Expression of heterosis for productive traits in F1 eggplant Solanum melongena L. Send correspondence to J. A randomized complete block design with three replications was used. Significant heterosis relative to the parental means was detected for all traits studied. The eggplant Solanum melongena L.
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Hybrid vigor is defined by mechanisms such as dominant complementation, over-dominance, and epistasis. Eggplant Solanum melongena L. Given the economic and nutritional significance of eggplants, breeding efforts focus on developing high-yielding varieties—mostly F 1 hybrids—with important traits. Studies indicate the successful exploitation of heterosis in the eggplant for a considerable improvement with respect to quantitative traits. In this direction, estimating heterosis for yield-related traits could well be useful for examining the most beneficial hybrid mix with the exploitation of top-quality hybrid.
This review examines the current perception of the breeding and molecular aspects of heterosis in eggplants and cites several studies describing the mechanisms. Rendering and combining recent genomics, epigenetic, proteomic, and metabolomics studies present new prospects towards the understanding of the regulatory events of heterosis involved in the evolution and the domestication of the eggplant ideotype.
Eggplant, popularly known as brinjal or aubergine Solanum melongena L. The cultivated area under eggplant cultivation is around 1. Moreover, to overcome yield targets and to fulfil the demand, the researchers are focusing on delivering high yielding eggplant hybrids [ 4 , 5 ]. The value of heterosis in vegetable crops is evident from the drastic yield increases measured over the last 50 years, following the introduction of hybrids into crop production.
Hybrids and improved agronomic techniques have resulted in a steady linear increase in the performance of vegetable crops [ 7 , 8 ]. In the case of eggplant, first-time Kakizaki [ 9 ] found the potential use of hybrids as commercially, citing the higher yields of hybrids compared to a standard for the years [ 10 ]. Further, the authors also determined that the level of heterosis is directly proportional to the diversity among the parents, which brought together several favorable diverse alleles of several genes.
Thereafter several studies comforting the possibility of heterosis for every possible character have been published [ 11 ]. Heterosis has been extensively utilized in cultivated plants. In this direction, the genetic basis of heterosis has been studied for nearly a century.
Two concepts are farmed as the common explanations for heterosis phenomenon dominance and over-dominance hypothesis. In the dominance hypothesis, heterosis is regarded as the result of the complementation of the deleterious alleles that were present in the inbred parental lines.
Whereas, over-dominance hypothesis interpretation points out that the allelic interactions specific to the hybrid are such that the heterozygous alleles in the hybrid combination perform better than either of the homozygous ones [ 6 , 12 , 13 ]. Moreover, efforts are continuing to decode the molecular basis of heterosis correctly, but breeders continue to improve inbreds.
Whereas, new technologies such as gene expression profiling are underway; efforts are being made to exploit heterosis phenomena [ 14 ]. Due to a large part of eggplant cultivation relies on cultivated varieties rather than hybrids and being an autogamous vegetable crop, pure lines are quickly developed because that the genetic base of cultivated eggplant gradually narrowed down in the course of time [ 15 ].
Similarly, hand emasculation is easy to perform owing to the large size of eggplant flowers and a successful cross can produce somewhere between based on its genotype [ 3 , 16 , 17 ]. Moreover, male-sterility has been discovered; it is also facilitating the hybrid development in eggplant. Identification of good combiner parents is vital for hybrid development in eggplant. The combining abilities, namely general combing ability GCA and specific combining ability SCA values are critical in predicting the hybrid performance and suitability [ 18 ].
This review provides useful information concerning the heterosis for important traits in eggplant and will be a valuable resource for eggplant breeders to circumscribe the extent of heterosis for a particular trait, also presenting the genetic and molecular basis of heterosis in eggplant. Eggplant Solanum melongena L is a native to the Indian subcontinent. Most of the Solanum species, including eggplant, are characterized by flattened seeds and curved embryos [ 19 ].
Eggplant is a berry-producing vegetable belonging to the large family of Solanaceae, which has around different species distributed in across 90 genera [ 20 ]. Out of these Solanum is the largest, with approximately species [ 21 ]. Solanum melongena L. Likewise, scarlet S. By and large, Solanum melongena L. Noticeably, the wild relatives of eggplant usually have a smaller fruit size.
Several forms, shape and colors of eggplant are found across Southeast Asia, indicating that this area might be the secondary center of variation. Vavilov [ 22 ] considered its center of origin in the Indo-Burma region. Although, according to recent studies on the domestication of eggplants, still there are several unanswered queries for this process.
However, there are several shreds of evidence that suggested, eggplant domesticated from S. Interestingly, the evidential proof of cultivation of eggplant found both India and China equally.
Together with archaeological evidence about eggplant showed there was the utilization of eggplants started earlier in India than China, with a subsequent additional and independent center of domestication in the Philippines [ 25 ]. During the 8 th century, the eggplant was distributed eastward to Japan and westward via silk route into western Asia, Europe and Africa. It was introduced in the Americas in the 14 th century by the Europeans [ 26 ].
Still, some authors recognized Australia as a secondary center of diversity [ 27 ]. They also hypothesized, there was a long-distance dispersal event approx. In light of these findings, prospects and analysis of the relationships of Australian spiny solanums will undoubtedly help to explain its patterns of diversification and expansion in the region.
Several abiotic stresses feature by Australian solanums definitely will have a great interest to eggplant breeders in the coming future. The conventional breeding approaches to improve crop plants are the introduction, mass selection, pure-line selection, pedigree selection, single seed descent, bulk method, and backcross method. According to the situation and objectives, combinations of approaches have been found a valuable strategy. However, a lot of efforts are made in the direction of breeding for earliness, decreased fruit bitterness, and reduced prickliness.
Tremendous work has been done in the few decades by plant breeders on the adaptation of eggplant and its yield improvement under the greenhouse conditions.
Loss due to insect pests and diseases demands eggplant breeding for biotic stress resistance without compromising for yield [ 30 , 31 ].
Similarly, several quality factors are also considered, namely fruit shape, fruit color, plant prickliness, fruit palatability, and glossiness [ 32 ]. Wild relatives of eggplant come up with the excellent potential for their use in breeding programs. Instead of tremendous diversity and beneficial alleles for biotic and abiotic stress present in wild relatives, there has been little progress made on in its overall improvement [ 33 ].
One of the significant obstacles to the use of alleles of wild species into cultivated eggplant the is lack of a genome sequence database [ 34 ]. However, the recently mapping population developed from several crosses between eggplant and its wild relatives [ 35 ]. Species come under secondary or tertiary gene pool can be used for crossing with cultivated ones by the use of embryo rescue with varying rate of success [ 36 ].
It has been noticed that the degree of cross-compatibility is variable among the cultivated eggplant and wild relatives. It was also determined that the introgression of genes or segments of chromosomes from the wild species to cultivated species might be more comfortable in some cases. For improvement of eggplant, identification of best potential wild species for distance crosses depends upon extensive morphological phenotyping of the parents, F 1 s and their advancing progenies Figure 1 Table 1 [ 35 ].
Heterosis in the eggplant using wild relatives as the male parents taken from Kaushik et al. To evaluate a large number of lines, breeders have to make hundreds of test crosses and estimate F 1 to identify best hybrids in respect of yield and other quality traits.
Handling several crosses simultaneously is not an easy task. Because of that, it is crucial to identify the superior crosses with high heterotic potential. There are several ways for the prediction of heterosis, viz. Inadditiontotheseapproaches, inrecentstudies, geneexpressionisusedtopredictheterosis. Generally, heterosis prediction is estimated with per se performance, analysis of genetic diversity, combining ability analysis of parental lines. There are several reports in different crops found contrasting conclusions about the effectiveness of per se performance for the prediction of heterosis.
Contrarily selection of better parents which is based on per se performance found to be very useful in case of Triticale for several traits except for grain yield [ 39 ]. However, in tropical maize under extreme moisture stress condition, the performance of hybrid progenies can be predicted to some extent based on per se performance of their inbred parents [ 40 ].
Interestingly, there is absolutely no association located amongst per se functionality of parental lines and heterosis in F 1 hybrids in maize [ 41 ] and sugarcane [ 42 ]. For that reason, the prediction of heterosis only based on the per se performance of parents is not an essential indicator of heterosis. There is a necessary and robust correlation located amongst genetic distance and heterosis in rice [ 43 ], maize [ 44 ], wheat [ 45 ], sunflower [ 46 ] and rapeseed [ 47 ].
Moreover, the omics-based approaches have excellent potential for the prediction of heterosis. Zenke-Philippi et al. Even so, added investigation obtaining more massive data sets is essential to investigate the feasibility of selection prediction models.
The first results of the prediction of hybrids by using mRNA transcriptomics were determined by Frisch et al. General combining ability GCA or testcross performance-based hybrid prediction is a particular case of hybrid prediction and is regularly applied in eggplant breeding and hybrids development [ 51 , 52 , 53 ].
In this context, sometimes, the metabolites are also used as predictors [ 53 ]. Vacher et al. Although, heterosis is a genome-wide phenomenon covering the network of genes and their proteins leading to depictions in the form of the phenotype by changes and modifications in the plant metabolism. Still, there is a vast scope in advances in the expression-based prediction of heterosis, which provides new avenues for the same.
According to the dominance hypothesis, the independent set of deleterious alleles accumulates over time and illustrates their expression in the homozygous recessive condition during the inbreeding process [ 55 , 56 ].
The dominant alleles coming from one parent complements its counterpart, minor allele from the second parent, ultimately gives better phenotype. However, according to the over-dominance hypothesis, allelic interactions that stimulate heterozygous loci expression in hybrids [ 8 ]. Intra-allelic interaction having a significant role in over-dominance where the presence of multiple alleles gives excellent performance than homozygosity for either of alleles.
If over-dominance is a major cause of heterosis, breeding methods that maximize heterozygosity will result in the best performance. Whereas on the other hand, if dominance or epistasis is the primary cause of natural or breeding populations—as well as individuals behaving similarly to hybrids—by fixing up for favorable alleles. Hallauer et al. Moreover, Moll et al. Specifically, in a condition, when negative and positive alleles were linked in the repulsion phase.
None of these two hypotheses describes the effect of interactions between non-allelic loci. Epistasis is the inter-allelic interaction between two or more genes. Due to complexity, the role of epistasis with heterosis was not that fully understood. Afterward, the complex nature of the biological process and its networks which signify polygenic traits become understandable [ 6 ].
The role of epistasis concerning heterosis remains challenging to understand. In early studies because of limited experimental size and computational capacity, estimates of the epistatic variance of heterosis were minimal.
STUDIES ON HETEROSIS FOR YIELD IN BRINJAL (Solanum melongena. L)
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