AGICULTURE AND AGRI-FOOD CANADA
Cereal Research Centre, 195 Dafoe Rd, Winnipeg, Manitoba, Canada, R3T 2M9.
| Province | Wheat | Hectares seeded | Metric tons produced |
|---|---|---|---|
| Manitoba | Spring | 1,483,100 | 3,942,200 |
| Durum | 52,600 | 141,500 | |
| Winter | 44,500 | 182,300 | |
| Sskatchewan | Spring | 3,980,000 | 8,593,0000 |
| Durum | 2,165,100 | 4,757,300 | |
| Winter | 58,700 | 182,3000 | |
| Alberta | Spring | 2,540,000 | 6,493,100 |
| Durum | 424,900 | 748,400 | |
| Winter | 20,200 | 46,300 |
Steve Haber and Dallas L. Seifers, Kansas State University, Hays, KS.
As we reported here earlier (Haber et al. 1998), the continuing
expansion of winter wheat acreage in the southeastern Canadian
Prairies is increasing the threat of severe losses from WSMV in
both winter wheat and adjoining spring wheat crops. In recent
years, we have begun to address this concern in spring wheat by
a) identifying and exploiting tolerance in adapted, advanced spring
wheat lines (Haber et al. 1996); b) transferring the Wsm1
gene for WSMV resistance from advanced Kansas winter wheat lines
to adapted, advanced, western Canadian spring wheat germ plasm;
and c) combining tolerance and resistance (Pradhan and Haber 1999).
If a means of controlling WSMV losses in spring wheat needs to
be applied in the near term (the next 2-5 years), it would be
best to know which, if any, registered spring wheat cultivars
respond to WSMV infection with only small or moderate losses.
During assessment in indoor trials the contributions of tolerance
and resistance to overall performance under pressure from seedling
infection with WSMV, back-assay titrations from infected seedlings
identified intermediate levels of resistance at 18°C in the
spring wheat cultivars Pai Toborichi and AC Elsa (Table 1). Pai
Toborichi is not adapted to western Canada, but AC Elsa currently
is widely grown in the Canadian Prairies. This resistance, like
that conferred by Wsm1 in A. intermediumwinter wheat
translocation lines (Seifers et al. 1995) was defeated by continued
exposure to 25°C (Table 1). In indoor trials conducted at
18-20°C, Pai Toborichi exhibited mild foliar symptoms and
yield losses (compared to mock-inoculated controls) of about 30
%. By contrast, AC Elsa responded to seedling inoculation with
WSMV with pronounced foliar symptoms, stunting, delayed head emergence,
and poor seed set, resulting in yield losses of 70-85 %, typical
of lines considered susceptible.
| Dilution of infectious sap | Infectious titer @ 18°C: mean number (3 trials) of infected test plants / 10 | ||||
|---|---|---|---|---|---|
| AC Vista (suseptible check) | Pai Toborichi | AC Elsa | AC Elsa (+Wsm1) backcross line | KS95H103 (Wsm1 source) | |
| 25 | 9.3 | 8.0 | 4.7 | 0.0 | 0.0 |
| 50 | 9.0 | 7.2 | 5.2 | 0.0 | 0.0 |
| 100 | 8.0 | 6.1 | 3.0 | 0.0 | 0.0 |
| 200 | 6.7 | 4.1 | 1.1 | 0.0 | 0.0 |
| 400 | 3.4 | 3.0 | 0.3 | 0.0 | 0.0 |
| 800 | 1.4 | 0.3 | 0.0 | 0.0 | 0.0 |
| 1,600 | 0.7 | 0.0 | 0.0 | 0.0 | 0.0 |
| Infectious titre @ 25°C: mean number (3 trials) of infected test plants / 10 | |||||
| 25 | 10.0 | 10.0 | 10.0 | 10.0 | 10.0 |
| 50 | 9.3 | 10.0 | 10.0 | 10.0 | 10.0 |
| 100 | 9.0 | 9.6 | 6.9 | 9.0 | 10.0 |
| 200 | 6.8 | 8.0 | 6.7 | 6.7 | 6.7 |
| 400 | 4.4 | 4.7 | 5.3 | 4.8 | 7.7 |
| 800 | 2.7 | 1.4 | 2.7 | 1.7 | 7.3 |
| 1,600 | 0.3 | 0.4 | 0.7 | 0.0 | 2.4 |
We used AC Elsa on a continuing basis as a recurring backcross parent because of its excellent agronomic and quality traits. In both indoor and outdoor tests in which AC Elsa served as the susceptible parental check, we often observed a very few individual AC Elsa plants that responded to WSMV infection with mild symptoms, were not stunted, and had almost normal seed set. After three generations, seed from individual heads selected from such plants appears to breed true for this mild response to WSMV. In indoor trials, the line we have reselected from AC Elsa (the name SuperElsa is an unofficial internal designation) has the best performance under WSM disease pressure of any spring wheat line we have tested that did not incorporate the Wsm1 gene (Haber, unpublished). We do not yet know whether the improved performance of SuperElsa compared AC Elsa (Table 2; Fig. 1) results from better resistance or tolerance or both. Experiments are now underway to determine the inheritance of SuperElsa's response to WSMV and to examine the effects of combination with other sources of resistance. Field experiments followed by assessments of grain quality are planned to determine if a line reselected from AC Elsa might provide effective protection in the near term against severe losses from WSM outbreaks.
| Material | Mean delay of heading (d) compared to control | Mean plant height at maturity (cm) | Average head length at maturity (cm) | Mean main head mass at maturity (g) |
|---|---|---|---|---|
| AC Elsa (Control) | 0.0 | 74 | 9.5 | 1.59 |
| SuperElsa (WSMV) | 2.5 | 66 | 9.0 | 1.05 |
| AC Elsa (WSMV) | 11.0 | 53 | 6.7 | 0.46 |
 |
Fig. 1. SuperElsa responds to seedling WSMV infection with milder symptoms than AC Elsa. |
References.
J.J. Gold and A. Tekauz.
Disease presence on 30 spring wheat cultivars at nine sites across the Canadian prairies. An ongoing study focused on the presence of leaf spot diseases on 30 cultivars from six classes of spring wheat, in uninoculated plots at three sites each in Manitoba, Saskatchewan, and Alberta. Each year, disease pressures change at each site primarily depending on environmental conditions, i.e., a different member of the disease complex may predominate (P. tritici-repentis, B. sorokiniana, S. tritici, St. nodorum, and S. avenae). Considering the rankings at all sites for all 3 years, Canadian Western Extra Strong (CWES) and Canadian Western Amber Durum (CWAD) varieties showed fewest leaf-spot symptoms overall, whereas Canadian Western Red Spring (CWRS) wheats were most variable in reaction. Amazon, Glenlea, and AC Corinne (CWES) ranked the best over all. In the CWRS class, AC Elsa and Laura ranked highest. AC Avonlea trailed Kyle, the best rated in the CWAD class, and Genesis, AC Taber, and AC Nanda ranked best in the classes Canadian Prairie Spring White, Canadian Prairie Spring Red, and Canadian Western Soft White Spring, respectively.
Studies on Bipolaris sorokiniana. High levels of B. sorokiniana were found on wheat seeds and leaves in Manitoba, both in the work described above and in surveys. A study was conducted to assess the effect of B. sorokiniana infestation of seed. Reduction in germination and vigor of seedlings was correlated with the level of natural seed infestation, but seed infestation did not always affect yield (significant reduction was seen only for AC Crystal), probably because of variation among the six cultivars tested in compensatory tillering. Preliminary testing of a small number of B. sorokiniana isolates suggests considerable molecular variability (AFLP polymorphism) within and between populations and virulence differences. These results suggest that B. sorokiniana may have a strong adaptive capacity, which could exacerbate the potential for damage from this pathogen in prairie wheat fields.