Efficacy of resistance inducers, free‐radical scavengers and an antagonistic strain of Pseudomonas fluorescens for control of Rhizoctonia solani AG‐4 in bean and cucumber

Abstract

Sixteen chemicals from different groups of known resistance inducers were tested as a soil drench in a humosoil : sand mix infested with an isolate of Rhizoctonia solani AG‐4. Among these, 5‐nitrosalicylic acid (2 mM aqueous solution), o‐acetylsalicylic acid (2 mM), 2,6‐dichloroisonicotinic acid (0.25 mM), 2‐aminoisobutyric acid (2 mM) and lichenin (2 mM) controlled pre‐emergence damping‐off and post‐emergence seedling mortality of bean cv. Dufrix, but gave little or weak and variable disease control in cucumber cv. Delikatess. Two‐component mixtures of these five chemicals controlled the disease effectively in bean, mixtures containing 2‐aminoisobutyric acid being the most effective, with seedling stands of up to 94% in infested soil. As none of these five chemicals (≤ 2 mM) reduced mycelial growth of R. solani on PDA plates, induced resistance in seedling tissues is implied in their disease control. Control was augmented in both hosts when any one of the five inducers was applied in a mixture with a cell suspension (1 × 109 cells mL−1) of an antagonistic fluorescent strain of Pseudomonas fluorescens; these mixtures showed additive effects and provided much better disease control in bean than in cucumber. The free‐radical scavengers (antioxidants) ascorbic acid, benzoic acid, gluconic acid lactone and thiourea inhibited R. solani growth in vitro and efficiently controlled both pre‐emergence damping‐off and post‐emergence seedling mortality of bean; ascorbic acid and benzoic acid also offered significant protection in cucumber. However, disease control values were reduced substantially when inducers were applied with antioxidants, because of strong antagonistic interactions in most of these mixtures. Probable mechanisms of disease control by 5‐nitrosalicylic acid, o‐acetylsalicylic acid, 2,6‐dichloroisonicotinic acid, 2‐aminoisobutyric acid and lichenin and their interactions with P. fluorescens and antioxidants are discussed.

Acibenzolar-S-metil na indução de resistência de tomateiro e controle deRhizoctonia solanikuhnin vitro

“…Resultado contrariofoi observado utilizando ASM na concentração de 2 mM, a qual reduziu em 50% o crescimento micelial de R. solani (KATARIA et al,1997).…”

“…A partir da descoberta do ASM, foi dado um grande passo no campo da indução de resistência, já que o composto deu o impulso necessário para que empresas se interessassem na fabricação de produtos a partir de compostos passíveis de serem patenteados (SOBRINHO et al, 2005). KATARIA et al (1997), observaram que o ASM na concentração de 2 mM reduziu em 50% o crescimento micelial de Rhizoctoniasolani. Em tomateiro a aplicação de ASM em conjunto com fungicidas (ASM + mancozeb alternado com difenoconazole e azoxystrobin) reduziu a severidade da doença pintapreta causada por Alternaria solani (TOFOLI e DOMINGUES, 2005).…”

Salicylic acid on the induction of resistance of tomato plants and control ofRhizoctonia solaniKuhnin vitro

“…The AS regulates the resistance mechanisms in the infection location through the systemic acquired resistance (RSA), which results on the synthesis of the phytoalexins and the PR proteins (HEIL; BOSTOCK, 2002). KATARIA et al (1997), observed that the salicylic acid and the chloro-salicylic acid inhibited 100% of the mycelial growth of Rhizoctonia solani in the concentration of 10 mM, while the acibenzolar-Smethyl reduced in 50% in the concentration of 2 mM.…”

“…Possibly, this result is related to the concentration studied, since in assessing the effect of AS under more elevated concentrations, it was observed that under the concentration of 10 mM, occurred 100% inhibition of mycelial growth of R. solani (KATARIA et al, 1997). According to Kuć (2001), the resistance inducers can present fungitoxic effect, depending on the concentration used and the pathogen assessed.…”

Efeito de indutores de resistência em cafeeiro contra a mancha de Phoma

“…O fungicida tebuconazole inibiu totalmente o crescimento micelial em todas as doses testadas. Kataria et al (9) observaram que o ASM na dose de 2mM reduziu em 50% o crescimento micelial de Rhizoctonia solani, enquanto que o ácido salicílico e o ácido clorosalicílico inibiram 100% do crescimento micelial na dose de 10mM. Grant et al (7) também observaram redução do crescimento micelial de isolados de Phytophthora infestans com dosagem a partir de 1mM de fosfito.…”