Crown rust affects plant performance and interference ability of Italian ryegrass in the post-epidemic generation

This study investigated the effects of crown rust (caused by Puccinia coronata f.sp. lolii) in Italian ryegrass (Lolium multiflorum) on plant growth and interference ability in the post‐epidemic generation. Rust‐infected Italian ryegrass plants produced seeds with lower weights than healthy plants (on average proportionately 0·36 lower). Furthermore, the early seedling vigour of plants from rust‐infected parents was reduced by 0·50 compared with seed from healthy parents. Under disease‐free conditions in the post‐epidemic generation, mature plants from rust‐infected parents produced 0·13 less shoot dry weight, 0·15 fewer tillers, 0·11 fewer leaves and 0·25 less leaf area than plants from healthy parents. As such, the effects of crown rust in Italian ryegrass persisted for at least one post‐epidemic generation. Under rust‐infected conditions in the post‐epidemic generation, however, the difference in performance between plants from healthy and rust‐infected parents was minimal. This suggests that any advantage plants gain from having healthy parents, compared with rust‐infected parents, might be lost when the post‐epidemic generation is grown under conditions of rust infection. Irrespective of rust infection in the post‐epidemic generation, the magnitude of intra‐specific interference was greater in monocultures of Italian ryegrass from healthy parents than in those from rust‐infected parents. However, the magnitude of inter‐specific interference and the relative interference ability of plants of rust‐infected and healthy parents did not differ. The implications of these results to plant ecology are discussed.     

QTL analysis of crown rust resistance in perennial ryegrass under conditions of natural and artificial infection

Crown rust is an economically devastating disease of perennial ryegrass. Both artificial crown rust inoculations, with the possibility of several selection cycles in one year, as well as marker-assisted selection can be used for more efficient breeding of new resistant cultivars. The objective of this study was to map quantitative trait loci (QTL) for response to crown rust infection in perennial ryegrass. In order to identify relevant markers for response to crown rust infection, QTL mapping was performed on a ryegrass mapping population which was evaluated for resistance in the field for two years as well as by artificial pathogen inoculations using a detached leaf assessment. The broad sense heritability values for the field, detached leaf and combined assays were 0.42, 0.56, and 0.64, respectively, indicating a good potential for selection for crown rust resistance. A total of six QTLs were identified and mapped to linkage groups (LG) LG1, LG4 and LG5, explaining between 6.8% and 16.4% of the total phenotypic variation.     

Identification of resistance gene analogs as markers of disease resistance loci in oats, using near-isogenic lines

Genomic sequences with features of the major class of disease resistance genes and which bear nucleotide‐binding leucine‐rich repeat sequences (resistance gene analogs; RGA) were tested as potential markers of crown rust resistance loci in hexaploid oats. Two collections of paired near‐isogenic lines carrying resistance to different isolates of crown rust, Puccinia coronata were screened. Two out of the four RGAs assayed showed restriction fragment length polymorphism (RFLP) between one line of each collection and its recurrent parent. The paired lines X466 and D494 were polymorphic for RGA III2.2 and the pair of lines X470 and D504 were polymorphic for RGA III2.18. The III2.18 polymorphism was located in the hexaploid map Avena byzantina cv. ‘Kanota’ × A. sativa cv. ‘Ogle’ in linkage group KO17 in a region previously associated with crown rust resistance. In addition, 220 random primers were used for random amplified polymorphic DNA (RAPD) analysis to screen the two sets of NILs. Only one polymorphic band was obtained that differentiated the paired lines X470 and D504 from their parents. The RAPD band was used as a probe and the relevant RFLP that differentiated the NILs X470 and D504 was found at 1.7 cM from the III2.18 marker in KO17. RFLP analysis using probes previously mapped in KO17 confirmed differences for X470 and D504 in the region around the III2.18 marker. These results suggest that the resistance locus shared by this pair of NILs is probably linked to the markers revealed by RGA III2.18. The use of RGAs as RFLP probes in the screening of NILs with differences in crown rust resistance has proved to be more effective than RAPDs for finding polymorphic markers possibly linked to resistance loci.     

黑麦草冠锈病的发生发展规律和防治技术研究

黑麦草冠锈病是西安市禾草草坪上的重要病害,主要危害多花黑麦草,也危害早熟禾和剪股颖。3月上旬禾草返青后即开始发病,6～10月为发病最严重的时期,12月中旬以后越冬。机械剪草和喷灌是造成该病严重发生和流行的重要因素。通过试验,采用农业防治(减少剪草次数和喷灌次数)和化学防治(喷百理通、三唑酮、腈菌唑等农药)等项技术措施,可有效地控制该病的蔓延和危害。以上技术措施已在36hm2禾草草坪上连续应用两年,防病效果显著。     

吉林省的一种新病害--由冠柄锈菌引起的早熟禾锈病

在吉林省长春市吉林农业大学的草坪草上发现由冠柄锈菌原变种引起的早熟禾锈病。该病害为吉林省新记录。     

Introgression of crown rust (Puccinia coronata) resistance from meadow fescue (Festuca pratensis) into Italian ryegrass (Lolium multiflorum): genetic mapping and identification of associated molecular markers

Crown rust ( Puccinia coronata ) resistance (CRres), which had been introgressed from meadow fescue ( Festuca pratensis ) into the Italian ryegrass ( Lolium multiflorum ) background, was genetically mapped with amplified fragment length polymorphism (AFLP) and sequence tagged site (STS) markers to a terminal segment of chromosome 5. Comparative mapping had previously shown that this region of the Lolium / Festuca genome has a degree of conserved genetic synteny with chromosomes 11 and 12 of rice. Sequences from rice chromosome 12 were used as templates for identifying further STS markers that cosegregated with CRres. The relative genomic positions of molecular markers associated with CRres in L. multiflorum , L. perenne , F. pratensis and oats is discussed, along with their relationships to physical positions on rice chromosomes C11 and C12.     

Discovery and genotyping of high-throughput SNP markers for crown rust resistance gene Pc94 in cultivated oat

Crown rust caused by Puccinia coronata f. sp. avenae Eriks is a serious problem for oat production worldwide and pyramiding multiple resistance genes into new cultivars is a key objective of breeders. Many race specific resistance genes have been mapped and markers that are closely linked to them have been identified. However, the use of these markers in oat breeding practice has been limited due to the economics of marker assisted selection (MAS) deployment. Single nucleotide polymorphism (SNP) markers have been demonstrated to have a high-throughput capability with relatively low cost and numerous semi-automated SNP scoring platforms exist. Gene Pc94 has remained highly effective since it was first tested on the Canadian crown rust populations in 1993 and is one of the few effective genes available in Western Canada. In the present study, PCR products were amplified using primers derived from sequences of amplified fragment length polymorphism bands which have been shown to be linked to Pc94 . Genomic DNA from genotypes, with and without the Pc94 gene, were used as the PCR templates. By comparative sequence alignment amongst the PCR fragments, many putative SNP sites were identified. From these sites, four SNP sites were selected and validated by the single base extension method. One SNP site, Pc94 -SNP1a, was tested on two F_2:3 populations segregating for the resistance gene. The map distances between the SNP marker and Pc94 were 2.1 and 5.4 cM in the two different populations. Various oat cultivars and germplasm lines were also tested for a wider application of the SNP marker. Fluorescent technology and capillary electrophoresis allowed for the semi-automated, fairly high-throughput scoring of the SNP markers.     

A maternal factor conferring resistance to crown rust in Lolium multiflorum cv.'Axis'

The genetic basis for crown rust resistance was analysed in the progeny of reciprocal crosses between Lolium multiflorum plants that were either resistant (cv. ‘Axis’) or susceptible to crown rust. The progeny harvested from the resistant parent was two‐ to seven‐fold more resistant than the progeny harvested from the susceptible parent. These data indicate the presence of a maternal factor which increases resistance to crown rust in some of the ryegrass plants used as parents.     

Avena fatua L. subsp. fatua v. glabrata Peterm. subv. pseudo-basifixa Thell. as a source of crown rust resistance genes

Summary An accession of Avena fatua L. subsp. fatua v. glabrata Peterm. subv. pseudo-basifixa Thell. (A. fatua L. CS Sel. No. 1), collected in Czechoslovakia in 1971, was found to be resistant to a wide range of crown rust races. Analyses of crosses of this oat with cvs. Weikuss, Leanda, Mona, Rodney A, Rodney B, Rodney M, Dodge and K 316 indicated that the resistance of A. fatua CS Sel. No. 1 is conditioned by one recessive gene which is in interaction with one partially dominant gene with additive effect. The expression of rust reaction was affected by temperature. The crown rust resistance genes of A. fatua L. CS Sel. No. 1 were non-allelic with stem rust resistance genes Pg-2 (A) and Pg-4(B).