Phenotypic characterization and genetic diversity analysis of pineapple germplasm resources during the vegetative growth stage

【Objective】Pineapple, as an important tropical and subtropical economic fruit crop, has its fruit quality, yield and stress resistance closely related to the growth status during the vegetative growth period. The morphological traits at this stage are core indicators reflecting the growth vitality and genetic characteristics of the plant. Currently, the pineapple industry is facing challenges such as low utilization efficiency of germplasm resources and long breeding cycles for new varieties. There is an urgent need to reveal the genetic differences among different germplasm resources through systematic phenotypic trait evaluation. Therefore, this study systematically evaluated the morphological traits of pineapple during the vegetative growth period, deeply explored the phenotypic genetic diversity of germplasm resources, and clarified the intrinsic relationships among traits, with the aim of providing theoretical basis and practical guidance for the effective utilization of pineapple germplasm resources and the acceleration of new variety breeding.【Methods】To comprehensively and accurately assess the morphological characteristics of pineapple during the vegetative growth period, 114 pineapple accessions were used as materials. Quantitative traits such as plant height, number of leaves, leaf length and width, as well as descriptive traits such as leaf spines and leaf color, were systematically measured during the vegetative growth period. Correlation analysis, cluster analysis, and principal component analysis were comprehensively applied to conduct a comprehensive evaluation of the morphological characteristics of pineapple accessions during the vegetative growth period.【Results】The 114 pineapple accessions exhibited rich phenotypic variations during the vegetative growth period. Among them, four core quantitative traits showed varying degrees of variation at different growth stages, with the coefficient of variation ranging from 15.70% to 33.00%, indicating significant genetic diversity among the pineapple accessions. The variation characteristics of each growth stage trait are as follows: The coefficient of variation of the number of leaves remained relatively stable throughout the vegetative growth period, fluctuating between 21.00% and 25.00% , suggesting that this trait was less affected by the growth stage and had strong genetic stability. The coefficient of variation of plant height showed obvious stage differences, reaching the maximum value of 33.00% at the middle seedling stage, which was the fastest growth stage of the plant, and the genetic differences among the accessions were fully manifested. The coefficient of variation of leaf width showed an opposite trend to that of plant height, reaching the minimum value of 15.70% at the flower bud differentiation preparation stage, indicating that as the plant grew, the differences in leaf width among different accessions gradually decreased, and the growth states tended to be consistent. To further quantitatively evaluate the genetic diversity, the Shannon- Weaver index method was used to analyze the phenotypic data. The results showed that the genetic diversity of plant height and leaf width reached the peak at the middle seedling stage, with values of 1.89 and 2.08 respectively, which were at a high level of diversity, indicating that the genetic potential of plant height and leaf width had been fully expressed and tended to be stable at the later stage of vegetative growth. The genetic diversity of the number of leaves and leaf length reached the maximum at the small seedling stage, with values of 1.93 and 1.94 respectively, and then showed a downward trend, indicating that the differentiation of the number of leaves and leaf length was the most intense at the small seedling stage, which was a key period for early selection and identification. Correlation analysis showed that there were significant correlations among the traits. Among the 11 plant trait indicators, a total of 39 pairs of traits reached extremely significant correlations, of which 23 pairs were positive correlations and 16 pairs were negative correlations. Specifically, plant height was extremely significantly positively correlated with the number of leaves, leaf length, leaf width, leaf posture, leaf spine density and leaf spine distribution, with correlation coefficients of 0.447, 0.455, 0.312, 0.167, 0.120 and 0.172, respectively, while it was extremely significantly negatively correlated with leaf color and leaf stripe distribution, with correlation coefficients of -0.280 and -0.144, respectively. Principal component analysis extracted 5 principal components from the 11 measured traits, with a cumulative contribution rate of 71.670%. Among them, PC1 (contribution rate 23.348%) and PC2 (contribution rate 15.732%) were the two core dimensions explaining the trait variations, contributing nearly 40% of the information and effectively summarizing the main characteristics of the pineapple accessions. Cluster analysis divided the 114 pineapple accessions into 4 groups: Group Ⅰ had taller plants and longer leaves; Group Ⅱ was outstanding in plant height, leaf width and the number of leaves; Group Ⅲ had dense leaf spine distribution; Group Ⅳ represented the conventional resource type.【Conclusion】Pineapple accessions have relatively rich phenotypic genetic diversity during the vegetative growth period. Through systematic analysis, the research results provide important basis for the effective utilization of pineapple germplasm resources and the breeding of new varieties.