a<p>SM, spontaneous mutation. UV, UV-mutagenesis.</p>b<p>Survival frequency, number of mutants/total number of zoospores used for mutant generation.</p>c<p>EC<sub>50</sub>, the effective concentration for causing 50% inhibition of mycelial growth inhibition of <i>P. melonis</i>.</p>d<p>Resistance factor β=β EC<sub>50</sub> of resistant isolates at the 10<sup>th</sup> transfer/EC<sub>50</sub> of its parent.</p