Chitosan controls postharvest anthracnose in bell pepper by activating defense-related enzymes.

Anthracnose, a postharvest disease caused by the fungus Colletotrichum capsici is the most devastating disease of bell pepper that causes great economic losses especially in tropical climates. Therefore, the objective of this study was to evaluate the antifungal properties of chitosan (low molecular weight from crab shell, Mw: 50 kDa and 75-85 % deacetylated) against anthracnose by inducing defense-related enzymes. The concentrations of 0, 0.5, 1.0, 1.5 and 2.0 % chitosan were used to control the fungus in vitro and postharvest. There was a reduction in C. capsici mycelial growth and the highest chitosan concentration (2.0 %) reduced the growth by 70 % after 7 days incubation. In germination test, the concentration of 1.5 and 2.0 % chitosan reduced spore germination in C. capsici between 80 % and 84 %, respectively. In postharvest trial the concentration of 1.5 % decreased the anthracnose severity in pepper fruit by approximately 76 % after 28 days of storage (10 ± 1 °C; 80 % RH). For enzymatic activities, the concentration of 1.5 and 2.0 % chitosan increased the polyphenol oxidase (PPO), peroxidase (POD) and total phenolics in inoculated bell pepper during storage. Based on these results, the chitosan presents antifungal properties against C. capsici, as well as potential to induce resistance on bell pepper.

Effect of a novel edible composite coating based on gum arabic and chitosan on biochemical and physiological responses of banana fruits during cold storage.

The composite effects of gum arabic (GA) (5, 10, 15, and 20%) and chitosan (CH) (1.0%) on the biochemical and physiological characteristics of banana fruits stored at 13 ± 1 °C and 80 ± 3% relative humidity (RH) for 28 days and afterward for 5 days at simulated marketing conditions (25 °C, 60% RH) were investigated. Significant (P ≤ 0.05) differences were observed for the entire GA plus CH treatments as compared to the control. However, the results showed that after 33 days of storage, the weight loss and soluble solids concentration of fruits treated with 10% GA plus 1.0% CH composite coating were 24 and 54% lower, whereas fruit firmness, total carbohydrates, and reducing sugars were 31, 59, and 40% higher than the control, respectively. Furthermore, the composite edible coating of 10% GA plus 1.0% CH delayed color development and reduced the rate of respiration and ethylene evolution during storage as compared to the control. Similarly, sensory evaluation results also proved the effectiveness of 10% GA plus 1.0% CH composite coating by maintaining the overall quality of banana fruits. Consequently, the results of scanning electron microscopy also confirmed that the fruits coated with 10% GA plus 1.0% CH composite edible coating had very fewer cracks and showed a smooth surface. These findings suggest that 10% GA plus 1.0% CH as an edible composite coating can be used commercially for extending the storage life of banana fruits for up to 33 days.

Use of quantitative PCR to understand within-host competition between two entomopathogenic fungi.

Interactions between the entomopathogenic fungi Zoophthora radicans and Pandora blunckii infecting larvae of Plutella xylostella were investigated. This is the first report to quantify within-host growth of one fungus in the presence of another competing for the same host resource using quantitative PCR (qPCR) at regular time points during the infection process. In larvae inoculated only with Z. radicans, there was a cumulative increase in the quantity of Z. radicans DNA throughout the time course of infection. However, in dual-inoculated larvae, there was an initial accelerated rate of growth of Z. radicans compared to when it was inoculated alone, but by the time of host death it had been effectively excluded by P. blunckii. The implications of these results for co-existence of these fungal pathogens in the field are discussed.

Competition and co-existence of Zoophthora radicans and Pandora blunckii, two co-occurring fungal pathogens of the diamondback moth, Plutella xylostella.

The entomopathogenic fungi Zoophthora radicans and Pandora blunckii co-occur in field populations of Plutella xylostella and, therefore, are likely to interact during the infection process. We have investigated the possible outcomes of these interactions in the laboratory. Using four isolates, two of each fungal species, inter-specific interaction experiments were done in Petri dishes and on intact plants. In Petri dish experiments, larvae were inoculated directly using sporulating mats of mycelium, both species had the same opportunity to infect and only the relative concentration of conidia of each pathogen species applied was manipulated. In the intact plant experiments, larvae were placed onto fungus-contaminated plants, inoculation was passive and the probability of infection by either or both species of fungi depended on larval activity and proximity to inoculum. In the Petri dish experiment, the species with the largest concentration of conidia out-competed the other regardless of virulence, and results were similar in the intact plant experiment. The ecological implications for competition or co-existence of these two pathogens in the field are discussed.

Development of species-specific diagnostic primers for Zoophthora radicans and Pandora blunckii; two co-occurring fungal pathogens of the diamondback moth, Plutella xylostella.

Species-specific primers for Zoophthora radicans and Pandora bluckii were developed. To achieve this, partial sequences of DNA that encode for rRNA, more specifically, the ITS region (rDNA-ITS) were obtained from different isolates and analysed. Seven Z. radicans isolates (four from P. xylostella, and three from other lepidopteran hosts) and one P. blunckii isolate (from P. xylostella) were used. These isolates were selected based on PCR-RFLP patterns obtained from 22 isolates of P. blunckii and 39 isolates of Z. radicans. All P. blunckii isolates were from the same host (P. xylostella); 20 isolates were from Mexico, one from the Philippines, and one from Germany. The Z. radicans isolates were more diverse in geographical origin (Mexico, Kenya, Japan, New Zealand, Australia, Taiwan, Philippines, Malaysia, Uruguay, France, USA, Poland, Indonesia, Switzerland, Israel, China, and Denmark) and host origin (Lepidoptera, Hemiptera, Hymentoptera, and Diptera). Using conventional PCR, each pair of species-specific primers successfully detected each species of fungus from DNA extracted from infected host larvae either single- or dual-inoculated with both fungal species. The PCR-RFLP analysis also showed that Z. radicans was genetically more diverse than P. blunckii, although only a limited number of P. blunckii isolates from one country were considered. There was no direct relationship between genetic diversity and host or geographical origin. The relationship between genetic variation within both fungal species and host specificity or ecological adaptation is discussed.

Immunolocalization of deformed wing virus particles within the mite Varroa destructor.

Deformed wing virus (DWV) induces wing deformation when bees are infected during their pupal development. Field observations and laboratory experiments suggest that the mite Varroa destructor is a vector of the virus. Moreover, it has been stated that DWV replicates within this mite. In order to understand the role of V. destructor in the transmission of DWV, the objective of this work was to locate the sites of retention and/or replication of DWV within the mite by immunohistochemistry. There was no evidence that DWV was replicating in the mite as no tissues showed specific antibody binding to DWV. Also, there were no specific structures that could be suggested as retention sites. DWV was found only in the midgut lumen of V. destructor in structures resembling large, dense spheres, which were presumably faecal pellets.

Laboratory evaluation of temperature effects on the germination and growth of entomopathogenic fungi and on their pathogenicity to two aphid species.

As part of an approach to select potential mycoinsecticides for aphid biocontrol, we investigated the effects of temperature on the growth, germination and pathogenicity of some hyphomycete fungi. Commercially available mycoinsecticides (based on Beauveria bassiana (Balsamo) Vuillemin and Verticillium lecanii (Zimmermann) Viegas) and other isolates of B bassiana, V lecanii, Metarhizium anisopliae (Metschnikoff) Sorokin and Paecilomyces fumosoroseus (Wize) Brown & Smith were evaluated. The rate of in vitro conidial germination of all isolates was slower at 10 and 15 degrees C than at 20 and 25 degrees C. Similarly, in vitro growth of most isolates was adversely affected at 10 and 15 degrees C. The greatest reduction at 10 degrees C in rates of conidial germination and colony growth, compared with other temperatures, was for M anisopliae isolates. Germination of V lecanii (isolate HRI 1.72) was fastest at 10 degrees C compared with the other fungi. It was also the most pathogenic of three isolates tested against Aphis fabae Scopoli and Myzus persicae Sulzer at 10, 18 and 23 degrees C. Generally, A fabae was more susceptible than M persicae to infection by the fungal isolates tested. A significant interaction between aphid species and temperature indicated that the pathogenic nature of an isolate was dependent not only on the target aphid species but also the temperature conditions of the bioassay. The series of studies, detailed above, allowed a temperature profile to be formed for the different isolates. Verticillium lecanii isolate HRI 1.72 (commercialised as Vertalec) was the most promising isolate selected from results of the series of experiments. Temperature profiles in conjunction with infectivity assays can be useful in selecting appropriate isolates for a particular thermal environment.