In vitro evaluation of novel fungicides and bio-agents against pathogens associated with stem end rot of sweet orange (Citrus sinensis)

Abstract

Stem End Rot (SER) in sweet orange (Citrus sinensis), caused primarily by Colletotrichum gloeosporioides and Lasiodiplodia theobromae, leads to catastrophic postharvest losses exceeding 35% in Maharashtra, India. This exhaustive study isolated and characterized these pathogens from symptomatic fruits in Rahuri orchards, confirming pathogenicity through Koch’s postulates. Morphological, physiological, and cultural traits were rigorously analyzed across multiple media, pH gradients (5.0-8.5), and thermal spectra (5-35°C). In-vitro efficacy of six novel fungicide combinations and six bio-agents was evaluated against both pathogens. Results demonstrated Azoxystrobin 18.2% + Difenaconazole 11.4% SC as the most effective fungicide (95.92% inhibition against C. gloeosporioides; 94.44% against L. theobromae), while Trichoderma viride showed superior bio-control (74.22% inhibition). Optimal pathogen growth occurred on Potato Dextrose Agar (PDA) at pH 6.0-7.0 and 25-30°C. These findings establish a scientific foundation for integrated disease management strategies in citrus orchards, combining chemical and biological interventions to mitigate economic losses.