Nonparametric indices for the selection of hybrid citrus as rootstocks grafted with 'Valência' sweet orange

Abstract

The objective of this work was to evaluate five nonparametric selection indices for the selection of hybrid citrus rootstocks grafted with 'Valência' sweet orange, using horticultural traits relevant for the juice processing industry. Forty-six rootstocks were evaluated in a randomized complete block design, with three replicates and five trees in the plot, in the period from 2009–2015, in a rainfed cultivation. The means of the variables plant height, accumulated fruit yield, fruit yield efficiency, total soluble solids concentration, juice yield, and drought-tolerance were used to calculate the following indices: multiplicative index (I_Ei), sum of classification (I_MMi), genotype-ideotype distance (D_iI), and ranking indices (I_RKi, based on simple means; and I_RKii, based on linear normalization). The indices were efficient to classify the hybrids in relation to general performance. Spearman’s correlation showed a high similarity between most nonparametric indices, notably between I_RKi and I_RKii. The ranking indices, mainly I_RKii, provide a more coherent classification of the hybrids, which allows of the selection of more productive and drought-tolerant rootstocks to produce high-quality fruit for processing.