Search Results

You are looking at 11 - 20 of 43 items for :

  • "gene action" x
  • Refine by Access: All Content x
Clear All

This research was carried out in 1997 and 1998 in order to study the genetic structure of a hybrid population established from three CMS (cytoplasmic male sterile) lines and four pollen tester (restorer) lines, to identify the parents and crosses showing superior general and specific combining abilities and finally to evaluate F1 hybrid vigour. According to the results, the variance due to specific combining ability (SCA) was highly significant for seed yield, number of seeds per head and plant height. These traits of sunflower were influenced, mostly, by dominant gene actions. Neither general (GCA) nor specific combining ability (SCA) variances were found to be significant for head diameter and 1000-seed weight. most of the total genetic variation in these characteristics was caused by epistatic gene actions due to SCA variances, which were higher than GCA variances. The parental lines CMS381, CMS461, RHA684 and RHA892 had the highest positive GCA effects for seed yield and in terms of the other traits studied, but these effects were not significant for all the traits observed. The crosses CMS191×RHA723, CMS191×RHA892, CMS381×RHA684 and CMS461×RHA684 might be considered as promising combinations in terms of seed yield and yield components. The amounts of heterosis and heterobeltiosis ranged from -8.4 to +16.3% to -21.3 to +3.4% for plant height, from 46.3-82.3% to 20.3-48.3% for head diameter, from -14.8 to +52.6% to.-16.5 +46.9% for number of seeds per head, from -3.3 to +42.7 to -19.0 to +21.0% for 1000-seed weight and from 19.8-98.1 to 4.6-89.8% for seed yield.

Restricted access

To study the properties of some drought tolerance criteria and  agronomic characters in wheat, an eight-parental diallel cross, excluding reciprocals, was grown in a randomized complete block design with three replications under two different water regimes (irrigated and rainfed) for two years in the College of Agriculture at Razi University, Kermanshah, Iran. High broad-sense heritability estimates were observed for harvest index, grain yield, and earliness. Additive gene action was found to be predominant for grain yield, harvest index, relative water content and chlorophyll fluorescence. The results of combining ability analysis revealed that Plainsman was the best general combiner and Plainsman × Kobomugi was the best specific combination for improving drought tolerance. The pooled analysis of variance for combining ability over rainfed conditions reflected that the GCA × environment interaction was not significant for harvest index and chlorophyll fluorescence, and the SCA × environment interaction was  non-significant for relative water content and relative water loss, indicating that genes controlling osmoregulation and the other physiological traits mentioned are not affected in these varieties by different rainfed conditions and hence show static stability.

Restricted access

This research aimed to study the androgenesis and spontaneous chromosome doubling of five barley genotypes using an isolated in vitro microspore culture technique, involving a completely randomized design (CRD) with three replications. Statistical analysis of embryogenesis and cytogenetic results showed that genotype had a significant effect on haploid embryogenesis (P<0.01) and on spontaneous chromosome doubling (P<0.05). The genotype Igri was found to have the highest potential to produce haploid embryos (1577 embryos from 100 anthers), followed by the genotypes Boyer/Rojo, Afzal/Turkman/Kavir, Ashar/Hebo and Agrigashar/Matico with 369, 304, 278 and 150 embryos from 100 anthers, respectively. The highest percentage of spontaneous chromosome doubling (76%) was observed for the genotype which had the lowest embryogenesis (Agrigashar/Matico) and the lowest (65%) for the genotype with the highest androgenic capacity (Igri). Microspore embryogenesis also showed comparatively higher genotypic (109.2) and phenotypic (109.5) coefficients of variation, heritability (99.62) and genetic advance (1206.77), indicating the pre-dominance of additive gene action in the control of this character in the material studied. Estimates of genetic parameters (PCV, GCV and heritability) for microspore embryogenesis were higher than for spontaneous doubled haploids. These results indicated that selection for androgenic capacity would be more effective than for spontaneous doubled haploids. The findings showed a negative relationship (r= −0.68) between embryogenesis and spontaneous chromosome doubling in the barley genotypes studied. All the large embryos used had high regenerability and good plantlet formation.

Restricted access

Quantitative data were collected and analysed on 10 metric characters from F1s and F2s of sixteen green gram (Vigna radiata L. Wilczek) hybrids, developed from ten genetically diverse parents, to obtain information on variability, heritability, coheritability, and genotypic and phenotypic correlations. The increased genetic variability of F2 over F1 was observed for plant height, number of primary branches, pods/cluster, pods/plant, pod length and harvest index, suggesting the greater segregation and recombination of genes governing these characters. The high broad-sense heritability coupled with high genetic advance for plant height, days to 50% flowering and pod length in both F1s and F2s indicated the predominant role of additive gene action in their expression. The genotypic and phenotypic correlations between F1 and F2 were significant and positive for seven characters. The coheritability estimates between F1 and F2 had values of over 0.25 and were positive for six characters, but not for seed yield/plant, days to 50% flowering, clusters/plant or pods/plant. Within the F1 and F2 generations, seed yield/plant showed significant positive genotypic and phenotypic correlations with eight characters. The seed yield in green gram could be easily enhanced by practising selection on plant height, number of primary branches, pods/cluster, pod length and harvest index.

Restricted access

Twenty-four promising drought tolerant genotypes of IRRI and different parts of India were evaluated for genetic variability and drought susceptibility index (DSI) for 12 quality characters and grain yield under irrigated (E1) and drought (E2) conditions. In the present study differences among the genotypes are highly significant for all the characters; between the environments head rice recovery, alkali spreading value, water uptake, kernel length after cooking and yield were significant, while genotype × environment interaction was only significant for hulling, milling, head rice recovery and water uptake. Head rice recovery, alkali spreading value, water uptake and amylose content were observed to be governed by additive gene action under both the environments. Grain yield was positively correlated with kernel width and amylose content under stress environment while, kernel width was positively correlated with hulling and milling and kernel length was correlated with amylose content. The path coefficient analysis revealed that only kernel width in both the environments and amylose content in E2 had positive direct effect on yield. Most of the genotypes expressed low DSI value (<1) for yield and quality characters. However, Swarna and IR 78877-181-B-1-2 were identified as stable genotypes with low DSI value for seed yield and quality characters.

Restricted access

Loose smut of wheat is a disease of world wide significance. Resistant cultivars constitute a potentially useful and environmentally benign method of controlling this disease. The genetic basis of resistance in 20 wheat genotypes with resistance to Ustilago tritici race T11 was studied in crosses with the widely grown but susceptible Indian cultivar, PBW 343. These lines were also involved in 10 ‘resistant × resistant’ crosses, to infer diversity for resistance genes in this set. All 30 crosses were developed to the F3 stage. Fifteen parents were inferred to carry dominant genes for resistance to race T11. Ten of these resistant lines (ML 521, W 59, W 1616, W 2484, W 2531, W 5915, W 6202, WL 1786, WL 2956 and WL 3450) had resistance controlled by 2 dominant genes acting in a complementary manner whereas in 4 lines (W 4461, W 5100, W 2615 and WL 3951), there was a single dominant gene and in a single genotype, WL 5907, there were 2 dominant genes with duplicate gene action governing the resistance. In lines W 2139, W 3899, W 4985, W 5450 and W 5792 a single recessive gene conferred resistance. Inheritance in two crosses, one derived from a line possessing a single dominant gene and the other from a line possessing a single recessive gene was re-analyzed and successfully confirmed in F5 generation. The segregation of most of the ‘resistant × resistant’ crosses conformed to the inferences drawn about the parents in the ‘resistant × susceptible’ crosses.

Restricted access

To evaluate the genetic background of quantitative criteria of drought tolerance in wheat, six generations of a cross between the varieties of Plainsman and Cappelle Desprez were grown in a randomized complete block design with three replications in the greenhouse of the College of Agriculture of the University of Tehran in 1997. Genetic variation was found for yield potential (Yp), stressed yield (Ys), excised leaf water retention (ELWR), relative water loss (RWL), relative water content (RWC) and harvest index (HI) under water stress conditions. High heterosis and heterobeltiosis were observed in the F1 hybrid for Ys, HI and spike yield index (SYI). Genetic analysis exhibited overdominance in the inheritance of Ys, RWL, ELWR, HI, biomass and SYI, while RWC and Yp were controlled by the additive type of gene action. High narrow-sense heritability estimates were shown by ELWR, biomass and SYI. The high genetic advance for ELWR, RWC, HI and SYI indicated that direct selection could be effective for these traits. The epistatic effects (additive × additive=[i] for Yp, Ys and RWL, additive × dominance=[j] for ELWR, and dominance × dominance =[l] for RWL) were found to be outstanding.

Restricted access

Gene effects were analysed using mean stomatal number and specific leaf weight of 12 populations, consisting of both parents (P 1 and P 2 ), F 1 , F 2 , first backcross generations (BC 1 and BC 2 ), second backcross generations (B 11 , B 12 , B 21 , B 22 ) and backcross selfed generations (B 1 s and B 2 s) of four crosses involving three drought-tolerant and three drought-susceptible cultivars of Triticum aestivum L. to determine the nature of gene action governing stomatal number (SN) and specific leaf weight (SLW) through generation mean analysis in moisture stress (E 1 ) and moisture non-stress (E 2 ) environments. The digenic epistatic model was found to be inadequate for stomatal number and the additive-dominance model was found to be adequate for specific leaf weight in most of the crosses. Additive gene effects were predominant for SLW, while for SN both additive and dominance components of variance were important. Epistatic effects, particularly the additive × dominance (j) type of interaction, were present for both the characters. The duplicate type of epistasis was observed for stomatal number in the cross VL421/HS240 in the moisture stress environment. Significant heterosis was observed for the crosses Hindi 62/HS240 and VL421/HS240 over the standard check (SC) in the moisture stress environment (E 1 ) for both the characters. Genotype-environmental interactions and/or differential gene expression appeared to account for the different results found between environments. Hybridization systems, such as biparental mating and/or diallel selective mating, could be useful for the improvement of these traits, which would help in identifying drought-tolerant progenies.

Restricted access

Combining ability analysis in spring wheat (Triticum aestivum L. em. Thell) involving 10 diverse parents and their 45 F1 and F2 progenies indicated significant differences between the parents for GCA and between the crosses for SCA for all the characters studied. The GCA and SCA components of variance were significant for all the traits. However, the GCA component of variance was predominant, indicating the predominance of additive gene effects for the traits studied. Among the parents HD 2329, Raj 1972, HD 2285 and HD 2428 were the best general combiners for grain yield and average to high combiners for other important traits. The best specific crosses for grain yield were CPAN 3004 × Durgapura 65, Sonalika × HD 2329, Raj 3077 × CPAN 3004, Raj 3077 × HD 2428 and HD 2428 × WH 157.The parent Raj 1972 was the best general combiner for grain yield and protein content, while Raj 3077 and Lok-1 were the best general combiners for protein content. The most suitable specific crosses for protein content were HD 2329 x HD 2285, HD 2428 × Raj 1972 and CPAN 3004 × WH 157. Most of the specific crosses for grain yield and protein content involved high × average, average × average or average × poor general combiners. To ensure a further increase in grain yield along with high protein, combinations of desirable yield components are advocated. The exploitation of additive and non-additive gene actions through bi-parental mating and/or diallel selective mating systems are suggested for a tangible advance in grain yield coupled with high protein in spring wheat.

Restricted access

Gene effects were analyzed using mean excised-leaf water loss and relative water content of 12 populations viz., both parents (P 1 and P 2 ), F 1 , F 2 , first back cross generations (BC1 and BC2), second back cross generations (B 11 , B 12 , B 21 , B 22 ) and back cross-selfed generations (B 1 s and B 2 s) of four crosses involving three drought tolerant and three drought susceptible cultivars of Triticum aestivum L. to determine nature of gene action governing excised-leaf water loss (ELWL) and relative water content (RWC) through generation mean analysis under rainfed (E1) and irrigated (E2) environments. Both additive-dominance and digenic epistatic model were found to be inadequate in all the crosses for ELWL and in most of the crosses for RWC to explain genetic variation among the generation means. Additive gene effects were predominant for RWC, while for ELWL both additive and dominance component of variance were important. Epistatic effects, particularly dominance × dominance (1) type of interaction was more predominant for RWC, while additive × additive(i) for ELWL. Duplicate type of epistasis was observed in the crosses Hindi 62/HS240 and VL421/HS240 for RWC and in the cross S4/HPW89 for ELWL under both the environments. Complementary type of epistasis was observed only in the cross VL421/PBW175 for ELWL under E1. Hybridization systems, such as biparental mating and/or diallel selective mating could be useful for improvement of these traits which would help in isolating drought tolerant progenies.

Restricted access