Annual Research & Review in Biology

Aims: To investigate the favorable temperature regimes for growth of Macrophomina phaseolina isolates in vitro and the adaptability of the isolates in relation to different climatic conditions of Iran.
Methodology: Forty-three isolates of M. phaseolina from different host (canola, cotton, melon, olive, pine, potato, safflower, soybean, sunflower, tomato and watermelon) collected in three different areas of Iran (north, northwest, southwest) were subjected to growth rate (GR) tests at 5, 10, 15, 20, 25, 30, 33, 35 and 40ºC.
Results: The optimum temperature for growth was 25ºC for 33 isolates and 33ºC for 10 isolates. Isolates GR varied considerably at all temperatures (p≤0.01) but the maximum variability between isolates occurred at 20 and 33ºC. Isolates from the north (colder area) grew better at lower temperatures than other isolates. Isolates from the southwest had the faster GR at 33ºC but the worst GR at the lowest temperature tested. The predicted relationship of GR and temperature for high optimum temperature isolates differ from other isolates. The results show the complete microsclerotial melanization at >30ºC for high optimum temperature isolates. The correlation was detected for the first time.
Conclusion: The environmental condition of the north and northwest areas of Iran are similar but differ from those of the southwest. High optimum temperature was detected among some isolates especially for growth of southwest isolates as warm area. It is possible that environmental conditions and cropping systems in the southwest have encouraged Macrophomina isolates to adapt to the higher temperature better than in other warm areas. On the basis of this study, we can affirm that combined GR values at 20 and 33ºC can be indicative of climatic areas of origin and that the fungus has adapted to these climatic conditions, which are far from the best, especially the colder conditions.