Whilst plants are susceptible at all stages of growth disease symptoms are rarely observed prior to fruit set on trusses 3-4. However, it is important to remember that the pathogen can be seed-borne and, whilst it is unusual to see early symptoms during propagation of the crop, wilting may occur especially on grafted plants and localised lesions may also form as a result of bacterial transmission under high humidity conditions. Whilst such infected seedlings may be quickly killed or produce weak stunted plants, if conditions are unfavourable for the pathogen, infected seedlings may initially develop into apparently healthy plants without obvious disease symptoms. Such symptomless or latent infections are potentially a major problem with respect to early detection on the nursery. It is also important to remember that from localised lesions the pathogen can enter the plant via natural openings (e.g. stomata and hydathodes) from where it can gain entry into the vascular system and become systemic when the crop is handled (e.g. de-leafed / trimmed). Speed of symptom expression The time taken from initial infection to the onset of visible symptoms varies considerably and delays of 4-6 weeks and as long as 3 months between first outbreaks and secondary spread to adjacent plants has been observed previously. Experimental and other observations in infected crops have shown that the time between infection and appearance of symptoms can vary by as much as 10-34 days. This is likely to be due to a differential temperature (the optimum temperature for growth of the pathogen is in the range of 24-27oC so cooler temperatures will slow down the infection progress), plant age (5 week old transplants appear to have a longer latent period prior to symptom expression than 3 week old transplants) and inoculum potential (the more bacteria present initially the quicker the symptom development).