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a Dep. of Agronomy and Plant Genetics, Univ. of Minnesota, St. Paul, MN 55108
b USDA-ARS, Cereal Disease Lab., Univ. of Minnesota, St. Paul, MN 55108
c Texas A&M Agric. Research Center, Amarillo, TX 79106
d USDA-ARS, National Small Grains Germplasm Research Facility, Aberdeen, ID 83210
* Corresponding author (yuejin{at}umn.edu).
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Abbreviations: DON, deoxynivalenol • FHB, Fusarium head blight • MR, moderately resistant • MS, moderately susceptible • NSGC, National Small Grains Collection • PDA, potato dextrose agar • R, resistant • S, susceptible • VR, very resistant • VSK, visual scabby kernel
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ACKNOWLEDGMENTS |
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NOTES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Received for publication February 28, 2007.
a Dep. of Agronomy and Plant Genetics, Univ. of Minnesota, St. Paul, MN 55108
b USDA-ARS, Cereal Disease Lab., Univ. of Minnesota, St. Paul, MN 55108
c Texas A&M Agric. Research Center, Amarillo, TX 79106
d USDA-ARS, National Small Grains Germplasm Research Facility, Aberdeen, ID 83210
* Corresponding author (yuejin{at}umn.edu).
Fusarium head blight (FHB; caused by Fusarium graminearum Schwabe) is one of the most destructive wheat (Triticum aestivum L.) diseases worldwide. Sources of FHB resistance are limited. The objectives of this study were to screen selected spring wheat accessions in the USDA National Small Grains Collection for FHB reactions using FHB index, visual scabby kernel (VSK), and deoxynivalenol (DON) content. A total of 1035 spring wheat accessions were initially screened in unreplicated field evaluation nurseries in 1998 and 1999. Accessions with low FHB were selected as putative resistant materials and were tested in replicated trials from 1999 to 2002. After three or more years of evaluation, 73 accessions with resistance were identified, including 10 accessions previously reported as resistant to FHB. Selections from Europe had the highest percentage of resistance to VSK, followed by selections from South America and Asia. We concluded that there is diversity for FHB resistance in wheat. Fusarium head blight resistance identified from Europe appeared to be unique in that these accessions normally displayed a moderate level of disease in the field, but a higher level of resistance based on VSK and DON. The discovery of diverse resistant sources will provide diversity so that higher levels of resistance could be developed. The novelty and types of FHB resistance in these selections should be further characterized using molecular markers and different inoculation techniques.
Abbreviations: DON, deoxynivalenol • FHB, Fusarium head blight • MR, moderately resistant • MS, moderately susceptible • NSGC, National Small Grains Collection • PDA, potato dextrose agar • R, resistant • S, susceptible • VR, very resistant • VSK, visual scabby kernel
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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A few sources of resistance to FHB have been identified in wheat previously. Reported sources of FHB resistance in spring wheat include a few landraces; ‘Sumai 3’ and its derivatives from China; ‘Nobeoka Bozu’ and ‘Sin Chunaga’ and its relatives from Japan; and ‘Frontana’ and ‘Encruzilhada’ from Brazil (Ban, 2000; Ban and Suenaga, 2000; Liu and Wang, 1991; Mesterhazy, 1987; Schroeder and Christensen, 1963; Yu et al., 2006). Winter wheat cultivars Arina, Renan, and Praag-8 with FHB resistance were reported in European wheat germplasm (Gervais et al., 2003; Ruckenbauer et al., 2001; Snijders, 1990). Fusarium head blight resistance in ‘Ernie’ and ‘2375’ may not be related to the aforementioned sources of resistance (Rudd et al., 2001), likely representing resistance from native U.S. germplasm. Novel FHB resistance was also postulated to be present in several recently released cultivars, including Truman (McKendry et al., 2005), Steele-ND (Mergoum et al., 2005), and Glenn (Mergoum et al., 2006). Sumai 3, including its derived lines, is the most widely used source of FHB resistance (Rudd et al., 2001). The resistance in Sumai 3 is partial, and cultivars with this resistance can sustain substantial damage from FHB when environmental conditions are conducive to the disease. Identification and characterization of additional sources of resistance is important for enhancing the level of resistance and for introducing genetic variation to the breeding materials.
The National Small Grains Collection (NSGC) maintains a large collection of common wheat and represents gene pools from all major wheat growing regions of the world. This worldwide collection of germplasm is a valuable gene pool for genetic improvement of modern wheat cultivars. The FHB resistance in this collection has not been assessed systematically. The objectives of this research were to assess the FHB reaction in selected spring wheat accessions in the NSGC and to identify and characterize FHB resistant germplasm based on measurements of FHB index, visual scabby kernel (VSK), and deoxynivalenol (DON) concentration.
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MATERIALS AND METHODS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Replicated FHB Evaluation Nursery
Heading date data collected from the nonreplicated screening nursery were used to group the FHB resistant selections into three maturity groups: early, intermediate, and late. The replicated FHB evaluation nursery was planted and managed in the same manner as described above. Maturity groups were planted into separate blocks and treated as separate experiments for nursery management and data analysis. Fusarium head blight resistant selections were planted with three replications in a randomized complete block design, and evaluated for at least three consecutive years. Selections initially made from the 1998 and 1999 nonreplicated FHB evaluation nursery were planted in replicated trials for four years (1999–2002) and three years (2000–2002), respectively.
Inoculum Preparations
To generate consistent and maximum disease pressure in the field, corn (Zea mays L.) kernels colonized with F. graminearum and conidial suspension of the fungus were applied in the FHB screening nurseries. The macroconidial inoculum consisted of 10 F. graminearum isolates isolated from infected wheat spikes collected in several wheat fields from eastern South Dakota in 1996 and 1997. These isolates, each derived from a single-spore culture, were selected from a collection of 30 isolates based on two criteria: producing abundant macroconidia when cultured on acidic potato dextrose agar (PDA) in petri plates and producing typical symptoms on the susceptible check cultivar Wheaton. After incubation for 7 d, agar of well-colonized plates was cut into 1-cm2 cubes and dried under a flow hood for 72 h. The dried fragments of cultures were stored in a sterile glass vial at –80°C as stock cultures. This method of culture maintenance reduces the need for frequent transfers. For mass production of conidia, pieces of the dried stock culture were plated onto modified acidic PDA medium (19.5 g potato dextrose, 10 g agar, 1 L water, 2.0 mL lactic acid after autoclaving). After 5 to 7 d of incubation at 23°C, 2 mL of sterile water was added to each culture plate and macroconidia and mycelial fragments were suspended using a hockey stick–shaped sterile glass rod. The culture suspension was transferred to new plates by streaking the suspension evenly onto new plates. Compared to transferring agar blocks, we observed that streaking suspension to cover the entire agar surface appeared to promote the production of macroconidia while suppressing mycelium growth. Macroconidia were harvested after 3 to 5 d incubation by flooding the plates with sterile water and gently rubbing culture surface with a sterile glass rod. The spore suspension was poured off and strained through two layers of sterile cheesecloth to remove hyphal fragments. Macroconidia could be harvested for a second time after an additional incubation period of 3 to 5 d after the first harvest as long as a strict sterile procedure is followed. Spore suspensions for equal numbers of petri plates of 10 isolates were mixed and adjusted to 70,000 conidia mL–1. The macroconidial inoculum suspension was prepared 2 to 4 h before field inoculation and maintained in an ice tray until use.
Stainless steel trays (53 cm long by 33 cm wide by 7 cm high) and 4.5-L milk jars were used to increase F. graminearum on corn kernels. About one-half (2.5–3.8 cm) of the stainless steel tray was filled with red or yellow dent corn. Then water was added until about three-quarters of the tray was filled with water and corn. The grain was soaked in the water for 18 to 24 h and excess water was drained. After washing the soaked corn with clean water, water was added until it was about 0.32 to 0.64 cm above the corn surface. The tray was covered with two layers of aluminum foil and autoclaved for 2 h. The tray was cooled at room temperature for about 5 h, drained if excessive water was present, and inoculated with two petri plates of a single isolate of F. graminearum. Then the tray covered with two layers of aluminum foil was incubated on a laboratory bench at 20 to 22°C. The tray was shaken vigorously every 24 h. Seven to ten days after inoculation, the corn kernels were fully colonized. The colonized corn kernels were dried on a greenhouse bench, and stored at 4°C for up to a month before field application. To increase colonized corn kernels in the milk jars, about one-third of the jar was filled with corn. After being soaked in water for 18 to 24 h, the corn was washed clean, and excess water was drained. Fresh water was added until about 0.32 to 0.64 cm above the corn surface. The milk jar was sealed with a cotton plug and autoclaved for 45 min. After the jar was cooled, one petri dish of F. graminearum culture was added into the jar and mixed evenly with the corn in a flow hood. The sealed milk jar was incubated at room temperature, and shaken every 24 h. Seven days after incubation in the milk jar, the corn was fully colonized and ready to be dried or used immediately in the field. Equal amount of F. graminearum colonized corn grains (corn spawn) measured by weight of each isolate was mixed and used for field inoculation.
Nursery Inoculation
Beginning at the jointing stage of the earliest maturing test entries, each row was inoculated with 7 to 8 g of corn spawn weekly for three consecutive weeks. To promote production of ascospores, the plots were daily mist-irrigated for 3 min with a 30-min recess between 2000 and 0800 hours. On hot and windy days, irrigation was extended to 5 min with a 30-min recess. Mist-irrigation was continued until the last disease recording. At the heading stage, each plot was marked with colored plastic tape so that the plot could be identified for inoculation and disease scoring at the appropriate time. The field was tagged three times a week. At the heading stage, each plot was spray-inoculated with approximately 40 mL of macroconidial suspension using a backpack sprayer. A second spray inoculation was applied 5 d later. All spray inoculations were conducted after 1900 hours when the environment was conducive for infection.
FHB Evaluation and Selection
Disease severity of each plot was rated by evaluating 20 randomly selected spikes 3 wk after the first spray inoculation. Fusarium head blight incidence was recorded as percentage of infected spikes of the 20 spikes used for the FHB severity assessment (i.e., incidence = 100 x number of nonzero spikes/20). The FHB index of each plot was derived by the product of average FHB severity and FHB incidence multiplied by 100. A preliminary selection for reduced kernel damage was made in the nonreplicated FHB evaluation nursery by tactile estimation of kernel filling, independent of FHB index. At the hard dough stage of plant development, each plot was assessed for kernel damage by repeatedly squeezing several handfuls of spikes throughout the plot. Because little kernel filling occurred in susceptible lines due to high and consistent disease pressure in the nursery, a seed set of moderate level could be identified regardless of visual disease symptoms. This method was particularly useful for identifying plants that were resistant to kernel damage but appeared to have high FHB index. Individual plots were also carefully inspected visually to identify individual plants or spikes that might be showing resistance among susceptible plants.
Entries or individual heads within an entry having a low FHB index and/or good seed set in the nonreplicated FHB evaluation nursery were harvested by hand. Selections of entire rows (row selections) were first threshed by a plot combine at minimum air pressure, then threshed and cleaned with a single head thresher at minimum air pressure. Heads selected within an entry (head selections) were bulked and threshed with a single head thresher at minimum air pressure. Single plants of low disease within an entry were selected as single plant selections. Percentage of VSK of each selection was recorded. Accessions with high VSK were discarded.
The replicated FHB evaluation nursery was hand harvested and immediately threshed with a plot combine at minimum air pressure in the field. Because a high proportion of diseased spikelets with chaffs were often retained in the initial threshing with the combine at a low air pressure, the field-threshed materials were threshed two to three times again at low air pressure using a single plant thresher to remove chaffs. Percentage of VSK of each entry was determined by counting 200 random seeds from each sample. A 15-g seed sample from each plot was analyzed for DON concentration. In 2000, the seed samples of some selections were tested by Dr. Paul Schwarz (Dep. of Plant Sciences, North Dakota State University, Fargo, ND). In 2001 and 2002, the seed samples were tested for DON concentration by Ms. Beth Tacke (Dep. of Veterinary Diagnostic Services, North Dakota State University, Fargo, ND). Each year, the lines with high FHB index and high DON levels were discarded. Final selections from the 2002 replicated FHB evaluation nursery constituted the final list of FHB resistant germplasm.
Data Presentation and Analysis
To simplify interpretation of the data, FHB index, VSK, and DON of the resistant selections were classified into five groups using the criteria presented in Table 2
. The criteria for the classification were based on the mean values and ranges of the four standard checks. Under moderate to low disease pressure, FHB levels of ND 2710 and BacUp are similar. Our nursery disease pressure was consistently high enough to differentiate the FHB levels between ND 2710 and BacUp. Therefore, accessions with less FHB than ND 2710 were grouped into the very resistant (VR) category. Measurements of FHB index, VSK, and DON of the test entries in each year were analyzed using GLM procedures of SAS 9.1 (SAS Institute, Inc., Cary, NC) by maturity group. To detect effects of year and year*entry in each maturity group, 3-yr data of the entries in the 2002 replicated screening nursery were used for analysis of variance.
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RESULTS |
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In 1998, 36 of the 424 accessions failed to germinate and provide at least five plants for FHB evaluation. In 1999, 352 of the 999 accessions failed to germinate or produced less than five plants for FHB evaluation. The complete dataset of the FHB index of the remaining 388 accessions evaluated in 1998, and 647 accessions evaluated in 1999 were submitted to the Germplasm Resources Information Network (http://www.ars-grin.gov/cgi-bin/npgs/html/desc.pl?65066). Those accessions displayed a wide range of FHB disease indices from highly resistant to highly susceptible (Fig. 1 ). In 1998, 11 accessions had FHB indices of 0 to 30%, and 156 accessions had disease indices more than 70%. In 1999, seven accessions had FHB indices of 0 to 30%, and 402 accessions had disease indices more than 70%. Accessions with low FHB index or good seed set were selected for evaluation of FHB reaction in the replicated trials in the following year. Based on the FHB index and our visual selection for seed set, 48 accessions were selected from the 1998 nonreplicated FHB evaluation nursery and 123 accessions from the 1999 nonreplicated evaluation nursery as putative sources of FHB resistant germplasm. We observed heterogeneous reactions to FHB in some of the accessions. The 1998 selections consisted of 32 head- or single-plant selections and the remainder was whole row selections. The 1999 selections consisted of head-selections from 78 accessions and the remainder was whole row selections. Those selections were planted in the replicated screening nursery in the following year.
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The susceptible checks Sonalika and Wheaton had the highest FHB index, VSK, and DON (Table 3 ). ND 2710 was more resistant than BacUp across the maturity groups and years (Table 3). ND 2710 had lower FHB indices and DON than BacUp in every maturity group and year, and lower VSK than BacUp in all the years except in 2002. During the 2002 FHB inoculation period daily temperatures were above normal and most of the days were windy. ND 2710 had very high percentage of discolored and plump kernels. The discoloration might have resulted from heat stress instead of direct damage by FHB. The VSK ratings in 2002 could be partly inflated due to heat stress in the disease nursery as indicated by a higher mean VSK in 2002 in each maturity group than the means in the other years (Table 3). This hypothesis is supported by the similar DON concentration of ND 2710 and many resistance selections in 2002 as in 2000 and 2001. Seventy-three accessions were selected as putative sources of FHB resistance after evaluations in replicated field trials in three to four consecutive years. Among these, FHB resistance in 10 accessions has been reported in previous studies. The 10 accessions of known FHB resistance were CItr 12470 (Frontana), PI 113948 (Kooperatorka), PI 132856 (Mentana), PI 182561 (Sin Chunaga), PI 182591 (Norin 61), PI 213833 (Funo), PI 382144 (Encruzilhada), PI 382153 (Nobeoka Bozu), PI 382154 (Nyu Bai), and PI 462151 (Shu Chou Wheat No. 3) (Tables 3 and 4 ) (Ban, 2000; Ban and Suenaga, 2000; Liu and Wang, 1991; Snijders, 1990). Because FHB resistance was first determined by disease index in the field, we ranked the resistance selections by FHB indices in each maturity group in Table 3. Most of the resistant selections had much lower FHB index, VSK frequency, and DON content than the susceptible checks Sonalika and Wheaton except Kooperatorka (late maturity) and two well-known FHB resistant lines, Frontana (late maturity) and Sin Chunaga (intermediate maturity). Thirty-six selections were head selections. The seed of the head selections were deposited in the NSGC with new accession numbers. For simplicity, we used the accession number and name of the original seed source throughout the report. Detailed selection type and new accession numbers for the head selections are presented in Table 4, including the origin, pedigree of the original seed source, maturity group, and the FHB reactions of the resistant selections.
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Accessions PI 584934, of intermediate maturity, and CItr 12470, PI 113948, and PI 113949, of late maturity, had FHB indices greater than 60% and were classified as S (Tables 3 and 4). PI 113948 (Kooperatorka) and CItr 12470 (Frontana) were as susceptible as the susceptible checks Sonalika and Wheaton (Table 3). Kooperatorka and Frontana have been reported to have lower FHB indices than Sumai 3 and Nobeoka Bozu (Snijders, 1990). In our disease nursery, the former two lines were consistently very susceptible as measured by FHB index. Their susceptibility in our nursery could be due to the seed source, or perhaps these lines responded differently in our testing environment.
FHB Resistance Measured by VSK
Mean VSK of the 73 FHB resistant selections ranged from 21 to 79% (Table 3). We classified 27 accessions as VR to R, 26 accessions as MR, 17 accessions as MS, and three accessions as S (Table 1). Accessions with VSK comparable to ND 2710 and rated VR were PI 382161 (Tokai 66), of early maturity; PI 104131 (Excelsior), PI 382153 (Nobeoka Bozu), and PI 382154 (Nyu Bai), of intermediate maturity; and PI 185380, PI 192660 (Prodigio Italiano) and PI 81791 (Sapporo Haru Komugi Jugo), of late maturity. Accessions with VSK within the range of BacUp and classified as R included six accessions of early maturity, six accessions of intermediate maturity, and six accessions of late maturity (Tables 3 and 4). The VSK measurements in the R class were stable and consistently low across years. Seven accessions, including PI 213833 (Funo) and CItr 12470 (Frontana), were classified as MS and had some of the highest values of VSK of 56 to 60% among the selections from this study. Field-based evaluation of VSK on Funo has not been reported. The VSK level of Frontana in our study was much higher than that reported by Mesterhazy et al. (2005). There were four accessions classified as S, including PI 182561 (Sin Chunaga), and two accessions derived from Sin Chunaga (PI 411132, Gogatsu-Komugi and PI 182586, Norin 43), and PI 182583 (Chuko) (Table 4). These four lines were rated as R to MR according to FHB index (Table 3). Seeds from those lines grown in the FHB nursery were frequently discolored and classified as MS to S. However, most of the discolored kernels were plump and light weight, and lacked the pink color that is characteristic of FHB damage. The discoloration of the seed was most likely due to frequent mist-irrigation and other environmental stresses during kernel development. This hypothesis was supported by relatively low DON on these lines (Table 3).
FHB Resistance Measured by DON Concentration
Average DON of the resistant selections ranged from 2.1 to 14.5 µg g–1 (Table 3), which was much lower than means of DON for the susceptible checks. We selected for FHB resistance primarily based on FHB index and VSK; DON was a secondary criterion. Lower DON in the FHB resistant selections suggested that selection based on head blight intensity and visible seed damage successfully selected for resistance to DON. Twenty-five accessions had DON levels in the VR to R classes, 39 had DON levels in the MR class, and only nine accessions had DON in the MS class (Table 1). The four accessions rated VR were PI 382161 (Tokai 66) and PI 382140 (Abura) in the early maturity group, and PI 382154 (Nyu Bai) and PI 382153 (Nobeoka Bozu) in the intermediate maturity group (Tables 3 and 4). The four VR accessions consistently had DON levels lower than that of ND 2710 in the three years of the replicated evaluation nursery (Table 3). Among the 21 accessions classified as R, PI 382167 and PI 264927 in the late maturity group had DON levels similar to ND 2710. Of the 43 accessions with DON levels classified as MR, PI 345731 and PI 351743, in the early maturity group, and PI 185380, PI 83729, PI 192219, and CItr 11215, in the late maturity group, had 8.3 to 8.5 µg g–1 DON, which was only 0.2 to 0.4 µg g–1 higher than BacUp (Table 3). Nine accessions were rated MS, including known resistant sources Frontana (CItr 12470), Mentana (PI 132856), and Funo (PI 213833). Mesterhazy et al. (2005) reported that Frontana had about 69 to 263% of the DON concentration of Nobeoka Bozu. In our study the DON level of Frontana was about seven times higher than that of Nobeoka Bozu. The higher level of DON of Frontana in our study could be due to differences in seed source or environment.
Correlation among FHB Index, VSK, and DON Concentration
Among the 73 selections, DON concentration was significantly correlated with FHB index (r = 0.40, P < 0.01) and VSK (r = 0.24, P < 0.05) (Table 5
); however, FHB index and VSK was not correlated. We believe a group of germplasm with relatively low FHB index but high VSK, represented by PI 182561 (Sin Chunaga), PI 182583 (Chuko), PI 182586 (Norin 43), and PI 41132 (Gogatsu-Komugi), contributed to the poor correlation between FHB index and VSK. For example, when these four lines were removed from the correlation analysis, the correlation between FHB index and VSK became significant (r = 0.33, P < 0.01), while the correlation coefficients between the other traits were similar to that when these lines were not removed. A positive correlation between FHB index and plant height (r = 0.22, P < 0.05) and a negative correlation between VSK and plant height (r = –0.66, P < 0.001) were observed. Although a wide range of maturity was observed, days-to-heading was not correlated with any of the FHB measurements, indicating that the disease pressure was consistent during the evaluation period.
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DISCUSSION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Out of the 1045 accessions of spring wheat from Asia, South America, and Europe evaluated in this study, 73 accessions were selected as putative FHB resistant sources. Among these, FHB resistance in 63 of the 73 accessions has not been reported previously. Resistant accessions were identified from all the geographic regions evaluated. Thirty-two resistant accessions were from four countries in South America, 26 accessions were from nine countries in Europe, and 15 accessions were from China and Japan (Table 1). Therefore, FHB resistance of European origin consisted of 36% of FHB resistant selections in this study. Most of the accessions from China and Japan had a VR to MR reaction based on FHB index. Only one European accession, PI 192660 (Prodigio Italiano), was classified as R based on FHB index, while the remaining European lines were MR to S. Selections classified as VR to R based on VSK consisted of 13 accessions from Europe, 10 accessions from South America, and four accessions from Asia. More selections from Europe fell in the groups VR to R based on VSK, compared to selections from South America and Asia. Low DON concentration was more common in selections from China and Japan than from Europe and South America. We believe that the European spring wheat FHB resistance gene pool appeared to be unique in that selected accessions were moderately resistant in the field and produced sound seed as measured by VSK and reduced DON contamination.
Among the 63 accessions of putative new FHB resistant sources, known FHB resistant cultivars Frontana and Shin Chunaga appeared in the pedigrees of seven accessions (Table 4), and 11 accessions were landraces. The landraces and modern breeding lines without known resistance in the pedigrees may represent new genes for resistance. For example, the two new Chinese resistant accessions, CItr 2492 and PI 57364, were landraces from Heilongjiang Province in northeastern China. Those lines might have FHB resistance different from that in modern cultivars represented by Sumai 3 and its relatives from the spring wheat regions in the middle and lower Yangtze River Valley and South China (Liu and Wang, 1991; Wan et al., 1997; Yu et al., 2006).
There was a wide range of FHB reaction in terms of FHB index, VSK, and DON. Accessions of the best FHB resistance were PI 382153 (Nobeoka Bozu), PI 382154 (Nyu Bai), and PI 382161(Tokai). Accession PI 382140 (Abura) was rated as R based on FHB index, MS based on VSK, but VR based on DON. Brazil was the seed source of PI 382161 and PI 382140 in NSGC. However, the names Tokai 66 and Abura suggest that they were originally from Japan and may have been introduced to Brazil (T. Ban, personal communication, 2006). Molecular marker data results suggest that the above four accessions might have the Sumai 3 FHB resistance gene Fhb1 on the chromosome 3BS (Liu and Anderson, 2003; S. Liu, personal communication, 2007). In our work these lines were more resistant to DON contamination than Sumai 3 and should be valuable for introducing a higher level of resistance to DON in wheat cultivars.
In our study, selections with low VSK were generally associated with low DON contaminations. Nine of the 27 accessions classified as VR to R based on VSK, nine were also classified as VR to R and 16 were classified as MR, based on DON. However, this was not always the case. PI 184512, PI 285933, and PI 81791 were classified R for VSK, but MS for DON accumulation. Resistance measured based on FHB index did not necessarily indicate resistance expressed as a low frequency of VSK. Significant correlation of index and VSK with DON indicated that selection based on field visual estimate and kernel appearance generally would result in lower DON levels, but the extent of DON reduction based on the index and VSK varies among genotypes. The discovery of potentially diverse FHB resistance sources of spring wheat germplasm in this study will provide diversity and may produce higher levels of resistance when different sources are combined in breeding. The diverse sources of resistance will also provide materials for studies of mechanisms of FHB resistance in wheat. The addition of European spring wheat germplasm for FHB resistance is encouraging for future discovery of resistance in nontraditional FHB resistance gene pools. The novelty and types of FHB resistance in these selections should be further characterized in the greenhouse by point inoculation and by haplotyping using closely linked and diagnostic molecular markers.
This research was conducted at South Dakota State University, Brookings, SD. We thank Regina Rudd, Terrence Hall, and Laurence Osborne for providing technical support. We acknowledge the enormous help of numerous graduate, undergraduate, and high school students who were associated with the Small Grains Pathology Project of the Plant Science Department at South Dakota State University during 1998 to 2002. We also thank Dr. Paul Schwarz, Dep. Plant Sciences, and Ms. Beth Tacke, Dep. of Veterinary Diagnostic Services, North Dakota State University, Fargo, ND, for determining the DON concentration of the seed samples. Finally we thank Dr. James A. Anderson at the University of Minnesota for his critical review and valuable suggestions of the manuscript. This material is based on work supported by the USDA under Agreement No 59-0790-9-045. This is a cooperative project with the U.S. Wheat & Barley Scab Initiative. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of USDA.
All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.
Received for publication February 28, 2007.
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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