Survey and identification of leaf spot diseases of Jatropha curcas L. in the Philippines and utilization of fungal endophyles and epiphyles as biological control agents against Colletotrichum sp.

Leaf spot, the most prevalent foliar fungal disease of Jatropha caused by a species of Colletotrichum was characterized by having circular to angular spots, water-soaked appearance and grayish while center with dark brown margins contained by cholorotic yellow halos or rings. Prick and Spray (P+S) inoculation was the most effective method of introducing the isolates, thereby producing typical symptoms at shortest possible time. Colletotrichum sp. JPS6 from Dasmariñas, Cavite [Philippines] was the most aggressive isolate for it consistently initiated the onset of the disease both on young (94.44%) and old leaves (100%) six days after inoculation. Its optimum growth and sporulation was enhanced in V-8 Juice Agar (V-8JA) medium, pH 5.5 to 8.5 and temperature of25 deg C. Continuous darkness supported optimum growth but sporulation was enhanced when subjected to continuous light. Sixteen endophytic and 31 epiphytic fungi were isolated from asymptomatic Jatropha leaves. Assemblage of endophytic fungal isolates included the following taxa: 4 Hyphomycetes, 1 Coelomycete and 1 Ascomycete. Community of epiphytic fungal isolates was predominantly Hyphomycetes (14) while one was chlamydospore-forming. The remaining isolates were non-spore forming or sterile mycelia. Endophytic and epiphytic fungal isolates were evaluated for their antagonistic activity in vitro and in vivo against Colletotrichum sp. JPS6. Two endiphytes and 5 epiphytes were identified as potential biological control agents after in vitro screening using the dual culture test. Geotrichum sp. ENF-JPS6, Aspergillus sp. ENF-JPS17; Geotrichum sp. EPF-JPS5, Geotrichum sp. EPF-JPS30, Aspergillus sp. EPF-JPS31, Geotrichum sp. EPF-JPS33, and Aspergillus sp. EPF-JPS35 showed high degree of antagonism by outpacing the growth of the pathogen and caused 46.47, 44.74, 33.87, 39.66, 61.31, 27.93 and 68.71 percent inhibition of radial growth (PIRG), respectively. In vivo test showed that endophytic fungal isolates, Geotrichum sp. ENF-JPS6 and Aspergillus sp. ENF-JPS17 were not effective biological control agents against the pathogen, whereas epiphytes applied as protectant effectively controlled the disease with incidence ranging from 0 to 2.5%, not significantly different to systematic fungicide Carbendazim.