Level of the adaptive potential of courgette lines for traits of productivity

Abstract

Introduction. Created domestic varieties and hybrids of F₁ courgette in temperate climates (10-15 years later), unfortunately under the current climatic conditions, have partially lost their testing characteristics and do not meet the current market requirements. That is why the main purpose of the research was to create a highly adaptive starting material for the breeding of this vegetable plant.

Purpose of the investigation. To evaluate the adaptive potential of a collection of courgette lines, based on samples of foreign breeding, to select environmentally stable linear genotypes on the traits of productivity.

Methods. In the paper, a three-year (2016–2018) field evaluation of the adaptive potential of a collection of courgette produced by the method of breeding and inbreeding (F₆I₆ generation) from samples of foreign breeding on a set of traits that determine the yield structure was conducted. Collection of foreign samples of courgette was provided by breeding company “A. L. Tozer Ltd” (United Kingdom) in the framework of a joint genetic-breeding research agreement with the Institute of Vegetables and Melon Growing of the National Academy of Agrarian Sciences. This collection consisted of 21 courgette lines originating from the USA, UK, Spain and Italy. The domestic variety of Chaklun was chosen as the standard. Field studies were conducted at the experimental base of the Institute of Vegetable and Melon Growing of the NAAS, located in the Left Bank Forest Steppe Forest-Steppe of Ukraine in the central medium-moist area of Kharkiv region. The climate of the agroclimatic zone is temperate, with an average rainfall of 520 mm per year. In this zone, the growing season for thermophilic vegetable species, including courgette, begins on 25 April at temperatures above 10 °C and ends on 30 September.

In general, the weather conditions of 2016–2018 proved unacceptable for the growth and development of courgette plants, as they adversely affected the process of fertilization, reduced yield and marketability of the fruits and led to the defeat of plants with powdery mildew and intensive ash settlement.

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).

Results and Discussion. As a result of the statistical calculations, 9 prospective courgette lines were selected for further breeding work, which had a level of manifestation of the trait "Total yield" at the level of the standard Chaklun in the range of 44,73–63,35 t/ha           (A_m = 18.62 t/ha) and the value of the indicator "Breeding value of the genotype " (BVG_i) at the level of 14.59-43.61. In particular, these are samples such as LC 17-5, LC 17-8, LC 17-10, VL-90, VL-91, VL-92, LC 17-44, LC 17-45, LC 17-48. The highest indicator of "BVG_i" was in the line VL-90, in the variety standard Chaklun this indicator was 39,94.

According to the results obtained, the studied sample of courgette lines was divided into three groups, the first of which had a value of the coefficient “b_i” less than one and which included the Chaklun variety and the VL-90 line with a low response to the growing conditions and the influence of environmental factors. The second group included 6 lines for which the value of environmental plasticity coefficient was greater than one (b_i = 1,14 ... 1,98) - LC 17-5, LC 17-8, LC 17-10, LC 17-44, LC 17-45 and LC 17-48. That is, these lines referred to the intensive type of cultivation as they showed high sensitivity to climatic conditions and dependence on agrophone cultivation. Also highlighted are 2 lines, VL-91 and VL-92, which had medium plasticity (values of the “b_i” factor within a unit).

The selected linear material, which was estimated on the basis of "Total yield", was studied by another quantitative trait "Total productivity of one plant", which is a structural component of the productivity of courgette plants. According to the generalized three-year data for the whole sample of courgette samples, the variation range of this trait ranged from 2,36 to 3,11 kg/plant with the amplitude of variation Am = 0,91 kg/plant. In the variety Chaklun this figure was 2.88 kg/plant. Statistical indicators that determine the adaptive properties of the variety-standard for this trait are as follows: b_i = 0,91; GAC_i = 0,70; SAC_i = 0,78; Sgi = 30,80 %; BVG_i = 2,02. There was one linear sample, the VL-90, which not only had a clear tendency to increase the level of manifestation of this trait within the error of the variety-standard experiment (Xmed = 3,11 kg/plant.), But also for the majority of statistical indicators determining adaptive genotype properties had the best performance (GAC_i = 0,93; SAC_i = 0,90; Sg_i = 30,51 %; BVG_i = 2,19).

According to the ecological plasticity coefficient “b_i”, a sample of courgette specimens on the trait of “Total productivity of one plant” was studied, which had a somewhat different distribution into groups of linear genotypes with different response to growing conditions and environmental factors. The group of courgette samples with a low reaction to the growing conditions should include the variety Chaclun and 4 lines – LC 17-7, VL-90, VL-91, VL-92 (b_i = 0,06 ... 0,87). The second group includes 3 lines for which the manifestation of this trait depended on external factors of cultivation (bi> 1) - LC 17-5, LC 17-44, LC 17-45. Also highlighted are 2 lines, VL-91 and LC 17-48, which had average plasticity (values of the coefficient “b_i” within a unit).

Results and Discussion. According to the adaptability indicators for the two above mentioned features, only one VL-90 line and the Chaklun variety standard had low dependence on growing conditions (b_i < 1). There were 3 lines, VL-90, LC 17-7 and VL-92, for which the manifestation of the first trait did not depend on the growing conditions. 3 lines on the manifestation of the two studied features should be attributed to the intensive type of cultivation (b_i > 1) - LC 17-5, LC 17-44 and LC 17-45. Created source material has practical value for creating varieties and hybrids of F₁ with high ecological-plastic properties and intensive type of cultivation.