Comparison between non-parametric indexes in the selection of biofortified curly lettuce

Abstract

Selection indexes can be applied to simultaneous analysis of traits, increasing the efficiency of breeding in choosing the genotypes that meet the needs of both the market and the consumer. While it is a technic applied to several cultures, there are few studies about it in lettuce lines. For this reason, the aim of this study was to comparate assess the efficiency of different selection indexes for selecting biofortifiedleaf lettuce lines with good agronomic traits. The experiment was carried out at the Estação Experimental de Hortaliças of Federal University of Uberlândia (UFU), campus Monte Carmelo, in 2018. The experiment was designed in full randomized blocks of 3 repetitions with 25 leaf lettuce genotypes (22 lines from cultivars Pira 72 versus Uberlândia 10000 and 3 commercial cultivars – cv. Grand Rapids, UFU-Biofort and Uberlândia 10000). The lines are part of the UFU biofortified lettuce breeding program and were assessed for the total green mass (g), the stem diameter (cm), commercial leaves count, plant diameter (cm), foliar temperature (°C), SPAD index, anthocyanin content (mg 100g-1 sample), and bolting (days after sowing). To estimate selection gains, 10 genotypes were selected using both direct and indirect selection, as well as the traditional index, the sum of ranks index, Willians base index, and the multiplicative index. Mulamba and Mock sum of ranks index and Subandi multiplicative index provided the biggest total gains for the traits assessed in biofortified leaf lettuce. Both indexes were similar in selecting genotypes.

Genetic parameters and selection of biofortified lettuce genotypes based on selection indices

“…The direct selection gains obtained for the variables evaluated were, in decreasing order: 32.17% for the chlorophyll index, 27.20% for the number of leaves, 23.73% for the stem diameter, and 22.89% for the plant diameter (Table 3). In this study, direct selection provided individual gains greater than those of indirect selection, similar to the results found by Peixoto et al (2020).…”

“…The values obtained for the CVg/CVe ratio were close to or greater than one for all the evaluated traits, which corroborates that genetic variation is the main factor responsible for the estimated variation of the character, as when the CVg/CVe ratio approaches a value of one or greater, the selection gain is increased (Vencovsky & Barriga, 1992). Similar results were also observed by Souza et al (2008) and Peixoto et al (2020), who evaluated lettuce genotypes and found CVg/CVe ratios close to or greater than one for the variables analyzed.…”

“…These values show that the genotype has a greater effect on the evaluated trait, and the h 2 is considered high for values greater than 0.7 (Baldissera et al, 2014). Characters with a high h 2 indicate a high component of the inheritable fraction of the variation (genetic component) in their phenotypic expressions, demonstrating that gains can be achieved through visual selection (Silva et al, 2019), as performed in the present study Peixoto et al (2020) estimated the genetic parameters of eight variables analyzed in 25 lettuce genotypes from the same breeding program (generation F7) and also found high h 2 values for the number of leaves (91.42%), SPAD index (95.96%), and plant diameter (72.77%), confirming the high magnitude of h 2 for these traits. In contrast to this study, Oliveira et al (2019) found low heritability estimates of 6.94% for the chlorophyll index, which may be related to the fact that although it was carried out in the same experimental area with the same cultural practices, different parents were used.…”

“…The stem diameter showed a significant positive correlation with the number of leaves (Table 2). Peixoto et al (2020) correlated six variables of biofortified lettuce and observed that the stem diameter was positively correlated with the number of leaves and plant diameter. In addition, the plant diameter was negatively correlated with the SPAD index, similar to these results.…”

“…Cândido et al (2017) found CV values of 7.79% for the number of leaves in lettuce. Peixoto et al (2020), in their study h² -Narrow sense heritability; CVg -Coefficient of genetic variation; CVe -Coefficient of experimental variation; GMS -Genotype mean square; EMS -Error mean square; ** -Significant at p ≤ 0.01 by F test on biofortified curly lettuce, found CV values similar to those found in the present study for stem diameter (11.99%), and lower values for the number of leaves (9.77%), plant diameter (7.99%), and SPAD index (6.24%).…”