Inheritance of resistance to wheat yellow rust at adult plant stage

In order to investigate on inheritance and gene action for resistance to yellow rust, the resistant line C.B227 was crossed with the susceptible variety Avocet. Parents (P1 and P2) and the resulting F1, F2 and F3 generations were planted in a randomised complete block design with two replications in the field. The plants were inoculated with 70E0A⁺ pathotype of yellow rust in the research station of Gharakhil, Iran, and evaluated for resistance at adult plant stage. Disease severity and infection type of flag leaf were recorded for each single plant and final coefficient of infection was calculated. The results of weighted ANOVA indicated that the difference among the generations was significant (p?<?0.01) for the trait final infection type. Generation mean analysis showed that dominant effect was more important than additive one. The degree of dominance indicated the presence of complete dominance. Additive, dominance and epistasic additive?×?additive [i] effects were important in genetic control of resistance. The results of generation variance analysis were consistent with generation mean analysis.     

Genetics of adult plant stripe rust resistance in CSP44, a selection from Australian wheat

Wheat line CSP44, a selection from an Australian bread wheat cultivar Condor, has shown resistance to stripe rust in India since the last twenty years. Seedlings and adult plants of CSP44 showed susceptible infection types against stripe rust race 46S119 but displayed average terminal disease severity of 2.67 on adult plants against this race as compared to 70.33 of susceptible Indian cultivar, WL711. This suggests the presence of nonhypersensitive adult plant stripe rust resistance in the line CSP44. The evaluation of F₁, F₂ and F₃ generations and F₆ SSD families from the cross of CSP44 with susceptible wheat cultivar WL711 for stripe rust severity indicated that the resistance in CSP44 is based on two genes showing additive effect. One of these two genes isYr18 and the second gene is not yet described.     

Inheritance of adult field resistance to yellow rust disease among broad-based hexaploid spring wheat germplasm

 Complete F₁ and F₂ diallel crosses were used to investigate the inheritance of yellow rust resistance among eight bread wheat lines, developed by CIMMYT for the East African Highlands, which showed a wide response to this disease. Both diallel sets were grown at a site with a high incidence of yellow rust, although for one season, during which the F₁ diallel was grown, disease incidence was unusually low. Analyses disclosed the presence of additive, dominance and epistatic effects among those genes controlling rust resistance, with the former being the most important. At normal disease levels, excluding two arrays having resistant common parents removed non-allelic interactions from the F₁ diallels. For all F₂ diallels, and the remaining F₁ diallel, omitting two arrays based on susceptible parents removed these interactions. Local selection of material from a broadly based germplasm appears to be a feasible method of developing adapted cultivars resistant to endemic diseases. Received: 1 March 1998 / Accepted: 19 March 1998     

Genetic analysis of Karnal bunt (Neovossia indica) resistance in wheat

Embryos excised from seeds of six generations (P₁, P₂, F₁, BC₁, BC₂ and F₂) of a cross WH 283 x WH 533 were cultured on modified MS medium already inoculated with secondary sporidia ofNeovossia indica. Significant variations for callusing response (CR) (54.55–75.55%) were observed among generations but the presence or absence ofN. indicia did not affect callusing response. A clear inhibition zone (IZ) was formed around each embryo showing callusing. The diameter of IZ varied significantly among generations and was maximum in the resistant genotype, WH 283 (3.60 cm). Fresh weight and dry weight of calli, initiated from embryo cultured and inoculated withN. indica, varied significantly among generations. Coefficient of infection as well as percentage of infection reflected the overdominance of susceptibility. Generation mean analysis showed that the three parameter model was adequate for diameter of IZ only. Six-parameter model showed that additive (in presence ofN. indica), additive and additive x dominance (in absence ofN. indica) effects were also significant. Complementary type of epistasis for fresh weight of calli and dominance, and dominance x dominance effects for dry weight of calli were observed in the presence ofN. indica. Magnitude of additive effects was higher for diameter of IZ in three parameter model. Therefore, selection might assist in improving this trait and thus indirectly help in attaining the resistance towardsN. indica.     

Analysis of a combined F1/F2 diallel cross in wheat

Analysis of a conventional diallel cross offers only perfect-fit estimates of the genetic components of variation, but no test for the goodness of fit of the model based on these estimates. When F₂ progenies are available, however, combining F₁ and F₂ diallels in a single experiment overcomes these problems. Least-squares estimates of these components can be calculated, errors attached to them and the goodness of fit of the resultant model tested. This analysis was applied to data on the severity of yellow rust infection in an F₁/F₂ half-diallel cross among eight bread wheat lines adapted to the East African highlands. After removing two interacting arrays, genetic analysis indicated that an additive/dominance model of gene action satisfactorily explained the variation observed among the remaining six parents and their progenies, in both the individual F₁ and F₂ diallels and the combined F₁/F₂ diallel. Resistance to yellow rust was dominant to susceptibility and genes for increased resistance were more frequent. Received: 25 May 2000 / Accepted: 31 July 2000     

Mutations in wheat showing altered field resistance to yellow and brown rust.

Intensive screening of a small population of mutagenised wheat lines revealed a large number of lines with altered resistance to both yellow and brown rust. The parental cultivar Guardian has an intermediate level of adult plant resistance to this disease; mutants were therefore isolated that showed either enhanced resistance or enhanced susceptibility to yellow rust. Seven lines were identified that gave an altered yellow rust disease phenotype as adult plants under both field and greenhouse conditions. Simultaneous field testing for brown rust infection identified two of these lines as having increased resistance to brown rust.     

Quantitative trait loci for resistance against Yellow rust in two wheat-derived recombinant inbred line populations

Yellow rust, which is a major disease in areas where cool temperatures prevail, can strongly influence grain yield. To control this disease, breeders have extensively used major specific resistance genes. Unfortunately this kind of resistance is rapidly lost due to pathogen adaptation. More-durable resistance against yellow rust can be achieved using quantitative resistance derived from cultivars with well-established durable resistance. The winter wheat Camp Remy has maintained a high level of resistance for over 20 years. In order to map quantitative trait loci (QTLs) for durable yellow rust resistance, we analysed a set of 98 F₈ recombinant inbred (RI) lines derived from the cross Camp Remy×Michigan Amber. We also mapped QTLs for adult resistance to yellow rust using the International Triticae Mapping Initiative RI population (114 lines derived from the cross Opata85×synthetic hexaploid). Two and five QTLs, respectively, were identified from these two populations. This work has highlighted the importance of the centromeric region of chromosome 2B and the telomeric regions of chromosomes 2AL and 7DS in durable yellow rust resistance. The same chromosomal regions are also implicated in resistance to other pathogens. Received: 8 December 2000 / Accepted: 17 April 2001     

Inheritance of components of partial resistance of barley to Rhynchosporium secalis with particular reference to race specificity

Six spring barley cultivars with no known genes for resistance to specific virulences but varying in partial resistance to Rhynchosporium secalis, were crossed in all combinations (6 × 6 diallel including reciprocals). In addition to seeds from naturally selfed plants, seeds of all parent cultivars were also produced by artificial selfing (emasculation followed by pollination using pollen from the same cultivar). This ensured comparability between seeds of parents and F₁. Both sets of parents, F₁ and F₂ families were grown in the field as single spaced plants and inoculated at Zadoks growth stage 49 with spore suspensions (2 × 10⁶ spores ml^-1) of three races (pathotypes) of R. secalis (Zadoks, Chang & Konzak, 1974). Components of partial resistance, incubation period (ICP), infection frequency (IF) and spore production per lesion (SP/L) were assessed on each plant. There were highly significant differences for all three components of partial resistance in both sets of parent cultivars but rank order in both sets was similar as evidenced by correlation coefficients, r= 0.96 for ICP and IF and r= 0.87 for SP/L. All three components of partial resistance were strongly correlated with NIAB (National Institute of Agricultural Botany, Cambridge, UK) resistance ratings. Means of F₁ and F₂ families were correlated with mid-parent values for ICP and IF but not SP/L. No difference in aggressiveness was found between races but for each component of partial resistance there was a significant interaction between race and parent cultivar (artificial selfs) and, for IF and ICP, a significant interaction between race and F₁ family. There was no evidence of interaction between parent (natural selfs) and race nor between race and F₂ family. Examination of genetic control of resistance showed evidence of strong additive effects (combining ability) in both F₁ and F₂ for ICP and IF but not for SP/L. There was no evidence for maternal or reciprocal differences, but there was evidence for dominance effects although their nature differed between components of partial resistance and between F₁ and F₂ generations. In the F₁, but not the F₂ generation, several elements of dominance (direction, distribution of dominant genes between parent cultivars, specific combining ability) showed for ICP or IF (but not SP/L) significant interaction with race.     

Heritable,De Novo Resistance to Leaf Rust and Other Novel Traits in Selfed Descendants of Wheat Responding to Inoculation with Wheat Streak Mosaic Virus

Stable resistance to infection with Wheat streak mosaic virus (WSMV) can be evolved de novo in selfing bread wheat lines subjected to cycles of WSMV inoculation and selection of best-performing plants or tillers. To learn whether this phenomenon might be applied to evolve resistance de novo to pathogens unrelated to WSMV, we examined the responses to leaf rust of succeeding generations of the rust- and WSMV-susceptible cultivar ‘Lakin’ following WSMV inoculation and derived rust-resistant sublines. After three cycles of the iterative protocol five plants, in contrast to all others, expressed resistance to leaf and stripe rust. A subset of descendant sublines of one of these, ‘R1’, heritably and uniformly expressed the new trait of resistance to leaf rust. Such sublines, into which no genes from a known source of resistance had been introgressed, conferred resistance to progeny of crosses with susceptible parents. The F₁ populations produced from crosses between, respectively, susceptible and resistant ‘Lakin’ sublines 4-3-3 and 4-12-3 were not all uniform in their response to seedling inoculation with race TDBG. In seedling tests against TDBG and MKPS races the F₂s from F₁ populations that were uniformly resistant had 3∶1 ratios of resistant to susceptible individuals but the F₂s from susceptible F₁ progenitors were uniformly susceptible. True-breeding lines derived from resistant individuals in F₂ populations were resistant to natural stripe and leaf rust inoculum in the field, while the ‘Lakin’ progenitor was susceptible. The next generation of six of the ‘Lakin’-derived lines exhibited moderate to strong de novo resistance to stem rust races TPMK, QFCS and RKQQ in seedling tests while the ‘Lakin’ progenitor was susceptible. These apparently epigenetic effects in response to virus infection may help researchers fashion a new tool that expands the range of genetic resources already available in adapted germplasm.     

Nature and type of gene action governing resistance to Helminthosporium turcicum leaf blight in maize (Zea mays L.)

Six generations, consisting of three resistant parents, three susceptible parents, their 15 possible F₁ crosses, 15 F₂'s, 15 BC₁'s (F₁ x resistant female parent) and 15 BC₂'s (F₁ x susceptible male parent) were analysed following Hayman (Heredity 12: 371–390, 1958) to evaluate the nature and type of gene action governing resistance to H. turcicum. The results showed that all types of gene effects, viz., additive, dominance and epistasis (i.e., additive x additive, additive x dominance and dominance x dominance) were operating in one cross or the other in controlling resistance. However, it was additive gene action and dominance x dominance type of epistasis with duplicate nature that were important in controlling resistance in most crosses. Depending upon the final objectives, one of the breeding methods, viz., recurrent selection, heterosis breeding, back-cross method or full-sib selection (bi-parental mating) may be followed.     

Comparison of methods for calculating the heritability of adult field resistance to yellow rust and grain yield in spring wheat

Several methods are available for estimating heritability in disomic species, including parent-offspring regression, realized heritability, intraclass correlations of recombinant inbred lines, and diallel-cross analysis. Estimates were obtained by these various methods for a set of eight bread wheat (Triticum aestivum) lines adapted to the East African highlands, which had been intercrossed and selfed in a half-diallel arrangement to give F₁, F₂ and F₃ generations, and F₆ recombinant inbred lines. Significant genetic variation existed among parents and crosses for both grain yield and yellow rust resistance in all generations. Based on the heritability calculated from the analysis of F₆ recombinant inbred lines, analysis of the F₂ diallel crosses was recommended for determining the heritability of both characters in early segregating generations. The results also suggest that a form of tandem selection may be effective in developing locally adapted germplasm which combines high grain yield with yellow rust resistance. Received: 15 February 1999 / Accepted: 11 March 1999     

Genetic Analysis of the Latent Period of Stripe Rust in Wheat Seedlings

Genetics of slow‐rusting resistance to yellow rust (Puccinia striiformis f.sp. tritici) was studied by a half‐diallel design using six wheat varieties, Tiritea (susceptible), Tancred, Kotare, Otane, Karamu, and Briscard. The parents and 15 F₁ progenies were evaluated in the greenhouse by three pathotypes 7E18A^?, 38E0A⁺, and 134E134A⁺. The latent period was measured as the number of days from inoculation to the appearance of the first pustule. For each pathotype a randomized complete block design was used and data were analysed by methods of Griffing and Hayman. The range of average degree of dominance was from complete dominance to over‐dominance. Positive and negative degrees of dominance were observed for each pathotype that showed the reversal of dominance. Analysis of variance showed the importance of both additive and dominance effects in controlling the latent period. Broad‐sense heritabilities were 0.99 and narrow‐sense heritabilities ranged from 0.85 to 0.94. Briscard and Karamu for the pathotypes 38E0A⁺ and 134E134A⁺, Kotare for the pathotype 7E18A^? and Tancred for the pathotype 38E0A⁺ had significant and positive general combining ability (GCA) (more resistance) for latent period. The crosses of Kotare with Tancred, Briscard and Karamu indicated the highest and positive specific combining ability (SCA) for the pathotype 7E18A^?. Significant additive genetic component and moderate narrow‐sense heritability indicate the possibility of improving for longer latent period of stripe rust in breeding programmes.     

Undescribed wheat gene for partial leaf rust and stripe rust resistance from Thatcher derivatives RL6058 and 90RN249 carryingLr34

Inheritance of partial leaf rust and stripe rust resistance of a Thatcher wheat 90RN2491, earlier reported to carry two doses of the gene pairLr34-Yr18 and the reference line RL6058 (6*Thatcher/PI58548) for theLr34-Yr18 gene pair was studied against predominant and highly virulent Indian races. Thatcher derivatives 90RN2491 and RL6058 were intercrossed as well as crossed with the leaf rust and stripe rust susceptible Indian cultivar WL711. The F₁, F₂ and F₃ generations from these crosses were assessed for rust severity against leaf rust race 77-5 and stripe rust race 46S119. The F₂ and F₃ generations from the crosses of RL6058 and 90RN2491 with WL711, segregated 15 resistant : 1 susceptible (F₂) and 7 homozygous resistant : 8 segregating : 1 homozygous susceptible (F₃) ratios, respectively, both for leaf rust and stripe rust severity. Therefore, partial resistance against each of the leaf rust and stripe rust races in both RL6058 and 90RN2491 is ascribed to two independently inherited dominant genes. One of the two genes for leaf rust and stripe rust resistance in 90RN2491 and RL6058 isLr34 and the linked geneYr18, respectively. The second leaf rust resistance gene in both the Thatcher lines segregated independently of stripe rust resistance. Therefore, it is notLr34 and it remains unidentified.     

Studies on inheritance of resistance and allelic relationships for strain 2 of pigeonpea sterility mosaic pathogen

Inheritance of resistance and allelic relationships were studied in three resistant pigeonpea sources for strain 2 of sterility mosaic pathogen. The resistant genotypes (ICP 7035, ICP 7349 and ICP 8850) were crossed with susceptible genotypes (BDN1 and LRG30) to determine the inheritance of resistance. The resistant and susceptible genotypes were also crossed among themselves to obtain information on their allelic relationships. Parents, F₁ and F₂ generations were sown in pots and screened using infector-hedge technique. Observations in parents, F₁ and F₂ generations, indicated dominance of resistance in certain crosses and the dominance of susceptibility in others. Disease reaction appeared to be governed by two independent non-allelic genes, with at least three multiple alleles, at one of the loci.     

Number of genes controlling slow rusting resistance to leaf rust in five spring wheat cultivars

The number of genes controlling slow rusting resistance to leaf rust (Puccinia triticina) was estimated in five spring wheat (Triticum aestivum) cultivars using quantitative formulae. Parents and F₆ families were evaluated in replicated field trials under epidemics initiated by artificial inoculation. The F₆ families resulted from a diallel cross involving the fast-rusting cultivar Yecora 70 and five slow-rusting wheat cultivars: Sonoita 81, Tanager ‘S’, Galvez 87, Ures 81, and Moncho ‘S’. The area under the disease progress curve (AUDPC) was used to measure leaf rust severity over time. Results indicate that cultivar Sonoita 81 has three or four genes, Tanager ‘S’ has two or three genes, Galvez 87 has three genes, and both Ures 81 and Moncho ‘S’ have two genes for slow rusting resistance to leaf rust. Based on this result and previously reported moderate to high narrow-sense heritability estimates for slow rusting resistance in these materials, early-generation selection for slow leaf rusting would be effective.     

Identification of QTL for live weight and growth rate using DNA markers on chromosome 3 in an F2 population of Japanese quail

The Japanese quail (Coturnix japonica) is an important agricultural species and is an animal model for genetic researches. This study was conducted to identify quantitative trait loci (QTL) affecting live weight and growth rate on chromosome 3 in quail. Two strains of Japanese quail including wild and white were crossed reciprocally and F₁ generation was created. The birds from F₂ generation were measured for growth traits and all of 472 birds (8 pairs from the parental strains, 34 F₁ birds and 422 F₂ birds) were genotyped for microsatellite markers on chromosome 3. The results indicated chromosome wide significant QTL for hatching weight (P < 0.01) and weight at 1, 2, 3 and 4 weeks of age, average daily gain from hatch to 1, 1–2 and 3–4 weeks of age and Kleiber ratio (P < 0.05), an indirect criterion of feed efficiency. The highest QTL additive and imprinting effects (2.72 and 0.79 % of the trait variation in the F₂ population, respectively) were related to hatching weight. The identified QTL for this trait (at 7 cM relative to the centromeric region of the chromosome) had significant interaction with sex and hatch (P < 0.01). The dominance effect of QTL was significant (P < 0.05) for bodyweight at one week of age accounting for 1.69 % of the trait variation in the F₂ population.     

Quantitative resistance of some Elite wheat lines to Puccinia striiformis f. sp. tritici

Host resistance is the most economical way to manage wheat stripe rust caused by Puccinia striiformis f. sp. tritici. Slow rusting, a type of quantitative resistance, has been reported to last for a long time. Quantitative resistance, in terms of slow rusting parameters including final rust severity (FRS), apparent infection rate (r), relative area under disease progress curve (rAUDPC) and coefficient of infection (CI), was evaluated in a set of 29 wheat genotypes along with susceptible control during 2008–2009 and 2009–2010 cropping seasons. This study was conducted in field plots at Ardabil Agricultural Research Station (Iran) under natural infection conditions with two times artificial inoculation. Artificial inoculation was carried out by yellow rust inoculum having virulent genes against Yr2, Yr6, Yr7, Yr9, Yr22, Yr23, Yr24, Yr25, Yr26, Yr27, YrA and YrSU. Results of mean comparison for resistance parameters showed that lines C-86-1, C-86-2, C-87-1 and C-87-3 along with susceptible had the highest values of FRS, CI, r and rAUDPC, therefore were selected as susceptible lines. The lines C-86-3, C-86-9, C-87-2, C-87-6, C-87-8, C-87-11 and C-87-18 were susceptible at the seedling stage and had low level infection at adult plant stage. Consequently, these lines with low different parameters most probably have slow rusting resistance. The remaining lines had no infection or were at low level of infection. Thus, they were selected as resistant or moderately resistant lines. In this study, correlation coefficient between different parameters of slow rusting was significantly high (r = 0.92–0.99).     

Genetics of durable resistance to leaf rust and stripe rust of an Indian wheat cultivar HD2009

The Indian bread wheat cultivar HD2009 has maintained its partial resistance to leaf rust and stripe rust in India since its release in 1976. To examine the nature, number and mode of inheritance of its genes for partial leaf rust and stripe rust resistance, this cultivar was crossed with cultivar WL711, which is susceptible to leaf rust and stripe rust. The F1, F2, F3 and F5 generations from this cross were assessed separately for adult plant disease severity under artificial epidemic of race 77-5 of leaf rust and race 46S119 of stripe rust. Segregation for rust reaction in the F2, F3 and F5 generations indicated that resistance to each of these rust diseases is based on 2 genes, each with additive effects. Although the leaf rust resistance of HD2009 is similar in expression to that conferred by the gene Lr34, but unlike the wheats carrying this gene, cultivar HD2009 did not show leaf tip necrosis, a morphological marker believed to be tightly linked to the leaf rust resistance gene Lr34. Thus, the non-hypersensitive resistance of HD2009 was ascribed to genes other than Lr34.     

Breeding Potential of Introgression Lines Developed from Interspecific Crossing between Upland Cotton (Gossypium hirsutum) and Gossypium barbadense: Heterosis,Combining Ability and Genetic Effects

Upland cotton (Gossypium hirstum L.), which produces more than 95% of the world natural cotton fibers, has a narrow genetic base which hinders progress in cotton breeding. Introducing germplasm from exotic sources especially from another cultivated tetraploid G. barbadense L. can broaden the genetic base of Upland cotton. However, the breeding potential of introgression lines (ILs) in Upland cotton with G. barbadense germplasm integration has not been well addressed. This study involved six ILs developed from an interspecific crossing and backcrossing between Upland cotton and G. barbadense and represented one of the first studies to investigate breeding potentials of a set of ILs using a full diallel analysis. High mid-parent heterosis was detected in several hybrids between ILs and a commercial cultivar, which also out-yielded the high-yielding cultivar parent in F₁, F₂ and F₃ generations. A further analysis indicated that general ability (GCA) variance was predominant for all the traits, while specific combining ability (SCA) variance was either non-existent or much lower than GCA. The estimated GCA effects and predicted additive effects for parents in each trait were positively correlated (at P<0.01). Furthermore, GCA and additive effects for each trait were also positively correlated among generations (at P<0.05), suggesting that F₂ and F₃ generations can be used as a proxy to F₁ in analyzing combining abilities and estimating genetic parameters. In addition, differences between reciprocal crosses in F₁ and F₂ were not significant for yield, yield components and fiber quality traits. But maternal effects appeared to be present for seed oil and protein contents in F₃. This study identified introgression lines as good general combiners for yield and fiber quality improvement and hybrids with high heterotic vigor in yield, and therefore provided useful information for further utilization of introgression lines in cotton breeding.     

Mode of Inheritance of Amitraz Resistance in a Brazilian Strain of the Southern Cattle Tick, Boophilus microplus (Acari: Ixodidae)*

The southern cattle tick, Boophilus  microplus (Canestrini), has developed resistance to amitraz in several countries in recent years. A study was conducted at the USDA Cattle Fever Tick Research Laboratory in Texas to investigate the mode of inheritance of amitraz resistance with cross-mating experiments. The Muñoz strain, a laboratory reared acaricide-susceptible reference strain, was used as the susceptible parent and the Santa Luiza strain, originating in Brazil, was used as the resistant parent. A modified Food and Agriculture Organization Larval Packet Test was used to measure the levels of susceptibility of larvae of the parental strains, F₁, backcross, F₂, and F₃ generations. Results of reciprocal crossing experiments suggested that amitraz resistance was inherited as an incomplete recessive trait. There was a strong maternal effect on larval progeny’s susceptibility to amitraz in both the F₁ and the subsequent generations. The values of the degree of dominance were estimated at ?0.156 and ?0.500 for the F₁ larvae with resistant and susceptible female parents, respectively. Results of bioassays on larval progeny of the F₁ backcrossed with the resistant parent strain and that of the F₂ generations suggested that more than one gene was responsible for amitraz resistance in the Santa Luiza strain. Comparisons of biological parameters (engorged female weight, egg mass weight, and female-to-egg weight conversion efficiency index) indicated significant differences between different genotypes. The differences appeared to be heritable, but not related to amitraz resistance. Results from this study may have significant implications for the management of amitraz resistance.