Verónica Obregón
Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bella Vista; Argentina
[email protected]


Corrientes province develops a very important horticultural activity in the NEA, where protected vegetables, mainly tomato and pepper, predominate from February to December. This long cycle, together with the intensive use of soil with greenhouse monoculture, increases the population of soil pathogens, causing plant losses. Solarisation arises as an alternative for the elimination of atmosphere ozone-depleting methyl bromide (Pinkerton et al., 2000, 2002, Chauhan et al., 1998; Stapleton, 1997; Banu et al., 1998; 2001, Katan et al., 1976), and it is also a tool with low environmental impact that fits perfectly with integrated pest and disease management. This technique has been developed in Corrientes by INTA B. Vista and was adopted by farmers. Important soil pathogens affecting horticultural crops include Damping-off (fungal complex), which causes wilting and death of plants at the beginning of the crop, and tomato bacterial wilt (Ralstonia solanacearum), a systemic bacterium that enters through the root from contaminated soil and can occur at any time during the crop cycle. For many years, several experiments have been carried out to evaluate the efficacy of solarisation against soil pathogens.

The first trial was aimed at reducing the initial inoculum of R. solanacearum through different variants of solarisation: total mulch (T1), in the plantation line (T2), confined atmosphere (closed greenhouse without plastic cover on the soil) (T3) and a control outside the greenhouse in the open air (T4). The experiment consisted of placing a concentrated bacterial suspension (5×108) in eppendorf tubes buried at 20, 40 and 70 cm in each treatment and colonies were identified and quantified in the laboratory by Petri dishes dilution technique in Kelman culture medium with TZC at 15, 30 and 45 days after solarisation. T4 differed significantly from the rest of the treatments (according to duncan α = 0.05) at 20, 40 and 70 cm, but T1, T2 and T3 did not at any of the depths tested. Under the test conditions, Ralstonia solanacearum was not recovered from the solarised soils at T1, T2 and T3 because of the action of temperatures during solarisation.

In the second trial, thermal efficacy was evaluated for the control of Pythium aphanidermatum, Rhizoctonia solani, Sclerotinia sclerotiorum (mycelium and sclerotia). Soil treatments were: total solarisation (T1), plantation line solarisation (T2), and confined atmosphere (T3). Pathogens were plated on potato glucose agar (APG), and kept in an oven at ± 27ºC until the Petri dish was full. Agar discs with the fungus were then cut and placed in eppendorf tubes.  The tubes were buried at 20, 40 and 70 cm depth in each treatment for 15, 30 and 45 days. At the end of each period, the tubes were removed and viability was determined by seeding the respective fungal discs in APG. Highly significant differences were observed between P. aphanidermatum, which survived in a confined atmosphere at 70 cm for up to 15 days, and the fungi R. solani and S. sclerotiorum, which were controlled by thermal action in the three treatments, depths and residence time evaluated.

These experiences show that biosolarisation is an effective tool for the management of soil diseases in protected crops. On the one hand, the population of bacteria and phytopathogenic fungi can be reduced for a prolonged period of time, but the physical, chemical and microbiological phenomena that occur in the soil using this technique still need to be studied.