Genetic Appraisal of Derived Brassica juncea Amphiploids
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Date
2012
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Punjab Agricultural University, Ludhiana
Abstract
ABSTRACT
Derived Brassica juncea (AABB) lineages were analyzed to study the genetic changes that follow allopolyploid formations. Most of genotypes showed normal fertility with normal 18II chromosome configuration during meiosis1. Disomic chromosome substitution was indicated for DJ 15, DJ 18, DJ 19-2, DJ 21, DJ 38, DJ 58, DJ 61, DJ 92, DJ 97, DJ 103 and DJ 113. These substitution lines were expected to involve A/ C substitutions. Some individual plants showed novel phenotypes like determinate growth habit, terminal siliquae; however, there appeared to be no direct correlation between the examined molecular alterations and deviant phenotypes. There was a significant increase in sequence loss across generations within both subgenomes. There was a bias towards losing more sequences from the B. rapa (A) subgenome. We did not find any evidence of total sequence loss on the phenotypic means. Diversity analysis could also nicely resolve the test progenies into three very distinct groups, determinate juncea, crop Brassica parents and dipoid donors and indeterminate type of derived B. juncea. A total of 134 markers could be resolved on 18 linkage groups with an LOD score value greater than 3.0. The total genetic length of the map was 1010 cM with an average distance of 7.53 cM between adjacent loci. Resynthesis of new polyploid plants by derived resynthesis rout led to immediate and striking reactions of genomes to evolution. Gene loss, gene gain, gene movement and chromosome structural changes such as translocation and inversion were indicated and these collectively contributed to the process of diploidisation. A large number of hybrids were developed by hand crossing the set of derived B. juncea genotypes with natural B. juncea testers namely PBR210, RLC1, CBJ002 and AMH2. Heterosis over best commercial check PBR210, during 2010-2011 ranged from -76.5 to 103 percent with an average of -8.66 percent for the hybrids involving PBR 210 as male parent. The corresponding ranges for RLC1, CBJ002 and AMH2 were: -68.4 to 82.7 percent,-11.09 (60 hybrids), -83.6 to 79.6 percent, -3.96 (70 hybrids) and -78.3 to 59.0 percent,-14.53 (64 hybrids). During 2011-12, corresponding range and means for hybrids for involving same male parents were: PBR210 (-42.8 to 102.7; 16.87 for 35 hybrids); RLC1 (-52.7 to 104.8; 14.97 for 34 hybrids); CBJ002 (-55.9 to 117; 23.73 for 35 hybrids) and AMH2 (-51.8 to 69.6; 8.23 for 34 hybrids). Many of the putatic heterotic combinations will find their use in developing commercial hybrids. The concept of derived juncea developed by Brassica group at PAU stood validated by these studies.
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