Effects of cluster thinning and irrigation amount on water relations, growth, yield and fruit and wine composition of Tempranillo grapes in Extemadura (Spain)

Abstract

<p style="text-align: justify;"><strong>Aim</strong>: The effects of cluster thinning and irrigation regime on vine performance and grape and wine quality of Tempranillo grapevines were studied in a field experiment carried out in Extremadura in Spain.</p><p style="text-align: justify;"><strong>Methods and results</strong>: Treatments were combinations of two irrigation doses (25% and 100% of estimated crop evapotranspiration) and two crop levels (thinned and unthinned vines). Cluster thinning was performed just before veraison to retain five clusters per m2 of vine leaf area. Results showed that irrigation amount produced important differences in stem water potential, leaf area index and berry growth but cluster thinning did not significantly affect these parameters. However, cluster thinning independently of the irrigation amount, advanced by seven days grape maturity and largely affected the main grape quality parameters, increasing total soluble solids concentration, pH, total anthocyanins and phenolic content and reduced must yield. Wines made from grapes of the thinned treatments also had higher contents of anthocyanins, tanins and colour index. This increasing effect was more noticeable in the lower irrigation dose. Similarly, the higher irrigation amount reduced phenolic content of wines.</p><p style="text-align: justify;"><strong>Conclusion</strong>: Both, lower irrigation rates and cluster thinning, despite decreased yield, improved wine composition. Overall thinning had a larger impact on grape and wine composition than irrigation.</p><p style="text-align: justify;"><strong>Significance and impact of study</strong>: In the semi-arid environment of the Extremadura region of Spain, irrigation in Tempranillo is important to obtain economically sound yield. However, the irrigation dose to apply might vary depending on the desired wine style. Irrigation to replace potential evapotranspiration should be avoided for premium wine production and, in these cases; deficit irrigation is probably preferred as a tool to increase yields but minimizing the negative effects on fruit and wine quality. Cluster thinning, performed just before veraison, can be also applied to accelerate ripening improving the overall fruit phenolic composition.</p>