Evaluation of screening methods and fruit composition in relation to anthracnose fruit rot resistance in blueberries

Anthracnose fruit rot is an important disease of blueberries, and losses are common in humid growing regions. Most commercial cultivars are susceptible and the disease is usually managed with fungicides. However, a few cultivars are considered resistant. The objectives of this study were to: (i) compare different inoculation techniques for anthracnose fruit rot resistance screening, (ii) screen ripe fruit from a range of blueberry cultivars using selected techniques, and (iii) investigate the role of fruit characteristics in anthracnose fruit rot resistance. The following inoculation methods were evaluated on ripe fruit of a susceptible and resistant cultivar using a conidial suspension: spray, droplet, and injection inoculation of whole fruit; and droplet inoculation of the open surface of cut fruit. All whole‐fruit inoculations yielded similar results. Despite the removal of the epidermis, resistance was also expressed in cut fruit but relatively fewer conidia were produced. The cut‐fruit assay required substantially less time and half the amount of fruit to accomplish than whole‐fruit assays. Detached ripe fruit from 24 cultivars in 2008 and 26 cultivars in 2009 were screened for resistance. Results from the cut‐fruit assay correlated best with published resistance ratings. To determine the possible role of fruit characteristics in resistance, fruit pH, titratable acidity, sugar content and firmness were regressed against various fruit rot resistance measures. Fruit rot resistance was positively correlated with sugar content. On defined media, mycelial growth was restricted as sugar concentration increased and pH decreased, suggesting that fruit composition may play a role in the resistance phenotype.     

Development of protocols for detection of Colletotrichum acutatum and monitoring of strawberry anthracnose using real-time PCR

Real-time PCR (TaqMan®) assays were developed for the specific detection and discrimination of Colletotrichum spp., C. acutatum and C. gloeosporioides causing anthracnose in strawberry using the most divergent area of the internal transcribed spacers (ITS1 and ITS2) and 5·8S ribosomal RNA (rRNA) gene region. The specificity of the new assays was tested using DNA from six species of Colletotrichum and nine fungal species commonly found associated with strawberry material, and additionally by comparing the sequences with those from databases using a blast search. The sequences only showed identity with homologous sequences from the desired target organisms. The new assays were 10–100 times more sensitive than conventional PCR methods previously published for the diagnosis of strawberry anthracnose. When real-time PCR was compared with ELISA methods, PCR improved the sensitivity of the identification by obtaining positive results for samples of strawberry plant material that tested negative with ELISA. The development of C. acutatum was monitored using artificially infected strawberry crowns from two strawberry cultivars (Camarosa and Ventana) and a real-time PCR assay specific for this species between January and June 2006. The amount of C. acutatum detected using real-time PCR varied significantly by month ( P  < 0·001), but not by cultivar ( P  = 0·394). The new assays were shown to be useful tools for rapid detection and identification of these pathogens and to allow rapid and accurate assessment of the casual agents of anthracnose in strawberry.     

Effects of nitrogen, phosphorus, potassium and calcium nutrition on strawberry anthracnose

The effects of a range of concentrations of four nutrients – nitrogen, phosphorus, potassium and calcium – in fertilizer solutions on the severity of anthracnose on strawberry cv. Nyoho cultivated under a noncirculation hydroponics system were determined after inoculation with Colletotrichum gloeosporioides . Crop growth and tissue nitrogen, phosphorus, potassium and calcium contents of the entire above-ground parts of the plant were also investigated. Elevated nitrogen and potassium concentrations in the fertilizer solution increased disease severity in contrast to phosphorus and calcium. Treatment with either NH₄ or NO₃ nitrogen was not significantly different. The dry weight of the strawberry plants increased significantly with elevated concentrations of nitrogen ( R ² = 0·9078) and phosphorus ( R ² = 0·8842), but was not influenced by the elevated amounts of potassium ( R ² = 0·8587) and calcium ( R ² = 0·6526) concentrations.     

Components of genetic variation for resistance of strawberry to Phytophthora cactorum estimated using segregating seedling populations and their parent genotypes

Strawberry ( Fragaria × ananassa ) seedlings from 50 bi-parental crosses among 20 elite genotypes were evaluated for resistance to Phytophthora cactorum after artificial inoculation. Plots of seedlings or runner plants were rated using a disease severity score and the percentage of stunted plants per plot. The distribution of cross means for percentages of plants with stunting was highly skewed; 79% of the inoculated seedlings showed some level of stunting compared to non-inoculated control seedlings, and all but one of the crosses had 50% or more stunted plants. Disease severity scores for the bi-parental crosses were normally distributed and expressed a range of variation not reflected by the percentage of visibly stunted plants. Factorial analysis based on seedling plot means demonstrated significant additive genetic variance for the disease severity score, and the additive genetic variance was 1·9 times greater than the estimated dominance variance. The cross-mean heritability was     for the severity score. Estimates of the additive genetic variance component using the covariance of severity scores obtained from the seedling analysis and with severity scores for their parents evaluated in a commercial environment were similar,     and 0·30, respectively. Most of the selection response obtained through genotypic selection would thus be transferred to segregating offspring.     

Epidemiology,histopathology and aetiology of olive anthracnose caused by Colletotrichum acutatum and C. gloeosporioides in Portugal

Anthracnose is an important disease affecting mature olive fruits, causing significant yield losses, and poor fruit and oil quality. In Portugal, high anthracnose incidence was recorded during 2003–2007 with 41% of 908 orchards surveyed displaying disease symptoms. In another 14% of the orchards, the pathogen was recorded in symptomless plants. Disease severity was on average 36%, frequently reaching 100%. In Portugal, anthracnose is endemic to neglected orchards of susceptible cultivars, but under favourable conditions it can also severely affect less susceptible cultivars. Pathogens were genetically heterogeneous, with Colletotrichum acutatum genetic group A2 as the most frequent (80%), followed by group A4 (12%) and group A5 along with C. gloeosporioides (3–4%), while groups A3 and A6 of C. acutatum were sporadic. Important geographic variations were observed in the frequencies of these populations, accompanied by year‐to‐year populational shifts. Epidemiology and histopathology studies showed the presence of the pathogens on vegetative organs year‐round, particularly on olive leaves and branches, and on weeds. These represent inoculum reservoirs where secondary conidiation occurs, and conidia are then dispersed by spring rains reaching flowers and young fruits or by autumn rains reaching pre‐mature fruits. Unripe fruits were colonized without showing symptoms up to penetration of the cuticle, but further colonization and symptom production was completed only as fruits matured. These findings challenge current control practices, particularly the timing of fungicide treatment, and contribute to improved disease management.     

11个草莓品种对炭疽病的田间抗性表现

在田间自然发病条件下,对种植在北京市昌平区的11个草莓品种的炭疽病发生情况进行了调查和分析比较。结果表明：草莓同一品种的三个部位（叶片、叶柄和匍匐茎）对炭疽病的抗性表现不一致,除‘莫哈维’和‘叙利亚’叶柄的病情指数高于叶片和匍匐茎外,其他品种都是匍匐茎的病情指数最高,‘波特拉’匍匐茎的病情指数高达73。根据叶柄对炭疽病的表现,在所调查的草莓品种中,品种‘森格纳’表现免疫,‘甜查理’、‘阿尔比’和‘圣安德瑞斯’为高抗,‘本尼西亚’和‘波特拉’表现为抗病,‘叙利亚’为高感,其他品种为感病。     

UV-C照射对草莓炭疽病3种致病菌生活力和致病力的影响

炭疽病是草莓种植中普遍发生、危害严重的病害之一,而UV-C对真菌的生长繁殖有极大的影响。为了探究UV-C辐照对引起草莓炭疽病的3种主要病原菌生长和致病力影响的差异,以果生炭疽菌Colletotrichum fructicola、胶孢炭疽菌C.gloeosporioides和暹罗炭疽菌C.siamense为供试菌,分析UV-C辐照对其分生孢子存活、菌丝生长和产孢能力及对草莓叶片致病力的影响。结果显示,在105～420 J/m~2辐照剂量(辐照30～120 s)范围内,3种炭疽菌孢子的相对存活率对UV-C辐照剂量的响应存在显著差异,C.gloeosporioides的耐受性最强,C.fructicola最为敏感,辐照剂量420 J/m~2(辐照120 s)下,3种炭疽菌孢子的相对存活率在4%或以下,接近分生孢子的致死剂量。840～1 260 J/m~2辐照剂量(辐照4～6 min)下,C.fructicola与C.gloeosporioides菌丝生长对UV-C辐照的耐受性相当;1 680～2 520 J/m~2辐照剂量(辐照8～12 min)下,3种炭疽菌对不同时间的UV-C辐照的耐受性...     

Morphological and molecular characterization of Colletotrichum spp. from citrus orchards affected by postbloom fruit drop in Brazil

Brazilian isolates of Colletotrichum spp. from citrus orchards affected by postbloom fruit drop were examined for colony colour, mycelial growth, benomyl-resistance, pathogenicity, and genetic variability by random amplified polymorphic DNA (RAPD) analysis. All isolates were obtained from flowers and persistent calyxes from different citrus hosts from Sao Paulo, Brazil. DNA polymorphisms detected after amplification with random 10-mer primers were used to classify the isolates into two groups. Group I isolates grew rapidly on potato-dextrose agar (PDA) and were sensitive to benomyl, and group II isolates grew slowly on PDA and were benomyl-resistant. Colletotrichum acutatum was analyzed by RAPD and had high genetic similarity with group II isolates of Colletotrichum from citrus. Probably, the group I is C. gloeosporioides and group II is C. acutatum.     

Shoot Blight and Leaf Spot of Blueberry Anthracnose Caused by <Emphasis Type="Italic">Colletotrichum acutatum</Emphasis>

Shoot blight and leaf spots were found on highbush blueberry trees in Tsukuba, Ibaraki, in 1999. The causal fungus was identified morphologically as Colletotrichum acutatum Simmonds ex Simmonds. This is the first report of blueberry anthracnose caused by C. acutatum in Japan. Received 16 November 2001/ Accepted in revised form 22 March 2002     

Survival,distribution and genetic variability of inoculum of the strawberry red core pathogen,Phytophthora fragariae var. fragariae,in soil

An experimental field infested with Phytophthora fragariae var. fragariae (Pff) and used for strawberry red core fungicide and cultivar resistance trials until 1981 was surveyed for the presence of inoculum of the pathogen 11 and 12 years later. Alpine strawberries, highly susceptible to all races of Pff, were grown from true seed and planted as a bait crop on a 0·5 m‐spaced grid. Rapid and widespread red core infection was observed, which provided good evidence that oospores had survived in soil for this extended period. Site elevation and the distribution of red core infected plants showed a strong correlation, with a higher frequency of infected and dead plants in the lowest areas of the field. The race designation of 18 recovered isolates were determined and AFLP fingerprint patterns of some of these and their single‐spore derivatives were analysed. The isolates differed little in race type, and the majority were genetically identical at 433 AFLP loci. Races used to inoculate the site in the 1970s were recovered. The fingerprints of the single variant isolate matched that of an isolation made by Hickman in the 1950s, originally used to inoculate the site. Clearly Pff is a very stable and long‐lived pathogen able to retain its genetic integrity and lie dormant in soil for many years, ensuring its survival between epidemiologically favourable conditions which occur erratically.     

滴灌施药对覆膜玉米茎腐病防效及产量影响

在辽西风沙半干旱地区,开展了人工接种茎腐病病原菌条件下覆膜滴灌施用多菌灵和戊唑醇防治玉米茎腐病效果研究.结果表明:滴灌施用50％多菌灵WP和25％戊唑醇WP对玉米茎腐病防治效果均在54％以上,两年平均防效最高的是25％戊唑醇可湿性粉剂140 g/667 m2滴灌处理,达到72.60％,平均产量为948.94 kg/66...     

Characterization of Lasiodiplodia species causing leaf blight,stem rot and fruit rot of fig (Ficus carica) in Malaysia

Fig (Ficus carica) is an exotic deciduous plant that is grown worldwide. Fungal diseases pose a major threat to fig plants, affecting their fruit quality and production. This study was conducted to characterize the fungal isolates associated with leaf blight, stem rot and fruit rot of F. carica in Malaysia through morphological analysis, DNA sequencing, multigene phylogenetic analysis and pathogenicity tests. From September 2018 to March 2019, 30 blighted leaves and 30 rotted stems and fruits of F. carica were collected from several nurseries in Malaysia. Thirty fungal isolates that belonged to Lasiodiplodia theobromae (27 isolates) and L. brasiliensis (three isolates) were identified based on morphological characteristics, comparison of DNA sequences and phylogenetic analysis of the internal transcribed spacer (ITS), elongation translation factor 1-α (tef1-α), β-tubulin (tub2) and DNA-directed RNA polymerase II subunit (rpb2). Among the 27 isolates of L. theobromae, nine isolates were obtained from leaves, eight isolates from stems and 10 isolates from fruits, whereas the three isolates of L. brasiliensis were obtained from stems (two isolates) and a leaf (one isolate). The results of pathogenicity tests revealed that L. theobromae and L. brasiliensis isolates were responsible for leaf blight and stem rot of F. carica, whereas fruit rot was caused by L. theobromae isolates. The present study highlighted two different species, L. theobromae and L. brasiliensis, as the causal agents of leaf blight and stem rot of F. carica. Additionally, L. theobromae caused fruit rot of F. carica in Malaysia.     

Medicago truncatula as a model host for studying legume infecting Rhizoctonia solani and identification of a locus affecting resistance to root canker

The broad‐host‐range necrotizing fungal pathogen Rhizoctonia solani is responsible for economically significant diseases to crops as diverse as wheat, maize, barley, canola, sugar beet, potato, soyabean, bean, lupin and alfalfa. Germplasm screens in many of the crop hosts have not identified strong genetic resistance which, together with the lack of effective control, mean the pathogen remains a substantial problem for agriculture in many parts of the world. Following the establishment of a robust inoculation assay, a germplasm collection of the model legume Medicago truncatula was screened with various legume‐infecting isolates of R. solani. While some significant differences in susceptibility/resistance were detected between some lines, in the majority of cases M. truncatula was susceptible to R. solani. Comparison of a legume‐ and cereal‐infecting AG8 isolate with a legume‐specific AG11 isolate revealed no difference in pathogenicity between the two isolates when infecting M. truncatula. The most significant differences in susceptibility occurred with an AG6 isolate, which caused root canker. This included significant differences between the moderate resistance of the M. truncatula reference genotype A17 and the high susceptibility of line A20. The analysis of a recombinant inbred line population derived from A17 and A20 revealed a single locus contributing to the resistance in A17. Interestingly, the locus only affected the development of post‐emergent (late) symptoms, such as necrosis of cotyledons at 11 days after inoculation and root‐ and above‐ground‐weights, but not pre‐emergent seedling damping off. These findings pave the way for further studies to dissect the genetic and molecular mechanisms of resistance.     

利用酵母双杂交系统筛选与草莓镶脉病毒移动蛋白P1互作的寄主因子

 构建感染草莓镶脉病毒(SVBV)森林草莓的酵母cDNA文库,利用酵母双杂交系统,筛选出与SVBV P1蛋白互作的15种寄主因子。生物信息学分析发现,这15种寄主因子参与茉莉酸途径、泛素化、光合作用、抗病抗逆、蛋白修饰、蛋白运输和氧化还原等多种生物过程。另外,这些寄主因子还具有其他分子功能,包括氧化还原酶活性、蛋白二硫化物异构酶活性和金属离子结合活性等。本研究初步探讨了P1与寄主因子的互作机理,为揭示SVBV侵染森林草莓以及SVBV在寄主中扩展的分子机制提供理论依据。     

Comparison of induced resistance activated by benzothiadiazole, (2R,3R)‐butanediol and an isoparaffin mixture against anthracnose of Nicotiana benthamiana

Resistance in Nicotiana benthamiana against anthracnose caused by the hemibiotrophic fungus Colletotrichum orbiculare was activated by benzothiadiazole (BTH), (2R,3R)­butanediol or PC1, an isoparaffin‐based mixture. In inoculation experiments, BTH, (2R,3R)­butanediol and PC1 reduced the number of lesions per leaf area caused by C. orbiculare by 98%, 77% and 81%, respectively. Foliar application of BTH induced expression of genes for the acidic pathogenesis‐related (PR) proteins, NbPR‐1a, NbPR‐3Q and acidic NbPR‐5. In contrast, soil application of (2R,3R)­butanediol or PC1 primed expression of genes for the basic PR proteins, NbPRb‐1b, basic NbPR‐2 and NbPR‐5dB. These results are consistent with the activation of salicylic‐acid‐dependent systemic acquired resistance (SAR) by BTH and that of jasmonate/ethylene‐dependent induced systemic resistance (ISR) by (2R,3R)­butanediol or PC1, and show that (2R,3R)­butanediol and PC1 can affect gene expression similarly to plant growth‐promoting rhizobacteria. However, the effects of (2R,3R)‐butanediol and PC1 were not identical. In addition to priming, (2R,3R)‐butanediol induced expression of basic NbPR‐2, whereas PC1 treatment induced expression of both NbPRb‐1b and basic NbPR‐2. Although a number of microbial products, such as (2R,3R)­butanediol, have been shown to produce ISR, this is the first demonstration that an isoparaffin‐based mixture, not derived from a microorganism, can produce ISR.     

棉花烂铃病的发生、品种抗病性及主要病原菌致病力分析

2011~2013年,调查了我国黄河和长江流域6省70县(市)200块棉田和不同栽培模式下棉花烂铃病发生情况,田间试验评价了棉花品种对烂铃病的抗性,采用离体棉铃人工接种方法分析了棉铃烂铃主要病原菌的致病力分化情况。结果表明:(1)所有调查的棉田均有棉花烂铃病发生,其中,棉铃疫病在各地发生最为普遍而且严重,仍属于我国黄河和长江流域棉区的最主要的棉花烂铃病,其病原菌为苎麻疫霉(Phytophthora boehmeriae)。(2)与春棉直播模式相比,3种套种模式均能显著减少棉花烂铃病的发生,其中麦-棉-西瓜12∶2∶1种植模式的防效最好,减少烂铃72.96%。(3)河北、山东和河南3省审定的50个棉花品种对棉花烂铃病的抗性存在显著差异,其中邯7860、邯棉103、锦科178、百棉1号和郑农棉4号5个品种对棉花烂铃病表现了较好的抗性,单株烂铃低于3.0个。(4)苎麻疫霉在棉铃上的致病力存在显著分化。     

Influence of competition and host plant resistance on selection in Phytophthora infestans populations in Michigan, USA and in Northern Ireland

Competition between genotypes of Phytophthora infestans was studied by inoculating potato cultivars with differing susceptibility to late blight in field experiments over three years in Northern Ireland, UK, and Michigan, USA. Multiple isolates of six genotype groups of P. infestans were chosen from the local populations in both N. Ireland and Michigan for inoculation of separate field trials planted in 2003, 2004 and 2005. Four cultivars were used in each trial; two (susceptible cv. Atlantic and the partially resistant cv. Stirling) were common to both locations, whereas the two additional cultivars (with partial resistance to late blight) were cvs Santé and Milagro in N. Ireland and cvs Pike and Jacqueline Lee in Michigan. Single-lesion isolates of P. infestans were obtained from leaves at 1% level of infection, characterized using pre-assigned markers and re-assigned to their respective genotype groups. Extreme selection occurred within the population of genotypes of P. infestans in N. Ireland in each year, with different genotype groups dominating the infection of different cultivars. Selection was observed on all cultivars tested, but was greatest on the more resistant cultivars. Over the 3 years, all of the 114 isolates obtained from cv. Milagro belonged to a single group, whereas among the 118 isolates from cv. Atlantic all six groups were represented. By contrast, in Michigan, the US-8 genotype dominated infection in all cultivars in each year; only 12 of 374 isolates characterized belonged to other genotypes (11 US-14 and a single US-10 isolate).     

Pathogenicity and genetic variation of Phytophthora cactorum from silver birch and strawberry

Phytophthora cactorum strains isolated from necrotic stem lesions on Betula pendula seedlings or from Fragaria ananassa plants suffering from crown rot were pathogenic to their host plants. Only isolates from birch caused clear lesions on non-wounded bark of birch. P. cactorum isolates from birch were not detrimental to strawberry. Random Amplified Polymorphic DNA (RAPD) analysis revealed variation within P. cactorum, isolates from silver birch having different banding patterns than those from strawberry. UPGMA analysis clustered isolates from silver birch and strawberry plants into separate groups. The data show that the recent outbreak in Finland of P. cactorum in birch could not be caused by the import of strawberry plants affected by crown rot.     

花椰菜幼苗叶片抗氧化酶系统与抗黑腐病关系的研究

 在盆栽条件下,花椰菜抗病品种雪峰和感病品种2003X-106的幼苗在接种黑腐病菌后,叶片组织内O₂^·产生速率,SOD、POD、PAL活性,MDA含量和膜透性都有不同程度的提高和增加。与2003X-106相比,雪峰的O₂^·产生速率和SOD、PAL活性的增加更为显著,POD活性也要高于2003X-106;而MDA含量和电导率的增幅要明显低于2003X-106。表明抗病品种雪峰比感病品种2003X-106具有更强的抗黑腐病能力和抗氧化能力。     

Simple diagnosis using ethanol immersion of strawberry plants with latent infection by Colletotrichum acutatum, Dendrophoma obscurans, and Fusarium oxysporum f. sp. fragariae

Simple diagnosis by ethanol immersion (SDEI) to detect Glomerella cingulata was used to detect three other fungi that also cause latent infection of strawberry plants. Signs on strawberry leaves with asymptomatic latent infection by Colletotrichum acutatum became visible using SDEI. Salmon-pink conidial masses were produced in the acervuli on the treated leaves 5 days after incubation at 28°C. In the case of Dendrophoma obscurans, pycnidia with amber conidial masses formed 5 days after incubation at 28°C. The pycnidia were observed mainly on the ribs, and conidial masses exuded from the ostiole. These macroscopic conidial masses were similar to those of G. cingulata and C. acutatum. When water was dripped onto a lesion caused by D. obscurans, the pycnidia exuded white filamentous conidial masses, making the distinction of D. obscurans from G. cingulata or C. acutatum. On petioles with latent infection by Fusarium oxysporum f. sp. fragariae, white aerial hyphae grew out from the vascular tissues on the cut surface 3 days after incubation at 28°C and were easily observed by eye or with a loupe. Thus, SDEI was also useful for diagnosing latent infection of strawberry plants by C. acutatum, D. obscurans, and F. oxysporum f. sp. fragariae.