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Jessica A. Gutierrez and Christopher S. Cramer

Fusarium basal rot (FBR), caused by Fusarium oxysporum Schlechtend.:Fr. f. sp. cepae (H.N. Hans.) W.C. Snyder & H.N. Hans, is a soilborne fungal disease that affects bulb onions (Allium cepa L.) worldwide. Short-day onion cultivars that are resistant to FBR are lacking. The goal of this project was to screen fall-sown onion germplasm for FBR resistance using a mature bulb field screening at harvest and after 4 weeks in storage. The project was conducted for 2 years, and in each year, 26 fall-sown onion lines were grown in a field known to produce a high incidence of fusarium-basal-rot-infected bulbs. When all the bulbs in a plot were mature, the basal plates of 20 bulbs were cut transversely and each plate was rated for disease severity on a scale of one (no diseased tissue) to nine (70% or more diseased). Bulbs were stored and rerated at 2 and 4 weeks after harvest. Disease severity and incidence were higher in the first year than in the second year. Both severity and incidence increased as bulbs were stored for 4 weeks. NMSU 00-25 exhibited the lowest disease severity and incidence in both years at harvest time and after storage. `Buffalo' and `Cardinal' exhibited the highest severities and incidences across both years and at harvest time and after storage. Other entries exhibited high or low disease severity and incidence but not consistently across years and between harvest time and after storage. In the development of FBR resistant cultivars, breeding lines should be evaluated over multiple years and bulbs should be stored for 4 weeks before being screened.

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Yang Sun, Wei Han, Xiuming Ma, Junfeng Wang, Guoqin Wei, and Jun Miu

Cherry leaf spot (CLS), caused by Passalora circumscissa, is a fungal disease that can cause decreased fruit quality and yield via inconsistent ripening or premature defoliation. Germplasm resource screening is the most reliable approach to disease control for economically important crops. However, information is limited in China about the resistance of cherry cultivars to leaf spot caused by P. circumscissa. The aim of this study was to identify the resistance levels of cherry cultivars. Fifty-two cherry cultivars, including 40 Prunus avium, four Prunus pseudocerasus, and eight Prunus cerasus cultivars were collected for resistance level characterization. These specimens were then used to screen for P. circumscissa resistance through both detached leaf assays and natural field infection. Significant differences in the disease index (DI) value among test cultivars, ranging from 5.7 (resistant) to 53.7 (highly susceptible) and 6.5 (resistant) to 53.2 (highly susceptible), were observed under the controlled and field conditions respectively. Correlation coefficients between DI in pairs of years were highly significant (0.77–0.86). Although resistance rankings for cherry cultivars between screening methods were variable, the resistance levels of 52 cultivars evaluated under controlled and field condition were comparable with a correlation coefficient of 0.70 (P < 0.01). The results indicated that, across cherry cultivars, responses to CLS in the detached leaf assay corresponded well to responses under field conditions. A detached leaf assay was developed as a complementary method to facilitate the screening of cherry cultivars for resistance to leaf spot caused by P. circumscissa. Our study provides a theoretical basis for cherry disease resistance breeding and rational cultivar utilization.

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D.W. Williams and P.B. Burrus

Perennial ryegrass (PR) (Lolium perenne L.) is often used as a low-mowed turf in the transition climatic zone. However, control of the fungal disease gray leaf spot (Pyricularia grisea (Cooke) Sacc.) has drastically increased the cost of PR management. Seeded bermudagrasses (SB) [Cynodon dactylon (L.) Pers.] are viable options for turfgrass management operations with limited pesticide budgets. Field trials in 2000 and 2001 tested the effects of two herbicides and several plant growth regulators (PGR) during renovation of mature PR to either of two cultivars of SB. The herbicides glyphosate and pronamide, and the PGR's trinexapac-ethyl, ethephon, paclobutrazol, and flurprimidol were applied at label rates to mature stands of PR. `Mirage' and `Yukon' SB were seeded separately either 1 or 7 days after applications (DAA) of chemicals. SB establishment, first-winter survival, and turfgrass quality (TQ) were rated and compared to an untreated control. Results indicated that only applications of glyphosate resulted in acceptable renovation of PR to SB, but also resulted in significantly lower (P< 0.05) TQ during the transition. Applications of pronamide resulted in significantly less (P < 0.05) SB transition than did applications of glyphosate, but pronamide plots maintained higher TQ. None of the PRG treatements had a significant effect (P < 0.05) on SB transition. There were no consistent significant effects (P < 0.05) due to DAA among any of the chemicals evaluated. First-winter survival was significantly higher (P < 0.05) with `Yukon' than with `Mirage' in both years. We conclude that among the chemicals tested, only applications of glyphosate resulted in acceptable transition of PR to SB, but a significant reduction of TQ should be expected during the transition. Chemical names used: [N-(phosphonomethyl) glycine] (glyphosate); [3.5-dichloro-N-(1,1-dimethyl-2-propynyl)-benzamide] (pronamide); [(2-chloroethyl) phosphonic acid] (ethephon); [4-(cyclopropyl-α-hydroxy-methylene)-3,5-dioxo-cyclohexane-cabroxylic acid ethyl ester] (trinexapac-ethyl); [(±)-(R*R*)β-[(4-chlorophenyl)-methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol] (paclobutrazol); [α-(1-methylethyl)-α-[4-(trifluromethoxy)phenyl]-5-pyrmidinemethanol] (flurprimidol).

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Brent A. Holtz

Pistachio (Pistacia vera) was successfully introduced into California and initially touted as a tree nut crop with no disease or insect pests. Unfortunately, these expectations were dashed as a number of diseases and pests followed commercial plantings, making plant protection practices integral to production. Verticillium wilt (Verticillium dahliae) devastated early plantings but is now controlled with the use of resistant rootstocks. Botryosphaeria blight (Botryosphaeria dothidea) and alternaria late blight (Alternaria alternata) are recently arrived foliar fungal diseases that blight fruit clusters and defoliate trees, respectively, and multiple fungicide applications are needed for control. The conversion to low volume irrigation systems, specifically to drip or buried drip, has reduced disease. Pruning out botryosphaeria blight infections has reduced overwintering inoculum and disease, while current research aims at accurately predicting infection events to increase fungicide efficacy. A number of hemipteran insect pests have been associated with epicarp lesion: spring treatments have been replaced with dormant carbaryl and oil applications which are less toxic to beneficial insects while controlling phytocoris (Phytocoris californicus and P. relativus) and soft scale pests. Early season insect damage can be tolerated because trees compensate by maturing a higher percentage of remaining fruit kernels. Some mirid (Calocoris spp.) pests can be effectively reduced by eliminating alternate hosts in an effective weed control program. If lygus (Lygus hesperus) populations are present, weeds should not be disturbed from bloom until shell hardening to prevent movement by insects into the trees where feeding can result in epicarp lesion. Stink bugs (Pentatomidae) and leaffooted bugs (Leptoglossus clypealis and L. occidentalis) can penetrate the hardened shell and cause internal nut necrosis along with epicarp lesion. Trap crops are used to monitor pest populations in order to develop treatment thresholds. Degree-day based timing of treatments increase insecticide efficacy for the control of navel orangeworm (Amyelois transitella) and obliquebanded leafroller (Choristonuera rosaceana), but navel orangeworm populations are more effectively managed by destroying unharvested over wintering fruit. Bacillus thuriengiensis sprays, liquid-lime-sulfur, and biological control show promise in controlling obliquebanded leafroller.

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Gehendra Bhattarai, Shawn A. Mehlenbacher, and David C. Smith

Eastern filbert blight (EFB) is a serious fungal disease of european hazelnut (Corylus avellana) in North America. The causal agent is the pyrenomycete Anisogramma anomala, which is native in the eastern United States where it occasionally produces small cankers on the wild american hazelnut (C. americana). However, most commercial cultivars of european hazelnut are susceptible. Infection leads to perennial cankers, girdling of branches, and premature tree death. Cultural practices including scouting, pruning out infected branches, and fungicide applications are recommended to slow disease spread but are expensive and not completely effective. EFB resistance from ‘Gasaway’ is conferred by a dominant allele at a single locus and has been extensively used in the Oregon State University hazelnut breeding program, but there is concern that this resistance could be overcome by isolates now present in the eastern United States or that a new race of the pathogen could arise in Oregon. Segregation for EFB resistance from ‘Uebov’, a new source from Serbia, was studied in three progenies by a combination of structure exposure and greenhouse inoculation. The frequency of resistant seedlings following structure exposure was about 20% in all three progenies. The ratios failed to fit the expected 1:1 ratio but did fit a ratio of 1 resistant:3 susceptible, which would be expected if resistance were conferred by dominant alleles at two independent loci. Seedlings from a cross of susceptible selection OSU 741.105 and ‘Uebov’ were used to study correlation of disease response and presence of alleles at microsatellite marker loci. Resistance was highly correlated with the presence of alleles at marker loci on linkage group 6 (LG6), and these markers also showed segregation distortion. We conclude that EFB resistance from ‘Uebov’ maps to a single locus on LG6 in the same region as resistance from ‘Gasaway’, although only about 20% of the seedlings are resistant because of segregation distortion. ‘Uebov’ has large, well-filled, round nuts and is suitable as a parent in breeding for the in-shell market, but its low nut yields and a high frequency of shells with split sutures are the drawbacks. Its use would expand options for breeding and ‘Uebov’ resistance could be combined with other resistance alleles with an expectation of more durable EFB resistance. Durable resistance would not only sustain the hazelnut industry in Oregon but would also allow expansion of plantings to new areas.

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W.P. Cowgill Jr., M.H. Maletta, T. Manning, W.H. Tietjen, S.A. Johnston, and P.J. Nitzsche

Research trials, conducted from 1991 to 1998, evaluated early blight forecasting systems for use in fresh-market tomato (Lycopersicon esculentum) production in northern New Jersey. Initial trials focused on determining which of three forecast systems—NJ-FAST, CU-FAST, TOM-CAST—would optimize fungicide use. The TOM-CAST system generated fungicide application schedules that reduced foliar disease rating compared to the untreated check and, in 1 year, controlled diseases as well as a weekly schedule with 3 rather than 14 applications. TOM-CAST was easier to use than NJ-FAST or CU-FAST because it required fewer weather data inputs and simpler forecast calculations. Subsequent trials evaluated and defined thresholds for using TOM-CAST in northern New Jersey and evaluated the efficacy of several fungicides with TOM-CAST. Of the six TOM-CAST modifications evaluated, TOM-CAST beginning fungicide applications at 25 cumulative dew severity values (dew SV) and reapplying fungicide at 15 or 25 cumulative dew SV reduced disease rating as much as a weekly schedule in 1995 and 1996 and with fewer applications. After 5 years of trials, decision thresholds for using TOM-CAST in northern New Jersey were chosen and this new version of the forecast system designated NJ-TOM-CAST. It was verified in 1997 and 1998 and shown to generate fungicide application schedules that reduced foliar disease rating compared to the untreated check in both years and as much as the weekly schedule in one year. From 1995 through 1998, the conservative TOM-CAST schedules, TOM-CAST 25-15 or NJ-TOM-CAST, required on average 6 fungicide applications per year compared to weekly schedules that required on average 15 applications per year. In 1996, marketable yield was increased with TOM-CAST scheduled treatment compared to the untreated check and was the same as or greater than yield with weekly treatment. In the other 3 years, fungicide applications, whether applied on a calendar-based or TOM-CAST-based schedule, did not increase marketable yields compared to the untreated check. Fungicides shown to be effective when used with NJ-TOM-CAST schedules included both low cost and new chemistry materials. Copper fungicides, some of which are allowed in organic crop production, did not consistently control fungal diseases when applied on the NJ-TOM-CAST schedule. Applying fungicides on the NJ-TOM-CAST schedule instead of calendar-based schedules did not increase bacterial disease severity. Powdery mildew damage was more severe with NJ-TOM-CAST-scheduled applications than weekly applications in 1 year, affirming the importance of disease monitoring in the field when using NJ-TOM-CAST. By 2000, through a cooperative effort of Rutgers Cooperative Extension and SkyBit, Inc. (Boalsburg, Pa.), a commercial weather service, NJ-TOM-CAST was available to northern New Jersey tomato growers by subscription.

Open access

Merve Şekerli, Golnaz Komaei Koma, Jacob W. Snelling, and Shawn A. Mehlenbacher

Eastern filbert blight (EFB), caused by Anisogramma anomala, is a fungal disease threatening the european hazelnut (Corylus avellana) industry in the Willamette Valley of Oregon. The pathogen is endemic to the eastern United States where it causes little damage to the wild Corylus americana but causes severe cankers on most cultivars of the commercially important european hazelnut. The host genetic resistance in ‘Gasaway’ is conferred by a dominant allele at a single locus on linkage group 6 (LG6), and resistance from several other sources has been mapped to the same region. Some fungal isolates can overcome ‘Gasaway’ resistance, prompting a search for other sources of resistance. Resistance from other sources has been mapped to LG2 and LG7, for which additional simple sequence repeat (SSR) markers would facilitate marker-assisted selection (MAS). In this study, an in silico approach was used to develop new polymorphic SSR markers in the EFB resistance regions on LG2 and LG7. Starting with a search of 17 contigs of the ‘Jefferson’ genome sequence, 45 new polymorphic SSR markers were developed, characterized, and placed on the linkage map. The new SSR markers had an average of 10.18 alleles per locus, and average values for expected heterozygosity, observed heterozygosity, polymorphism information content, and frequency of null alleles of 0.72, 0.65, 0.68, and 0.068, respectively. Of the 42 new polymorphic SSRs segregating in the mapping population, 24 were on LG2, 12 were on LG7, and six were placed on other LGs. The new and previously developed SSR markers were used to study six new sources of EFB resistance, four from Russia and two from Crimea. Six resistant selections were crossed with susceptible selections, resulting in 7 progenies. Phenotyping for disease response revealed that segregation in progenies of the two Moscow selections (#2 and #27), one Russian selection (OSU 1187.101), and one Crimean selection (H3R12P62) fit the 1:1 segregation ratio expected for control of resistance by a dominant allele at a single locus; but in progenies of the other Russian selection (OSU 1166.123) and the other Crimean selection (H3R07P11), there was an excess of resistant seedlings. Correlation of disease scores and alleles at SSR loci indicated that resistance from three Russian selections (Moscow selections #2 and #27 and OSU 1166.123) and the Crimean selection H3R12P62 was on LG7, while resistance from Russian selection OSU 1187.101 was on LG2. Resistance from Crimean selection H3R07P11 was not correlated with markers on LG6, or LG2, or LG7. These sources and new SSR markers will be useful in MAS and the pyramiding of resistance genes in the breeding of new EFB-resistant cultivars.

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Pavel Pavloušek

similar to the fruit of sweet cherry. The name ‘Cerason’ originates from the Latin botanical name Cerasus avium . Fig. 1. Mature cluster of ‘Cerason’. Origin At the end of the 19th century, the most important fungal diseases and pests of grapevine in

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M.L. Stratton

on fungal diseases is 25 pages long. The sections on each fungus present the genus and species of the organism, symptoms, the disease cycle when important for management, the epidemiology, if known, management, and selected references. The sections on

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Peter Boches, Brooke Peterschmidt, and James R. Myers

further for horticultural quality (including flavor) in the field trial ( Table 1 ). Fungal diseases including powdery mildew ( Oidium lycopersicum ) and gray mold ( Botrytis cinerea ) were a problem in some accessions and strong genotype