Comparison between two methods of mycelia growth evaluation of some Oomycetes species

Abstract

Oomycetes pathogens causes devastating crop diseases worldwide. In this study, we compared mycelium growth of 7 Oomycetes species using the calculated area (CA) method obtained by perpendicular diameter of colony and measured area (MA) method. Results revealed a significant difference between Oomycetes species inhibition ratio using CA and MA, at lower mefenoxam concentrations. The interval of variation between MA/CA methods was variable according to Oomycetes specie. The largest interval (0.01-1000 ?g/ml) was detected with Pythium aphanidermatum and Phytopythium mercuriale. The second interval (0.01-100 ?g/ml) was determined by Phytophthora cryptogea, P. aphanidermatum, P. ultimum and P. mercuriale. An interval ranged from 0.01?g/ml to 31.6?g/ml was recorded with P. cryptogea and Phytopythium vexans. An interval from 0.01 ?g/ml to 10?g/ml was determined with Pythium dissotocum and P. vexans; while the shortest interval (0.01-1?g/ml) was noted with P. nicotianae. In addition, present findings recorded a difference in Pearson’s correlation index between growth factors (medium, evaluation dates, mefenoxam concentration) and Oomycetes mycelium growth using MA and CA methods. A statistical significance difference (P<0.05), weas noted more in case MA method and was more expressed in case of CA method.