A protocol for cdentifying characteristic sucrose accumulation curves of sugarcane genotypes (Saccharum spp.)

Abstract

Sucrose accumulation curves represent the maturity profile of sugarcane cultivars, which is considered as a character of interest for the selection of genotypes in breeding programs. However, variations due to the environment (E) and interaction between genotype and environment (G × E) may be confused with the effect of genotype (G) and hinder the selection process of promising clones. The objective of this study was to identify a group of accumulation curves with high intra-group genotypic variability in the sucrose accumulation process throughout several E. This group is then used to select genotypes according to their maturity profile. A protocol is presented whereby the following statistical tools are integrated: (i) classification of nonlinear accumulation curves according to parameters associated with the beginning of the maturity process, sucrose accumulation rate and the time elapsed until the accumulation rate decreases, (ii) estimation of the genotypic contribution to intra-group variability of each accumulation curve parameter within each group and (iii) identification of the group of accumulation curves with the higher contribution of genotypic variability to total variance of sucrose accumulation parameters. The novelty of the work lies in the sequence of analytical steps to identify information useful to select genotypes according to their maturity profile. The protocol involves estimating parameters of nonlinear models for fitting maturity curves in multi-environment trials, clustering of curves according to the sucrose accumulation parameters and estimation of variability due to G, E and G × E within each cluster to identify the group with characteristic genotypic curves. Its implementation is illustrated using 175 sucrose accumulation curves of nine sugarcane clones evaluated in different crop cycles (first and second ratoons) and several environments (7 to 50 for each clone) in Tucumán, Argentina. The proposed protocol allows identifying sucrose accumulation curves that exhibit a high genotypic variance, thus facilitating the selection of the best clones.