Genetic Analysis of Weight per Fruit and Fruit Length in Bitter Gourd

Ziji LIU, Yu NIU, Yan YANG, Baibi ZHU

1. Tropical Crops Genetic Resources Institute, Chinese Academy of Tropical Agricultural Sciences, Haikou 571011, China; 2. Hainan Key Laboratory of Vegetable Biology, Vegetable Research Institute, Hainan Academy of Agricultural Sciences, Haikou 571199, China

Abstract [Objectives] The paper was to verify the genetic mechanism of weight per fruit and fruit length in bitter gourd and to provide guidance for formulating breeding strategy. [Methods] In this study, a cross was made between CN19-1 and Thai4-6, and a F2 segregation population was also constructed. The genetic characteristics of weight per fruit and fruit length were analyzed by employing major gene plus polygene mixed genetic model. [Results] The weight per fruit and fruit length showed continuous distribution in F2 segregation population. The optimal model for weight per fruit and fruit length was the same (A-1 model). The major gene additive effect value of weight per fruit was 46.147 4, the dominant effect value was -46.100 5, and the major gene heritability was 52.47%. The major gene additive effect value of fruit length was 2.456, the dominant effect value was -2.455, and the major gene heritability was 52.52%. The results showed that weight per fruit and fruit length were mainly controlled by a pair of major genes. [Conclusions] This study can provide a theoretical basis for bitter gourd breeding.

Key words Bitter gourd; Genetic model; Weight per fruit; Fruit length; Genetic analysis

1 Introduction

MomordicacharantiaL., originated from Africa, a kind of vine, belongs toMomordicagenus of Cucurbitaceae, and is widely distributed in the tropical, subtropical and temperate regions[1-2]. Bitter gourd is rich in vitamin C, vitamin E and many kinds of minerals, with high nutritional value. In addition, the pharmacological active components of bitter gourd have many functions such as anti-tumor[3], anti-inflammatory[4]and anti-virus[5]. As a kind of high quality processing resource, bitter gourd has a very wide application prospect in medicine, health food, food processing industry and so on.

Recently, the major gene plus polygene mixed genetic model has been widely used in plant quantitative traits genetic analysis, such as soybean root traits[6], rapeseed oil content[7], rapeseed lodging resistance[8]and rapeseed plant type[9]. The genetic study of weight per fruit and fruit length in bitter gourd has been less reported. Therefore, the study on the inheritance of weight per fruit and fruit length in bitter gourd could provide reference for the breeding of bitter gourd. In this study, a cross was made between CN9-1 and Thai4-6, and the genetic characteristic of weight per fruit and fruit length was analyzed by employing the major gene plus polygene mixed genetic model based on F2segregation population.

2 Materials and methods

2.1 MaterialsThe parent materials were CN19-1 and Thai4-6. The weight per fruit of CN19-1 was about 350 g, and the fruit length was about 23 cm. The weight per fruit of Thai4-6 was about 240 g and the fruit length was about 17 cm.

In 2016, F1 seeds were obtained by making cross between Thai4-6 and CN19-1 in the vegetable base of Tropical Crops Genetic Resources Institute, Chinese Academy of Tropical Agricultural Sciences. A F2segregation population used for genetic analysis was constructed through F1selfing. In 2017, 21 seeds of CN19-1, 21 seeds of Thai4-6 and 142 seeds of F2were soaked in warm water at 55℃ for 10 min. Then these seeds were planted in the bowl. When the seedlings grew out 2 leaves, they were transplanted to field with uniform soil condition. According to the convention management, the weight per fruit and fruit length of the F2segregating population was investigated during the full bearing period.

3 Results and analysis

3.1 Phenotype data analysisThe average weight per fruit of CN19-1 was 353.1 g, and the average weight per fruit of Thai4-6 was 246.4 g. The independent samplettest showed that there were significant differences in weight per fruit between parents (P<0.05). The average fruit length of CN19-1 was 23.13 cm, and the average fruit length of Thai4-6 was 17.37 cm. The independent samplettest showed that the fruit length of parent materials was significantly different (P<0.05). The weight per fruit and fruit length in F2segregation population derived from the cross between CN19-1 and Thai4-6 were grouped, and the frequency distribution was statistically analyzed. The weight per fruit and fruit length in F2segregation population were continuously distributed. The skewness values of the weight per fruit and fruit length were 0.828 and 0.782, and the kurtosis values were 0.598 and 0.856, respectively. Both of the 2 traits were positive skewed distribution, with widely genetic variation. There were obvious major genes controlling the weight per fruit and fruit length (Figs.1-2).

Fig.1 The frequency distribution of weight per fruit of F2 population derived from the cross between CN9-1 and Thai4-6

Fig.2 The frequency distribution of fruit length of F2 population derived from the cross between CN19-1 and Thai4-6

1 AIC values of 11genetic model

Tables for weight per fruit and fruit length of the F2 population derived from the cross between CN19-1 and Thai4-6

3.3 Estimate value of first and second order genetic parametersBased on the optimal genetic model A-1, the first and second order genetic parameters of weight per fruit and fruit length were estimated (Table 3). The additive effect value of a pair of major genes controlling weight per fruit was 46.147 4, showing a positive effect, and the dominant effect value was -46.100 5, showing a negative effect. The dominance degree of the major genes is -0.99, indicating that the major genes were incomplete dominance. The heritability of the major genes was 52.47%. The additive effect value of a pair of major genes controlling fruit length was 2.456, showing a positive effect, and the dominant effect value was -2.455, showing a negative effect. The dominance degree of the major genes is -0.99, indicating that the major genes were incomplete dominance. The variance of the major genes was 3.578 and the heritability was 52.52%.

Table 2 Fitness test of selected genetic models for weight per fruit and fruit length of the F2 population derived from the cross between CN19-1 and Thai4-6

Table 3 Estimate values of genetic parameters for weight per fruit and fruit length of the F2 population derived from the cross between CN9-1 and Thai4-6

4 Conclusions and discussion

(i) A hybrid combination derived from the cross between CN19-1 and Thai4-6 was made, and a F2segregation population was constructed. The weight per fruit and fruit length showed continuous distribution. In this study, the best genetic model was selected by adopting F2generation segregation analysis method of major gene plus polygene mixed genetic model, which could avoid the error to some extent.

(ii) The inheritance of weight per fruit and fruit length were consistent with the A-1 genetic model. Both of the 2 traits were controlled by a pair of additive-dominant major genes, and the heritability of major genes were 52.47% and 52.52%, indicating that these 2 traits could be selected in the early generation of breeding.

(iii) In this study, the genetic characteristics of weight per fruit and fruit length of bitter gourd were preliminarily revealed. In future research, the genes controlling the weight per fruit and fruit length will be mapped, and the markers close linked with the major genes will be identified.