No effect of PGRs on FHB
Plant growth regulators did not affect Fusarium head blight disease in spring wheat. PGRs could allow growers to select taller, FHB-resistant wheat cultivars while managing plant height and lodging to improve yield.
Most cultivars with improved Fusarium head blight (FHB) resistance tend to be taller, but they come with trade-offs of increased lodging risk. Semi-dwarf varieties generally perform better in high yield areas under intensive management. This semi-dwarf trait comes from semi-dwarfing alleles, Rht-B1b and Rht-D1b, that are found in over 70% of wheat varieties worldwide. However, the semi-dwarf alleles in spring wheat can increase the frequency of anther retention during flowering that may increase infection by Fusarium graminearum, the pathogen responsible for FHB.
A solution for growers may be to grow taller varieties with better FHB resistance, and to use plant growth regulators (PGRs) to reduce wheat height and lodging risk – theoretically helping to improve wheat production.
A research study was conducted to determine the effect of two PGRs on five spring wheat cultivars with different levels of FHB resistance and height on anther retention and FHB.
Field trials were conducted at Winnipeg and Carman, MB in 2019 and 2020. Five spring wheat cultivars were grown in the research trials:
- AAC Tenacious: CPSR class; 101 cm tall; R to FHB; no semi-dwarf alleles,
- AAC Penhold: CPSR; 71 cm tall; MR to FHB; Rht-D1b allele,
- AAC Brandon: CWRS; 81 cm tall; MR to FHB; Rht-B1b allele,
- AAC Cameron: CWRS; 94 cm tall; I to FHB; no semi-dwarf alleles,
- Prosper: CNHR; 84 cm tall; I to FHB; Rht-B1b allele.
The PGR treatments included an untreated control, Manipulator (620 g/L of Chlormequat chloride) applied to the plants at the Zadoks GS 30 (start of stem elongation) at the recommended rate of 0.73 L/ac (1.8L/ha) as a single application, and Ethrel (240 g/L of Ethephon) applied at Zadoks GS 37 to 45 (flag leaf stages) at the recommended rate of 0.51 L/ac (1.25 L/ha).
Nitrogen (N) fertilizer was broadcast applied to target 133 lbs/ac (150 kg/ha) of soil + fertilizer N. Phosphate fertilizer was applied with the seed at a rate of 31 lbs/ac (35 kg/ha) of 11-52-0 monoammonium phosphate.
Plots were inoculated with four different isolates of F. graminearum at 50% anthesis (GS65) and three days later. After each inoculation, plots were irrigated with overhead mist to promote FHB development. These inoculated plots were compared to un-inoculated controls.
Plots were visually assessed for FHB disease incidence and severity 18 to 21 days after the first inoculation. The FHB index was calculated by incidence x severity and divided by 100.
During the two years of trials, total precipitation was between 69% and 72% of the long term average. Temperatures in June and July were at least 1% to 11% hotter than normal.
PGRs did not affect FHB
Overall, Ethrel reduced plant height to 29.7 inches (75.35 cm) compared to the control without PGRs at 31.6 in (80.25 cm). Plants treated with Manipulator were slightly taller than Ethrel at 30.7 inches (78 cm).
Across all treatments over the four site-years, AAC Tenacious was the tallest cultivar at 36 inches (91.3 cm), followed by AAC Cameron at 34 inches (86.5 cm), Prosper at 29.6 inches (75.3 cm), and AAC Brandon at 28.1 inches (71.4 cm). AAC Penhold was the shortest cultivar 25.6 inches (64.9 cm).
The PGRs did not affect anther retention or FHB of the tested cultivars under dry conditions.
In these relatively dry years, plots that were not inoculated with F. graminearum had very low FHB index, FDK% and Don levels. In these plots, FHB index and FDK% were less than 1%, and DON was less than 0.17 ppm. The Ethrel, Manipulator and control plots were statistically similar.
When the plots were inoculated, the FHB index ranged from 34.6% to 42.9%, and was statistically similar for the Ethrel, Manipulator and control plots. FDK ranged from 5.39% to 5.88% across the PGR and control plots, and were statistically similar. Don levels were statistically similar for the PGR and control plots ranging from 8.90 to 9.75 ppm.
As expected, FHB impacted the cultivars differently. AAC Tenacious (R) had significantly lower FHB index (2.1%), FDK (0.28%) and DON (0.76 ppm). The other MR and I varieties had similar FHB index, FDK% and DON. For example, AAC Cameron (I) was in the middle of the remaining varieties for FHB index (23.1%), FDK (2.70%) and DON (4.91 ppm).
It is important to note that the application of PGRs did not have an impact on FHB disease parameters. The research showed that growers could choose a taller, high-yielding, FHB-resistant variety and manage crop height with PGRs to reduce lodging and yield losses.
This research was funded by the Governments of Manitoba and Canada through the Canadian Agricultural Partnership, Manitoba Wheat and Barley Growers Association, Western Grains Research Foundation, and the University of Manitoba.
Younyoung Lee, Anita L. Brûlé-Babel, Yvonne E. Lawley, and Maria-Antonia Henriquez. 2024. Assessing the impact of plant growth regulators on anther retention and Fusarium head blight in spring wheat (Triticum aestivum L.) infected by Fusarium graminearum in field conditions. Canadian Journal of Plant Science. 104(2): 129-143.
OPEN ACCESS https://doi.org/10.1139/cjps-2023-0059
Photo by Younyoung Lee
