**1. Introduction**

Eggplant or brinjal (*Solanum melongena* L.; 2n = 2x = 24) is considered a rich member of the species Solanaceae, which contains approximately 1300 species. It can be grown

**Citation:** Uddin, M.S.; Billah, M.; Afroz, R.; Rahman, S.; Jahan, N.; Hossain, M.G.; Bagum, S.A.; Uddin, M.S.; Khaldun, A.B.M.; Azam, M.G.; et al. Evaluation of 130 Eggplant (*Solanum melongena* L.) Genotypes for Future Breeding Program Based on Qualitative and Quantitative Traits, and Various Genetic Parameters. *Horticulturae* **2021**, *7*, 376. https:// doi.org/10.3390/horticulturae7100376

Academic Editor: Yuyang Zhang

Received: 2 September 2021 Accepted: 3 October 2021 Published: 8 October 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

in diversified climatic conditions of various ecological regions. It possesses high species richness with considerable flexibility of phenotypic adaptability that made the species the most important vegetable economically. Eggplant is a general term for various Solanum species cultivated for their fruits, including the East Asian aubergine (*S. melongena* L.) and the two African native eggplants, Scarlet (*S. aethiopicum* L.) and Gboma (*S. macrocarpon* L.) [1]. Eggplant has become prominent due to its health-promoting properties. Therefore, eggplant and its relatives have numerous medicinal applications, with 77 distinct medicinal properties [2]. Eggplant is a widespread vegetable that grown from the subtropics to the Mediterranean region, popularly in Asia, Africa, and the southern part of the USA, with significant production in 2019 globally (55.15 million tons). Asia produces more than 90% of global eggplant production with 87% of the growing area coverage [3,4]. It ranks second most-produced vegetable after potato in Bangladesh.

It occupies roughly 15% of total vegetable farmland and produces about 8% of total vegetable production [5]. However, wild forms grow in sympatry with landraces and cultivars throughout their distinct areas of origin and domestication. Natural gene flow between wild and cultivated materials, followed by natural and human selection, has resulted in intermediate phenotypes that correlate with many wild features. The contribution of features of breeding importance to diversity is unequal. The variables that contributed the most to the divergence between accessions in Indian landraces of *S. melongena* were yield per plant, fruit width, number of long-styled flowers per plant, flowering earliness, total phenolic content, and ascorbic acid content [6]. Nevertheless, the results depend on the sample size used. To date, there has not been any large-scale study of a representative sample containing the complete phenotypic diversity of each cultivated eggplant. In Bangladesh, eggplant is grown throughout the country, however, the yield is not sufficient due to the lack of improved and desired variety and remarkable infestation of insect pests. However, morphological characterization has been useful in studying the relationship and diversity of various eggplant varieties. The European Eggplant Genetic Resources Network (EGGNET) defined the morphological characterization for eggplant [7], which has been validated and used in the characterization of eggplant breeding materials in numerous studies [8–10]. Therefore, creating variation through mutation, hybridization, and biotechnology approaches is an expensive and time-consuming method [8]. Consequently, characterizing collected germplasm (populations) is required to identify lines suitable for new variety development [11]. Plant breeders are interested in genetic diversity studies based on qualitative and quantitative traits because such traits can be scored quickly and easily using low-cost methods.

The phenotypic variation of fruits, plants, and other interesting traits has been demonstrated in many articles on Solanum or *S. aethiopicum* or two or more eggplant species [12–19]. Moreover, summarizing the phenotypic diversity of eggplants following the Mendelian or quantitative heredity patterns of traits of interest have been widely studied in many reports [20–22]. Different scientists [23–25] studied in-depth genetic diversity, heritability and genetic advance in eggplant genotypes. Consequently, breeders face a challenge in selecting genotypes that combine high yields in multiple attributes, which requires a reliable decision support tool. In plant breeding studies, a strong selection approach can save a lot of time and resources.

The Smith–Hazel Index (SH index) is widely utilized in plant breeding as a multi-trait selection index [26]. Reversing a phenotypic covariance matrix and a vector of economic weights is required to calculate the SH index. As a result of the presence of multicollinearity, poorly conditioned matrices and biased index coefficients would occur, affecting genetic gain estimations [26]. To account for the multicollinearity issue in multi-trait indexes, a combination of multivariate approaches is effective in overcoming their limits. FAI-BLUP is a factor analysis-based model in which each ideotype's factorial scores are created based on desirable and undesirable elements [26]. Then, depending on the genotype-ideotype distance, a geographic probability is calculated allowing genotype ranking. Olivoto and Nardino [27] offered a new multi-trait genotype-132 ideotype distance

index (MGIDI) and the entire current index is combined with the exercise calculations in the R-Metan package, which contains all the functions required for genotype selection in plant breeding programs.

In Bangladesh, however, numerous genotypes of eggplant are available. The Bangladesh Agricultural Research Institute (BARI Plant)'s Genetic Resource Center (PGRC) collects and preserves several types of eggplant germplasm from all around Bangladesh. Studying the level of accessible diversity in a crop development program is a crucial stage in crop improvement, which can be accomplished through the collection and evaluation of germplasm. Therefore, the present study was carried out to determine the inherent variation of local eggplant germplasm to identify the promising germplasm that exhibits genetic diversity for crop improvement programs through advanced multi-disciplinary analysis.
