DNA transfer by highly asymmetric somatic hybridisation in Medicago truncatula (+) Medicago rugosaand Medicago truncatula(+) Medicago scutellata

Unlocking the hidden variation from wild repository for accelerating genetic gain in legumes

The fluctuating climates, rising human population, and deteriorating arable lands necessitate sustainable crops to fulfil global food requirements. In the countryside, legumes with intriguing but enigmatic nitrogen-fixing abilities and thriving in harsh climatic conditions promise future food security. However, breaking the yield plateau and achieving higher genetic gain are the unsolved problems of legume improvement. Present study gives emphasis on 15 important legume crops, i.e., chickpea, pigeonpea, soybean, groundnut, lentil, common bean, faba bean, cowpea, lupin, pea, green gram, back gram, horse gram, moth bean, rice bean, and some forage legumes. We have given an overview of the world and India's area, production, and productivity trends for all legume crops from 1961 to 2020. Our review article investigates the importance of gene pools and wild relatives in broadening the genetic base of legumes through pre-breeding and alien gene introgression. We have also discussed the importance of integrating genomics, phenomics, speed breeding, genetic engineering and genome editing tools in legume improvement programmes. Overall, legume breeding may undergo a paradigm shift once genomics and conventional breeding are integrated in the near future.

Investigation of Nicotiana tabacum (+) N. suaveolens cybrids with carpelloid stamens

To investigate cytoplasmic effects on homeotic floral morphology, Nicotiana tabacum and N. suaveolens protoplasts were fused and cybrids obtained to contrast with the sexual alloplasmic line Nta(sua)S. Nta(sua)S contains the nucleus of N. tabacum and cytoplasm of N. suaveolens while cybrids derive from fused cells where the cytoplasms can interact. The three male-sterile somatic cybrid plants analyzed contained mitochondria with N. tabacum and N. suaveolens mtDNA sequences, but not all the N. tabacum or all the N. suaveolens mtDNA sequences were present. The flowers were N. tabacum-like but with a split corolla (not observed in Nta(sua)S) and the whorl of stamens replaced by a whorl of carpel-like structures. Based on scanning electron microscopy the carpelloid stamens had a characteristic N. tabacum stigma, a style of variable length and a pseudo-ovary with ovule-like structures. The Southern blot data were consistent with mtDNA recombination. These genomic changes were maternally inherited. Chloroplasts were either of the N. tabacum or N. suaveolens type. AFLP analysis showed transfer of variable amounts of N. suaveolens nuclear DNA. However, it is the presence of the N. suaveolens sequences and/or absence of N. tabacum sequences in the mitochondria that correlates with the homeotic floral morphology. These cybrids will facilitate the analysis of the role of mitochondrial DNA sequences in floral organ identity; which has received limited attention in genetic flowering models based primarily on Arabidopsis research.

Cytogenetic characterization and fae1 gene variation in progenies from asymmetric somatic hybrids between Brassica napus and Crambe abyssinica

Sexual progenies of asymmetric somatic hybrids between Brassica napus and Crambe abyssinica were analyzed with respect to chromosomal behavior, fae1 gene introgression, fertility, and fatty-acid composition of the seed. Among 24 progeny plants investigated, 11 plants had 38 chromosomes and were characterized by the occurrence of normal meiosis with 19 bivalents. The other 13 plants had more than 38 chromosomes, constituting a complete chromosomal set from B. napus plus different numbers of additional chromosomes from C. abyssinica. The chromosomes of B. napus and C. abyssinica origin could be clearly discriminated by genomic in situ hybridization (GISH) in mitotic and meiotic cells. Furthermore, meiotic GISH enabled identification of intergenomic chromatin bridges and of asynchrony between the B. napus and C. abyssinca meiotic cycles. Lagging, bridging and late disjunction of univalents derived from C. abyssinica were observed. Analysis of cleaved amplified polymorphic sequence (CAPS) markers derived from the fae1 gene showed novel patterns different from the B. napus recipient in some hybrid offspring. Most of the progeny plants had a high pollen fertility and seed set, and some contained significantly greater amounts of seed erucic acid than the B. napus parent. This study demonstrates that a part of the C. abyssinica genome can be transferred into B. napus via asymmetric hybridization and maintained in sexual progenies of the hybrids. Furthermore, it confirms that UV irradiation improves the fertility of the hybrid and of its sexual progeny via chromosomal elimination and facilitates the introgression of exotic genetic material into crop species.Key words: asymmetric somatic hybrid, Brassica napus, Crambe abyssinica, cytogenetics, fae1 gene.