鞘腐病发生程度与玉米倒伏及产量损失间的相关性分析

为深入探讨鞘腐病的发生对玉米倒伏及产量的影响,通过温室接种法测定了玉米不同发育阶段鞘腐病的发病程度及相关防御酶活性,以确定玉米鞘腐病的易感时期;并通过田间接种不同浓度的层出镰孢菌获得不同发病级别的玉米鞘腐病病株,于乳熟期调查病害发生程度,利用YYD-1B数显植物茎秆强度检测仪测定每株玉米茎秆的抗倒伏能力,收获后测定其产量。结果显示,玉米鞘腐病的易感时期为开花期,郑单958和浚单20在此时期鞘腐病的发病率分别为64.36%和40.22%;病情指数分别达42.73和19.58,均高于其它时期;玉米自交系OH43Ht1、郑58和杂交品种郑单958的茎秆抗倒伏能力均随着玉米鞘腐病发病级别的升高而降低;郑58和郑单958的产量随玉米鞘腐病发病级别的升高而降低,每公顷产量损失郑58从13.84%增加到29.53%、郑单958从3.99%增加到16.72%。表明玉米鞘腐病严重发生时能够降低玉米的抗倒伏能力和产量,且对自交系的影响大于杂交品种,生产中应引起高度重视。     

Fusarium crown and root rot of tomatoes in the UK

Fusarium crown and root rot caused by Fusarium oxysporum f. sp. radicis-lycopersici was found in the UK in 1988 and 1989 mainly in rockwool-grown tomato crops. Up to 14% of plants were affected in individual crops. In experiments, leaf and stem symptoms did not appear until the time of first fruit harvest even when the plants were inoculated at planting, first flowers or fruit set. Conidial inoculum at 10⁶ spores/plant applied at seed sowing killed 70–83% of tomato seedlings, whereas similar levels of inoculum applied to young plants caused root and basal stem decay, and eventually death but only after fruit harvest began. Disease incidence and symptom severity increased with inoculum concentration. Experimentally, the disease was more severe in peat- or compost-grown plants than in rockwool. Disease spread was only a few centimetres in 50 days in experimental rockwool-grown plants. All tomato cultivars tested were highly susceptible. Prochloraz-Mn was highly effective against the pathogen in vitro and controlled the disease in the glasshouse, but only when applied preventively. Non-pathogenic Fusarium oxysporum isolates and Trichoderma harzianum also reduced FCRR disease levels.     

Monilia mumecola, a new brown rot fungus on Prunus mume in Japan

In 1982, an anamorphic fungus in the genus Monilia was first isolated as the causal agent of brown rot disease of Japanese apricot or mume (Prunus mume) in Oita Prefecture, Kyushu, Japan. Inoculation of flowers, shoots, and fruit of P. mume with the fungus reproduced brown rot disease symptoms similar to those found in nature. The fungus somewhat resembled the colony appearance of Monilinia (anamorph Monilia) laxa, the apricot brown rot fungus, on PSA plates, but it differed from the latter and the other two brown rot fungi, M. fructigena and M. fructicola, in terms of growth rate, temperature optima for mycelial growth and sporulation, morphology and germination pattern of conidia, nuclear number in the conidium, and nucleotide sequences in the ITS region of ribosomal DNA. It is newly described as Monilia mumecola Y. Harada, Y. Sasaki & T. Sano. A key to anamorphic states of four brown rot fungi of fruit trees is provided.     

Vegetative Compatibility Grouping of Fusarium oxysporum f. sp. gladioli from Saffron

Fusarium corm rot of saffron (Crocus sativus L.), incited by Fusarium oxysporum f. sp. gladioli, causes severe yield losses in Italy. Major symptoms during flowering (October–November) include yellowing and wilting of shoots, basal stem rot and corm rot. Sixty-four isolates of F. oxysporum f. sp. gladioli, obtained from infected saffron crops located in Italy (Abruzzi, Tuscany and Umbria) and in Spain, were characterized by pathogenicity and vegetative compatibility. Chlorate-resistant, nitrate-nonutilizing (nit) mutants were used to determine vegetative compatibility among the isolates of the pathogen with the aim of examining the genetic relatedness among populations from different locations. All the isolates belonged to vegetative compatibility group 0340. Since saffron shares susceptibility to F. oxysporum f. sp. gladioli with other ornamental plants of the Iridaceae (Crocus, Gladiolus, Iris and Ixia), it is likely that a clone of the pathogen (VCG 0340) was introduced with other hosts and is responsible for the disease outbreak observed on saffron in Italy. Alternatively, or additionally, the clone of F. oxysporum f. sp. gladioli causing disease on saffron in other countries may have spread to the saffron fields in Italy through the import and dispersal of infested propagation material.     

Epidemiology of root rot caused by <Emphasis Type="Italic">Leptosphaeria maculans</Emphasis> in <Emphasis Type="Italic">Brassica napus</Emphasis> crops

The infection of above-ground tissues of Brassica napus by Leptosphaeria maculans is well understood. However, root infection (root rot) under field conditions, the development of root rot over time and its relationship to other disease symptoms caused by L. maculans has not been described. A survey of B. napus crops was conducted in Australia to investigate the incidence and severity of root rot. Additionally, the pathway of root infection was examined in field experiments. Root rot was present in 95% of the 127 crops surveyed. The severity and incidence of root rot was significantly correlated with that of crown canker; however, the strength of this relationship was dependent on the season. Root rot symptoms appeared before flowering and increased in severity during flowering and at maturity, a pattern similar to crown canker suggesting that the infection of the root is an extension of the crown canker phase of the L. maculans lifecycle. All isolates of L. maculans tested in glasshouse experiments caused root rot and crown canker in B. napus and Brassica juncea. In the field, the main pathway of root infection is via invasion of cotyledons or leaves by airborne ascospores, rather than from inoculum in the soil. Root rot was present in crops in fields that had never been sown to B. napus previously, in plants grown in fumigated fields, and in glasshouse-grown plants inoculated in the hypocotyl with L. maculans.     

Gnomonia fragariae, a Cause of Strawberry Root Rot and Petiole Blight

Gnomonia fragariae has been occasionally listed among the fungi associated with diseased strawberry plants. However its pathogenicity has not been established. During the investigation on strawberry decline in Latvia and Sweden, a fungus was repeatedly recovered from discoloured root and crown tissues of severely stunted plants. Attempts to induce sporulation of the isolates grown on several agar media resulted in the formation of mature ascomata only on potato carrot agar and oatmeal agar. On morphological grounds and comparisons with reference herbarium specimens these isolates were identified as Gnomonia fragariae. The pathogenicity of the fungus was evaluated initially in the detached leaf assay and subsequently in three bioassays on strawberry plants. All the bioassays showed that G. fragariae was pathogenic on strawberry and capable of causing severe root rot and petiole blight. The symptoms that developed in the greenhouse experiments closely resembled those observed in the fields. The fungus did not cause rapid plant death but growth and development of inoculated strawberry plants was severely affected. To our knowledge this is the first time when pathogenicity of G. fragariae as a root rot pathogen has been clearly established. Our study shows that G. fragariae is one of the serious pathogens involved in the root rot complex of strawberry in Latvia and Sweden.     

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.     

Dumontinia root rot of liver leaf caused by <Emphasis Type="Italic">Dumontinia tuberosa</Emphasis>

Foliar wilt as well as crown and root rot with sclerotia formation has affected potted liver leaf (Hepatica nobilis var. japonica f. magna) in Ojiya, Niigata Prefecture, Japan, since 2006. Apothecia developed from the sclerotia on soil surface of pots with the diseased plants in March. A fungus forming the apothecia was identified as Dumontinia tuberosa (Sclerotiniaceae) based on its morphology and demonstrated to cause the disease. We coined the name “Dumontinia root rot (Dumontinia-negusare-byo in Japanese) of liver leaf” for the new disease.     

Effects of sowing date on severity of blight caused by <Emphasis Type="Italic">Ascochyta rabiei</Emphasis> and yield components of five chickpea cultivars grown under two climatic conditions in Tunisia

Five chickpea cultivars, Chitoui, Neyer, Kasseb, Beja 1 and Bouchra, were planted on three sowing dates at two Experimental Stations in Tunisia: Bou Salem in the north and the more southerly Mornag, where the climate is drier. Severity of blight, caused by Ascochyta rabiei, was measured on a 1–9 scale (defined) on vegetative parts and on pods as percent infected and percent infected that were empty. At both locations, disease was essentially absent on plants sown on the third dates but present on plants sown on the two earlier dates. At Bou Salem, disease severity was highest for the second sowing date whereas at Mornag it was highest for the first sowing date; but for each sowing date, disease severity was lower at Mornag than at Bou Salem. Yield components were measured as number of pods per plant, number of seeds per plant, number of seeds per 100 pods, 100 seed weight and weight of seeds per plant. Both disease severity and yield differed significantly among sowing dates (differently at each location) and also among cultivars for each sowing date, these differences depending both on sowing date and location. A lower yield was always associated with a higher disease severity, although the quantitative relationship differed between cultivars and locations. Cultivar Beja 1 had the lowest vegetative disease scores at both locations and both sowing dates 1 and 2. Beja 1 also scored well for all yield components. Plants sown on the third (latest) date gave the highest yields for all cultivars at both locations (except for an unusually high yield of Neyer at Mornag on sowing date 2), in some instances being more than double those from the earlier sowing dates. Thus, in contrast to other studies, late sowing did not result in yield loss.     

Detection and prediction of post harvest carrot diseases

Specific PCR primers were developed for identifying two post harvest pathogens, Mycocentrospora acerina and Fibularhizoctonia carotae, which cause liquorice rot and crater rot respectively, during prolonged low temperature storage of carrots. The methods allow routine detection of less than 0.3 pg of M. acerina DNA and less than 0.03 pg F. carotae DNA, even in the presence of large excess of plant or soil DNA. Standard PCR and quantitative PCR gave similar results and either method could be used in a practical situation. Experiments were carried out testing these methods on different types of carrot tissue- and soil- samples. Soil was sampled before sowing, and soil adhering to the roots or root tissue was sampled at different times during the growing season or at harvest. Soil adhering to the carrots at harvest had the best predictive ability for liquorice rot development during storage (R² predicted 74.9% using standard PCR), but samples taken during the growing season also gave reasonably good predictive ability values. PCR data from soil samples taken in the spring were not as good as a predictor for this disease. A dense sampling strategy using 20 m between sampling points generally gave better correlation between PCR data and disease data than using 40 m between the sampling points. Use of the developed methods in an IPM strategy for liquorice rot is discussed. For crater rot the correlation between PCR data and disease data was generally poor for all types of samples. These results are discussed in relation to the biology of F. carotae.     

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.     

Stem and root rot of scarlet runner bean (Phaseolus coccineus) caused by Pythium myriotylum

A severe rot was found on the stems and roots of scarlet runner bean (Phaseolus coccineus) in Ibaraki Prefecture (Japan) in August 2004. The causal fungus was identified as Pythium myriotylum. We propose the name of stem and root rot of scarlet runner bean (“Kuki-negusare-byo” in Japanese) for this new disease.     

The effect of three irrigation practices on phytophthora crown and root rot of apple trees under field conditions

The effect of microjet, drip, and two durations of sprinkler irrigation systems on phytophthora crown and root rot of apple trees was examined under field conditions. This eight year study indicates that crown and root rot caused byPhytophthora cactorum was most severe where young MM. 106 rootstock trees were watered by microjet irrigation for 2.3 h each day. There was no difference in infection byP. cactorum when trees were irrigated either by drip or sprinkler irrigation systems. The MM.106 apple rootstock trees watered by drip irrigation for 2.6 h each day were least affected by phytophthora crown and root rot.     

小麦茎基腐病生防菌株YB-161的分离鉴定及防效测定

为筛选防治小麦茎基腐病的高效生防菌株,采用稀释涂布法从小麦茎基腐病病土中分离细菌,以假禾谷镰孢Fusarium pseudograminearum为靶标菌,通过平板对峙培养法和室内盆栽试验筛选优良菌株并测定其田间防治效果,分析优良菌株发酵滤液对假禾谷镰孢的抑菌能力,并结合形态特征、Biolog微生物自动鉴定系统和gyrA序列分析对其进行种类鉴定,以及测定该菌株的抑菌谱。结果表明,10份供试土样中共分离到98株细菌,对假禾谷镰孢的菌丝生长抑制率超过40.00%的菌株有14株,其中菌株YB-161对假禾谷镰孢的菌丝生长抑制率最高,达63.50%。室内盆栽试验结果显示,菌株YB-161处理小麦的病情指数最低,为31.40,对小麦茎基腐病的防治效果最好,为68.15%,其对小麦也表现出较好的促生作用。田间调查结果显示,菌株YB-161菌液拌种处理对小麦茎基腐病的田间防治效果高于52.35%,并对小麦具有一定的增产作用。菌株YB-161的发酵滤液5倍稀释液和10倍稀释液对假禾谷镰孢的菌落抑制率分别达66.67%和44.33%,该菌株被鉴定为解淀粉芽胞杆菌Bacillus amyloliquefaciens。此外,菌株YB-161对辣椒炭疽病菌Colletotrichum capisci、烟草疫霉病菌Phytophthora parasitica等5种植物病原真菌均有较好的拮抗作用。表明生防菌株YB-161对绿色防控小麦茎基腐病具有良好的开发利用潜能。     

Testing variability in pathogenicity ofPhytophthora cactorum, P. citrophthora andP. syringae to apple, pear, peach, cherry and plum rootstocks

The relative virulence ofPhytophthora cactorum andP. syringae originating from almond trees, and ofP. citrophthora originating from citrus, to apple, pear, peach, cherry and plum rootstocks, was studiedin vivo andin vitro. Results of the different experiments were in good agreement. All testedPhytophthora isolates showed little virulence to pear rootstocks-causing only minor crown rot symptoms - and no virulence at all to apple rootstocks. In contrast, they were highly virulent to stone fruit rootstocks, causing crown rot disease. The non-pathogenicity of these isolates to pome rootstocks could be interpreted as strict host specificity.     

Field evaluation for resistance to the black rot pathogen <Emphasis Type="Italic">Xanthomonas campestris</Emphasis> pv. <Emphasis Type="Italic">campestris</Emphasis> in cabbage (<Emphasis Type="Italic">Brassica oleracea</Emphasis>)

Black rot, caused by Xanthomonas campestris pv. campestris, (Xcc), is one of the most serious diseases of crucifers world-wide. Forty-nine genotypes were evaluated for resistance under field conditions in Tanzania after artificial inoculation with Xcc race 1. Open pollinated white cabbage cultivars were generally susceptible, while Portuguese and pointed cabbages exhibited partial resistance. Some F1 white cabbage cultivars were highly susceptible, whereas others exhibited a high level of partial resistance. The most promising of the hybrid cultivars were T-689 F1, Gianty F1, No. 9690 F1, N 66 F1, and SWR-02 F1. Breeding line Badger I-16 exhibited the highest level of resistance of all genotypes. The genotypes accounted for 72.9–75.5% of the variation of the disease severity when assessed on the leaves, and 71.4% of the variation when assessed as internal black rot in heads at harvest. High correlations (equal to or above 0.7) were found between disease severities assessed on leaves three times during the growing season and also with the amount of internal black rot in heads. Leaf loss also was correlated with disease severity. The high genetic determination of the trait and the high correlations between disease assessments indicate that selection for resistance to black rot will be efficient when field screenings are carried out. Evaluation of genotypes for disease severity on leaves during the growing season combined with evaluations of head resistance in the most promising genotypes may be a simple method to select resistant cultivars.     

Development of Stem-base Pathogens on Different Cultivars of Winter Wheat Determined by Quantitative PCR

The progress of development of stem-base pathogens in crops of second winter wheat was plotted in nine experiments in three years. The amount of each pathogen present was determined by quantitative PCR. Where Tapesia yallundae was present in quantifiable amounts, it usually developed earlier than the other eyespot pathogen, T. acuformis. Both species were usually present in greater amounts on cultivars which are more susceptible to eyespot. The sharp eyespot pathogen, Rhizoctonia cerealis, developed more erratically than either of the Tapesia spp. and there were no consistent effects on different cultivars. Fusarium spp., the cause of brown foot rot, were rarely present in quantifiable amounts, but Microdochium nivale was usually present as one or both of the varieties nivale and majus. Late-season (after anthesis) decreases in M. nivale suggest that any brown foot rot symptoms attributable to this fungus would have fully developed earlier. Cultivar differences in amounts of M. nivale were most clear in stems during internode extension and when relatively large amounts of DNA were present. Such differences approximately reflected eyespot susceptibility, cv. Soissons containing most and cv. Lynx containing least DNA. The results emphasise the difficulty in relating diagnoses, by quantitative PCR or other means, at early growth stages when decisions to apply fungicides against stem-base disease are made, to later disease severity.     

Inhibition of Botrytis cinerea growth and suppression of botrytis bunch rot in grapes using chitosan

Chitosan inhibited growth of Botrytis cinerea in liquid culture and suppressed grey mould on detached grapevine leaves and bunch rot in commercial winegrapes. Germination of B. cinerea was completely inhibited in malt extract broth containing chitosan at concentrations greater than 0·125 g L^?1. However, treated conidia were able to infect detached Chardonnay leaves and pathogenicity was not affected, even after incubation for 24 h in chitosan at 10 g L^?1. When added after conidial germination, chitosan inhibited B. cinerea growth and induced morphological changes suggestive of possible curative activity. The effective concentration of chitosan that reduced mycelial growth by 50% (EC₅₀) was 0·06 g L^?1. As a foliar treatment, chitosan protected detached Chardonnay leaves against B. cinerea and reduced lesion diameter by up to 85% compared with untreated controls. Peroxidase and phenylalanine ammonia‐lyase activities were also induced in treated leaves. In vineyard studies, Chardonnay winegrapes exhibited 7·4% botrytis bunch rot severity at harvest in 2007 after treatment with an integrated programme that included chitosan sprays from bunch closure until 2 weeks preharvest, compared with 15·5% in untreated controls and 5·9% with fungicide treatment. In the following season, botrytis bunch rot severity was 44% in untreated Chardonnay at harvest and the integrated programme (21%) was less effective than fungicides (13·8%). However, in Sauvignon blanc winegrapes, the integrated and the fungicide programme each reduced botrytis bunch rot severity to 4% and were significantly different from the untreated control (11·5%). This study provides evidence that suppression of botrytis in winegrapes by chitosan involves direct and indirect modes of action.     

Pythium rot of Chinese cabbage (Brassica rapa L. subsp. pekinensis) caused by Pythium aphanidermatum

Severe rot was found at the base of leaves and stems of Chinese cabbage (Brassica rapa L. subsp. pekinensis) in Ibaraki Prefecture every year in early September from 2002 through 2004. The causal fungus was identified as Pythium aphanidermatum (Edson) Fitzpatrick. This is the first report of P. aphanidermatum on Chinese cabbage. A similar disease of Chinese cabbage caused by P. ultimum Trow var. ultimum is known as Pythium rot. We propose adding P. aphanidermatum as a new pathogen of this disease.     

Hot water treatment of Japanese pear trees is effective against white root rot caused by <Emphasis Type="Italic">Rosellinia necatrix</Emphasis> Prillieux

Hot water was dripped into the rhizosphere of Japanese pear trees (Pyrus serotina Rehd. grafted on P. betulifolia Bunge.) infested with the white root rot fungus Rosellinia necatrix Prillieux, to destroy the fungus. Isolates of R. necatrix from diseased roots of Japanese pear were vulnerable to water at temperatures above 35°C, and the fungus was eradicated from the colonized substrate when water at 35°C was provided for 3 days. The time required to eradicate R. necatrix decreased exponentially with increasing temperature. Japanese pear trees tolerated a temperature of 45°C without reduction in vigor. Field experiments demonstrated the practical use of hot water drip irrigation (HWD). HWD at 50°C completely destroyed white root rot mycelia on diseased roots, and many rootlets grew after the treatment. HWD at this temperature caused no injury to the trees. HWD of diseased orchard trees was assessed in Takamori and Iida in southern Nagano, Japan. The fungus recurred in two of four trees 28 months after treatment in Takamori and in two of ten trees 16 months after treatment in Iida. The new mycelia emerged on thick roots deep within the soil. Although there is a possibility of recurrence, HWD treatment is a practical control measure for white root rot.