This study was conducted to evaluate eco-friendly control agents (carvone, cuminaldehyde, and linalool) against Rhizoctonia solani, which causes root rot disease either by induction of defense response or direct antifungal activity. The induction of resistance was examined by detecting the transcription of defense genes and the effect of the tested control agents on the growth and the yield of common bean plants. The growth of R. solani was significantly inhibited after treatment with the tested compounds compared to the untreated control under laboratory conditions. The disease severity of root rot was decreased in common bean plants treated with the tested compounds compared to untreated control plants under greenhouse conditions. Common bean plants treated with the tested control agents expressed defense genes (Phenylalanine ammonia lyase and β-1,3-Glucanase) involved in jasmonic acid (JA) and salicylic acid (SA) signaling pathways with 2–5 fold higher than the control. Treatment of common beans with the tested control agents and fungicide significantly improved the growth and yield characteristics of common bean. Therefore, the use of monoterpenes could be a novel strategy to control this pathogen and consider the first report.
Fungal diseases have a significant role in the low productivity of common bean crops. The use of fungicides is the most effective solution to control fungal pathogens, but excessive and indiscriminate fungicide use causes negative effects on the plant and the ecosystem. The quick advancement of nanotechnology seems to offer a novel solution to controlling phytopathogens. Different concentrations of three nanoparticles, Ag2O-NPs, CuO-NPs, and CaO-NPs were tested individually against Sclerotium rolfsii, the cause of root and crown rots. A significant effect was observed at 50 µg/mL. Our findings showed that the commercial fungicide Rizolex-T 50 WP and CaO-NPs did not perform as well as Ag2O-NPs and CuO-NPs in reducing disease incidence and severity caused by S. rolfsii. However, the three tested nanoparticles improved crop yield, defense enzymes (catalase, peroxidase, and polyphenol oxidase), and characteristics of plant development.
Carrot (Daucus carota L.) is a member of family Apiaceae and is an important vegetable crop. Interestingly, a severe infection of leaf blight was detected on carrot cultivars in Qalubiya governorate, Egypt during the growing season in November 2019. Leaf blight was widely spread in the cultivated area. Initial symptoms were observed on the smaller leaflets such as a-water-soaked lesions, irregularly shaped and sized, dark brown to black numerous lesions without yellow halos, then with disease progress, the lesions expanded to involve entire leaves, causing the leaves to turn a brown color and ultimately collapsed, decayed and died (Figs. 1 & 2). Although, all carrot leaves can be attacked, however, older leaves are the most susceptible to infection. Disease incidence of 20-30% was observed in the affected carrot fields. It seems that the occurrence of the disease on carrot plants was generally related to high levels of soil moisture which was predominantly conformable to the tacky drainage systems of soil. Intense foliar infections resulted in decreasing productivity and reducing the effectiveness of manual harvesting. Therefore, the associated fungus was isolated from the margins of carrot leaves and roots using potato dextrose agar (PDA) amended with ampicillin and the plates were incubated at 26°C for one week. Subsequently, pure cultures were maintained using the single spore and/or the hyphal tip technique and preserved at 25°C for further studies. Characterization of the isolated fungus was carried out according to its cultural and morphological characteristics. Microscopic examinations demonstrated that conidia are dark olivaceous brown (Fig. 3). The conidia measured 20.3 -32.6 × 6.9 -12.4 µm, including a filamentous beak (7.8 -13.7 × 2 -3.9 µm) as well as the conidiophore was 30.2 -50.7 × 7.2 -9.3 µm. Accordingly, the isolated fungus was identified as Alternaria alternata (Fr.) Keissler. Moreover, pathogenicity tests were performed where leaf blight symptoms on inoculated healthy carrot plants were displayed again and Alternaria alternata was re-isolated and reidentified. Pathogenicity tests were performed in growth chambers under laboratory conditions using carrot root (Fig. 4 a and b) and under greenhouse conditions, using carrot seedlings at the five-leaf stage, by spraying healthy leaves with a conidial suspension 1 × 10 4 conidia /ml. Subsequently, inoculated plants were covered with polyethylene bags and incubated at 26°C with a 16 h photoperiod. Disease symptoms on carrot leaf were observed within 10 days post inoculation (Fig. 4C). The obtained symptoms were similar to those observed under natural infection conditions. Based on these results, Alternaria alternata (Fr.) Keissler is considered the causal agent of carrot leaf blight in Egypt. As the authors are far aware the current study is considered the first record of Alternaria leaf blight on carrot caused by Alternaria alternata (Fr.) Keissler under Egyptian conditions. The genomic DNA of the targeted fungus was isolated, and the amplified DNA...
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