Allometric models for leaf area estimation and ceptometer validation in assessing the leaf area index of ‘Cabernet Franc’ and ‘Malbec’ grape cultivars produced under cycle inversion

Leaf area is an important parameter for analyzing the growth and development of grapevines, which has been obtained using direct non-destructive methods and mathematical models based on the relationship between assessed and estimated leaf area. This study aimed to adjust and validate mathematical equations for estimating the leaf area of ‘Cabernet Franc’ and ‘Malbec’ grape cultivars trained to a three-wire vertical trellis and submitted to the cycle inversion technique in São Roque - SP. In addition, the use of the AccuPAR® ceptometer was validated to determine the leaf area index. Leaves of different sizes wererandomly collected, and the central and lateral veins were measured, obtaining leaf area using the WinRHIZO® system. Linear and non-linear models were tested, and the quadratic equation for ‘Cabernet Franc’ grape and the power equation for‘Malbec’ grape had the best fits, with determination coefficients = 90%. In thevalidation, all models showed correlation and no statistical differences with the evaluated leaf area. It was, therefore, possible to obtain leaf area data using a simpleand non-destructive method. For ‘Cabernet Franc’ grape, the suggested equation was y = 0.5215 x2 – 4.473 x + 32.235, and for ‘Malbec’ grape, y = 0.5428 x1.8599.When the leaf area index was indirectly obtained using the AccuPAR® ceptometer, LAI values obtained at the ripening stage were underestimated.