After reading this article you will learn about the application of biotechnology in brinjal.
In vitro androgenesis has been successfully applied and adapted to eggplant. In addition to the rapidity of this method for yielding homozygous material, it has other important advantages such as the simplification of the analysis of traits genetic inheritance, as well as the increased probability to obtain multi-recessive genotypes. This technique is routinely used since the end of the eighties by seed companies carrying out eggplant breeding programs.
This method is based on the in vitro fusion of somatic cells (generally, diploid cells of the leaf mesophyll of two plant partners), followed by the regeneration of plants from the fusion product. It has been successfully applied to eggplant since the 1980s for obtaining inter-specific hybrids, in particular with species not sexually, crossable with eggplant.
The first inter-specific somatic hybrids were obtained between eggplant and S. sisymbriifolium, which is, promising source of disease resistances. Using the PEG (Poly Ethylen Glycol) as a fusion agent, aneuploid somatic hybrids, have been reported. But, in terms of application to breeding purposes, this technique has not delivered desired results.
The applications of interspecific somatic hybridization to eggplant and its wild relatives did not bring so far, substantial progresses (when compared to sexual hybridization) for transferring genes of interest into eggplant genome.
However, as the electro-fusion technique works well for yielding well balanced tetraploid somatic hybrids and as there are many more Solanum species that would be worth to be used in somatic fusion experiments (those, which did not yield, so far fertile progenies when crossed with eggplant), one can expect that sooner or later, somatic hybridization will prove itself as a precious method for transferring genes from wild germplasm into S. melongena genome. The return to the diploid level is (relatively) easily obtained by using anther culture.
Resistant cells and derived plantlets have been reported from cell suspensions exposed in a liquid medium to culture filtrate of Verticillium dahliae. The potential of somaclonal variation induced by auxins applied to cells culture undergoing somatic embryogenesis has been investigated and no concert results in terms of practical applications are available.
As eggplant is easily manipulated in vitro, genetic engineering via Agrobacterium tumefasciens vector has been successfully applied to it from the 80s. The genetic transformations carried out so far concern mostly resistance to insects and abiotic stresses.
A synthetic cryl Ab gene coding for an insecticidal crystal protein (ICP) of Bacillus thuringiensis (Bt) has been transferred to brinjal at National Research Centre for Plant Biotechnology, IARI, New Delhi by co-cultivating cotyledonary explants with Agrobacterium tumefaciens.
Transformed plants resistant to kanamycin were regenerated. Hybridization experiments demonstrated gene integration and mRNA expression. Double antibody sandwich ELISA analysis revealed Bt toxin protein expression in the transgenic plants.
The expression resulted in a significant insecticidal activity of transgenic brinjal fruits against the larvae of fruit borer (Leucinodes orbonalis). The results also demonstrated that a synthetic gene based on monocot codon usage can be expressed in dicotyledonous plants for insect control.
Resistance to Colorado beetle (Leptinotarsa decemlineata), one of eggplant pests against which no eggplant germplasm resistance is described, has been successfully engineered by using a Bt gene encoding for the CrylllB toxin. Field experiments with natural Colorado beetle infestation demonstrated the effectiveness of the resistance.
Transgenic plants suffer a lesser infestation level than the control, the hence, produce a better yield. The observations on the experimental crop did not detect any deleterious effect on other insects, thus, confirming the specificity of the CrylllB toxin expressed by the transgenic plants. The technical success of this genetic transformation could not be transferred into practice, due to reluctance by consumers and NGOs.
Resistance to Leucinodes orbonalis (eggplant fruit borer, a very serious problem on eggplant in Asia), was engineered with a synthetic crylAb gene coding for an insecticidal crystal protein of Bacillus thuringiensis, and the transgenic material had a significant insecticidal activity against the insect larvae.
Next researches have led to the creation of genetic material carrying the cry 1 Ac gene associated to the CaMV35S promoter, and displaying an insecticidal activity (about 100% of larvae mortality) efficient against Leucinodes orbonalis and also Helicoverpa armigera.
This material is engaged since the beginning of the 2000s in many biosafety investigations for obtaining the authorisation to be commercialized, and agronomic production strategies of the transgenic resistance are under study in various institutes. In India, Bt brinjal hybrids developed by Mahyco, TNAU-Coimbatore and UAS-Dharwad have been approved by GEAC but final approval from Minister of Environment and Forest pending.
A population of 300 putative transgenic eggplants (Solanum melongena L.) carrying the syncry IIIA gene was produced and tested for resistance to the Colorado potato beetle [CPB ; Leptinotarsa decemlineata (Say)]. Toxicity tests in planta and in vitro demonstrated that 69% of the transformed plants were resistant to neonate larvae and adult CPB.
Transgenicity of the plants was confirmed by studies of GUS expression and Southern and Northern analysis. Primary transformants, having a single insert of the construct, upon selfing, produced progenies co-segregating for the uidA and syn crylllA genes at the expected 3:1 ratios with a few exceptions in which only one of the genes was expressed.
The latter was attributed to the gene silencing phenomenon. The segregating resistant R1 seedlings showed the same level of resistance as the parental genotypes in growth chamber tests and under field conditions. One genotype carrying two copies of the construct, upon selfing, segregated at a 15:1 ratio for GUS expression and resistance to CPB, while Southern analysis revealed a 9:3:3:1 genotypic segregation ratio for individual copies of the construct.
Molecular Mapping, Markers and Marker Assisted Selection:
Genetic mapping in eggplant has been initiated in the last decade only. The first molecular map was developed on an interspecific F2 population with RAPD markers defining 13 linkage groups. This map was completed with AFLPs and SSR and contains on the whole 162 markers in 17 LGs encompassing 716.9 cM at an average spacing of 4.9 cM.
The strong conservation between eggplant and tomato chromosomes suggest that the genomic resources developed for tomato will be useful for eggplant genetic research. 273 AFLP and RAPD markers encompassing 736 cM in 12 LGs have been reported. Current progress is being made for saturating these maps with the addition of other PCR-based markers as reviewed and summarised by Daunay (2008).
Genes and QTLs mapping for horiticultural traits has gained momentum since the establishment of the first maps, but so long the different existing maps are not anchord to each other, the comparison of the genes and QTLs locations obtained on the one or the other is very difficult.
The traits focused to for mapping purposes include Verticillium wilt resistance, bacterial wilt resistance, fruit shape and colour, stem and calyx violet colour and a wide range of characteristics (number, shape, size, violet colour, etc.), of many plants organs (flower, ovary, fruit, leaf, prickles, hair).
Marker assisted selection of eggplant has been limited so far, but the ongoing genetic studies will provide within a short time the convenient tools for implementing it into the breeding programmes. Genomic resources for eggplant are developed actively such as ESTs. Further, the current international effort to sequence the tomato genome will provide a wealth of information applicable to eggplant.