Dynamics of soilborne Rhizoctonia solani in the presence of Trichoderma harzianum: effects on stem canker, black scurf and progeny tubers of potato

Stem canker and black scurf are diseases of potato caused by the fungus Rhizoctonia solani . Spatiotemporal experimentation and empirical modelling were applied for the first time to investigate the effect of antagonistic Trichoderma harzianum on the dynamics of soilborne R. solani on individual potato plants. Trichoderma harzianum reduced the severity of symptoms, expressed as 'rhizoctonia stem lesion index' (RSI), during the first 7 days post-inoculation when the inoculum of R. solani was placed at certain distances (30–60 mm) from the host. For example, with inoculum at 40 mm from the host, RSI was 6 and 40 with and without T. harzianum , respectively. At later observation times, the antagonistic effect was overcome. Trichoderma harzianum reduced the severity of black scurf on progeny tubers. Furthermore, the mean number of progeny tubers per potato plant was reduced by the biocontrol treatment (means of 6·5 ± 1·1 and 9·9 ± 2·7 tubers per plant with and without T. harzianum , respectively), as was the proportion of small (0·1–20·0 g) tubers (48% and 66% with and without T. harzianum , respectively). Additionally, there were fewer malformed and green-coloured tubers in pots treated with T. harzianum than in those without T. harzianum .     

宁夏马铃薯主栽品种对黑痣病的抗性鉴定

为明确宁夏马铃薯主栽品种对黑痣病的抗性水平,利用田间和室内接种相结合的方法对供试马铃薯品种的抗病性进行评价。室内接种试验表明,供试的20份马铃薯材料中没有免疫及高抗品种,接种量与抗性水平呈负相关,其中‘陇薯7号’,‘黑美人’,‘青薯9号’在接种量为5~15g水平上表现为中抗。通过聚类分析,接种量为5g和10g时,以欧式距离13作为最佳聚类分割点,供试品种可分为3个类群。田间接种综合评价分析表明,不同品种间抗性存在显著差异,通过聚类分析,以欧式距离13作为最佳聚类分割点,试验品种可分为4个高感品种、11个中感品种和5个中抗品种。     

Dynamics ofRhizoctonia solani (black scurf) in successive potato crops

The position of plants withRhizoctonia solani sclerotia (black scurf) on progeny tubers was mapped for an experimental field at Haren where potatoes were grown continuously and in rotation with other crops for five successive years, and for another field at Borgercompagnie with a 12 frequency of potatoes during three potato crops. Initially, the distribution of plants with black scurf on both fields was rather dense and homogeneous. In the following years the distribution became heterogeneous and patchy. The local decline ofR. solani AG 3 (the common potato pathogen) in Haren was apparently caused by an unknown factor selectively suppressingR. solani AG 3, while simultaneouslyR. solani AG 5 increased in mass. This AG 5 type proved to be an inferior competitor of AG 3 on the potato plant in a laboratory experiment. The specificR. solani antagonistVerticillium biguttatum did not play a role. A similar factor could have reduced the formation of black scurf in the experimental field at Borgercompagnie, whereV. biguttatum was also too infrequent to account for the decline.R. solani AG 5 was not present here and could not indicate the presence of a selective factor against AG 3.     

碳酸氢盐对马铃薯黑痣病菌毒力及田间防效

为明确碳酸氢盐对马铃薯黑痣病菌的毒力及田间防效,采用菌丝生长速率法,测定了碳酸氢盐对马铃薯黑痣病菌的毒力;并通过盆栽防治试验及田间防治试验,研究了碳酸氢盐对马铃薯黑痣病的防治效果。结果表明:碳酸氢铵抑制马铃薯黑痣病菌菌丝生长的有效中浓度EC50仅为0.71g/L,碳酸氢钾EC50为3.8g/L;在PSA培养基中同时加入0.79g/L碳酸氢铵、1g/L碳酸氢钾与在PSA培养基中含1.58g/L碳酸氢铵的抑菌效果一样;尿素对马铃薯黑痣病没有防治效果。碳酸氢铵与碳酸氢钾混配对该病有良好的防治作用,相对尿素最高防治效果可达到63.4%。覆膜栽培能够提高碳酸氢盐的防效和马铃薯产量。碳酸氢盐可用于田间马铃薯黑痣病的防治。     

Factors affecting the temporal progress of stem canker (Rhizoctonia solani ) on potatoes (Solanum tuberosum)

The effects of different densities of tuber-borne inoculum, selected agronomic treatments (date of planting, irrigation and size of seed tubers) and their interactions on the temporal progress of stem canker ( Rhizoctonia solani ) on potato plants ( Solanum tuberosum ) were investigated in a multifactorial experiment. Data comprising stem number and the incidence and severity of stem canker from planting until tuber initiation in two consecutive growing seasons were analysed using linear contrasts, quadratic contrasts and the area under the disease progress or host growth curve. Differences in the incidence and severity of stem canker were dominated by the effect of different densities of tuber-borne inoculum. The majority of disease progress curves were nonmonotonic for the incidence and severity of stem canker with a rapid rise in disease up to stem emergence and a decline thereafter. Most treatments affected the area under the curve and to a lesser extent the average rate of increase in disease. Of the agronomic treatments, later dates of planting and pre-emergence irrigation reduced the levels of stem canker whereas size of seed tubers did not affect the progress of disease. Little additional information was revealed by scoring for the severity rather than the incidence of stem canker.     

云南省马铃薯黑痣病病原菌融合群鉴定及8种药剂对其的毒力

由立枯丝核菌引起的马铃薯黑痣病是一种常见的土壤和种薯传播病害,在世界各地均有发生。本试验对分离纯化的67个丝核菌菌株进行融合群测定,结果表明:67个菌株都属于AG3融合群;对其中来自6个不同地域的11个菌株进行ITS测定,11个菌株的相似度为99%。8种药剂对马铃薯黑痣病菌的毒力测定结果表明,20%氟胺·嘧菌酯水分散粒剂50mg/L和25g/L咯菌腈悬浮种衣剂50mg/L的抑菌效果较好,室内抑菌效果可达100%。     

Genetic variability and pathogenicity of Rhizoctonia solani associated with black scurf of potato in New Zealand

Isolates (a total of 129) of Rhizoctonia solani were collected from black scurf on potato tubers from different potato‐growing regions in New Zealand. Sequence analysis of the nuclear ribosomal DNA internal transcribed spacer (rDNA–ITS) regions from these isolates identified three anastomosis groups (AGs), AG‐3PT, AG‐2‐1 and AG‐5. Isolates classified as AG‐3PT were widely distributed, whereas AG‐2‐1 and AG‐5 were confined to distinct locations. Sequence heterogeneity was identified in the ITS regions of 100 AG‐3PT and AG‐2‐1 isolates. Variation in the sequence and length of the rDNA–IGS1 region was also observed for selected isolates of AG‐3PT and AG‐2‐1. Phylogenetic studies found all AG‐2‐1 isolates belong to AG‐2Nt, a subset of AG‐2‐1 previously associated with solanaceous crops in other countries. AG‐2‐1 isolates were consistently more aggressive than those of AG‐3PT. Delayed emergence, severe infection on stolons, formation of aerial tubers and considerable yield losses were associated with AG‐2‐1, but they caused negligible black scurf. In contrast, AG‐3PT caused black scurf on progeny tubers but variable effects on stem emergence and stolons. Furthermore, AG‐2‐1 isolates caused severe tuber malformation, but isolates of other AGs did not. This is the first report on the AG composition, genetic variability and pathogenicity of R. solani isolates associated with black scurf of New Zealand potatoes.     

Infection process of Rhizoctonia solani on Solanum tuberosum and effects of granular nematicides

The infection process ofRhizoctonia solani AG-3 was studied on potato sprouts, cv. Bintje, in growth chamber trials at 15 °C. Initially hyphae ofR. solani grew predominantly in the longitudinal direction of the sprouts (runner hyphae). They tended to follow the junctions between epidermis cells as was observed by SEM. The hyphae formed side-branches mainly half-way of the subterranean parts of the sprouts. They branched several times with short swollen cells to form infection cushions. Lesions developed only underneath the infection cushions and were first observed five days after inoculation. The necrotic area was proportional to the area covered with infection cushions on the sprouts. Depth of the lesions could extend up to the vascular bundle. Sprouts were colonized only in healthy tissue in the epidermal layer underneath the infection cushion and in necrotic tissue. A few days after appearance of the lesions,R. solani formed brown, uninfective mycelium on and in the circumference of these lesions.Aldicarb did not influence any part of the infection process. Ethoprophos delayed the emergence of sprouts, but increased the number of sprouts per tuber. As soon as sprouts had emerged, growth was considerably promoted by ethoprophos. Ethoprophos delayed the appearance of lesions and reduced their size. Oxamyl showed the same effects to a smaller extent.As the size of lesions appears to be proportional to the size of the infection cushions, any agents that change the size of the infection cushions, such as pesticides or antagonists, may alter the severity of the disease.Samenvatting Het infectieproces vanRhizoctonia solani AG-3 werd bestudeerd op aardappelspruiten, cv. Bintje, in een klimaatcel bij 15C. Aanvankelijk groeide de schimmel met runnerhyfen voornamelijk in de lengterichting van de spruit. Via SEM kon waargenomen worden, dat de hyfen hierbij vooral over de begrenzingen van de epidermiscellen groeiden. Het mycelium vormde veel zijvertakkingen, bestaande uit iets gezwollen korte cellen, welke voornamelijk halverwege op het ondergrondse deel van de spruit gevormd werden. Een dichte massa van deze cellen vormde een infectiekussentje. Lesies, welke vanaf vijf dagen na inoculatie werden waargenomen, bevonden zich slechts onder spruitoppervlak bezet met infectiekussentjes. De lesiegrootte was recht evenredig met het spruitoppervlak dat bezet was met infectiekussentjes. De diepte van de lesies reikte tot aan de vaatbundels. De spruit werd alleen door de schimmel gekoloniseerd in gezond epidermisweefsel onder het infectiekussentje en in necrotisch weefsel. Enkele dagen na verschijning van lesies vormde R.solani bruin, niet infectieus, mycelium op en rondom de lesies.Aldicarb had geen effect op het infectieproces. Ethoprophos vertraagde de opkomst en verhoogde het aantal tot ontwikkeling gekomen spruiten per knol in gestoomd zand. Direct na opkomst had ethoprophos echter een sterk groeistimulerend effect. Ethoprophos vertraagde de lesievorming en reduceerde de lesiegrootte, vergeleken met onbehandelde planten. Oxamyl vertoonde deze effecten in geringere mate.Daar de lesiegrootte direct gecorreleerd blijkt met de grootte van het infectiekussentje, mag verwacht worden dat elke beïnvloeding van de ontwikkeling van het mycelium van R.solani, bijvoorbeeld door pesticiden of antagonisten, een verandering van de lesiegrootte ten gevolge heeft.     

Emergence of silver scurf (Helminthosporium solani) as an economically important disease of potato

During the 1990s, silver scurf (causal agent Helminthosporium solani ) emerged as an economically important disease of table stock and processing potatoes ( Solanum tuberosum ). The pathogen attacks the periderm of the potato tuber causing blemishes. The disease cycle of silver scurf has both field and storage phases. Primary infection occurs in the field and high relative humidity favours the spread and increase of silver scurf in potato stores. Control of the disease by chemical and cultural practices remains difficult. Increase in disease has been attributed to H. solani isolates resistant to the postharvest fungicide thiabendazole (TBZ). Polymerase chain reaction (PCR)-based detection methods for H. solani and TBZ-resistant isolates are rapid and more specific than traditional identification. This review discusses the biology of the pathogen, epidemiology of the disease, detection of the pathogen and integrated control measures for the management of silver scurf in both field and potato tuber stores.     

Influence of abiotic factors,inoculum source,and cultivar susceptibility on the potato tuber blemish diseases black dot (Colletotrichum coccodes) and silver scurf (Helminthosporium solani)

Black dot and silver scurf are potato blemish diseases whose economic impact has increased in recent years. Because their symptomatology on tubers is visually similar, disease assessment does not usually differentiate between the two pathogens, which share the same ecological niche. The epidemiology of black dot has been extensively studied, especially in the UK, but the factors that influence silver scurf have been less investigated. In this study, the influence of cultivar, source of inoculum, and environmental conditions on both diseases was studied in field trials over a three-year period (2016–2018) in Switzerland. Planting minitubers did not prevent either disease in daughter tubers, indicating the contribution of soil as an inoculum reservoir. An arbitrary threshold of Colletotrichum coccodes soil inoculum could be set to discriminate between low and high disease risk. For the first time, Helminthosporium solani DNA was detected in stolons, and infections appeared earlier in stolons than in tubers. H. solani stolon and tuber infections usually appeared later in the season than those of C. coccodes. Black dot severity correlated positively with precipitation, while silver scurf severity correlated positively with temperature. Table potato cultivars commonly grown in Switzerland exhibited significant differences in susceptibility to both diseases, and cultivars with low susceptibility to both silver scurf and black dot were identified. These results gave new insights into understanding the factors driving the epidemiology of potato blemish diseases and may contribute to building a risk assessment scheme to manage both diseases simultaneously.     

Inoculum density and spatial pattern of Rhizoctonia solani in field plots of Solanum tuberosum: effects of cropping frequency

Bait plants, comprising micropropagated and commercial seed tubers, were used to estimate the effects of rotation on the density and spatial pattern of inoculum of Rhizoctonia solani in large field plots of potatoes. Soilborne inoculum of R. solani produced economically significant levels of stem canker and its incidence and severity varied with rotation, with most disease in 2-year and less in 4- and 6-year rotations. The rates of loss of inoculum during intercrop periods differed amongst rotations with a rapid fall to low levels occurring after 1 year in a 6-year rotation and after 2 years in a 4-year rotation. Replenishment of inoculum to soil was rapid following the growth of a susceptible crop, with comparatively high levels of infection and disease, even in long rotations. Disease occurred in patches and the size of patches and the density of R. solani within patches differed with cropping frequency. The degree of spatial autocorrelation also differed amongst rotations but there was no evidence for any significant differences in the rate of change of spatial autocorrelation during intercrop periods in the three rotations.     

Anastomosis groups and pathogenicity of binucleate Rhizoctonia isolates associated with stem canker of potato in China

Potato stem canker caused by Rhizoctonia solani commonly occurs in potato-growing regions around the world, but little is known about whether binucleate Rhizoctonia (BNR) can incite this disease on potato plants in China. In the present study, a total of 69 BNR isolates were recovered from cankered subterraneous stems of potato collected from 17 provinces, autonomous regions, and municipalities of China. Based on the morphological characteristics and sequence analysis of the internal transcribed spacers of the ribosomal DNA, 48 isolates were classified as anastomosis group (AG)-A with a ratio of 69.56 %, 15 isolates (21.74 %) were AG-K, four isolates (5.80 %) were AG-F, one isolate (1.45 %) was AG-I and one isolate (1.45 %) was AG-U. Pathogenicity tests under glasshouse conditions revealed that all BNR isolates, except for the AG-I isolate, could induce symptoms of stem canker on potato plants with disease incidence ranging from 5.26 to 55.56 % and disease index ranging from 1.32 to 13.89, respectively. To our knowledge, this is the first detailed report about BNR AGs causing stem canker on potato plants in China.     

不同贮藏条件下龙葵种子的季节性休眠特性

龙葵是农田恶性杂草?为明确龙葵种子休眠与季节温度的关系, 研究了室内和室外不同贮藏条件下其种子萌发对温度的响应规律?结果表明, 室外贮藏条件下的龙葵种子萌发呈季节性变化, 从10月到翌年5月, 龙葵种子萌发率均在95%以上, 随着夏季温度的升高, 萌发率从6月开始下降, 9月达到最低值(25.4%), 由此进行年际间休眠和非休眠周期的循环?夏季6月-9月的高温可诱导龙葵种子进入休眠状态, 而秋冬季的相对低温有利于解除种子休眠, 使种子恢复萌发状态?龙葵种子休眠和非休眠状态之间的切换受季节性温度变化的影响?室内贮藏的种子, 由于环境温度较为稳定, 其萌发率年际变化较小, 在20%~50%之间?本文明确了龙葵种子休眠的周期性变化规律, 有助于精准预测其出苗时间, 研究结果可为阐明龙葵种子休眠萌发机制和制订基于萌发调控的绿色防控策略提供依据?     

马铃薯黑痣病生防菌的筛选和鉴定及其生长条件的研究

从甘肃省景泰县条山农场不同连作年限的马铃薯地块中取根际土样品,分离筛选马铃薯黑痣病病原菌-立枯丝核菌(Rhizoctonia solani)的拮抗菌。采用土壤平板稀释、对峙法筛选拮抗菌;结合形态特征、生理生化及16Sr DNA分子鉴定;采用单因素试验设计对G1菌株的生长条件进行初步试验。通过初筛和复筛,从108株细菌中获得1株对立枯丝核菌拮抗效果稳定、拮抗能力较强的细菌G1。采用平板对峙法测定其拮抗作用,抑菌带宽度达6mm,抑菌圈直径2.5 cm,抑菌率为66.7%。结合形态特征、生理生化及16Sr DNA分子鉴定,G1为类芽孢杆菌(Paenibacillus sp.);采用单因素试验设计对G1菌株的生长条件进行初步试验。结果表明,菌株G1在4℃~45℃,p H 5~10,盐浓度0~50 g·L-1都能生长,碳源、氮源利用广泛,最适条件为:温度37℃,p H 7,蔗糖为碳源,蛋白胨为氮源,盐浓度为10 g·L-1。拮抗菌G1被鉴定为类芽孢杆菌,该菌株抑菌带较宽、抑菌效果稳定,生长条件与马铃薯生长的大田环境基本相符,具有作为一株优良生防菌的必要条件。     

Evaluation of Brassica species for resistance to Rhizoctonia solani and binucleate Rhizoctonia (Ceratobasidum spp.) under controlled environment conditions

Isolates of R. solani AG 2–1, AG 8, AG 10 and binucleate Rhizoctonia (Ceratobasidium spp.) were tested for virulence on Brassica crops in growth chamber experiments. Isolate virulence and genotype resistance were determined based on percent of seedling survival, shoot length reduction, and shoot fresh weight. Isolates had significant effects on all tested measurements, compared to the non-inoculated controls. Rhizoctonia solani AG 2–1 appears to be the most aggressive pathogen on all tested genotypes followed by R. solani AG 8, binucleate Rhizoctonia and R. solani AG 10, respectively. Genotype by isolate interaction effects were found to be significant for percent of seedling survival and shoot length reduction. None of the tested genotypes exhibited any level of resistance to R. solani AG 2–1, but three promising genotypes with moderate levels of resistance to R. solani AG 10, R. solani AG 8 and binucleate Rhizoctonia were identified. Moderate heritability (0.57) was observed for the percent of seedling survival in the resistant genotype KS4022.     

灌溉对14个小麦新品种(系)产量和农艺性状适应性的GGE分析

于2018—2019年在山东省泰安市马庄试验田采用随机区组设计,包含品种、灌溉两因素,选用14个小麦新品种（系）,水分处理分别为出苗后不浇水（E1）、浇拔节水（E2）和浇拔节+开花水（E3）,3次重复,共126个小区。分别考察不同处理的小区产量、株高、单穗粒重、单穗穗粒数、单穗小穗数、单穗不孕小穗数等6个性状的变化情况,应用方差分析法和R语言的GGE双标图方法分析性状的基因型效应、环境效应、基因型与环境的互作效应。结果表明,节水型小麦新品系均存在基因型效应(G)、环境效应(E)和基因型×环境互作效应(GE)且均表现出极显著差异（P<0.05）,基因型效应(G)的变异范围为1.07%～60.17%,环境效应(E)的变异范围为14.42%～86.97%,基因型×环境互作效应(GE)的变异范围为4.33%～47.88%。不同品种（系）的群体产量性状和个体农艺性状在不同环境下的适应性不同,表现为在不同灌水条件下,不同品种（系）处于不同多边形的顶角位置不同;小麦新品种（系）不同个体性状在不同浇水环境下表达程度不同。E1环境有利于单穗不孕小穗数的表达,E2有利于单穗粒重的表达,E3有利于株高的表达;不同环境对群体产量性状和个体农艺性状的鉴别力和代表性不同,E1环境比E2、E3环境具有更好的鉴别力和代表性。综上,在黄淮麦区,本研究所选用的14个节水型小麦新品种（系）农艺性状基因型效应及其与环境互作效应差异显著,E1环境有利于小麦节水新品种（系）群体产量和个体农艺性状的选择。     

Additive effect of the root-lesion nematode Pratylenchus penetrans and the fungus Rhizoctonia solani on potato yield and damage

Journal of Plant Diseases and Protection - The significance of nematodes for disease development caused by other soil-borne pathogens has been demonstrated in many crops throughout the world and...     

Relationships between agronomic factors and epidemics of Phytophthora branch canker of citrus in southwestern Spain

Phytophthora branch canker, caused by Phytophthora citrophthora, has been an increasing problem in clementine (Citrus reticulata) production in Spain during last years. The disease was particularly severe in the new citrus-growing areas of the southwestern coastal areas in Huelva Province. Recent studies revealed that disease emergence was not related to either genetic drift or host specificity changes in P. citrophthora population. Therefore, the possible association of agronomic factors with the disease was investigated. A total of 110 orchards were selected arbitrarily from the main citrus-growing areas in Huelva Province. The presence of branch cankers together with agronomic factors including soils, cultivars, rootstocks, irrigation, pruning, techniques to improve fruit production, fungicide treatments, presence of brown rot of fruit and frost damage were recorded. Logistic regression analysis was used to detect correlations between the agronomic factors studied and disease prevalence. Phytophthora branch canker was significantly associated with mature clementine orchards. Sweet orange and hybrid cultivars as well as young clementine orchards were less affected by the disease. Although disease was less frequent in Salorthid soils, alternative high resolution procedures are required to draw conclusions about the effect of soil properties on disease prevalence. As in other Phytophthora-induced diseases, soil flooding during the rainy season was correlated positively with the prevalence of branch cankers. Improving fruit production by branch scoring showed a strong positive correlation with Phytophthora branch canker. This is the first time that girdling has been associated with Phytophthora disease epidemics on a fruit tree crop, but further research is needed to determine the cause of this relationship. Cultural practices including pruning, regulated deficit irrigation, additional phosphonate sprays, and abiotic and disease factors such as frost damage and presence of brown rot of fruit were not significantly correlated with disease prevalence.