Mehak Gupta

Population structure and breeding value of a new type of Brassica juncea created by combining A and B genomes from related allotetraploids

Key messageDerived amphiploidy helped to resynthesize agronomically superiorB. junceagermplasm which showed high heterosis in crosses with naturalB. juncea. This new procedure facilitates a seamless flow of variation acrossBrassicadigenomics.AbstractBrassica digenomics, artificially resynthesized by hybridizing extant genome donor diploids, show poor breeding value due to the linkage drag associated with diploid donors. We recently developed a method that involves resynthesis through hybridization between related allotetraploids. Derived B. juncea was created by combining A and B genomes extant in B. napus and B. carinata, respectively. Large genomic and agronomic modifications resulted. Population structure analysis based on the DNA polymorphism generated using 108 locus-specific SSR primers helped to identify three pools of allelic diversity. Thirteen progenies with determinate plant growth habit were discovered, and these aligned closely with B genome of the donor species like B. nigra and B. carinata. The indeterminate group showed greater genetic affinity with extant B. juncea. Derived genotypes possessed high agronomic potential. Importantly, high heterosis was observed in crosses between derived and natural B. juncea. Some derived juncea progenies figured in heterotic combinations during both the years of F1 hybrid evaluation. In essence, the hybrids between derived B. juncea and natural B. juncea can be considered as interspecific hybrids between B. juncea and B. napus for A genome and between B. juncea and B. carinata for B genome. This possibly explains their high heterosis-inducing potential. Integrating genetic diversity with the inherent breeding value allowed more efficient prediction of heterosis. Besides generation of new novel variability of huge economic importance and operational simplicity, the method of derived amphiploidy allows a seamless flow of heritable variation across Brassica digenomics.

Mapping resistance responses to Sclerotinia infestation in introgression lines of Brassica juncea carrying genomic segments from wild Brassicaceae B. fruticulosa

Sclerotinia stem rot (Sclerotinia sclerotiorum) is a major disease of Brassica oilseeds. As suitable donors to develop resistant cultivars are not available in crop Brassicas, we introgressed resistance from a wild Brassicaceae species, B. fruticulosa. We produced 206 B. juncea-B. fruticulosa introgression lines (ILs). These were assessed for pollen grain fertility, genome size variations and resistance responses to Sclerotinia following stem inoculations under disease-conducive conditions. Of these, 115 ILs showing normal fertility and genome size were selected for cytogenetic characterization using florescent genomic in situ hybridization (Fl-GISH). B. fruticulosa segment substitutions were indicated in 28 ILs. These were predominantly terminal and located on B-genome chromosomes. A final set of 93 highly fertile and euploid (2n = 36) ILs were repeat-evaluated for their resistance responses during 2014–15. They were also genotyped with 202 transferable and 60 candidate gene SSRs. Association mapping allowed detection of ten significant marker trait associations (MTAs) after Bonferroni correction. These were: CNU-m157-2, RA2G05, CNU-m353-3, CNU-m442-5, ACMP00454-2, ACMP00454-3, EIN2-3-1, M641-1, Na10D09-1 and Na10D11-1. This is the first time such a molecular mapping technique has been deployed with introgression lines carrying genomic segments from B. fruticulosa, and the first to show that they possess high levels of resistance against S. sclerotiorum.

Segregation for fertility and meiotic stability in novel Brassica allohexaploids

Key messageAllohexaploidBrassicapopulations reveal ongoing segregation for fertility, while genotype influences fertility and meiotic stability.AbstractCreation of a new Brassica allohexaploid species is of interest for the development of a crop type with increased heterosis and adaptability. At present, no naturally occurring, meiotically stable Brassica allohexaploid exists, with little data available on chromosome behaviour and meiotic control in allohexaploid germplasm. In this study, 100 plants from the cross B. carinata × B. rapa (A2 allohexaploid population) and 69 plants from the cross (B. napus × B. carinata) × B. juncea (H2 allohexaploid population) were assessed for fertility and meiotic behaviour. Estimated pollen viability, self-pollinated seed set, number of seeds on the main shoot, number of pods on the main shoot, seeds per ten pods and plant height were measured for both the A2 and H2 populations and for a set of reference control cultivars. The H2 population had high segregation for pollen viability and meiotic stability, while the A2 population was characterised by low pollen fertility and a high level of chromosome loss. Both populations were taller, but had lower average fertility trait values than the control cultivar samples. The study also characterises fertility and meiotic chromosome behaviour in genotypes and progeny sets in heterozygous allotetraploid Brassica derived lines, and indicates that genotypes of the parents and H1 hybrids are affecting chromosome pairing and fertility phenotypes in the H2 population. The identification and characterisation of factors influencing stability in novel allohexaploid Brassica populations will assist in the development of this as a new crop species for food and agricultural benefit.