Disease resistance. Insensitivity to the toxins produced by Pyrenophora tritici-repentis and Stagonospora nodorum.

Tsn1

Background information

The Tsn1 gene confers sensitivity to the proteinaceous host-selective toxins Ptr ToxA produced by the tan spot fungus (Pyrenophora tritici-repentis) (1) and SnToxA produced by Stagonospora nodorum (Friesen et al. in preparation). Sensitivity to the toxins is conferred by the dominant allele, while insensitivity is conferred by the recessive and null alleles.

In the tan spot pathogen, Ptr ToxA produces extensive necrosis in sensitive genotypes. The toxin was shown to be a major virulence factor in some wheat genotypes (2), but had little association with the manifestation of disease in others (3, 4). It should be noted that the tan spot pathogen is capable of producing additional toxins that are associated with the development of extensive chlorosis in susceptible genotypes as well.

Multiple SnToxA-producing isolates of S. nodorum have recently been identified (Friesen et al., unpublished). Thus far, our data indicate that SnToxA is a major factor associated with the development of Stagonospora nodorum leaf blotch in susceptible wheat genotypes, and the Tsn1 locus accounts for as much as 68% of the phenotypic variation (Faris et al. unpublished).

Methods

Several microsatellites markers have been discovered close to Tsn1, and can be used for marker assisted breeding. Detailed laboratory procedures are available in the methods section.

Available germplasm

The recessive tsn1 allele conferring toxin insensitivity is found in multiple cultivars of hexaploid wheat, but it may be less common among tetraploid varieties. However, many accessions of T. dicoccoides are also known to carry the tsn1 allele. Some common hexaploid varieties known to carry tsn1 include the soft red winter wheat Atlas66, and the hard red spring wheat varieties Oklee, Dapps, Chinese Spring, Erik, Opata85, and BR34. The synthetic hexaploids W-7984, W-7976, TA4152-19, TA4152-37, TA4152-44, and TA4152-60 also harbor tsn1. Among 11 North Dakota durum wheat varieties tested, only Montrail was found to carry the tsn1 allele.

References

1. Chromosomal location of a gene conditioning insensitivity in wheat to a necrosis-inducing culture filtrate from Pyrenophora tritici-repentis. Faris JD, Anderson JA, Francl LJ, Jordahl JG. In: Phytopathology, 1996, 86: 459-463. [abstract]

2. Host-parasite interaction in tan spot (Pyrenophora tritici-repentis) of wheat. Strelkov SE, Lamari L In: Canadian Journal of Plant Pathology, 2003, 25: 339-349. [abstract]

3. Identification of quantitative trait loci for race-nonspecific resistance to tan spot of wheat. Faris JD, Friesen TL In: Theoretical and Applied Genetics, 2005, 111: 386-392. [abstract]

4. Role of host sensitivity to Ptr ToxA in development of tan spot of wheat. Friesen TL, Ali S, Kianian S, Francl LJ, Rasmussen JB In: Phytopathology, 2003, 93: 397-401. [abstract]

5. Genomic targeting and high-resolution mapping of the Tsn1 gene in wheat. Haen KM, Lu HJ, Friesen TL, Faris JD In: Crop Science, 2004, 44: 951-962.[abstract]