Evolutionary aspects of direct or indirect selection for seed size and seed metabolites in Brassica juncea and diploid progenitor species
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Seed size and seed metabolites have been the targets of direct or indirect selection during domestication and subsequent crop breeding. Understanding these traits and associated genetics can prove very useful for plant translational research. Large germplasm assemblage (235) of Brassica juncea and its progenitor species (B. rapa and B. nigra) was evaluated to establish seed trait variations for seed size and seed metabolites. Seeds were smallest in B. nigra and largest in B. juncea. Australian B. juncea and Indian B. rapa var brown sarson types averaged more seed oil content. Seed size and oil content were generally higher in modern cultivars in comparison to the land races. Allelic diversity for known associated genes for seed-size and oil-content (AP2, ARF2, TTG2, GRF2, GL2, CYP78A5, CYP78A6, MINI3, IKU2, IKU1, BRI1, DGAT, GPDH, LPAAT, GPAT and DA1) was studied so as to infer the effect of domestication on seed traits. Three genes (IKU1, IKU2, AP2) in B. rapa, two (TTG2 and GL2) in B. nigra and two (IKU1 and GRF2) in natural B. juncea were identified as targets of selection on the basis of Fst outlier and/or sequence diversity tests. We report parallel divergence for seed traits between B. juncea and B. rapa. Directional selection appeared stronger for seed-size as compared to correlated seed metabolites. Positive selection on seed-size is likely to have played a significant role in structuring regional variation in the germplasm.
KeywordsBrassica rapa Brassica nigra Domestication Directional selection Calorific value Fatty acids
The studies were financially supported by the Indian Council of Agricultural Research under ICAR National Professor Project “Broadening the genetic base of Indian mustard (Brassica juncea) through alien introgressions and germplasm enhancement” awarded to S.S.B. The authors thank “Plant Gene Resources of Canada, Agriculture and Agri-Food Canada” for providing many of the germplasm lines used in our studies.
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Conflict of interest
The authors declare that they have no conflict of interest.
Research involving human participants and/or animals
This article does not contain any studies with human participants or animals performed by any of the authors.
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