Authors:Q. Mo, C.Y. Wang, C.H. Chen, Y.J. Wang, H. Zhang, X.L. Liu, and W.Q. Ji
Thinopyrum ponticum (2n = 10x = 70) has donated rust resistance genes to protect wheat from this fungal disease. In the present study, the line ES-7, derived from the progeny of the crosses between common wheat cultivar Abbondanza and Triticum aestivum–Th. ponticum partial amphiploid line Xiaoyan784, was characterized by cytological, fluorescence in situ hybridization (FISH), genomic in situ hybridization (GISH) and EST-STS marker techniques. Cytological observations revealed that the configuration of ES-7 was 2n = 42 = 21 II. GISH and FISH results showed that ES-7 had two St chromosomes and lacked 5A chromosomes compared to common wheat. The 4A chromosome of ES-7 had small alterations from common wheat. Two EST-SSR markers BE482522 and BG262826, specific to Th. ponticum and tetraploid Pseudoroegneria spicata (2n = 4x = 28), locate on the homoeologous group 5 chromosomes of wheat, could amplify polymorphic bands in ES-7. It was suggested that the introduced St chromosomes belonged to homoeologous group 5, that is, ES-7 was a 5St (5A) disomic substitution line. Furthermore, ES-7 showed highly resistance to mixed stripe rust races of CYR32 and CYR33 in adult stages, which was possibly inherited from Th. ponticum. Thus, ES-7 can be used for wheat stripe rust resistance breeding program.
Authors:S. Figlan, T.A. Baloyi, T. Hlongoane, T.G. Terefe, H. Shimelis, and T.J. Tsilo
Phenotypic and genotypic evaluation of wheat genetic resources and development of segregating populations are pre-requisites for identifying rust resistance genes. The objectives of this study were to assess adult plant resistance (APR) of selected wheat genotypes to leaf rust and stem rust and to develop segregating populations for resistance breeding. Eight selected Kenyan cultivars with known resistance to stem rust, together with local checks were evaluated for leaf rust and stem rust resistance at seedling stage and also across several environments. Selected diagnostic markers were used to determine the presence of known genes. All eight cultivars were crossed with local checks using a bi-parental mating design. Seedling tests revealed that parents exhibited differential infection types against wheat rust races. Cultivars Paka and Popo consistently showed resistant infection types at seedling stage, while Gem, Romany, Pasa, Fahari, Kudu, Ngiri and Kariega varied for resistant and susceptible infection types depending on the pathogen race used. The control cultivars Morocco and McNair consistently showed susceptible infection types as expected. In the field, all cultivars except for Morocco showed moderate to high levels of resistance, indicating the presence of effective resistance genes. Using diagnostic markers, presence of Lr34 was confirmed in Gem, Fahari, Kudu, Ngiri and Kariega, while Sr2 was present in Gem, Romany, Paka and Kudu. Seedling resistance gene, Sr35, was only detected in cultivar Popo. Overall, the study developed 909 F6:8 recombinant inbred lines (RILs) as part of the nested mating design and are useful genetic resources for further studies and for mapping wheat rust resistance genes.
One important aim of hybrid breeding is to exploit the heterosis effect appearing in the F1. Nevertheless, the breeders of commercial F1 hybrids have no real information on the extent of heterosis manifested in the combinations they produce, since the mean value of the combination in question is never compared with that of the parents or of the better parent, but only with that of the most popular control variety it is hoped to surpass. The complex variety value of a new hybrid should be greater than that of the control. In the case of pepper hybrids the factors that make up the complex variety value can be divided into four groups: the early and total yield potential predicted from the individual value of the parents (P), special consumption and production traits resulting in F1 quality (Q), F1 resistance value (R) and the heterosis effect (H). The importance of these four factors in the complex variety value of a given pepper hybrid may be summed in innumerable variations, but the individual yield potential and quality traits of the parents are of outstanding importance. This is the basis, without which combining ability, resistance value and heterosis effect will remain unexploited. When selecting pepper lines for combining ability, risks may be involved in over-strict selection for general combining ability alone, so a combined crossing system involving a carefully constructed partial diallel is normally employed to obtain information on the general combining ability of lines preliminarily screened for individual plant performance and on the specific combining ability of their combinations. Cross-breeding aimed at the development of parental lines and constant varieties makes use of single crosses, crossing series, backcrossing and resistance breeding.
Authors:S.M. Pirseyedi, A. Kumar, F. Ghavami, J.B. Hegstad, M. Mergoum, M. Mazaheri, S.F. Kianian, and E.M. Elias
Fusarium head blight (FHB) damage in durum wheat (Triticum turgidum L. var. durum Desf., turgidum) inflicted massive economic losses worldwide. Meanwhile, FHB resistant durum wheat germplasm is extremely limited. ‘Tunisian108’ is a newly identified tetraploid wheat with FHB resistance. However, genomic regions in ‘Tunisian108’ that significantly associated with FHB resistance are yet unclear. Therefore, a population of 171 backcross inbred lines (BC1F7) derived from a cross between ‘Tunisian108’ and a susceptible durum cultivar ‘Ben’ was characterized. Fusarium graminearum (R010, R1267, and R1322) was point inoculated (greenhouse) or spawn inoculated (field) in 2010 and 2011. Disease severity, Fusarium-damaged kernel (FDK) and mycotoxins were measured. Analysis of variance showed significant genotype and genotype by environment effect on all traits. Approximately 8% of the lines in field and 25% of the lines in greenhouse were more resistance than Tunisian108. A framework linkage map of 267 DArt plus 62 SSR markers was developed representing 239 unique loci and covering a total distance of 1887.6 cM. Composite interval mapping revealed nine QTL for FHB severity, four QTL for DON, and four QTL for FDK on seven chromosomes. Two novel QTL, Qfhb.ndsu-3BL and Qfhb.ndsu-2B, were identified for disease severity, explaining 11 and 6% of the phenotypic variation, respectively. Also, a QTL with large effect on severity and a QTL with negative effect on FDK on chromosome 5A were identified. Importantly, a novel region on chromosome 2B was identified with multiple FHB resistance. Validation on these QTL would facilitate the durum wheat resistance breeding.
Authors:B. Kumar, K.S. Hooda, R. Gogoi, V. Kumar, S. Kumar, A. Abhishek, P. Bhati, J.C. Sekhar, K.R. Yathish, V. Singh, A. Das, G. Mukri, E. Varghese, H. Kaur, V. Malik, and O.P. Yadav
Maydis leaf blight (MLB), a serious foliar fungal disease of maize, may cause up to 40% losses in yield. The present studies were undertaken to identify the stable sources of MLB resistance, its inheritance study, and testing of MLB resistance linked markers from diverse background in the Indian adapted tropical maize genotypes. A set of 112 inbred lines were screened under artificially created epiphytotics conditions at three hotspot locations. Analysis across multi-locations revealed significant effects of genotypes and environments, and non-significant effects due to genotypes × environment interaction on disease incidence. A total of 25 inbred lines with stable resistance were identified across multi-locations. Inheritance of resistance was studied in six F1s and two F2s of resistant and susceptible parents. The null hypothesis of segregation of resistance and susceptible for mono and digenic ratios in two F2 populations was rejected by Chi-square test. The non-significant differences among the reciprocal crosses depicted the complete control of nuclear genome for MLB resistance. Partial dominance in F1s and normal distribution pattern in F2s of resistant and susceptible parents suggested polygenic nature of MLB resistance. Correlation studies in F2 populations exhibited significant negative correlation between disease score and days to flowering. Five simple sequence repeats (SSRs) markers, found associated to MLB resistance in different studies were unable to differentiate amongst MLB resistance and susceptible parents in our study. This emphasizes the need of fine mapping for MLB resistance in Indian germplasm. The identified stable sources of resistance and information on inheritance study can be used further in strengthening of resistance breeding against MLB.
Large numbers of genetically stable, homozygous plants are needed for classical and molecular breeding programmes. In vitro anther culture has proved to be a useful tool for haploid/doubled haploid (DH) induction in pepper (Capsicum annuum L.) for more than twenty years. The present paper reports on a great improvement in the in vitro haploid induction and genome duplication methods routinely used for resistance breeding in sweet and spice peppers by two Hungarian research institutions, the Agricultural Biotechnology Center in Gödöllő and the Budapest Research Unit of the Vegetable Crops Research Institute. As a result of the colchicine-stimulated early genome induction method, the critically low (<0.1%) regeneration frequency of spice pepper types became ten times greater, reaching a value of around 1.0%, though this was still considerably lower than that achieved in pepper varieties for fresh consumption (5-10%). Moreover, the ratio of useful doubled haploids was far higher (H:DH = 1:2 or 1:4) in some cases after colchicine treatment than that of untreated control plants (H:DH = 2:1 or 3:1, depending on the genotype). An efficient method with good reproducibility, requiring less manual work, was elaborated for the in vitro genome duplication of pepper haploid regenerants using colchicine. When the haploid induction ability of plants conventionally cultured in the greenhouse was compared to that of plants raised under artificial conditions in phytotron chambers (satisfactory day and night temperatures, illumination, humidity), the responsiveness of the latter microspores (ratio of plant regeneration) was found to be almost twice as high. The application of 3% maltose for six days at 35°C resulted in a 1.45% increase in the ratio of responding anthers and a 0.34% increase in plant regeneration, averaged over all the variety types. Phenosafranin staining was used for the analysis of microspore viability. The reduction in viability during the induction period proved to be less pronounced in lines with better androgenetic responses than in those with poorer responsiveness.
Authors:C.C. Dweba, H. Shimelis, T. Tapera, and T.J. Tsilo
Fusarium head blight (FHB) is an important disease of wheat causing significant yield and quality losses globally. Breeding for host plant resistance is an economic approach to FHB control and management. The aim of this study was to identify potential sources of resistance from newly developed recombinant inbred lines (RILs) of wheat. A total of 778 RILs were developed through a bi-parental mating design followed by continuous selfing and selection. The RILs along with their eight parental lines (Baviaans, Buffels, Duzi, #910, #936, #937, #942 and #1036) and FHB resistant check cultivar ‘Sumai 3’ and susceptible check ‘SST 806’ were field evaluated across four environments in South Africa. Fusarium graminearum isolates were artificially inoculated to initiate infection and disease development. The percentage of wheat spikes showing FHB symptoms were scored. The research identified six percent of the RILs with disease resistance. Heritability for FHB resistance was the highest (64%) indicating the possibility of achieving higher selection gains for FHB resistance across the selected environments. The following five RILs were identified as potential sources of resistance: 681 (Buffels/1036-71), 134 (Duzi/910-8), 22 (Baviaans/910-22), 717 (Baviaans/937-8) and 133 (Duzi/910-7) with mean FHB scores of 6.8%, 7.8%, 9.5%, 9.8% and 10%, respectively. The selected lines expressed comparatively similar levels of resistance compared with that of Sumai 3. The identified RILs are useful genetic resources for resistance breeding against FHB disease of wheat. Since the presence of the F. graminearum is associated with deoxynivalenol (DON) accumulation, the DON levels amongst the selected lines should be determined to ensure the release of improved wheat cultivars with reduced levels of DON accumulation.