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Saltol, a major QTL for salt exclusion, was derived from ‘Pokkali’, a salt-tolerant rice cultivar. Apart from Pokkali, many genotypes with wide variation for salinity tolerance offer ample scope for identifying new genes or QTLs underlying various tolerance mechanisms. Such genes could be aggregated into high-yielding backgrounds to reinforce a breeding programme. To identify potential donors for salt tolerance and prospective parental combinations for developing high-yielding salt-tolerant cultivars, ten genotypes were subjected to salt stress and evaluated for morpho-physiological traits and marker-allele polymorphism in the Saltol-QTL region. Although the salt-susceptible high-yielding varieties clustered together in a 3-D plot, principal component analysis showed marked spatial isolation among the tolerant genotypes. Unlike Pokkali and its derivative FL496, Rahspunjar maintained a higher level of K+ despite high Na+ influx in shoots. The wider genetic distances observed at both phenotypic and genotypic levels suggest the possibility of getting transgressive segregants among the offspring of crosses between Rahspunjar and Gayatri or Swarna Sub1. Similarly, SR 26B, which coped with the stress by diluting the Na+ load by maintaining a higher growth rate, differed from Pokkali or Nona Bokra: these two coped with the stress by regulating the transmission of Na+ from roots to photosynthetically active sites. The F2:3 population derived from Savitri × SR 26B showed wide morpho-physiological diversity for salt tolerance. SR 26B was the most distant genotype from Pokkali in the Saltol QTL region and was salt tolerant despite the absence of Pokkali alleles in this region.
, K., Takamure, I., Sano, Y. 2006. Transgressive segregation due to linked QTLs for grain characteristics of rice. Euphytica 150 :27–35. Sano Y. Transgressive segregation due to
Results of work to transfer FHB resistance from Sumai 3 to modern Romanian winter semi dwarf wheat and chances to obtain transgressive segregation for resistance are presented. Four F2 populations of Sumai 3 top-crossed to advanced winter lines, with various levels of FHB resistance were included in the study.
Two segregating populations of doubled haploid (DH) wheat lines derived androgenetically from crosses ‘Svilena’ (susceptible) × A-38b-4-5-3-3 (highly resistant) and ‘Svilena’ × WWRN (moderately resistant to moderately susceptible) were characterized for resistance to common bunt. Disease incidence was evaluated after inoculation of seeds with a mixture of Tilletia foetida teliospores in two autumn sown field experiments. Two-gene model of inheritance of resistance in line A-38b-4-5-3-3 was suggested. The transgressive segregation in the latter population was indicative for a quantitative mode of inheritance. The DH lines were assessed for plant height, heading time and important yield components in a three-year field experiment without bunt infection. In both populations, transgressive segregation was observed for all agronomic characteristics. Although the disease incidence was positively correlated with most of the agronomic traits, genotypes combining bunt resistance with good yield potential were isolated from ‘Svilena’ × A-38b set of lines. These genotypes are valuable for breeding varieties designed for growing in low-input and organic farming systems. The two DH populations are suitable to be used for further studies on the genetic basis of bunt resistance.
A study was conducted during 2008–2010, to estimate heterosis for yield component traits and protein content in bread wheat under normal and heat-stress environment by utilizing a set of 45 half diallel cross combinations, involving 10 diverse parents. Analysis of variance revealed significant differences for the two environements, whereas differences over the years were non-significant for all the traits. The pooled data over the years, exhibited highly significant differences for all the traits under both normal and heat-stress environments. The number of tillers/plant exhibited maximum degree of standard heterosis under normal and heat-stress environment (with value of 12.62% and 53.75%), respectively. In general, spike length (16.02%) and number of grains/spike (52.10%), showed higher magnitude of standard heterosis under normal environment than heat-stress environment, whereas number of tillers/plant (53.75%) and gain filling duration (43.68%) showed higher standard heterosis in heat-stress environment than the normal one. For grain yield/plant, 1000-grain weight and protein content, the number of cross combination showing standard heterosis were almost same in both the environments. The ten crosses, out of forty-five crosses, namely HD 2733/WH 542; PBW 343/UP 2425; HD 2687/PBW 343; PBW 343/UP 2382; PBW 343/HD 2285; WH 542/UP 2425; PBW 343/PBW 226; UP 2382/HUW 468; PBW 343/WH 542 and PBW 226/HD 2285 can be used to select transgressive segregants for normal as well warmer wheat growing areas. These ten combinations can be used by involving, the trait grain filling duration, tillers per plant, spike length, grains per spike, 1000-grain weight to improve grain yield for warmer areas. In all 45 cross combinations, six cross combinations were identified for better per se performance for grain yield as well as protein content under heat-stress environment. These combinations may thus be used for developing superior genotypes through fixation of heterosis are also supported by high SCA. Besides, results of present study also revealed ample scope for developing transgressive segregants involving some of these parents to develop high yielding genotypes in wheat suitable for heat stress environments.
Rice straw represents a significant energy source for ruminant animals, and fibers and lignin contents of rice straw are negatively related to intake potential of forages. For improvement of the digestibility of rice straw, it is necessary to understand the genetic basis of the related traits. In present study, mapping of quantitative trait loci (QTL) for acid detergent fiber (ADF), neutral detergent fiber (NDF), and acid detergent lignin (ADL) was carried out using a doubled haploid (DH) population derived from a cross between indica variety Zai-Ye-Qing 8 (ZYQ8) and japonica variety Jing-Xi 17 (JX17). The results indicated that all three parameters were continuously distributed among the DH lines, but many DH lines showed transgressive segregation for all the three traits. A total of three main-effect QTLs were identified for ADF and ADL, two of which, qADF-9 and qADL-9, shared the same region on chromosome 9. These two main-effect QTLs explained more than 20% of the total phenotypic variations, whereas the other QTL, qADF-5, explained 12.8% of the total phenotypic variation for ADF. In addition, another two epistatic QTLs, qADF-2 and qADF-3 could explain 17.6% of the total variations. Thus, we concluded that both main-effects and epistatic QTLs were important in controlling the genetic basis of ADF.
Combining ability analysis was carried out in the F1 and F2 generations of a 10 × 10 parents half diallel for peduncle length and flag leaf area in spring wheat under three environments. The mean squares for both general combining ability (GCA) and specific combining ability (SCA) were significant for peduncle length in both the generations, indicating the involvement of both additive and non-additive gene actions in the inheritance. However, the high values of GCA variance showed the greater importance of additive gene action in the inheritance of this trait. Flag leaf area was observed to be controlled by non-additive gene action. The environment played a significant role in the expression of both the traits. The GCA × environment interaction exhibited greater sensitivity in all cases than the SCA × environment interaction. The varieties Kharchia 65 and Durgapura 65 emerged as desirable general combiners for peduncle length, whereas Pavon and Moncho had high mean performance for flag leaf area. These parents could be used as donors in future breeding to develop a physiologically efficient wheat genotype with high production. The crosses Moncho × Brochis and Durgapura 65 × Raj 821 were the most desirable specific combinations for flag leaf area and Kharchia 65 × Chiroca for both the traits. Desirable transgressive segregants can be expected from these crosses. Diallel selective mating or bi-parental crossing could be useful for the genetic improvement of these physiological traits.
The F1 and F2 progenies of a ten-parent diallel cross (excluding reciprocals) were analysed for the combining ability of quantitative traits in six-rowed barley (Hordeum vulgare L.). significant differences were indicated between the parents, F1s and F2s for all the characters studied. The gca and sca components of variance were significant for all the traits. Both additive and non-additive gene effects were involved in the genetic control of the characters; however, non-additive gene effects were observed to be predominant. Among the parents RD 2035, RD 2052, RD 2503 and BL 2 were the best general combiners for grain yield and average to high combiners for other important traits.The parents RD 2552 and RD 387 were the best general combiners for dwarfness. The best specific crosses for grain yield were RD 2503 × RD 2585,RD 2035 × RD 2052, RD 2035 × BL 2, RD 2052 × BL 2, RD 2508 × RD 2552, RD 2552 × RD 2585 and Rd 2052 × RD 2552 in both the F1 and F2 generations. These crosses were higher yielders and in most of the crosses one of the parents involved was a good combiner, indicating that such combinations can be expected to produce desirable transgressive segregants. All the best crosses for grain yield also showed average to high sca effects for most of the yield components. Most of the specific crosses for grain yield involved high × average, average × average and average × poor general combiners. To ensure a further increase in grain yield, the combination of desirable yield components is advocated. The inclusion of F1 hybrids showing high sca, and having parents with good gca, in multiple crosses, bi-parental mating or diallel selective mating could prove a worthwhile approach for further amelioration of grain yield in six-rowed barley.
Sweet sorghum (Sorghum bicolor (L.) Moench) is a potential raw material for production of ethanol that on blending in petrol is expected to meet the energy demand and address the environmental issues. Well-developed hybrid technology will make the crop remunerative to the farmers. Hence, gene action and best combining female and male parents for sugar yield in sweet sorghum (Sorghum bicolor (L.) Moench) and the association of sugar yield with other agronomic traits was studied in 171 hybrids developed by crossing 19 female parents with nine male parents in line × tester design and evaluated during both rainy and postrainy seasons of 2006. The significant differences between the seasons for all the traits suggested that these traits are greatly influenced by the environment. The lines (female parents) ICSA 38, ICSA 479, ICSA 702, ICSA 675 and ICSA 474 and the restorers (male parents), SSV 74 and SSV 84 combined well for sugar yield during rainy season and the lines, ICSA 702, ICSA 38 and ICSA 474 and the restorers, ICSV 93046, SPV 1411 and ICSV 700 combined well during postrainy season. The magnitude of SCA variance was higher suggesting the importance of non-additive gene action in inheritance of all the traits though both additive and dominant genes controlled overall sugar yield during both the seasons. Hence, selection in early generation would be ineffective and recurrent selection with periodic intercrossing is advocated. However, breeding good combining restorer parents can fetch high sugar yield in postrainy season. There is an indication of existence of transgressive segregation for sugar yield that can be exploited. The sugar yield was weak though significantly correlated with high brix and poor grain yield during both the seasons requiring extensive crossing to improve these traits simultaneously. Keeping in view mean performance, SCA effects and heterobeltiosis, the hybrids, ICSA 474 × SSV 84, ICSA 24001 × ICSR 93046 and ICSA 474 × SPV 422 were identified promising for rainy season and the hybrids ICSA 24001 × SPV 1411 and ICSA 511 × ICSV 93046 were identified for postrainy season.
Aghnoum, R., Niks, R.E. 2011. Transgressive segregation for very low and high levels of basal resistance to powdery mildew in barley. J. Plant Physiol. 168 :45–50. Niks
