Pak. J. Bot., 51(5): 1877-1882, 2019. DOI: http://dx.doi.org/10.30848/PJB2019-5(13) BIO-EFFICACY OF TRICHODERMA ISOLATES AND BACILLUS SUBTILIS AGAINST ROOT ROT OF MUSKMELON CUCUMIS MELO L. CAUSED BY PHYTOPHTHORA DRECHSLERI UNDER CONTROLLED AND FIELD CONDITIONS MUHAMMAD ZOHAIB ANJUM 1 , MUHAMMAD USMAN GHAZANFAR 1* AND IMTIAZ HUSSAIN 2 1 Department of Plant Pathology, College of Agriculture, University of Sargodha, 40100, Pakistan 2 Department of Animal Sciences, College of Agriculture, University of Sargodha, 40100, Pakistan * Corresponding author’s email: usmanghazanfar1972@gmail.com Abstract Root rot of muskmelon caused by Phytophthora drechsleri (Tucker) is considered the most important disease limiting muskmelon production in Pakistan. In this study, three molecularly characterized isolates of Trichoderma (T. harzianum HK, T. harzianum HM, T. asperellum TH) and phenotypically characterized isolate of Bacillus subtilis were evaluated against P. drechsleri under laboratory conditions. The different antagonism assays such as, dual culturing, non-volatile, volatile metabolites and field conditions were tested. The results showed that all tested isolates of Trichoderma and Bacillus subtilis significantly (p<0.001) inhibited the mycelial growth of the pathogen. In all dual cultures, T. asperellum TH showed maximum mycelial inhibition followed by T. harzianum HK, T. harzianum HM and Bacillus subtilis. Non-volatile metabolites were more effective against pathogens than volatile metabolites. Under field conditions, percent disease incidence was decreased while percent plant survival, dry root and shoot weight significantly ( p<0.001) were increased by the application of To (combination of all tested Trichoderma isolates and B. subtilis) followed by T. asperellum TH during both growing seasons. It is suggested that bio-control agents can be used for the sustainable management of root rot of muskmelon. (Cucumis melo L.) Key words: Biocontrol agents, P. drechsleri, Inhibitory effect, Metabolites, Disease incidence, Plant survival. Introduction Root rot caused by Phytophthora drechsleri is an economically important disease of muskmelon in Pakistan (Majid et al., 1994). This soil-borne pathogen survive as oospores for several years (Jee et al., 2001) and produces zoospores that infect plant tissues and are dispersed by the irrigation water (Zhang et al., 2010). Some agronomic practices like mulching, crop rotation, use of synthetic chemicals and soil moisture management reduced the disease severity (Lamour & Hausbeck, 2000). Phytophthora species have different bio-chemical pathways, due to which the chemical fungicides gave no appropriate control (Drenth & Sendall, 2001). The use of bio-control agents has great potential as an alternative to noxious chemicals. Trichoderma and Bacillus species are being used as bio-control agents against Phytophthora species (Chung et al., 2008; Wang et al., 2013). Trichoderma species are known as the best biological control of many fungal plant pathogens, especially pathogens against soil-borne (Elad, 2000; Keswani et al., 2014; Srinivasa & Devi, 2014). Trichoderma spp. has different interactional mechanisms like mycoparasitism, competition and antibiotics to antagonize the phytopathogens (Pal & Gardener, 2006). Several species produced nonvolatile and volatile metabolites substances specially tricholin, massoilactone, gliovirin, heptelidic acid, alamethicins, peptaibols, harianic acid and glisoprenins which are lethal to plant pathogens (Qualhato et al., 2013). Antagonistic potential of Trichoderma isolates against P. drechsleri and P. cryptogea have been reported as effective under the laboratory conditions (Moayedi & Ghalamfarsa, 2011). Some bacterial isolates were also reported as effective biocontrolling agents against disease incited by Phytophthora (Thanh et al., 2009). Different isolates of Bacillus subtilis and Pseudomonas fluorescens were antagonistic to P. drechsleri (Singh & Dubey, 2010). Furthermore, applications of chemical fungicides on fruit crops have drawbacks, like harmful residual effects, environment pollution and development of resistance in pathogens. Considering this, there is a need for alternative approaches which are environment friendly, non-toxic to human health and have long-term effectiveness against pathogens. The objective of this study was to evaluate the antagonistic potential of different biocontrol agents against root rot of muskmelon under laboratory and field conditions for its sustainable management. Material and Methods Collection, Isolation, and identification of Pathogen: Diseased samples were collected from a muskmelon field located at District Jhang (30 º 35´N; 71º39´E), Punjab, Pakistan. The samples were kept in zipped (sterile) bags and brought to the laboratory of Department of Plant Pathology, College of Agriculture, University of Sargodha for further processing. Isolation was performed from root samples on PARP medium (corn meal agar 17g L -1 , 0.4ml Pimaricin L -1 , 0.25g Ampicilline L -1 , 0.01g Rifampcin L -1 , 5mL Pentachloronitrobenzene (PCNB) L -1 , 1mL Dimethylsulphooxide (DMSO) L -1 ) by using the tissue segment method described by Rangaswamy (1958). The pathogen was identified via cultural and morphological characteristics reported in literature (Bush et al., 2006; Jadesha, 2014). The isolated strains were maintained on PDA (potato starch 4g L -1 , agar 20g L -1 and dextrose 20g L -1 ) and stored at 4°C for further use.