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

Abstract

The aim of this work was evaluation of 24-epibrassinolide influence 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 efficient water capacity (EWC); the critical value of the EWC was 80% for optimally irrigated fields (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 after planting, and C – application of 24-epibrassinolide 2 x (immediately after planting and then after 14 days after 1st application). Concentration of 24-epibrassinolide was 10−6. Following parameters of head lettuce were set after 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. Influence of 24-epibrassinolide on single lettuce head weight was not significant, decrease of head weight was evident after 24-epibrassinolide application in some variants. Significant increase of marketable heads number and their percentages were noted after 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 (nonsignificant) of total marketable yield (in t/ha) was noted after 24-epibrassinolide application. No significant differences 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 after 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 influence of 24-epibrassinolide application on the nitrate content was not significant, but the trend of nitrates decrease in optimal irrigation conditions is evident.

Keywords

• 24-epibrassinolide
• lettuce
• yield
• quality
• ascorbic acid
• nitrates