Ecology of pitaya stem rot caused by Gilbertella persicaria and its biological control by phyllosphere bacteria

Gilbertella persicaria stem rot is a disease that causes rotting in the stem nodules and fruits of pitaya. Here, we aimed to study the ecology of G. persicaria and its biological control using several Bacillus subtilis strains isolated from the phyllosphere. Sporangiospores of G. persicaria were detected on different parts of the plant, with maximum density (c.239.9 propagules/cm(2)) found on the petals after flowering, and spore germination was observed to be considerably affected by humidity. Furthermore, the study revealed that an incision wound of at least 2 mm depth was necessary for infection by the pathogen to the stem nodule, and exposure to high temperatures (50 degrees C) accelerated disease incidence, by disrupting resistance to the spread of the pathogen. Additionally, biological control of G. persicaria was effectively achieved by inoculation with B. subtilis strains isolated from pitaya stem nodules. Intriguingly, treatment with antagonistic bacteria reduced stem rot incidence to zero (bacterial suspension: PNB-5, PNB-7, and PNB-93; culture filtrate: PNB-7, PNB-93, and PNB-95), equivalent to that achieved by fungicide application in both prophylactic and simultaneous treatments. Collectively, this is the first study to demonstrate the ecology of G. persicaria and to show the potential applicability of phyllosphere bacterial strains for biological control of G. persicaria in pitaya, which could help develop effective integrated disease management strategies for the control of pitaya stem rot.