Analysis Of Relationship Between Heterosis And Genetic Distance In Cucumber

Good parent is key to breeding new varieties by heterosis in cucumber breeding work,which determines whether we can get good hybrid varieties or not.Exploring correlation between genetic distance?GD?and heterosis in different cucumber parents is meaningful to improve the efficiency of parent selection and shorten the breeding period.In the study,132cucumber materials were collected at home and abroad,based on the genetic relationship,clustering analysis was performed.Then,hybridization was carried out by 22 collections and121 combinations were obtained based on the incomplete diallel crossing design.The 18traits of F₁ were tested.Correlation between total combining ability,heterosis and GD were analyzed.The study,provides a theoretical basis for the utilization of cucumber heterosis.The main results are as follows:1.Genetic diversity analysis of cucumber germplasm materials30 primers were used to the clustering analysis of 132 cucumber germplasms,the result showed that GD ranged from 0 to 0.82 with a average of 0.40.132 collections were divided into two sub-clusters.Average GD of K1 sub-cluster was 0.42,with the Fst-value of 0.45,which indicated a great genetic differentiation in K1.Average GD of K2 was 0.25,with a Fst-value of 0.18,showed a high level of genetic differentiation.Hua'bei-type and Hua'nan-type collections were separately divided into two sub-clusters,which indicated a great genetic difference between two different Chinese cucumber germplasms,the Hua'nan-type may have a higher genetic diversity,but Euro-American type possesses the highest level of genetic diversity comparing with the former two and with a closer GD with Hua'nan-type.2.Analysis of yield component traitsCorrelation analysis showed that there was a significant correlation between the number of fruit,the weight of fruit,the thickness of fruit flesh,the diameter of seed-cavity,the length of fruit stem,the number of female flowers in the first 20 days,the node of first female flower,indicated that these traits were the main factors affecting the yield of cucumber.3.Study on heterosis and combining abilityAnalysis showed that Euro-American type cucumber have an outstanding performance in the number of fruit,early maturity,disease resistance in powdery mildew and downy mildew and suitable for the improvement of local cucumber in breeding work.Hua'bei-type are suitable for the improvement of fruit shape.Hua'nan-typ are suitable for autumn protected cultivation and also can be used to the improvement of fruit shape.4.Correlation between combining ability and genetic distanceAnalysis showed that there is no significant correlation between total combining ability value and GD in the hybrid population of cucumber in different ecotype,while in the specific combination,there is a significant correlation between total combining ability value and GD,such as Hua'nan-type×Hua'nan-type,Hua'bei-type×Hua'bei-type,Euro-American type×Euro-American type,Hua'bei-type×Hua'nan-type,which indicated that GD can be used to predict the total combining ability in hybrid population with a simple genetic composition,but remains to be further explored in population with a complex genetic composition.5.Analysis between yield heterosis and parental GDAnalysis showed that there is no significant relationship between parental GD and yield heterosis in 121 germplasms containing different ecotype materials.But significant linear correlations were observed between GD and MPH of first female flower node and HPH of fruit number among Hua'nan-type cucumber combinations;In Hua'bei-type cucumber combinations,MPH of the node of first female flower decreased with GD;In Euro-American type combinations,HPH of the number of female flowers in the first 20 days increased with the GD,and HPH of the first female flower node decreased with the increase of GD.The above indicated parents with the larger GD could increase the probability of heterosis.