Selection of culture media and in vitro assessment of temperature-dependent development of Nomuraea rileyi

Seleção do meio de cultura e avaliação in vitro do desenvolvimento de Nomuraea rileyi dependente da temperatura

In vitro development - radial growth and sporulation - of Nomuraea rileyi isolates from Anticarsia gemmatalis Hübner and Plusiinae larvae was studied on four culture media: Sabouraud, maltose, agar and yeast - SMAY; SMAY plus rice extract - SMAYR; complete medium for N. rileyi - CMNr and maltose agar yeast with potato extract - MAYP. Their development on a selected medium (MAYP) was analysed at five temperatures. Two mathematical models were fitted to in vitro and in vivo temperature dependent radial growth rates and thermal requirements were estimated. The medium with potato and yeast extract induced the highest growth rate in most cases, while SMAY induced the lowest rates for the tested isolates. Estimated optimum temperatures for mycelium in vitro growth ranged from 22ºC to 26ºC. No differences between the proportion of sporulation of colonies maintained at 20ºC and 26ºC were detected. Few or no colonies sporulated at 12, 16 and 30ºC. The relative production of conidia per fungal biomass was very variable, ranging from 0.5 to 16 conidia per centigram of mycelium. Therefore, this was not a useful criterion for selecting a culture medium. Based on present findings, a medium based on potato extract, or enriched slices could be used for N. rileyi experimental and eventually mass production. Because of the similarities found between in vitro and in vivo thermal requirements, thermal traits of the mycosis could be simply estimated on the basis of the environmental temperature.

Entomopathogenic fungus; radial growth; mathematical model; biological control

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