Exploration of quantitative traits related to density of flower cluster’s secondary peduncles of loquat and development of a new discriminant technique

【Objective】Loquat inflorescences belong to terminal panicles. The density of flower cluster’ s secondary peduncles is an important trait to describe the density of inflorescence branches. The appropriate density of flower cluster’s secondary peduncles can facilitate the operation of flower and fruit thinning and bagging in production, which has certain breeding value. The purpose of this study was to explore quantitative traits related to the density of flower cluster’s secondary peduncles, and to develop a measurement method for roughly describing the density of flower cluster’s secondary peduncles, so as to reduce visual error and improve the credibility of density of flower cluster’s secondary peduncles evaluation. It would provide reliable data support for the genetic breeding of loquat inflorescence traits and develop a reliable judgment method for evaluating the density of flower cluster’s secondary peduncles.【Methods】We selected a number of quantitative traits, such as the length of flower cluster, the width of flower cluster, the number of secondary peduncles of flower cluster, the mean internode length of flower cluster, the first branch length of flower cluster, the first branch angle of flower cluster, the second branch length of flower cluster and the second branch angle of flower cluster as the referencecharacter description of the density of flower cluster’s secondary peduncles, using diversity analysis, correlation analysis, principal component analysis, and cluster analysis. In addition, the inflorescence density information of the germplasms was obtained by the rotating shooting and software processing methods. The correlation analysis and principal component analysis were used to determine whether inflorescence density could basically represent the density of flower cluster’s secondary peduncles, and whether it could be used as a new method to judge the density of flower cluster’s secondary peduncles. 【Results】The coefficients of the variation of the length of flower cluster, the width of flower cluster, the number of secondary peduncles of flower cluster, the mean internode length of flower cluster, the first branch length of flower cluster and the second branch length of flower cluster were between 20% and 26%, indicating that these characters had great differences among different germplasm accessions, and the performance of these characters was not stable. Each of the eight selected inflorescence traits were distributed in the most of their grades. The results of the correlation analysis showed the length of flower cluster, the width of flower cluster, the mean internode length of flower cluster, the first branch length of flower cluster and the second branch length of flower cluster were significantly correlated with the density of secondary peduncles of flower cluster, while the number of secondary peduncles of flower cluster, the first branch angle of flower cluster and the second branch angle of flower cluster were not significantly correlated with the density of secondary peduncles of flower cluster. The length of flower cluster, the width of flower cluster, the mean internode length of flower cluster, the first branch length of flower cluster and the second branch length of flower cluster could be used to describe the density of secondary peduncles of flower cluster well. The principal component analysis was carried out on the significantly correlated characters and all the selected characters respectively. It was found that there was no significant difference between the two results, and the absolute value of the correlation coefficient with the results of the visual measurement of the inflorescence ramus density was above 0.8. At the same time, the cluster analysis was carried out on the significantly correlated traits and all the selected traits respectively, and the results of the two were quite different, in which the significantly correlated traits as clustering factors were obviously better than all the selected traits as factors. If the inflorescence density was added as an index to evaluate the density of secondary peduncles of flower cluster, the correlation coefficient between the inflorescence density and the density of secondary peduncles of flower cluster would be up to 0.945, which could basically reflect the density of secondary peduncles of flower cluster. The inflorescence density and the significantly correlated characters were analyzed by principal component analysis. The distribution of the comprehensive evaluation results was consistent with the visual measurement of the inflorescence ramus density. The boundary of inflorescence density between the sparse type and the medium type might be 36.45%-40.31%, and the boundary of inflorescence density between the medium type and the dense type might be 41.58%-46.34%.【Conclusion】 The inflorescence density could be used as a new quantitative index of the density of secondary peduncles of flower cluster, and could accurately distinguish the three types of inflorescences: sparse, medium and dense in typical germplasms. In addition, the information of inflorescence density could be obtained efficiently by means of the rotating shooting with computer program processing.