Management of colletotrichum gloeosporioides on papaya fruits using biological control agents and moringa oleifera leaf extract.

Abstract

Colletotrichum gloeosporioides (Penzig) Penzig & Saccardo is one of the major pathogens causing anthracnose on several plants. This fungal pathogen causes infection both in the field and during postharvest, leading to reduced production and severe economic losses. There is a need to develop eco-friendly strategies to reduce the number of losses in production and the use of synthetic chemicals and their negative impact on human health and the environment. The aim of the current study was to control C. gloeosporioides of papaya using biological control agents and Moringa oleifera leaf extract. A total of 45 yeast and 55 Bacillus isolates were obtained from the fruit surfaces of guava (Psidium guajava L.), papaya (Carica papaya L.), cassava (Manihot esculenta Crantz), aloe (Aloe vera L.) and syringa (Syringa vulgaris) and screened against C. gloeosporioides. Twenty-seven yeast and fifty-one Bacillus isolates successfully inhibited the mycelial growth of C. gloeosporioides by greater than 50% during the in vitro preliminary trial. In the secondary screening, 21 yeasts and 47 Bacillus isolates managed to control the mycelial growth of the pathogen, and the reduction was significantly different (P<0.05) compared to the control treatment. Yeast isolates YCR3, YSY1 and Bacillus isolates BMR2 and B16 provided the best control of C. gloeosporioides both in primary and secondary in vitro trials. The scanning electron microscopy studies indicated that yeasts and Bacillus isolates inhibited the mycelial growth and spore production of C. gloeosporioides. Preventive application of the Bacillus isolate B16 resulted in a reduced incidence of anthracnose on papaya fruits, with a percentage of 88.67% at day 10 post-inoculation. The water control treatment had the lowest incidence of anthracnose (16.67%) and it was significantly different (P≤0.001) from fruits inoculated with pathogen-only control (100%). Five concentrations of moringa leaf extract were prepared (MLE1%, MLE1.5%, MLE2%, MLE2.5% and MLE3%) and these concentrations showed better performance during the primary in vitro trial with a significant difference of (P<0.05) when compared to the untreated control. On the secondary screening, MLE2.5% and MLE3% were further screened against C. gloeosporioides and inhibited mycelial growth by 96.9% and 97.5%, respectively. The preventive application of MLE2.5% (88.67%) at day 7 post inoculation, provided a better control and delayed anthracnose incidence when compared to MLE3% (100%) and water control (16.67%) in vivo. MLE2.5% treated fruits developed anthracnose incidence of 66%, compared to Bacillus megatarium treated fruit with 55% at day 7 after inoculation. However, the anthracnose incidence increased with each successive day of the trial leading to an incidence of 33% for water control. The integrated control of MLE2.5% with B. megatarium was the most effective treatment for the control of anthracnose and delayed anthracnose incidence when compared to MLE3% integrated with B. megatarium at day 3, 5, 7 and 10 days post-inoculation. Anthracnose incidence on papaya fruits treated with MLE2.5%+B16 (B16 being the label used to represent B. megatarium isolate) was 55%, and 100% on the fruits treated with MLE3%+B16 compared to 100% anthracnose incidence on pathogen-treated fruits at day 10 after inoculation. The physicochemical properties of papaya fruits, weight loss and total soluble solids, were not negatively affected by MLE2.5% + B. megatarium treatment. Bacillus megatarium can be integrated with moringa leaf extracts to manage anthracnose of papaya.