Deciphering the Morpho-molecular and Physiological Characterization of Rhizopus stolonifer Affecting Jackfruit Rot

Abstract

Fruit rot caused by Rhizopus stolonifer (Ehrenb.) Vuill. is a common fungal disease of jackfruit (Artocarpus heterophyllus L.) that leads to fruit rotting in vegetative and maturity phases which restrains the emergence of flowers and fruits. Further identification of the pathogen was done by performing cultural, morphological, molecular and physiological characterization. On potato dextrose agar R. stolonifer produced whitish grey cottony growth initially followed by blackish mycelial growth in later days as its growth advanced. The fruit rot pathogen exhibited diverse mycelial growth patterns ranging from flat, raised to fluffy and densely cottony growth as it has the tendency to spread rapidly that covers entire Petri plate (90 mm). Morphologically, brownish straight sporangiophores along with globose sporangium was identified. Rhizopus stolonifer (black bread mold), thrive on damaged or decaying fruits. The fungus rapidly colonizes fruits under warm and humid conditions. It is highly destructive, with visible colonization and spoilage occurring within 24–48 hours. Fruit injuries and sugar content significantly influence fungal growth rates and spread​. Potato starch serves as a carbon source for Rhizopus, supporting its growth in industrial and laboratory settings. Rhizopus stolonifer are used in fermentation processes to saccharify starch into sugars. Growth is typically optimized with additional nutrients or under controlled conditions, as ungelatinized starch alone isn't fully utilized by the fungus. Columella was hyaline and cylindrical shaped that measured about 25.17 µm. Rhizoids were present profusely and stolons were also found. Among six different temperatures levels examined using potato dextrose broth, the highest average fresh and dry mycelium weight (920.17 and 260.62 mg) was observed at 35 °C and least dry mycelium weight (0.00 mg) was observed at 15 °C and at 40 °C on liquid media (potato dextrose broth). Among six different pH levels studied using potato dextrose broth, maximum growth of the fungus was recorded at pH 7.0 (981.76 mg of fresh and 302.78 mg of dry weight respectively) followed by pH 7.5 (924.13 mg and 269.26 mg) and pH 6.5 (748.51 mg and 183.32 mg). Least growth of the fungus was observed at pH 5.0 (330.71 mg and 82.43 mg). Pathogen was identified as Rhizopus stolonifer having 99.99 per cent homology and accession number PQ26879.