水稻纹枯病菌拮抗细菌的筛选及鉴定

为获得对水稻纹枯病有生防效果的拮抗细菌,从江苏南京、徐州和常州等地采集的土样中分离细菌分离物1914株,采用平板对峙法筛选获得70株对水稻纹枯病菌有较强抑菌活性的分离物,其中11株对5种水稻病害病原菌均有抑制作用;对11株拮抗菌进行田间防效和室内促生试验,测定菌株分泌的抑菌物质和促生物质,并进行种属鉴定.结果表明,拮抗菌对水稻纹枯病的盆栽和田间小区防效在48.41％和43.03％以上;均可产生蛋白酶与嗜铁素,而不产生几丁质酶,除XF-174外其余10个菌株均可产生纤维素酶;对水稻苗株高和鲜重具有促生作用,并均可产生赤霉素(GA3);除ZF-273和XF-174外的9个菌株可产生吲哚乙酸(IAA),且细菌发酵液中IAA和GA3含量与水稻株高和鲜重的增长率呈正相关.结合各菌株形态特征、生理生化特性和16S rDNA与gyr-B序列分析结果,鉴定SF-181为枯草芽胞杆菌Bacillus subtilis,XF-174为荧光假单胞菌Pseudomonas fluorescens,其余9个菌株为解淀粉芽胞杆菌B.amyloliquefaciens.     

稻田土壤8种真菌对4种杀菌剂的敏感性分析

基于ITS-5.8s rDNA区序列,初步鉴定了浙江大学试验基地稻田土壤的8种常见真菌。采用菌丝生长速率法测定了井冈霉素、多菌灵、咪鲜胺和三唑酮4种常用杀菌剂对这8种土壤真菌的抑菌活性,以及多菌灵与咪鲜胺混用对禾柄锈菌、黑曲霉和长枝木霉3种真菌菌丝生长的抑制作用。结果表明:8种真菌对咪鲜胺最敏感,EC50值在0.091~3.1 mg/L之间;多菌灵的EC50值在0.15~1.8 mg/L之间;三唑酮的EC50值在0.57~8.5 mg/L之间;井冈霉素的敏感性最低,EC50在12~94 mg/L之间。由4种杀菌剂的SSDs曲线分析结果得出,不同真菌对杀菌剂敏感性存在显著差异。当多菌灵与咪鲜胺按其EC50值分别以体积比3∶2、1∶1和7∶3混用时,增效系数分别为1.615、1.039和1.042,表现出一定的协同或相加作用。本研究结果为进一步阐明杀菌剂对稻田生态系统真菌群落的生态效应及杀菌剂的科学合理使用提供了重要依据。     

<Emphasis Type="Italic">Bacillus</Emphasis> species as the most promising bacterial biocontrol agents in rhizosphere and endorhiza of plants grown in rotation with each other

In this study, a total of 550 cultivable bacterial isolates were isolated from rhizosphere and endorhiza of rice, Berseem clover, and oilseed rape grown in rotation with each other. The potential of antifungal activity of all isolates against five rice pathogenic fungi was investigated under in vitro conditions. Of 550 isolates, 139 inhibited the mycelial growth of at least one fungal rice pathogen. The results also showed that rhizosphere and endorhiza of every third plant (three studied plants) harbored the bacteria (139 isolates) with good potential for inhibiting fungal rice pathogens in vitro. Based on biochemical tests and by comparison of 16S rDNA sequences, of the superiors six endophytic and rhizosphere isolates, which showed strong inhibitory effects against the mycelial growth of all the five fungal rice pathogens (Magnaporthe oryzae, M. salvinii, Fusarium verticillioides, F. fujikuroi, and F. proliferum), were identified. Two isolates REN₄ and CEN₂, isolate CEN₆, isolate CEN₃, and two isolates REN₃ and CEN₅ were closely related to Bacillus mojavensis, B. amyloliquefaciens, B. subtilis, and B. cereus respectively. Strains REN₄ and REN₃ were obtained from rhizosphere and endorhiza of rice, while strains CEN₆ and CEN₂, and strains CEN₅ and CEN₃ were isolated from rhizosphere and endorhiza of clover and oilseed rape respectively. Therefore, it can be concluded that plants cultivated in rotation with rice and grown on the same soil harbor protective bacteria such as genus Bacillus and that may be potential reservoirs of bio-control agents for control of the rice pathogenic fungi tested in this study.     

Antimicrobial activity of some N-(arylalkyl)maleimides

A series of N-(arylalkyl)maleimides was prepared for the reaction of maleic anhydride and N-(arylalkyl) amines, and their antimicrobial activities were examined. All compounds exhibited antibacterial activity against gram-positive bacteria such as Bacillus subtilis and Staphylococcus aureus. Almost all compounds exhibited antibacterial activity against the gram-negative bacterium, Escherichia coli, but were inactive against Pseudomonas aeruginosa. Activities against gram-positive bacteria were independent of the nature of the substituent on the benzene ring or the length of alkyl group, but that against gram-negative bacteria was influenced by these parameters. All N-(arylalkyl)maleimides showed activity against yeasts and mycelial fungi.     

微生物菌剂处理增加了生姜土壤中有益微生物的相对丰度

作物连作易导致土壤中病原菌大量积累, 促使土传病害频发, 影响作物生长?本试验采用微生物菌剂(富含哈茨木霉Trichoderma harzianum TH7?淡紫拟青霉Purpureocillium lilacinum PL22以及高效枯草芽胞杆菌Bacillus subtilis)处理具有多年生姜种植历史的地块, 并采用分离培养法和宏基因组测序技术对处理后土壤中的微生物进行检测, 明确微生物菌剂对生姜土壤中微生物群落组成的影响?结果表明, 与对照相比, 微生物菌剂处理后, 土壤中细菌属和种的数量增加, 而真菌属和种的数量减少?从微生物菌剂处理后的土壤中分离出3个门水平, 24个属水平和42个种水平细菌, 以及3个门水平, 20个属水平和24个种水平真菌, 其中分离频率较高的细菌和真菌种分别为温哥华假单胞菌Pseudomonas vancouverensis和Musidium stromaticum?从未经微生物菌剂处理的土壤(对照)中分离出导致生姜茎基腐病的病原菌尖镰孢Fusarium oxysporum和腐皮镰孢 F. solani?宏基因组测序结果表明, 微生物菌剂处理对真菌多样性的影响大于对细菌?与对照相比, 微生物菌剂处理提高了土壤中根瘤菌属Rhizobium?假单胞菌属Pseudomonas?芽胞杆菌属Bacillus等细菌属及Musidium?被孢霉属Mortierella等真菌属物种的相对丰度?综上, 微生物菌剂处理增加了生姜土壤中细菌属和种的数量, 增加了土壤中与有益微生物相关的细菌和真菌的相对丰度, 并且抑制了病原菌的生长?     

苏云金杆菌乳剂防治二代棉铃虫保护天敌控制伏蚜的研究

在二代棉铃虫Heliothis armigera卵高峰期,一般年份用200倍,大发生年份用100倍苏云金杆菌(B.t.)乳剂喷雾防治效果达75%以上,可将虫口密度压低到经济损失允许水平以下。防治后调查生防田主要捕食性昆虫天敌比化防田高3倍左右,对伏蚜有较好的控制作用。伏蚜高峰期主要捕食性天敌与伏蚜之比,维持在1:200以上水平,可将防治伏蚜时间推迟10—15天,减少防治1—2次。     

Risikofolgeabschätzung für den Einsatz mikrobieller Antagonisten: Gibt es Effekte auf Nichtzielorganismen?

Biological control of phytopathogenic fungi using antagonistic microorganisms is an environmentally friendly alternative in plant protection. However, possible non-target effects of the applied antagonists on ecologically important soil-microbes need to be considered. Therefore, the aim of this study was to analyse the effect of biological control agents (BCAs) on non-target microbes in the field. Whereas the bacterial BCAs Serratia plymuthica HRO-C48 and Streptomyces sp. HRO-71 were applied to control the pathogen Verticillium dahliae on strawberry and potato, the bacterial strains Pseudomonas trivialis 3Re2-7, P. fluorescens L13-6-12, S. plymuthica 3Re4-18 and the fungal antagonists Trichoderma reesei G1/8 and T. viride G3/2 were introduced to control Rhizoctonia solani on lettuce and potato. As the analysed BCAs belong to different microbial groups like grampositive (HRO-71) and gramnegative (HRO-C48, L13-6-12, 3Re2-7, 3Re4-18) bacteria or the ascomycota (G1/8, G3/2) and originated from different micro-habitats like the rhizosphere or the endorhiza, general conclusion could be drawn from our results. After BCA treatment we did not observe any long-term effect on the plant-associated microbes in any tested pathosystem. Therefore, no sustainable risks could be seen for the indigenous micro-organisms. Our new findings may help to improve the development as well as the registration procedures of future microbial plant protection products.     

Effects of rhizobacteria on parasitism by Meloidogyne ethiopica on grapevines

Meloidogyne ethiopica is one of the most important plant-parasitic nematodes affecting vines in Chile and is very aggressive and difficult to control. This study evaluated 16 strains of rhizobacteria, originally isolated from roots of grapevines, for their effects on parasitism and nematode damage to potted vine plants. The antagonistic effect of rhizobacteria was assessed by treating 2-month-old plants of cv. Chardonnay in 3-l pots with a suspension containing 1?×?10⁶?cfu?ml^?1 of the bacteria and 1,000 nematode eggs. After 6?months of growth, the plants were cut and root and canopy weights, nematode populations and root damage determined. The effect of rhizobacterial culture filtrate on hatching of nematode eggs was also assessed in vitro. Seven strains of rhizobacteria proved effective in inhibiting damage or reproduction of the nematode. These were strains of Serratia marcescens, Comamonas acidovorans, Pantoea agglomerans, Sphingobacterium spiritivorum, Bacillus mycoides, Alcaligenes piechaudii and Serratia plymuthica. A further three strains, of Bacillus megaterium, P. agglomerans and Pseudomonas savastanoi, significantly increased root weight, but did not decrease nematode damage or population density. The supernatant of all strains significantly decreased hatching of juvenile nematodes after 24?h of immersion, with isolates of P. putida and B. megaterium being the most effective.     

温度对小麦矮腥黑穗病菌冬孢子萌发的影响

温度对小麦矮腥黑穗病菌冬孢子萌发影响的试验结果表明,TCK冬孢子在-2～12℃范围内都可以萌发,5℃为最佳萌发温度。同一分离菌冬孢子在不同温度处理的萌发特性和萌发率有差异;不同分离菌冬孢子在相同温度下的萌发特性和萌发率有很大差异。在5℃下5个分离菌中,冬孢子萌发起始时间最短的为15 d,最长为35 d,培养60 d时分离菌T_t1、T_t2、T_y、T_m和T_u冬孢子的萌发率分别为86.4%、23.9%、23.3%、44.3%和81.0%。根据分离菌T_t2不同温度下培养50 d时的萌发率,建立了萌发率(Y)与温度(X)的模型为Y=0.150 8 exp[-0.02949(X-4.957 6)]2,此结果为TCK的风险评估提供了基础数据。     

<Emphasis Type="Italic">In vitro</Emphasis> Selection of Maize Rhizobacteria to Study Potential Biological Control of <Emphasis Type="Italic">Aspergillus</Emphasis> Section <Emphasis Type="Italic">Flavi</Emphasis> and Aflatoxin Production

The aims of this study were to select bacterial isolates from the non-rhizophere of maize soil and to examine their antagonistic activity against Aspergillus section Flavi strains. The first selection was made through ecophysiological responses of bacterial isolates to water activity (a_w) and temperature stress. Subsequently, an Index of Dominance test (I_D), ecological similarity and inhibition of the lag phase prior to growth, growth rate and aflatoxin B₁ accumulation were used as criteria. From the first assay nine bacterial strains were selected. They grew well at 25 and 30 °C, with growth optima between 0.982 and 0.955 a_W using 48 h of incubation. There was ecological similarity between the bacterial strains Bacillus subtilis (RCB 3, RCB 6), Pseudomonas solanacearum RCB 5, Amphibacillus xylanus RCB 27 and aflatoxigenic Aspergillus section Flavi strains at 0.982 at 25 °C. The predominant interaction between all selected bacteria and fungi in dual culture was mutual intermingling at 0.982. Mutual inhibition on contact and mutual inhibition at a distance was observed at 0.955 a_w, between only four bacteria and some Aspergillus strains. Bacillus subtilis RCB 55 showed antifungal activity against Aspergillus section Flavi strains. Amphibacillus xylanus RCB 27, B.␣subtilis RCB 90 and Sporolactobacillus inulinus RCB 196 increased the lag phase prior to growth and decreased the growth rate of Aspergillus section Flavi strains. Bacillus subtilis strains (RCB 6, RCB 55, RCB 90) and P. solanacearum RCB 110 inhibited aflatoxin accumulation. Bacillus subtilis RCB 90 completely inhibited aflatoxin B₁ accumulation at 0.982 a_W. These results show that the bacterial strains selected have potential for controlling Aspergillus section Flavi over a wide range of relevant environmental conditions in the stored maize ecosystem.     

四株虫生真菌的鉴定及其对小菜蛾的室内毒力

为了明确4株虫生真菌在小菜蛾防治中的应用潜力,采用生物测定法测定其室内毒力,并通过多相分类法研究其分类地位。结果表明:菌株GZU-BCECWC113对小菜蛾的毒力最强,在1.6×108孢子/mL浓度下对小菜蛾的校正死亡率最高,达到89.47%;半致死时间LT50值最小,为3.33天;感染8天时的LC50值最小,为0.45×105孢子/mL。根据形态特征、培养性状及ITS序列分析结果明确4株菌的分类地位,即GZU-BCECWC113为环链拟青霉Paecilomyces catenianulatus,GZU-BCECWQ16为玫烟色拟青霉P.fumosorosenus,GZU-BCECW122为蝉拟青霉P.cicadae,GZU-BCEC-WKKS2为细脚拟青霉P.tenuipes。     

Genetic diversity and identification of race 3 of <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> f. sp. <Emphasis Type="Italic">lactucae</Emphasis> in Taiwan

Sorghum is an important drought tolerant crop cultivated for food and fodder purposes. Anthracnose disease caused by Colletotrichum graminicola is a major constraint in sorghum productivity in India. Certain antagonistic fungi, that were isolated in the previous study from the rhizosphere and rhizoplane of perennial grasses in India, were studied for their antagonism in vitro to C. graminicola, root colonization ability and rhizosphere competence. Out of 138 isolates tested, 89 were antagonistic. Fifteen fungal isolates with greater than 70 % in vitro inhibition zone to the pathogen tested positive for root and rhizosphere colonization abilities. Three isolates – Chaetomium globosum isolate 57, Trichoderma harzianum isolate 184 and Fusarium oxysporum (NSF isolate 9) with prominent biocontrol potentials were tested for the control of sorghum anthracnose in greenhouse and field. Chaetomium globosum, Trichoderma harzianum and Fusarium oxysporum isolates decreased seedling mortality, and incidence and severity of disease at different growing stages. They promoted plant growth (dry biomass- 45.3, 40.0 and 46.7 %) and increased yield (grain biomass- 33.3, 23.8 and 49.2 %) respectively, over control in field. The population of the above fungi in soil was moderately high at harvest stage. The present investigation revealed that fungal isolates from rhizosphere and rhizoplane of perennial grasses could be employed to manage anthracnose and enhance plant growth and yield potentialities in sorghum, at the same time.     

Comparative toxicology of AC 217,300 in various species of insects

AC 217,300 was highly toxic by topical application to adult Musca domestica and Blattella germanica, and larvae of Spodoptera eridania, with LD₅₀ values in μg/g of 20, 19, and 61, respectively. It was relatively nontoxic to Diabrotica undecimpunctata howardi beetles and Heliothis virescens larvae with LD₅₀ values of 165 and >883. When incorporated into baits, AC 217,300 was still highly toxic to M. domestica, B. germanica, and S. eridania. A significant increase in toxicity to H. virescens was observed although the percentage mortality was only 45%. AC 217,300 was not effective against D. undecimpunctata with either mode of application. A comparison of toxicity with tissue residues indicated that AC 217,300 was highly toxic to M. domestica, B. germanica, H. virescens, and S. eridania if it was absorbed. However, D. undecimpunctata appeared to be much less sensitive to AC 217,300, as only 18% mortality was observed with corresponding tissue concentrations two to six times those producing 95–100% mortality in M. domestica and S. eridania. Exposure of M. domestica to an AC 217,300-treated bait for 3–6 hr was sufficient to cause 50–100% mortality after 2 days and 95–100% mortality by 7 days. With B. germanica, a 1- to 3-day exposure resulted in 75–90% control within 7 days, while exposure for 3–7 days gave 90–100% control. Environmental temperature had a pronounced effect on the toxicity of AC 217,300 to both M. domestica and B. germanica. A 20-fold increase in toxicity was observed when the environmental temperature was raised from 21 to 32°C. This observation, in concert with the symptoms of intoxication, support the hypothesis that AC 217,300 is an inhibitor of energy production. Approximately 85 and 87% of the total residue of AC 217,300 extracted from treated M. domestica and B. germanica, respectively, was parent material. Six minor metabolites were detectable, of which three were tentatively identified by cochromatography with authentic standards. None of the identified metabolites had any insecticidal activity in vivo, suggesting that AC 217,300 is the actual toxicant.     

菌株BM-24的分离鉴定及对香蕉枯萎病菌的抑菌活性

为了从饼肥发酵液中分离筛选出对香蕉枯萎病菌Fusarium oxysporum f.sp.cubense有良好拮抗效果的菌株,以香蕉枯萎病病原菌为指示菌进行拮抗菌分离筛选.筛选得到29株拮抗菌,其中分离自菜子饼的菌株BM-24拮抗效果最显著.利用平板对峙法测定菌株BM-24抑菌谱,根据形态特征、培养特征及生理生化特征和16S rDNA序列分析对其进行鉴定,并测定其发酵液不同处理的抑菌活性.经鉴定,此菌株为甲基营养型芽胞杆菌Bacillus methylotrophicus,该菌株对供试的12种植物病原真菌均有很强的抑制作用,尤其对香蕉枯萎病菌1号和4号小种菌丝生长抑制作用最强,抑菌率分别达到87.2％和80.4％,其发酵液对香蕉枯萎病菌具有很强抑菌效果,抑菌活性主要源于菌体竞争.     

Localizing the action of two thiadiazolyl herbicidal derivatives

Enzymatically isolated leaf cells from navy beans (Phaseolus vulgaris L., cv. “Tuscola”) were used to study the effect of buthidazole (3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone) and tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea) on photosynthesis, protein, ribonucleic acid (RNA), and lipid synthesis. The incorporation of NaH¹⁴CO₃, [¹⁴C]leucine, [¹⁴C]uracil, and [¹⁴C]acetic acid as substrates for the respective metabolic process was measured. Time-course and concentration studies included incubation periods of 30, 60, and 120 min and concentrations of 0.1, 1, 10, and 100 μM of both herbicides. Photosynthesis was very sensitive to both buthidazole and tebuthiuron and was inhibited in 30 min by 0.1 μM concentrations. RNA and lipid syntheses were inhibited 50 and 87%, respectively, by buthidazole and 42 and 64%, respectively, by tebuthiuron after 120 min at 100 μM concentration. Protein synthesis was not affected by any herbicide at any concentration or any exposure time period. The inhibitory effects of buthidazole and tebuthiuron on RNA and lipid syntheses may be involved in the ultimate herbicidal action of these herbicidal chemicals.     

Effect of Foliar Application of Urea on Rhizosphere and Rhizoplane Microflora of Wheat1)

The effect of urea leaf treatment on plant growth and rhizosphere microorganisms was studied under controlled environmental conditions with spring wheat at 2 growth stages, and at 2 inorganic nutrient levels of the soil. The increase in dry weight of shoots and roots was inhibited by the urea treatment. Treatment of seedlings also resulted in a delay in the formation of tillers and nodal roots, especially in low fertilized soil. A temporary increase of rhizoplane bacteria was demonstrated after 7–9 days due to a stimulation of fast growing strains. A quantitative effect on rhizoplane fungi was only apparent, on day 9 after treatment of seedlings, as a decrease in total numbers and coincided with the increase in numbers of bacteria and actinomycetes. At this time the numbers of fungi known to be early root colonizers like Penicillium spp. and Mortierella spp. decreased after initially being stimulated, while numbers of late colonizers like Fusarium spp. and Trichoderma spp. increased after 9 days after initially being reduced in comparison with the control. Investigation of the rhizosphere effect (R/S) of wheat by the soil dilution plate method and fluorescence microscopy showed a 200% increase in total numbers of micro-organisms in the rhizosphere soil when the former method was used, but a 10–30% reduction when fluorescence microscopy was employed.     

Control of infection and sporulation ofBotrytis cinerea on bean and tomato by saprophytic bacteria and fungi

Sixty isolates of saprophytic microorganisms were screened for their ability to reduce the severity of grey mould (Botrytis cinerea) infection and sporulation. Isolates of the bacteriaXanthomonas maltophilia, Bacillus pumilus, Lactobacillus sp., andPseudomonas sp. and the fungusGliocladium catenulatum reduced germination of conidia of the pathogen and controlled disease on bean and tomato plants. Their activity under growth room conditions was good, consistent, and similar to the activity of the known biocontrol agent,Trichoderma harzianum T39 (non-formulated). Although the tested isolates may for nutrients with the germinating conidia ofB. cinerea, resistance induced in the host by live or dead cells were also found to be involved. Inhibitory compounds were not detected on treated leaves. Sporulation ofB. cinerea after its establishment on leaves was also reduced by the above mentioned isolates and byPenicillium sp.,Arthrinium montagnei, Ar. phaeospermum, Sesquicillium candelabrum, Chaetomium globosum, Alternaria alternata, Ulocladium atrum, andT. viride. These sporulation-inhibiting fungi did not reduce the infection of leaves byB. cinerea. Most of these selected fungi and bacteria were capable of reducing lesion expansion.     

Interconversion of chloroneb and 2,5-dichloro-4-methoxyphenol by soil microorganisms

The stability of the chloroneb fungicide (1,4-dichloro-2,5-dimethoxybenzene) and its principal degradation product, 2,5-dichloro-4-methoxyphenol (DCMP), was tested in the presence of individual soil microorganisms. Both the fungicide and DCMP were unaltered in liquid shake cultures of the organisms when growth was minimal or static. However, in nutrient broth where active microbial growth was supported, several organisms converted chloroneb to DCMP and/or DCMP to chloroneb. Of 23 organisms grown in the presence of 5 μg chloroneb/ml, 13 demethylated the fungicide to produce DCMP. Liquid shake cultures of Fusarium spp. were most active in this respect, converting more than 50% of the chloroneb to DCMP in 5 days. When grown in the presence of 5 μg DCMP/ml, 8 organisms, especially Trichoderma viride and Mucor ramannianus, converted up to 20% of the DCMP to chloroneb. Cephalosporium gramineum, Rhizoctonia solani, Mucor ramannianus and Fusarium fungi could both methylate and demethylate DCMP to produce chloroneb and 2,5-dichlorohydroquinone, respectively. Microbial synthesis of chloroneb from DCMP, its principal degradation product, may account in part for the relative stability and long term effectiveness of the fungicide in soil.     

Induction of a viable but not culturable (VBNC) state in some Pseudomonas syringae pathovars upon exposure to oxidation of an apoplastic phenolic,acetosyringone

Acetosyringone is a phenolic metabolite often found in plant apoplasts. Its oxidation by hydrogen peroxide and peroxidase results in a prolonged increase in the redox potential of the reaction mixture, similar to redox increases observed in tobacco suspension cells upon treatment with incompatible bacteria. Since high redox potentials, being oxidative, are generally detrimental to bacteria, the effect of acetosyringone oxidation on bacterial viability was examined. Pseudomonas syringae pv. syringae was added to reaction mixtures containing acetosyringone, hydrogen peroxide and peroxidase and samples were removed to determine viability by dilution plating. Initial studies were done with low bacterial concentrations, 10⁵ CFU ml⁻¹, to ensure that scavenging of H₂O₂ was negligible and did not interfere with the reaction mixture. No colonies were formed by bacteria that had been added to reaction mixtures with acetosyringone ranging from 25 to 100 μΜ. Examination of the bacteria by microscopy and flow cytometry, using fluorescent stains that indicate bacterial membrane integrity, suggested that these bacteria had maintained their membrane integrity. In addition they were able to respire based on oxygen uptake. When bacteria were added to on-going reaction mixtures at a time point after the prolonged redox response, the CFU ml⁻¹ increased indicating that a stable reaction product was not responsible for the non-culturability bioactive effect. Other bacterial isolates, P. s. pv. tabaci and Pseudomonas fluorescens, were less susceptible to the bioactive effect of the acetosyringone oxidation. Other phenolics were tested and had lesser degrees of bioactivity and in some cases reduced the bioactivity of acetosyringone oxidation. The ‘viable but non-culturable’ (VBNC) state of the bacteria in this study is compared to that described for other medical and plant pathogens.     

Biological control of avocado white root rot with combined applications of Trichoderma spp. and rhizobacteria

This study tested the effectiveness of single and combined applications of Trichoderma and rhizobacterial strains to control white root rot (WRR) caused by Rosellinia necatrix in avocado plants. Three Trichoderma, two T. atroviride and one T. virens monoconidal strains and four bacterial strains (Bacillus subtilis, Pseudomonas pseudoalcaligenes and two P. chlororaphis) were assayed to determine their compatibilities in vitro. In addition, the effects of the bacterial filtrates were evaluated against the Trichoderma strains and reciprocally; these filtrates were applied alone or in combination to determine their effectiveness against R. necatrix. Individual control agents or combinations of them were applied to avocado plants that were artificially inoculated with a virulent R. necatrix strain. Compatibility between the combined Trichoderma applications and the bacterial strains was observed and these combinations significantly improved the control of R. necatrix during the in vitro experiments. A relative protective effect of some Trichoderma and bacteria was observed on the control of avocado WRR when they were applied singly. The combinations of T. atroviride strains with bacterial strains P. chlororaphis and P. pseudoalcaligenes showed a better control of avocado WRR, whereas the rest of Trichoderma and bacteria combinations also reduced significantly the level of disease and induced a delay at the onset of disease with respect to avocado plants inoculated either with Trichoderma or bacteria.