ANTIFUNGAL ACTIVITY OF CHITOSAN AGAINST Rhizopus stolonifer

These days instead of chemical pesticides, various natural alternatives have been used for the management of post-harvest diseases. This research was carried out to evaluate the antifungal potential of different chitosan concentrations viz., 5, 10, and 15 mg/µl against Rhizopus stolonifer by the agar dilution and well diffusion methods. The evaluation was carried out after seven days of incubation by measuring the inhibition of R. stolonifer mycelial growth. Results of the study revealed that the chitosan had a significant inhibitory effect on mycelial growth and maximum mycelial growth inhibition was reported at the 10 and 15 mg/µl concentrations and these two treatments are not significantly different. Based on these results, the best concentration (15 mg/µl) was further evaluated by the well diffusion technique. The average inhibition zones formed by the higher concentration was 25mm. Results of the study suggested that chitosan can be used for the management of post-harvesting diseases of tomatoes.

Iturin A Induces Resistance and Improves the Quality and Safety of Harvested Cherry Tomato

The soft rot disease caused by Rhizopus stolonifer is an important disease in cherry tomato fruit. In this study, the effect of iturin A on soft rot of cherry tomato and its influence on the storage quality of cherry tomato fruit were investigated. The results showed that 512 μg/mL of iturin A could effectively inhibit the incidence of soft rot of cherry tomato fruit. It was found that iturin A could induce the activity of resistance-related enzymes including phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), peroxidase (POD), glucanase (GLU), and chitinase (CHI), and active oxygen-related enzymes including ascorbate peroxidases (APX), superoxide dismutases (SOD), catalases (CAT), and glutathione reductase (GR) of cherry tomato fruit. In addition, iturin A treatment could slow down the weight loss of cherry tomato and soften the fruit. These results indicated that iturin A could retard the decay and improve the quality of cherry tomato fruit by both the inhibition growth of R. stolonifera and the inducing the resistance.

Restricted Nitrogen and Water Applications in the Orchard Modify the Carbohydrate and Amino Acid Composition of Nonpareil and Carmel Almond Hulls

Hull rot disease of almond (Prunus dulcis), caused by the fungus Rhizopus stolonifer, is prevalent in well maintained orchards where trees are provided plenty of water and nitrogen to increase the growth and yield. The predominantly grown variety Nonpareil is considered very susceptible to hull rot, while the pollinator variety Carmel is more resistant. Reduced nitrogen rates and restricted irrigation scheduling decreased the incidence and severity of hull rot in Californian orchards. As a part of our research, the hull composition of Australian almond fruits of Nonpareil and Carmel varieties, grown under two levels of irrigation (high and low) and two levels of nitrogen (high and low), were analysed using 1H NMR-based metabolomics. Both Nonpareil and Carmel hulls contained sugars such as glucose, sucrose, fructose and xylose, and amino acids, particularly asparagine. Variety was the major factor with Nonpareil hulls significantly higher in sugars and asparagine than Carmel. Within varieties, nitrogen influenced the relative concentrations of glucose, sucrose and asparagine. In Nonpareil, high nitrogen high water (the control) had relatively high glucose and asparagine content. High nitrogen low water increased the sucrose component, low nitrogen high water increased the glucose component and low nitrogen low water increased the sucrose and asparagine components. In Carmel, however, high nitrogen low water and low nitrogen high water increased sucrose and asparagine, and low nitrogen low water increased sucrose and glucose. Hull rot symptoms are caused by fumaric acid production by R. stolonifer growing within the hull. These changes in the hull composition under different nitrogen and water scenarios have the potential to affect the growth of R. stolonifer and its metabolite production in hull rot disease.

Engineered Nanomaterials Suppress the Soft Rot Disease (Rhizopus stolonifer) and Slow Down the Loss of Nutrient in Sweet Potato

About 45% of the world’s fruit and vegetables are wasted, resulting in postharvest losses and contributing to economic losses ranging from $10 billion to $100 billion worldwide. Soft rot disease caused by Rhizopus stolonifer leads to postharvest storage losses of sweet potatoes. Nanoscience stands as a new tool in our arsenal against these mounting challenges that will restrict efforts to achieve and maintain global food security. In this study, three nanomaterials (NMs) namely C60, CuO, and TiO2 were evaluated for their potential application in the restriction of Rhizopus soft rot disease in two cultivars of sweet potato (Y25, J26). CuO NM exhibited a better antifungal effect than C60 and TiO2 NMs. The contents of three important hormones, indolepropionic acid (IPA), gibberellic acid 3 (GA-3), and indole-3-acetic acid (IAA) in the infected J26 sweet potato treated with 50 mg/L CuO NM were significantly higher than those of the control by 14.5%, 10.8%, and 24.1%. CuO and C60 NMs promoted antioxidants in both cultivars of sweet potato. Overall, CuO NM at 50 mg/L exhibited the best antifungal properties, followed by TiO2 NM and C60 NM, and these results were further confirmed through scanning electron microscope (SEM) analysis. The use of CuO NMs as an antifungal agent in the prevention of Rhizopus stolonifer infections in sweet potatoes could greatly reduce postharvest storage and delivery losses.

Quitosanos y compósito quitosano-octanoato de sodio reducen la pudrición de fresa en poscosecha

La fresa (Fragaria x ananassa) es un alimento exquisito, que proporciona beneficios a la salud, por lo que es la frutilla de mayor producción y exportación en México. Sin embargo, es altamente perecedera, susceptible de sufrir daños en poscosecha, por Botrytis cinerea y Rhizopus stolonifer, entre otros. El uso de plaguicidas en precosecha es la estrategia de control de estos patógenos; no obstante, está documentado que los plaguicidas dañan la salud humana y al ecosistema, lo que muestra la necesidad de estudiar alternativas amigables. El quitosano grado reactivo (QGR) es un polímero inocuo con actividad antifúngica ampliamente reportada, mientras que el octanoato de sodio (8:0) (OS) también tiene esta propiedad; sin embargo, hasta el momento se desconoce si el quitosano grado comercial (QGC) disponible en México, tiene el mismo efecto. Por lo tanto, el objetivo de esta investigación fue evaluar la efectividad de QGR y el compósito QGR-OS en la protección de fresa en poscosecha y compararla con la de QGC y el compósito QGC-OS. Los compuestos se asperjaron sobre los frutos y se incubaron simulando las condiciones de exportación. Los resultados mostraron reducción significativa de la severidad y la incidencia de las enfermedades fúngicas de fresa en poscosecha luego de la aplicación de QGR, QGC y QGR-OS, QGC-OS, no así del OS aplicado solo. El QGC y el compósito QGC-OS son excelentes candidatos para ser utilizados en un estudio comercial de mayor alcance.

Nutritional changes induced by fungi on cowpea (Vigna unguiculata L. Walp) seeds

Seeds are usually infected by microorganisms and pests during storage, causing deterioration and reduction in the nutritive and market value of these seeds. In this study, the proximate composition of Vigna unguiculata seeds inoculated with different fungal organisms was determined to ascertain the level of deterioration caused by fungi on the seeds. The fungi used in the study were Botryodiplodia theobromae, Fusarium oxysporum, Rhizopus stolonifer and Aspergillus niger. There was a significant increase (p<0.05, 0.008) in the protein content of seeds inoculated with fungi. Fusarium oxysporum (29.45%) caused the highest increase in protein followed by Aspergillus niger (28.14%), Botryodiplodia theobromae (27.85%) and Rhizopus stolonifer (27.50%). The increase could be attributed to the proteineous content of the fungal mycelia. There was a significant increase (p<0.05, 0.005/0.014) in moisture and ash content of inoculated seeds respectively. Fusarium oxysporum caused the highest increase in ash (7.93) while Rhizopus stolonifer (5.4) caused the lowest increase. The increase in ash content is due to the presence of minerals like potassium and phosphorus in the mycelia of the fungi. There was a significant decrease (p<0.05, 0.019) in the carbohydrate, lipid, fibre and dry matter content of fungi-inoculated seeds when compared with the control. Fusarium oxysporum (36.6) caused the highest decrease while Rhizopus stolonifer (43.2) caused the lowest decrease in dry matter of inoculated seeds. Decrease in dry matter may be as a result of production of enzymes by these fungi.

Studies on Microbial Contaminants Associated with Arecanut Leaf Sheath Plates

Arecanut is being grown in an area of 2.71 lakh ha in Karnataka and contributes 65 per cent area to the country. Arecanut sheds the leaf sheath and they are widely used for consumption and packing of food in various occasions. The survey was conducted to know the microbial contaminants associated with leaf sheath plates and during the survey visited to 30 plates manufacturing units situated in Shivamogga and Davanagere districts in Karnataka. Randomly collected areca plates were used for laboratory study to know the contaminants. From these, fungal and bacterial contaminants were isolated and identified by cultural, morphological and biochemical studies. The result revealed that Rhizopus stolonifer, Penicillium citrinum, Aspergillus niger, Aspergillus flavus and Trichoderma harzianum and prevalence of Pseudomonas sp. (32×10-6 CFU/mL), Bacillus sp. (19×10-6 CFU/mL), Micrococcus sp. (12×10-6 CFU/mL) and E. coli (4×10-6 CFU/mL) were observed in contaminated plates under laboratory studies. The study concluded that the prevalence of fungi and bacteria may cause deleterious effects on human health is a chance factor. In future, it is required to concentrate on the sterilizing process which may prevent the health hazardous on human beings.