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: Thirty six Indian mustard genotypes were evaluated to estimate variability, heritability and genetic advance in yield and yield components at Anand Agricultural University (Gujarat). The experiment was conducted using a Randomized Complete Block Design with three replications. Significant genotypic variability among the test genotypes was observed for all traits studied. Higher values of phenotypic co-efficients of variation and genotypic co-efficients of variation were observed for number of secondary branches per plant, number of siliqua per plant and yield per plant indicating the existence of higher magnitude of variability among the test genotypes for effective selection in respect of the above characters. Higher heritability estimates values were recorded for number of siliqua per plant, yield per plant, number of seeds per siliqua, length of main branch, days to 50 per cent flowering, 1000 seed weight, number of secondary branches, Siliqua length, protein content and plant height, indicating these traits were less influenced by environmental factors and selection for them is fairly easy. Higher values of expected genetic advance as per cent of mean was recorded for yield per plant, number of siliqua per plant, number of secondary branches, number of seeds per siliqua, length of main branch, siliqua length, and 1000 seed weight, indicating that selection would be more useful to improve these traits. High heritability values coupled with high genetic advance was observed in case of number of siliqua per plant, plant height, length of main branch and yield per plant, indicating that selection for these traits would be effective in Indian mustard improvement. Inter-character association studies were also conducted. The characters which showed positive significant genotypic and phenotypic correlation with yield were plant height, length of main branch and number of siliqua per plant. These characters are playing important role in indirect selection for yield.Key Words : Heritability, Indian mustard, Genetic advance, Genotypic variation, Phenotypic variation, Tomato, Yield View Point Article : Akabari, V.R. and Niranjana, M. (2015). Genetic variability and trait association studies in Indian mustard (Brassica juncea).Internat. J. agric. Sci., 11 (1): 35-39.

Leaf rolling is an important mechanism to mitigate the effects of moisture stress in several plant species. In the present study, a set of 92 wheat recombinant inbred lines derived from the cross between NI5439 × HD2012 were used to identify QTLs associated with leaf rolling under moisture stress condition. Linkage map was constructed using Axiom 35 K Breeder’s SNP Array and microsatellite (SSR) markers. A linkage map with 3661 markers comprising 3589 SNP and 72 SSR markers spanning 22,275.01 cM in length across 21 wheat chromosomes was constructed. QTL analysis for leaf rolling trait under moisture stress condition revealed 12 QTLs on chromosomes 1B, 2A, 2B, 2D, 3A, 4A, 4B, 5D, and 6B. A stable QTL Qlr.nhv-5D.2 was identified on 5D chromosome flanked by SNP marker interval AX-94892575–AX-95124447 (5D:338665301–5D:410952987). Genetic and physical map integration in the confidence intervals of Qlr.nhv-5D.2 revealed 14 putative candidate genes for drought tolerance which was narrowed down to six genes based on in-silico analysis. Comparative study of leaf rolling genes in rice viz., NRL1, OsZHD1, Roc5, and OsHB3 on wheat genome revealed five genes on chromosome 5D. Out of the identified genes, TraesCS5D02G253100 falls exactly in the QTL Qlr.nhv-5D.2 interval and showed 96.9% identity with OsZHD1. Two genes similar to OsHB3 viz. TraesCS5D02G052300 and TraesCS5D02G385300 exhibiting 85.6% and 91.8% identity; one gene TraesCS5D02G320600 having 83.9% identity with Roc5 gene; and one gene TraesCS5D02G102600 showing 100% identity with NRL1 gene were also identified, however, these genes are located outside Qlr.nhv-5D.2 interval. Hence, TraesCS5D02G253100 could be the best potential candidate gene for leaf rolling and can be utilized for improving drought tolerance in wheat.

Leaf rust (Puccinia triticina) is a major biotic stress affecting wheat yields worldwide. Host-plant resistance is the best method for controlling leaf rust. Aegilops speltoides is a good source of resistance against wheat rusts. To date, five Lr genes, Lr28, Lr35, Lr36, Lr47, and Lr51, have been transferred from Ae. speltoides to bread wheat. In Selection2427, a bread wheat introgresed line with Ae. speltoides as the donor parent, a dominant gene for leaf rust resistance was mapped to the long arm of chromosome 3B (LrS2427). None of the Lr genes introgressed from Ae. speltoides have been mapped to chromosome 3B. Since none of the designated seedling leaf rust resistance genes have been located on chromosome 3B, LrS2427 seems to be a novel gene. Selection2427 showed a unique property typical of gametocidal genes, that when crossed to other bread wheat cultivars, the F showed partial pollen sterility and poor seed setting, whilst Selection2427 showed reasonable male and female fertility. Accidental co-transfer of gametocidal genes with LrS2427 may have occurred in Selection2427. Though LrS2427 did not show any segregation distortion and assorted independently of putative gametocidal gene(s), its utilization will be difficult due to the selfish behavior of gametocidal genes.

The mega wheat variety HD2967 was improved for leaf and stripe rust resistance by marker-assisted backcross breeding. After its release in 2011, HD2967 became susceptible to stripe rust and moderately susceptible to leaf rust. The leaf rust resistance gene LrTrk was transferred into HD2967 from the durum wheat genotype Trinakria. Then, HD2967 was crossed with Trinakria to produce F1 plant foreground selection for LrTrk and background selection for the recurrent parent genotype was carried out in BC1F1, BC2F1 and BC2F2 generations. Foreground selection was carried out with the linked marker Xgwm234, while polymorphic SSR markers between parents were used for background selection. Background selection resulted in the rapid recovery of the recurrent parent genome. A morphological evaluation of 6 near isogenic lines (NILs)—2 resistant to leaf and stripe rust, and 4 resistant to leaf rust only—showed no significant differences in yields among NILs and the recurrent parent HD2967. All of the 6 NILs showed the presence of 2NS/2AS translocation, carrying the linked genes Lr37/Sr38/Yr17 present in HD2967 and the targeted leaf rust resistance gene LrTrk. Two NILs also showed additional resistance to stripe rust. Therefore, these NILs with rust resistance and an at par yielding ability of H2967 can replace the susceptible cultivar HD2967 to reduce yield losses due to disease.

Aegilops is a genus belonging to the family Poaceace, which have played an indispensible role in the evolution of bread wheat and continues to do so by transferring genes by wide hybridization. Being the secondary gene pool of wheat, gene transfer from Aegilops poses difficulties and segregation distortion is common. Gametocidal genes are the most well characterized class of segregation distorters reported in interspecific crosses of wheat with Aegilops. These "selfish" genetic elements ensure their preferential transmission to progeny at the cost of gametes lacking them without providing any phenotypic benefits to the plant, thereby causing a proportional reduction in fertility. Gametocidal genes (Gc) have been reported in different species of Aegilops belonging to the sections Aegilops (Ae. geniculata and Ae. triuncialis), Cylindropyrum (Ae. caudata and Ae. cylindrica), and Sitopsis (Ae. longissima, Ae. sharonensis, and Ae. speltoides). Gametocidal activity is mostly confined to 2, 3, and 4 homeologous groups of C, S, S, S, and M genomes. Removal of such genes is necessary for successful alien gene introgression and can be achieved by mutagenesis or allosyndetic pairing. However, there are some instances where Gc genes are constructively utilized for development of deletion stocks in wheat, improving genetic variability and chromosome engineering.

TSD276-2, a wheat genetic stock derived from the cross Agra Local/T. spelta 276 showed broad spectrum resistance against leaf rust pathogen. Genetic analysis was undertaken using F1, F2, F2:3 and BC1F1 generations derived from the cross TSD276-2/Agra Local. The results revealed a single recessive gene for leaf rust resistance, tentatively named as LrTs276-2, in TSD276-2. Molecular mapping of leaf rust resistance gene LrTs276-2 in TSD276-2 was done using SNP-based PCR and SSR markers. For Bulked Segregant Analysis (BSA), two bulks viz. resistant bulk and susceptible bulk, and the parents TSD276-2 and Agra Local were genotyped for SNPs using AFFYMETRIX 35K Wheat Breeders' AXIOM array. T. spelta 276 was also genotyped and used as a check. BSA indicated that the gene for leaf rust resistance in TSD276-2 is located on chromosome arm 1DS. Putatively linked SNPs on chromosome arm 1DS were converted into PCR-based markers. Polymorphic SSR markers on chromosome arm 1DS were also identified. Final linkage map was constructed using one SNP-based PCR and three SSR markers. The rust reaction and chromosomal location suggest that LrTs276-2 is a new leaf rust resistance gene which may be useful in broadening the genetic base of leaf rust resistance in wheat.

Resistance genes for leaf and stem rusts in bread wheat line Selection212 are recessive in nature. Both leaf and stem rust resistance genes, named tentatively as LrSel212 and SrSel212, have been mapped to the short arm of chromosome 2B separated by genetic distance of 16.4 cM. Xwmc474 was the closest marker located between two genes, 5.6 cM proximal to LrSel212 and 10.8 cM distal to SrSel212. Leaf rust pathotype 77-5 is virulent to leaf rust resistance genes located on chromosome 2B viz., Lr13, Lr16, Lr23, Lr35 and Lr73, but avirulent to Selection212, suggesting that LrSel212 is distinct from these genes. Six stem rust resistance genes have been assigned to chromosome 2B viz., Sr19, Sr20, Sr23, Sr36, Sr39 and Sr40. Stem rust pathotype 40A used in genetic analysis was virulent to Sr19 and Sr20, but avirulent to Selection212; and the latter showed a significantly lower infection type in comparison to Sr39. Sr23 and Sr36 showed susceptibility to few other stem rust pathotypes to which Selection212 was resistant. While the response of Sr40 to Indian pathotypes of Pgt is not known, differences in the genetic distance and nature of inheritance between Selection212 and Sr40 indicate their distinct identity. However, test of allelism with Sr40 is required to confirm whether SrSel212 represents a different locus. Selection212 may be useful in broadening the genetic base of rust resistance in wheat.