Biopriming and foliar apllication of biocontrol agents and endophytes for the management of major foliar fungal diseases of bush cowpea

Abstract

The study entitled “Biopriming and foliar application of biocontrol agents and endophytes for the management of major foliar fungal diseases of bush cowpea” was conducted at College of Agriculture, Vellayani and Coconut Research Station, Balaramapuram during 2020-2022. The objective was to develop best ecofriendly management practice involving biopriming, foliar application of endophytes and biocontrol agents for the control of major foliar fungal diseases in bush cowpea with special emphasis on Cercospora leaf spot and anthracnose. Symptomatology and etiology of anthracnose and Cercospora leaf spot were studied under field condition from different locations in Trivandrum district viz., Vellayani, Pappanchani, Venganoor, Balaramapuram, Nedumangad and Parassala. The pathogens were isolated and studied their morphological characteristics. Bush cowpea seeds were collected from five agro-ecological zones of Kerala viz., Northern, High range, Central, Special problem and Southern zones and the seeds were assessed for both externally and internally seed borne microflora. Percentage of infection was calculated by blotter method. The lowest percentage of infection was found in seed samples collected from Wayanad (16.7%) and the highest in Thrissur (38.2%). The diseased leaf samples showing anthracnose were collected from five locations of Thiruvananthapuram district and isolated Colletotrichum gloeosporioides from each location. Pathogenecity of isolated pathogen was proved by detached leaf assay and seedling assay. Vellayani isolate (C1) was found to be the most virulent pathogen and recorded lesion size of 4.33cm and 1.82cm in detached leaf assay and seedling assay on seventh day respectively. The isolate C1 was used for further studies. In vitro evaluation of biocontrol agents like Trichoderma asperellum T6 (KAU), Trichoderma koningiopsis (TRKR2), Trichoderma harzianum (TRMW2), Piriformospora indica (No. INBA 3202001787), Bacillus amyloliquiefaciens VLY 24, Bacillus velezensis (CBRE5), Bacillus amyloliquefaciens (CBSE5) and Pseudomonas fluorescens PN026 (KAU isolate) against Colletotrichum gloeosporioides and Cercospora sp. were carried out. Dual culture method of Colletotrichum gloeosporioides against biocontrol agent recorded highest percentage inhibition of mycelia by T. asperellum (64.76) followed by Trichoderma strain TRKR2 (52.63) which was on par with bacterial strain CBRE5 and least for Psuedomonas fluorescens. In vitro pathogen suppression by spore germination assay on Cercospora sp. by 145 biocontrol agents revealed that maximum inhibition of conidia germination was by T. asperellum (36.25 %) followed by Trichoderma strain TRKR2 and Trichoderma strain TRMW2 whereas least inhibition percentage was observed with Piriformospora indica (14.96). Peroxidase and polyphenol oxidase assay on bush cowpea pods and seeds showed that fungus infected tissues had relatively higher activity of these oxidase enzymes in comparison to healthy pods. Enzyme activities were higher in pods and seeds treated with Bacillus strain CBRE5, T. asperellum and Trichoderma strain TRKR2. Standardization of priming techniques revealed that soaking of seeds for 2h was found effective for Trichoderma asperellum, Bacillus velezensis (CBRE5) and Bacillus amyloliquiefaciens VLY 24 and 4h for Trichoderma strain TRKR2. The soaking duration is followed for the treatments in in vivo studies. Based on the in vitro studies, the best three treatments viz., Trichoderma asperellum, Trichoderma strain TRKR2 and Bacillus strain CBRE5 were taken for in vivo studies. In vivo studies on the effect of seed biopriming and spraying of biocontrol agent suspension at 4 leaf, 50 per cent, flowering and pod set stages revealed lowest disease severity of anthracnose was recorded for Trichoderma asperellum treated plants with disease suppression over control 41.74 per cent followed by carbendazim, Trichoderma strain TRKR2 and Bacillus strain CBRE5. In the case of Cercospora leaf spot Trichoderma asperellum treated plants shown highest disease suppression (63.47%) over control followed by carbendazim, Trichoderma strain TRKR2 and Bacillus strain CBRE5. Bacillus strain CBRE5 recorded least disease suppression over control in anthracnose and Cercospora leaf spot while comparing other treatments. Highest number of pods per plant (34.75), seeds per pod (15.25), plant height (46.05 cm) and yield (232.47 g) were shown by bacterial strain CBRE5 treated plants. Thus, the present study indicated that the seed biopriming for 2 h along with foliar application of Trichoderma asperellum suspension at 4 leaf , 50 per cent flowering and pod set stages was most effective treatment for the management of major foliar fungal diseases like anthracnose and Cercospora leaf spot of bush cowpea whereas seed biopriming for 2 h along with foliar application of Bacillus velezensis suspension at 4 leaf stage, 50 per cent flowering stage and pod set was the best treatment in plant growth promotion in vivo which could be used as an eco-friendly measure to produce safe to eat crop.