Genetic Diversity of Ascochyta rabiei in Canada.

Assessment of variability of Ascochyta rabiei (teleomorph: Didymella rabiei) was based on virulence tests of 40 isolates and on random amplified polymorphic DNA (RAPD) analysis of 39 isolates from Canada. In addition, isolates of A. rabiei from other countries were assessed in the virulence (18 isolates) and RAPD (20 isolates) analyses. Seven isolates of A. lentis (teleo-morph: Didymella lentis) and two of A. pinodes (teleomorph: Mycosphaerella pinodes) also were included in the RAPD analysis. Significant line-isolate interactions in the virulence tests indicated that certain isolates were virulent only on certain lines. Canadian isolates were grouped into 14 pathotypes using eight chickpea differentials. These groupings also encompassed 17 of the 18 isolates from other countries. RAPD analysis of all 68 isolates using 8 primers produced 112 fragments, of which 96% were polymorphic. Similarities among A. rabiei isolates from Canada ranged from 20 to 100%. In the RAPD dendrogram, all five A. rabiei isolates from Australia, three of six from Syria, three of five from the United States, and one of two from India clustered within the major groups of Canadian isolates. There was a weak association between RAPD and pathotype groups. A. rabiei was 45% similar to A. lentis and only 14% similar to A. pinodes. The levels of DNA variability and virulence among isolates show that the population of A. rabiei in Canada is highly diverse.

Identification of Lentil Germ Plasm Resistant to Colletotrichum truncatum and Characterization of Two Pathogen Races.

ABSTRACT A total of 1,771 lentil accessions from the U.S. lentil collection (U.S. Department of Agriculture-Agricultural Research Service, Pullman, WA) and the Institut für Pflanzengenetik und Kulturpflanzenforschung (Gatersleben, Germany) were screened for resistance to Colletotrichum truncatum, the cause of anthracnose. About 95% of the accessions were susceptible when inoculated with a single isolate in the field. Retesting, under controlled conditions, of accessions rated as resistant or moderately resistant in the field resulted in identification of anthracnose resistance in four accessions from the U.S. collection (PI 320937, PI 320952 [cv. Indianhead], PI 345629, and 468901), and 12 accessions from the German collection (Lens 3, 102, 104, 106, 107, 119, 122, 134, 135, 177, 195, and 209). Seven of the accessions were used as host differentials to characterize pathogenic variability of 50 single-spore isolates collected in Manitoba and Saskatchewan, Canada. The presence of two distinct races was demonstrated. Isolates of C. truncatum avirulent on cv. Indianhead, PI 320937, PI 345629, PI 468901, Lens 102, Lens 104, and Lens 195 were designated race Ct1. Isolates that were virulent on these seven entries were designated race Ct0, indicating their lack of avirulence genes. Race Ct0 was isolated more frequently from commercial seed samples than race Ct1, but the two races were isolated with similar frequency from plants in commercial fields planted to susceptible cultivars. Race Ct0, to which no resistance has yet been identified, presents a high risk to lentil production in Canada and potentially worldwide.

Genetics of resistance to anthracnose and identification of AFLP and RAPD markers linked to the resistance gene in PI 320937 germplasm of lentil (Lens culinaris Medikus).

Anthracnose, caused by Colletotrichum truncatum, is a major disease problem and production constraint of lentil in North America. The research was conducted to examine the resistance to anthracnose in PI 320937 lentil and to identify molecular markers linked to the resistance gene in a recombinant inbred line (RIL) population developed from a cross of Eston lentil, the susceptible parent, and PI 320937, the resistant parent. A total of 147 F(5:6) RILs were evaluated for resistance to anthracnose in the greenhouse using isolate 95B36 of C. truncatum. Bulked segregant analysis (BSA) strategy was employed and two contrasting DNA bulks were constructed based on greenhouse inoculation of F(5)-derived F(6) RILs. DNA from the parents and bulks were screened with 700 RAPD primers and seven AFLP primer combinations. Analysis of segregation data indicated that a major dominant gene was responsible for resistance to anthracnose while variations in the resistance level among RILs could be the influences of minor genes. We designate the major gene as LCt-2. MapMaker analysis produced two flanking RAPD markers OPEO6(1250) and UBC-704(700) linked to LCt-2 locus in repulsion (6.4 cM) and in coupling (10.5 cM), respectively. Also, three AFLP markers, EMCTTACA(350) and EMCTTAGG(375) in coupling, and EMCTAAAG(175) in repulsion, were linked to the LCt-2 locus. These markers could be used to tag the LCt-2 locus and facilitate marker-assisted selection for resistance to anthracnose in segregating populations of lentil in which PI 320937 was used as the source of resistance. Also, a broader application of the linked RAPD markers was also demonstrated in Indianhead lentil, widely used as a source of resistance to anthracnose in the breeding program at the Crop Development Centre, University of Saskatchewan. Further selection within the few F(5:6) lines should be effective in pyramiding one or several of the minor genes into the working germplasm of lentil, resulting in a more durable and higher level of resistance.