Aims: To investigate antifungal effect of thyme oil on Geotrichum citri‐aurantii arthroconidia germination and germ tube elongation, to reveal effects of thyme oil on morphological structures on fungal hyphae and arthroconidia and to assess potential bio‐control capacities of thyme oil against disease suppression in vivo conditions. Methods and Results: Thyme oil controlled the growth of G. citri‐aurantii effectively. Arthroconidia germination and germ tube elongation in potato dextrose broth was greatly inhibited by thyme oil. At 600 μl l−1, it inhibited the germination of about 94% of the arthroconidia and the germ tube length was only 4·32 ± 0·28 μm. Observations using light microscope, scanning electron microscope and transmission electron microscope revealed ultrastructural modifications caused by thyme oil that included markedly shrivelled and crinkled hyphae and arthroconidia, plasma membrane disruption and mitochondrial disorganization. Thyme oil applied to ‘Satsuma’ mandarin oranges that had been artificially wounded and inoculated with G. citri‐aurantii reduced sour rot from 78·1% among untreated control fruit to 14·1% after 5 days at 26°C. Thyme oil applied to intact fruits reduced the decay from 76% among untreated control fruit to 35% after 30 days at 20°C. Thyme oil treatment did not harm ‘Satsuma’ mandarin oranges when they were examined after treatment and storage at 20°C for 30 days. Conclusions: Thyme oil may provide an alternative means of controlling postharvest sour rot on citrus fruit. Significance and Impact of the Study: The use of such essential oil may constitute an important alternative to synthetic fungicides. They can be exploited in commercial production and applied under storage and greenhouse conditions.
Aims: This study was conducted to measure the efficacy of the marine antagonist Rhodosporidium paludigenum in the suppression of postharvest decay of Chinese winter jujube caused by Alternaria alternata and to explore the possible mode of action involved. Methods and Results: The efficacy of controlling postharvest diseases by R. paludigenum was examined. Rapid yeast colonization of wounds was observed during the first 48 h at 25°C. The yeast at 1 × 108 cells ml−1 of washed cells suspension provided better control of A. alternata than any other treatment. The concentration of the antagonist had significant effects on biocontrol effectiveness: as the concentration of R. paludigenum was increased, the disease incidence decreased. Meanwhile, R. paludigenum significantly inhibited the natural development of decay and did not damage fruit quality parameters including lightness values, hue angle, firmness, soluble solids, ascorbic acid and titratable acidity in 21 days’ storage at 25°C. Conclusions: Rhodosporidium paludigenum was effective in controlling postharvest decay of Chinese winter jujube and did not impair fruit quality parameters. Significance and Impact of the Study: Rhodosporidium paludigenum can be used as a nonchemical agent in postharvest biological control of Chinese winter jujube.
Aims: To investigate antifungal effects of two antagonistic yeasts on postharvest sour rot caused by Geotrichum citri‐aurantii in citrus and evaluate possible mechanisms. Methods and Results: Cell suspension of Cryptococcus laurentii at 108 to 109 cells per ml effectively reduced sour rot incidence from 55·6% among untreated control fruit to 29·9–20·7% after 5 days of incubation at 26°C. Application of cell‐free culture filtrate of C. laurentii was effective in reducing the sour rot, but the effectiveness was lower than that of the cell suspension (1 × 108 cells per ml). In addition, C. laurentii multiplied more rapidly than Rhodosporidium paludigenum at 26°C. The fruit inoculated with the two yeasts demonstrated changes in peroxidase and superoxide dismutase activity. Cryptococcus laurentii, in particular, was capable of inducing a striking response in treated citrus fruits. Conclusions: The antifungal ability of C. laurentii can be attributed to the competitions of nutrients and space, defensive responses and possible secretion of antibiotic compounds. Significance and Impact of the Study: The use of such antagonists may constitute an important alternative to synthetic fungicides for controlling postharvest sour rot in citrus.
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