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Indian mustard [Brassica juncea (L.) Czern.] is a major edible oil crop of India. The Indian Council of Agricultural Research—National Bureau of Plant Genetic Resources (ICAR-NBPGR) and ICAR—Directorate of Rapeseed Mustard Research (DRMR) together conserve one of the largest global collection of Indian mustard germplasm comprising 5950 accessions which includes indigenously collected landraces, exotic accessions, breeding lines, Improved/released cultivars, registered genetic stocks and other type of material of unknown origin. However, only a small fraction of this huge collection has been deployed in the breeding programme due to lack of information on majority of accessions. The objective of this study was to develop a core collection of Indian mustard to enhance utilization of conserved germplasm in crop improvement programme. For this purpose, the accessions were characterized at one ideal site (Bharatpur) using 14 agro-morphological traits and the resultant data was analysed using three state-of-the-art core collection construction tools—MSTRAT, Power Core and Core Hunter 3 (CH3), to obtain three core sets each with 595 accessions. The quality of these core sets was evaluated and compared using two genetic distance based metrices (E-NE & A-NE), several summary statistics, Shannon diversity index, phenotypic correlations etc. The core collection generated using CH3 which optimized simultaneously for both representativeness and diversity was found the best in capturing the genetic variation existed in the base collection for all the 14 traits. The diversity represented in the core collection will therefore, be a guideline to breeders for a wider use of the Indian mustard genetic resources available in the genebank for identification and introgression of new useful traits, as well as for delineation of their genetic basis particularly through marker-trait association.

Brassica rapa (2n = 20, AA genome) is an important oil yielding species of the family Brassicaceae and characterized by wide range of genetic and morphological subtypes suitable for cultivation under diverse agro-climatic regions of India. In this study, genetic diversity among three subspecies of B. rapa including yellow sarson, toria and outlier brown sarson was estimated using various agro-morphological traits and simple sequence repeat (SSR) markers. Maximum variability was recorded for siliqua angle (Coefficient of variation = 30.9%), followed by seeds/siliqua (CV = 18.8%), leaf length (CV = 10%) and plant height (CV = 16.8%). Principal component analysis explained more than 50% of the total observed morphological variability for first two components. Of the 107 SSR markers tested, 80 generated reproducible, clear and distinct amplicons of which, 65 (81.25%) were found polymorphic. The number of alleles at each locus ranged from 2 to 7, with an average of 3.03 alleles per marker. A total of 197 alleles were detected at 65 SSR loci with average PIC value of 0.457 and a mean resolving power of 3.04. Neighbor-Joining cluster analysis based on morphological traits and SSR markers separately classified all the 28 genotypes into five major groups. The population structure analysis resulted into three sub-populations with certain extent of admixture among the earlier established taxonomic sub-groups. Twenty-three unique alleles were detected in thirteen B. rapa varieties. The clustering analysis and principal coordinate analysis outlined the genetic relationships among different varieties belonging to the three subspecies of B. rapa. Genetically diverse genotypes as illustrated by score plots and from the clustering patterns brought out the wide range of diversity present among B. rapa genotypes and the underlying options available for selecting parental genotypes for hybridization and developing high yielding cultivars suitable for Indian conditions.

Genetic engineering offers one of the most potential techniques for modification of many horticulturally important traits, which have been found impossible so far to incorporate in elite backgrounds via conventional breeding methods without affecting their phenotypic traits. Thus this technique assists in circumventing the problems of a long generation period, which hampers the scope of genetic improvement particularly in perennial horticultural tree species. Advancements in molecular biology and genetic transformation have made it possible to identify, isolate, and transfer desirable genes from any plants or microbes. The introduction or enhancement of desirable traits is traditionally done by breeding. This is time consuming and also not very precise. On the other hand, genetic engineering creates plants with specific changes in the background of a proven cultivar without disturbing their genetic constitution. Expression of undesirable genes can be blocked by the application of antisense gene technology and RNAi technology. Biotechnological interventions that could increase the efficiency of horticultural crop improvement are essential to generate plants with several desirable traits.

Background Oilseed Brassica represents an important group of oilseed crops with a long history of evolution and cultivation. To understand the origin and evolution of Brassica amphidiploids, simple sequence repeat (SSR) markers were used to unravel genetic variations in three diploids and three amphidiploid Brassica species of U’s triangle along with Eruca sativa as an outlier. Results Of 124 Brassica-derived SSR loci assayed, 100% cross-transferability was obtained for B. juncea and three subspecies of B. rapa, while lowest cross-transferability (91.93%) was obtained for Eruca sativa. The average % age of cross-transferability across all the seven species was 98.15%. The number of alleles detected at each locus ranged from one to six with an average of 3.41 alleles per primer pair. Neighbor-Joining-based dendrogram divided all the 40 accessions into two main groups composed of B. juncea/B. nigra/B. rapa and B. carinata/B. napus/B. oleracea. C-genome of oilseed Brassica species remained relatively more conserved than A- and B-genome. A- genome present in B. juncea and B. napus seems distinct from each other and hence provides great opportunity for generating diversity through synthesizing amphidiploids from different sources of A- genome. B. juncea had least intra-specific distance indicating narrow genetic base. B. rapa appears to be more primitive species from which other two diploid species might have evolved. Conclusion The SSR marker set developed in this study will assist in DNA fingerprinting of various Brassica species cultivars, evaluating the genetic diversity in Brassica germplasm, genome mapping and construction of linkage maps, gene tagging and various other genomics-related studies in Brassica species. Further, the evolutionary relationship established among various Brassica species would assist in formulating suitable breeding strategies for widening the genetic base of Brassica amphidiploids by exploiting the genetic diversity present in diploid progenitor gene pools.

Genetic engineering technique offers myriads of applications in improvement of horticultural crops for biotic and abiotic stress tolerance, and produce quality enhancement. During last two decades, a large number of transgenic horticultural crops has been developed and more are underway. A number of genes including natural and synthetic Cry genes, protease inhibitors, trypsin inhibitors and cystatin genes have been used to incorporate insect and nematode resistance. For providing protection against fungal and bacterial diseases, various genes like chitinase, glucanase, osmotin, defensin and pathogenesis-related genes are being transferred to many horticultural crops world over. RNAi technique has been found quite successful in inducing virus resistance in horticultural crops in addition to coat protein genes. Abiotic stresses such as drought, heat and salinity adversely affect production and productivity of horticultural crops and a number of genes encoding for biosynthesis of stress protecting compounds including mannitol, glycine betaine and heat shock proteins have been employed for abiotic stress tolerance besides various transcription factors like DREB1, MAPK, WRKY, etc. Antisense gene and RNAi technologies have revolutionized the pace of improvement of horticultural crops, particularly ornamentals for color modification, increasing shelf-life and reducing post-harvest losses. Precise genome editing tools, particularly CRISPR/Cas9, have been efficiently applied in tomato, petunia, citrus, grape, potato and apple for gene mutation, repression, activation and epigenome editing. This review provides comprehensive overview to draw the attention of researchers for better understanding of genetic engineering advancements in imparting biotic and abiotic stress tolerance as well as on improving various traits related to quality, texture, plant architecture modification, increasing shelf-life, etc. in different horticultural crops.