Estimates of repeatability and path coefficients on grapes

The objective of this study was to estimate the repeatability coefficient, the minimum number of evaluations to which a trait should be subjected and the effect of the inter-relationships of five characters on grapevine (Vitis spp.) yield, aiming at getting useful information for breeding strategies of this fruit crop. Repeatability coefficients were estimated for the following characters: total soluble solids (TSS); total titrable acidity (TTA); TSS/TTA ratio; berry length, diameter and weight; bunch length, width and weight, and number and yield of bunches per plant on eleven seedless grape varieties in five yield cycles (1997 and 1998) in Petrolina-PE. The repeatability estimates were obtained by the main components method from the correlation matrix. The simple correlation coefficients were calculated and they were partitioned into direct and indirect effects by the path analysis. The estimated repeatability coefficients ranged from 0.4750 to 0.8372 associated to the coefficients of determination from 81.9% to 96.26%. The traits TSS, TTA and bunch length presented low repeatability coefficients, meaning a low regularity of performance from one measurement to another. The other characters showed regularity on the repetition of the behavior of the genotypes. The results of the path analysis showed that the studied variables satisfactorily explain the character yield per plant.