育期收集冠层光谱信息,调查食叶级别,并在收获时统计蛀孔率和产量。结果表明:(1)各生育期食叶级别和对应生育期内的冠层光谱反射率值呈显著负相关,且各个级别之间方差分析差异显著;(2)各波段冠层光谱反射率值和每株虫孔数量的相关性分析得到相关性曲线,750～900nm相关系数较高,可作为监测的敏感波段;(3)乳熟期光谱数据、平均每株虫孔数量和产量及产量损失率之间均可建立极显著回归方程。用光谱仪所测数据估测产量损失率的精确度比用传统查虫数据估测产量损失率的精确度高,且省时省工。     

茶树链格孢叶斑病的病原鉴定

茶树是我国重要的经济作物,茶园叶病的流行会造成严重的经济损失。2017年10月到2018年1月从安徽、福建和湖北省茶区的9个茶树品种上采集代表性茶叶斑病叶,该病害的发病症状与由Colletotrichum spp.引起的茶炭疽病相似。采用组织分离法从发病叶片组织分离获得26株菌落形态一致的真菌分离物,显微镜观察结果显示,各菌株分生孢子的产生方式和形态特征相似。为进一步明确菌株的分类地位,选取2株来自安徽庐江和宣城地区的代表性菌株(EC-6和XBC1-3)进行多基因片段的PCR扩增和序列分析。结果表明,代表性菌株EC-6和XBC1-3的ITS、gpd、tef-1a基因序列分别与交链格孢Alternaria alternata参考菌株CBS 107.27的序列(KP124300, KP124157, KP125075)相似性为100%、99%和100%,结合菌株形态学观察以及柯赫氏法则验证,证实交链格孢是引起该茶树叶斑病的致病菌。这是在安徽茶区首次发现由致病性链格孢引起茶树叶斑病。     

Towards the Development of a Novel In Vitro Strategy for Early Screening of Fusarium Ear Blight Resistance in Adult Winter Wheat Plants

A novel in vitro bioassay is described for screening Fusarium ear blight (FEB) resistance in adult winter wheat plants. Seven winter wheat cultivars were assessed for components of partial disease resistance as 28 day-old detached leaf segments in the laboratory using isolates of Microdochium nivale var. nivale and M. nivale var. majus. Results were compared with disease data obtained at anthesis using the same cultivars as whole plants and the same isolates under glasshouse conditions. Significant cultivar differences were observed using detached leaves, with cv. Avalon (a Fusarium culmorum ear susceptible cultivar) having the shortest leaf incubation period, greatest leaf lesion development and shortest leaf latent period compared to cv. Spark (a Fusarium culmorum ear resistant cultivar), which had the longest leaf incubation period, least leaf lesion development and longest leaf latent period. Using whole plants, cv. Avalon had the shortest ear incubation period and greatest ear disease severity, whilst cv. Spark had the longest incubation period and least ear disease severity. Overall, cultivars of intermediate F. culmorum ear resistance expressed intermediate responses to M. nivale isolates, using both detached leaves and whole plants. Significant correlations were found with ear disease severity and ear incubation period in whole plants and components of partial disease resistance in detached leaves, with significant correlations obtained between leaf incubation period and ear disease parameters using the M. nivale var. nivale isolate. In addition, leaf latent period and leaf lesion size showed significant correlations with whole plant reactions using M. nivale var. nivale and var. majus isolates. The in vitro screening of cultivars as detached leaves using M. nivale isolates may offer a real possibility of a rapid bioassay for the early screening of FEB resistance in wheat and other cereals.     

Survival analysis of time to abscission of blueberry leaves affected by septoria leaf spot

ABSTRACT In the southeastern United States, Septoria leaf spot, caused by Septoria albopunctata, can result in premature defoliation of blueberry plants during summer and fall, thereby reducing yield potential for the following year. The effects of disease severity and leaf attributes (leaf age and leaf location in the canopy) on the dynamics (timing and extent) of defoliation were quantified in field plots of Premier rabbiteye blueberry (Vaccinium ashei) in 2002 and 2003. In each year, 50 shoots were selected for assessment in early spring, and all leaves on these shoots (n = 410 and 542 in 2002 and 2003, respectively) were monitored individually for disease progress and time of abscission at 3- to 10-day intervals throughout the season. In both years, disease progress was characterized by an exponential increase in disease severity up to late September, followed by a decline toward the end of the assessment period in late November. Defoliation was sporadic up to late August, followed by more rapid and sustained levels of leaf loss. Abscission of severely infected leaves could explain the decline in disease severity toward the end of the season. Final disease severity (i.e., disease severity on the last assessment date before leaf drop) was highest for leaves that abscised early and lowest for leaves that had not abscised by the end of the assessment period. Survival analysis revealed that older leaves (located on the lower halves of shoots) and leaves with high levels of disease (>/=5 spots/leaf at the time of fruit harvest in mid-June) abscised significantly (P < 0.0001) earlier than younger leaves and leaves with lower disease severity. Relative to their respective reference groups, mean times to abscission were approximately 2 weeks shorter for the older leaf group and approximately 3 weeks shorter in the leaf group afflicted by high disease severity. When an accelerated failure time model was fitted to the data, the resulting parameter estimates indicated that each additional leaf spot present at harvest accelerated time to leaf abscission (expressed using late August as a starting point) by 1.9 and 4.5% in 2002 and 2003, respectively. Leaf location in upper or lower portions of the canopy had no significant effect on time to abscission (P > 0.05).