RESUMEN
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.
RESUMEN
Aims: The efficiency of Verticillium dahliae inoculum density (ID) on tolerant cotton Verticillium wilt in cotton growing of northern province of Iran (Golestan) and the influence of temperature (T) and relative humidity (RHA) on this relationship. Place and Duration of Study: In several fields in Golestan province, northern Iran, between 1992-2009. Methodology: The microscleotia per gram of soil samples and disease severity of cotton Verticillium wilt were determined in several fields. Physiological time was determined as the cumulative number of degree-days from the time of sowing. Results: ID for overall fields and years varied between 2 and 47 propagules per gram of air-dried soil with average 18.961 ± 0.730. The pattern of diseased plants varied with fields and years. Linear regression analysis between ID (propagules per gram of air-dried soil) of V. dahliae at planting time and the disease severity for all years closely followed the linear curves. The straight line models described the increase in disease intensify index over the accumulated physiological time from sowing. The effect of temperature, number of days with above 28ºC and the area under RHA from sowing with respect of pathogen ID in soil (MS) on the final disease severity (Y) were significant and fitted a Y= 65.840- 0.0034 RHA + 0.57MS- 1.7T model with R2 = 0.859 and significant F function (p≤ 0.0001). Conclusion: this study revealed that Verticillium wilt severity of cotton related to V. dahliae ID in soil at planting and negative exponential models described the relationships. This work also demonstrated the influence of temperature (days with above 28°C) and relative humidity on the efficiency of Verticillium ID for disease severity. This simulation may be important to consider when selecting a cotton cultivar for planting or in breeding programs.