Characterization Of Stripe Rust Resistance Biology Essay

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Stripe rust, caused by Puccinia striiformis Westend. f. sp. tritici Eriks. E. Henn., is an important foliar disease of wheat. It was first recognized in the Western U.S. in 1915 (Carleton 1915). However, its presence was traced back at least 23 years prior by examination of herbarium specimens (Humphrey at al. 1924). The disease did not appear east of the Rocky Mountains until 1941 when it was found in Texas (Humphrey et al. 1941). The disease spread further north into the Great Plains in the late 1950s, however no yield losses were reported east of the Rocky Mountains until the 1980s and 1990s when occasional yield losses were reported in Texas, Louisiana, and Arkansas (Line 2002). A total of 59 races of stripe rust were identified before 2000, with the predominate race east of the Rocky Mountains being PST-3 (Chen 2005).

Race identification in the U.S. is conducted on a set of 20 differential lines in growth chambers programmed to gradually change from a low of 2 to 5°C to a high of 18 to 20°C with a 16-h photoperiod (Chen 2000). Infection types are recorded 20 to 22 days after inoculation using the 0 to 9 infection type scale for stripe rust (Line and Qayuom 1991). Avirulence is determined by a score from 0 to 4, and virulence by a score of 5 to 9 (Chen 2000).

Between 2000 and 2004, stripe rust epidemics occurred in the Great Plains and South Central U.S. causing yield losses from 3% to 10% in states such as Arkansas, Kansas, Nebraska, and Colorado (Chen 2005). These epidemics were caused by new a new strain of stripe rust (Markell & Milus 2008). Within this strain, races had virulence on Yr9, a common resistance gene in winter wheat (Chen et al. 2002). Isolates were also more aggressive as they had shorter latent periods, produced larger lesions, more spores, and tolerated warmer temperatures better than previous isolates (Milus et al. 2006, Milus et al. 2009). Since 2000, more than 60 races of stripe rust have been identified, with the predominate race east of the Rocky Mountains for approximately 10 years being PST-78 (Wan et al. 2012). The pathogen has continued to evolve, becoming virulent on more resistance genes, making the disease increasingly important where wheat is grown (Chen 2007).

Planting resistant cultivars is the most economical and effective way to manage stripe rust (Line and Chen 1995). There are two major types of resistance, all-stage resistance and adult plant resistance (APR). All-stage resistance can be detected from the seedling stage through all stages of plant growth and confers a high level of resistance across diverse environments (Qayoum and Line 1985). However all-stage resistance is race specific and usually overcome by new races (Chen 2005). With APR, seedlings are susceptible, resistance increases with maturity, and the level of resistance can be affected by environmental conditions (Qayoum and Line 1985). For example high-temperature adult plant resistance (HTAP) is only expressed with high temperatures. APR can be race specific or non-specific (McIntosh et al. 1995). HTAP appears to be durable, race non-specific, and present in several cultivars from the Pacific Northwest (Qayoum and Line 1985).

Molecular markers are available for the identification of certain stripe rust resistant genes, but only markers for Yr9, Yr17, and Yr18 are believed to be diagnostic. A rye-specific SSR (simple sequence repeat marker) located on the chromosome arm 1RS is available for the race specific, all stage resistance gene Yr9 that was translocated from rye (Secale cereale) at the 1BL.1RS translocation (Saal and Wricke 1999). A PCR marker using a pair of primers is available for the detection of Yr17 (Helguera et al. 2003). For the detection of the APR gene Yr18 an STS (sequence-tagged site) marker (Lagudah et al. 2006), and a gene-specific marker are available (Lagudah et al. 2009).

The resistance gene Yr17 is classified as a race-specific, all-stage resistance gene (Bariana & McIntosh, 1993). It is located on the 2NS/2AS translocation from Triticum ventricosum and is closely linked or plieotropic with the stem and leaf rust resistance genes Sr38 and Lr37, respectively (McIntosh et al. 1995). The gene was shown to be the only effective all-stage resistance gene against stripe rust east of the Rocky Mountains (Sthapit 2012). However expression of resistance was shown to vary with genetic background and environmental conditions. Bariana and McIntosh (1994) found that when inoculated with avirulent isolates, wheat lines with Yr17 produced susceptible responses at 10°C under low light intensity and resistant responses at 18°C under high light intensity. Also, the resistant infection type associated with Yr17 has also been shown to change over time. Sthapit (2012) found that when lines with Yr17 were inoculated with race PST-78 the resistant infection type (IT) 14 days after inoculation (dai) developed into a susceptible IT 19 dai. In the U.S. virulence on Yr17 was first identified as race PST-45 in 1990. Yr17 virulence became more prevalent in 2002 in the Western U.S. (X. Chen, 2005). In 2008 Yr17 virulence was reported in Mexico (X. Chen, 2012) and it appeared in the Southeastern U.S. in 2010.

The objectives of this study were to determine how to best identify Yr17 resistance in wheat seedlings and avirulence/virulence to Yr17 in pathogen isolates and to determine the level of adult plant resistance in wheat lines with Yr17.

Materials and Methods

Twenty-four wheat lines believed to have Yr17 and three susceptible checks were selected for this study(tables 1 and 2). Lines represented those grown in both the Southeastern U.S. and the Great Plains.

To determine the presence of the stripe rust resistance genes for which there are molecular markers that are believed to be diagnostic, leaf samples from five seedlings of each of the lines were collected, stored in 1.1 ml micro tubes with silica gel, and shipped to the USDA-ARS Eastern Regional Small Grains Genotyping Lab at Raleigh, NC, where molecular markers were used for assessment of the presence of Yr9, Yr17, and Yr18. A rye-specific SSR marker (Xscm9) located on the 1RS chromosome of rye (Saal and Wricke 1999) was used to determine the presence of Yr9. A linked marker was assayed with primers (VENTRIUP-LN2) to amplify the N-allele of the Xcmwg682 RFLP marker for the detection of Yr17 (Helguera et al. 2003). The STS marker csLV34 (Lagudah et al. 2006), and the co-dominate marker cssfr5 derived directly from the Yr18 sequence (Lagudah et al. 2009) was used for detection of Yr18.

Four single-lesion isolates of P. striiformis f. sp. tritici were used in this study. Isolate AR90-01 (race PST-3 and avirulent on Yr17) is representative of the population east of the Rocky Mountains before 2000. Isolate AR00-05 (race PST-78 and avirulent on Yr17) and representative of the population east of the Rocky Mountains from 2000 to 2009. Isolate AR10-04 (race PSTv-37 and virulent on Yr17), and representative of the Yr17 virulent population east of the Rocky Mountains since 2010. The type isolate of race PST-127, is virulent on Yr17, and representative of the Yr17-virulent population in the western U.S.

Urediniospores were increased on seedlings of cultivar Florida 302. Approximately 20 to 25 seeds were planted in 8-cm-square pots filled with potting mix (six parts peat moss, four parts vermiculite, two parts perlite, three parts Roxana silt loam soil, and three parts sand). Seedlings were grown in a greenhouse (approximately 24/15°C, day/night and 14-h photoperiod) and fertilized on 7-d intervals after emergence with Peters 20-20-20 NPK fertilizer (1 g L-1). To stop further leaf production and increase sporulation, seedlings were treated with 20 ml per pot of a 0.33 g L-1 solution of 3,6 dihydroxypyridazine (a form of maleic hydrazide, Aldrich Chemical Company, Inc., Milwaukee, WI) when the second leaves were approximately 3 cm long. Approximately 2 to 3 days later plants were inoculated with urediniospores suspended in Solrol 170 mineral oil (Chevron-Phillips Chemical Company, Houston,TX). After the oil dried from the leaves, seedlings were placed in a dew chamber at 12°C for approximately 24 h and then transferred to a growth chamber programmed to gradually change from 10 to 18°C with a 14-h photoperiod. To prevent cross contamination among isolates and collect spores, plants in each pot were covered with a cellophane bag when the first symptoms of infection were evident (approximately 10 days after inoculation (dai)). Urediniospores were collected several times within 14 to 28 dai. After urediniospores completed atleast two reproductive cycles, only freshly collected spores were used in experiments. Extra spores were dried over night in desiccators at 5°C and stored at -80°C for future use.

To determine how to best identify Yr17 resistance in wheat seedlings and avirulence/virulence to Yr17 in pathogen isolates, the 24 wheat lines were inoculated with the four isolates of Puccinia striiformis f. sp. tritici and incubated at three temperatures. Lines were planted in 8-cm-square pots filled with potting mix with four lines per pot and approximately six plants per line. When the second leaves reached 5 to 7 cm in length, plants were inoculated with urediniospores of each isolate (1 g ml-1). Two replications of each line-race combination were incubated in growth chambers at constant 10°C, constant 18°C (Bariana and McIntosh 1994), and a gradually changing regime from 5 to 18°C (Chen 2000) with 16-h photoperiods. Infection types were recorded on the second leaves at approximately 17, 20, and 23 dai for lines incubated at a constant 10°C regime and 14, 17, and 20 dai for lines incubated at the 5-18°C gradually changing temperature regime, and the constant 18°C regime, based on the 0 to 9 infection type scale for stripe rust(table 3) (Line and Qayuom 1991). The experiment was replicated 5 times. Data from seedling experiments was analyzed as the percentage of virulent ITs (IT ≥5) across all lines for each of the four races and three temperature regimes for all three data collecting dates for all five experiments.

To determine the level of APR in the field, the 24 wheat lines were planted at 4 locations in October of 2010 and 2011. Seed was treated with imidaclorprid (Gaucho 600 Flowable, Bayer Crop Science) at 2.27 g a.i. kg-1 seed to control aphids and barley yellow dwarf and with difenoconazole plus mefenoxam fungicides (Dividend Extreme, Syngenta Crop Protection Inc.) at 0.16 g a.i. kg-1 seed to control loose smut and Stagonospora blotch. Recommended herbicides and insecticides were used as needed to control weeds and aphids, respectively. At each location the experimental design was a randomized complete block with six replications. Individual plots were 1 m long on 30-cm centers, and were drilled at a rate of approximately 3 g of seed per plot. At each location infection types and the percentage of leaf area diseased were recorded twice between GS 10.5 and 11.1. Infection types were recorded using the previously stated scale and percentage of leaf area diseased was recorded using the following percentages and ranges 0, 2 (trace- 4), 7 (5-10), 15 (11-20), 30 (21-40), 50 (41-60), 70 (61-80), 85 (81-90), 93 (91-96) and 98 (>96). If more than one infection type was observed on an individual plot, infection type was recorded as a range with the predominate IT first. At each location the predominate infection type was considered the predominate IT among the six replications of each line. The percentage of leaf area diseased for all locations was analyzed as a randomized complete block using Proc GLM, SAS version 9.1.3 (SAS Institute, Cary, NC, USA). Means were separated using least significant difference (LSD) tests at P=0.05, based on analysis of variance.

To compare reactions of Yr17 virulent and Yr17 avirulent isolates, two fields were planted approximately 500 m apart at the Arkansas Agriculture Research and Extension Center in Fayetteville, AR. When lines reached Feekes GS8 (jointing) lines in one field were inoculated with AR00-05 (avirulent on Yr17) and lines in the other field with AR10-04 (virulent on Yr17). A backpack mist blower was used to apply urediniospores suspended in Soltrol 170 mineral oil (1 mg ml-1). Overhead irrigation was used to promote dew for infection.

To determine the reaction to stripe rust under natural conditions, the 24 lines were planted at the Newport Research Station at Newport, AR and the Vegetable Research Station at Kibler, AR. Infection type and percentage of leaf area diseased were recorded beginning at heading stage using the previously described scales. To determine which races were present at these locations, one leaf with a single stripe rust lesion was collected from a susceptible check in each of the six replications. Spores were collected using a small vacuum spore collector and increased as previously described. Pathogen race was determined on the U.S. standard set of 20 differentials in growth chambers programmed to gradually change from a low of 2 to 5°C to a high of 18 to 20°C with a 16-h photoperiod.

To evaluate APR under controlled conditions, 16 of the 24 lines were selected based on their range of resistance among field locations in 2011. Lines were inoculated at heading, when expression of adult plant resistance should be high, with two Yr17-virulent isolates (AR10-04 and PST-127) and incubated at a gradually changing temperature regiment. Seeds of the 16 lines were germinated on germination paper and one vigorous seedling was transfered per cone to plastic cones (410cc D25L Deepots, Stew and Sons Inc. Corvalis,OR) filled with potting mix. After emergence plants were vernalized in a growth chamber for 8 wk programmed to change from 5 to 8°C with a 12-h photoperiod, followed by 1 to 3 wk at 8 to 12°C depending on the maturity of the line. Plants were then moved to the greenhouse (approximately 24/15°C, day/night and 14-h photoperiod), fertilized with Peters 20-20-20 fertilizer 1 g L-1, soluble trace element mix (8 mg a.i./cone, The Scotts Company LLC, Marysville, OH), and osmocote 14-14-14 slow release NPK fertilizer ( 3 g/cone, The Scotts Company LLC, Marysville, OH). To control aphids and thrips, plants were treated with imidacloprid insecticide (0.63 mg a.i./cone, Marathon II, Olympic Horticulture Products Co., Mainland, PA) after vernalization and every 3 wk until inoculation. To synchronize maturity among plants of the 16 lines the first plants to reach early boot stage were moved to a growth chamber programmed to gradually change from 10 to 15°C with a 14 hr photoperiod, to slow development. Plants in the chamber were returned to the greenhouse at least 48 h before inoculation. At heading stage (spikes emerging from sheath), flag leaves on three plants of each line were inoculated with PSTv-37, and flag leaves on the other three plants of each line were inoculated with race PST-127. Inoculations were done using an atomizer (Sunrise Medical HHG Inc., Somerset, PA) with spores mixed with talc powder (30 mg g-1) After approximately 24 h in a dew chamber at 12°C, plants were kept in a growth chamber programmed to gradually change from 10 to 18°C with a 14-h photoperiod. The infection type and percentage of leaf area diseased was recorded 14, 17, and 20 dai using the scales described previously. The experiment was done twice and the experimental design was a full factorial with 16 lines, two isolates, one temperature, and three replications. The percentage of flag leaf area diseased was used with the three collection dates to calculate area under disease progress curve. Area under disease progress curve data was analyzed using Proc GLM, SAS version 9.1.3 as a completely randomized factorial design (2 races x 16 lines) with three replications per treatment combination. Race and line were fixed effects, and experimental run was a random effect. The area under disease progress could not be calculated for two race x replication combinations due to premature plant death so least square means were compared using a proteted LSD at P=0.05

Results

Marker Analysis

Molecular marker assays revealed all 24 lines have the stripe rust resistance gene Yr17 (table.). Two were heterozygous, VA06HRW108 and VA08HRW-98, Yr17 was detected in four and two of the five samples, respectively. Only one line, HV9W04-1594R also had the stripe rust resistance gene Yr9. None of the lines had the APR gene Yr18.

Seedling Tests

Susceptible checks (Croplan Genetics 514W, Croplan Genetics 554W, and FL302) always had high infection types for all races at all incubation temperatures. The 21lines with Yr17 used in all 5 runs of the experiment had varied responses to the four races at the three temperatures (table 4 and 5.). At 5-18°C, a temperature regime commonly used for seedling tests to determine resistance for wheat lines and virulence for pathogen isolates, both races virulent on Yr17 were similar, and the percentage of ITs classified as virulent increased from 14 dai to 20 dai but never reached 100%. Of the races avirulent on Yr17, PST-3 rarely produced virulent ITs, but PST-78 had an increasingly greater percentage of virulent ITs with time and reached approximately 39% total virulent Its 20 dai. At 10°C, the percentage of virulent Its for both races virulent on Yr17 increased from 17 to 23 dai and reached almost 100% virulent Its 23 dai. Of the avirulent races, PST-3 increased from 10% to 39% total virulent ITs over time, and PST-78 increased from 35% to 69% total virulent ITs over time. At 18°C three lines, HV9W06-509R, NC05-19896, TAM 401 consistently produced resistant ITs (IT≤4) to the Yr17-virulent isolate AR10-04 at all times, and two lines, SS8641 and TAM 203 consistantly produced resistant ITs to the Yr17-virulent race PST-127, resulting in a lower total percentage of virulent ITs for virulent races at 18°C. The total percentage of virulent ITs at 18°C increased from 66 to 77% total virulent ITs over time. Of the avirulent races, PST-3 had no virulent ITs, and PST-78 had <10% total virulent ITs. When the percentages of ITs virulent for the four races at 20 dai were compared across the three temperatures, all races had the highest percentage of virulent ITs at 10°C and the least percentage of virulent ITs at 18°C. The two virulent races decreased from close to 100% total virulent ITs at 10°C to 77% total virulent ITs at 18°C. Of the avirulent isolates, PST-78 decreased from 69% total virulent ITs at 10°C to 10% total virulent ITs at 18°C, and PST-3 decreased from 26% total virulent ITs at 10°C to no virulent ITs at 18°C.

Field and growth chamber results indicate that Jagger may be the only line without an allele or gene for race specific APR. Of the five experimental runs it was included in three with Yr17 isolines from both the thatcher (Lr37) and avocet (AvsYr17NIL) backgrounds. At 10°C, 23 dai, Jagger had virulent ITs 33% of the time to PST-3, while Lr37 and AvsYr17NIL never produced a virulent IT, while PST-78 resulted in no virulent ITs on AvsYr17NIL and 75 and 80% total virulent ITs on Jagger and Lr37. Isolate AR10-04 and PST-127 resulted in 100% virulent ITs on Jagger and Lr37, with AvsYr17NIL producing only 17% total virulent ITs to AR10-04 and 100% total virulent ITs to PST-127. At 5-18°C 20 dai PST-3 resulted in no virulent ITs on the three lines with only Yr17, PST-78 resulted in 33, 17 and 0 % for Jagger, AvsYr17NIL, and Lr37, respectively. Jagger and Lr37 had 100% total virulent ITs to AR10-04, while AvsYR17NIL had no total virulent ITs. Jagger and Lr37 had the same results to PST127 while AvsYR17NIL had 50% total virulent ITS. At 18°C 20 dai PST-3 and PST-78 had no virulent ITs on all three lines. AvsYR17NIL had no virulent ITs to AR10-04 and PST-127 while Jagger and Lr37 had 67,100 and 100, 75%total virulent ITs, to AR10-04 and PST-127 respectively (table 6 and 7.

Field Resistance

The ITs on the susceptible checks (Croplan Genetics 514W, Croplan Genetics 554W, and FL302) were high (IT 8) for both the Yr17 virulent race PST-78, and the Yr17 virulent race PSTv-37 in 2011 and 2012. The ITs were also high on the susceptible checks under natural stripe rust conditions at Kibler, AR in 2011 and 2012. At Fayetteville, AR in 2011 race PST-78 caused virtually no symptoms or disease on lines with Yr17, indicating Yr17 provides a high level of resistance to PST-78 at adult plant stages. Analysis of the percentage of flag leaf area diseased, based on least significant differences (P=0.05) shown that Croplan genetics 554W and FL302 had significantly less leaf area diseased (12.3 to 12.7%) when compared to Croplan Genetics 554W (46%), all lines with Yr17 had no leaf area diseased, meaning they are significantly more resistant than the susceptible checks (table 9). In 2012, the field inoculated race PST-78 was infected with the Yr17 virulent race PSTv-37 from a breeding nursery that was inoculated early in the growing season. The ITs from lines in 2011 and 2012 inoculated with PSTv-37 at Fayetteville, AR were similar, even when natural infection occurred in the field inoculated with race PST-78. Ten lines, 26R87,Jagger, SS8641, VA07W-415, VA07W-429, HV9W04-1594R, LA821, VA06HRW108, and LA01139D-56-1-C were highly susceptible (IT 7-8) to race PSTv-37. Five lines, AGS2060, Fuller, NEO5426, NEO6545, and Overly were moderately susceptible (IT 5-6). Nine lines, AGS2026, TAM401, HV9W03-1596R, HV9W05-1125R, LA841, HV9W06-509R, NC05-19896, TAM203, and VA08HRW-98 were resistant (IT 0-3), indicating the presence of at least one gene or allele conveying APR against race PSTv-37. Three of these lines, HV9W06-509R, NC05-19896, TAM 401 expressed resistance to PSTv-37 at 18°C in seedling tests. Analysis of the percentage of flag leaf area diseased, based on least significant differences (P=0.05) shown that Croplan genetics 554W and FL302 had significantly less leaf area diseased when compared to Croplan Genetics 554W. The Lines VA07W-415W and HV9W04-1594R, while having significantly less leaf are diseased than CG514W, had significantly more leaf area diseased than other lines with Yr17. The ITs from lines planted at Kibler, AR in 2011 and 2012 for stripe rust under natural conditions was similar to ITs from PSTv-37 on inoculated lines in Fayetteville, AR (table 10). The same nine lines produced all resistant ITs, lines susceptible or moderately susceptible to PSTv-37, were also susceptible or moderately susceptible at Kibler, AR, except LA821 produced a moderately susceptible IT, and Fuller and NEO6545 produced susceptible ITs, suggesting a possible difference in races due to race specific APR. Analysis of the percentage of flag leaf area diseased, based on least significant differences (P=0.05) was similar to results from field data for race PSTv-37, making it likely that VA07W-415 and HV9W04-1594R do not have other genes for stripe rust resistance. Stripe rust data was unable to be collected at Newport, AR for both years due to low levels of the pathogen.

Resistance at heading

The susceptible check, Croplan Genetics 514W, was highly susceptible to both PSTv-37 and PST-127 (IT 8-9). The cultivar Jagger was also highly susceptible to both races, indicating it is likely to only have Yr17. Ten lines, VA07W-415, HV9W04-1594R, VA08MAS412, VAHRW108, SS8641, LA01139D-56-1-C, LA821, NEO5426, HV9W03-1596R, and HV9W05-1125R were susceptible to PSTv37 (IT 6-9), but resistant to PST-127 (ITs 2, 2-5). Indicating these lines have race specific resistance to PST-127. SS8641 also expressed resistance to PST-127 at 18°C in seedling tests. AGS2060 gave mixed results in that it was susceptible to both races in run one and resistant to both races in run 2. Three lines, TAM401, AGS2026, and NEO6545 were resistant to both races (ITs 2, 2-4) (table 12).

Statistical analysis of area under disease progress curve showed that there was a significant race x line(P=<0.0001) interaction. The susceptible check, Croplan Genetics 514W had high AUDPC values for both races (471 and 578 for races PST-127 and PSTv-37, respectively). There was also no significant differences in AUDPC for the cultivar Jagger (408 and 450 for PSTv-37 and PST127, respectively). Of the ten lines that had susceptible ITs to PSTv-37 and resistant ITs to PST127, eight lines, VA07W-415, HV9W04-1594R, VA08MAS412, VAHRW108, SS8641, LA821, HV9W03-1596R, and HV9W05-1125R had significantly lower AUDPC to race PST-127 than PSTv-37, indicating race specific resistance. The two other lines, LA01139D-56-1-C and NEO5426 that indicated race specific resistance to PST-127 based on ITs, had no significant difference in AUDPC between the two races. The three lines, TAM 401, AGS2026, and NE06545 resistant to both races based on ITs also had no significant difference in AUDCP between races.

Discussion

The resistance gene Yr17 is difficult to accurately phenotype to virulent and avirulent isolates in the seedling stage. Incorrect ITs based upon race classification for virulence on Yr17 was random and not specific to certain lines for the exception of those lines that expressed resistant ITs when incubated at 18°C to PSTv-37 or PST-137. A study by Sthapit et. Al published in 2012 also found that although marker data revealed presence of Yr17 in lines, phenotyping these lines for resistance to the avirulent race PST-78 was not accurate across all lines. Results from this study found 18°C provided the most accurate phenotyping for avirulent races in seedling tests. However, at this temperature phenotypes for virulent isolates was not completely accurate. This could be due to lines expressing APR at the seedling stage, as was the case for a few lines used in this study, or it could be due to a temperature effect on races of P. striiformis. Since Yr17 was unable to be accurately phenotyped to avirulent isolates when incubated at three temperatures at the seedling stage, but was highly resistant in the field it may be more accurately classified as a gene for Adult plant resistance. As all-stage resistance genes are typically stable across environments and genes for APR can have varying resistance across environments. Also the pleitropic gene for leaf rust resistance, Lr37 is classified as a gene for APR making it likely that the Yr17 stripe rust resistance gene is also a gene for APR (McIntosh et. Al 1995). The Yr17 isoline Lr37 in the thatcher background more closely matched the results at the seedling stage of the lines with Yr17 used in this study. It appears that AvsYR17NIL, used in race ID, has some other gene present as it produced resistant ITs to PSTv-37 at 10, 5-18, and 18°C, and produced resistant ITs to PST-127 at 5-18 and 18°C.

Results from inoculated and naturally infected fields show that cultivars and lines with Yr17 East of the Rocky Mountains, still have some resistance, with some being highly resistant to PSTv-37. It is likely this resistance is race specific APR, as when lines were inoculated with PSTv-37, and PST-127, only Jagger was susceptible to both, the others had some form of race specific resistance conveying resistance to PST-127. Since stripe rust epidemics usually occur in in the spring East of the Rocky Mountains, there would be benefit to classifying races based upon reactions on adult plants versus seedlings as currently used. The results of this study show AUDPC can be used in conjunction with infection types to classify race specific resistance.

Table 1. Pedigree for 14 soft red winter wheat lines used in this study.

Line

Pedigree

26R87

Avalon/3/VPM/Moisson//Champlein/Aronde/4/Ck6815*3/CI14115/5/Ck6815*3//McNair1813/Ck 797/6/252

AGS2026

GA881130/Coker 9134

AGS2060

FL302/FR81-19,85430-D17-2-P1//CK9663

Croplan Genetics 514W

Croplan Genetics 554W

FL302

McNair1813/Ck 797/6/252

LA01139D-56-1-C

LA841/LA422//PIO26R61

LA821

AGS2060/LA95209BUB45-2(MV17/PIO2684/3/CK9904/PIO2548//C9877)

LA841

GA8665/FL85238-C3-AB3

NC05-19896

Bur/NC96BGTA6sib//Natchez

SS8641

GA881130/2*GA881582

VA07W-415

VA98W-895/GA881130LE5//VA98W-627

VA07W-429

VA08MAS-412

Table 2. Pedigree for 13 hard red winter wheat lines used in this study

Line

Pedigree

NE05426

NE06545

TAM 401

TAM 203

HV9W06-509R

HV9W05-1125

HV9W03-1596R

HV9W04-1594R

VA06HRW108

HEYNE (KS85W633-11-6-42) / RENWOOD 3260 (VA96-54-326= SC861562/CK9803) // 92PIN#135,F10

VA08HRW-98

KS01HW54(94HW123-5/BTY SIB) / PROVINCIALE,F8

Jagger

Overley

Fuller

Table 3. Infection types of wheat stripe rust caused by Puccinia striiformis West. accoring to Line and Qayoum (1991).

Infection Type

Signs and symptoms

0

No visible signs or symptoms

1

Necrotic and/or chlorotic flecks; no sporulation

2

Necrotic and/or chlorotic blotches or stripes; no sporulation

3

Necrotic and/or chlorotic blotches or stripes; trace sporulation

4

Necrotic and/or chlorotic blotches or stripes; light sporulation

5

Necrotic and/or chlorotic blotches or stripes; intermediate sporulation

6

Necrotic and/or chlorotic blotches or stripes; moderate sporulation

7

Necrotic and/or chlorotic blotches or stripes; abundant sporulation

8

Chlorosi behind sporulating area; abundant sporulation

9

No necrosis or chlorosis; abundant sporulation

Table 4. The percentage of virulent infection types (IT ≥5) observed for 21 wheat lines with Yr17 when inoculated with two Yr17 avirulent isolates across two replications, for 5 experimental runs, for three incubation regiments at three times post inoculation.

Percentage of virulent ITs

Race

Temperature

Days after inoculation

Exp1

Exp2

Exp3

Exp4

Exp5

Mean

PST-3

10° C

17

2

.

0

7

26

10

20

14

.

5

31

52

26

23

29

.

14

55

58

39

5-18° C

14

0

0

0

0

0

0

17

0

0

0

2

12

3

20

2

10

0

5

12

6

18° C

14

0

0

0

0

0

0

17

0

0

0

0

0

0

20

0

0

0

0

0

0

PST-78

10° C

17

39

.

28

26

46

35

20

78

.

56

41

74

62

23

80

.

65

56

74

69

5-18° C

14

5

26

0

0

12

9

17

29

50

42

13

37

34

20

40

48

43

19

47

39

18° C

14

2

15

5

5

10

7

17

5

20

0

10

15

10

20

0

22

2

10

14

10

Table 5. The percentage of virulent infection types (IT ≥5) observed for 3 wheat lines with Yr17 when inoculated with two Yr17 virulent isolates across two replications, for 3 experimental runs, for three incubation regiments at the last post inoculation date.

Percentage of virulent ITs

Race

Temperature

Days after inoculation

Exp1

Exp2

Exp3

Exp4

Exp5

Mean

AR10-04

10° C

17

77

.

57

34

71

60

20

92

.

82

87

95

89

23

100

.

82

100

98

95

5-18° C

14

40

69

63

42

66

56

17

81

85

87

83

88

85

20

83

85

95

77

95

87

18° C

14

37

73

69

50

78

61

17

54

78

73

65

80

70

20

71

78

85

75

79

78

PST-127

10° C

17

87

.

88

55

100

83

20

90

.

97

79

100

92

23

90

.

97

87

100

94

5-18° C

14

55

38

47

43

82

53

17

88

69

88

65

98

82

20

93

80

95

67

98

87

18° C

14

45

86

87

40

90

70

17

50

89

82

52

90

73

20

57

89

86

55

90

75

Table 6. The percentage of virulent infection types (IT ≥5) observed for Jagger or 2 Yr17 isolines when inoculated with two Yr17 avirulent isolates across two replications, for 3 experimental runs, for three incubation regiments at 23 dai for 10°C and 20 dai for 5-18 and 18°C.

Race

Temperature

Line

Percent Virulent ITs

PST-3

10° C

Jagger

33

AvsYr17NIL

0

Lr37

0

5-18° C

Jagger

0

AvsYr17NIL

0

Lr37

0

18° C

Jagger

0

AvsYr17NIL

0

Lr37

0

PST-78

10° C

Jagger

75

AvsYr17NIL

0

Lr37

80

5-18° C

Jagger

33

AvsYr17NIL

17

Lr37

0

18° C

Jagger

0

AvsYr17NIL

0

Lr37

0

Table 7. The percentage of virulent infection types (IT ≥5) observed for Jagger or 2 Yr17 isolines when inoculated with two Yr17 virulent isolates across two replications, for 3 experimental runs, for three incubation regiments at 23 dai for 10°C and 20 dai for 5-18 and 18°C.

Race

Temperature

Line

Percent Virulent ITs

AR10-04

10° C

Jagger

100

AvsYr17NIL

17

Lr37

100

5-18° C

Jagger

100

AvsYr17NIL

0

Lr37

100

18° C

Jagger

67

AvsYr17NIL

0

Lr37

100

PST-127

10° C

Jagger

100

AvsYr17NIL

100

Lr37

100

5-18° C

Jagger

100

AvsYr17NIL

50

Lr37

100

18° C

Jagger

100

AvsYr17NIL

0

Lr37

75

Table 8. Results of statistical analysis for main effects for percent leaf area diseased with stripe rust at inoculated fields in Fayetteville, AR and fields under natural stripe rust pressure at Kibler, AR

Probability >F

Location/Year

Race

Effect

Percent Leaf Area Diseased

Fayetteville, AR

PST-78

Rep

0.1417

2011

Line

<0.0001

Fayetteville, AR

PSTv-37

Rep

0.0028

2011

Line

<0.0001

Kibler, AR

Natural

Rep

0.0005

2011

Line

<0.0001

Fayetteville, AR

PST-781

Rep

0.0471

2012

Line

<0.0001

Fayetteville, AR

PSTv-37

Rep

0.0912

2012

Line

<0.0001

Kibler, AR

Natural

Rep

0.0032

2012

Line

<0.0001

1Field was inoculated with race PST-78, but infected with PSTv-37 from a breeding nursery inoculated earlier in the season

Table 9. Infection type (IT) and percentage of leaf area diseased for Lines with Yr17 when inoculated with PST-78 or PSTv-37 at Fayetteville, AR in 2011 and 2012.

Inoculated Race

2011

PST-78

2011

PSTv-37

2012

PST-782

2012

PSTv-37

Line

IT1

Leaf area Diseased (%)

IT1

Leaf area Diseased (%)

IT1

Leaf area Diseased (%)

IT1

Leaf area Diseased (%)

26R87

0

0

8

40

8

10

8

5

CG514W

8

46

8

83

8

84

8

57

CG554W

8

13

8

40

8

15

8

9

FL302

8

12

8

60

8

38

8

31

Jagger3

.

.

.

.

8

5

8

4

SS8641

0

0

8

37

8

11

7

3

VA07W-415

0

0

8

78

8

23

8

42

VA07W-429

0

0

8

16

8

7

8

8

VA08MAS-412

0

0

8

25

8

9

8

5

HV9W04-1594R

0

0

8

60

7

15

8

18

LA821

0

0

8

32

7

9

7

7

VA06HRW108

0

0

8

39

7

8

8

7

LA01139D-56-1-C

0

0

8

31

6

8

7

4

AGS2060

0

0

4

10

5

2

5

5

Fuller3

.

.

.

.

5

3

5

2

NEO5426

0

0

6

9

5

4

5

5

NEO6545

0

0

7

19

5

4

6

5

Overley3

.

.

.

.

5

2

6

1

AGS2026

0

0

4

18

3

1

3

1

TAM401

0

0

2

8

3

1

0

0

HV9W03-1596R

0

0

3

17

2

1

3

5

HV9W05-1125R

0

0

2

10

2

1

0

0

LA841

0

0

2

9

2

2

2

2

HV9W06-509R

0

0

2

6

0

0

2

1

NC05-19896

0

0

2

4

0

0

0

0

TAM203

0

0

3

8

0

0

2

1

VA08HRW-98

0

0

2

10

0

0

0

0

LSD at 5%

4

12

8

9

1Infection types based on 0 to 9 scale as described in Table 3.

2Field was inoculated with PST-78, but was infected with PSTv-37 from a breeding nursery inoculated early in the season, therefore results represent PSTv-37.

3Lines were increased in 2011 for planting use 2012, therefore data was unable to be collected for 2011.

Table 10. Infection type (IT) and percentage of leaf area diseased for Lines with Yr17 when under natural conditions at Kibler, AR in 2011 and 2012.

2011

2012

Line

IT1

Leaf area Diseased (%)

IT1

Leaf area Diseased (%)

26R87

7

20

7

19

CG514W

8

63

8

91

CG554W

8

26

8

81

FL302

8

66

8

83

Jagger2

.

.

7

11

SS8641

6

7

7

8

VA07W-415

8

17

8

52

VA07W-429

8

9

7

14

VA08MAS-412

8

12

6

4

HV9W04-1594R

8

49

7

28

LA821

5

5

6

17

VA06HRW108

8

23

6

10

LA01139D-56-1-C

5

9

6

18

AGS2060

4

4

5

12

Fuller2

.

.

7

17

NEO5426

8

6

5

2

NEO6545

8

14

7

16

Overley2

.

.

6

4

AGS2026

3

2

3

1

TAM401

2

2

0

0

HV9W03-1596R

2

5

4

23

HV9W05-1125R

2

8

0

0

LA841

2

2

0

0

HV9W06-509R

2

2

0

0

NC05-19896

2

2

0

0

TAM203

3

3

0

0

VA08HRW-98

2

2

2

12

LSD at 5%

14

12

1Infection types based on 0 to 9 scale as described in Table 3.

2Lines were increased in 2011 for planting use 2012, therefore data was unable to be collected for 2011.

Table 11. Statistical tests for main effects and interactions for run, race, and line for percentage of flag leaf are diseased on 16 wheat lines inoculated with races PSTv-37 and PST-127 at heading stage and incubated at 10-18°C.

Source

DF

F Value

Probability > F

Race

1

107.25

<0.0001

Line

15

15.65

<0.0001

Race x Line

15

5.48

<0.0001

Run

1

87.05

<0.0007

Rep (Run)

4

0.51

0.7296

Table 12. Infection types for both experimental runs, and area under disease progress curve data across experiments for 16 lines with Yr17 when inoculated at heading and incubated at 10-18°C

PSTv-37

PST-127

Line

ITs Run 1

ITs Run 2

AUDPC

ITs Run 1

ITs Run 2

AUDPC

HV9W05-1125

6

7

215

4

2-3

69

TAM401

4

4

122

3

2-4

41

HV9W03-1596R

7

3

520

2-5

2-4

227

AGS 2026

4

3

306

4

2-4

205

NEO5426

7

8

203

4

2-4

136

LA821

9

9

463

2-7

2-4

155

LA01139D

8

7

341

2-4

2-4

416

NEO6545

3

2

169

3-6

2-4

101

SS8641

7

7

413

3

2-4

88

VAHRW108

9

6

493

2-5

2-5

207

VA08MAS-412

9

8

377

2-5

2-4

146

HV9W04-1594R

9

9

458

2-5

2-4

118

VA07W-415

9

9

510

2-5

2-4

239

AGS 2060

8

2-4

301

7

2-4

329

Jagger

8

9

408

9

7

450

CG541W

9

9

578

8

8

471

LSD at 5%1

117

`117

1LSD for comparing NEO5426 inoculated with PSTv37 or VAHRW108 inoculated with race PST-127 to any other mean is 123, The LSD for comparing the two to each other is 129.

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