Effect of fluorescent pseudomonades and Trichoderma sp. and their combination with two chemicals on Penicillium digitatum caused agent of citrus green mold.

Citrus green mold (Penicillium digitatum) causes economic losses. Chemical fungicides such as imazalil provide the primary means for controlling green mold decay of citrus fruits. Continuous use of fungicides has faced two major obstacles- increasing public concern regarding contamination of perishables with fungicidal residues, and proliferation of resistance in the pathogen populations. The aim of this research was to determine if the attacks of green mold on orange could be reduced by usage of biocontrol agent alone or in combination with low dosage of imazalil or sodium bicarbonate. Pseudomonas fluorescens isolate PN, P. fluorescens isolate PS and Trichoderma virens isolate TE were evaluated as potential biological agents for control of green mold of oranges caused by P. digitatum. Increasing concentration of SB decreased spore germination of P. digitatum. In laboratory tests, a cell suspension (10(8) cells per ml.) of bacterial strains reduced the incidence of green mold. On fruits surface biocontrol activity of antagonistic isolates was significantly increased when combined with low dosage of imazalil (500ppm) or sodium carbonate (5%). Effect of Trichoderma virens on controlling P. digitatum was better than others with or without these chemicals.

Composition and antifungal activity of essential oils of Mentha piperita and Lavendula angustifolia on post-harvest phytopathogens.

The general antifungal activity of essential oils is well documented. The advantage of essential oils is their bioactivity in the vapor phase, a characteristic that makes them attractive as possible fumigants for stored product protection. Essential oils of aerial parts of Mentha piperita and Lavendula angustifolia were obtained with hydrodistillation and oils composition identified with GC-MS. Menthanol (36.24%) and menthone (32.42%) were the major compounds of the M. piperata essential oil. The essential oil of L. angustifolia was rich in linalool (49.2%) , linalyl acetate (12.3%), Lavendul acetate (6.5%), 4-terpineol (5.9%). Fungal toxicity of the essential oils were evaluated against three pathogenic fungi (Rhizopus stolonifer, Botrytis cinerea and Aspergillus niger) in vitro. Plate assayes showed that the different concentrations of essential oils have antifungal activity against these fungi, and the essential oil of L. angustifolia showed stronger fungistatic activity. Lavendula oil exhibited complete growth inhibition of all pathogens at 1000 ppm and minimum EC50 (311.24 ppm) resulted on B. cinerea.

Chemical composition and antifungal activity of the essential oils of three species of Artemisia on some soil-borne phytopathogens.

Various species of the genus Artemisia are used for their pharmacological, antimicrobial, antioxidant activity. Three species of this genus, Artemisia scoparia, A. sieberi and A. aucheri are widely distributed in desert area of Iran. In order to identify the chemical composition, aerial parts of A. scoparia, A. sieberi and A. aucheri were collected from Bajestan (Khorasan province) at flowering stage. The essential oils were obtained by hydro-distillation of air-dried samples and their chemical composition identified by GC-MS. Oxygenated monoterpens were the major components of the oils of three species. alpha-thujone (81.7%), beta-thujone (14.5%) and 1,8-cineol (1.9%) were the major compounds in the essential oil of A. scoparia. The essential oil of A. aucheri was rich in linalool (44.1%), gernyl acetate (10.7%), (E)-citral (9.7%) and (Z)-citral (7.7%), and the essential oil of A. sieberi was rich in beta-thujone (19.8%), alpha-thujone (10.5%), camphor (19.5%), verbenol (9.7%), p-mentha-1,5-dien-8-ol (6.4) and davanone (5.8%). The essential oils of the three species were tested for their antifungal activity against some soil-borne pathogenic fungi. Results of bioassay showed that the oils of A. aucheri and A. sieberi has stronger antifungal activity. Minimum EC50 (41.406 microL/L), resulted from A. aucheri on Rhizoctonia solani. The oil of A. sieberi showed fungistatic activity against, Tiarosporella phaseolina (MIC = 1000 microL/L, EC50 = 203.419 microL/L), Fusarium moniliforme (MIC=750 microL/L, EC50 = 211.072 microL/L), Fusarium solani (MIC = 750 microL/L, EC50 = 188.134 microL/L) whereas against R. solani (MIC = 250 microL/L, EC50 = 121.798 microL/L) exhibited high fungicidal activity.

Changes in specific activities of peroxidase, chitinase and phenylalanine ammonia-lyase and phenolic content in cucumber leaves inoculated with Podosphaera fusca, the causal agent of powdery mildew.

In this investigation, the effects of powdery mildew disease [caused by Podosphaera fusca (syn. Sphaerotheca fuliginea)] on specific activities of several defense-related enzymes and phenolic content were studied in cucumber leaves. Spore suspension of the fungus was sprayed on cucumber (cv. Super Dominus) plants in greenhouse and leaves from both inoculated and non-inoculated control plants were sampled at 0, 24, 48, 72 and 144 hours after inoculation (HAI). Spore germination and tissue colonization of P. fusca were microscopically studied on the inoculated surface of leaf samples. Further, Phenolic content (PHE) and specific activities of peroxidase (POX), chitinase (CHI) and phenylalanine ammonia-lyase (PAL) were spectrophotometrically measured in leaf extracts. Time-course of disease progress on the leaf surface showed that maximum spore germination occurred within 24 HAI and host penetration and disease development process began during 24-48 HAI. Evaluation of enzyme activities showed that POX specific activity in inoculated plants significantly increased at 72 HAI onwards and reached 2.5 times of that of control at 144 HAI. CHI specific activity showed a transient reduction in inoculated plants between 48-72 HAI and thereafter increased significantly in relation to control. PAL specific activity in inoculated plants was not significantly different from that of control. PHE in inoculated plants showed a significant increase compared to control at 48 HAI and thereafter. Comparison of time-course of disease progress with changes in enzyme activities indicated that POX activity had an increasing trend during disease progress whereas CHI activity showed a transient decrease at the early stages and then increased during the later stages of infection: PAL activity did not show any changes during the infection and PHE increased at the early stages of infection process and remained constant at rest of the time.

Effects of Acibenzolar-S-methyl on the specific activities of peroxidase, chitinase and phenylalanine ammonia-lyase and phenolic content of host leaves in cucumber-powdery mildew interaction.

One of the properties of systemic acquired resistance in plants is its concomitance with the biochemical changes including enhancement of activities of defense-related enzymes. In this study, the effects of Acibenzolar-S-methyl (ACI) on the some of defense responses of the cucumber plants (healthy or inoculated with spore suspension of Podosphaerafusca, the causal agent of cucumber powdery mildew) were surveyed via in vivo tests. Changes of defense responses in ACI-treated cucumber plants, inoculated with pathogen or not, were studied and compared with those of non-treated control plants. Results indicated that specific activity of peroxidase increased significantly in treated plants. Increase in enzyme activity was higher in pathogen-inoculated than non-inoculated plants, thus pathogen attack stress to plant plays a role in enhancement of enzyme activity. Specific activity of phenylalanine ammonialyase showed no changes in ACI-treated non-inoculated plants, but in inoculated plants it Increased due to interaction between ACI treatment and pathogen attack stress. Specific activity of chitinase increased in both inoculated and non-inoculated ACI-treated plants at 24 hours after treatment onwards, and pathogen attack stress did not affect it. Phenolic content of ACI-treated plant tissues, despite of small fluctuations, did not show any definite pattern of changes.