Spent mushroom substrates are potential for controlling plant diseases. This study examined the abilities of spent substrates of Shiitake (L. edodes) and Oyster (P. ostreatus) mushrooms to inhibit the growth of R. solani in vitro and control dampingoff disease in tomato seedling. The in vitro experiment examined the abilities of water extract of spent mushroom substrate non-sterile and sterile to inhibit the pathogen using poisonous food method. In the nursery experiment, substrates were mixed with the planting medium, 1:1, 1:2, and 1:3 (v/v). The result showed that the water extract of spent substrates of L. edodes and P. ostreatus inhibited the growth of R. solani by 29.1%-40.6%. Non sterile water extract of spent substrate of P. osteratus showed highest inhibition level (40%). In tomato nursery, mixing spent substrates of L. edodes or P. ostreatus with planting medium 1:2, and 1:3 (v/v) inhibited damping-off disease in tomato seedling by 57.5%-100%. Application of P. ostreatus spent substrate in the planting medium, 1:2 and 1:3 (v/v) resulted in 100% inhibition of the disease.

Early blight disease caused by Alternaria solani is an important disease in tomatoes. An environmentally friendly control measure is the use of organic matter, such as spent mushroom substrates (SMS). SMS controls plant diseases primarily through microbial activity that can inhibit the pathogen. The objective of this study is to examine the potential of bacteria and fungi isolated from spent substrate of shiitake mushrooms (Lentinula edodes) and oyster mushrooms (Pleurotus sp.) to induce resistance against early blight disease in tomatoes. The isolation from SMS of L. edodes resulted in seven bacterial isolates and four fungal isolates and the isolation from SMS of Pleurotus sp. resulted in five bacterial isolates and two fungal isolates. The isolates were examined for their ability to inhibit early blight disease in tomatoes. The experiment was arranged in randomised complete block design with three replicates. The results showed that the application of the fungal and bacterial isolates in the planting holes inhibited the development of early blight disease in tomatoes by 23.0%-51.6%. The isolates that showed the greatest disease reduction were two bacterial isolates (SB4 and SB7) from spent shiitake substrate. These isolates increased the activities of pathogenesis-related proteins (β-1,3-glucanase and chitinase), indicating the induction of host resistance.