Screening the antifungal properties of essential oils against Phytophthora colocasiae

Recently Microbicidal and micro-static activities of naturally obtained botanicals have been extensively explored, generally in response to the devastating apprehension of consumers towards the safety of edible products. However, scientists are paying more interest in using bio pesticides and phytochemicals that constitute environmentally favorable, non-toxic, long-lasting, and productive substitutes for preventing many hazardous plant pathogens. This research aimed to investigate the antifungal capabilities of sage and tea tree essential oils towards taro leaf blight, the most important cause of worldwide production losses. Using synthetic fungicides is a rapid and effective approach for controlling plant diseases, but it also creates human health risks, environmental threats, and chances of pathogen resistance. The essential oils of sage and tea tree were obtained by microwave-assisted hydro-distillation, and their chemical components were analyzed using FTIR spectroscopy. The main components of the oil were Thujone and Terpinen-4-ol, in sage and tea, respectively. A casual disease agent isolated from symptomatic taro leaves is used as a test fungus and identified as Phytophthora colocasiae. The antifungal properties of both essential oils were evaluated against mycelium, sporangium, zoospores, leaf necrosis, and corm lesions. Repeated experiments showed that the minimum concentrations for obtaining 100% inhibition of mycelium, zoospore germination, sporangia formation, and leaf necrosis were estimated at 2.5 and 5.0 mg/mL of sage and tea tree oils, respectively. Outcomes of this study provide an allusion for the prevention and curation of plant diseases promptly, economically, and environmentally by using phytochemicals and plant essential oil derivatives.

Biological Management of Colocasia Blight Incited by Phytophthora colocasiae using Native Strains of Antagonists in North Western Himalayas

Background: Colocasia is cultivated globally for its edible corm and leaves. Leaf blight incited by Phytophthora colocasiae is the most destructive disease of colocasia. The current study aims at biological management of the disease. Methods: Nine Trichoderma isolates from the colocasia rhizosphere soil along with five designated isolates of Trichoderma spp. already available in the Department of Plant Pathology, CSK HPKV, Palampur were tested in vitro for antagonistic activity against P. colocasiae. Similarly, six unidentified bacterial strains isolated from colocasia phylloplane and available Pseudomonas fluorescens were evaluated for antagonistic activity against P. colocasiae under in vitro conditions. The bioagents found best under in vitro conditions were evaluated in vivo. Result: Trichoderma isolate Ti-6 was found significantly superior bioagent as it resulted in 72.9 per cent mycelial growth inhibition of P. colocasiae followed by Ti-5 (63.2%), Ti-4 (60.1%) and Ti-1 (54.5%). Amongst bacterial antagonists, Pseudomonas fluorescens gave maximum mycelial growth inhibition of 50.5 per cent followed by Pb-3 (31.4%) and Pb-6 (30.5%). The efficacy of five Trichoderma spp isolates viz., Ti-6, Ti-5, Ti-4, Ti-1, T. viride and one bacterial isolate of P. fluorescens found effective under in vitro were also evaluated in vivo using three delivery systems under net house condition. Corm treatment with bioagents was found superior for management of colocasia blight. Corm treatment with Ti-6 was found to be significantly superior to other treatments as 93.74 per cent of disease control was observed. For drenching, bioagent Ti-6 was proved best in managing blight disease (88.91%) followed by Ti-5 (88.90%). However, Ti-5 isolate of Trichoderma sp. as soil application was found superior with 90.02 per cent disease control.

Severity of Phytophthora leaf blight disease and susceptibility of two local varieties of Colocasia to Phytophthora colocasiae Raciborski in Nsukka zone of South Eastern Nigeria

Leaf-blight disease of Colocasia caused by Phytophthora colocasiae Raciborski has been a serious impediment to cocoyam production in Nigeria. Disease severity and susceptibility of the two most cultivated local varieties “Ugwuta” (Colocasia esculenta var. antiquorum) and “Nkashi Colocasia esculenta var. esculenta) were investigated. Disease severity was visually estimated as the percentage leaf surface affected by blight, lesion or lesion-related chlorosis for each leaf of a plant using a seven-point scale of 0, 5, 10, 25, 50, 75 and 100% in three locations: Ede-Oballa, Nsukka Urban and Obukpa. Susceptibility was assessed on 2 months old potted plants of each variety inoculated with a 7-day old culture of P. colocasiae. Diameters of lesions on inoculated leaves were recorded from the 3rd - 8th day after inoculation. Data on severity were subjected to ANOVA and susceptibility of the varieties was compared with t-test. Results revealed significant LSD=4.96 (0.05) and varying degrees of leaf blight severity among varieties and locations. Variety antiquorum had significantly higher severities of 42.08, 46.40 and 47.42% at Ede-Oballa, Nsukka Urban and Obukpa respectively, compared to 34.85, 36.55 and 28.19% recorded by var. esculenta at these locations, respectively. Similarly, var. antiquorum had greater lesion diameter ranging from 0.65±0.07 cm - 3.70±0.14 cm and average diameter of 2.4±0.16cm compared to var. esculenta which had 0.41±0.14cm - 3.12±0.19 cm and average diameter of 1.80±0.16. This research has shown that varieties and locations affect the severity and susceptibility of Phytophthora leaf blight disease. This could be a guide to farmers having known that var. esculenta is less severe to Phytophthora leaf blight disease.

Mating-Type and Sexual Differentiation of Phytophthora Colocasiae in Japan

In Japan, Phytophthora colocasiae causes the leaf blight of taro, which has resulted in huge losses since 2015. To investigate the causes of disease persistence and expansion, it is important to clarify the basic properties of this pathogen. We collected in total 317 P. colocasiae isolates from 99 fields in 7 prefectures during 2014 to 2020. The mating-type of each isolate was examined, and two or more isolates which were collected in single fields or taro leaves were selected to analyze the mating-type complexity. We found five kinds of mating types were identified: heterothallic A1 and A2, self-fertile (SF) A1, A2 and A1/A2 types, and a complex and diverse distribution of mating-types was present in one field or leaf. In addition, the stability of each mating-type was analyzed by single hyphae, zoospore and zoosporangium. The results suggested that the SF isolates were shown to be genetically unstable, while heterothallic isolates had a stable property. In the pathogenicity test of different mating-type isolates, heterothallic A1 isolates were less pathogenic than heterothallic A2 and SF isolates. However, there was no relationship between the pathogenicity and the growth rate on culture medium.

Efficacy of Methanolic and Aqueous Extracts of Thevetia peruviana (pers.) K. Schum on Growth of Phytophthora colocasiae Racib, Causal Agent of Taro Late Blight in Cameroon

This study aims to evaluate the antifungal activities of methanolic and aqueous extracts of Thevetia peruviana seeds on the in vitro growth of Phytophthora colocasiae. A randomized sample block design containing four treatments (T-: absolute control, AE, ME and Callomil Plus at the dose of 12.5 μL/ml) with three repetitions was used. Plant extracts were used at three concentrations: C1: 12.5 µl/ml; C2: 25 µl/ml and C3: 50 µl/ml. The study took place in the University of Yaoundé 1, Faculty of Sciences, Department of Plant Biology, Laboratory of Phytopathology and Crop Protection, and in the Institute of Agricultural Research for Development (IARD) of Yaoundé, Laboratory of Phytopathology, during the year 2019-2020. Aqueous and methanolic extracts of T. peruviana were prepared and used at the concentrations of 12.5, 25 and 50 μL/ml. P. colocasiae was isolated from infected taro leaf cultivars "Macumba/Ibo coco" located in three different regions in Cameroon: West, Littoral and Centre. The different leaf explants of taro were put in V8 agar medium and maintained in pure culture. Mycelial fragments of P. colocasiae of about 0.8 cm in diameter were cut and placed in sterile Petri dishes containing Potato Dextrose Agar (PDA) medium supplemented with different concentrations of plant extracts and incubated at 23±1°C for seven days for the evaluation of the radial growth. Methanolic and aqueous extracts have completely inhibited the growth of West and Littoral strains at 25 μL/mL while total inhibition of the pathogen was not obtained with strain of Centre region. The lowest inhibition was obtained with the strain of Centre region (85.1%) for aqueous extract and (70.95%) for methanolic extract compare to 100% for West and Littoral region at highest concentration. The aqueous extract at the concentration of 25 μL/ml totally inhibited the in vitro radial growth of some strains of P. colocasiae. This extract, active against P. colocasiae could be used as alternative to fungicides for the control of taro leaf blight. In other hand, the strain of Littoral region was most sensible to extracts than the others. This strain could be used to provide a genetic resource for future trials in natural conditions in greenhouse and in the field.

Antifungal potential of cinnamon essential oils against Phytophthora colocasiae causing taro leaf blight

Background Taro leaf blight, caused by a severely destructive oomycete fungus Phytophthora colocasiae, is responsible for threatening yield loss worldwide. The pathogen has the ability to germinate and spread rapidly to other plants during favorable conditions resulting in acute decline and even death, causing 100% crop loss. Farmers usually rely on highly toxic systemic fungicides to control the disease, which is effective, but residual effects and resistance of these agrochemicals is still a concern. Recently as returning to nature people tend to use chemical-free products, especially edible stuff produced in organic agriculture. Therefore, the use of bio-pesticides and phytochemicals is gaining special attention by scientists as they are ecofriendly non-hazardous, sustainable, and potent alternatives to control many virulent plant pathogens The present research was conducted to assess the antifungal potential of cinnamon essential oils against P. colocasiae. Materials and methods The essential oils from cinnamon bark were extracted using microwave-assisted hydrodistillation equipment, and then their chemical constituents were evaluated using ATR FTIR spectroscopy. The antifungal potential of essential oil was assessed against mycelium, sporangia, zoospore, leaf necrosis, and corms lesions under laboratory conditions at, 0.156, 0.312, 0.625, 1.25, 2.5, 5.0 mg/mL concentrations. Hymexazol was used as positive control and no essential oil as negative control, while each treatment have three replications and experiment repeated twice. Results The main component of oil was identified as cinnamaldehyde. The pathogen isolated from infected taro leaves was identified as P.colocasiae and then was used as a test fungus in the current study. Repeated experiments show maximum inhibition percentage of mycelial growth, zoospore germination, and sporulation of the fungus were observed at 0.625 mg/mL, whereas leaf necrosis was 100% inhibited at 1.25 mg/mL concentration. Conclusion This research can be a reference for easy, cost-effective and environment-friendly management and control of taro leaf blight with phytochemicals and plant essential oil derivatives. Graphic abstract

Genome Sequence Resource of Phytophthora colocasiae from China Using Nanopore Sequencing Technology

Phytophthora colocasiae is a destructive oomycete pathogen of taro (Colocasia esculenta), which causes taro leaf blight. To date, only one highly fragmented Illumina short-read-based genome assembly is available for this species. To address this problem, we sequenced strain Lyd2019 from China using Oxford Nanopore Technologies (ONT) long-read sequencing and Illumina short-read sequencing. We generated a 92.51-Mb genome assembly consisting of 105 contigs with an N50 of 1.70 Mb and a maximum length of 4.17 Mb. In the genome assembly, we identified 52.78% repeats and 18,322 protein-coding genes, of which 12,782 genes were annotated. We also identified 191 candidate RXLR effectors and 1 candidate CRN effectors. The updated near-chromosome genome assembly and annotation resources will provide a better understanding of the infection mechanisms of P. colocasiae.

Evaluation of Fungicide against Taro Leaf Blight Disease Caused by Phytophthora colocasiae in Three Agro-Ecological Zones of Cameroon

Globally the taro leaf blight (Phytophthora colocasiae) disease causes between 50 to 70% yield loss. Four taro landraces were planted in three agroecological zones of Cameroon; the Western Highlands (Bambui), Mono-Modal Humid Forest (Ekona), and the Bimodal Humid Forest (Nkolbisson) and evaluated for taro blight severity in four successive growing seasons in March and July, 2018 and 2019. Different concentrations of copper oxide (600 g)–Metalaxyl (120 g) fungicide were applied to control taro blight before and during plant growth. Results showed that, in all the field sites, the disease severity of Phytophthora colocasiae greatly decreased below 1.5 with varying concentrations of copper oxide (600 g)–Metalaxyl (120 g) fungicide applied at two-week intervals. The control field at Ekona recorded the highest taro blight severity of 7.8. There was no significant difference in taro blight severity (P≤0.05) between landraces treated with the different concentrations of copper oxide (600 g)–Metalaxyl (120 g) fungicide. Therefore, lower concentrations (0.33% and 0.27%) of copper oxide (600 g)–Metalaxyl (120 g) can be effectively used in the pre and post control of taro blight in the field. All the landraces in the screen house experiments were susceptible to P. colocasiae. In all the zones, Landrace L2 (red petiole small leaves) was highly resistant to P. colocasiae and should be recommended to farmers for optimum taro production in the three agro-ecological zones and zones with similar characteristics.