Compatibility interactions between the host and the fungal proteins are necessary to successfully establish a disease in plants by fungi or other diseases. Photochemical and antimicrobial substances are generally known to increase plant resilience, which is essential for eradicating fungus infections. Through homology modeling and in silico docking analysis, we assessed 50 phytochemicals from cucumber (Cucumis sativus), 15 antimicrobial compounds from botanical sources, and six compounds from chemical sources against two proteins of Pseudoperonospora cubensis linked to cucumber downy mildew. Alpha and beta sheets made up the 3D structures of the two protein models. According to Ramachandran plot analysis, the QNE 4 effector protein model was considered high quality because it had 86.8% of its residues in the preferred region. The results of the molecular docking analysis showed that the QNE4 and cytochrome oxidase subunit 1 proteins of P. cubensis showed good binding affinities with glucosyl flavones, terpenoids and flavonoids from phytochemicals, antimicrobial compounds from botanicals (garlic and clove), and chemically synthesized compounds, indicating the potential for antifungal activity.

Fifteen isolates of Ceratocystis fimbriata collected from different locations in Karnataka were characterized using ITS gene technology. It produced an amplification size of 600–650 bp, which indicated that all the isolates belong to the genus Ceratocystis, thus confirming the identity of the pathogenic isolates. To test genetic variability, isolates were analyzed using microsatellite markers. An UPGMA dendrogram for genetic variation among the isolates showed that all the isolates fell into two major clusters. The first cluster consisted of isolate Cf-10 and the second cluster was further divided into two sub-clusters. Sub-cluster one consisted of isolate Cf-2. Sub-cluster two was again divided into five groups. The first group included isolate Cf-13, the second group consisted of isolate Cf-14, the third group included isolates Cf-1, Cf-4, Cf-6, Cf-7, Cf-8 and Cf-9, the fourth group included Cf-5 and Cf-11, and the fifth group consisted of Cf-3, Cf-12 and Cf-15. The dissimilarity coefficient ranged from 0.00 to 0.20 among the isolates. Isolates Cf-1, Cf-3, Cf-4, Cf-5 Cf-6, Cf-7, Cf-8, Cf-9, Cf-11, Cf-12 and Cf-15 were found to be highly similar, as their dissimilarity coefficient was zero. Maximum dissimilarity (0.20) was found between isolate Cf-10 and all the other isolates, suggesting they were genetically distinct.

Watermelon (Citrullus lanatus) is an important cucurbitaceous crop cultivated worldwide. The cultivation of watermelon and other species of the family Cucurbitaceae is severely affected by several diseases like anthracnose, Alternaria leaf spot, bacterial fruit blotch, powdery mildew and gummy stem blight. Among the diseases, gummy stem blight is an emerging and devastating disease caused by Didymella bryoniae producing a serious threat to the economics of production of cucurbits like watermelon. A roving survey was carried out in eight districts of Karnataka (Chamarajanagara, Chikkaballapura, Gulburga, Vijayapur, Bengaluru urban, Kolar, Mysuru and Yadgiri) from 2021 to 2023 to record the incidence of gummy stem blight (GSB) disease on watermelon. The survey data revealed that GSB disease was observed in all areas. The per cent disease index ranged from 29.6 to 51.2 per cent. The maximum mean per cent disease index of (51.2%),) Bengaluru urban district and the lowest was seen in the Mysuru district (29.6%) followed by Chikkaballapura district (31.0%). The pathogen associated with gummy stem blight disease was isolated and proved the pathogenicity of the isolate and fulfilled the Koch’s postulates.