MSc

Characterization and management of fungal pathogens of cabbage (Brassica oleracea var.captitata L.) and cauliflower (Brassica oleracea var. botrytis L.)

Cabbage (Brassica oleracea var. capitata L.) and cauliflower (Brassicaa oleracea var. botrytis L.) are the most popular and widely cultivated cruciferous vegetables in Kerala. One of the main constraints in the production of these crops is the occurrence of fungal diseases, on which no detailed systematic studies have been conducted in Kerala. The study was carried out during 2015-2017 at College of Agriculture, Padannakkad with the objective to identify and characterize the fungal diseases of cabbage and cauliflower occurring in the selected districts of Kerala and to study the management of most severe and predominant diseases under in vitro and in vivo conditions. Purposive sampling surveys were conducted for the occurrence of fungal diseases in cabbage and cauliflower in Thrissur, Wayanad, Idukki and Kasargod districts and diseased plant samples were collected. Results of survey showed prevalence of eight different fungal diseases with a range of 5.4-69.3 per cent disease incidence and 8.1-68.3 percent disease severity in case of cabbage. In cauliflower, PDI and PDS were with a range of 3.1-52.2 percent and 4.9-44.2 percent respectively.

Isolations done from the infected specimens collected during the survey yielded eight genera of fungal pathogens. For selecting the most potent isolate, virulence test was conducted, and used for further studies. Characterisation 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 Alternaria brassicicola, Rhizoctonia solani, Collectotrichum gloeosporioides, Curvularia lunata, Choanephora cucubitarum, Pythium aphanidermatum and Fusarium equiseti. Symptomatology of these fungal diseases were studied in detail both under natural and artificial conditions. In vitro evaluation of fungicides and biocontrol agents was done against the selected sever pathogens. Ten fungicides at three concentrations and three bio control agents were selected for the studies.

In vitro studies showed that against A. brassicicola the most effective fungicides at the recommended concentration were, trifloxystrobin 25% + tebuconazole 50%, tebuconazole 5EC and Bordeaux mixture with 100 percent inhibition. Against R. solani and C.lunata six fungicides viz., tebuconzole 5EC, copper oxy chloride 50 WP, trifloxystrobin 25%+tebuconazole 50%, propineb 70 WP and Bordeaux mixture produced 100 percent inhibion. Trifloxystobin 25%+tebuconazole 50%, tebuconazole 5EC and Bordeaux mixture were the three effective fungicides against C.gloeoporioides, F.equiseti and C. cucurbitarum which recorded 100 percent inhibition over control. But against P.aphanidermatum from cauliflower, copper fungicides showed a lead in the inhibition viz., copper oxycholride 50WP, copper hydroxide 77WP, Bordeaux mixture followed by mancozeb 75 WP.

In vitro evaluation of biocontrol agents showed that T.viride was the most effective for controlling P.aphanidermatum with 75 percent inhibition followed by A.brassicicola with 67 percent inhibition. Antagonistic reaction of T.asperellum was mostly overgrowth on test pathogen. Similarly, P.fluorescens also showed maximum inhibition against P.aphanidermatum (50%). Effectiveness of the bacterial bioagent, B.subtilis showed maximum inhibition against R.solani.

Three major pathogens viz., A. brassicicola, R.solani in cabbage and P.aphanidermatum in cauliflower were selected for the in vivo studies. Three biocontrol agents and funficides which showed inhibition above 60 percent were selected for in vivo evaluation.

In vivo evaluation of fungicides for the management of Alternaria leaf blight of cabbage showed that trifloxystrobin 25%+tebuconazole 50% (0.03%) and tebuconazole 5EC (0.1%) were the best two fungicides showed 50 percent disease reduction over control followed by Bordeaux Mixture(1%). Yield of cabbage was also highest for these three treatments. Among biocontrol agents, T. viride was most effective in controlling the disease with a higher yield. For the management of Rhizoctonia leaf blight of cabbage, same two fungicides viz., trifloxystrobin 25%+tebuconazole 50% (0.03%) and tebuconazole 5EC(0.1%) were found to be most effective. B.subtilis was more effective than other two biocontrol agents which was significantly higher than control treatment. In vivo studies for the management of Pythium curd rot of cauliflower showed that trifloxystrobin 25%+tebuconazole 50% could produce 79 percent of disease reduction over control with higher yield. Among the bioagents, T.viride produced higher yield with 62 percent disease reduction.

The present work resulted a detailed systematic study on the fungal pathogens of cabbage and cauliflower in selected districts of Kerala and emphasizes that trifloxystrobin 25%+tebuconazole 50% (0.03%) is the best chemical and T.viride is the effective biocontrol agent for field application for the management of these fungal diseases. Future line work should be concentrated on the residue analysis of these fungicides and formulation of a bio-intensive management strategy.