Exogenous application of phenylacetic acid promotes root hair growth and induces the systemic resistance of tobacco against bacterial soft-rot pathogen Pectobacterium carotovorum subsp. carotovorum.

Phenylacetic acid (PAA) was evaluated for its capability to promote plant growth and induce systemic resistance in tobacco (Nicotianum tabacum L cv. Xanthi) against the bacterial soft rot pathogen Pectobacterium carotovorum subsp. carotovorum (PCC). Exogenous application of PAA influenced root formation, the activities of defence-related enzymes and the expression of defence and growth-related genes. Increased formation of lateral roots can be observed in tobacco treated with higher PAA concentrations. The highest elicitation of induced systemic resistance (ISR) was found in plants treated with 0.5mM PAA, where the phytotoxic effect was minimal. The activities of the defence enzymes phenylalanine ammonia-lyase (PAL), peroxidase (POD) and polyphnenoloxidase (PPO) were modulated upon treatment with different PAA concentrations. Reverse transcription-PCR analyses showed that 0.5mM PAA modulated the expression of the growth-related genes NtEXP2 and NtEXP6, and the defence-related genes Coi1, NPR1, PR-1a and PR-1b. These results showed that different concentrations of PAA can elicit different responses and effects on tobacco growth and resistance. This study presents the important role of PAA not only on plant growth but also for plant immunity against phytopathogens.

Linoleic acid-induced expression of defense genes and enzymes in tobacco.

Linoleic acid (LA) is a naturally occurring fatty acid (FA) found to elicit induced systemic resistance (ISR) of tobacco against the bacterial soft rot pathogen, Pectobacterium carotovorum subsp. carotovorum (PCC). In this study, we examined effects of six doses of exogenous LA on the induction of defense genes and enzymes. The optimum ISR activity was observed in plants treated with 0.1mM LA where the effect of LA on membrane permeability was minimal. The application of LA as a root drench enhanced the activity of defense enzymes such as phenylalanine ammonia-lyase (PAL), peroxidase (POD), and polyphenol oxidase (PPO) and induced the expression of ß-glucuronidase (GUS). PAL and POD activities were increased in a concentration dependent manner while the maximum PPO activity was observed after treatment with 0.01mM LA. An RT-PCR analysis of the defense-related genes, Coi1, NPR1, PR-1a and PR-1b, of tobacco plants treated with 0.1mM LA revealed an association of LA with elicitation of ISR in tobacco.

Determinants of Plant Growth-promoting Ochrobactrum lupini KUDC1013 Involved in Induction of Systemic Resistance against Pectobacterium carotovorum subsp. carotovorum in Tobacco Leaves.

The plant growth-promoting rhizobacterium Ochrobactrum lupini KUDC1013 elicited induced systemic resistance (ISR) in tobacco against soft rot disease caused by Pectobacterium carotovorum subsp. carotovorum. We investigated of its factors involved in ISR elicitation. To characterize the ISR determinants, KUDC1013 cell suspension, heat-treated cells, supernatant from a culture medium, crude bacterial lipopolysaccharide (LPS) and flagella were tested for their ISR activities. Both LPS and flagella from KUDC1013 were effective in ISR elicitation. Crude cell free supernatant elicited ISR and factors with the highest ISR activity were retained in the n-butanol fraction. Analysis of the ISR-active fraction revealed the metabolites, phenylacetic acid (PAA), 1-hexadecene and linoleic acid (LA), as elicitors of ISR. Treatment of tobacco with these compounds significantly decreased the soft rot disease symptoms. This is the first report on the ISR determinants by plant growth-promoting rhizobacteria (PGPR) KUDC1013 and identifying PAA, 1-hexadecene and LA as ISR-related compounds. This study shows that KUDC1013 has a great potential as biological control agent because of its multiple factors involved in induction of systemic resistance against phytopathogens.

Biological control and plant growth promoting capacity of rhizobacteria on pepper under greenhouse and field conditions.

Plant growth promoting rhizobacteria Ochrobactrum lupini KUDC1013 and Novosphingobium pentaromativorans KUDC1065 isolated from Dokdo Island, S. Korea are capable of eliciting induced systemic resistance (ISR) in pepper against bacterial spot disease. The present study aimed to determine whether plant growth-promoting rhizobacteria (PGPR) strains including strain KUDC1013, strain KUDC1065, and Paenibacillus polymyxa E681 either singly or in combinations were evaluated to have the capacity for potential biological control and plant growth promotion effect in the field trials. Under greenhouse conditions, the induced systemic resistance (ISR) effect of treatment with strains KUDC1013 and KUDC1065 differed according to pepper growth stages. Drenching of 3-week-old pepper seedlings with the KUDC-1013 strain significantly reduced the disease symptoms. In contrast, treatment with the KUDC1065 strain significantly protected 5-week-old pepper seedlings. Under field conditions, peppers treated with PGPR mixtures containing E681 and KUDC1013, either in a two-way combination, were showed greater effect on plant growth than those treated with an individual treatment. Collectively, the application of mixtures of PGPR strains on pepper might be considered as a potential biological control under greenhouse and field conditions.