Pathogenic variability of Ascochyta rabiei in Saskatchewan

Non-Peer ReviewedForty isolates of Ascochyta rabiei collected in Saskatchewan Canada and 18 obtained from other countries were assessed for pathogenicity on eight chickpea differential lines/cultivars under controlled conditions. Each assessment was repeated once. Based on the differential by isolate interactions, 15 distinct pathotypes were identified among the isolates from Saskatchewan. This demonstrates that many races of A. rabiei are present in Saskatchewan. Formation of new virulent races through gene recombination is possible. This will have large impact on Ascochyta blight development and its control. Plant breeders should anticipate a highly diverse A. rabiei population with a high potential for change

Growing irrigated lentil

Non-Peer ReviewedSince 1987, research was conducted at the Saskatchewan Irrigation Development Centre (SIDC), Outlook, to develop technology suitable for irrigated lentil (Lens culinaris Medikus) production. Diverse germplasm and various management practices were evaluated. Under irrigation, Eston, CDC Richlea, and Rose lentil produced higher seed yield than Laird. Supplemental irrigation of Eston produced marked yield increases in the low rainfall years. For example, in 1988 which received 95 mm (3.8 in) of precipitation during the growing season, addition of 130 mm (5.1 in) and 225 mm (8.9 in) of water produced approximately a 5-6 fold yield advantage. Excessive irrigation in wet years or at flowering reduced yield, likely through excessive vegetative growth and increased disease incidence. Under excess moisture conditions, Eston and Laird were more susceptible to diseases than CDC Richlea, or 458-57. Seeding rates (100 plants/m2, i.e. 9-10 plants/ft2) and row-spacing (20 em, i.e. 8 in) recommended for dryland production appeared suitable for irrigation although in one year, positive yield responses were obtained up to a population density of 175 plant/m2

RAPD and AFLP markers linked to anthracnose resistance gene in PI 320937 lentil (Lens culinaris Medik.)

Non-Peer ReviewedColletotrichum truncatum (Schwein.) Andrus & W.D. Moore is the causal fungus for anthracnose disease in lentils. A germplasm accession, ‘PI 320937’, is among the lines used as a resistance source to develop cultivars in the breeding program. A cross of Eston (susceptible) and PI 320937 (resistant) was used to develop 147 recombinant inbred lines (RILs) to study the genetics of resistance and identify markers associated to the resistance gene. The F5:6 RILs were inoculated with C. truncatum isolate 95B36 at 105 conidia ml-1 and scored for anthracnose reactions over 2 replications in the greenhouse. About 600 RAPD and 10 AFLP primers were screened. We used bulk segregant analysis to construct contrasting DNA bulks, one containing only resistant and the other only susceptible plants based on the greenhouse tests. These polymorphic markers between parental lines were used to genotype RILs and make linkage analysis. Segregation data indicated that a single major gene (LCt-2) confers resistance. Minor genes also modified the level of resistance. Two RAPD markers; namely, OPE O61250 and UBC 704700 were linked in repulsion and coupling at 6.4 and 10.8 cM, respectively, to the resistance gene. Also, 3 AFLP markers were identified within 30 cM distance from the resistance locus. These markers will be useful in lentil breeding via marker-assisted selection towards developing cultivars with anthracnose resistance

Partial stem resistance in Brassica napus to highly aggressive and genetically diverse Sclerotinia sclerotiorum isolates from Australia

Sclerotinia sclerotiorum is a fungal pathogen that causes stem rot in oilseed rape (Brassica napus). Previously, B. napus accessions with partial stem resistance to a Canadian S. sclerotiorum isolate (#321) were identified using a stem test in which flowering plants were inoculated with mycelium plugs. The present study examined the partial stem resistance of four of these accessions, PAK54, PAK93, DC21 and K22, following inoculation with Australian isolates. Mycelial compatibility groups and intergenic spacer (IGS) region haplotypes were identified among 71 isolates from Australian oilseed rape and lupin fields. Eleven genetically diverse isolates showed differences in aggressiveness when inoculated onto nine oilseed rape varieties and one Chinese accession. Isolates CU8.24, CU10.17 and CU11.19 were selected based on genetic diversity, growth rate in vitro and high aggressiveness in the initial screen and subsequently inoculated onto the four B. napus accessions. These accessions developed significantly smaller lesions compared with the susceptible control varieties (‘AV Garnet’ and ‘Westar’), with the average frequency of soft and collapsed lesions being less than 20% in PAK54, DC21 and K22, 29% in PAK93 and greater than 88% in the susceptible controls. Microscopic examination revealed that hyphae were typically confined to the stem cortex in the smallest lesions, but could be found in the stem pith in larger lesions. These results show that B. napus accessions PAK54, PAK93, DC21 and K22 can be used in Australia for development of varieties with partial stem resistance to S. sclerotiorum

Genetic study of Ascochyta blight resistance in chickpea and lentil

Non-Peer ReviewedAscochyta blight is responsible for severe crop losses in most chickpea and lentil production areas around the world. The research was conducted to study the genetic basis for Ascochyta blight resistance in chickpea and lentil by means of QTL analysis, and PCR-based approaches to identify resistance gene analogues (RGA) sequences in the lentil genome. An AFLP and three SSR markers were linked to the gene(s) for Ascochyta resistance in a chickpea population derived from a cross between CDC Chico and CDC Marengo. Two QTL that explained 36 % and 29 % of the disease reaction variability were identified in a lentil RI population derived from a cross between ILL5588 and L692-16-1. These markers were converted into SCAR markers to simplify their use for marker-assisted selection

Revisiting strategies for breeding anthracnose resistance in lentil: the case with wild species

Non-Peer ReviewedBreeders at the Crop Development Centre (CDC) have up to now only used germplasm resources available in the cultivated lentil to develop new varieties with resistance to diseases. Based on recent studies, the available cultivated germplasm does not offer sufficient genetic variation for resistance to anthracnose and ascochyta diseases. Lentil crop is attacked by two major diseases (anthracnose and ascochyta) that can cause 100% loss in the worst scenarios. Since anthracnose is only a major lentil disease in North America, no work has been done to improve resistance to this disease elsewhere. Wild species of many crops are known to carry many disease resistance genes lacking in the cultivated crop. We began the search for anthracnose resistance in the six wild species of lentil (world collection), of which two can be easily crossed with the cultivated type. Two strains of anthracnose (race 1 and race 2) with varying degrees of virulence were reported. The 2002 field data suggested that some of the Lens ervoides and Lens lamottei accessions exhibited no lesions at all when exposed to the combination of the two anthracnose strains. The cultivated types that show resistance to the less virulent strain were severely affected by anthracnose. In the greenhouse study the wild species were inoculated with the two strains separately and results indicate that no accession is immune to the more virulent type. However, some of the L. ervoides and L. lamottei accessions had good resistance compared to their cultivated counterparts. As a long term strategy, the lentil breeding program at CDC, University of Saskatchewan has a goal of fully utilizing the available resistance sources. However, these two species cannot be easily crossed with the cultivated types using the conventional/manual crossing techniques. A tissue culture procedure involving embryo rescue is used to facilitate crossing. We have been able to successfully rescue some embryos from crosses with Lens ervoides. The hybrid plants produce some fertile seeds which will be evaluated for resistance to both anthracnose and ascochyta. The selected resistant lines will then be backcrossed to the adopted backgrounds in order to deploy resistance genes

Influence of plant age on resistance to Ascochyta rabiei in chickpea cultivars

Non-Peer ReviewedAscochyta blight of chickpea, which is caused by the fungal pathogen Ascochyta rabiei, can cause severe losses in yield and seed quality. When environmental conditions favour blight development, even resistant cultivars may become heavily infected (Nene and Reddy 1987). Plant age has no impact on disease reaction in susceptible cultivars (Trapero-Casas and Kaiser 1992). However, two previous studies of the reaction of resistant cultivars as the plants mature had conflicting results, with resistance increasing in one study and declining in the other (Hafiz 1952, Sattar 1933). The objective of this study was to investigate the impact of plant age on Ascochyta blight severity in partially resistant and susceptible chickpea cultivars adapted for western Canada

Resistance in chickpea to Ascochyta rabiei is conferred by genes encoding pathogen recognition and other genes in basic defense pathways

This study examines the molecular basis of resistance to Ascochyta rabiei in chickpea. An inter-specific population of RIL derived from C. arietinum ICC4958 x C. reticulatum PI489777 was used to develop a high-density linkage map consisting of 1328 SNP and SSR markers. Progenies were inoculated separately with two isolates from Canada and one from Syria using a detached leaf-assay. This allowed an accurate record of lesion development over time that was used to calculate the area under the disease progress curve (AUDPC). The parental lines interacted differentially with the isolates as AUDPC were 20.6, 9.3 and 4.4 in ICC4958 compared to 2.0, 3.2 and 9.3 in PI489777. Ten quantitative resistance loci (QRL) explained 5 to 26% of the phenotypic variation. The two parents contributed to resistance at different loci. Each QRL interacted with a single isolate, except one that interacted with two isolates. Since a portion of the SNP markers were designed in exonic sequences a search of GenBank and Medicago data bases revealed annotated gene function. A major discovery was a match of SNP markers at six QRL with genes encoding serine/threonine kinase proteins involved in pathogen recognition, innate immune response, programmed cell death and signal transduction. Genes at the remaining QRL were associated with well known basic defense pathways such as thaumatin, chalcone-stilbene, peroxidase and ethylene. Evidence suggest that recognition of A. rabiei results in qualitative disease phenotypes seen in some studies, while the quantitative nature of resistance in other studies might be a result of activation of additional networks of basic defense pathways