Evaluation of yield potential of mutant lines of leaf lettuce under different climatic conditions of growing

Abstract

Introduction. In the current climate of global climate change, the main task of the breeding of vegetable species is to create new varieties and hybrids of F₁ with increased potential for adaptability to stress factors of cultivation. Success in solving this task depends on the level of study of the source material, the breeding of parental pairs for hybridization, optimization of the method of breeding for adaptability by adhering to the principles of breeding of the original forms on the signs that are closely correlated with adaptability.

Purpose of the investigation. To analyze the adaptive properties of leaf lettuce lines created by chemical mutagenesis for the stability of the manifestation of the "Yield" trait under different climatic conditions of cultivation in the agro-climatic zone of the Northern Forest-Steppe of Ukraine.

Methods. Field studies were conducted during 2017–2019 at the experimental station of the Mayak Research Station of the Institute of Vegetable and Melon Growing of the NAAS, located in the village of Baklanovo, Nizhyn district, Chernihiv region. Subject of research: mutant lines of leaf lettuce generation M₃–M₅ created by chemical mutagenesis based on the domestic variety Zhnich. To obtain mutant plants of leaf lettuce were carried out pre-sowing treatment of seeds of biologically active substances of mutagenic action. Among the studied drugs of mutagenic action, the dimethyl sulfate (DMS) is the standard. The drugs D₃MU, DMU-10A and DMU-9 are chemical analogues of DMS, which were created at the experimental base of the Institute of Bioorganic Chemistry and Petrochemistry of NAS of Ukraine.

During 2017–2019, mutant samples of the M₃–M₅ generation were studied in the field under the complex of quantitative and qualitative traits and phenology of plant growth and development. The following indicators were used to evaluate the adaptive potential of the lines: general and specific adaptive capacity of the genotype (GAC_i and SAC_i); relative genotype stability (Sg_i); coefficient of environmental plasticity (b_i); breeding value of the genotype (BVG_i). The yield estimation of leaf lettuce was carried out in the first decade of June, during the phenological period, when the samples were in the vegetative phase of development.

Results and Discussion. As a result of the statistical calculations, there were isolated 9 mutant lines that had an advantage over the variety-standard Shar malinovij (K-7431) in terms of yield. First, these lines significantly exceeded this variety in terms of the breeding value of the genotype (BVG_i  = 7.75… 11.88). Second, they either had a statistically significant excess of the level of manifestation of the trait, or the level of its manifestation was at the level of the variety- standard within the margin of experiment error (X_med = 8.85… 15.79 t/ha). According to the yield index the lines of B-6 (K-266), B-38 (K-296), B-7 (K-267), B-8 (K-268), B-24 (K-283) and B-11 (K-271) statistically significantly exceeded by 41.9–94.2 % the variety-standard Shar malinovij  (K-7431) and by 34.1–86.4 % of the original form – the Zhnich (K-46) variety. The average yields for the B-2 (K-262), B-14 (K-274) and B-16 (K-275) lines were within the error range for the variety-standard and original form, but they tended to be an increase in its performance compared to similar indicators of the variety-standard and the original form. Among the linear material studied, there are 3 lines – B-6 (K-266), B-7 (K-267) and B-8 (K-268), which had the highest level of manifestation of the "Yield" sign (X_med = 15, 20–15.79 t/ha) and the index of the breeding value of the genotype (BVG_i  = 10.89–11.88).

According to the obtained results, the studied sample of 9 mutant leaf lettuce lines was divided into three groups, the first of which had a value of plasticity bi <± 1 and which included linear genotypes with low response to growing conditions and influence of environmental factors. In particular, these are the following lines: B-24 (K-283) (b_i = -0.35); B-14 (K-274) (b_i = -0.23); B-2 (K-262) (b_i = -0.12); B-38 (K-296) (b_i = 0.20); B-6 (K-266) (b_i = 0.21); B-16 (K-275) (b_i = 0.37).

The second group included 2 mutant lines of lettuce B-8 (K-268) (b_i = 1,57) and B-11 (K-271 ) (b_i = 1.67)) for which the value of the environmental plasticity coefficient was greater than one (b_i > 1). These lines referred to the intensive type of cultivation as they showed high sensitivity to climatic conditions and dependence on agrophone cultivation, respectively.

The third group included the line B7 (K-267) and the original form, the Zhnich

(K-46) variety (K-46), in which the plasticity coefficient was less than minus one             (b_i < -1), indicating that these leaf lettuce samples showed specific response to growing conditions. Namely, among the studied sample of genotypes, they tended to increase yields to a certain limit under worse growing conditions.

Results and Discussion. According to the obtained results, the 6 mutant lines of leaf lettuce were defined with low response to growing conditions and influence of environmental factors (b_i <± 1). The yield of leaf mass in this sample of mutant lines varied within 8.85–15.20 t/ha. Selected lines are a valuable starting material for creating eco-plastic varieties.

In the course of the research the high efficiency of the drugs of mutagenic action of domestic production of D₃MU and DMU-10A was confirmed, the use of which allowed to create 7 mutant lines (50% of the total number) with high adaptive properties and yields within 8,85–15,79 t/ha .