Morphological and molecular identification and determination of some thermotolerance aspects of four entomopathogenic fungal isolates recovered from Palestine

Abstract EN

In this study, four entomopathogenic fungi isolates were collected from the Midwest area of the West Bank in Palestine, and identified based on their morphological traits followed by molecular identification based on sequence analysis of the Internal Transcribed Spacers (ITS) 1 & 2 of the rDNA.

Furthermore, the thermotolerance of spore germination and mycelium growth of each isolate was determined at temperatures of 25, 30, 32, 34 and 36oC.

Comparing the collected morphological data with the corresponding data available in the literature revealed that two of the isolates are Metarhizium anisopliae and were designated as PAL-M01 and PAL-M02, while the other two are Beauveria bassiana and were designated as PAL-B01 and PAL-B02.

Moreover, the ITS sequences of the newly identified Metarhizium anisopliae isolates showed a 100% homology with the corresponding sequences of this fungal species available in the Gene Bank.

Similarly, the ITS sequences of the Beauveria bassiana new isolates showed 99% homology.

Spore germination of all isolates was not affected by temperatures of 25, 30, and 32oC.

However at 34oC, the spore germination rates of the M.

anisopliae isolates: PAL-M01 and PAL-M02 (99 and 83%, respectively) were significantly higher than those of the B.

bassiana isolates PAL-B01 and PAL-B02 (13 and 27% respectively).

At 36oC, spore germination of all isolates was severely inhibited, not exceeding 10%.

The maximal growth rates of mycelia of all isolates was recorded at 25oC without significant differences among them.

At 30oC, these rates were reduced substantially (by 11-49%) in all isolates.

However, as the temperature was increased to 32oC, the mycelial growth of the B.

bassiana isolates: PAL-B01 and PAL-B02 was significantly inhibited by 33 and 63%, respectively, whereas, the growth of the M.

anisopliae isolates: PAL-M01 and PAL-M02 was severely inhibited (98 and 83%, respectively).

Mycelial growth of all isolates was totally inhibited at 34oC.

The above effects of temperature imply that spore germination of both M.

anisopliae and B.

bassiana isolates tolerate higher temperatures than mycelia growth.

Furthermore, within a given fungal isolate, heat tolerance of spore germination is not necessarily coupled with heat tolerance of mycelial growth.