A method to induce significant production of conidia from Monilinia fructigena, Monilia polystroma, and Monilia yunnanensis

Abstract

Brown rot, caused by Monilinia fructicola, Monilinia fructigena, Monilinia laxa, Monilia polystroma, and Monilia yunnanensis, is an important disease of stone and pome fruits. The conidia of these fungi commonly form on infected tissues and serve as the main inoculum source throughout the growing season. Epidemiological research, such as fruit inoculation, often requires a large quantity of inocula. However, the sporulation of M. fructigena, M. polystroma, and M. yunnanensis on artificial media is inferior to that of M. fructicola and M. laxa. In this study we compared the sporulation of these species on potato dextrose agar (PDA), cherry juice agar (CA), oatmeal tomato agar (OTA), rye tomato juice agar (RTA) and apple fruits, and developed an efficient conidial production method on PDA for these fungi. In this method, a regular PDA plate was inoculated by spreading mycelial fragments of the fungi on the surface and incubated at 22 °C for approximately 2.5 days in the dark. Then, the mycelia were scraped and washed off using sterilized distilled water. The surface of the medium was then covered with two layers of gauze and incubated at 22 °C for between 36 and 48 h. Without scraping, the range of sporulation on PDA per plate was sparse to 10³ conidia, while with scraping it increased to 10⁶–10⁷ conidia per plate. On apple fruit, the range of sporulation was sparse to 10⁵ conidia per fruit depending on the isolates used. This scraping method led to the abundant production of conidia from brown rot fungi on the medium.