Effect of variety choice and use of resistant rootstock on crop yield and quality parameters of tomato plants grown in organic, low input and conventional production systems/growth media Theodoropoulou, A.1, Giotis, C .1,2, Hunt, J. \ Gilroy, J .1, Toufexi, E .1, LiopaTsakalidis, A.3, Markellou, A.4, Lueck, L .1, Seal, C .1 & Leifert, C.1 Key words: organic, low input, conventional, tomato production, resistant rootstocks, fruit quality Abstract Soil-borne diseases are one of the most important problems in organic and other ‘low input’ soil-based greenhouse production systems. While chemical soil disinfection has been the method of choice in conventional farming systems, soil steaming has been the main strategy for the control of soil borne diseases in organic production. Both methods are extremely expensive and have been increasingly restricted for environmental reasons by government and organic standard setting bodies respectively. The use of tolerant varieties and of grafting onto resistant rootstocks were evaluated as potential replacements for soil steaming in organic and low input systems and found to be as effective in reducing root disease and increasing root fresh weight, fruit yield and number. The effects on fruit yield and quality characteristics were then further evaluated using different varieties for grafting and different growth media typically used in (a) organic (soil amended with manure), and (b) conventional (perlite fertilised with mineral fertilisers via the irrigation system) growth media/fertilisation regimes, and also a (c) novel ‘low input’ growth medium designed to provide better aeration of the rooting zone. Fruit numbers, diameters and weights and total fruit yields were significantly different between growth media and highest for plants grown in the ‘low input’ system, slightly lower for plants grown in the perlite and lowest for plants grown in the organic system. The potential for replacing chemical and steam soil disinfection methods in organic and ‘low input’ soil based greenhouse production systems is discussed. Introduction The most important reasons for yield losses in soil-based and organic tomato production systems are soil-borne root and vascular diseases, in particular corky root rot (Pyrenocheta lycoperici) and Verticillium spp. (Pegg & Brady, 2002). In conventional greenhouse production chemical soil disinfection (e.g. methyl bromide, chloropicrin, isothiocyanide) is widely used to control soil borne diseases, while soil steaming is widely used in organic greenhouse production systems (Overmans & Jones, 1986; Pegg & Brady, 2002; Georgakopoulos, 2002).
1 Nafferton Ecological Farming group, Newcastle University, Stocksfield NE43 7XD, UK, E-mail:
[email protected] or
[email protected] 2 Department for Ecological Agriculture, Technological Educational Institute (TEI) of the lonion Islands, Argostoli, Kefalonia, Greece 3 Department of Agricultural Machinery and Irrigation, Technological Educational Institute (TEI) of Messolongi. Messolongi, Greece 4 Laboratory of Efficacy Evaluation of Pesticides, Department of Pesticides Control & Phytopharmacy, Benaki Phytopathological Institute, 7 Ekalis Street, Kifissia, Greece
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Chemical and steam soil disinfection methods have both been linked to significant negative environmental impacts. For example, soil steam treatments were shown to significantly increase the energy/fuel use in glasshouse production and both soil steaming and chemical soil treatments were shown not only to eliminate fungal pathogens, but also the saprophytic and beneficial soil microflora and fauna (Bennett et at. 2003; van Loenen 2003). In addition, methyl-bromide treatments are known to contribute to the depletion of the atmospheric ozone layer and associated human health impacts (e.g. higher risk of skin cancer) (Workneh & van Bruggen, 1994). The main objectives of the study reported here were to (a) identify alternative strategies for the control of soil borne diseases and (b) to evaluate the impact of such novel control methods on fruit yield, size and quality parameters. Materials and methods Soils and substrates: In both experiments soil shown to be infected with corky root rot and Verticillium (presence of root rot symptoms on >60% of plants in the previous seasons crop and confirmation of the presence of both pathogens by standard mycological tests) was collected from different parts of a commercial organic glasshouse unit and then mixed with manure and homogenised using a concrete mixer to minimise differences in substrate structure, texture and inoculum density and then placed into pots (15 L volume). In experiment 2, two additional substrates were used: Perlite (P) (the standard growth medium used in conventional ‘out-of soil’ tomato production systems in Greece) were also used and a novel ‘low input’ substrate consisting of equal amounts (v/v/v) of soil, gravel and perlite (SGP, which was developed at Theodoropoulou nurseries, Nafpaktos, Greece, and designed to provide better aeration of the rooting zone). Treatments: In experiment 1 the performance of plants grafted onto resistant rootstocks (the fruiting cultivar ‘Star fighter’ was grafted onto rootstock ‘Beaufort’ that is resistant to corky root rot) was compared with that of plants grown in steam disinfected (positive control) soil and non-grafted plants grown in untreated soil (negative control). For steam treatment a commercial soil-steaming machine used for horticultural substrates (Camplex HD5116 Electric Soil Steriliser, Thermoforce Ltd. Cumbria, U.K) was used. Soil was heat treated at 81 °C for 30 minutes. Several other soil treatments were also included in Experiment 1, but are not reported here. In experiment 2, a factorial design was used with (a) 3 different substrates (see above), (b) 3 different cultivars (Belladonna, Electra and cultivar 984) with different levels of tolerance to Verticillium spp. and (c) grafting or non-grafting of the corky root rot resistant rootstock R5872 as factors. Assessments Fruits were collected at ‘uniform red’ stage (according to colour charts used in commercial glasshouse production) and fruit number, weight and size recorded. At the end of the experiment the roots of all plants were rinsed under tap water and root fresh weight was determined. Finally roots were dried in an oven (at 80oC for 24h) and root dry weight was measured. The difference in root fresh and dry weights between plants grown in steam disinfected and non-steam disinfected soils was used as a measure of overall root damage caused by soil borne pathogens. Sugar and antioxidant levels in fruit were analysed using standard protocols (FRAP, Benzie & Strain, 1996; TEAC, Re etal., 1999). Results and discussion In experiment 1, yields, root fresh and dry weight of plants grafted onto resistant rootstocks were significantly higher compared with untreated (negative) control plants,
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but not significantly different from those grown in steam disinfected soils (positive controls) (Table 1). Table 1. Effect of soil amendments, grafting onto resistant rootstocks and soil steaming on tomato fruit yield, number, and, root fresh weight in the presence of significant soil borne disease pressure (Experiment 1) % difference compared with negative control plants Treatment Root fresh weight Fruit number Fruit yield 1. Untreated control Ob Ob 0 be 22 ab 2. Resistant rootstock 59 a 71 a 41 a 3. Soil steam disinfection 78 a 79 a Means in the same column followed by the same letter are not significantly different according to Tukey’s Honest Significant Difference Test (p
