Trichoderma harzianum : A Biocontrol Agent Effective Against

ELAD, Y., 1. CHET, and J. KATAN. 1980. Trichoderma harzianum: A biocontrol agent effective against Sclerotium rolfsii and Rhizocionia solani. Phytopathology 70:119-121. An isolate of Trichoderma harzianum capable of lysing mycelia of The wheat bran preparation of T. harzianum increased growth of bean Sclerotium rolfsii and Rhizoctonia solani was isolated from a soil naturally plants in a noninfested soil and it controlled S. rolfsii more efficiently than a infested with those pathogens. In culture, T. harzianum grew better than S. conidial suspension of the same antagonist. An uninoculated wheat bran rolfsii and invaded its mycelium under growth conditions adverse to the preparation increased disease incidence. In naturally infested soils, wheat pathogen; eg, high pentachloronitrobenzene concentrations, high pH bran preparations of T harzianum inoculum significantly decreased levels, or low temperatures. Under greenhouse conditions, incorporation of diseases caused by S. rolfsii or R. solani in three field experiments with the wheat-bran inoculum preparation of T harzianum in pathogen-infested beans, cotton, or tomatoes, and they significantly increased the yield of soil significantly reduced bean diseases caused by S. rolfsii, R. solani, or beans. both, but its biocontrol capacity was inversely correlated with temperature. Additional key words: integrated control, PCNB. Biological control of soilborne plant pathogens by the addition vertisol soil (30% sand, 17.5% silt, 52% clay, and 0.5% organic of antagonistic microorganisms to the soil is a potential matter; pH 7.95) either artificially or naturally infested with S. nonchemical means for plant disease control. The species of rolfsii. Trichoderma capable of hvperparasitizing pathogenic fungi, are Artificial infestation of soil was accomplished by adding S. rolfsii highly efficient antagonists (2,5). Weindling (12) reported the sclerotia from a 10-day-old dried SM-agar culture. Unless parasitism of Trichoderma lignorum (Tode) Harz on Sclerotium otherwise stated, final sclerotial concentration was 0.1 g (dry rolfsii Sacc. and Rhizoctonia solani Kiihn. This effect was also wt)/kg soil. shown, under field conditions, by Wells et al (13) using T. The antagonistic fungus was grown on a wheat bran: sawdust: harzianum grown on ryegrass. Similarly, Backman and Rodrigueztap water mixture (3:1:4, v/v) autoclaved for 1 hr at 121 C, on 2 Kabana (1) controlled S. rolfsii in peanuts by using molassessuccessive days. Autoclavable plastic bags, containing this enriched clay granules as a food base for T. harzianum. Recently, medium, were inoculated with T. harzianum and incubated in Hadar et al (6) found that T. harzianum directly attacked R. solani illuminated chambers for 14 days at 30 C. The T. harzianum mycelium. Wheat-bran-grown cultures of this antagonist added to preparation (65% moisture), at various concentrations, was mixed soil in greenhouse plantings reduced damping-off caused by R. with the soil before planting. Experiments with beans (Phaseolus solani in beans, tomatoes, and eggplants. The efficiency of vulgaris L. 'Brittle Wax') were carried out in plastic boxes (9 X 9 X Trichoderma was improved when integrated with pentachloro10 cm) each containing 500 g of soil. Greenhouse temperatures were nitrobenzene (PCNB) at sublethal doses (3). kept at 23-30 C and treatments in all experiments were replicated In the present study, an antagonistic strain of T. harzianum six times in randomized blocks. capable of controlling both S. rolfsii and R. solani was isolated Conidial suspension was prepared from an SM-agar-grown from pathogen-infested soil and its behavior was studied under culture of Trichoderma. Numbers of conidia (haemocytometer laboratory, greenhouse, and field conditions. count) were adjusted to those of the wheat-bran T. harzianum preparations. MATERIALS AND METHODS Field experiments. The wheat-bran preparation of T. harzianum inoculum was mixed with the soil to a depth of 7-10 cm with a Fungi were isolated from the soil on Martin's agar medium as rotary hoe. Three experiments were conducted, all in a naturally described (8). Their antagonistic activity towards pathogens was infested alluvial soil and in a six-replicate, randomized block design. determined according to the method of Dennis and Webster (4), In the first experiment (T. harzianum preparation concentration but using a solidified synthetic medium (SM) (10). Different pH 150 g [fr wt]/m ) beans (cultivar Tender green) were sown on 21 levels were obtained by the addition of 0.1 N NaOH or 0.1 N HC1 to September 1978, in three 12-m rows. In the second experiment (7T. the medium before sterilization. PCNB as Terraclor (75% a.i. Olin harzianum inoculum preparation concentration 30 g [fr wt]/ m of Chemicals, Little Rock, AR 72200) was added to SM agar before row), cotton (Gossypium hirsutum L. 'SJ') was sown 2 June 1978 sterilization. in a 5-m row in a commercial cotton field. The percentage of Greenhouse experiments. These were carried out in an alluvial diseased plants was recorded on 1 July 1978. In the third experiment (T harzianum preparation concentration 50 g [fr wt]/_M_2), tomatoes (Lycopersicon esculentun Mill 'VF 317') were 0031-979X/80/02011903/$03.00/0 sown 20 April 1978, in a 10 X 3.6-m plot and the percentage of 01980 The American Phytopathological Society diseased plants was recorded on 20 August 1978. Analysis of Vol. 70, No. 2,1980 119 variance was used for statistical analysis. The significance level of culture media. A disc of mycelium from the zone where S. rolfsii P = 0.05 was used throughout. grew was therefore removed daily at various distances from the meeting line of the two fungi, and transferred to SM agar in order RESULTS to determine the presence of T harzianum. T. harzianum progressed faster through the S. rolfsii mycelium at lower Antagonistic activity. Fungi were isolated from a field soil temperatures (<27 C) and at high PCNB concentrations or high pH naturally infested with both S. rolfsii and R. solani. Of the 150 levels which were more favorable for growth of T. harzianum. isolates tested, it was mainly the Trichoderma spp. that were Greenhouse studies. A wheat bran inoculum preparation of T. antagonistic to S. rolfsii, and usually this was expressed as a strong harzianum was added to S. rolfsii-inoculated soil sown with beans. lysis of the mycelium. A more efficient biological control of the pathogen was achieved at One isolate, identified as T. harzianum Rifai aggr. (11) was used higher concentrations of the T harzianum preparation and lower throughout this study. Its spectrum of antagonism, tested in concentrations of the S. rolfsii inoculum in the soil (Fig. 1). culture, was found to include R. solani and Pythiumr In another experiment, T harzianum (3 g/kg) was added to soil aphanidermatum Edson (Fitz), but not Fusarium oxysporum f. sp. naturally infested with pathogens capable of inducing damping-off. vasinfesctum, Sclerotium bataticola Taub, Sclerotinia sclerotiorum Thereafter, beans were sown in this soil. The proportion of plants (Lib.) de Bary, Dematophora necatrix Hartig, Verticillium dahliae attacked by S. rolfsii in the control and the Trichoderma-treated Kleb., or a Phytophthora sp. This isolate of T. harzianum, soils were 47 and 8%, respectively; the corresponding data for therefore, differs from the one used by Hadar et al (8), its plants attacked by R. solani were 42 and 18%, respectively. In both antagonistic ability extends in addition to R. solani, P. cases, the differences between the treatments were statistically aphanidermatum, and S. rolfsii. significant. The efficiency of S. rolfsii control by T harzianum The growth rate of T. harzianum in culture was greater than that declined with the increase in temperatures (Fig. 2). of S. rolfsii at high PCNB concentrations (10-30 Ag/g culture Biological control by T harzianum depended on the type of medium) or pH levels (7.0--8.5), or at low temperatures. inoculum and the time of soil inoculation (Table 1). The wheat bran T. harzianum invaded S. rolfsii mycelium in encounters on agar preparation was much more efficient than the conidial suspension, especially in a delayed sowing. In contrast, autoclaved wheat bran, with or without autoclaved T. harzianum, increased the incidence TABLE 1. Effect of type of Trichoderma harzianum inoculum and time of of disease, caused by S. rolfsiiin beans by 21-46%, and wheat bran, application on biological control of a bean disease caused by Sclerotium inoculated with a mixture of microorganisms from a natural soil, rolfsii did not affect disease incidence at all. When the Trichoderma Diseased plants ( preparation was mixed with autoclaved wheat bran (1:3, w/w) its efficiency remained unimpaired. When applied to noninfested soil, Inoculum type the wheat bran preparation of T harzianum significantly increased Time of sowingy Not Conidial Wheat bran both the size and weight of bean plants (Table 2). Uninoculated (days) inoculated suspension preparation wheat bran, however, had no significant effect on the plants. 0 64 bz 45 c 20 e Field studies. Beans were sown in a soil naturally infested with S. 15 40 c 28 d 19 e rolfsiiand R. solani. Throughout the growth period, dead seedlings 30 80 a 43 c 4 f with typical symptoms of damping-off caused by either S. rolfsii or 'Number of days between T. harzianum application to soil and sowing. R. solani, were recorded. T harzianum significantly delayed the zNumbers followed by the same letter are not significantly different (P = progress and incidence of both diseases for 9 wk (Fig. 3). Eleven 0.05). There were six replications.