Performance of two isolates of Isaria fumosorosea from hot climate zones in solid and submerged cultures and thermotolerance of their propagules

Abstract

Isaria fumosorosea frequently causes mycosis of agricultural pests in the hot semiarid and dry tropical regions of Mexico. Because temperature tolerance restricts the use of fungal biopesticides, we investigated two isolates from these areas for possible development into mycoinsecticides for use in hot weather agricultural zones. We studied the effects of culture system (solid or submerged cultures) and temperature on the fungal growth, extracellular enzyme production, pathogenicity, and thermotolerance of the produced propagules. Between 20 and 28 °C, the specific growth rates of the isolate PCC were higher on solid media, but in the submerged culture, the isolate P43A grew faster even at temperatures of up to 34 °C. On solid media, P43A produced 1.5-fold more proteases than PCC, but in the submerged culture, both strains had similar activities. Under the same culture conditions, PCC produced a blastospore:conidia ratio of 1:2, and P43A produced a ratio of 1:5. PCC aerial conidia had the shortest Lethal Time 50 (LT(50), the time to reach 50 % mortality) against Galleria mellonella larvae, but LT(50) was equal for the aerial conidia and the submerged propagules of P43A and PCC. The submerged and aerial propagules of P43A were more thermotolerant than those of PCC. Each isolate performed differently in each culture system, and we concluded that the intended production method should be included as a criterion for screening of entomopathogenic fungus. We found that thermotolerance is a specific characteristic of an isolate from a given species. Because of its specific characteristics, P43A shows more promise for the development of a submerged conidia-based mycoinsecticide for foliar application in aqueous form in hot climate regions.

Biological Control beneath the Feet: A Review of Crop Protection against Insect Root Herbivores

“…Thus, one of the problems in employing massively produced commercial EPFs can be their variation in pathogenicity when used in different climatic conditions [87]. Further, Esther et al [88] showed that different Isaria fumosorosea EPF strains express different thermal tolerance towards the growth rate according to the temperature range of their geographical origins. Therefore, specific selection and commercialization of different EPF isolates adapted to different climatic conditions and soil properties can compensate for the EPFs’ potential lack of efficiency as root pest bio-control.…”

Enhancing >i<Dalbulus maidis>/i< (Hemiptera: Cicadellidae) control: an integrated approach combining >i<Cordyceps javanica>/i< (Ascomycota: Hypocreales) and insecticides

“…Thus, the optimization performed in the culture medium based on Esther et al (2013) was satisfactory and can be adopted for submerged conidia production of C. javanica.…”

“…There was a significant difference among the tested modified culture media (P < 0.05) (Figure 10). The M4, Esther et al (2013) modified with NS1 as the nitrogen source yielded a significantly higher final production of 2.61 × 10 8 submerged conidia mL -1 .…”

“…On the other hand, submerged conidia are a relatively unexplored structure and have not yet been commercially developed as a biological agent for arthropod control. Characteristics including hydrophobicity, temperature tolerance, desiccation tolerance, virulence against insects, and germination rate differ among aerial conidia, submerged conidia, and blastospores (Bidochka et al, 1995;Poprawski;Behle et al, 2006;Shapiro-Ilan et al, 2008;Esther et al, 2013;Iwanicki et al, 2023).…”

“…Consequently, culture media were modified and tested to attain a sufficiently concentrated yield of these propagules, enabling the execution of experiments. Nevertheless, in the medium proposed by Esther et al (2013), NH4NO3 is as the nitrogen source (NS) employed, subject to restrictions and controlled by the Brazilian Army. Therefore, alternative sources were investigated as possible substitutes, namely NS1, NS2, and NS3 (Table 2).…”