Biological Control of Pichia bruneiensis AL3 against Green Mould Disease on Oranges

Abstract

Agriculture plays an essential role in Thailand economy. However, to control plant pathogens and maximize crop yield, pesticides are overused and misused. This results in toxic pollutants that are harmful to humans and the environment. Biological control offers an alternative to the use of synthetic chemicals. Mandarin orange (Citrus reticulata) is widely grown and consumed in Thailand, but it is threatened by green mould disease caused by Penicillium digitatum, which usually occurs at post-harvest storage. A total of 40 isolates of epiphytic yeasts were isolated from symptomless orange peels. They were screened for antagonistic activity against P. digitatum originally isolated from a diseased orange using a dual culture method. Five isolates exhibited at least 70% inhibition; therefore, they were further screened for their activity on orange using fruit inoculation. An isolate, AL3, reduced the disease incidence (79%) and lesion size (34.75±2.57 mm) caused by P. digitatum compared to the control treatments (disease incidence, 100% and lesion size, 50.00±1.03 mm, respectively). The yeast was analyzed using molecular data based on Internal Transcribed Spacers (ITS region) and it was identified as Pichia bruneiensis AL3. Its mode of action on anti-sporulation was studied. When tested on agar plates, living cells and culture broth of P. bruneiensis AL3 were able to inhibit spore germination of P. digitatum resulting in 33.2 and 38.2% germination, respectively, compared to the control treatment (76.8% germination). These results showed that P. bruneiensis AL3 has the potential to develop as a biological control agent (BCA).