Fusarium Head Blight Situation

Fusarium Head Blight (FHB or scab) of barley has been epidemic in Minnesota and neighboring states since 1992 and growers have suffered major losses in each of the last five years. Buyers of barley for malt are going to Canada and to the western United States to obtain barley low and/or free of deoxynivalenol (vomitoxin). Unlike wheat, where the grain yield can be reduced dramatically, the primary concern in barley has been the presence of deoxynivalenol. As a consequence, the Minnesota barley improvement program is directing the majority of it's efforts to the control of Fusarium Head Blight in barley.

Greenhouse Testing

Greenhouse screening of barley genotypes continues to contribute towards identifying promising breeding lines in the Minnesota Barley Breeding/Pathology programs. Two hundred lines were screened in the winter and fall of 1997. Differences were apparent among improved agronomic types. The reliability of greenhouse testing seems to be improving and the coefficients of variation have declined indicating improvement in screening methodology.

Repeatability of Fusarium Head Blight Reaction in Barley Genotypes

Based on the success of previous field inoculation methods (1996 Barley Newsletter, 40:38-40), a research effort was initiated in 1997 to evaluate repeatability of FHB reaction among four check-cultivars and eleven experimental barley genotypes over three locations in Minnesota. Several of the eleven genotypes had exhibited promising levels of FHB-resistance in a greenhouse and/or field testing in previous assessments. Due to their promise and combinations of favorable agronomic characteristics, many of these lines have been used as parents in crosses. Thus, the main objective was to reconfirm and further evaluate these barley genotypes' reaction to FHB over several field environments. The research trial was planted at St. Paul, Morris, and Crookston, Minnesota, in the spring of 1997. The cultivars Robust, Stander, and Karl were included for FHB-susceptible comparisons whereas Chevron was included for FHB-resistant comparisons. Plots were planted in a randomized complete split(strip)-block design with three replications. Blocks were split with one half receiving inoculum and the other half being noninoculated. Plots were sprayed at heading and thereafter at five day intervals for a total of three applications. Applications of inoculum were made using a CO₂ backpack sprayer (40 psi/Teejet ss80015 spray tip). All locations were mist-irrigated following inoculation. Inoculum consisted of macroconidial suspensions (2 X 10⁵/ml) of three F. graminearum isolates obtained from locations in the Red River Valley of Minnesota during the summers of 1994 and 1995. Percentage FHB-severity was assessed approximately 20 days post-inoculation from the first spray application at each location. Grain yield and kernel weight were assessed following harvest. Gas chromatography/mass spectrometry analysis was used to determine deoxynivalenol concentration in parts-per-million (ppm) in grain samples as well.

There were significant differences among locations for mean FHB-severity (Table 1). Disease levels were highest at Morris, followed by Crookston and St. Paul respectively. Disease levels in inoculated split(strip)-block plots were higher than typically observed in producers fields. There was a significant location X genotype X inoculation interaction for all four variables discussed, thus, data were presented separately for each of the three locations (Table 1). Disease severity in noninoculated split(strip)-block plots at St. Paul were much lower than Morris and Crookston indicating that background levels of ascospore inoculum and wind-borne macroconidia were apparently much lower as well as St. Paul being a much drier location. Chevron exhibited good resistance to FHB at each of the three locations. Genotypes MNBrite (MNS 85) and MNS 93 were not as resistant as Chevron however they exhibited better resistance to FHB over locations than the other 9 experimental genotypes when evaluating their performance over the four variables (Table 1) as a whole. The high degree of concordance among genotype rank-correlations that were inoculated (Table 2) suggest that backpack inoculations with macroconidial inoculum provided a reliable inoculum for testing lines of barley for resistance to FHB. This may prove especially valuable in seasons where weather conditions do not favor ascospore development in residue or on colonized-seed inoculum. We intend to expand use of macroconidial inoculations to test promising barley genotypes for resistance to FHB in the future.

Breeding For Resistance to Fusarium Head Blight

The first variety to be released in response to the epidemic, MNBrite (tested as MNS 85), will become available to growers in 1999 following seed production in 1998. Justification for a comparatively early release was the improved resistance exhibited by MNBrite and the devastating FHB epidemic.

MNBrite was obtained from a breeding effort dating back to 1970 and continuing through 8 cycles of breeding. Selection in each cycle was for resistance to kernel infecting diseases. Chevron was the original source of resistance. Testing of MNBrite began in 1995, but extensive testing in off-station trials in Minnesota and in North and South Dakota was limited to 1997. MNBrite is a six rowed barley. Data from non-inoculated but replicated trials typical of what would be expected in grower fields indicate that MNBrite has less than one half as many infected kernels as Robust or Stander (Table 3). In inoculated trials with high scab severity levels, MNBrite again had about one-half as many infected kernels as the checks (Table 4). MNBrite kernels have reduced levels of deoxynivalenol compared to Robust and Stander. It appears that MNBrite will have reduced DON (ppm) by about one-half compared to the checks, however, DON is difficult to evaluate and more data are needed.
 

Table 1. 1997 Barley A-Screening Nursery: Mean comparisons of four check-cultivars and eleven genotypes for their reaction to Fusarium Head Blight (FHB). The test was conducted over three locations in Minnesota based on visual assessment of the percentage of kernels-per-spike exhibiting FHB symptoms in inoculated and noninoculated randomized complete split(strip)-block plots
Cultivar/genotype	St. Paul		Morris		Crookston
	inoc.	noninoc.	inoc.	noninoc.	inoc.	noninoc.
Robust	12.2	1.2	66.0	18.9	39.8	23.6
Stander	26.1	1.4	66.3	24.6	49.6	33.5
Chevron	2.2	0.2	15.7	2.1	16.9	5.9
Karl	25.4	5.0	72.9	24.5	50.8	31.1
MNS 85 (MNBrite)	9.8	0.8	19.5	6.6	30.2	16.0
MNS 93	7.8	0.3	37.1	4.2	26.0	9.5
SI 2-13	14.4	1.0	73.7	16.8	50.1	36.9
SI 2-26	16.3	1.3	71.3	18.4	40.5	16.6
SI 3-2	7.8	1.3	58.5	14.1	30.8	9.5
SI 3-6	13.9	1.8	72.1	16.7	30.0	12.1
SI 3-29	7.0	0.3	57.9	12.4	29.7	16.0
SI 4-4	12.8	0.6	65.1	18.3	30.9	16.2
SI 4-5	21.7	1.1	85.6	24.9	44.7	14.1
SI 4-29	13.7	1.9	67.2	21.4	34.7	16.9
M93-193	21.6	2.7	83.7	27.8	53.1	26.3
Mean	14.2	1.4	60.8	16.8	37.2	18.9
Standard Error	3.3	0.6	7.6	3.9	4.5	5.2

 
 

Table 2. 1997 Barley A-Screening Nursery: Spearman's rank correlations among four check cultivars and eleven genotypes as affected by Fusarium Head Blight. The test was conducted over three locations in Minnesota in inoculated and noninoculated randomized complete split(strip)-block plots
Variable location	St. Paul		Morris
	inoculated	noninoculated	inoculated	noninoculated
FHB severity
Morris	0.84**	0.72**
Crookston	0.87**	0.53*	0.81**	0.67**
* and ** represent significance at P=0.05 and 0.01 levels of probability, respectively

 
 

Table 3. Fusarium Head Blight severity (percentage of infected spikelets) for Robust, Stander, and MNBrite barleys in noninoculated nurseries in 1996 and 1997.
	1996 & 1997		1997		1997
	Minnesota		North Dakota		Canada
	Crookston	Stephen	Langdon #1	Langdon #2	Winnipeg	Mean (7 trial)
Robust	8	8	20	10	6	7.4
Stander	10	12	19	11	7	8.4
MNBrite	5	1	7	5	1	2.7

 
 

Table 4. Severity of Fusarium Head Blight (percentage of infected spikelets) for MNBrite, Robust, Stander, and Foster barleys in nurseries inoculated with F. graminearum. These cultivars were included in the 1997 MINNDAK nursery grown at Crookston, MN; St. Paul, MN; Fargo, ND; and Langdon, ND and in the 1997 A-Screening nursery which was conducted at three locations; St.Paul, Morris and Crookston, MN.
	MINNDAK	A-Screening Nursery
	(4 locations)	(3 locations)
Robust	20	39
Stander	29	47
Foster	20	-
MNBrite	12	20