Pyramiding of Meloidogyne hapla resistance genes in potato does not result in an increase of resistance

High levels of resistance against Meloidogyne hapla have been identified in wild species of tuber-bearing potatoes, but only QTL with partial effects have been identified so far in back crosses with cultivated potato. This study was designed to test if pyramiding of two previously identified resistance genes, R Mh-tar and R Mh-chc A, will result in improved or even an absolute level of resistance. R Mh-tar and R Mh-chc A introgressed from the wild tuber-bearing potato species Solanum tarijense and Solanum chacoense were combined in a segregating diploid Solanum tuberosum population. With the aid of AFLP markers, descendants from this segregating population were classified into four groups, carrying no R gene, with only R Mh-tar , with only R Mh-chc A and a group with the pyramided R Mh-tar and R Mh-chc A. Upon inoculation with M. hapla isolate Bovensmilde, the group containing only R Mh-chc A showed a decline of 88% in average number of developed egg masses compared to the group without R Mh-chc A and R Mh-tar . The group of genotypes containing only R Mh-tar , but not R Mh-chc A, showed a decline of 55% in the number of developed egg masses compared to the group without R Mh-chc A and R Mh-tar . Unfortunately, the latter effect of R Mh-tar was not significant. The effect of both loci, R Mh-tar and R Mh-chc A combined, did not further reduce the number of egg masses compared to the level of R Mh-chc A alon

Resistance Breeding in Apple at Dresden-Pillnitz

Resistance breeding in apple has a long tradition at the Institute of Fruit Breeding now Julius Kuehn-institute in Dresden-Pillnitz. The breeding was aimed at the production of multiple resistance cultivars to allow a more sustainable and environmentally friendly production of apple. In the last decades a series of resistant cultivars (Re®-cultivars) bred in Dresden-Pillnitz has been released, ‘Recolor’ and ‘Rekarda’ in 2006. The main topic in the resistance breeding programme was scab resistance and the donor of scab resistance in most cultivars was Malus x floribunda 821. Due to the development of strains that are able to overcome resistance genes inherited by M. x floribunda 821 and due to the fact that single resistance genes can be broken easily, pyramiding of resistance genes is necessary. Besides scab, fire blight and powdery mildew are the main disease for which a pyramiding of genes is aspired in Pillnitz. Biotechnical approaches are necessary for the early detection of pyramided resistance genes in breeding clones. This paper will give an overview of the resistance breeding of apple in Pillnitz and the methods used

Pyramiding of Ryd2 and Ryd3 conferring tolerance to a German isolate of Barley yellow dwarf virus-PAV (BYDV-PAV-ASL-1) leads to quantitative resistance against this isolate

Barley yellow dwarf virus (BYDV) is an economically important pathogen of barley, which may become even more important due to global warming. In barley, several loci conferring tolerance to BYDV-PAV-ASL-1 are known, e.g. Ryd2, Ryd3 and a quantitative trait locus (QTL) on chromosome 2H. The aim of the present study was to get information whether the level of tolerance against this isolate of BYDV in barley can be improved by combining these loci. Therefore, a winter and a spring barley population of doubled haploid (DH) lines were genotyped by molecular markers for the presence of the susceptibility or the resistance encoding allele at respective loci (Ryd2, Ryd3, QTL on chromosome 2H) and were tested for their level of BYDV-tolerance after inoculation with viruliferous (BYDV-PAV-ASL-1) aphids in field trials. In DH-lines carrying the combination Ryd2 and Ryd3, a significant reduction of the virus titre was detected as compared to lines carrying only one of these genes. Furthermore, spring barley DH-lines with this allele combination also showed a significantly higher relative grain yield as compared to lines carrying only Ryd2 or Ryd3. The QTL on chromosome 2H had only a small effect on the level of tolerance in those lines carrying only Ryd2, or Ryd3 or a combination of both, but the effect in comparison to lines carrying no tolerance allele was significant. Overall, these results show that the combination of Ryd2 and Ryd3 leads to quantitative resistance against BYDV-PAV instead of tolerance

Specific Resistance Genes in Wheat Chinese Landrace ‘Wangshuibai’ against Two Iranian Mycosphaerella Graminicola Isolates

Abstract Septoria tritici blotch, caused by the fungus Mycosphaerella graminicola, is currently the major foliar disease of wheat world-wide, and new sources of resistance and knowledge about the genetics of resistance are needed to improve breeding for resistance against this disease. An F10 recombinant inbred population from a cross between ‘Wangshuibai’ (Chinese landrace) and the susceptible cultivar ‘Seri82’ was tested at seedling stage under controlled greenhouse conditions. Two isolate-specific genes for resistance to Iranian M.graminicola isolates IPO08002 and IPO08003 were detected on Chromosomes 2BL and 7DS, respectively. For both genes the resistance was derived from ‘Wangshuibai’ at positions where Stb9 (on 2BL) and Stb4 (on 7DS) have been reported previously. These two genes are closely linked to microsatellite markers, which can be used for marker-assisted selection. ‘Wangshuibai’ may therefore be a valuable source of resistance to STB for wheat breeding, especially in Mediterranean environments

Identification and mapping of the novel apple scab resistance gene Vd3

Apple scab, caused by the fungal pathogen Venturia inaequalis, is one of the most devastating diseases for the apple growing in temperate zones with humid springs and summers. Breeding programs around the world have been able to identify several sources of resistance, the Vf from Malus floribunda 821 being the most frequently used. The appearance of two new races of V. inaequalis (races 6 and 7) in several European countries that are able to overcome the resistance of the Vf gene put in evidence the necessity of the combination of different resistance genes in the same genotype (pyramiding). Here, we report the identification and mapping of a new apple scab resistance gene (Vd3) from the resistant selection “1980-015-25” of the apple breeding program at Plant Research International, The Netherlands. This selection contains also the Vf gene and the novel V25 gene for apple scab resistance. We mapped Vd3 on linkage group 1, 1 cM to the south of Vf in repulsion phase to it. Based on pedigree analysis and resistance tests, it could be deduced that 1980-015-25 had inherited Vd3 from the founder “D3.” This gene provides resistance to the highly virulent EU-NL-24 strain of race 7 of V. inaequalis capable of overcoming the resistance from Vf and Vg

Identification and mapping of quantitative resistance to late blight (Phytophthora infestans) in Solanum habrochaites LA1777

Late blight (Phytophthora infestans) can have devastating effects on tomato production over the whole world. Most of the commercial cultivars of tomato, Solanum lycopersicum, are susceptible. Qualitative and quantitative resistance has been described in wild relatives of tomato. In general qualitative resistance can more easily be overcome by newly evolved isolates. Screening of three S. habrochaites accessions (LA1033, LA2099 and LA1777) through a whole plant assay showed that accession LA1777 had a good level of resistance to several isolates of P. infestans. To explore the potential in this wild species, an introgression line (IL) population of S. habrochaites LA1777 was used to screen individual chromosome regions of the wild species by a detached leaf assay. Two major isolates (T1,2 and T1,2,4) were used and two parameters were measured: lesion size (LS), and disease incidence (DI). Substantial variation was observed between the individual lines. QTLs were identified for LS but not for DI. The presence of five QTLs derived from LA1777 (Rlbq4a, Rlbq4b, Rlbq7, Rlbq8 and Rlbq12) results in unambiguous higher levels of resistance. All QTLs co-localized with previously described QTLs from S. habrochaites LA2099 except QTL Rlbq4b, which is therefore a novel QT

Wheat rusts never sleep but neither do sequencers: will pathogenomics transform the way plant diseases are managed?

Field pathogenomics adds highly informative data to surveillance surveys by enabling rapid evaluation of pathogen variability, population structure and host genotype

Economic Impact Analysis of Marker-Assisted Breeding in Rice

The benefits of developing and releasing salinity-tolerant and phosphorous-deficiency-tolerant rice in Bangladesh, India, Indonesia and the Philippines were estimated for marker-assisted breeding as compared to conventional breeding using economic surplus analysis. Marker-assisted breeding is estimated to save at least 2 to 3 years in the breeding cycle and result in incremental benefits over 25 years in the range of $300 to$800 million depending on the country, stress, and time lags. Salinity and phosphorous deficient soils are difficult problems to solve through conventional breeding because of “genetic load” or undesirable traits that accompany desirable ones during backcrossing. MAB, enabled by advances in genomics and molecular mapping is more precise and hence time-saving. Solving salinity and P-deficiency problems is important, regardless of whether MAB or CB is used, as the cumulative benefits are at least $220 million and as much as$4 billion over the next 25 years depending on the problem and country.Crop Production/Industries,

Implementing technologies and strategies to maintain resistance to sunflower rust

This project proposes to implement resistance gene pyramiding strategies through close collaboration with Pacific Seeds. These strategies have been developed by Department of Primary Industries and Fisheries (DPI&F) researchers in two previous GRDC projects, DAQ356 and DAQ537. The gene pyramids will be incorporated into elite breeding material using techniques and technologies developed by DPI&F. These include the use of DNA markers. If successful, a range of elite lines/commercial hybrids containing strategic resistance gene pyramids will be available to growers. These lines will provide the industry with a directed strategy to manage the sunflower rust pathogen and reduce the risk of outbreaks of the disease

Seedling salt tolerance in tomato

Soils with higher concentrations of salt are becoming more and more a constraint for many crops to obtain high yields. Wild tomato species, adapted to adverse environments, are a potential reservoir for genes underlying quantitative trait loci (QTL) related to salt tolerance in tomato. In this study two introgression line (IL) libraries derived from two different wild species, Solanum pennellii LA716 and Solanum lycopersicoides LA2951, were used to identify QTLs for salt tolerance in the seedling stage. In the S. pennellii IL library, four major QTLs were identified on chromosomes 6, 7 and 11. In the S. lycopersicoides IL library, six major QTLs were discovered which are located on chromosomes 4, 6, 9 and 12. Co-localization of QTLs on chromosome 6 in the two IL libraries and previously reports hinted that this locus might be conserved in the tomato crop. Three S. pennellii ILs (IL6-2, IL7-1 and IL7-5) harboring QTLs on chromosome 6 and 7 were crossed. Semi-dominance and dominance were shown for these three QTLs, and non-additive and epistatic interactions between them were observe