Cumagun C.J.R., Aguirre J.A., Relevante C.A., Balatero C.H. (2010): Pathogenicity and aggressiveness of Fusarium oxysporum Schl. in bottle gourd and bitter gourd. Plant Protect. Sci., 46: 51-58.Fusarium oxysporum is responsible for a large range of diseases on economically important crops such as bitter gourd and bottle gourd. Pathogenicity and aggressiveness of F. oxysporum in bitter gourd and bottle gourd isolated from two breeding stations of East-West Company in the Philippines namely San Ildefonso, Bulacan and Lipa, Batangas were tested. Eleven F. oxysporum isolates from bitter gourd and 12 isolates from bottle gourd were inoculated on 7-day and 1-month-old bitter gourd and bottle gourd plants in the greenhouse. All F. oxysporum isolates from bitter gourd were pathogenic on 7-day-old and 1-month-old bitter gourd and nine out of 12 isolates from bottle gourd were pathogenic on bottle gourd. Three isolates from the infested soil were non-pathogenic on bottle gourd. There was a significant difference in aggressiveness of the isolates on their natural hosts (P ≤ 0.05). There also was a significant difference in the aggressiveness of isolates pathogenic on bitter gourd from Batangas and Bulacan (P ≤ 0.05) but isolates from Batangas and Bulacan had similar aggressiveness as bottle gourd (P ≥ 0.05). Aggressiveness of F. oxysporum on 7-day-old bitter gourd and bottle gourd was significantly different compared to those on 1-month-old plants, demonstrating an effect of the host age onaggressiveness. Correlations between aggressiveness of F. oxysporum isolates on 7-day-old and 1-month-old bitter gourd and bottle gourd were moderate (r = 0.63, 0.78). Out of 12 isolates from bottle gourd, only one isolate was pathogenic on 7-day-old bitter gourd. Four of the isolates from bitter gourd were pathogenic on 7-day-old bottle gourd but not on 1-month-old bottle gourd. No cross infection was observed on mature plants.