Native Endophytic Pseudomonas putida as a Biocontrol Agent against Common Bean Rust Caused by Uromyces appendiculatus

This study aimed to evaluate the efficacy of endophytic bacterium to control common bean rust disease under greenhouse conditions. Endophytic bacterium Pseudomonas putida ASU15 was isolated from fresh asymptomatic common bean, identified using biochemical and molecular characteristics. In vitro, the inhibitory effect of different concentrations of P. putida (1 × 104, 1 × 105 and 1 × 106), as well as fungicide ortiva (0.01%) on uredospores germination of Uromyces appendiculatus were tested using water agar medium. The concentration showing the highest reduction of uredospores germination was at 1 × 106, while there was complete inhibition of uredospores germination associated with using ortiva. Scanning electron microscope exhibited the ability of P. putida cells to attack the cell wall of the fungal uredospores germ tubes of U. appendiculatus, causing obvious cell wall breakdown. The activities of chitinase, lipase, and protease produced by P. putida ASU15, in vitro, were evaluated spectrophotometrically. Chitinolytic, proteolytic, and lipolytic activities were exhibited, contributing 55.26, 3.87, and 26.12 U/mL, respectively. Under greenhouse conditions, treated plants with P. putida ASU15 (two days before pathogen inoculation or at the same time of pathogen inoculation) or fungicide reduced the disease severity, compared to the control. Applying P. putida ASU15 at the same time of pathogen inoculation showed reduction in disease severity (69.9%), higher than application before pathogen inoculation (54.9%). This study is considered the first report that demonstrates the mycoparasitic strategy of P. putida for controlling U. appendiculatus. In conclusion, our results revealed that P. putida ASU15 affords a significant disease reduction that may be attributed to direct suppression of pathogen spores germination.

Fungicidal Efficacy of Drying Plant Oils in Green Beans against Bean Rust (Uromyces appendiculatus)

As biorationals, plant oils offer numerous advantages such as being natural products, with low ecotoxicological side effects, and high biodegradability. In particular, drying glyceride plant oils, which are rich in unsaturated fatty acids, might be promising candidates for a more sustainable approach in the discussion about plant protection and the environment. Based on this, we tested the protective and curative efficacy of an oil-in-water-emulsion preparation using drying plant oils (linseed oil, tung oil) and a semi-drying plant oil (rapeseed oil) separately and in different mixtures. Plant oils were tested in greenhouse experiments (in vivo) on green beans (Phaseolus vulgaris L.) against bean rust (Uromyces appendiculatus). We observed that a 2% oil concentration showed no or very low phytotoxic effects on green beans. Both tested drying oils showed a protective control ranging from 53–100% for linseed oil and 32–100% for tung oil. Longer time intervals of 6 days before inoculation (6dbi) were less effective than shorter intervals of 2dbi. Curative efficacies were lower with a maximum of 51% for both oils when applied 4 days past inoculation (4dpi) with the fungus. Furthermore, the results showed no systemic effects. These results underline the potential of drying plant oils as biorationals in sustainable plant protection strategies.

RESISTANCE IN COMMON BEAN TO UROMYCES APPENDICULATUS UNDER FIELD AND GREENHOUSE CONDITIONS

Bean rust, caused by Uromyces appendiculatus, is a major disease in common bean which occurs annually in The Rhodope Mountains and sporadic in the plains of Bulgaria. The present study aims to find sources of resistance in common bean to the pathogen for using in a breeding program. The reaction of fifty-five Phaseolus vulgaris accessions to the pathogen was monitored under field condition. Infection type, disease intensity and area under the disease progress curve were calculated. Twelve common bean cultivars were inoculated with eight pathotypes of races 20-2, 20-16, and 20-18 in the greenhouse, and infection type was estimated. Twelve accessions had an immune reaction, eight accessions had resistant a reaction, two accessions had a middle resistant reaction, and seven accessions had a susceptible reaction to U. appendiculatus population in both field estimations. Five cultivars showed resistant phenotype to the eight pathotypes in the greenhouse, four of which were resistant in the field (Abritus, Beslet, Trakiya, and Prelom). Five cultivars had a susceptible or resistant reaction to the pathotypes of the same race, resulting from different interaction between resistant genes in the host and virulent genes in the pathogen. Nine accessions showed race-nonspecific resistance in the field expressed in low disease intensity and susceptible/resistant phenotype.

Identification of black bean (Phaseolus vulgaris L.) genotypes resistant to anthracnose and rust for Veracruz and Chiapas, Mexico

Objective: to determine the reaction of 53 lines and three varieties of black bean (Phaseolus vulgaris L.) to inoculation with Uromyces appendiculatus and Colletotrichum lindemuthianum, to identify genotypes resistant to rust and anthracnose.Design/methodology/approach: 10 seedlings of each genotype were inoculated in the greenhouse with a suspension of U. appendiculatus uredospores and another 10 with a suspension of C. lindemuthianum conidia. At 14 days after inoculation, the reaction of the genotypes to rust was evaluated with a severity scale of 1 to 6, and to anthracnose, with ascale of 0 to 4. The data were analyzed in a completely randomized design with 10 replications per treatment and LSD at 0.05 was applied for the separation of averages.Results: 41 genotypes showed a hypersensitivity reaction to rust, of which 25 had a reaction value of 2.0, statistically lower than those of controls. In turn, 45 genotypes were resistant to anthracnose, of which 18 had a value of 1.0, statistically similar to that of Negro Jamapa and lower than those of the rest of the genotypes.Study limitations/implications: due to the diversity of races of both pathogens, the genotypes were inoculated with monopustular isolates of the principal races of U. appendiculatus and with monosporic cultures of C. lindemuthianum, which occur in the bean crops of Veracruz and Chiapas.Findings/conclusions: 25 lines resistant to rust and 18 to anthracnose were identified, which stood out for presenting the least damage from these diseases.