甘肃省甜瓜黄萎病的病原鉴定

【背景】2013年11月在甘肃省兰州市皋兰县的日光温室秋冬茬甜瓜种植棚发现黄萎症状的甜瓜植株,病株率约为1%。【目的】明确甜瓜黄萎病的病原。【方法】采用组织分离法进行病原菌分离;通过科赫氏法则(Koch’s法则)明确分出病菌的致病性;采用形态学和分子生物学方法对病原菌进行种类鉴定。【结果】分离得到轮枝菌属真菌8株,轮枝菌属真菌的病株分出率达100%;2个代表性菌株GLTG-2和GLTG-5(显微特征相似但菌落形态和生长速率不同),在温度18-24℃及昼/夜光周期为11.5 h/12.5 h的试验条件下,人工接种可引起甜瓜苗矮化、枯萎;接种后40 d,枯死株率分别为70%和40%;BLASTn分析结果显示,菌株GLTG-2的rDNA-ITS序列与Verticillium dahliae菌株MRHf7的序列相似性达99.78%,菌株GLTG-5的rDNA-ITS序列与V.dahliae菌株MRHf7和Vd414的序列相似性达100.00%。【结论】引起甜瓜黄萎病的病原菌被鉴定为大丽轮枝菌(V. dahliae),这是大丽轮枝菌引起甜瓜黄萎病在我国和亚洲地区的首次报道。     

Systemic fungicides in the control of strawberry wilt (Verticillium dahliae)

In a series of experiments between 1970 and 1973 the application of benomyl or thiophanate methyl to field-grown strawberries, planted on Verticillium-mtested land, gave control of wilt for up to 5 months, the duration of control being related to the amount of fungicide applied in the spring. Treatment of inoculated plants grown on in chloropicrin-fumigated soil was effective for at least two seasons. An autumn-planted multi-factorial experiment in heavily-infested soil showed that, to achieve maximum wilt control, it was advantageous to grow cv. Gorella rather than cv. Cambridge Vigour; to drench the runners at planting rather than to dip them in the fungicide suspension; and to use a high concentration (0–075 % a-i-) and large volume (600 ml per plant) for a supplementary treatment in May rather than a lower concentration (0.025 %) ^or smaller volume (400 ml). There were small but significant advantages in applying benomyl rather than thiophanate methyl, and in using 0–2% a.i. suspension at planting rather than 0–05%. No advantage was gained by dividing the spring application into two equal doses applied 2 wk apart. Extrapolation from the logarithmic relation between wilt index and total dose of fungicide applied in the spring suggested that I.I g/plant would have given almost complete control until October; such control had been achieved in an earlier experiment in which 1–2 g/plant was applied. Crop yield in the second year was determined by the treatment applied in the first year, but although these treatments had given significantly better control of wilt in Gorella than in Cambridge Vigour, the greater growth and yield potentials of the latter cultivar had an over-riding effect on crop production; Cambridge Vigour yielded more than Gorella under all chemical treatments, but in the absence of treatment Gorella gave a larger crop than Cambridge Vigour. A proposed regime, entailing spring and autumn applications, is aimed at minimizing the colonization of the plant throughout the year, thus reducing the production of new inoculum and, by limiting the quantity of the pathogen in contact with the systemic chemicals, minimizing the probability of selecting fungicide-resistant variants of V. dahliae.     

Effect of Initial Nematode Population Density on the Interaction of Pratylenchus penetrans and Verticillium dahliae on 'Russet Burbank' Potato

Four similar growth chamber experiments were conducted to test the hypothesis that the initial population density (Pi) of Pratylenchus penetrans influences the severity of interactive effects of P. penetrans and Verticillium dahliae on shoot growth, photosynthesis, and tuber yield of Russet Burbank potato. In each experiment, three population densities of P. penetrans with and without concomitant inoculation with V. dahliae were compared with nematode-free controls. The three specific Pi of JR penetrans tested varied from experiment to experiment but fell in the ranges 0.8-2.5, 1.8-3.9, 2.1-8.8, and 7.5-32.4 nematodes/cm³ soil. Inoculum of V. dahliaewas mixed into soil, and the assayed density was 5.4 propagules/gram dry soil. Plants were grown 60 to 80 days in a controlled environment. Plant growth parameters in two experiments indicated significant interactions between P. penetrans and V. dahliae. In the absence of V. dahliae, P. penetrans did not reduce plant growth and tuber yield below that of the nematode-free control or did so only at the highest one or two population densities tested. In the presence of K dahliae, the lowest population density significantly reduced shoot weight and photosynthesis in three and four experiments, respectively. Higher densities had no additional effect on shoot weight and caused additional reductions in photosynthesis in only one experiment. Population densities of 0.8 and 7.5 nematodes/cm³ soil reduced tuber yield by 51% and 45%, whereas higher densities had no effect or a 15% additional effect, respectively. These data indicate that interactive effects between P. penetrans and V. dahliae on Russet Burbank potato are manifested at P. penetrans population densities less than 1 nematode/cm³ soil and that the nematode population density must be substantially higher before additional effects are apparent.     

Growth and wilt (Verticillium dahliae) development in strawberry cultivars over a transition between two soil series

On a site infested with V. dahliae the incidence of wilt was low consistently in strawberry cvs Talisman and Redgauntlet, high in Merton Herald and Gorella, and very high in Merton Ruby, Cambridge Vigour, Prizewinner, Templar and Crusader. Changes in mean volume per plant for the whole population of each cultivar were closely related to disease incidence and therefore differed between high-resistance and low-resistance cultivars. Height and spread measurements of diseased and symptomless plants in certain cultivars showed differences in the severity of the effect of the pathogen on growth that were not closely related to wilt incidence. Gradients of disease incidence and plant growth in 1966 and 1967 were associated with a transition from one soil series to another. Review of two earlier experiments on the same site revealed a similar gradient of disease incidence in 1963-64, but a reversed gradient in 1960-62. Variations related to soil conditions were smaller in the earlier experiments than in 1966-67.     

Evaluation of fungicides for the control of Verticillium wilt (V. dahliae) of strawberry

The treatment of soil or plants before planting, in September 1969, significantly reduced Verticillium wilt on strawberry in the following season. One application of benomyl or thiabendazole (both 0–5% a.i.) at 6728 l/ha to soil 24 h before planting, dusting roots with formulated benomyl powder (50% a.i.) at planting, or a combination of both benomyl dust + drench treatments were effective. However, although the double treatment gave the most disease control in 1970, plants from the soil-drench treatments gave the highest yields. Residual effects of the 1969 applications were still evident in 1971 from increased vigour, lack of wilt and high yield, especially with the benomyl treatments.     

Interactions Among Pratylenchus penetrans,P. scribneri,and Verticillium dahliae in the Potato Early Dying Disease Complex

Microplots were infested with combinations of the fungus Verticillium dahliae and Pratylenchus penetrans and P. scribneri to test for individual and combined effects of these organisms on potato yield and nematode reproduction. Verticillium dahliae alone caused yield losses in all 3 years of the experiment, and the interaction between P. penetrans and V. dahliae was significant (P ≤ 0.05) in 2 years. Pratylenchus penetrans alone caused yield losses in 2 years and P. scribneri alone caused yield losses in 1 year. No two-way or three-way interaction was found involving P. scribneri. In 1987, reproduction for low densities of P. penetrans was 5 times higher when P. scribneri was also present than when it was absent, and 3.5 times higher in 1988. In nematode species mixtures, reproduction of P. scribneri was decreased by V. dahliae in 1987-88. The final population density of P. scribneri was negatively affected by V. dahliae and positively related to the initial proportion of P. scribneri to P. penetrans. In species mixtures with proportions of P. penetrans ranging from 0.1 to 0.5, reproduction of P. penetrans was negatively affected by V. dahliae and decreased linearly in relation to the increase in the initial proportion of P. penetrans in both years. The final population density of P. penetrans was affected only by V. dahliae.     

Soil Temperature Effects on Onion Seedling Injury by Pratylenchus penetrans

The effect of soil temperatures 7-25 C upon injury to seedling onions by Pratylenchus penetrans was investigated. At 7-13 C < 100 nematodes/g of root caused significant reduction in onion root weights by the fifth week. More than 400 nematodes/g were required to produce comparable injury at 16-25 C.     

Variation in the virulence of Verticillium dahliae from strawberry

Isolates of V. dahliae from strawberry, tested in 1968 against cv. Cambridge Vigour, showed differences in virulence; in cvs Talisman and Cambridge Favourite there were no significant differences between plants that were inoculated and those that were not. Evidence from this experiment, and from an earlier non-replicated experiment with Cambridge Favourite, in which differences of virulence had been apparent, showed that environmental factors can cause variations in disease development that are of similar magnitude to those attributable to genetic variations in host and parasite.     

Soil inoculum density of Verticillium dahliae and Verticillium wilt of olive in Lebanon

In the Mediterranean basin, Verticillium Wilt of Olive (VWO) is diffused throughout its range of cultivation, causing severe yield losses and tree mortality. The disease was reported in almost all the Mediterranean and Middle East countries, and in Lebanon it is of increasing significance also on many valuable crops. The disease has already been reported on potato, peach and almond in the Bekaa valley; however, to date no information is available about the incidence of VWO and the inoculum density of Verticillium dahliae microsclerotia in soil of the main agricultural areas of Lebanon. Results from the present investigations demonstrate a high V. dahliae frequency in soils (75.3%), coupled with a mean soil inoculum density of 17.0 MS g^?1, clearly indicating a great impact on the production of susceptible hosts in Lebanon, mainly in Bekaa region. Molecular method to assess the microsclerotia inoculum density in soil allowed the detection of a higher frequency of infested soils, as compared with the traditional plating, thus confirming its higher sensitivity. The overall Verticillium wilt prevalence in the inspected olive orchards was 46.2%, and the frequency of V. dahliae‐infected trees was 25.7%. The widespread presence of V. dahliae in all olive growing areas of Lebanon enforces the adoption of measures aimed at reducing the soil inoculum density before any new olive plantation, and the use of strong phytosanitary regulations to improve the certification schemes of propagating material.     

Effects of the nematicide imicyafos on soil nematode community structure and damage to radish caused by Pratylenchus penetrans

The effects of the non-fumigant nematicide imicyafos on soil nematode community structure and damage to radish caused by Pratylenchus penetrans were evaluated in two field experiments in consecutive years (2007 and 2008). Nematode densities in soil at 0 - 10 cm (the depth of nematicide incorporation) and 10 - 30 cm were measured. The application of imicyafos had a significant impact on the density of P. penetrans at 0 - 10 cm but had no effect on free-living nematode density. PCR-DGGE analysis conducted using extracted nematodes showed that the nematode community structure 12 d after application in 2007 was altered by the application of imicyafos at the 0 - 10 cm depth, but not at 10 - 30 cm. No significant differences were observed in the diversity of the nematode community at harvest (89 and 91 d after application) between the control and imicyafos treatments in both depths and both years. In both years, the damage to radish caused by P. penetrans was markedly suppressed by the nematicide. Overall, the nematicide imicyafos decreased populations of P. penetrans in soil and thereby decreased damage to radish, while having little impact on the soil nematode community.     

Infection of Pratylenchus penetrans by Nematode-pathogenic fungi

Eleven fungal isolates were tested in agar dishes for pathogenicity to Pratylenchus penetrans. Of the fungi that produce adhesive conidia, Hirsutella rhossiliensis was a virulent pathogen; Verticillium balanoides, Drechmeria coniospora, and Nematoctonus sp. were weak or nonpathogens. The trapping fungi, Arthrobotrys dactyloides, A. oligospora, Monacrosporium dlipsosporum, and M. cionopagum, killed most of the P. penetrans adults and juveniles added to the fungus cultures. An isolate of Nematoctonus that forms adhesive knobs trapped only a small proportion of the nematodes. In 17-cm³ vials, soil moisture influenced survival of P. penetrans in the presence of H. rhossiliensis; nematode survival decreased with diminishing soil moisture. Hirsutella rhossiliensis and M. ellipsosporum were equally effective in reducing numbers of P. penetrans by 24-25% after 4 days in sand. After 25 days in soil artificially infested with H. rhossiliensis, numbers of P. penetrans were reduced by 28-53%.     

Infectivity of Pratylenchus penetrans on Alfalfa

The infectivity of Pratylenchus penetrans on alfalfa seedlings cv. Du Pulls was studied. The dense root-hair zone was the preferred zone of penetration by females, males, and third-stage larvae. A lesion initially appeared as a water-soaked area at the root surface, becoming yellow and elliptical as the nematode entered the cortex, with dark-brown cells later appearing in the centre as the nematode fed. At 20 C, females penetrated roots earlier, faster, and in greater numbers than either males or third-stage larvae. Females penetrated roots at temperatures from 5 to 35 C, with maximum penetration between 10 and 30 C, while males and third-stage larvae penetrated roots only between 10 and 30 C with maximum penetration a t 20 C. Penetration of roots by females, males, and third-stage larvae increased after storage of 5 C for 35 days, but decreased after storage of 140 days or more. Combinations of the three life stages in pairs neither enhanced nor inhibited penetration of roots by individual life stages; males were not attracted to females. Increasing inoculum density up to 20 nematodes/seedling did not affect penetration.     

Proteomic analysis of the sea-island cotton roots infected by wilt pathogen Verticillium dahliae

Verticillium wilt of cotton is a vascular disease mainly caused by the soil-born filamentous fungus Verticillium dahliae. To study the mechanisms associated with defense responses in wilt-resistant sea-island cotton (Gossypium barbadense) upon V. dahliae infection, a comparative proteomic analysis between infected and mock-inoculated roots of G. barbadense var. Hai 7124 (a cultivar showing resistance against V. dahliae) was performed by 2-DE combined with local EST database-assisted PMF and MS/MS analysis. A total of 51 upregulated and 17 downregulated proteins were identified, and these proteins are mainly involved in defense and stress responses, primary and secondary metabolisms, lipid transport, and cytoskeleton organization. Three novel clues regarding wilt resistance of G. barbadense are gained from this study. First, ethylene signaling was significantly activated in the cotton roots attacked by V. dahliae as shown by the elevated expression of ethylene biosynthesis and signaling components. Second, the Bet v 1 family proteins may play an important role in the defense reaction against Verticillium wilt. Third, wilt resistance may implicate the redirection of carbohydrate flux from glycolysis to pentose phosphate pathway (PPP). To our knowledge, this study is the first root proteomic analysis on cotton wilt resistance and provides important insights for establishing strategies to control this disease.     

Effects of Pratylenchus penetrans on the Infection of Strawberry Roots by Gnomonia comari

The fungus Gnomonia comari, causal agent of strawberry leaf blotch, was inoculated at the crown of young axenized strawberry plants growing in sterilized sand. Only the roots were colonized, and the infection was symptomless. When the fungus colonized the roots in the presence of the root lesion nematode Pratylenchus penetrans, the plants were extremely stunted and their root system was necrotic. Fungal conidiospores were found attached to the cuticle of nematodes extracted from soil inoculated with the two pathogens. These findings indicate that P. penetrans could transport conidiospores through soil.     

Effect of Ditylenchus dipsaci and Pratylenchus penetrans on Verticillium Wilt of Alfalfa

Verticillium albo-atrum wilt symptoms appeared faster and were significantly more severe in the presence of Ditylenchus dipsaci in Vernal, a wilt-susceptible cultivar, than in Marls Kabul, a wilt-resistant cultivar. Winter kill in the field was not affected by the nematode during the first winter, but 50% of plants were killed in the second winter. Forage yield from nematode-infected plants was significantly reduced the second year. Interaction with V. albo-atrum did not significantly reduce forage yields below that of D. dipsaci alone. Pratylenchus penetrans did not increase the severity of wilt symptoms in the presence of V. albo-atrum, nor did it affect forage yield in the greenhouse. It did, however, reduce alfalfa yields in presence of V. albo-atrum under field conditions. D. dipsaci and P. penetrans reproduced faster in Vernal than in Maris Kabul when the fungus was present.     

Verticillium wilt of cacao in Uganda: the relationship between Verticillium dahliae and cacao roots

Isolates of Verticillium dahliae Kleb. from wilted cacao (Theobroma cacao L.), cotton (Gossypium hirsutum L.), and okra (Abelmoschus esculentus Medik.) penetrated all regions of living cacao tap and lateral roots and progressed intracellularly from the epidermis to the xylem in 4–6 days. The hypocotyl and tissues of the unerupted lateral roots beneath the epidermis resisted invasion. Host reactions included browning of extensively colonized cells, alteration (with apparent granulation) of the cytoplasm, and accumulation of materials in the lumina of endodermal cells. Resistance in the hypocotyl was associated with occasional thickening of inner tangential walls of colonized epidermal cells. The fungus formed conidia, microsclerotia, and narrow and wide hyphae within root tissues. The narrow hyphae predominated at the front of mycelial invasion of tissues while the broad hyphae developed behind this front. Limited studies under non-sterile conditions indicated that the apparent host-parasite interactions were similar to those observed with sterile roots and cultures of V. dahliae.     

The Influence of Pratylenchus penetrans on the Incidence and Severity of Verticillium Wilt of Potato

The influence of Pratylenchus penetrans on the incidence and severity of Verticillium wilt was examined in the potato cultivars ''Kennebec'', ''Katahdin'', and ''Abnaki''. Single-stem plants were grown in soil maintained at a temperature of 22 ± 1 C. Axenically cultured nematodes were suspended in water and introduced to the soil, at a rate of ca 5,000/25.4-cm pot, through holes made around each stem. Ten days after infestation with nematodes, conidial suspensions of Verticillium albo-atrum were introduced into the soil at a rate of ca 1,000,000/pot. Among Katahdin plants, the severity of foliar symptoms was increased in the presence of both pathogens 2 and 3 weeks after soil intestation. During the remaining 5 weeks, severity of foliar symptoms was not different between plants infected by both pathogens and those infected by Verticillium alone. Within the wilt-susceptible cultivar Kennebec and the resistant eultivar Abnaki, no effects on foliar symptom severity were observed. When plant heights, shoot weights, and tuber yields were analyzed, a Pratylenchus-Verticillium interaction was not evident within any of the cultivars tested. Nematode populations in roots and rhizosphere were suppressed in Kennebec and Katahdin plants in the presence of Verticillium.