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KOUDELA, M., HNILIČKA, F., MARTINKOVÁ, J., SVOZILOVÁ, L., DOLEŽALOVÁ, J.: Yield and quality of head lettuce a er 24-epibrassinolide application under optimal and reduced irrigation. Acta univ. agric. et silvic. Mendel. Brun., 2012, LX, No. 3, pp. 93–100 The aim of this work was evaluation of 24-epibrassinolide infl uence on yield and quality of head lettuce in optimal and reduced moisture conditions and work out recommendation of 24-brassinosteroids use for lettuce in growers praxis. Field trials were carried out on land belonging to the Demonstration and Research Station of CULS in Prague – Troja in 2009 and 2011. Planting on 27. 8. 2009 and 20. 8. 2011 was done at planting space 0.25 × 0.30 m, each variant in four repetition (single plot 4,5 m2). Seedlings of head lettuce (cultivar Santoro – Rijk Zwaan) were used. Irrigation was carried out by microspraying, and was based on current values of effi cient water capacity (EWC); the critical value of the EWC was 80% for optimally irrigated fi elds (irrigation O), and 50% for variants with reduced levels of irrigation (irrigation S). The total amount of irrigation water during vegetation were as follows: the variant with optimal levels of irrigation (O) had 131 mm in 2009 and 123 mm in 2011; the variant with reduced levels of irrigation (S): 58 mm in 2009 and 63 mm in 2011 Three variants were in both (O and S) conditions: A – no application of 24-epibrassinolide, B – 1 × 24-epibrassinolide application immediately a er planting, and C – application of 24-epibrassinolide 2 x (immediately a er planting and then a er 14 days a er 1st application). Concentration of 24-epibrassinolide was 10−6. Following parameters of head lettuce were set a er harvesting (10.–12. 10. 2009 and 14.–15. 10. 2011): weight of single heads, marketable heads, marketable yield (in pcs/ha and t/ha) and ascorbic acid and nitrate contents. Infl uence of 24-epibrassinolide on single lettuce head weight was not signifi cant, decrease of head weight was evident a er 24-epibrassinolide application in some variants. Signifi cant increase of marketable heads number and their percentages were noted a er 24-epibrassinolide application in optimal moisture conditions – in variant B of 12 261 heads/ha (11.1 %) and in variant C of 16 279 heads/ha (14.7 %) compared with non treated variant A. This trend was not visible in reduced moisture conditions. Increase (nonsignifi cant) of total marketable yield (in t/ha) was noted a er 24-epibrassinolide application. No signifi cant diff erences were founded among the ascorbic acid contents in each irrigation variant. A higher ascorbic acid content (by approximately 11.9 % in variant C compared with control A) is evident a er application of 24-epibrassinolide in the variant with lower levels of irrigation – S. Contrarily, decrease ascorbic acid content is indicated in the optimal levels of irrigation – O (by approximately 16.8 % in variant C compared with control A). The infl uence of 24-epibrassinolide application on the nitrate content was not signifi cant, but the trend of nitrates decrease in optimal irrigation conditions is evident. 24-epibrassinolide, lettuce, yield, quality, ascorbic acid, nitrates The imbalance in the water status (more water defi cit) can occur wilting plants. The absence of accessible water in the soil usually occurs a er the initial and transition stage of wilting the permanent wilting (the irreversible wilt) (Šebánek et al., 1983). As shown by (Malý et al., 1998) most vegetables have a high transpiration rate, ranging from 280 to 830 ml of water to 1 g dry weight, the transpiration rate of 94 M. Koudela, F. Hnilička, J. Martinková, L. Svozilová, J. Doležalová cabbage gives Vogel, (1996) value between 500 and 580. Malý et al. (1998) also defi nes a limit value of 50% of the effi cient water capacity, which when it drops below the value of all vegetables are suff ering water shortages. In this context it is necessary to seek means to reduce the negative impact of water defi cit for growers praxis. Applications of brassinosteroids could be one way to limit the negative impact of water deffi cit in vegetable production, because this hormons help by reducing of environmental stress impact of plant physiology, e.g. in connection to temperature (Ogweno et al., 2008), to water defi ciency (Jager et al., 2008) or water excess (Takematsu and Takeuchi, 1999). The hypothesis of this work was: application of 24-epibrassinolide during vegetation can minimize negative infl uence of water deffi cit in head lettuce production. MATERIAL AND METHODS Field trials were carried out on land belonging to the Demonstration and Research Station of CULS in Prague – Troja in 2009 and 2011, which is situated 195 m above sea level, in a mild warm and dry area. Soil of the Demonstration and Research station in Troja is clasifi ed as modal fl uvisol with a pH of 6.6–6.9. Average temperatures during the vegetation period were 15.8 oC in 2009 and 16.9 oC in 2011. Planting on 27. 8. 2009 and 20. 8. 2011 was done at planting space 0.25 × 0.30 m, each variant in four repetition (single plot 4,5 m2). Seedlings of head lettuce (cultivar Santoro – Rijk Zwaan) were used. Irrigation was carried out by microspraying, with an amount 10–20 mm (with respect to the development of the vegetation) and was based on current values of effi cient water capacity (EWC); the critical value of the EWC was 80% for optimally irrigated fi elds (irrigation O – continuous line in graphs), and 50% for variants with reduced levels of irrigation (irrigation S – discontinuous line in graphs). The total amount of irrigation water during vegetation were as follows: the variant with optimal levels of irrigation (O) 131 mm in 2009 and 123 mm in 2011; for the variant with reduced levels of irrigation (S): 58 mm in 2009 and 63 mm in 2011. In the optimal conditions and also in the lower levels of irrigation were three variants: A – no application of 24-epibrassinolide, B – 1 × 24-epibrassinolide application immediately a er outplanting, and C – application of 24-epibrassinolide 2 × (immediately a er planting and then a er 14 days a er 1st application). Concentration of 24-epibrassinolide was 10−6. The lettuce was cultivated in accordance with techniques recommended by Petříková et al. (2006). Standard fertilizer applications (according to the analysis) and weed control practices were used. Following parameters of head lettuce were evaluated a er harvesting (10.–12. 10. 2009 and 14.– 15. 10. 2011): weight of single heads, marketable heads, marketable yield (in pcs/ha and t/ha) and ascorbic acid and nitrate content. The contents of ascorbic acids, nitrates, dry matter, and values of total antioxidative capacity were also evaluated. The refl ectometric method (Refl ectoquant – Merck) was used for ascorbic acid and nitrate content determination. Mixed samples from three plants from each repetition (each trial variant was grown in 4 repetitions) were prepared for analysis. The measured values were statistically analyzed using the STATISTICA Cz, versions 9.0 so ware system for data analysis. RESULTS AND DISCUSSION Average values of the evaluated lettuce parameters are given in Table I. Infl uence of 24-epibrassinolide on single lettuce head weight was not signifi cant, but decrease of head weight was evident a er 24-epibrassinolide application in variant with lower irrigation and 1 x application of 24-epibrassinolide – compared to control variant. Increase of marketable heads number and their percentages were noted a er 24-epibrassinolide application. This increase was signifi cant in optimal moisture conditions in variant B with 12 261 heads/ha (of 11.1 %) and in variant C with 16 279 heads/ha (of 14.7 %) compared with non treated variant A. This trend was not visible in reduced moisture conditions. Increase of total marketable yield was noted a er 24-epibrassinolide application, but eff ect was not signifi cant. But lettuce is sold for price per piece in praxis, therefore number of marketable heads has a greater interpretative value for praxis. As indicated by numerous studies, application of brassinosteroids can reduce negative environmental impacts, e.g. application of brassinosteroids limits negative infl uence of salinisation (El-Fattah, 2007), pesticides (Xia et al., 2006) or biotic stressors (Masuda et al., 2007). The increase of marketable heads (pcs/ ha) a er 24-epibrassinolide is infl uenced mainly by reduction of heads rooting. The aditional protective eff ect is also reported by Nakashita et al. (2003). The positive eff ect of brassinosteroids are therefore not refl ected only in increased volumes of phytomass, but by its higher quality, which has considerable signifi cance for quality classifi cation. It can lead to greater profi tability of production for per piece sold vegetables such as for lettuce. Average values of the ascorbic acid and nitrates contents are given in Table II. However signifi cant diff erences in ascorbic acid content was not infl uenced by irrigation, a higher ascorbic acid content is evident a er application of 24-epibrassinolide in the variant with lower levels of irrigation (by approximately 11.9% in variant C compared with control A). Contrarily, decreasing ascorbic acid content is evident in the optimal levels of irrigation – O (by approximately 16.8% in variant C compared with control A). The increase antioxidant compounds (including ascorbic acid) in plants due to abiotic stresses is mentioned by Babu and Devaraj (2008) in trials with Phaseolus vulgaris L., Nair et al. (2008) in trials with Vigna unguiculata L. and Koudela et al. (2011) in Yield and quality of head lettuce a er 24-epibrassinolide application under optimal and reduced irrigation 95 trials with caulifl ower. The eff ect of oxidative biotic and abiotic stress on the increase of antioxidant components in plants is also reported by Hernandez et al. (2009). The infl uence of 24-epibrassinolide application on th

Yield and quality of head lettuce after 24-epibrassinolide application under optimal and reduced irrigation