一株兼具秸秆腐解能力玉米促生菌的筛选、鉴定及发酵优化

【背景】砂姜黑土地区存在秸秆腐解缓慢、秸秆还田后作物幼苗生长不良等问题。【目的】从砂姜黑土区农田筛选一株兼具秸秆腐解能力的玉米促生菌MC29,以促进秸秆腐解和玉米作物生长。【方法】通过16S rRNA基因序列分析对该菌株进行鉴定;采用液态摇瓶及盆栽试验验证菌株实际促腐、促生能力及土壤养分的提升效果,并且探究菌株的最佳生长及产吲哚乙酸(indole-3-acetic acid, IAA)条件;采用电击转化法将绿色荧光蛋白(green fluorescent protein, GFP)基因导入菌株细胞,并通过PCR琼脂糖凝胶电泳进行验证。【结果】分离筛选的玉米促生菌鉴定为纤维化纤维微细菌(Cellulosimicrobium cellulans)。该菌株MC29羧甲基纤维素(carboxymethyl cellulose, CMC)酶活可达13.32 U/mL,产IAA量为8.63 mg/L。与对照相比,施用菌株MC29后秸秆腐解率显著提高24.8%;玉米soil and plant analyzer development (SPAD)值、植株总重、根表面积和根长分别提高7.6%、21.3%、30.9%和18.3%;土壤碱解氮含量显著提高68.1%,土壤速效磷及土壤速效钾含量分别提高5.8%及6.0%。菌株MC29最佳生长条件为pH 7.0、装液量为25/250 mL、碳源为麦芽糖、氮源为酵母粉;最佳产IAA条件为pH 7.0、装液量为50/250 mL、碳源为果糖、氮源为硝酸钾;成功构建荧光标记菌株MC29-GFP,并据此追踪到其接入砂姜黑土15 d后定殖量为2.8×10⁵-9.5×10⁵ copies/g。【结论】所筛选的纤维化纤维微细菌MC29对于指导砂姜黑土区多功能秸秆促腐菌剂、微生物菌肥的研制及提升作物产量有一定的积极意义,并为探究其在砂姜黑土中的实际应用奠定基础。     

Geographic range, impact, and parasitism of lepidopteran species associated with the invasive weed Lantana camara in South Africa

Six isolates of Trichoderma were screened for antagonism to Armillaria in tea stem sections buried in the soil. The inability of Armillaria to invade Trichoderma-colonized stem sections and the reduction of its viability in the plant materials following invasion of these by Trichoderma were used as indicators of antagonism. Four isolates of the species Trichoderma harzianum significantly (P<0.001) reduced the incidence of the pathogen in the plant materials. Isolate T4 completely eliminated the pathogen from plant materials in sterile soil and also antagonized two different isolates of the pathogen in nonsterile soil. Application of this T. harzianum isolate to the soil as a wheat bran culture significantly (P<0.001) reduced viability of Armillaria in woody blocks of inoculum. Soil amendment with coffee pulp also reduced the inoculum viability but did not affect the incidence of Trichoderma in the blocks of inoculum. We conclude that the direct application of wheat bran-formulated T. harzianum into soil surrounding woody Armillaria inoculum sources can suppress the pathogen. Further, no organic amendment is needed to enhance development of the antagonist in the soil as a pre-requisite to suppressing the pathogen.     

Antagonistic actions of Pythium oligandrum and Trichoderma harzianum against phytopathogenic fungi (Fusarium oxysporum and Pythium ultimum var. ultimum)

Abstract

The possible biological control of damping-off fungi, Fusarium oxysporum and Pythium ultimum by Pythium oligandrum or Trichoderma harzianum was in vitro investigated. Results of comparing the antagonistic activity of P. oligandrum and T. harzianum in dual plates against the tested phytopathogens indicated different degrees of antagonism. After 12 days of incubation colony of the phytopathogenic fungus was completely overgrown by the antagonist, except for the interaction between T. harzianum and F. oxysporum which showed no overgrowth or any hyphal penetration by the antagonist. However, growth and proliferation of F. oxysporum colony was repressed. T. harzianum and P. oligandrum produced chitinase and β-1,3-glucanase when they were grown on liquid culture medium supplemented with chitin or fungal dried mycelium as a sole carbon source, and enzyme production was higher by T. harzianum comparing with P. oligandrum under the same condition. Fungal dried mycelium of F. oxysporum was the most selective carbon source for enzyme production, on the other hand, chitinase production was significant locked when P. ultimum dried mycelium was used as a carbon source. Production of volatile compounds by P. oligandrum or T. harzianum against F. oxysporum and P. ultimum was examined using the inverted plates method. F. oxysporum was inhibited by the antagonist volatile compounds and it is inhibited 100% by increasing the amount of inoculum size. Production of potential biocontrol agents provided with economically features and working under field conditions are recommended.     

Biological Control of Fusarium spp. in Cotton, Wheat and Muskmelon by Trichoderma harzianum

A new isolate of Trichoderma harzianum (T-35) was isolated from the rhizosphere of cotton plants from a field infested with Fusarium. Under glasshouse conditions, the antagonist was applied to soil growing in a bran/peat mixture (1:1, v/v) or as a conidial suspension or used as a seed coating. When T. harzianum was tested against Fusarium oxysporum f. sp. vasinfectum, F. oxysporum f. sp. melonis or F. roseum‘Culmorum”, a significant disease reduction, was obtained in cotton, melon and wheat, respectively. Biological control of Fusarium wilt of cotton was achieved when tested at two inoculum levels of the pathogen (2 × 10⁷ and 2 × 10⁸ microconidia/kg soil), decreasing the Fusarium spp. soil population. The long term effect of T. harzianum on Fusarium wilt of cotton was studied using successive plantings. The antagonist persisted in soil throughout three consecutive plantings, reducing the Fusarium, wilt incidence in each growth cycle. At the first planting the largest amount of preparation was found superior, whereas at the third planting, no significant difference could be observed between the four rates of Trichoderma preparation. T. harzianum (T-35) controlled Fusarium wilt in cotton and muskmelon when applied in both naturally or artificially infested alluvial vertisol and sandy-loam soils, respectively. Soil or seed treatments with the antagonist provided a similar disease control of F. roseum‘Culmorum’ and of F. oxysporum f. sp. melonis.     

<Emphasis Type="Italic">Trichoderma harzianum</Emphasis>: a biocontrol agent against <Emphasis Type="Italic">Bipolaris oryzae</Emphasis>

Rice brown spot, caused by Bipolaris oryzae, can be a serious disease causing a considerable yield loss. Trichoderma harzianum is an effective biocontrol agent for a number of plant fungal diseases. Thus, this research was carried out to investigate the mechanisms of action by which T. harzianum antagonizes Bipolaris oryzae in vitro, and the efficacy of spray application of a spore suspension of T. harzianum for control of rice brown spot disease under field conditions. In vitro, the antagonistic behavior of T. harzianum resulted in the overgrowth of B. oryzae by T. harzianum, while the␣antifungal metabolites of T.␣harzianum completely prevented the linear growth of B. oryzae. Light and scanning electron microscope (SEM) observations showed no evidence that mycoparasitism contributed to the aggressive nature of the tested isolate of T. harzianum against B. oryzae. Under field conditions, spraying of a spore suspension of T. harzianum at 10⁸ spore ml⁻¹ significantly reduced the disease severity (DS) and disease incidence (DI) on the plant leaves, and also significantly increased the grain yield, total grain carbohydrate, and protein, and led to a significant increase in the total photosynthetic pigments (chlorophyll a and b and carotenoids) in rice leaves.     

微生物菌剂对秸秆降解及秸秆中微生物变化规律的影响

为明确不同微生物菌剂对秸秆降解率及秸秆降解过程中秸秆周围微生物变化规律的影响，在温室大棚内进行不同微生物菌剂降解秸秆试验。以玉米秸秆为基质，设玉米秸秆（对照组）、玉米秸秆+哈茨木霉（Trichoderma harzianum）（处理1）、玉米秸秆+哈茨木霉+地衣芽胞杆菌(Bacillus licheniformis)（处理2）三个处理。研究结果显示，单独用哈茨木霉处理可显著提高秸秆降解率，前期作用尤其明显；在秸秆降解的前30 d，秸秆降解率与秸秆中可培养真菌、细菌、放线菌呈显著正相关。不同微生物菌剂对秸秆中可培养微生物数量变化有显著影响，单独接种哈茨木霉后，秸秆中可培养真菌、细菌、放线菌数在前30 d显著高于对照组和混合菌剂处理，不同处理可培养活菌数均在90～120 d达到峰值，然后开始下降。研究结果表明，不同微生物菌剂对秸秆降解有显著影响，单独用哈茨木霉处理可显著提高秸秆降解率；不同处理对秸秆中可培养真菌、细菌、放线菌的影响有显著差异。可为秸秆降解与微生物相关性研究提供参考。     

The reactions of susceptible and resistant tomato cultivars to strains of Verticillium albo-atrum

Three strains of Verticillium albo-atrum causing severe wilt of tomato (T), progressive (Hp ) and fluctuating (HF) wilt of hop, were inoculated through the roots of four tomato cultivars at different inoculum concentrations. Symptoms were assessed visually 42 days after inoculation, and quantitatively on the change in total leaf area compared with controls. Distribution of mycelium and tyloses was determined by sections at 2 cm intervals of root, stem and petiole. Cultivars Loran Blood and Moscow showed resistance to disease expression at all levels of inoculum concentration with the T strain. Bonny Best and Potentate were both susceptible to this strain, but whereas in Potentate, disease severity increased from mild to severe with increase in inoculum concentration, Bonny Best was severely diseased at the lowest level of inoculum. All cultivars showed some susceptibility to the HP and HF strains; the ‘resistance’ of Loran Blood and Moscow was no longer apparent and Bonny Best was most severely affected. The relative susceptibilities to the strains were HF Bonney Best > Loran Blood > Potentate > Moscow, HP Bonny Best > Loran Blood, Moscow > Potentate, T Bonny Best > Potentate > Loran Blood, Moscow. In general, vascular colonization was less in the cultivars Loran Blood and Moscow with all three fungal strains at io⁵propagules/ml level of inoculum, but this was not always correlated with an increase in disease severity. With the exception of the host-pathogen combinations Bonny Best/T, Bonny Best/HF, Potentate/T and Moscow/T, increasing the inoculum concentration to 10⁷propagules/ml increased disease severity but had little or no effect of increasing vascular colonization. In Bonny Best/T, Bonny Best/HF and Potentate/T vascular colonization was reduced with the higher level of inoculum. Moscow showed complete resistance to symptom expression and little vascular colonization with the T strain at 10⁵prop./ml. At 10⁷prop./ml resistance was maintained but there was very extensive growth of mycelium in the vessels. Tylosis resulted from an interaction of host, fungal strain and the level of inoculum and was not always correlated with the degree of vascular colonization. Contrary to previous reports the resistant varieties Loran Blood and Moscow developed acute disease symptoms after inoculation with HP and HF and these were associated with a high level of tylosis rather than mycelial growth. Tylosis and disease severity but not mycelial growth increased with higher levels of inoculum. The results suggested that susceptibility to Verticillium wilt was a complex response depending on host cultivar, fungal strain and the initial inoculum concentration. In some cultivar-pathogen combinations susceptibility was directly proportional to the amount of mycelium present in the vessels, while in others a physiological resistance mechanism independent of the degree of colonization appeared to operate. In a third category, increased disease development rather than resistance was associated with high levels of tylosis.     

Genes Involved in Cyclic Lipopeptide Production Are Important for Seed and Straw Colonization by Pseudomonas sp. Strain DSS73

Survival in natural bulk soil and colonization of sugar beet seeds and barley straw residues were determined for Pseudomonas sp. strain DSS73 and Tn5 mutants in amsY (encoding a peptide synthetase involved in production of the cyclic lipopeptide amphisin) and gacS (encoding the sensory kinase of the two-component GacA/GacS regulatory system). No differences in survival or growth in response to carbon amendment (citrate) were observed in bulk soil. However, both mutants were impaired in their colonization of sugar beet seeds and barley straw residues by an inoculum established in the bulk soil. The two mutants had comparable colonization phenotypes, suggesting that amphisin production is more important for colonization than other gacS-controlled traits.     

Effect of Trichoderma harzianum on microelement concentrations and increased growth of cucumber plants

The potential of the biocontrol agent Trichoderma harzianum strain T-203 to induce a growth response in cucumber plants was studied in soil and under axenic hydroponic growth conditions. When soil was amended with T. harzianum propagules, a 30% increase in seedling emergence was observed up to 8 days after sowing. On day 28, these plants exhibited a 95 and 75% increase in root area and cumulative root length, respectively, and a significant increase in dry weight (80%), shoot length (45%) and leaf area (80%). Similarly, an increase of 90 and 30% in P and Fe concentration respectively, was observed in T. harzianum inoculated plants. To better characterize the effect of T. harzianum during the early stages of root colonization, experiments were carried out in a gnotobiotic hydroponic system. An increased growth response was apparent as early as 5 days post-inoculation with T. harzianum, resulting in an increase of 25 and 40% in the dry weight of roots and shoots, respectively. Similarly a significant increase in the concentration of Cu, P, Fe, Zn, Mn and Na was observed in inoculated roots. In the shoots of these plants, the concentration of Zn, P and Mn increased by 25, 30 and 70%, respectively. Using the axenic hydroponic system, we showed that the improvement of plant nutritional level may be directly related to a general beneficial growth effect of the root system following T. harzianum inoculation. This phenomenon was evident from 5 days post-inoculation throughout the rest of the growth period, resulting in biomass accumulation in both roots and shoots.     

Gypsum Biomineralization in Sulphide-rich Hardpans by a Native Trichoderma harzianum Rifai Strain

Natural acid mine drainage affects abandoned sulfide mines worldwide, causing hardpan formation and heavy metal leaching. Hardpans are characterized by very low permeability, thus representing a significant limiting factor for oxygen and water circulation in the rhizosphere. Our work shows the results concerning the gypsum biomineralization capability of a native Trichoderma harzianum Rifai strain in sulfide -rich hardpans. Two months after the fungal inoculum, hardpan clasts resulted, completely covered by T. harzianum mycelium, where newly formed gypsum crystals occur. Our study provided the first evidence about interaction between T. harzianum and sulfide -mineralized hardpans as well as about its influence on gypsum genesis.     

Effect of aromatic plant species on vesicular-arbuscular mycorrhizal establishment in Pistacia terebinthus

The inoculation of Pistacia terebinthus with vesicular-arbuscular mycorrhizal (VAM) fungi and the spread of the infection were studied using a mixed cropping system, under glasshouse conditions, with Salvia officinalis, Lavandula officinalis and Thymus vulgaris colonized by Glomus mosseae as an inoculation method. This method was compared with soil inoculum placed under the seed or distributed evenly in the soil. Indirect inoculation with all the aromatic plants tested significantly increased VAM root colonization of P. terebinthus compared with the use of soil inoculum, although the effect on plant growth was different for each one of the aromatic species used as inoculum source. Inoculation with L. officinalis and T. vulgaris were the best treatments resulting in high VAM colonization and growth enhancement of P. terebinthus.     

Improvement of antagonistic capability of Trichoderma harzianum by UV-Irradiation for management of Macrophomina phaseolina

Antagonistic capability of Trichoderma harzianum was improved through UV-irradiation. Four different type of mutants, T. harzianum - M_a (Th-M_a), T. harzianum - M_b(Th-M_b), T. harzianum - M_c (Th-M_c), T. harzianum - M_d (Th-M_d) of T. harzianum and the parent strain (Th-P) were selected for further studies. Th-M_a and Th-M_b showed more antagonistic capability against Macrophomina phaseolina than its parent strain Th-P in dual culture. Biochemical analysis of these four mutants and the parent strain showed that Th-M_a releases higher level of two lytic enzymes i.e. chitinases and cellulases and Th-M_b produces more β-1,3-glucanase activity than the parent strain. Culture filtrate of Th-M_a also showed antifungal properties. Study of the competitive saprophytic ability (CSA) of these four mutants and the parent strain were also made. Th-M_a exhibited higher CSA than the parental isolate while Th-M_d had less CSA than all other mutants and the parent strain of T. harzianum.     

Recombinant and wild-type Pseudomonas aureofaciens strains introduced into soil microcosms: effect on decomposition of cellulose and straw

The effect of a genetically engineered Pseudomonas aureofaciens (Ps3732RNL11) strain (GEM) and the parental wild-type (Ps3732RN) on decomposition of cellulose paper, straw and calico cloth was assessed after 18 weeks incubation in laboratory soil microcosms. Effect(s) of inoculum density (10³, 10⁵, and 10⁸ cells/ g dry soil) and single versus multiple bacterial inoculations were also investigated. Cellulose paper was completely decomposed after 18 weeks in all treatments. There were no significant differences (95% level), between treatments, in percentage decomposition of either straw or calico cloth. Recovery of the GEM at 18 weeks, using viable plating, was limited to treatments originally receiving 10⁸ cells/g dry soil. Log 1.8 CFU/g dry soil were recovered from the single dose treatment while log 4.2 CFU/g dry soil were recovered from the multiple dose treatment Biolog metabolic tests were used to determine if the GEM or parental wild-type had any effect on overall carbon utilization in soil. Results suggested they did not. Detection of the recombinant lacZY gene sequence in soil using PCR suggested the possibility of viable but nonculturable cells and/or persistence of chromosomal DNA.     

Effect of soil texture and its organic content on the efficacy of Trichoderma harzianum (MIAU 145 C) in controlling Meloidogyne javanica and stimulating the growth of kidney beans

The efficiency of Trichoderma harzianum (MIAU 145 C) in promoting kidney bean (cv. Goli) growth in different soil texture (sandy loam, loam and clay loam) and organic matter content (0.5 and 2% of leaf litter) was assessed in a factorial experiment in the absence of Meloidogyne javanica. In another factorial experiment, the effect of soil texture, soil organic content and control measure (no control, 10?ml of T. harzianum containing 10⁶ spore ml^?1 and 2?mg ai cadusafos kg^?1 soil) was determined on nematode-infected kidney bean’s growth, fungus controlling activity and M. javanica reproduction. Except for the shoot length, the fungus improved plant growth. Clay loam was not a proper soil type for the cultivation of kidney bean plants (even in the soil without nematode), but the plant grew better in sandy loam and loam soil. The presence of leaf litter in the soil enhanced plant growth, increased fungal efficiency and increased nematode reproduction. It seems that T. harzianum can activate the plant defence system in sandy loam soil. T. harzianum was more effective in sandy loam or loam soil containing 2% organic matter (leaf litter) and reduced the reproduction factor of the nematode in the tested soil textures equally to the chemical nematicide treatment.     

Phytoextraction of soil cadmium and zinc by microbes-inoculated Indian mustard (Brassica juncea)

Abstract

A pot experiment was carried out to evaluate the effect of Pseudomonas fluorescens and Trichoderma harzianum inoculation on the uptake of zinc (Zn) and cadmium (Cd) by Indian mustard (Brassica juncea) from the soil having three different concentrations of Zn (300, 600, 900 mg/kg) and Cd (5, 10, 15 mg/kg) separately. Microbial inoculation resulted in significantly better plant growth, available metal content and their uptake than control (without microbes). Available Zn was enhanced, ca.1.6- and 1.4-fold and Cd ca. 2.5- and 1.8-fold, by P. fluorescens and T. harzianum, respectively. P. fluorescens resulted in an increase in Zn uptake by 113.9, 51.9 and 58.4% and T. harzianum by 42.6, 32.1 and 33.9% over control from soils having 300, 600 and 900 mg Zn, respectively, while of the corresponding results for Cd were 110.2, 48.9 and 58.1% with P. fluorescens and 42.6, 30.9 and 33.4% with T. harzianum from soil having 5, 10 and 15 mg Cd, respectively, after 90 days of treatment. In general the rate of metal uptake was higher during the initial 30 days and declined later.     

Enhanced growth and nutrition of micropropagated Ficus benjamina to Glomus mosseae co-inoculated with Trichoderma harzianum and Bacillus coagulans

A greenhouse investigation was conducted to study the influence of the arbuscular mycorrhizal (AM) fungus Glomus mosseae and the plant growth-promoting rhizomicroorganisms (PGPRs) Bacillus coagulans and Trichoderma harzianum on the growth and nutrition of micropropagated Ficus benjamina plantlets. The AM fungus was inoculated either singly or in combination with the PGPRs. Plants showed maximum plant height, biomass, P content, mycorrhizal root colonization, spore numbers and populations of T. harzianum and B. coagulans in root zone soil when all the three organisms were inoculated together. Thus, when G. mosseae co-inoculated with PGPRs enhances growth and nutrition of Ficus benjamina. T. harzianum and B. coagulans are thus designated as mycorrhizal helper organisms.     

Mycolytic effect of extracellular enzymes of antagonistic microbes to Colletotrichum falcatum,red rot pathogen of sugarcane

Strains of selected bacteria and Trichoderma harzianum isolated from sugarcane rhizosphere and endosphere regions were tested for the production of chitinolytic enzymes and their involvement in the suppression of Colletotrichum falcatum, red rot pathogen of sugarcane. Among several strains tested for chitinolytic activity, 12 strains showed a clearing zone on chitin-amended agar medium. Among these, bacterial strains AFG2, AFG 4, AFG 10, FP7 and VPT4 and all the tested T. harzianum strains produced clearing zones of a size larger than 10 mm. The antifungal activity of these strains increased when chitin was incorporated into the medium. Trichoderma harzianum strain T5 showed increased levels of activity of N-acetylglucosaminidase and -1,3-glucanase when grown on minimal medium containing chitin or cell wall of the pathogen. Lytic enzymes of bacterial strains AFG2, AFG4, VPT4 and FP7 and T. harzianum T5 inhibited conidial germination and mycelial growth of the pathogen. Enzymes from T. harzianum T5 were found to be the most effective in inhibiting the fungus. When mycelial discs of the pathogen were treated with the enzymes, electrolytes were released from fungal mycelia. The results indicated that antagonistic T. harzianum T5 caused a higher level of lysis of the pathogen mycelium, and the inhibitory effect was more pronounced when the lytic enzymes were produced using chitin or cell wall of the pathogen as carbon source.     

An integrated approach to managing Rhizoctonia solani on maize in marginal soils: field studies

Abstract

A study was conducted over two seasons in a marginal soil with an acid saturation of 54%. A plant growth promoting rhizobacterium, Bacillus megaterium, a commercial biocontrol agent, Trichoderma harzianum Strain kd (Eco-T^®), and soluble potassium silicate were used in this study. The objective was to control maize yield reduction caused by Rhizoctonia solani AG2 root rot isolated from infected maize. R. solani reduced maize yields significantly by 34% in the first season. However, the losses decreased in the second season from 34% to 10%. In the first season, combination of T. harzianum, B. megaterium and potassium silicate increased maize yields by 130%. The highest yield in the presence of R. solani was treatments with T. harzianum (216%) followed by T. harzianum plus potassium silicate (214%) and lastly T. harzianum plus B. megaterium (178%). However, in the second season, T. harzianum plus potassium silicate treatment resulted in the highest yields.     

Biological control of anthracnose of chilli with rhizosphere and rhizoplane fungal isolates from grasses

The fungal species from rhizosphere and rhizoplane of perennial grasses of the Western Ghats of India were studied for their pathogenicity, antagonism in vitro, substrate and root colonization abilities, rhizosphere competence, growth in different soil pH and inoculum shelf-life. Out of 138 non-pathogenic fungal isolates tested, 85 were antagonistic in vitro to chilli anthracnose pathogen Colletotrichum capsici. Fifteen isolates with >60% inhibition zone to pathogen culture had saprophytic and root and rhizosphere colonization abilities. The sorghum grain inocula of test antagonistic fungi- Fusarium oxysporum, Chaetomium globosum and Trichoderma harzianum had the shelf-life of 90 days at 20?±?2?°C and required optimum soil pH of 6.5. The above fungal isolates when tested for biocontrol of anthracnose disease in greenhouse and field caused reduction in seedling mortality and decreased disease incidence and severity at various plant growth stages and significant reduction in chilli fruit and seed infection. The test antagonistic fungi promoted seedling and mature plant growth and increased fruit and seed yield. Populations of these antagonistic fungi were fairly high in chilli rhizosphere at harvest. The present study indicated that antagonistic fungi from grass rhizosphere and rhizoplane could be used to control anthracnose and promote plant growth, and increase yield of chilli in field.     

Effect of peat-bran inoculum ofTrichoderma species on biological control ofRhizoctonia solani in lettuce

A range of known biocontrol or plant growth-stimulating species ofTrichoderma orGliocladium were grown on peat-bran substrate to yield between 5×10⁷–3×10¹⁰ colony forming units (cfu's)g^–1 substrate after 14 days growth. Inocula were incorporated into peat:sand potting compost infested withRhizoctonia solani to give 7–8 × 10⁴ cfu's of antagonist g^–1 compost and assessed for biological control activity using lettuce seedlings. Six of the eight antagonists decreased daming-off and three of these consistently increased yield in comparison withR. solani treatment alone.Subsequently, peat-bran inoculum ofT. harzianum isolate TH1 was incorporated at 0.5% w/v intoR. solani infested potting compost. Both autoclaved and nonautoclaved inoculum ofT. harzianum TH1 decreased disease and increased yield. Incorporation of ethyl acetate-extracted autoclaved inoculum ofT. harzianum TH1 resulted in similar levels of biocontrol and improved plant growth as did incorporation of nonautoclaved and autoclavedT. harzianum TH1 inoculum. The need to standardize inocula and controls is emphasized.