Suppression of Fusarium wilt of spinach with compost amendments

The effect of different organic composts on the suppression of wilt disease of spinach caused by Fusarium oxysporum f. sp. spinaciae was evaluated in a continuous cropping system in both containers and in microplot field trials. Test soils infested with the pathogen were amended with wheatbran, wheatbran and sawdust, coffee grounds, chicken manure, or mixture of different composts with and without 5% (w/w) crab shell powder either once (5%, w/w) or continuously (2.5%) into the test soils infested with the pathogen. In the container trials, the soil amended with composts became suppressive to disease development on the second and third cropping. The suppressive effect was notable in the soil amended with the mixture of compost with and without crab shell powder. The coffee compost lowered soil pH but became suppressive to the disease after modifying the soil pH. In the field trial using the mixture of the different composts containing 5% crab shell powder, a combination of 5% before the first cropping and 2.5% every second cropping gave stable disease control and promoted plant growth. After compost amendment, populations of fungi, bacteria and actinomycetes as measured by dilution plate counting and the total microbial activity as evaluated by fluorescein diacetate hydrolysis increased and population of the pathogen gradually decreased. These phenomena were especially notable in soils amended with the mixture of different composts. These results indicate that diversity in the organic materials promotes higher microbial activity and population in the soil thereby enhancing disease suppressiveness.     

Potato brown rot incidence and severity under different management and amendment regimes in different soil types

Ralstonia solanacearum race 3 biovar 2, the causative agent of potato brown rot (bacterial wilt), is an economically important disease in tropical, subtropical and temperate regions of the world. In view of previous reports on suppression of the disease by organic amendments, and the expansion of organic agriculture, it was timely to compare the effects of organic and conventional management and various amendments on brown rot development in different soils (type: sand or clay; origin: Egypt or the Netherlands). Brown rot infection was only slightly reduced in organically compared to conventionally managed sandy soils from Egypt, but organic management significantly increased disease incidence and pathogen survival in Dutch sandy and clay soils, which correlated with high DOC contents in the organic Dutch soils. There was no correlation between disease incidence or severity and bacterial diversity in the potato rhizosphere in differently managed soils (as determined by 16S DGGE). NPK fertilization reduced bacterial wilt in conventional Egyptian soils but not in Dutch soils. Cow manure amendment significantly reduced disease incidence in organic Dutch sandy soils, but did not affect the bacterial population. However, cow manure did reduce densities of R. solanacearum in Egyptian sandy soils, most probably by microbial competition as a clear shift in populations was detected with DGGE in these and Dutch sandy soils after manure amendment. Amendment with compost did not have a suppressive effect in any soil type. The absence of a disease suppressive effect of mineral and organic fertilization in Dutch clay soils may be related to the already high availability of inorganic and organic nutrients in these soils. This study shows that the mechanism of disease suppression of soil-borne plant pathogens may vary strongly according to the soil type, especially if quite different types of soil are used.     

Soil receptivity toFusarium solani f. sp.pisi and biological control of root rot of pea

Potential antagonists ofFusarium solani f. sp.pisi (Fsp) were selected from soil samples with varying degrees of receptivity to this pathogen. They were tested against Fsp isolate 48 (Fs48), in increasingly complex systems. Most species testedin vitro were able to antagonize Fs48. No relation could be establishedin vitro between the receptivity of the soil from which an isolate originated and its antagonism to Fs48. In soils naturally infested with pea root rot pathogens, which were stored humid at 4°C for a period longer than a year, various isolates ofFusarium, Gliocladium andPenicillium spp. were able to reduce root rot. After sterilization of these soils, onlyGliocladium roseum isolates, added at 10⁵ conidia g^–1 dry soil, significantly reduced disease severity and prevented root weight losses caused by Fs48 at 10⁴ conidia g^–1 dry soil. In soils in which the biota were activated by growing peas before the assays, doses of 10⁶ and 10⁷ ofG. roseum were required to reduce root rot. In these soils, the antagonistic effects of fluorescent pseudomonad strains from soil of low receptivity to Fsp were variable. Some strains of fluorescent pseudomonads, from soil moderately receptive to Fsp and from highly infested soils, were also able to reduce root rot. Disease suppression by pseudomonad strains was more evident in the absence than in the presence ofAphanomyces euteiches in the root rot pathogen complex. The role of receptiveness of the soil with regard to potential antagonists is discussed.     

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.     

Comparison of Physical, Chemical and Biological Methods of Controlling Garlic White Rot

Treatment of garlic cloves with tebuconazole (at 1ml of Folicur 25% l^–1) achieved a significant reduction in the rate of disease progress and the final incidence of plant death by Sclerotium cepivorum: garlic yields were improved. Although soil solarization provided the best control of garlic white rot, bringing soil populations of S. cepivorum to negligible levels, similar levels of disease control and garlic yields were achieved when tebuconazole was sprayed to stem bases of plants grown from cloves also treated with tebuconazole. This double treatment almost doubled the yield compared with untreated plants and significantly increased bulb quality under high disease pressure conditions. Soil solarization was also highly effective in a second consecutive crop of garlic, with significant improvements in yield and garlic quality. In contrast, lower levels of disease control were obtained when selected isolates of Trichoderma harzianum and Bacillus subtilis were applied to the soil and cloves respectively.     

Soil properties related to suppression of Rhizoctonia solani on tobacco fields from northwest Argentina

Biotic and abiotic factors from soils have been implicated in the disease suppression of Rhizoctonia solani. This study included a Eucalyptus twig baiting assay, disease index and qPCR quantification of R. solani, and physicochemical analysis of 10 tobacco soils from five different locations (V: Vaqueros, C: Cerrillos, R: Rosario de Lerma, SA: San Agustín, CH: Chicoana) in the northwest of Argentina. Levels of Rhizoctonia soil inoculum quantified by baiting assay and qPCR were positively correlated. However, there was no correlation with root rot disease index in tobacco fields. Soils from V1, SA2 and CH2 fields, which reduced root rot disease on tobacco plants, were suppressive to R. solani infection. High clay, pH, organic matter content and physical stability in tobacco soils were the main physicochemical properties that limited Rhizoctonia development. Interestingly, growth of R. solani subgroups AG4-HGI and AG4-HGIII was highly suppressed in V1 and CH2 fields, and in SA2 fields, respectively. Undisturbed soil from a local forested mountain also resulted in reduction of growth of AG4-HGIII and AG4-HGI, while AG2-1 was less affected, suggesting that high soil organic matter contributed to suppression of R. solani. Soils highly suppressive of R. solani had significantly different populations of culturable bacteria, Pseudomonas and fungi, but populations of actinobacteria and Trichoderma spp. did not differ. These different populations may be involved in the inhibition of fungal growth. The results demonstrated that physicochemical and biological properties of soil suppressive to R. solani could act as an alternative for controlling Rhizoctonia diseases on tobacco.     

Infection and colonization of jojoba byGanoderma lucidum

In arid conditions in India,Ganoderma lucidum (Leyss: Fr.) P. Karsten was found to cause root rot diseases in jojoba (Simmondsia chinensis (Link) Schneider) plants. In the rainy season, 10–15-year-old jojoba plants growing in the proximity of aGanoderma-infectedAcacia tortilis tree, developed disease symptoms. Twigs of affected plants started drying from the top of the branch; leaves turned yellowish brown and finally abscissed; plants dried up within 1 to 3 months. Basidiocarps developed from decaying roots near the collar region and produced colored stalks and fruiting caps. Pathogenicity of the fungus was established by keeping the infected root segments in direct contact with roots of healthy jojoba plants. Root rot symptoms were expressed within 5 months in inoculated plants subjected to moisture stress.     

Investigations on the Biological Control of Some Insect Pests in Bolivia

Abstract

Greenhouse experiments were conducted to evaluate the effects of organic amendments and captafol on the parasitic potential of Paecilomyces lilacinus (Thom) Samson against Meloidogyne incognita in sterile field soil. Tomato cv. Moneymaker plants were used as a host. Organic matter from Tagetes minuta L., Ricinus communis L. and Datura strammonium L. stimulated egg parasitism, while the fungicide captafol inhibited it. Galling intensity and the population of juveniles were significantly lower in soils amended with organic matter. However, no significant differences were detected among the different organic additives. The amended soils supported plants with significantly heavier shoots and roots. The implications of these results on the management of root‐knot nematodes are discussed.     

Enkele waarnemingen over het opreden van de verwelkingsiekte bij luzerne in Zeeland in 1957

Summary Some observations have been made on lucerne wilt disease during the growing season in 1957, and in experimental inoculation tests in a glasshouse in 1958. In the province of Zeeland the disease does harm to the crop and prevents many farmers from keeping their crops longer than two years.In a survey data have been collected on soil type, preceding crops, green manuring and manuring with stable dung, pH, structure and weeds. No correlations between these factors and the degree of attack by the disease could be proved, except that on heavy soils the disease was less severe than on lighter soils (as a mean of all observations).Development of the disease is facilitated by damage caused by mechanical equipment to the crop. Damage to the crown of the plants should be avoided as much as possible. The disease is distributed extensively after frequent mowing. On attacked leaves left behind on the mowed stalks, and on decayed leaves dropped to the soil, masses of spores ofVerticillium albo-atrum are produced, which form a potential source of infection in a weakened crop.It seems that the disease is more air-borne than soil-borne, since one year old crops are seldom attacked.From attacked lucerne plants in the field the following fungi have been isolated:Verticillium albo-atrum Reinke & Berth.,Gliocladium roseum Bain andFusarium avenaceum (Fr.) Sacc. (table 1).Isolations have been made from 50 different species of weeds, out of which the following fungi were obtained:Verticillium albo-atrum Reinke & Berth. fromCapsella bursa-pastoris Med. andPlantago major L.,V. dahliae Kleb. fromPrunella vulgaris L.,Capsella bursa-pastoris Med. andThlaspi arvense L., andV. lecanii (Zimm.) Viegas fromPlantago major L.In inoculation experiments with all these isolates, in roots, stalks and on cut plants of lucerne, onlyV. albo-atrum, both from lucerne and weeds, andV. lecanii proved to be able to cause wilting of leaves and stalks. WithGliocladium, Fusarium andVerticillium dahliae no such symptoms could be obtained. The results were the same whatever method of inoculation was used.     

Selection of fungal biological control agents of Sclerotium cepivorum for control of white rot by sclerotial degradation in a UK soil

A range of fungal isolates was tested in a three-stage screening system for their ability to degrade sclerotia of Sclerotium cepivorum on agar and in soil, and to reduce white rot disease on onion seedlings. Biological control agents (BCAs) were identified that could degrade up to 60% of sclerotia in soil and significantly reduce white rot disease on onion seedlings. The efficacy of the BCAs was enhanced when applied as wheat bran cultures compared with spore suspensions, and two of the best BCAs from the screening procedures were both identified as Trichoderma viride (L4, S17A). When L4 and S17A were fluid-drilled in guar gum with bulb onion seed in the field white rot symptoms were significantly reduced, but stem base applications applied mid-season had little effect. The strategy of selecting and using BCAs that degrade sclerotia of S. cepivorum and integration with other control methods is discussed.     

Biological Soil Disinfestation (BSD), a new control method for potato brown rot,caused by <Emphasis Type="Italic">Ralstonia solanacearum</Emphasis> race 3 biovar 2

The potential of Biological Soil Disinfestation (BSD) to control potato brown rot, caused by Ralstonia solanacearum race 3 biovar 2, was investigated. BSD involves the induction of anaerobic soil conditions by increasing microbial respiration through incorporation of fresh organic amendments (here: grass or potato haulms) and by reducing re-supply of oxygen by covering with airtight plastic sheets. Control treatments were left without cover and amendment, or amended without covering or covered only without amendment. The effect of BSD on survival of R. solanacearum was tested at three different scales: in 1-l glass mesocosms under laboratory conditions, in 1.2-m-diam microplots positioned in an outdoor quarantine field, and in a naturally infested commercial field. Within a few days, anaerobic conditions developed in the BSD-treated soils. In the mesocosm and microplot experiment, anaerobic conditions persisted till the end of the 4-week experimental period. In the field experiment, the period of anaerobiosis was shorter due to birds damaging the plastic cover. In all three experiments, BSD reduced soil populations of R. solanacearum significantly by 92.5% to >99.9% compared to the non-amended and uncovered control treatments. In the field experiment, BSD also resulted in a significant reduction of R. solanacearum survival in potato tubers buried at 15 or 35 cm and in the rapid decomposition of superficially buried potatoes remaining after harvesting, thus destroying an important inoculum reservoir of R. solanacearum. The treatments with grass amendment only or covering with only plastic did not result in anaerobic conditions and did not decrease R. solanacearum populations during the experimental period. PCR-DGGE analyses of 16S-rDNA from soil samples of the various treatments in the mesocosm and microplot experiments revealed that BSD hardly affected bacterial diversity but did result in clear shifts in the composition of the bacterial community. The possible implications of these shifts are discussed. It is concluded that BSD has the potential to strongly decrease soil infestation levels of R. solanacearum and to become an important element in a sustainable and effective management strategy for potato brown rot, especially in areas where the disease is endemic.     

Aphanomyces euteiches as a component of the complex of foot and root pathogens of peas in Dutch soils

The occurrence ofAphanomyces euteiches Drechs. in Dutch soils is reported for the first time. Isolates of the pathogen were obtained from peas (Pisum sativum L.). A bioassay was used that baited the pathogen from soil into the cortex of stem and root of seedlings of a highly susceptible pea cultivar. The pathogen could subsequently be isolated on a semi-selective medium. Screening of soil samples from 13 fields known to be infested with fungi causing foot and root rot demonstrated the presence ofA. euteiches in 10 cases. In a second screening on soil samples from 43 fields, the pathogen was present in 16 cases. A positive correlation was found between the disease severity caused byA. euteiches in the seedling bioassay and the disease severity caused by the complex of foot and root pathogens in the same soils as evidenced by a mature plant bioassay. It is considered probable thatA. euteiches has since long been a common component of the foot and root rot complex in Dutch soils but has not been detected previously due to inadequate sampling and isolation techniques.Samenvatting De aanwezigheid vanAphanomyces euteiches Drechs. in Nederlandse gronden is voor het eerst aangetoond. Isolaten van het pathogeen werden verkregen van erwten (Pisum sativum L.). De pathogene schimmel werd in petrischalen uit grond in het schorsweefsel van wortel en stengel van een zeer vatbaar erwteras gelokt. Met behulp van een semiselectief medium konden vervolgens isolaten van de schimmel worden verkregen. Toetsing van grondmonsters afkomstig van 13 percelen, waarvan bekend was dat ze besmet waren met schimmels die voetziekten in erwten veroorzaken, toonde de aanwezigheid vanA. euteiches aan in 10 gevallen. In een tweede biotoets op grondmonsters van 43 percelen bleken 16 monsters het pathogeen te herbergen. Er werd een positieve correlatie gevonden tussen de ernst van de aantasting doorA. euteiches van kiemplanten en de aantasting van volwassen planten in een biotoets in de kas. Het is waarschijnlijk dat de schimmel reeds lang in Nederlandse akkers voorkomt, maar door inadequate bemonsterings- en isolatietechnieken over het hoofd is gezien.     

Survival of pathogens of Brussels sprouts (Brassica oleracea Gemmifera Group) in crop residues

Mycosphaerella brassicicola (ringspot), Alternaria brassicicola and A. brassicae (dark leaf spot) and Xanthomonas campestris pv. campestris (black spot) can infect leaves of Brussels sprouts resulting in yield losses. Infections of outer leaves of sprouts cause severe losses in quality. Crop residues can be a major primary inoculum source of the pathogens. Their population dynamics were followed in residues of leaves and stalks of crops of Brussels sprouts during 24 months using real‐time PCR assays. Leaf residues on the soil surface or buried in soil decomposed within 4 months. However, residues of stalks were present in the field after 24 months. In such residues, M. brassicicola populations increased during the first 2 months, but decreased thereafter and the pathogen was found only occasionally in the second year. Alternaria brassicicola multiplied on stalks exposed on the surface of field soil and was present on such residues after 24 months. Survival was less on residues buried in soil. Alternaria brassicae population increased in stalks exposed on the soil surface during the first months but decreased thereafter under the detection limit. Xanthomonas campestris cv. campestris populations fluctuated in time but 1 × 10⁴ cells mg^?1 stalk residue were still found after 24 months. Additionally, the four pathogens were present in residues of 11 commercial rapeseed crops that were analysed. The observed variation in population sizes of the pathogens between individual pieces of crop residues indicates a stochastic spread of pathogens. Unravelling the underlying processes will support the development of novel methods for sustainable disease prevention.     

Evaluation ofAmaranthus sp. andVernonia amygdalina, and soil amendments with poultry manure for the management of root-knot nematodes on eggplant

The suppressive effect of vernonia (Vernonia amygdalina), amaranth (Amarathus sp.) and poultry manure on root-knot nematodes (RKNs) (Meloidogyne spp.) infecting eggplant (Solanum macrocarpon) was studied at two sites in southern Benin naturally infested with these nematodes. After 3 months, soil and root-inhabiting RKN populations were significantly less (P≦0.05) in the plots cropped with vernonia, amaranth, and eggplant amended with poultry manure (PM) at the rate of 40 t ha⁻¹ as compared with the rate of 20 t ha⁻¹ and with the control. Poultry manure was more effective after 2 months than after 3 months. Overall, vernonia was the most effective treatment affecting RKN populations in the roots and the soil. The use of these treatments in nematode management through rotation and co-planted crops is discussed. http://www.phytoparasitica.org posting August 6, 2008.     

Inactivation of Macrophomina phaseolina Propagules during Composting and Effect of Composts on Dry Root Rot Severity and on Seed Yield of Clusterbean

Survival of a heat-tolerant pathogen Macrophomina phaseolina, causing dry root rot of clusterbean, was studied by incorporation and retrieval of infected residue samples at various stages of the composting process of pearl millet (Pennisetum glaucum) and clusterbean (Cyamopsis tetragonoloba) residues. During the heating phase, temperatures varied from 48–51°C at 30cm and 60–62°C at 60cm depth in compost pits. Reduction in survival of M. phaseolina propagules (13–23%) was significantly higher in the residues enriched with 4% urea-N and kept at 60cm compared to 2% urea-N and at 30cm. However, a heat phase (48–62°C) was not enough to completely eradicate M. phaseolina propagules from infected residues. Further reductions (54–61%) in survived propagules were achieved by sub-lethal temperatures (48–53°C) when moistened compost materials were exposed to heat during summer days. Beneficial effects of composts were ascertained on dry root rot intensity, seed yield of clusterbean and densities of M. phaseolina, Nitrosomonas and antagonists in soil. In a two-year field study, all the composts significantly reduced plant mortality due to dry root rot and increased the yield of clusterbean. The highest disease suppression and yield promotion were recorded in soil amended with pearl millet compost and cauliflower leaf residue compost, respectively. Soil amendment with compost also lead to a significant reduced density of M. phaseolina and an increased density of antagonistic actinomycetes, lytic bacteria and Nitrosomonas. Among composts, greater potential of cauliflower compost in enhancing population of antagonists in soil was discernible.     

Biocontrol agents in combination with Moringa oleifera extract for integrated control of Sclerotium-caused cowpea damping-off and stem rot

Damping-off and stem rot disease-causing Sclerotium rolfsii has been reported as a destructive soil-borne pathogen of numerous crops, especially in the tropics and subtropics. Trials were conducted to test the efficacy of biocontrol agents alone or combined with Moringa oleifera leaf extracts for the control of the disease. In the laboratory, PDA was amended with Moringa leaf extract, and mycelial growth of S. rolfsii was measured. In the greenhouse and field, Trichoderma Kd 63, Trichoderma IITA 508 and Bacillus subtilis were evaluated as seed treatments, soil drench or sprinkle, separately or combined with Moringa leaf extracts. Percentage disease incidence, severity and control were recorded. In the laboratory, the higher the extract concentration the less the mycelial growth and no mycelial growth occurred on extract at 15 or 20 g leaves 10 ml⁻¹ water. In the greenhouse, the highest disease control was observed at a Moringa extract concentration of 15 kg leaves 10 l⁻¹ water (w/v). Seed treatments using Trichoderma Kd 63, and soil sprinkle using Trichoderma IITA 508 had a significantly (P = 0.05) higher effect on a disease incidence than Bacillus. Disease severity followed the same pattern. Moringa seed treatment combined with Trichoderma soil sprinkle resulted in significantly more than 94% and 70% disease control in the greenhouse and field, respectively, with significant yield increase in the field. This is the first report of Moringa leaf extract combined with Trichoderma as an integrated control for Sclerotium damping-off and stem rot of cowpea in the field.     

Soybean plants expressing an active oligomeric oxalate oxidase from the wheat gf-2.8 (germin) gene are resistant to the oxalate-secreting pathogen Sclerotina sclerotiorum

Sclerotinia stem rot (SSR) caused by Sclerotinia sclerotiorum (Lib.) De Bary is a serious fungal disease of soybean. Senescing petals provide a starting nutrient source for the invasion of healthy tissue by the advancing oxalic acid secreting fungal hyphae. Since oxalic acid is a major pathogenicity factor of SSR, transgenic soybean capable of degrading oxalic acid may be resistant to the pathogen. Transgenic soybean plants were produced byAgrobacterium -mediated transformation with the wheat germin gene (gf-2.8) encoding an oligomeric protein, oxalate oxidase (OxO), which oxidizes oxalic acid to carbon dioxide and hydrogen peroxide (H₂O₂). Transgenic soybean homozygous for 35S- gf-2.8 produced an approx. 130 kDa protein indistinguishable from wheat germin, and with OxO activity. OxO activity was prominent in cell walls proximal to the site of pathogen attack. The transgenics had greatly reduced disease progression and lesion length following cotyledon and stem inoculation with S. sclerotiorum indicating that the germin gene product conferred resistance to SSR. This is the first report of plant resistance to the fungal pathogen S. sclerotiorum in transgenic plants expressing OxO.     

Association of the western flower thrips (Frankliniella occidentalis) with cultivated sunflower (Helianthus annuus) in Israel

In 1992 and 1993, sunflower (Helianthus annuus L.) crops in Israel were heavily damaged by the western flower thrips (WFT),Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). Adult females appear in the heads of sunflower just as the latter begin to blossom; the population decreases towards completion of anthesis. The damage to kernels is greatest at the periphery of the heads, where flowers appear first, and lowest at the center. Fields sown early in the season (in March) are usually the ones infested most by WFT and suffering the greatest damage. Fields sown one month later are less infested, since predatory bugs of the genusOrius are very active at that time.     

玉米内生菌L10的分离、鉴定及拮抗活性

为获得对玉米茎腐病主要病原菌禾谷镰孢Fusarium graminearum有明显拮抗作用的玉米内生菌,采用平板对峙法从成熟健康玉米茎秆中筛选禾谷镰孢拮抗菌株,并分析其抗菌谱;通过形态特征、生理生化特性及16S rDNA序列分析进行菌种鉴定;利用盆栽生防试验检测其对玉米茎腐病的防治效果。结果表明,共分离获得了164株玉米内生细菌菌株,其中L10菌株对禾谷镰孢具有较好的抑制效果,抑菌圈半径达1.68 cm;该菌对玉米大斑病菌Setosphaeria turcica、层出镰孢F. proliferatum、禾谷镰孢F. graminearum、拟轮枝镰孢F. verticilliodes、玉米弯孢叶斑病菌Curvularia lunata、玉米小斑病菌Bipolaris maydis、立枯丝核菌Rhizoctonia solani、茄链格孢Alternaria solani共8种植物病原菌均有拮抗作用,尤其对禾谷镰孢抑制效果最佳;结合形态特征、生理生化性质及16S rDNA序列分析,将L10菌株鉴定为多粘类芽胞杆菌Paenibacillus polymyxa。L10菌株脂肽类物质对禾谷镰孢菌具有较好的抑制活性,且盆栽生防试验结果显示该菌株对玉米茎腐病具有一定的防治效果。表明菌株L10对玉米镰孢茎腐病的防治具有一定潜力。     

Genetic diversity and population structure of Lasiodiplodia theobromae from different hosts in northeastern Brazil and Mexico

Lasiodiplodia theobromae is one of the most frequent fungal pathogens associated with dieback, gummosis, leaf spot, stem-end rot and fruit rot symptoms in cashew, mango, papaya and grapevine. In this study, the variation in the genetic diversity of 117 L. theobromae isolates from northeastern Brazil (n = 100) and Mexico (n = 17), which were collected from these four crops, was analysed using microsatellite markers. The results revealed low genetic diversity among L. theobromae populations and the existence of two genetic groups. All Mexican isolates were grouped with Brazilian isolates, suggesting a low level of differentiation between these populations. Furthermore, no evident host or climate-based population differentiation was observed for L. theobromae in Brazil. The populations studied were mostly clonal, but additional studies are needed to better understand the mode of reproduction of the pathogen. The low genetic diversity of L. theobromae populations in northeastern Brazil suggests that resistant cultivars could be used as a durable management strategy to reduce the impact of the diseases caused by this pathogen.