Factors influencing external fruit rot of cucumber caused by Didymella bryoniae

Steekelenburg, N.A.M. van

Factors influencing external fruit rot of cucumber caused by Didymella bryoniae

1982

Steekelenburg, N.A.M. van (Instituut voor Plantenziektenkundig Onderzoek, Wageningen (Netherlands))

Several factors influencing the occurrence and extent of external fruit rot caused by Didymella bryoniae on cucumbers in the post harvest period were studied. The minimum, optimum and maximum temperatures for growth of the fungus on fruits were circa 10, 23 and 35 deg C, respectively. The influence of the temperature on the growth of the fungus in vitro and in vivo was about similar. The fitness of the fungus diminished by storing inoculated fruits at about the maximum temperature for growth of the fungus for one day, but this temperature influenced fruit quality negatively. Storing at 10 to 12 deg C is more advisable. Isolates of D. bryoniae showed variation in virulence. There was a linear relationship between growth on fruits and growth in vitro of these isolates, but no correlation was found with disease incidence on plants. The degree of fruit rot was increased by more severe wounding, by storing in the dark instead of in the light and by higher nitrogen fertilization of the crop. Relative humidity during storage had no effect on fruit decay. It is very likely that the amount and composition of available nutrients for fungus growth determine the degree of rotting of the fruits. With the present cultivars, external fruit rot can be best controlled by reducing the chances of wounding in the pre- and post-harvest period.

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