Evaluation of Methods to Disinfect Tomato Seeds Against Bacterial Canker (Clavibacter michiganensis subsp. michiganensis)

Abstract

Bacterial canker is a very important tomato disease in Uruguay. Its causal agent, Clavibacter michiganensis subsp. michiganensis (Cmm) is seed borne and, due to its high dissemination by water, labor, etc., the use of infected seed, even in low proportion, can lead to huge losses. Several methods for seed disinfection are recommended, but their effect in our conditions is not known yet. Sodium hypochlorite (1% active chlorine, one minute) and hot water baths (50 ºC, 25 minutes with and without a 37 ºC, 10 minutes pre-treatment) were compared to a non treated control. Seed was collected from diseased plants of Coral (2006) and Acuario (2007 and 2008) cultivars. Nine experiments were performed (approximately 760 seeds per treatment). Germination percentages and seedling vigor were evaluated. Seedlings were transplanted to sterilized substrate and cultivated at 23 ºC. Isolation to NAD was performed from stems when plants were over 20 cm high. Bacterial colonies similar to Cmm, were separated and subjected to the following tests: gram (KOH method), hypersensitive reaction on Mirabilis jalapa and DAS-ELISA. Isolates that did not show typical Cmm reaction were discarded. No detrimental effects were observed on the germination or in the vigor of seedlings. The percentage of plants on which Cmm was detected by DAS ELISA was: 5.6 (control), 2.03 (50 ºC water bath), 1.0 (50 ºC water bath with 37 ºC pre-bath) and 0.98 (sodium hypochlorite). Cmm detection was remarkably lower on seedlings derived from disinfected seed, confirming the benefits of this measure in the management of this disease.