Biological control of Rhizoctonia solani in tomatoes with Trichoderma harzianum mutants

Biocontrol of Rhizoctonia solani in tomatoes cultivated under greenhouse and field conditions was analyzed using the Trichoderma harzianum mutants Th650-NG7, Th11A80.1, Th12A40.1, Th12C40.1 and Th12A10.1 and ThF2-1, respectively. Their innocuousness on tomato cultivars 92.95 and Gondola (greenhouse assays), and on cultivar Fortaleza (field assays) was established. Alginate pellets (1.7 g pellets/L soil) containing c.a1 x 10(5) colony forming units (cfu)/g pellet were applied to a soil previously inoculated with R. solani at transplant (greenhouse) or to a naturally infected soil (field). Controls considered parental wild strains, a chemical fungicide and no additions. Th11A 80.1, Th12A10.1 and Th650-NG7 prevented the 100% mortality of tomato plants cv. 92.95 caused by R. solani, and the 40% mortality in tomato plants cv. Gondola (greenhouse assays). Mortality reduction was reflected in canker level lessening and in plant parameters increases (development, fresh and dry weights). A different degree of susceptibility of tomato plants was observed, being Gondola cv. more resistant than 92.95 cv. to infection in a soil previously inoculated with R. solani. Tomato plants of cv. Fortaleza did not show mortality in naturally infected soils (field assays), where the mutant ThF2-1 reduced significantly the canker level caused by R. solani.

Biocontrol capacity of wild and mutant Trichoderma harzianum (Rifai) strains on Rhizoctonia solani 618: effect of temperature and soil type during storage

Wild (Th11, Th12 and Th650) and mutant (Th11A80.1, Th12A40.1, Th12C40.1 and Th650-NG7) Trichoderma harzianum strains were stored for 180 days at 5ºC or at 22ºC, in two types of soils. Strains recovered at 90, 120 and 180 days from the two types of soils, retained their full capacity to biocontrol Rhizoctonia solani 618, that produces crown and root rot of tomatoes. Recovery, estimated as colony forming units (cfu) of the wild and mutant strains, showed that all increased their cfu after storage independently of the type of soil and temperature, although kinetic behavior differed among strains. Ratios of recovery after storage in type B soil/ type A soil or at 22ºC/5ºC, higher or lower than one respectively, allowed to establish that Th11 and Th12 were the most appropriate strains for the biocontrol of R. solani in conditions where growth of the phytopathogen is optimal.

New strains obtained after UV treatment and protoplast fusion of native Trichoderma harzianum: their biocontrol activity on Pyrenochaeta lycopersici

The obtainment of 30 new strains from native Trichoderma harzianum after UV light irradiation (UV-A and UV-C), and of 82 strains resulted from protoplast fusion were accomplished. The new strains, initially selected for their growing rate under low temperature and high pH conditions, as well as for their innocuousness on tomato plants, were tested for in vitro inhibition of Pyrenochaeta lycopersici in dual cultures and due to secretion of volatile and diffusible metabolites. All the UV-A and UV-C selected candidate mutants were innocuous to tomato plants, but none of them showed improvement in their biocontrol activity on P. lycopersici. Th12A20.1 increased 1.3 and 1.9 fold the total fresh weight of Fortaleza tomato plants when compared to its parental strains Th12 and Th11, respectively. The selected candidate mutants obtained through protoplast fusion were also innocuous to tomato plants, but only ThF1-2 and ThF4-4 inhibited 1.3 fold (in dual cultures) and 5 fold (due to secretion of volatile metabolites) the growth of P. lycopersici, respectively, in relation to the mean inhibitory effect of both parents. Therefore, these candidate mutants could be included in experiments under field conditions.

Biocontrol of root and crown rot in tomatoes under greenhouse conditions using Trichoderma harzianum and Paenibacillus lentimorbus: additional effect of solarization

Trichoderma harzianum 650 (Th650) and Paenebacillus lentimorbus 629 (Pl629) selected earlier for their ability to control Rhizoctonia solani, Fusarium solani and F. oxysporum in vitro, were applied alone or combined with solarization (summer assay) and/or with methyl bromide (MeBr) (summer and winter assays) to a soil with a high inoculum level, for the control of tomato root rot caused by the complex F. oxysporum f. sp. lycopersici - Pyrenochaeta lycopersici - Rhizoctonia solani. Evaluations were also performed independently for root damage caused by P. lycopersici, and also for R. solani in the summer assay. MeBr decreased tomato root damage caused by the complex from 88.7 percent to 21.2 percent and from 78.4 percent to 35.7 percent in the summer and in the winter assay, respectively. None of the bio-controllers could replace MeBr in the winter assay, but Th650 and Pl629 reduced root damage caused by this complex in the summer assay. Treatments with bio-controllers were improved by their combination with solarization in this season. Independent evaluations showed that the positive control of Th650 towards R. solani and the lack of effect on P. lycopersici correlates well with the endochitinase pattern expressed by Th650 in response to these phytopathogens. Root damage caused by R. solani can be controlled at a similar level as it does MeBr in summer assays, thus representing an alternative to the use of this chemical fungicide for the control of this phytopathogen.

Identificación de grupos de anastomosis de cepas de Rhizoctonia solani K³hn, aisladas de tomates en la V Región de Chile / Rhizoctonia solani K³hn anastomosis groups identification of strains isolated from tomato crops at the V Region of Chile

Una de las enfermedades que ataca al tomate (Lycopersicon esculentum) en la V Región de Chile es Rhizoctonia solani, desconociendose a la fecha los grupos de anastomosis presentes en esta zona; por tal motivo, se estudiaron cepas del hongo obtenidas a partir de plantas enfermas. En las cepas estudiadas, se determinó la presencia de los grupos de anastomosis GA-4 y GA-2-1, ubicßndose cuatro en el grupo de anastomosis 4. Todas las cepas fueron virulentas, siendo la mes agresiva la cepa 618 perteneciente al GA-4 y la menos agresiva la 509 V perteneciente al GA-2-1. TambiÚn se estudió el efecto de la temperatura, pH y salinidad en las cepas de los dos grupos identificados. Las cepas del GA-4 crecieron mejor a una temperatura de 22°C con un pH entre 5 y 7 y con una salinidad cercana a 0 mM de NaCl, mientras que las GA-2-1 crecieron mejor a 20 °C con pH 7,0 y salinidad de 50 mM.

Identificación de Fusarium solani (Mart.) Sacc. como agente causal de la podredumbre del piÚ de tomate / Identification of Fusarium solani (Mart.) Sacc. as the causing agent of the foot rot in tomato

Se investigó la etiología de una pudrición basal y radical causada por Fusarium sp. en plantas de tomate enfermas en invernaderos fríos de la V Región de Chile. Se identificó como patógeno a Fusarium solani, hongo que ha sido descrito en otros países causando síntomas similares a los observados en este trabajo. Los síntomas en terreno y en las plantas inoculadas fueron: pudrición radical, podredumbre del pie y necrosis vascular.

Características de cepas chilenas de Pyrenochaeta lycopersici y perspectivas de control biológico / Characteristics of chilean Pyrenochaeta lycopersici strains and perspectives of biological control

Raíz corchosa es una de las principales enfermedades que afecta al cultivo de tomate que se produce bajo invernadero frío en Chile. En esta investigación se entregan antecedentes referentes a las principales características reproductivas de su agente causal, Pyrenochaeta lycopersici, como: picnidios, conidióforos y conidios. Ademßs, antecedentes sobre la estrategia de control biológico de esta enfermedad. En base a estudios preliminares, se determinó a Trichoderma harzianum, como el taxa mßs promisorio (según cultivos duales). Se caracterizaron cepas de ambas especies de acuerdo a crecimiento micelial a diferentes temperaturas, pH, y salinidad (NaCl). Finalmente, se efectuó un ensayo bajo condiciones controladas de invernadero, destacßndose la cepa Th11 como la mßs promisoria en el biocontrol de este patógeno.

Principales hongosfitopatógenos asociados a bulbos almacenados de ajo elefante (Allium ampeloprasum var. holmense) de la zona de Quillota y Nogales (Chile) / Main phytopathogenic fungi associated to stored bulbs of ajo elefante (Allium ampeloprasum var. holmense) from the zone of Quillota and Nogales (Chile)

Se presentan los primeros antecedentes fitopatológicos referentes a una prospección de hongos presentes en bulbos almacenados y plantas de Allium ampeloprasum var. holmense (ajo elefante) provenientes de las zonas de Quillota y Nogales (V Región). A partir de bulbos con diferentes lesiones, se realizaron aislamientos fúngicos correspondientes a los siguientes taxa: Penicillium hirsutum, P.aurantiogriseum, P.echinulatum, P.funicullosum, P.rugulosum, Fusarium oxysporum y Embellisia allii. Estos se inocularon para efectuar pruebas de patogenicidad; tanto en bulbos como en plantas en maceta (salvo Penicillium spp.). Los resultados obtenidos en bulbos almacenados indicaron que el principal problema en las muestras analizadas fue Penicilluim hirsutum, asociado a lesiones inicialmente hendidas, secas, rodeadas de un halo blanquecino, presentando al cabo de 7 días una pudrición blanda acuosa que involucraba la totalidad del bulbo, apareciendo posteriormente el moho azul en las lesiones. Los problemas de importancia secundaria para esta especie vegetal en la zona estudiada fueron Fusarium oxysporum y Embellisia allii. El principal problema en las plantas en maceta fue E.allii, el cual bajo condiciones de humedad previa y en períodos cercanos a la cosecha, afectó al bulbo cubriéndolo de un micelio negro.

The expression of extracellular fungal cell wall hydrolytic enzymes in different Trichoderma harzianum isolates correlates with their ability to control Pyrenochaeta lycopersici

Four isolates of Trichoderma harzianum (ThN3, Th11, Th12 and Th16) were selected for their ability to control the in vitro development of the tomato root pathogen Pyrenochaeta lycopersici. Analysis of the mechanisms involved in biocontrol showed that the formation of non-volatile metabolites appears to be one of those involved in biocontrol of P. lycopersici by all T. harzianum isolates tested. Nevertheless, the higher secretion of chitinases, both in number of isoenzymes and activity by the Th11 strain, correlated well with its higher ability to control this agent in laboratory and greenhouse experiments as compared to the other T. harzianum isolates tested. The secretion of ß -1,3-endoglucanases and/or proteases appeared to have less significance than endochitinases in the biological control of P. lycopersici