Disease Progress Curve Values Research Articles

Field Response of Cucurbit Hosts to Pseudoperonospora cubensis in Michigan.

Downy mildew, caused by Pseudoperonospora cubensis, is a severe foliar disease of many cucurbit crops worldwide. Forty-one cucurbit cultigens (commercial cultivars and plant introductions) from five genera (Cucumis, Citrullus, Cucurbita, Lagenaria, and Luffa) were assessed for susceptibility to P. cubensis in a research field exposed to natural inoculum in Michigan. Eight cultigens from a differential set for pathotype determination were included within the 41 cultigens to detect changes in dominant P. cubensis pathotypes present. No pathotype differences were found between 2010 and 2011. Cucumis melo cultigen MR-1 was less susceptible to Michigan P. cubensis populations than other C. melo cultigens. No symptoms or signs of infection were detected on cultigens of Cucurbita moschata and C. pepo. Disease onset was later in 2011 than 2010; greater than 90% disease severity in pickling cucumber 'Vlaspik' was observed in both years. This study confirmed that Cucumis is the most susceptible cucurbit genus, while Citrullus and Cucurbita cultigens were the least susceptible genera to populations of P. cubensis in Michigan. Area under the disease progress curve values indicated that disease progress was limited on all Citrullus cultigens compared with Cucumis cultigens, and pathogen sporulation was not detected under field conditions. Future studies should evaluate the ability of a reduced fungicide program to control downy mildew on less susceptible Cucumis melo 'Edisto 47', 'Primo', 'Athena', 'Strike', 'Ananas', 'Banana', and 'Tam-Dew'. Many of the melon cultivars evaluated were selected on the basis of reported resistance to downy mildew, yet they showed significant disease symptoms. It is important to evaluate candidate cultigens for resistance to local P. cubensis populations.

Banana Moko disease management with resistance inducers and chlorine dioxide

The plant disease Moko, caused by Ralstonia solanacearum, is the most important bacterial disease in banana and plantain crops worldwide. In the present study, chlorine dioxide and seven resistance inducers in banana plants (Musa sp.) infected with this bacterium were evaluated under greenhouse conditions. For the evaluation of chlorine dioxide, three doses were used (10, 30 and 50 mg L-1). The evaluation of the resistance inducers included the following: sodium salicylate 0.4 g L-1; hydrogen peroxide 1 mM; potassium phosphite 1.5 mL L-1; 3-aminobutanoic acid 1.0 g L-1; methyl jasmonate 0.2 g L-1; acibenzolar-s-methyl 0.3 mL L-1 and chitosan 3.0 mg mL-1. The results showed a significant reduction of 74% in the area under the disease progress curve (AUDPC) value, which was calculated for the disease development when the injected chlorine dioxide dose was 50 mg L-1. The AUDPC value for the resistance inducers was reduced by 45.4% for chitosan, 75.5% for methyl jasmonate and 65.5% for 3-aminobutanoic acid. Therefore, the results indicated that these molecules have the potential to be used for control of the Moko disease.

The Influence of Irrigation Frequency on the Onset and Development of Verticillium Wilt of Olive.

The influence of irrigation frequency on the onset and development of Verticillium wilt of olive (VWO) was studied. A split-plot design in microplots with naturally infested soil was established for studying four irrigation frequencies for three olive cultivars with differing levels of disease resistance. Final disease incidence (DI) and mortality in 'Picual' plants subjected to daily irrigation treatment (T1) reached values of 100 and 63%, respectively. For Picual-T1 samples, the area under the disease progress curve values were significantly different between 15 December 2012 and 15 July 2013 (14.8 to 42.8%) compared with the average results of the other treatments, which were weekly (T2), biweekly (T3), and deficit (T4) (0.4 to 11.5%). No significant differences between the irrigation treatments were observed in 'Arbequina', although the DI progressed consistently (60% in all treatments). In 'Frantoio', little disease developed. We conclude that a daily irrigation treatment encourages VWO development in susceptible Picual. Therefore, in susceptible cultivars growing in infested soils under daily irrigation regimes, the extension of irrigation frequency may reduce disease incidence. In the context of an integrated control, the use of resistant cultivars seems to be more relevant than the detrimental effects observed in frequent irrigation schedules.

Optimizing Conditions of a Cell-Free Toxic Filtrate Stem Cutting Assay to Evaluate Soybean Genotype Responses to Fusarium Species that Cause Sudden Death Syndrome.

Cell-free toxic culture filtrates from Fusarium virguliforme, the causal fungus of soybean sudden death syndrome (SDS), cause foliar symptoms on soybean stem cuttings similar to those obtained from root inoculations in whole plants and those observed in production fields. The objectives of this study were to (i) optimize the production conditions for F. virguliforme cell-free toxic culture filtrates and the incubation conditions of the stem cutting assay used to test the toxicity of the cell-free toxic culture filtrates, and (ii) use the optimized assay and a whole plant root inoculation assay to compare four SDS-causing isolates on a panel of selected soybean genotypes. Area under the disease progress curve (AUDPC) values were highest (P = 0.05) when cuttings were immersed in culture filtrate of fungus grown in soybean dextrose broth, in filtrate produced from the fungus grown for 18 or 22 days, and when stem cuttings were incubated at 30°C. AUDPC values and shoot dry weights from the whole plant root inoculations and the AUDPC values from the stem cutting assay differed (P < 0.05) among nine soybean genotypes tested with F. virguliforme and F. tucumaniae isolates, and the AUDPC values from the two assays were positively correlated (r = 0.44 at P < 0.0001).

Methods and Evaluation of Soybean Genotypes for Resistance to Colletotrichum truncatum.

Anthracnose of soybean (Glycine max) occurs throughout the soybean production areas of the world. There is little information on evaluating inoculation techniques or evaluating soybean germplasm for resistance. The objectives of this study were to develop a reliable inoculation technique for evaluating soybean for resistance to Colletotrichum truncatum and to evaluate soybean genotypes for resistance. Inoculated plants incubated in a dew chamber for 48 or 72 h had higher (P = 0.05) area under disease progress curve (AUDPC) values than when incubated for 24 h. Three experiments evaluated soybean genotypes for resistance to C. truncatum. In the first experiment using 15 soybean genotypes, 'Mandarin' had lower (P = 0.05) AUDPC values than all the other genotypes except for 'Mandarin 507', 'Mandarin (Ottawa)', and 'Boone'. In the second experiment using 28 soybean genotypes, Mandarin 507 had lower (P = 0.05) AUDPC values compared with all other soybean genotypes except 'Early White Eyebrow', 'Mandarin Yowa', Boone, and 'Manchuria'. In the third experiment, Mandarin 507 had lower (P = 0.05) AUDPC values compared with 23 other soybean genotypes except 'Spry', Mandarin, and 'Iroquois'. Plants of Mandarin 507 and 'Williams 82' were inoculated at the vegetative and reproductive growth stages; Mandarin 507 had lower (P = 0.05) AUDPC values compared with Williams 82 for both growth stages evaluated, and Mandarin 507 had less (P = 0.05) pod area covered by lesions compared with the pods of Williams 82. This study provided a descriptive method to inoculate soybean plants with C. truncatum and identified soybean genotypes with resistance to anthracnose.

The Effect of Open-Ended High Tunnels in Western Washington on Late Blight and Physiological Leaf Roll Among Five Tomato Cultivars

A 3-year study in western Washington from 2010 to 2012 evaluated five tomato cultivars for tomato disease development and yield in open-ended high-tunnel versus open-field settings. Findings in 2010 revealed that severity of late blight, caused by Phytophthora infestans (US-11), was significantly (P = 0.002) lower in high-tunnel compared with open-field experimental plots based on area under disease progress curve (AUDPC) values of 0.02 versus 321, respectively. In spite of rescue foliar fungicide applications to open-field plots in 2011 and 2012, the mean number of late blight infections across cultivars was 1.8 to 30.8 compared with only 0 to 6.5 in high tunnels for these years. Furthermore, accumulated hours of leaf wetness were fewer in high tunnels than the open field each year (857 versus 1,060 in 2010, 598 versus 998 in 2011, and 885 versus 923 in 2012). Cultivar susceptibility to late blight could not be differentiated in high tunnels due to low disease pressure. However, all five cultivars proved susceptible in the open field, with 'Oregon Spring' consistently having the most lesions. In contrast, high-tunnel production contributed to an increased severity of physiological leaf roll compared with open-field production each year, and these values differed significantly (P = 0.0335 and 0.0252) in 2011 and 2012, respectively. AUDPC values for physiological leaf roll showed that Oregon Spring was significantly (P = <0.0001) less susceptible than other cultivars each year. Physiological leaf roll correlated positively (r values of 0.758 to 0. 960) and significantly (P < 0.05) with leaf wetness and air temperature in all years in both high-tunnel and open-field settings but the same was not true for relative humidity. Even with severe physiological leaf roll, high-tunnel production in 2010 resulted in significantly (P < 0.0001) greater total tomato yield than open-field production (35.0 versus 10.6 t ha-1). Although a significant interaction between production system and cultivar occurred in 2011 and 2012, tomato yield always was greater in high-tunnel than open-field plots. Open-ended high tunnels offer tomato growers a potential tool for managing late blight in western Washington while also increasing yield, and could be especially useful in organic production.

Metabolic profiles of soybean roots during early stages of Fusarium tucumaniae infection.

Soybean germplasm exhibits various levels of resistance to Fusarium tucumaniae, the main causal agent of sudden death syndrome (SDS) of soybean in Argentina. In this study, two soybean genotypes, one susceptible (NA 4613) and one partially resistant (DM 4670) to SDS infection, were inoculated with F. tucumaniae. Disease symptoms were scored at 7, 10, 14, and 25 days post-inoculation (dpi). The greatest difference in the area under the disease progress curve (AUDPC) values among genotypes was observed at 25 dpi. In order to detect early metabolic markers that could potentially discriminate between susceptible and resistant genotypes, gas chromatography-mass spectrometry (GC-MS) analyses of root samples were performed. These analyses show higher levels of several amino acids and the polyamine cadaverine in the inoculated than in the uninoculated susceptible cultivar at 7 dpi. Principal component analysis (PCA) revealed that the metabolic profile of roots harvested at the earliest time points from the inoculated susceptible genotype was clearly differentiated from the rest of the samples. Furthermore, variables associated with the first principal component were mainly amino acids. Taken together, the results indicate that the pathogen induced the susceptible plant to accumulate amino acids in roots at early time points after infection, suggesting that GC-MS-based metabolomics could be used for the rapid characterization of cultivar response to SDS.

First Report of Seedling Blight of Eastern Poison Ivy (Toxicodendron radicans) by Colletotrichum fioriniae in Virginia

Colletotrichum fioriniae is a member of the large cosmopolitan C. acutatum species complex (2). Known agricultural hosts of C. acutatum include apple, European blueberry, grape, olive, papaya, and strawberry (2). In contrast, the life history of C. fioriniae ranges from an epizootic of certain scale insect populations to an endophyte of plants (3,4). The present study extends the phytopathology of C. fioriniae to include poison ivy seedlings. Poison ivy (Toxicodendron radicans) drupes were collected from solitary lianas in Roanoke and Montgomery counties, Virginia. These drupes were subjected to experiments aimed at producing sterile seedlings (1); however, there was extensive blighting and wilting in the germinated seedlings. Associated with the drupes and seedlings was a fungus with white to pale olivaceous grey mycelium with orange blister-like conidiomata and sclerotial masses enclosing the drupe mesocarp as well as conidiomata emerging from blighted, necrotic leaves. Condiomata were plated onto acidified potato dextrose agar (APDA) and oatmeal agar (OA). This consistently yielded colonies identical to those described from diseased tissues and were putatively identified as C. acutatum based on the presence of acervuli containing hyaline, smooth-walled, aseptate conidia with acute ends, the absence of setae, and formation of red pigments in culture (2). Conidial dimensions of four isolates most closely aligned with reported measurements for C. fioriniae (4): mean length ± SD × width ± SD = 15.1 ± 1.7 × 4.9 ± 0.3 μm, L/W ratio = 3.04 on OA. Fungal DNA was isolated and used as template in PCR reactions using oligonucleotide primer pairs corresponding to the internal transcribed spacer (ITS) region, and a portion of the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genes. The resulting PCR fragments were sequenced and used as queries in BLASTN searches of the GenBank NR database. All of the amplified ITS DNA sequences (497 bp KF944356 and KF944357) were identical to Glomerella/Colletotrichum fioriniae (JN121190 and KF278459). Similarly, the amplified (672 bp) GAPDH sequences (KF944354 and KF944355) were 99.6% similar over the 254 bp overlapping with C. fioriniae (JQ948622). Pathogenicity of two randomly chosen C. fioriniae isolates, TR-123 and TR-126, was confirmed by placing 4.75 mm diam. inoculated agar plugs from 8-day-old fungal cultures or a sterile plug (negative control) at the base of an axenic young seedling ~1.5 to 6.5 cm in height with at least one set of true leaves (1). Each treatment was replicated five times. Acute wilt and blighting of leaves and production of orange acervuli on cotyledons disease symptoms developed by 3 weeks post inoculation (WPI). By 7 WPI all but one of the Colletotrichum-inoculated plants were dead, whereas all of the control plants were healthy with significantly lower area under the disease progress curve values. Colletotrichum was consistently re-isolated, and confirmed morphologically and molecularly, from six of seven diseased seedlings, whereas two of two randomly chosen control seedlings remained asymptomatic and did not yield Colletotrichum. In summary, C. fioriniae may represent a natural biocontrol agent against poison ivy and scale insect herbivores thereof.

Sensitivity of Mycosphaerella graminicola isolates to demethylation-inhibiting (DMI) fungicides

Mycosphaerella graminicola (Fuckel) J. Schrot. (anamorph Zymoseptoria tritici (Desm.) Quaedvlieg & Crous) causes Septoria leaf blotch disease of wheat. The disease can be responsible for yield losses of 30–50% and, when severe, requires management with a fungicide. Single picnidia isolates collected from different locations of Lithuania were tested in vitro for sensitivity to demethylation-inhibiting (DMI) fungicides epoxiconazole, cyproconazole and prothioconazole. Fungicide concentrations were chosen from the proposed Fungicide Resistance Action Committee (FRAC) methods. Microtitre plates with 96-wells were inoculated with suspensions of pycnidiospores taken from single pycnidia of leaves. In total, 196 isolates from 34 locations were tested over the three experimental years (2009–2011). The results showed reduced sensitivity of M. graminicola isolates to epoxiconazole and cyproconazole. The average EC 50 values over three experimental years for epoxiconazole varied between 1.02 and 3.15 mg l -1 , for cyproconazole – 1.51 and 10.66 mg l -1 . The sensitivity to prothioconazole of 64 isolates from 13 locations (2011) ranged from 0.43 to 32.28 mg l -1 . Results of field experiments (2007– 2011) showed that fungicides epoxiconazole and prothioconazole significantly reduced the area under the disease progress curve (AUDPC) values of Septoria leaf blotch compared with untreated plots in winter wheat. In most cases, a single fungicide application significantly increased grain yield and a thousand grain weight weight.

Cultivation technology influences the occurrence of potato early blight (Alternaria solani) in an organic farming system

Nowadays, organically produced products have become more popular than ever and interest in them is still growing fast. The early blight causal pathogen Alternaria solani has not been considered a great threat to potato in northern climate conditions in the past and has not been routinely sprayed against. During our study early blight was evaluated in 2010 and 2011 on the plants of a potato cultivar ‘Reet’ in an organic farming experiment. In our study, both growing seasons were very favourable for early blight development. Significant differences between the two cultivation technologies were found (F1,12 = 4.84, p = 0.048). In 2010, the area under disease progress curve (AUDPC) value was 303 on cover crop (CC) plots and 990 on CC + M (manure) plots that is three times higher, whereas in 2011, the AUDPC value was 967 on CC plots and 1195 on CC + M plots. Our results confirm that potato early blight has become a serious problem in North-East European organic potato fields and thus susceptible potato cultivars cannot be recommended for growing in an organic farming system. However, it is possible to influence the development severity of early blight by selecting the proper growing technology. Since, in the changing climate conditions and in susceptible cultivars, early blight is a potato disease that can cause early defoliation of plants and crop death, there is a need for resistant potato cultivars.

Phenotypic Stability and Genome-Wide Association Study of Late Blight Resistance in Potato Genotypes Adapted to the Tropical Highlands

Potato genotypes from a breeding population adapted to tropical highlands were analyzed for the stability of late blight resistance and also for marker-phenotype association. We harmonized the historical evaluation data, consisting of observations spanning 6 years from two field sites utilizing a resistance scale constructed by comparing the area under the disease progress curve (AUDPC) values of 172 genotypes with that of susceptible control 'Yungay'. In total, 70 potato genotypes had a coefficient of variability <0.5 and were considered stable across the environments tested. A principal component analysis demonstrated that the ensemble of experiments formed two distinct groups that reflect the stability of genotype resistance to late blight. Phytophthora infestans isolates present in the experimental fields belonged to the EC-1 clonal lineage and showed variation in virulence beyond the concept of the avirulence determined by the conventionally used R1-R11 differential set. A single-nucleotide polymorphism (SNP) marker on chromosome 9 was associated with late blight resistance and linked to instability. Genotypes with either AACC or AAAC combinations for this SNP were highly resistant only in some environments, while the genotypes with the AAAA combination had more moderate levels of resistance but were stable across environments.

QTL Analysis of Late Blight Resistance in a Diploid Potato Family of Solanum spegazzinii × S. chacoense

Several quantitative trait loci (QTL) for resistance to late blight have been reported in diploid potatoes. The diploid wild potato species Solanum chacoense possesses a high degree of horizontal resistance to late blight. In the present study, we report on QTL mapping for late blight resistance in a diploid mapping population of 126 F1 of Solanum spegazzinii (susceptible) × S. chacoense (resistant). The area under the disease progress curve (AUDPC) values for late blight resistance using the “whole plant in vitro assay” and the “detached leaf assay” on the mapping population displayed quantitative variation. Out of 64 AFLP primer-pairs combinations and SSR markers, a total of 209 significant AFLP loci were placed onto the 12 linkage group of potato covering a total map length of 6548.1 cM. QTL analysis based on the AUDPC dataset of the “whole plant in vitro assay” using the interval-mapping option identified two QTL (LOD > 2.5) located on linkage groups IX and X, which explained 14.70 and 3.40% variation, respectively. The present study revealed the presence of potential new genetic loci in the diploid potato family contributing to quantitative resistance against late blight.

Tuber Blight Development in Potato Cultivars in Response to Different Genotypes of Phytophthora infestans

Migrations or introduction of new genotypes of Phytophthora infestans to a specific region imposes a different perspective for potato production. During 2009–2010, a late blight epidemic affected the Northeastern United States, which quickly spread through several states. The epidemic was characterized by the appearance of a new genotype of P. infestans designated US-22, which was isolated from tomato and potato. Potato tubers are an essential component of late blight epidemics where the pathogen cannot overwinter on Solanaceous plants. Six potato cultivars were inoculated with 12 isolates of P. infestans (five different genotypes), including isolates of the genotype US-22. Tuber blight development was characterized in terms of tissue darkening expressed as area under the disease progress curve values and lenticel infection. The responses indicated that US-8 was more aggressive than US-22, but US-22 isolates obtained from potato were more aggressive on potato than those acquired from tomato. Tuber periderm responses to infection were limited, yet US-8 isolates infected the periderm more often than US-22 isolates. There were significant differences among the cultivars tested but cv. Jacqueline Lee was the most resistant overall. Although isolates of P. infestans genotype US-22 were less aggressive in comparison with US-8 isolates, US-22 isolates still infected potato tubers and were as aggressive us US-8 isolates on some cultivars. Management of late blight caused by isolates of US-22 through host resistance may be feasible but imposes a different set of criteria for consideration from those that US-8 imposed.

&amp;lt;i&amp;gt;In vitro&amp;lt;/i&amp;gt; and greenhouse evaluation for resistance to early blight of potato isolated from &amp;lt;i&amp;gt;Alternaria alternata&amp;lt;/i&amp;gt;

Early blight of potato is caused by the fungus Alternaria alternata, one of the most destructive foliar diseases, especially in hot climates under irrigation. In this study, the virus free potato seedlings were obtained from the National Plant Gene Bank of Iran and were inoculated in vitro with a culture filtrate of A. alternate. The leaflets received a 1000-μl droplet of the A. alternata culture filtrate and were inoculated by spraying with a suspension of 105 conidia/ml of isolate A. alternata in the greenhouse method. The experimental design was a completely randomized design (CRD) with three replications and seven genotypes, which have been infected with the two leaves of each iteration. In vitro selection of fungal isolates of A. alternata, chlorotic and necrotic symptoms began 1 to 2 days after inoculation, but the assessment of greenhouse symptoms appeared 6-10 days after inoculation. The area under the disease progress curve values were presented by analysis of variance (ANOVA), and they were compared using Duncan’s test (a = 0.01%). In both methods, there was a significant difference between the potato genotypes (P In vitro selection and evaluation greenhouse, Casmos were resistant to at least figure and Marfona genotype had the highest resistance.

An Evaluation of Cucurbits for Susceptibility to Cucurbitaceous and SolanaceousPhytophthora capsiciisolates

Cucumber (Cucumis sativus) and squash (Cucurbita spp.) production in Michigan is limited by the oomycete pathogen Phytophthora capsici. Cucumber, summer squash, and winter squash fruit were evaluated for susceptibility to five isolates of P. capsici. Detached fruit were inoculated with a 5-mm-diameter culture plug of mycelia and sporangia and were incubated in a laboratory or greenhouse. Lesion and pathogen growth diameters were measured and pathogen growth density was visually assessed. All P. capsici isolates incited rot, with significant differences found among fruit type and pathogen isolate. Straightneck squash (Cucurbita pepo), slicing cucumber, and butternut squash (C. moschata) exhibited more severe symptoms than the other fruit tested. Summer and winter squash seedlings were evaluated in greenhouse experiments, in which P. capsici-infested millet seed (approximately 1 g) were placed on the surface of soilless potting media. Disease severity was visually assessed every 2 days for 14 days post inoculation. Crop type, pathogen isolate, or the crop type-pathogen isolate interaction term were significant for symptom appearance and area under the disease progress curve values. Differences in susceptibility of butternut squash and zucchini cultivars were observed following inoculation with solanaceous isolate 13351. Results from this study can refine management programs for Phytophthora rot.

Grafting Tomato to Manage Bacterial Wilt Caused by Ralstonia solanacearum in the Southeastern United States.

Bacterial wilt, caused by Ralstonia solanacearum, can result in severe losses to tomato (Solanum lycopersicum) growers in the southeastern United States, and grafting with resistant rootstocks may be an effective strategy for managing this disease. However, R. solanacearum populations maintain considerable diversity, and little information is known regarding the efficacy of commercially available rootstocks to reduce bacterial wilt incidence and subsequent crop loss in the United States. In this study, tomato plants grafted onto 'Dai Honmei' and 'RST-04-105-T' rootstocks had significantly lower area under the disease progress curve (AUDPC) values compared with nongrafted plants (P < 0.05). Across three locations in North Carolina, final bacterial wilt incidence for non- and self-grafted plants was 82 ± 14 to 100%. In contrast, bacterial wilt incidence for the grafted plants was 0 to 65 ± 21%. Final bacterial wilt incidence of plants grafted with Dai Honmei rootstock was 0 and 13 ± 3% at two locations in western North Carolina but 50 ± 3% at a third site in eastern North Carolina. Similarly, grafting onto RST-04-105-T rootstock significantly reduced AUDPC values at two of the three locations (P < 0.05) compared with that of the nongrafted plants, but performed poorly at the third site. Total fruit yields were significantly increased by grafting onto resistant rootstocks at all three sites (P < 0.05). Regression analyses indicated that yield was significantly negatively correlated with bacterial wilt AUDPC values (R2 was 0.4048 to 0.8034), and the use of resistant rootstocks enabled economically viable tomato production in soils naturally infested with R. solanacearum.

Stability of Slow-Rusting Resistance to Puccinia asparagi and Managing Rust in Asparagus.

The stability of slow-rusting resistance to Puccinia asparagi in several asparagus cultivars was evaluated in two replicated field trials. Rust epidemics were monitored in each trial for 8 years spanning a period of 13 years (1983-1990 and 1987-1995). Inoculum of P. asparagi, an autoecious macrocyclic rust, originated each year as teliospores. In the first trial, the cultivars Jersey Titan, Jersey Centennial, Jersey Giant, Delmonte-361, and UC-157 had consistently lower area under the disease progress curve (AUDPC) values than Wash T2 and WSU-1. Cultivar Mary Washington was intermediate between the two groups of resistant and susceptible cultivars in 6 of 8 years. Jersey Titan consistently ranked number 1 for resistance with the lowest AUDPC values all 8 years. In the second trial, Jersey Giant, Delmonte-361, and UC-157 had consistently lower AUDPC values than Larac, Gynlim, Cito, Largo 17-3, and Franklim in each of 8 years. Jersey Giant, Delmonte-361, and UC-157 always ranked low (1, 2, or 3) for AUDPC. A shift from rust-susceptible to rust-resistant asparagus cultivars began in central Washington around 1996. In 2011, resistant cultivars made up nearly 96% of the asparagus plantings. From 1996 to 2011, rust was not considered a problem in commercial fields with slow-rusting resistant cultivars. Use of durable, slow-rusting cultivars, along with sanitation practices that reduced levels of aecia in nonharvested nurseries and on volunteer asparagus plants and judicious irrigation management, has effectively managed asparagus rust in commercial fields for at least 29 years in south-central Washington.

Timing and Frequency Effects of Lightweight Rolling on Dollar Spot Disease in Creeping Bentgrass Putting Greens

ABSTRACTDollar spot (DS) (Sclerotinia homoeocarpa F.T. Bennett) is an important disease on golf course turfgrasses in the United States. The objective of this study was to elucidate disease reduction mechanisms related to lightweight rolling. Creeping bentgrass (Agrostis stolonifera L.) plots that were subjected to daily (5 d wk−1) rolling treatments (1x a.m., 1x p.m., 2x a.m.) showed significant DS reductions when compared with a nonrolled control. Treatments rolled in the afternoon (after dew and guttation fluid dissipated) exhibited similar area under disease progress curve (AUDPC) values as treatments rolled in the morning in 2008, 2009, and 2010. Both 1x rolling treatments resulted in significant DS reductions compared with the control in 2009 and 2010. The 2x d−1 treatment exhibited significantly less DS than the control in all years as well as significantly lower AUDPC values than both 1x rolling treatments in 2009 and 2010. Rolling 2x d−1 improved turfgrass quality compared with all other treatments in each year of the study. All rolling treatments exhibited higher root zone volumetric water content (%VWC) compared with the control in 2010, and significant effects on %VWC were observed on individual dates among treatments. Results indicate previously unidentified effects of rolling on putting greens, including added physical and biological effects, which may be contributing to DS suppression.

The dissection and SSR mapping of a high-temperature adult-plant stripe rust resistance gene in American spring wheat cultivar Alturas

Stripe rust is one of major diseases in wheat production worldwide. The best economic and efficient method is to utilize resistant varieties. Alturas has high-temperature adult-plant resistance. In order to determine stripe rust resistance characteristics, resistance gene combination and molecular map of the resistance gene(s), Alturas was crossed with Chinese susceptible cultivar Taichung29. The parents, F1, F2 progenies were tested with Chinese predominant mixed races CYR31, CYR32 and CYR33 in field experiments in 2010 and F3 progenies were evaluated at one site in Beijing, the other site in Langfang, Hebei Province. Infection type (IT) and disease severity (DS) were recorded three times for each plant for F1 and F2, and each progeny for F3 during each growing season. The DS data were used to calculate relative area under the disease progress curve (AUDPC) values. Both IT and AUDPC data showed continuous distributions, indicating that the Alturas HTAP resistance was controlled by quantitative trait loci (QTLs). A major HTAP QTL, designated as QYrAlt.syau-3BS, was consistently detected across environments and was located on chromosome 3BS. The gene contributed to 34.28 % of the phenotypic variation for average AUDPC and 50.20 % for average IT. Markers Xgwm389 and Xbarc238 flanking the major QTL, should be useful in breeding for obtaining durable and high-level resistance by combinations with other non-race-specific resistance genes.

Mapping QTL for Fusarium wilt Race 2 partial resistance in pea (Pisum sativum)

With 3 figures and 4 tablesAbstractFusarium oxysporum f.sp. pisi (Fop) exists in pea production regions worldwide and causes a vascular wilt resulting in significant crop losses. Four races of Fop have been identified, and resistance to each was reportedly conferred by an individual single dominant gene. Fnw confers resistance to Fop race 2, which can be a serious pathogen for both green and dry pea production in the Pacific Northwest region of the United States. The objectives of this research were to (i) place Fnw on the Pisum genetic map, (ii) detect additional genetic factors associated with resistance to race 2 and (iii) identify closely linked markers for use in pea breeding A recombinant inbred line (RIL) population of 187 F7‐derived lines from the cross ‘Shawnee’/‘Bohatyr’ was developed by single‐seed decent. All 187 RILs, the parents and one set of race 2 pea differential entries were inoculated with Fop race 2 under controlled conditions in three experiments, each with two or three replications per entry. Disease reactions were recorded as percentage diseased plants 10–14 days postinoculation or at regular intervals through flowering or early pod fill. Data for progressive wilting over time, typical of Fop race 2, were used to calculate area under disease progress curve (AUDPC) values. Data for percentage diseased plants placed the putative single gene Fnw on Pisum sativum linkage group IV, with LOD scores ranging from 40.0 to 65.6 and minor loci on LG III (LOD 3.97 and 4.60). AUDPC values allowed for the detection of additional QTL on linkage group III with LOD scores of 3.97 and 4.60. The presence of recombinants in the population indicated that complementary genes were contributed by each parent, both of which showed intermediate reaction to Fop race 2. Results of this research provide a basis for marker‐assisted selection of the major Fnw loci in both green and dry pea breeding programmes, but additional research is necessary to fully characterize the complementary gene action governing resistance of the two minor loci identified.