Heterosis of plant gross weight and heterotic group classification of inbred lines in Chinese cabbage (Brassica rapa L. ssp. pekinensis)

Abstract Heterotic groups have been well studied in hybrid breeding of grain crops, such as maize. However, little such information is available for Chinese cabbage. Plant Gross Weight (PGW) is one of the most important yield traits of Chinese cabbage. In this work, 48 F1 hybrids were obtained by incomplete diallel cross (6 × 8) of 14 Chinese cabbage inbred lines, then all parents and F1 hybrids were cultivated to evaluate heterosis performance on the PGW trait in two growing seasons (2017 and 2018) at Yangling, China. A total of five methods were used to determine the heterotic groups of tested inbred lines, which include 1) SCA method based on specific combining ability effect, 2) SCA-Y method based on SCA effect by Yang's method, 3) HSGCA method based on heterotic group specific and general combining ability, 4) HGCAMT method based on general combining ability of multiple traits. Besides, the 14 parental lines also clustered by 5) SSR method based on similarity of a core set of 28 simple sequence repeat (SSR) markers. The result showed that heterosis is obvious on the PGW trait in most F1 hybrids, with the mean value of Mid-parent heterosis (MPH) and Better-parent heterosis (BPH) is 111.17 % and 82.03 % respectively. PGW and MPH of F1 hybrids were used as final indexes to evaluate the efficiency of these five methods on heterotic group classification. The result revealed that HSGCA method and SCA method are most optimal to classify the heterotic groups in Chinese cabbage with identical division results. SSR method based on the core set of 28 SSR markers is also an effective way to predict heterosis in advance which can be used as the basis of field cross design. The 14 inbred lines of Chinese cabbage were classified into five heterotic groups based on common results of HSGCA method and SCA method. Furthermore, five inbred lines were selected as testers for further determining heterotic groups of other new inbred lines. This work is expected to raise the breeding efficiency of Chinese cabbage hybrid breeding and provide reference for classifying heterotic groups in other vegetable crops.