Antifungal potential of biocontrol agents against Penicillium georgiense causing onion mold in Pakistan

Onion is an important vegetable crop prone to many abiotic and biotic stresses. The blue mold rot of onion caused by Penicillium georgiense (P. georgiense) is one of the most damaging diseases in Pakistan and worldwide. The current study includes the factors that are responsible for losses at a considerable level where onion is being grown, transported, and stored. This study represents the first comprehensive integration of morphological and molecular identification of fungal pathogens isolated from onions (collected from different regions), showing the symptoms of blue mold rot. Standard tissue isolation and polymerase chain reaction (PCR) techniques were used for morphological and molecular characterization of the pathogen, respectively. Microscopic examination revealed the presence of short-chains of ellipsoidal to subspheroidal conidia, similar to the characteristic morphological features of P. georgiense. Further confirmation was done from sequencing of amplified Internal Transcribed Spacer (ITS) regions which showed 97-99% similarity to the P. georgiense species complex. Different biocontrol agents (BCAs) were evaluated against P. georgiense isolates under in vitro conditions, where Trichoderma sp., used as biocontrol agent, expressed maximum antagonistic effect. It significantly restricted the radial colony growth of the test fungus to only 37 mm, compared to control, where the colony reached upto 90 mm. In addition, other biocontrol agents such as Paecilomyces lilacinus (P.lilacinus) and Bacillus subtilis (B. subtilis) also demonstrated significant inhibitory effects on the radial colony growth of the test fungus. These BCAs inhibited the colonial growth to 59 and 67.67 mm, respectively. Based on the findings of the current study, P. georgiense is the significant causal agent of blue mold onion rot at all the studied locations, and can be efficiently controlled by using BCAs, a safe, environmental friendly and sustainable approach in agriculture.