MSc

A study entitled ‘Triazole, strobilurin and its combination fungicides for the management of anthracnose and fruit rot of chilli’ was conducted during 2016 - 18 at Department of Plant Pathology, College of Agriculture, Vellayani with the objectives to study the host range of the pathogen Colletotrichum capsici and to develop management strategy to control the disease using new generation fungicides.
A survey was conducted at Vellayani, Kumarakom, Thrissur, Pattambi, Ambalavayal and Padanakkad during 2016 – 17 to screen the most virulent isolate of C. capsici in chilli (Capsicum annuum). During the survey period, C. capsici was found causing the disease in five and C. gloeosporioides in one locations. The maximum disease incidence (70 %) and severity (45 %) by C. capsici was recorded from Padanakkad. Except from Ambalavayal, five pure cultures of C. capsici (C1 to C5) were obtained and Koch’s postulate is proved.
C. capsici produced white to dirty white, sparse mycelial growth on PDA, which later turned into dirty grey colour. Days taken to cover petridish (9 cm radius) ranged from 7.4 to 8.3 days. Mycelium was hyaline, septate and branched. Black colored acervuli were produced after 20 - 30 days of incubation and its diameter ranged from 21.85 - 45.82 μm, with 18 - 47 dark setae of 72.50 - 110.41 μm length. Conidiophores are hyaline, short and cylindrical with sickle shaped single celled conidia having an oil globule at the centre. The average size of the conidia was 20.04 - 23.48 μm x 2.58 - 3.22 μm.
Based on screening of isolates through leaf and fruits inoculation of chilli variety ‘Vellayani Athulya’, C3 was identified as the most virulent isolate. The identity of C. capsici (C3) was confirmed by PCR using ITS primers, sequencing of amplicon, BLAST and phylogenetic analysis.
The best solid and liquid media for growth and sporulation of C. capsici was potato dextrose medium, the optimum temperature was 30oC and pH was 6.5. The growth of C. capsici was studied under different light conditions and the fungus growth was maximum in 8 hour light and 16 hour dark under white light at 20 lux intensity.
Host range of C. capsici was studied in different vegetable crops viz. Capsicum chinense, C. frutescens, cowpea, brinjal, tomato and bhindi. C. capsici infected all the host plants tested and brinjal was found as the ideal host plant.
Among eight KAU varieties of chilli viz. Vellayani Athulya, Jwalamukhi, Jwalasakhi, Ujwala, Anugraha, Keerthi, Vellayani Thejus and Vellayani Samrudhi, screened against C. capsici with leaf and fruits inoculation, Vellayani Athulya was found to be the most susceptible variety to the disease, whereas Vellayani Thejus and Vellayani Samrudhi were found comparatively resistant to leaf and fruit infection.
Under in vitro evaluation of new generation fungicides by poisoned food technique, azoxystrobin 11 % + tebuconazole 18.3 % SC at 10 ppm, pyraclostrobin 20 % WG at 50 ppm and hexaconazole 5 % EC + pyraclostrobin 20 % WG at 100 ppm completely inhibited the mycelial growth and proved to be most effective.
All fungicides significantly inhibited spore germination of C. capsici. Hexaconazole 250 ppm completely inhibited germination. Pyraclostrobin 20% WG at 10 ppm, hexaconazole 5 % EC + pyraclostrobin 20 % WG at 50 ppm, tebuconazole 25.9 % EC and hexaconazole 5 % EC at 100 ppm were also equally effective in inhibiting germination of spores and were statistically on par.
A pot culture study was conducted with chilli variety ‘Vellayani Athulya’ to evaluate the efficacy of selected new generation fungicides. The selected treatments were imposed only once, after 18 days of flowering when at least 25 per cent of fruits were at maturity stage. At recommended dose, the maximum disease suppression was
recorded with 0.24 % of copper oxy chloride 50 % WG (90.59 %), followed by 0.1 % of hexaconazole 5 % EC + pyraclostrobin 20 % WG (73.50 %), 0.15 % of azoxystrobin 11 % + tebuconazole 18.3 % SC (70.94 %) and 0.1 % of tebuconazole 25.9 % EC (68.70 %). At higher (double the recommended) doses of respective fungicides, disease suppression was more. Biocontrol agents were also effective, but the disease suppression was less with 22.22 per cent for Trichoderma viride and 43.58 per cent for Pseudomonas fluorescens compared to the new generation fungicides.
Hence anthracnose and fruit rot of chilli can be effectively managed by foliar spray of hexaconazole + pyraclostrobin combination fungicide and it may be subjected to mutlilocation and multiseasonal trials before recommendation.