Recent Late Blight Isolates in Florida and Updated Management Options

CASE STUDY In July, 1978 a 30-lb box of packed tomatoes (variety 'Improved Walter') was sent from a receiver in Orlando to the posthar-vest Pathology Laboratory in Gainesville (Bartz, 1980). The fruit had been grown and packed in the Quincy region. Since the area was new to tomato production back then, ripening rooms had not yet been constructed. So, this box had not been gassed. The shipment had been rejected by the receiver in Orlando due to progressive decay. When opened a day later , 60% of the fruit in the box had primary decay lesions. The survivors were stored at 68 o F for 1 week and an additional 5% of the original contents had developed lesions. At this point, the survivors were more or less fully red and were discarded. An investigation of the shipment revealed: • 59% of the lesions observed were directly beneath or beside the stem scar and internal. • 10% of the lesions were adjacent to or beneath the blossom scar and internal. • 29% of the lesions were midway between the blossom and stem scar and internal. • 2% of the lesions were directly connected with a wound on the fruit surface. • ≥ 6 different pathogens were isolated from lesions. • Fruit in the fi eld were not affected. • Tank capacity was limited in this new packing shed operation. • Ambient air temperatures were high. • Calcium hypochlorite was periodically added to the water system but free chlorine concentration was not measured. • Symptoms could be reproduced if a suspension of one of the pathogens was vacuum-infi ltrated into fruit. The pathogens were isolated, identifi ed and proven to be the causal agents with Koch's postulates. Each one was strictly a wound invader; none could penetrate directly through the tomato cuticle. Since only 2% of the lesions were clearly associated with wounds, the pathogens had to have entered the fruit, which is called internaliza-tion. An infi ltration of fruit by dump tank or washer water was implicated since fruit that were vacuum infi ltrated with water suspen-sions of bacteria developed symptoms like those in the outbreak box. The question then became: how this could have happened? Tomato fruits are fi lled with air-spaces. Mature-green tomatoes fl oat when dumped into water. They do not normally absorb water and certainly do not absorb any through their waxy surfaces. Gas exchange between the …