Multivariate analysis of qualitative and quantitative traits in bell pepper hybrid cultivars

Pepper (Capsicum annuum), with all unique flavors and varieties, maintains high consumption rates and economic value. The awareness of sustainable products among consumers has increased interest for bioactive constituents and plant extracts in the pharmaceutical, cosmeceutical and food industries. Pepper products containing capsaicinoids, carotenoids, and oleoresins are crucial in pharmaceutical, nutricosmetics and cosmeceuticals owing to their analgesic and antioxidant properties and ease of topical and oral administrations. A breeding program includes several activities such as maintaining a germplasm bank, evaluating genetic diversity, selecting superior genotypes, hybridization, and evaluating segregated populations. The information from genetic diversity is also helpful for conservation, evaluation, utilization of genetic resources and for determining the uniqueness and distinctness of genotypes. This study was accomplished to assess the relationships between different traits and identify parents with high genetic distances.

In this project, 14 bell pepper hybrids including six red varieties (Caoba, Neirvin, Plutonio, Insprision, Masilia, and Iitana), five yellow varieties (Lumus, Bachata, Harmony, Taranto, and Spring) and three orange varieties (Magno, Arankia, and Paramo), were investigated in a completely random design with three replications in the greenhouse in Isfahan. Seedlings were transplanted on 2nd August 2021; each plot contained four plants of each hybrid, 30 cm apart standard; cultural practices recommended for growing bell pepper crops. About five months after planting, the plant height was measured in centimeters. Average fruit yield per plant was recorded for six harvest times. After fruit harvesting, for each genotype, data were recorded on five ripe fruits randomly taken plants from each plot; quantitative and qualitative traits were measured as follows: fruit length and diameter, peduncle length, and fruit pericarp thickness were recorded with a digital caliper. The shape index trait was obtained from the ratio of the fruit length to the diameter. The total soluble solids were measured by a refractometer. Finally, the average was calculated to record the mean value in each replication for all the characters under study. Analysis of variance was done to determine differences among the genotypes. Mean separation was done using the LSD test at p-values < 0.05. Data for each genotype were averaged across the replications and then used for correlation, cluster and principal component analysis (PCA). The data were analyzed by software SAS V.9.4 and SPSS 27.0.1.

The results of variance analysis showed significant deference among hybrids for all quantitative and qualitative traits. The most variation was for fruit size traits (diameter and shape index). The orthogonal comparison for pepper colors showed significant differences in fruit length, diameter, shape index, and soluble solids. The results of trait correlation coefficients showed that the fruit yield per plant had a strong positive correlation with the fruit diameter and fruit weight traits, and there was a positive and significant correlation with the traits of fruit length, fruit pericarp thickness, and hundred seed weight. Based on cluster analysis results, the hybrids were placed in four separate groups. The first group hybrids include five hybrids: Aranika (Orange), Paramo (Orange), Spring book (yellow), Nirvin (Red), and Masilia (Red) with medium fruit yield. The second group with three hybrids: Magno (Orange), Pachata (Yellow), and Aitana (Red), showed the lowest quantity characters such as low fruit weight, shape index, fruit pericarp thickness, peduncle length, and meager fruit yield. Contrary to this, the third group with two hybrids Caoba (Red) and Plutonio (Red), had the highest quantity characters such as high fruit weight, neck diameter, hundred seed weight, and very high fruit yield. The dispersion and distribution of different bell pepper colors in separate groups confirm the high genetic distance between the hybrids. The first two components justified 39.67 and 18.24% of total variance principal component analysis showed that the first principal component (PC1) was related to fruit yield attribute. The second principal component (PC2) had positive correlation with qualitative attribute of the fruit (soluble solids).

The results of the current study were able to reveal the high diversity within the evaluated hybrids and partition them into meaningful groups. This can also be helpful for informed pepper breeding and improvement programs. High genetic variation between bell pepper hybrids and within each color for most of the studied traits can be effective in the breeding programs for pure line production.