S. E. Cambron

Identification of RAPD markers for 11 Hessian fly resistance genes in wheat

Abstract The pyramiding of genes that confer race- or biotype-specific resistance has become increasingly attractive as a breeding strategy now that DNA-based marker-assisted selection is feasible. Our objective here was to identify DNA markers closely linked to genes in wheat (Triticum aestivum L.) that condition resistance to Hessian fly [Mayetiola destructor (Say)]. We used a set of near-isogenic wheat lines, each carrying a resistance gene at 1 of 11 loci (H3, H5, H6, H9, H10, H11, H12, H13, H14, H16 or H17) and developed by backcrossing to the Hessian fly-susceptible wheat cultivar ‘Newton’. Using genomic DNA of these 11 lines and ‘Newton’, we have identified 18 randomly amplified polymorphic DNA (RAPD) markers linked to the 11 resistance genes. Seven of these markers were identified by denaturing gradient gel electrophoresis and the others by agarose gel electrophoresis. We confirmed linkage to the Hessian fly resistance loci by cosegregation analysis in F2 populations of 50–120 plants for each different gene. Several of the DNA markers were used to determine the presence/absence of specific Hessian fly resistance genes in resistant wheat lines that have 1 or possibly multiple genes for resistance. The use of RAPD markers presents a valuable strategy for selection of single and combined Hessian fly resistance genes in wheat improvement.

Phenotypic assessment and mapped markers for H31, a new wheat gene conferring resistance to Hessian fly (Diptera: Cecidomyiidae).

A new source of resistance to the highly virulent and widespread biotype L of the Hessian fly, Mayetiola destructor (Say), was identified in an accession of tetraploid durum wheat, Triticum turgidum Desf., and was introgressed into hexaploid common wheat, Triticum aestivum L. Genetic analysis and deletion mapping revealed that the common wheat line contained a single locus for resistance, H31, residing at the terminus of chromosome 5BS. H31 is the first Hessian fly-resistance gene to be placed on 5BS, making it unique from all previously reported sources of resistance. AFLP analysis identified two markers linked to the resistance locus. These markers were converted to highly specific sequence-tagged site markers. The markers are being applied to the development of cultivars carrying multiple genes for resistance to Hessian fly biotype L in order to test gene pyramiding as a strategy for extending the durability of deployed resistance.

Association of a DNA marker with Hessian fly resistance gene H9 in wheat

The Hessian fly [Mayetiola destructor (Say)] is a major pest of wheat (Triticum aestivum L.) and genetic resistance has been used effectively over the past 30 years to protect wheat against serious damage by the fly. To-date, 25 Hessian fly resistance genes, designated H1 to H25, have been identified in wheat. With near-isogenic wheat lines differing for the presence of an individual Hessian fly resistance gene, in conjunction with random amplified polymorphic DNA (RAPD) analysis and denaturing gradient-gel electrophoresis (DGGE), we have identified a DNA marker associated with the H9 resistance gene. The H9 gene confers resistance against biotype L of the Hessian fly, the most virulent biotype. The RAPD marker cosegregates with resistance in a segregating F2 population, remains associated with H9 resistance in a number of different T. aestivum and T. durum L. genetic backgrounds, and is readily detected by either DGGE or DNA gel-blot hybridization.

Characterization of new loci for Hessian fly resistance in common wheat

The discovery of several new loci for resistance to Hessian fly was reported here. QHf.uga-6AL, the late HR61 was recognized from wheat cultivar 26R61 on the distal end of 6AL with resistance to both biotypes E and vH13. It is the first gene or QTL found on this particular chromosome. QHf.uga-3DL and QHf.uga-1AL, physically assigned to the deletion bins 3DL2-0.27–0.81 and 1AL1-0.17–0.61, respectively, were detected for resistance to biotype vH13. Both QTL should represent new loci for Hessian fly resistance and the latter was detectable only in the late seedling stage when tolerance was evident. In addition, QHf.uga-6DS-C and QHf.uga-1AS had minor effect and were identified from the susceptible parent AGS 2000 for resistance to biotype E and vH13, respectively. QHf.uga-6DS-C is different from the known gene H13 on 6DS and QHf.uga-1AS is different from H9 gene cluster on 1AS. These loci also might be new components of Hessian fly resistance, although their LOD values were not highly significant. The QTL detections were all conducted on a RIL mapping population of 26R61/AGS 2000 with good genome coverage of molecular markers. The strategy used in the current study will serve as a good starting point for the discovery and mapping of resistance genes including tolerance to the pest and the closely linked markers will certainly be useful in selecting or pyramiding of these loci in breeding programs.

Survival of Hessian Fly (Diptera: Cecidomyiidae) Puparia Exposed to Simulated Hay Harvest Conditions, Location and Windrow Drying in Washington and California

ABSTRACT Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae) puparia are of regulatory concern in exported hay, and drying after harvest was evaluated as a cultural control technique for bales shipped from the western states. In total 16,836; 31,122; and 48,051 puparia were tested under drying conditions in environmental chambers, open air on location, and hay windrows, respectively. Regression lines for percentage of total adults emerging from puparia exposed to simulated drying conditions for 1–7 d in environmental chambers was significant for 1 September, Kittitas Valley, WA; 3 June, East Columbia Basin, WA; 15 May and 15 July, San Joaquin Valley, CA; and 15 May, 20 July, and 15 September, Imperial Valley, CA. In open air drying on location for 1–7 d, total percentage of puparia surviving to adults for all exposure days was 0.4% for 18 June, Kittitas Valley; 1.2% for 15 May, San Joaquin Valley; and 0% for 16 July, Imperial Valley; and significantly different between controls and exposure durations. In hay windrow drying for 1–6 d, total percentage of puparia surviving to adults for all exposure days was 5.4% on 28 June and 24.2% on 7 September in timothy, Phleum pretense, in the Kittitas Valley; 3.8% on 28 June in timothy in the East Columbia Basin; 2.2% on 20 July in alfalfa, Medicago sativa, in the San Joaquin Valley; and 6.3% on 21 July in Sudan grass, Sorghum bicolor sudanensis, in the Imperial Valley. The number of puparia surviving to adults in open air drying and in windrows was significantly different between controls and exposure durations for all test dates and locations. Puparial survival in field tests was related to mild temperatures and high humidities. Hay drying with subsequent field baling, storage, and export bale compression is discussed in relation to a systems approach for quarantine control of Hessian fly in exported hay.

Effectiveness of Genes for Hessian Fly (Diptera: Cecidomyiidae) Resistance in the Southeastern United States

Abstract The Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae), is the most important insect pest of wheat (Triticum aestivum L. subsp. aestivum) in the southeastern United States, and the deployment of genetically resistant wheat is the most effective control. However, the use of resistant wheat results in the selection of pest genotypes that can overcome formerly resistant wheat. We have evaluated the effectiveness of 16 resistance genes for protection of wheat from Hessian fly infestation in the southeastern United States. Results documented that while 10 of the genes evaluated could provide protection of wheat, the most highly effective genes were H12, H18, H24, H25, H26, and H33. However, H12 and H18 have been reported to be only partially effective in field evaluations, and H24, H25, and H26 may be associated with undesirable effects on agronomic traits when introgressed into elite wheat lines. Thus, the most promising new gene for Hessian fly resistance appears to be H33. These results indicate that identified highly effective resistance in wheat to the Hessian fly is a limited resource and emphasize the need to identify novel sources of resistance. Also, we recommend that the deployment of resistance in gene pyramids and the development of novel strategies for engineered resistance be considered.

Use of microsatellite and SNP markers for biotype characterization in Hessian fly.

Exploration of the biotype structure of Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae), would improve our knowledge regarding variation in virulence phenotypes and difference in genetic background. Microsatellites (simple sequence repeats) and single-nucleotide polymorphisms (SNPs) are highly variable genetic markers that are widely used in population genetic studies. This study developed and tested a panel of 18 microsatellite and 22 SNP markers to investigate the genetic structure of nine Hessian fly biotypes: B, C, D, E, GP, L, O, vH9, and vH13. The simple sequence repeats were more polymorphic than the SNP markers, and their neighbor-joining trees differed in consequence. Microsatellites suggested a simple geographic association of related biotypes that did not progressively gain virulence with increasing genetic distance from a founder type. Use of the k-means clustering algorithm in the STRUCTURE program shows that the nine biotypes comprise six to eight populations that are related to geography or history within laboratory cultures.