EXPEDIENCE OF USING SCORING ASSESSMENT OF QUALITY TRAITS IN LEAF LETTUCE BREEDING
Authors:   Institute of Vegetable Growing and Melon Growing of the National Academy of Agrarian Sciences of Ukraine, Kondratenko Serhii , Tkalych Yurii ,   Ukrainian Institute of Plant Varieties Examination
Published: June 2024

A significant reserve for increasing the efficiency of mutational breeding of lettuce (Lactuca sativa L. var. secalina) is the use of score (code) scales to assess the characteristics of the manifestation of quality traits that cannot be determined in physical units of measurement. The purpose of the experimental work is to establish the effect of a mutagenic factor (γ-irradiation) on the formation of qualitative traits that determine the phenotype of the leaf blade and to study the correlation between their manifestation and the manifestation of selective value quantitative traits in the created mutant generation M4 of leaf lettuce. The research methodology is based on the application of a physical mutagenic factor to expand the genetic diversity of leaf lettuce (pre-sowing γ-irradiation with doses of 7, 11 and 15 kR of air-dry seeds), a point (code) assessment of the peculiarities of the manifestation of quality traits in the M4 mutant generation, non-parametric criteria for the difference of the investigated biological objects, computational and analytical calculations of statistical indicators for quality features, correlation analysis. The results of the conducted research made it possible to differentiate γ-irradiation doses according to the degree of effectiveness in creating mutant lines of leaf lettuce with different degrees of genetic distance from the original form – the Divogray variety. The peculiarities of the mutagenic effect of γ-irradiation on the expansion of the spectrum of genotypic variability of leaf lettuce according to 17 qualitative features that determine the phenotype of the leaf blade have been clarified. Among the lines, four (D(7) (ind. selection – 1), D(11), D-1(15) and D-2(15) were selected, in which the range of variation of the indicator "Average index of normalized values" (Xmed = 0.77...1.47) was within the margin of error of the average statistical value of the corresponding indicator of the Divogray variety (Xmed = 1.07±0.69). The exception is line D(7), which had a statistically significant deviation from the original form (Xmed = 0.42±0.39). The most effective mutagenic factor turned out to be a dose of γ-irradiation of 7 kR, because under the conditions of its use, two mutant samples were formed (D(7) and D(7) (ind. selection – 1), which had the greatest genetic distance from the Divogray variety (rs = -0.45...0.40). Using two doses of γ-irradiation, 11 kR and 15 kR, one mutant sample was obtained, D(11) and D-1(15), respectively, which also had the lowest genetic affinity with the Divogray variety (rs = 0, 38...0.40). It was established that a correlation of medium strength (rs = -0.50...0.48) of the non-parametric statistical indicator "Average index of normalized values" occurred with the levels of manifestation of such quantitative features as "Height of socket", "Width of socket" and " The number of leaves on one plant” (rs = 0.48). Practical implications. Therefore, genetically inherited phenotypic changes in the morphology of the leaf blade are most correlated with quantitative traits that determine the architecture of lettuce plants and are a structural component of the yield of mutant samples. The established, statistically reliable, correlations make it possible to forecast phenotypic changes in the mutant generation M4 and above of leaf lettuce based on the above-mentioned quantitative characteristics, which is a factor in the optimization of the breeding process. Value/originality. The introduction into the selection process of methods for analyzing genetic changes of qualitative traits based on point evaluation allows for a more in-depth study of the patterns of inheritance of quantitative selection-important traits within a certain genotype of a vegetable plant species, to create more objective prognostic models of the formation of approbation traits of future varieties and F1 hybrids, to create working collections of original lines with the expected predicted result of phenotypic manifestation in the offspring.