Characterization of biointensive management of fungal fruit rots of cucurbits

Abstract

Cucurbits are the most popular and widely cultivated vegetables in Kerala. One of the main constraints in the production of these crops is the occurrence of fungal fruit rots, on which no detailed and systematic studies have been conducted in Kerala. The study was carried out during 2017-2019 at College of Agriculture, Padannakkad with the objective to identify and characterize the fungal pathogens causing fruit rots in cucurbits, occurring in the northern zone of Kerala and to study the management of selected fruit rot diseases under in vitro and most severe and predominant disease in vivo conditions. Purposive sampling surveys were conducted for the occurrence of fungal fruit rots in cucurbits in Kasargod, Kannur and Kozhikkode districts. Diseased plant samples were collected. Results of survey showed prevalence of seven different fungal diseases with a range of 6- 51 per cent disease incidence. Isolations done from the infected fruit samples collected during the survey yielded seven genera of fungal pathogens. Characterization of the selected pathogens were carried out based on the cultural and morphological characters and identified up to generic level. Further identification of species of each genus was done by molecular characterization by sequencing the ITS region of each fungus by in silico analysis and confirmed as Choanephora cucurbitarum, Sclerotium rolfsii, Rhizoctonia solani, Phytophthora nicotianae, Pythium deliense, Corynespora cassiicola and Fusarium equiseti. Symptomatologies of these fungal diseases were studied in detail both under natural and artificial conditions. In vitro evaluation of fungicides, botanicals and biocontrol agents was done against the selected five pathogens. Four fungicides and three botanicals at three concentrations and five biocontrol agents were selected for the studies.

In vitro studies showed that, against Choanephora cucurbitarum fruit rot, tebuconazole 5EC showed 100 per cent inhibition at all the three concentrations. Among botanicals, garlic extract at medium and higher concentrations and azadirachtin 0.1% at lower concentration were the best. Among biocontrol agents, Trichoderma viride was the best. Against Sclerotium rolfsii fruit rot, tebuconzole 5EC (Folicur), were significantly superior than all other fungicides at lower concentration, which showed 100 per cent inhibition. The fungicides tebuconzole 5EC and mancozeb 64% + cymoxanil 8% were superior at recommended and higher concentration and both of them showed cent per cent inhibition. Among botanicals, garlic extract and azadirachtin 0.1% were the most effective at the lower and recommended concentrations. At higher concentration garlic extract was the best. Among biocontrol agents, Bacillus subtilis and PGPM were the most effective treatments and they were at par with each other. Against Rhizoctonia solani fruit rot, all the chemical fugicides recorded cent per cent inhibition at all concentrations. Garlic extract was the best at all concentrations. The best biocontrol agets against Rhizoctonia solani was Trichoderma viride. Against Phytophthora nicotianae fruit rot, all the fungicides at all concentrations showed cent per cent inhibition. The data on the botanicals revealed that, garlic extract shows maximum inhibition (66.66%, 77.77%, 100%) at all concentrations. Among biocontrol agents, Trichoderma viridae and PGPM were the best treatments and they showed cent per cent inhibition. Against Corynespora cassiicola fruit rot, mancozeb 64% + cymoxanil 8% were superior (100% inhibition) at the lower concentration. At recommended concentrations, mancozeb 64% + cymoxanil 8% and mancozeb 64% + carbendazim 12% showed cent per cent inhibition. At higher concentrations, tebuconzole 5EC, mancozeb 64% + cymoxanil 8% and mancozeb 63% + carbendazim 12% were showed 100 per cent inhibition and they were significantly not different. Among the

botanicals garlic extract was the most effective at all concentrations. The best biocontrol agent against Corynespora cassiicola was PGPM, which showed cent per cent inhibition. In vivo evaluation of management of Choanephora cucurbitarum fruit rot in pumpkin emphasized that tebuconazole 5 EC and mancozeb 64%+cymoxanil 8% are the best treatments. Botanicals viz., azadirachtin 0.1 % and garlic extract came as next best treatments and biocontrol agents, T. viride and B.subtilis were the least effective treatments. These can be recommended as effective antipathogenic agents for field application for the management of the fungal fruit rot disease in pumpkin. The present work resulted in a detailed and systematic study on the fungal fruit rots of cucurbits in northern zone of Kerala. Future line work should be concentrated on the field level studies of all the fruit rots of cucurbits in different districts of Kerala and on the recommendations of local specific management practices.