​Management of Early Leaf Spot (Cercospora arachidicola) of Groundnut in Rajasthan

Background: Early leaf spot caused by Cercospora arachidicola Hori. is most destructive disease in all the groundnut growing areas of Rajasthan, under severe infestation it cause 30-50% losses in pod yield. Recently, Central Insecticide Board (CIB), Faridabade banned 27 pesticides including some important fungicides which are extensively used in plant disease management. Therefore, in the present investigation, our main emphasis was to find out some new fungicides for management of early leaf spot disease. Methods: Ten fungicides (hexaconazole 5% EC, difenconazole 25% EC, propiconazole 25% EC, tebuconazole 25.9% EC, trifloxystrobin 25% + tebuconazole 50% WG, mancozeb 50% WP, chlorothalonil 75% WP, carbendazim 50% WP, carbendazim 12% + mancozeb 63% WP and captan 70% + hexaconazole 5% WP) were evaluated against early leaf spot pathogen (C. arachidicola) both in lab as well as in field condition. The experiment was conducted at ARS, SKRAU, Bikaner during Kharif-2019 on most popular cv. HNG-69 in RBD design with the application of foliar spray of ten different fungicides at different concentrations against early leaf spot disease and compared with an untreated control. Result: Among all the fungicides used in the present investigation, Tebuconazole 25.9% EC was found most effective in inhibiting the mycelial growth of the pathogen followed by trifloxystrobin 25% + tebuconazole 50% WG. Under field condition, it gave maximum (70.73%) disease control with highest pod yield (31.5 q/ha) and net return (Rs 57,500/ha) when applied as foliar spray at 0.1% concentration followed by trifloxystrobin 25% + tebuconazole 50% WG at 0.2%. These treatments can provide an effective and economical management of early leaf spot disease for groundnut cultivators.

Synthesis, Antifungal Activity, 3D-QSAR, and Molecular Docking Study of Novel Menthol-Derived 1,2,4-Triazole-Thioether Compounds

A series of novel menthol derivatives containing 1,2,4-triazole-thioether moiety were designed, synthesized, characterized structurally, and evaluated biologically to explore more potent natural product-based antifungal agents. The bioassay results revealed that at 50 μg/mL, some of the target compounds exhibited good inhibitory activity against the tested fungi, especially against Physalospora piricola. Compounds 5b (R = o-CH3 Ph), 5i (R = o-Cl Ph), 5v (R = m, p-OCH3 Ph) and 5x (R = α-furyl) had inhibition rates of 93.3%, 79.4%, and 79.4%, respectively, against P. piricola, much better than that of the positive control chlorothalonil. Compounds 5v (R = m, p-OCH3 Ph) and 5g (R = o-Cl Ph) held inhibition rates of 82.4% and 86.5% against Cercospora arachidicola and Gibberella zeae, respectively, much better than that of the commercial fungicide chlorothalonil. Compound 5b (R = o-CH3 Ph) displayed antifungal activity of 90.5% and 83.8%, respectively, against Colleterichum orbicalare and Fusarium oxysporum f. sp. cucumerinum. Compounds 5m (R = o-I Ph) had inhibition rates of 88.6%, 80.0%, and 88.0%, respectively, against F.oxysporum f. sp. cucumerinu, Bipolaris maydis and C. orbiculare. Furthermore, compound 5b (R = o-CH3 Ph) showed the best and broad-spectrum antifungal activity against all the tested fungi. To design more effective antifungal compounds against P. piricola, 3D-QSAR analysis was performed using the CoMFA method, and a reasonable 3D-QSAR model (r2 = 0.991, q2= 0.514) was established. The simulative binding pattern of the target compounds with cytochrome P450 14α-sterol demethylase (CYP51) was investigated by molecular docking.

Evaluation of Leaf Spot Resistance in Wild Arachis Species of Section Arachis

Wild diploid Arachis species are potential sources of resistance to early (ELS) and late (LLS) leaf spot diseases caused by Passalora arachidicola (syn. Cercospora arachidicola Hori), and Nothopassalora personata (syn. Cercosporidium personatum (Berk. & Curt.) Deighton), respectively. Within section Arachis, limited information is available on the extent of genetic variation for resistance to these fungal pathogens. A collection of 78 accessions representing 15 wild species of Arachis section Arachis from the U.S peanut germplasm collection was evaluated for resistance to leaf spots. Screening was conducted under field (natural inoculum) conditions in Dawson, Georgia, during 2017 and 2018. Accessions differed significantly (P < 0.01) for all three disease variables evaluated, which included final defoliation rating, ELS lesion counts, and LLS lesion counts. Relatively high levels of resistance were identified for both diseases, with LLS being the predominant pathogen during the two years of evaluation. This research documents new sources of resistance to leaf spot diseases selected from an environment with high inoculum pressure. The presence of ELS and LLS enabled the selection of resistant germplasm for further introgression and pre-breeding.

Isolation and Characterization of Bacillus amyloliquefaciens TL6 as a Biological Control Agent for Peanut Early Leaf Spot Caused by Passalora arachidicola

Peanut early leaf spot caused by Passalora arachidicola (Cercospora arachidicola), is a worldwide common fungal disease in peanut leaves, which occurs in all production areas in China. To obtain biocontrol resources to control peanut early leaf spot, 60 healthy peanut leaves were collected from major peanut production areas in Liaoning Province. A total of 563 strains were screened from these leaves. Eighteen strains showed differing levels of resistance against P. arachidicola. Among these strains, strain TL6 inhibited the pathogen most strongly, and the diameter of inhibition zone was 64.3 mm. This strain was able to inhibit 10 other types of pathogens. It was identified as Bacillus amyloliquefaciens based on its morphological characteristics, physiological and biochemical reactions and a comparative analysis of its 16S rDNA sequence. The fermentation liquor of strain TL6 was effective at controlling peanut early leaf spot, and the field control effect was above 69.17% after spraying the fermentation liquid of TL6. The field control effect was more than 40.96% after spraying the fermentation liquid diluted 200 times. The field control effect of the TL6 fermentation liquid diluted 200 times and including the addition of 500 gL-1 carbendazim diluted 1000 times inhibited P. arachidicola by 81.33%. The combination of TL6 and carbendazim had a significant synergistic effect. This strain of B. amyloliquefaciens shows promise for commercial development and application.

Synthesis, Antifungal Activity, and 3D-QSAR Study of Novel Nopol-Derived 1,3,4-Thiadiazole-Thiourea Compounds

A series of novel nopol derivatives bearing the 1,3,4-thiadiazole-thiourea moiety were designed and synthesized by multi-step reactions in search of potent natural product-based antifungal agents. Their structures were confirmed by FT-IR, NMR, ESI-MS, and elemental analysis. Antifungal activity of the target compounds was preliminarily evaluated by in vitro methods against Fusarium oxysporum f. sp. cucumerinum, Cercospora arachidicola, Physalospora piricola, Alternaria solani, Gibberella zeae, Rhizoeotnia solani, Bipolaris maydis, and Colleterichum orbicalare at 50 µg/mL. All the target compounds exhibited better antifungal activity against P. piricola, C. arachidicola, and A. solani. Compound 6j (R = m, p-Cl Ph) showed the best broad-spectrum antifungal activity against all the tested fungi. Compounds 6c (R = m-Me Ph), 6q (R = i-Pr), and 6i (R = p-Cl Ph) had inhibition rates of 86.1%, 86.1%, and 80.2%, respectively, against P. piricola, much better than that of the positive control chlorothalonil. Moreover, compounds 6h (R = m-Cl Ph) and 6n (R = o-CF3 Ph) held inhibition rates of 80.6% and 79.0% against C. arachidicola and G. zeae, respectively, much better than that of the commercial fungicide chlorothalonil. In order to design more effective antifungal compounds against A. solani, analysis of the three-dimensional quantitative structure–activity relationship (3D-QSAR) was carried out using the CoMFA method, and a reasonable and effective 3D-QSAR model (r2 = 0.992, q2 = 0.753) has been established. Furthermore, some intriguing structure–activity relationships were found and are discussed by theoretical calculation.

Genetic Diversity of Cercospora arachidicola Associated with Peanut Early Leaf Spot in Shandong Province of China

Early leaf spot caused by Cercospora arachidicola is the major destructive foliar disease of cultivated peanut in Shandong province of China. Understanding the genetic variability of this pathogen is crucial for evolutionary comprehension and breeding strategies. The genetic diversity of C. arachidicola isolates obtained from different peanut growing regions of Shandong province were assessed using inter-simple sequence repeats (ISSR) markers. Thirteen ISSR primers generating polymorphic, clearly discernible and reproducible patterns were screened out for further analysis. A total of 113 distinct bands were amplified, of which 85.8% were polymorphic, suggesting high values of polymorphism among the isolates. Cluster analysis using UPGMA indicated that all the isolates tested were separated into three distinct generic groups. The genetic relatedness of C. arachidicola isolates roughly coincided with geographical origin. Analysis of molecular variance (AMOVA) revealed that the observed genetic variation mainly existed within populations, and the variation among populations was weak. This study characterized the genetic diversity of C. arachidicola isolates for the first time, which will provide necessary genetic information for effective management practices. © 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers © 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers© 2021 Friends Science Publishers©

Discovery of Cysteine and Its Derivatives as Novel Antiviral and Antifungal Agents

Based on the structure of the natural product cysteine, a series of thiazolidine-4-carboxylic acids were designed and synthesized. All target compounds bearing thiazolidine-4-carboxylic acid were characterized by 1H-NMR, 13C-NMR, and HRMS techniques. The antiviral and antifungal activities of cysteine and its derivatives were evaluated in vitro and in vivo. The results of anti-TMV activity revealed that all compounds exhibited moderate to excellent activities against tobacco mosaic virus (TMV) at the concentration of 500 μg/mL. The compounds cysteine (1), 3–4, 7, 10, 13, 20,23, and 24 displayed higher anti-TMV activities than the commercial plant virucide ribavirin (inhibitory rate: 40, 40, and 38% at 500 μg/mL for inactivation, curative, and protection activity in vivo, respectively), especially compound 3 (inhibitory rate: 51%, 47%, and 49% at 500 μg/mL for inactivation, curative, and protection activity in vivo, respectively) with excellent antiviral activity emerged as a new antiviral candidate. Antiviral mechanism research by TEM exhibited that compound 3 could inhibit virus assembly by aggregated the 20S protein disk. Molecular docking results revealed that compound 3 with higher antiviral activities than that of compound 24 did show stronger interaction with TMV CP. Further fungicidal activity tests against 14 kinds of phytopathogenic fungi revealed that these cysteine derivatives displayed broad-spectrum fungicidal activities. Compound 16 exhibited higher antifungal activities against Cercospora arachidicola Hori and Alternaria solani than commercial fungicides carbendazim and chlorothalonil, which emerged as a new candidate for fungicidal research.

RESEARCHES ON REPORTING THE ATTACK OF SOME PEANUTS DISEASES CULTIVATED ON SANDY SOILS

Peanuts (Arachis hypogaea L.) are widely grown as a food and oleaginous species. Cultivation of peanuts offers important economic benefits, but one of the most important challenges that growers confront is the fight against destructive diseases. Culture is susceptible to a variety of pathogens, such as bacteria, fungi, viruses, and nematodes, resulting in low yields and degradation of grain quality. Among the most devastating fungal diseases of peanuts are Cercospora arachidicola, Puccinia arachidis, Sclerotium rolfsii which cause substantial loss of production. Loss of yields due to the incidence of peanut disease may be up to 50%. Fungicides can be used to combat fungal diseases, but there are alternative disease control options, such as cultural practices, cultivation of resistant varieties, which can be useful in combating diseases by reducing the frequency of application of fungicides.