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Abstract
Determinant cultivars ‘VF 145B-7879’ and ‘VF 109’ of processing tomato (Lycopersicon esculentum Mill.) develop smaller root systems under field conditions with less root proliferation particularly below 60 cm than semideterminant fresh market cultivars, ‘Early Pak’ and ‘Pearson’. Following fruit set, K concentration in shoots of ‘VF 145’ and ‘VF 109’ decreased from about 4% to below 2% resulting in K deficiency symptoms, whereas no deficiency symptoms were observed in ‘Early Pak’ and ‘Pearson’. The data suggest that the K deficiency condition is due to the inability of the relatively small root systems of the determinant tomato cultivars to absorb K at a rate sufficient to meet the demands of the concentrated fruit set. ‘VF 145’ and ‘VF 109’ compensate for the stress condition by translocating K out of leaves and stems and into fruit as evidenced by a negative rate of accumulation of K in the shoots. They also partition a higher percentage of absorbed K into fruit rather than into continued vegetative growth than ‘Early Pak’ and ‘Pearson’.
Resistance to fungal and bacterial pathogens can be induced in cucurbit crops by limited inoculation of young plants with necrosis inducing pathogens or by treatment with certain salt solutions. In greenhouse experiments with pickling cucumber (cv. Flurry), foliar applications of 2,6-dichloroisonicotinic acid (CGA-41396; Ciba Geigy) to seedlings enhanced both acid peroxidase activity and reduced the number of lesions per leaf in a dose dependent manner following a challenge inoculation. Maximum response was obtained with 20-30 mg a.i./L CGA 41396 treatment. Soil drenches were equally effective in inducing resistance. Under field conditions, multiple foliar applications of 35 mg a.i./L of CGA 41396 prior to flowering reduced the incidence of angular leaf spot lesions by >70% on leaves at harvest. Pickling cucumber fruit yields were significantly lower in controls than in CGA treatments due to disease pressure.