Association of seedling and adult plant resistance to <Emphasis Type="Italic">Sclerotium rolfsii</Emphasis> in Jerusalem artichoke (<Emphasis Type="Italic">Helianthus tuberosus</Emphasis> L<Emphasis Type="Italic">.</Emphasis>) under field conditions

Stem rot caused by Sclerotium rolfsii is an important problem for Jerusalem artichoke production. Host plant resistance is the most promising method to control disease. If resistant genotypes can be identified in seedlings and this resistance is closely related to resistance at maturity, the evaluation of disease resistance in adult plants could be curtailed or omitted, increasing the speed and efficiency of screening. The objective of this study was to determine the relationship between resistance to S. rolfsii in Jerusalem artichoke in seedling and in adult stages under field conditions. Field experiments were set up in different soil fertility environments in the rainy season during July to October 2014. In each environment, 10 varieties of Jerusalem artichoke with differences in resistance to S. rolfsii were planted and inoculated either 15 or 45 days after transplanting. Higher disease incidence was observed on adult plant stage, but disease severity was similar for both plant stages. The correlations between seedling and adult responses were positive and significant for disease incidence, area under disease progress curve and severity index. Screening for resistance to S. rolfsii in Jerusalem artichoke can be carried out on seedlings, thus improving the efficiency of selection.     

<Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> inhibits the plant cell wall degrading enzymes of <Emphasis Type="Italic">Sclerotium rolfsii</Emphasis> and reduces the severity of groundnut stem rot

Three hundred and ninety-three groundnut-associated bacterial strains, applied both as seed treatment and soil amendment, were evaluated for control of stem rot disease (caused by Sclerotium rolfsii) of groundnut in a controlled environment. Twelve strains significantly (P=0.01) reduced the incidence of stem, rot of which groundnut seed endophytes Pseudomonas aeruginosa GSE 18 and GSE 19 reduced the seedling mortality by 54% and 58%, compared to the control. In dual cultures, the 12 biocontrol strains reduced the mycelial growth of S. rolfsii by 32%–74% as compared to the control. Cell- free culture filtrates of P. aeruginosa GSE 18 and GSE 19 inhibited the activity in vitro of the cell wall-degrading enzymes (CWDE) polygalacturonase and cellulase by S. rolfsii up to a maximum of 55% and 50%, respectively, when measured 6 days after inoculation. Pseudomonas aeruginosa GSE 18 and GSE 19 with a known tolerance to thiram, a commonly used seed dressing fungicide, suppressed the growth of S. rolfsii, inhibited the activity of CWDE, and reduced the incidence of stem rot, suggesting the usefulness of these biocontrol strains as components in the integrated management of groundnut stem rot.     

Screening for Sclerotinia resistance in Helianthus tuberosus L. (Jerusalem artichoke) varieties, lines and somaclones, in the field and in vitro

Yields in large-scale 'continuous' cultivation of H. tuberosus (Jerusalem artichoke) can be greatly reduced by Sclerotinia sclerotiorum , which causes a basal stem and tuber rot. In 34 varieties/lines of H. tuberosus from European, Russian and Canadian breeding programmes, responses to the pathogen varied from field resistance to 34% stem rot, cultivars Nahodka and Columbia showing c. 25% stem rot after three seasons of cultivation on the same site. Attempts to develop an in-vitro selection for S. sclerotiorum resistance based on culture of H. tuberosus nodes on media precolonized with Sclerotina were unsuccessful. There was a strong positive correlation between capacity of nodes to grow in vitro on calcium-free medium and field resistance. Somaclones of'Nahodka' selected on the latter basis showed no field infection when grown on land that was heavily contaminated with the pathogen, and they were resistant to artificial inoculation with the pathogen.     

Phenolic content as an indicator of tolerance of cowpea seedlings to <Emphasis Type="Italic">Sclerotium rolfsii</Emphasis>

The role of phenolics in plant tolerance to pathogen infection is well documented. The objective of the present preliminary investigation was to study phenolic metabolites involved in the tolerance or susceptibility of cowpea (Vigna unguiculata Walp.) cultivars to Sclerotium rolfsii Sacc. and to use their presence as a possible screening tool. Total, free acid, ester-bound and cell wall-bound phenolics of 10 cowpea cultivars were quantified. In healthy seedlings, the tolerant cultivars displayed the higher phenol content than the susceptible cultivars. In S. rolfsii infected seedlings, the highest increase was found from 48 h after inoculation. The net effect of inoculation was a 630% increase in total phenolics (soluble and insoluble) in the stem of tolerant cultivars while the total phenolic content increased only by 212% in the stems of susceptible cultivars. Although, no significant difference (P = 0.05) was detected among cultivars, in terms of free acid phenolics, the amount of ester-bound and cell wall-bound phenolics significantly increased, therefore demonstrating a similar trend to the one observed for the total phenolic content. These preliminary results showed that the presence of phenolics before and after S. rolfsii infection may be used as a rapid screening method for detection of tolerance to S. rolfsii damping-off and stem rot of cowpea.     

一种大豆对拟茎点茎枯病抗性鉴定技术体系的构建

 由Phomopsis longicolla(或Diaporthe longicolla)等拟茎点霉(间座壳)属真菌引起的拟茎点茎枯病是我国黄淮海等地大豆生产中的一种重要茎部病害。利用抗病品种是防控该病最为经济有效的措施。为构建一种大豆对拟茎点茎枯病的室内抗性鉴定技术体系,用于抗病资源的快速筛选,本研究比较了下胚轴创伤接种法、切茎接种法、黄化苗接种法、种子接种法和菌丝块贴茎法等5种接种方法,发现下胚轴创伤接种法具有操作简单、试验周期短、易于判定结果、结果稳定性好的优点。选取5个具有毒力强弱和地域代表性的P. longicolla菌株为鉴别菌株系,建立了抗性结果评价标准,形成了抗性鉴定技术体系。对2020年从黄淮海等地收集的62份大豆主栽品种进行抗性鉴定,发现对强毒力菌株DT3-3-1和弱毒力菌株ZZ1-1高抗的品种分别占31%和68%,有13个品种同时高抗5个菌株(占21%),表明我国大豆主栽品种中存在对拟茎点茎枯病的抗性种质资源。本研究为挖掘大豆对拟茎点茎枯病的抗性资源提供了新的候选方法。     

玉米大斑病菌人工接种方法研究

 The efficient and accurate method of inoculating Exserohilum turcicum on maize is most important for studying the corn leaf blight. In this study, four approaches including spore suspension spraying, inoculation with grinding infected maize leaves, inoculation liquid inoculum into the leaf whorl and inoculation with inoculated sorghum seeds were compared with natural induction in fields during different growth stages of maize in the greenhouse and field. The results showed that disease incidence of all varieties tested were up to 100% by inoculating with inoculated sorghum seeds during the booting stage (11 to 12 leaf stages). This method will not only guarantee the enough pathogen inocula but also be easy to use, and could be an effective way for disease resistance identification in field and greenhouse.      

Seed treatments enhance photosynthesis in maize seedlings by reducing infection with <Emphasis Type="Italic">Fusarium</Emphasis> spp. and consequent disease development in maize

Maize seed that was either treated with the fungicide Cruiser Extreme 250 ® (fludioxonil + azoxystrobin + mefenoxam + thiamethoxam) or not treated was planted at two Iowa locations in 2007. Root, mesocotyl and crown rot severity, incidence of Fusarium spp. colonisation and chlorophyll florescence (CF) were assessed at growth stages V2, V4 and V6, and stalk rot severity at R6. At both locations, seed treatment reduced disease severity and incidence of Fusarium spp. infection at all growth stages assessed. Measurements of CF decreased significantly with increased disease severity and incidence of Fusarium spp. at V2 and V4 at both locations, indicating that seedling disease negatively affected photosynthetic performance. Mesocotyl rot severity at V4 predicted crown rot severity at V6 at both locations, as well as crown rot at V6 and stalk rot at R6 at one location.     

Etiology of and effect of environmental factors on damping-off and stem rot of cowpea in Benin

Damping-off and stem rot are two types of diseases affecting cowpea (Vigna unguiculata (L.) Walp.) in the Quémé Valley, Benin. Of the fungal species isolated from diseased plants in the field during a 2-year experiment (2001 and 2002),Sclerotium rolfsii Sacc. was found to be solely responsible for these diseases. The disease incidence decreased with increasing distance of the field from the river. Measurement ofS. rolfsii initial inoculum, soil moisture and disease incidence in cowpea field plots revealed a positive correlation among these parameters. The multiple regression analysis showed that the disease incidence increase was 0.4% for one unit increase in soil moisture percent, whereas the disease incidence increase was 19.8% for one unit increase of the density of initial inoculum of the pathogen. This is the first comprehensive study of the effects of environmental factors on the incidence of cowpea damping-off and stem rot caused byS. rolfsii in Benin, and shows that the density of the initial inoculum is the main contributing factor of the disease in the field in the Quémé Valley. http://www.phytoparasitica.org posting Dec. 19, 2004.     

Effects of wounding, fruit age and wetness duration on the development of cherry brown rot in the UK

This research investigated the effects of wounding, fruit age and wetness duration on the development of cherry brown rot. Both Monilinia laxa and M. fructigena infected wounded detached cherry fruits, but M. laxa caused more infections than M. fructigena and only M. laxa efficiently infected intact detached fruits. Results from field monitoring and controlled inoculation in a polyethylene tunnel showed that the susceptibility of fruits to infection by M. laxa increased with fruit maturity. Infection of attached intact fruits by M. laxa was not affected by the length (3–24 h) of the wet period tested.     

Infection of apple fruit by Sphaeropsis pyriputrescens in the orchard in relation to Sphaeropsis rot in storage

Sphaeropsis rot, caused by Sphaeropsis pyriputrescens, is an important postharvest disease of apple in the United States. The objectives of this study were to determine the timing of apple fruit infection in the orchard in relation to development of Sphaeropsis rot in storage and to identify infection courts and mode of penetration by S. pyriputrescens on apple fruit. Fruit of apple cvs Red Delicious, Golden Delicious, and Fuji were inoculated in the orchard from 3 weeks after petal fall to 2 weeks before harvest at 5 to 6-week intervals in three consecutive seasons. All fruit were harvested and stored at 0?ºC to monitor decay development. Light and scanning electron microscopy were used to examine the infection courts and mode of penetration of the fungus on/in the host tissues. At harvest, the fungus was re-isolated from the stem (pedicel), sepal, anther, or filament of the inoculated fruit, but decay did not develop on fruit. Sphaeropsis rot developed on inoculated fruit during cold storage beginning 1–3 months after harvest. Stem-end rot was prevalent on cv. Golden Delicious, whereas calyx-end rot was prevalent on cv. Fuji. Both stem- and calyx-end rots were common on cv. Red Delicious. Infection also occurred at lenticels on fruit skin, particularly on cv. Golden Delicious, but at low incidence. Relationships between the incidence of Sphaeropsis rot in stored apple fruit and the timing of inoculation in the orchard varied with cultivar and year. On cv. Red Delicious apples, the incidence of Sphaeropsis rot generally increased as the timing of infection approached harvest. Histological studies indicated that infection took place through natural openings of plant organs such as stomata on stems and sepals and lenticels on fruit skin. Fungal penetration also was observed at micro-cracks on the stem and sepal and at trichome sockets where mechanical damage occurred in sepals. Direct penetration was observed on the stem and sepal of fruit, but most invasions were restricted between the cuticle and the epidermis. Our results indicate that wounding is not required for infection of apple fruit by S. pyriputrescens, though it may facilitate infections.     

Effect of aerated compost tea on grapevine powdery mildew, botrytis bunch rot and microbial abundance on leaves

Aerated compost tea (ACT), prepared from immature compost, was applied to foliage and fruit of grapevines (Vitis vinifera) to assess its potential for suppressing two important diseases: botrytis bunch rot, caused by Botrytis cinerea, and powdery mildew, caused by Erysiphe necator. An ACT applied to leaves of Cabernet Sauvignon vines in pots 7 days before inoculation with E. necator conidia reduced mean powdery mildew severity on the three youngest expanded leaves (at inoculation) to less than 1 %; mean severity on non-treated, inoculated leaves was 15 %. Multiple applications of ACTs at two vineyards in different growing seasons suppressed powdery mildew to <1 % mean severity on Chardonnay leaves (non-treated 79 % severity) and bunches (non-treated 77 % severity), and on Riesling leaves (non-treated 24 % severity). The same treatments reduced the incidence of Chardonnay bunches with latent B. cinerea and Riesling bunches with sporulating B. cinerea, although the level of botrytis bunch rot in both experiments was not economically damaging. The numbers of culturable bacteria, fungi and yeasts on Chardonnay leaves were higher than pre-treatment levels 10 days after ACT application, as were fungal numbers on Riesling leaves 21 days after treatment. Suppression by ACTs of two fruit and foliar pathogens of grapevine with different biology and epidemiology indicated potential for their use as a tactic in integrated disease management. Further testing of ACTs in a range of viticultural environments and application regimes will contribute to a better understanding of the impact of this tactic on disease, grape and wine quality.     

Pathological studies on the southern blight of China aster (<Emphasis Type="Italic">Callistephus chinensis</Emphasis>) caused by <Emphasis Type="Italic">Sclerotium rolfsii</Emphasis>

A severe outbreak of southern blight disease of China aster was observed during the post rainy season (September–November 2015) in the Mysore and Mandya Districts of Karnataka, Southern India. The disease incidence ranged between 12 and 47%. The typical disease symptoms include water-soaked lesions on leaves, stems and on the lower stem surfaces followed by quick wilting of the whole plant with abundant production of sclerotia near the stem-soil interface. The associated fungal pathogen was isolated on potato dextrose agar (PDA) medium, on which numerous reddish-brown sclerotia were seen. A total of 26 fungal isolates were isolated and studied for the mycelial compatibility. Isolate SrCCM 1 was used for pathogenicity analysis. The results of the study showed that, there was no variation among the isolates tested. Molecular identification of the pathogen by ITS-rDNA sequences of S. rolfsii showed 100% similarity with reference sequences. Based on the cultural, morphological and molecular characteristics, the fungal pathogen was identified as Sclerotium rolfsii Sacc. (Sexual morph: Athelia rolfsii (Curzi) C.C. Tu & Kimbr). Pathogenicity tests were performed on healthy leaves, roots and stems. Typical disease symptoms on leaves, stems and roots were evident after 5, 8 and 10 days of post-inoculation. Sclerotium rolfsii is known to cause diseases in economically important crop plants. However, no reports are available on the occurrence of S. rolfsii on China aster in India.     

<Emphasis Type="Italic">Aphelenchoides gorganensis</Emphasis> n. sp. (Nematoda: Aphelenchoididae)<Emphasis Type="Italic">,</Emphasis> a new species from Iran

Phytophthora capsici infection of chili pepper seedlings can cause substantial losses due to damping-off and collar rot diseases. Chemical control is no longer effective due to reported resistance development, on top of the related environmental concerns and the consumer demands for reduced use of fungicides. Biological control is a sustainable option, with several agents having been reported to be effective against this pathogen. This research focused on optimizing the application of strain THSW13 of Trichoderma hamatum and a bacterial isolate BJ10–86 with the objectives of improving chili pepper seed germination, reduce damping-off disease incidence, and improve the growth of the seedlings. Bacterial isolate BJ10–86 was subjected to molecular identification and found to be Pseudomonas aeruginosa. Chili pepper seeds treated with the biocontrol agents, individually or in combination, were seeded into commercial nursery media that had been pre-inoculated with P. capsici zoospores. Over a period of 35 days the chili pepper seed treatments significantly (P = 0.008) reduced the disease incidence of seedlings damping-off. Combined application of T. hamatum and P. aeruginosa was the best biocontrol treatment with an area under disease curve of only 36.61 units compared to 92.87 units for the control treatment. Similar results were observed in vitro where T. hamatum and P. aeruginosa synergistically inhibited P. capsici growth by 73.2 %. The inhibition activity of this treatment was similar to mefenoxam treatment, which implies that it is an effective and sustainable alternative for chili pepper seed treatment. The biocontrol seed treatment had no effect on seed germination and seedling growth.     

Infection of <Emphasis Type="Italic">Sorghum bicolor</Emphasis>, selected grass species and <Emphasis Type="Italic">Zea mays</Emphasis> by G<Emphasis Type="Italic">loeocercospora sorghi</Emphasis>, causal pathogen of zonate leaf spot

Zonate leaf spot (Gloeocercospora sorghi) is a common disease in Sorghum bicolor producing areas of the U.S., but little is known about its biology, virulence and severity on S. bicolor, Zea mays, and related crop grassweeds. Greenhouse studies were conducted to determine and compare the virulence and severity of G. sorghi on 10 commercially available sorghum hybrids, four Z. mays hybrids and selected grassweed species including Sorghum bicolor (grain sorghum and shattercane biotypes) and Sorghum halepense (Johnsongrass), two of the most problematic arable weeds. Plants from the respective species were inoculated with a local G. sorghi isolate and maintained in a dew-chamber at 24 °C for 24 h and then incubated under greenhouse conditions for 4 weeks. Plants were observed for lesion expression and rated using a modified Horsfall-Barrett scale (0–10). The first symptoms of infection were visible within 24 h following inoculation on shattercane and S. bicolor hybrids. Symptoms consisted of small, non-diagnostic purple lesions on the leaves. Results showed that S. bicolor, S. halepense and shattercane were susceptible to G. sorghi. All other species tested in this study were not infected. More particularly, disease severity, increased from a rating of 3 to 10 on sorghum and from 2 to 7 on S. halepense between 2 and 23 days after inoculation, respectively. However, disease severity on shattercane increased rapidly from 3.5 to 10 between 2 and 8 days after inoculation, respectively. Among the sorghum hybrids tested, FFR-322 appeared to be the most resistant to G. sorghi while Pioneer 83G66 appeared to be the most susceptible. Z. mays hybrids were not infected by the fungus used in this study. G. sorghi could be used effectively to manage shattercane and S. halepense infestations occurring in Z. mays and S. bicolor fields consisting of specific G. sorghi-resistant hybrids.     

Epidemiology of brown rot (Monilinia fructigena) on apple: infection of fruits by conidia

Effects of fruit maturity, wound age, temperature and the duration of wetness periods on infection of apple fruits by conidia of the brown rot fungus, Monilinia fructigena , were studied. Inoculation of fruits on potted apple trees and harvested mature fruits showed that wounding was essential for infection by M. fructigena . On potted trees, there was a significant difference between the susceptibility of cvs Cox and Gala and this difference depended on wound age. The incidence of brown rot was affected greatly by fruit maturity and wound age. Wounds on younger fruits were more resistant to infection than those on older fruits, whilst the older the wound, the more resistant it was to infection. Furthermore, the degree of wound age-related resistance was greater on younger fruits than on older fruits. These relationships were well described by regression models. The effect of the duration of wetness periods was very small: increasing the duration of wetness periods reduced the incidence of brown rot on older wounds. For detached fruits, all those wounded were rotted after inoculation, except for those in two treatments under 20°C on fruits with wounds which were 8 days old. The incubation period of the fungus was generally very short. Wound age was the single most important factor influencing the length of the incubation period; the incubation period increased as wound age increased.     

玉米禾谷镰孢茎腐病和穗腐病抗性鉴定接种方法的比较

田间采用不同人工接种鉴定方法对92份玉米种质同步进行玉米禾谷镰孢茎腐病和穗腐病抗性评价与筛选, 明确了东北春玉米产区玉米禾谷镰孢茎腐病?穗腐病抗性鉴定的最佳接种方法:茎节注射法在玉米禾谷镰孢茎腐病抗性精准鉴定中可更好地评价玉米种质的抗病性, 综合考虑接种方法的实用性和可操作性, 菌土覆盖法对大体量的规模化种质进行田间抗病性鉴定更具有优势; 双牙签法对玉米穗腐病抗性鉴定中在种质接种后发病的严重度?田间进行接种的可操作性和实用性等方面均优于花丝通道法?同时筛选出对玉米禾谷镰孢茎腐病抗性稳定的种质52份, 对穗腐病抗性稳定的种质66份, 对2种病害均表现稳定抗性的兼抗种质33份?     

Bacterial leaf and peduncle soft rot caused byPectobacterium carotovorum on tulips in Konya, Turkey

The etiology of a new soft rot disease of tulips, causing leaf spots, leaf blight, neck and bulb rot in Konya, Turkey, was investigated. This disease occurred in tulip fields grown for seed bulbs of various varieties in 2002. Bacteria were isolated from the lesions on leaf, bud neck and bulbs and the causal bacterium was identified asPectobacterium carotovorum on the basis of biochemical and physiological tests. Cells were Gram-negative, rod-shaped, fermentative, potato-rot positive. Colonies were capable of growth at 37°C. On nutrient agar the colonies were creamy-white. The isolates were non-fluorescent on King’s B medium, positive for acetoin production, gelatin liquefaction, acid-production-from-lactose, and catalase; and negative for gas from glucose, reducing substances from sucrose, and phosphatase activity. Additionally, tests for egg yolk (lecithin), sensitivity to erythromycin, and pigmentation on yeast dextrose carbonate agar were negative; growth on 5% sodium chloride was positive. All the bacterial isolates obtained from the leaf, bud neck and bulbs produced the original symptoms following inoculation to the susceptible tulip variety ‘Gander’. The rate of damage caused by this bacterium was evaluated on several tulip varieties under field and storage conditions. Gander was the most susceptible variety in the field whereas ‘Salmon Parrot’ exhibited the highest rate of bulb rot in storage. Disease severity was lower in 2003 than 2002. http://www.phytoparasitica.org posting May 14, 2006.     

我国部分省域甘蓝主要产区黑腐病菌鉴定及致病力分析

 为了明确我国甘蓝主栽区黑腐病菌株种类与致病力水平,为优化抗病性鉴定方法、筛选抗病品种及抗病品种的合理布局提供依据,分别采集了10个省域的黑腐病病叶,经过分离纯化与分子鉴定,获得了26个典型甘蓝黑腐病菌株;选用5个甘蓝抗、感品种作为鉴别寄主,以甘蓝黑腐病菌株的悬浮液为接种体,采用喷雾接种法测定致病力。结果表明:来源于不同省域的黑腐病菌株致病力存在显著差异,致病力最强的是YU,病情指数平均值为38.31;致病力最弱的是SH,病情指数平均值为17.03。来源于不同海拔高度的甘蓝黑腐病菌株致病力最强的是G1500,病情指数平均值为37.93;最弱的是G800,病情指数平均值为19.80。根据鉴别寄主抗感反应将26个黑腐病菌株划分为12类致病型,发现来自不同地域的甘蓝黑腐病菌株间存在着显著的致病性分化现象,对甘蓝品种的致病力存在着显著性差异,其中菌株YU致病力最强,菌株YU可作为甘蓝抗病性鉴定的主要致病菌株,指导抗病品种的选育。     

Infection criteria,inoculum sources and splash dispersal pattern of <Emphasis Type="Italic">Colletotrichum acutatum</Emphasis> causing bitter rot of apple in New Zealand

Infection of Malus x domestica cv. Royal Gala fruit by Colletotrichum acutatum causing bitter rot was studied in the temperate climate of New Zealand. Temperatures above 15 °C were required for lesions to develop on detached apple wound-inoculated or inoculated without wounding with C. acutatum spores, regardless of maturity. A wetness period of 72 h was required for infection of mature detached apple fruit without wounding. On wound-inoculated detached apple fruits, sporulation was related to temperature and followed a similar pattern. In the field, a mean temperature above 15 °C for 72 h after wound-inoculation was required for lesions to develop. Buds were a more important source of inoculum than twigs, and it was shown that C. acutatum could be isolated more frequently from outer bud scales than from inner scales. Asymptomatic infection of vegetative and reproductive buds was detected. C. acutatum was detected on asymptomic surface-sterilised petals and fruit, more commonly during summer than spring. Symptomless sterilised leaves generally yielded C. acutatum throughout the season, but isolations were more frequent in summer. Recovery of inoculum using a splash meter to detect vertical dispersal showed that in summer inoculum was primarily splashed up from the ground. In spring, inoculum was recovered in similar quantities from all heights up to a metre, suggesting that splash dispersal occurs from the canopy as well as from the ground. A disease cycle for C. acutatum infecting apples and causing bitter rot in New Zealand is suggested.     

我国部分省域甘蓝主要产区黑腐病菌鉴定及致病力分析

 为了明确我国甘蓝主栽区黑腐病菌株种类与致病力水平,为优化抗病性鉴定方法、筛选抗病品种及抗病品种的合理布局提供依据,分别采集了10个省域的黑腐病病叶,经过分离纯化与分子鉴定,获得了26个典型甘蓝黑腐病菌株;选用5个甘蓝抗、感品种作为鉴别寄主,以甘蓝黑腐病菌株的悬浮液为接种体,采用喷雾接种法测定致病力。结果表明:来源于不同省域的黑腐病菌株致病力存在显著差异,致病力最强的是YU,病情指数平均值为38.31;致病力最弱的是SH,病情指数平均值为17.03。来源于不同海拔高度的甘蓝黑腐病菌株致病力最强的是G1500,病情指数平均值为37.93;最弱的是G800,病情指数平均值为19.80。根据鉴别寄主抗感反应将26个黑腐病菌株划分为12类致病型,发现来自不同地域的甘蓝黑腐病菌株间存在着显著的致病性分化现象,对甘蓝品种的致病力存在着显著性差异,其中菌株YU致病力最强,菌株YU可作为甘蓝抗病性鉴定的主要致病菌株,指导抗病品种的选育。