Height and number of leaves in avocado rootstocks (Persea americana Mill.) as predictors of grafting readiness: a mixed-effects model and logistic regression approach

Grafting is the main propagation method used in avocado (Persea americana Mill.) seedling production, and accurate determination of rootstock maturity is essential for its success. While stem diameter measured at 15 cm above the soil (D15) is traditionally used as the maturity indicator, this study explores indirect traits of plant height (PH) and number of leaves (NL) as potential alternatives. We evaluated 88 plants weekly over 14 weeks, recording PH, NL, and D15. A mixed-effects model was used to assess the relationship between PH and NL with D15, and a logistic regression model was applied to predict grafting readiness (defined as D15 ≥ 6 mm). Both variables had significant effects on D15 and on the probability of readiness, with PH showing higher statistical precision than NL. Model evaluation was performed through residual analysis for the mixed model and ROC curve assessment for the logistic regression, both confirming satisfactory model fit and supporting the reliability of the resulting inferences. These findings support the use of PH and NL as non-invasive indicators of rootstock maturity, potentially reducing costs and simplifying decision-making in nursery operations.