Regular Article Morphological and Biological Characterization of Monosporascus cannonballus isolates, responsible of watermelon decline in Kairouan's area

Watermelon grown in Kairouan's region is infected by vine decline disease caused by M. cannonballus. In vitro tests showed that this pathogen produces perithecia with a diameter of 495 µm releasing ascospores with a diameter of 44 µm. The mycelium is very fine, rarely visible in the media KOMADA and TANAKA. The colony of different isolates on substrate culture such as Malt, MS and S, appears very dense. On PDA, the grayish brown color characteristic of this ascomycete was observed. The perithecia production in vitro test for this fungus requires relatively long period of incubation (45 days). The effect of culture media showed that the PDA, MS and Malt are the best for the mycelia development of M. cannonballus. The most favorable culture media for fructification are in descending order MS, S, PDA, Malt. M. cannonballus isolates tested in this study showed an optimum temperature of mycelial growth and reproduction of 30°C. MT15 and MT12 isolates originated from Chebika (Kairouan government) showed a significant mycelial growth at all temperatures of incubation. MT7 and MT14 isolates from the same region were the most fertile. The results of pH effect on M. cannonballus development have revealed that the maximum mycelial growth occurred at pH 6 for most of isolates and for the fructification occurred at pH 4 and pH 8. For the osmotic pression with the addition of NaCl and KCl, the optimal development for majority of isolates is registered at -0.5 MPa and -2 MPa, with a minimum at -4MPa. The inhibition of the fructification of the M. cannonballus isolates occurred beyond -2MPa.