Final Disease Severity Research Articles

Evaluation of Advanced Bread Wheat Lines for Field and Seedling Resistance to Stem Rust (<i>Puccinia graminis</i> f. sp. <i>tritici</i>)

Field-based adult plant resistance assessment at multi-location rust hot spot sites is a crucial job for those plant pathologists screening several wheat lines at a time against the rusts. Rust resistant bread wheat genotypes that have been extracted from previous studies have sustained wheat production in Ethiopia. The objective of this study was to evaluate advanced bread wheat lines extracted from wheat breeding trials against stem rust at adult plat stage under stem rust hot spot sites and at seedling stages in the greenhouse. Eighty three lines were further re-evaluated in consecutive two years. Check varieties were included for comparison. High disease pressure was developed on adult plant in the trial as it has been revealed by high severity on susceptible check varieties. Over years average final rust severity, co-efficient of infection and field reaction have used for differentiating Adult plant resistances. Based on ACI, the 843 genotypes evaluated in initial trial in 2013 were categorized into 10 resistance levels, of which 188 genotypes were in high level resistance category, revealing that various level of adult plant resistance is operating in these test materials. Most of 83 genotypes r-evaluated in consecutive two years after initial stage have sustained low final stem rust severity and coefficient of infection as compared with check varieties. Genotypes were varied by adult plant reaction to stem rust, however, lines ETBW7818, ETBW7819, ETBW7258, ETBW 8008, ETBW 8009, ETBW 8017, ETBW 8027, ETBW 8052, ETBW 8054 and ETBW 8055 concisely showed a reaction of R to R-MR invariably with environments. Of the 83 lines tested at seedling stages against four races, 21 lines exhibited resistance to three races JRCQC, TKTTF, TTKSK and TRTTF whereas 24 lines showed susceptibility to the latter three races. Based on adult reaction, final disease severity and coefficient of infection data, Sixty six bread wheat lines and two cultivars Shorima and Huluka sustained final rust severity <30% and low ACI are acceptable for rust resistance breeding in wheat, However, 52 lines showed comparable resistance to Shorima or Hulluka are the priority materials to be used for developing resistant cultivars potentially combining non-race specific and race specific genes which is more durable than cultivars with major resistance gene effect and more efficient than sole adult plant resistance. Inherent resistance genes of these lines are unknown and warrant further description.

Short-term disability progression in two multiethnic multiple sclerosis centers in the treatment era.

Background:Short-term disease progression is well documented in clinical trials, but there are limited published data on disease course in real-life practice.Methods:Patient-derived Multiple Sclerosis Severity Score (PMSSS), a disease severity rank score, was computed at each visit for consecutive MS patients attending two large, ethnically diverse MS centers in New York metropolitan area. Disability was assessed via Patient-Determined Disease Steps (PDDS). Clinicians recorded disease subtype and relapse status at each visit, but did not rate disability. PMSSS change from the first to the last visit was calculated for the cohort as a whole and for subgroups of interest. Multivariable regression models were constructed for predicting final PMSSS based on readily available predictor variables collected at the initial visit and relapse history during follow up.Results:A total of 1740 consecutive patients from New York University (n = 1079) and Barnabas (n = 661) MS Care Centers were included. During follow up (mean 2.4 ± 0.82 years, range 1–4 years), mean PDDS score increased from 1.9 ± 2.2 to 2.3 ± 2.2 (p < 0.0001), while PMSSS remained roughly unchanged (initial PMSSS = 3.71 ± 2.73, last PMSSS = 3.81 ± 2.76, paired t test, p = 0.28). The only major predictor of final PMSSS was the initial PMSSS. Demographic variables (age, sex, race) or relapse status did not predict final severity score.Conclusions:Baseline disability in two MS clinics was much lower than in the reference population from which PMSSS was derived. We observed no discernable slowing of disability accumulation during the short-term follow up in our cohort compared with the reference cohort. Overwhelmingly the most important predictor of final disease severity rank score was the initial disease severity rank score.

Soil applications of acibenzolar-S-methyl induce defense gene expression in tomato plants against bacterial spot

Acibenzolar-S-methyl (ASM), a plant activator known to induce plant resistance, has been used as foliar sprays to manage several plant diseases including bacterial spot on tomato caused by four distinct Xanthomonas species. This study aimed to investigate the effects of soil application rates of ASM on bacterial spot of tomato and the expression levels of the two pathogenesis-related (PR) genes, PR1a and PR1b, in leaf tissues. Tomato seedlings were leaf-applied with ASM at 18.8 mg/l corresponding to the labeled rate, soil-applied with ASM at 0.84 and 10 mg/l, and sprayed with water served as an untreated control. The soil application of ASM at 10 mg/l consistently reduced the final disease severity and disease progress compared to the untreated control in four growth chamber experiments, whereas the soil application of ASM at 0.84 mg/l and foliar spray of ASM significantly reduced the final disease severity and area under disease progress curve (AUDPC) in three out of the four experiments. The expression levels of PR1a and PR1b in the leaf tissues were significantly induced by both soil and foliar applications of ASM. In addition, field trial results suggested that the soil applications of ASM at 10 mg/l markedly reduced disease progress compared to the control and copper standard. Although the control efficiency of soil applications of ASM depends on rates used, this study suggests that ASM can be used as soil applications to induce tomato resistance against bacterial spot.

Management of Chocolate Spot ( Botrytis fabae L. ) on Faba Bean in Bale Highland’s, Ethiopia

Field experiment was conducted at Sinana Agricultural Research Center in the 2014 main cropping season with the objectives wasto study the reaction of faba bean varieties to infection of the chocolate spot and to assess yield losses caused by chocolate spot (Botrytis fabae) of faba bean four varieties. The highest mean final disease severity at (118 DAP) 38.29% was recorded on the main plots of the local variety and lowest mean final disease severity 32.75% was on the main plots of the variety Mosisa. The maximum Area Under the disease progress curves (AUDPC) was calculated on the unsprayed plots of local variety and Walki, which were 1817%-days and 1716.42%- days respectively. On unsprayed plots of variety local chocolate spot development was increasing at a rate of 0.03 units per day. For the variety local, chocolate spot severity index assessed from 90 DAP had significant negative correlation with yield and had highly significant negative correlation with hundred seed weight with coefficient of correlation ranging from(r=-0.67 to r=-0.62, P<0.05 and r–0.71 to r=-0.75, P<0.01) for yield and hundred seed weight, respectively. The linear regression of AUDPC better described the relationships between faba bean yield and disease severity compared to percent severity index for the variety Shallo. The estimate showed that for each unit increase in percent of chocolate spot AUDPC, there was a grain yield loss of 1.19 kg/ha The estimated slope of the regression line obtained for the variety Shallo was -1.19. Based on coefficient of determination (R2) value, the equations explained about 78% of variation in yield due to chocolate spot severity. Maximum relative grain yield losses of 47.8 and 46.7% were recorded due to chocolate spot severity on the varieties Mosisa and Sinana local, respectively.

Plant age and ambient temperature: significant drivers for powdery mildew (Erysiphe cruciferarum) epidemics on oilseed rape (Brassica napus)

Powdery mildew (Erysiphe cruciferarum) is an important disease in oilseed rape crops worldwide, but of sporadic importance in most southern Australian crops. Six Brassica napus cultivars were exposed to E. cruciferarum simultaneously in four plant age cohorts. First symptoms of powdery mildew appeared 9 days after inoculation (dai) on the oldest plants [42 days after seeding (das)], but 44 dai in the youngest plants that were exposed to inoculum from sowing, although final disease severity did not differ with the plant age at exposure. The maximum level of pod peduncle infestation was unaffected by plant age (P = 0.37) or cultivar (P = 0.28). The effect of temperature was also investigated. The development of disease on plants was slower and final severity reduced at a day/night temperature 14/10 °C compared with 22/17 °C. In vitro, maximum growth of germ tubes from conidia of E. cruciferarum was at 15–20 °C and survival of conidia reduced by temperatures &gt;30 °C. The results explain the sporadic nature of powdery mildew outbreaks in winter‐grown oilseed rape in Australia, where slow rates of infection occur when seasonal colder prevailing winter conditions coincide with the presence of younger plants, together curtailing rapid disease development until temperatures increase in late winter/early spring. These results explain why epidemics are most severe in the two warmer cropping regions, viz. the northern agricultural region of Western Australia and New South Wales. This study suggests that with increases in winter temperatures under future climate scenarios, earlier and more severe powdery mildew outbreaks in Australia will be favoured.

Climate change effects on leaf rust of wheat: Implementing a coupled crop-disease model in a French regional application

Abstract Leaf rust is responsible for significant wheat yield losses. Its occurrence and severity have increased in recent years, partly because of warmer climate. It is therefore critical to understand and anticipate the effects of climate change on leaf rust. Direct climate effects and indirect effects via host plants that provide a biophysical environment for disease development were both considered. The coupled STICS-MILA model simulates both crop and pathogen dynamics in a mechanistic way and their interaction is managed by two sub-models: one calculating the microclimate within the canopy and the other converting numbers of spores and lesions to affected surfaces. In this study, STICS-MILA was first calibrated and evaluated using leaf rust severity observed at various sites in France for multiple years. STICS-MILA was then run on three contrasting French sites under 2.6, 4.5 and 8.5 RCP future climate scenarios. Results focused firstly on changes in disease earliness and intensity, secondly on disease dynamics, particularly the synchronism between plant and disease developments, and finally on elementary epidemic processes. The calibration and evaluation of STICS-MILA revealed a high sensitivity to the initial amount of primary inoculum (a forcing variable in STICS-MILA) and thus the need to properly simulate the summering and overwintering pathogen survival. The simulations in the context of future climate showed a significant change in host-pathogen synchronism: in the far future, according to RCP 4.5 and 8.5 scenarios, disease onset is expected to occur not only with an advance of around one month but also at an earlier developmental stage of wheat crops. This positive effect results from rising temperatures, nevertheless partly counter-balanced during spring by lower wetness frequency. The crop growth accelerates during juvenile stages, providing a greater support for disease development. The resulting microclimate shortens latency periods and increases infection and sporulation efficiencies, thus causing more infectious cycles. An increase of final disease severity is thus forecasted with climate change.

Screening St. Augustinegrass Genotypes for Brown Patch and Large Patch Disease Resistance

Two diseases of St. Augustinegrass (SAG) [Stenotaphrum secundatum (Walt.). Ktze.] are caused by different anastomosis groups (AGs) of Rhizoctonia solani. Brown patch (BP) is a foliar disease of little economic importance, and large patch (LP) causes leaf sheath rot and death of affected turfgrass shoots and stolons. St. Augustinegrass genotypes were inoculated with an isolate that causes BP and an isolate that causes LP in repeated experiments. Three disease severity parameters were calculated from data recorded from each genotype, including final disease severity (Y), area under the disease progress curve (AUDPC), and the apparent infection rate (r L ). The inoculation protocol reliably produced symptoms, and both r L and AUDPC provided statistically significant separations between genotypes for their susceptibility to BP and LP. A significant interaction between isolate and genotype was observed, and some genotypes that were very susceptible to LP were among the least susceptible to BP. These data suggest that differences in resistance to LP can be quantified in SAG genotypes, but genotype response may be isolate dependent.

Influence of Humate Substances and Fungicides on the Control of Onion Downy Mildew

Downy mildew of onion (Allium cepa), caused by Peronospora destructor, is one of the most important onion diseases that mainly controlled by fungicides. This investigation aimed to evaluate the effect of foliar application of two forms of humic substances (HS) individually or in combinations with two fungicides against downy mildew, growth, photosynthetic capacity and metabolism changes of onion. The trials were carried out during the growing seasons 2016 and 2017. Final disease severity (FDS%) andarea under disease progress curve (AUDPC) were used to assess the potential of twoforms of (HS), and two fungicides to control downy mildew of onion. All treatments resulted in minimizing the FDS (%) and AUDPC, compared to control treatment, during the two seasons. The most effective treatment was (HS)-leonardite combined with fungicide Ridomil Gold 68% (WP), which exhibited a significant decrease in FDS (%) and AUDPC in relation to other treatments and control. All treatments improved onion growth parameters i.e., bulb diameter, plant height, dry eight/plant, dry matter, average yield compared to untreated control plants. The chemical changes in treated plants i.e., enzymes activities, total carbohydrates, total nitrogen (%), total soluble solids (TSS %) were also assessed. Principal component analysis gave evidence to the importance of all parameters in this study, especially FDS (%), as a reliable indicator for evaluation of these materials against downy mildew disease.

Evaluation of Greek grapevine cultivars for resistance to Phaeomoniella chlamydospora

In the present study, four Greek (Agiorgitiko, Asyrtiko, Roditis and Xinomavro) and one international (Soultanina) grapevine cultivars (Vitis vinifera L.) were screened for their resistance to Phaeomoniella chlamydospora. Artificial inoculation was carried out by drilling a hole into the trunk and injecting a concentrated conidial suspension into the vessels. Disease reactions were evaluated in an 87-day assessment period, on the basis of external symptoms (disease incidence, disease severity and mortality) and by calculating the relative areas under disease progress curves (relative AUDPC). The extension of vascular browning as well as the isolation ratio along the inoculated vine trunks were also taken into account as additional parameters for evaluating resistance. The results indicated that the resistance of grapevine cultivars to P. chlamydospora varied significantly. ‘Agiorgitiko’ and ‘Soultanina’ were susceptible, whereas ‘Asyrtiko’ and ‘Xinomavro’ were resistant; ‘Roditis’ showed an intermediate level of resistance. Cultivars’ resistance was mostly distinguished in terms of the extension of vascular browning and pathogen isolation ratio. On the contrary, the disease incidence, final disease severity, mortality and relative AUDPC provided less distinctive efficiency in resistance evaluation. The robust methodology presented here could be useful in rapid evaluation experiments for future screening programs to search and recognize natural resistant sources within grapevine genotypes against P. chlamydospora.

Stripe Rust Partial Resistance Increases Spring Bread Wheat Yield in South‐eastern Anatolia, Turkey

AbstractStripe rust caused by Puccinia striiformis f.sp. tritici is the most serious disease of wheat globally including south‐eastern Anatolia of Turkey, where wheat originated. In this study, 12 spring wheat genotypes were artificially inoculated and preserved in two locations, Diyarbakır and Adıyaman, during the 2011–2012 season to investigate loss in yield and yield components. Genotypes were evaluated at the adult plant stage using two partial resistance parameters: final disease severity and area under the disease progress curve (AUDPC). AUDPC ranged from 14.8 to 860 in Diyarbakır, and 74 to 760 in Adıyaman. Yield loss ranged from 0.6 to 68.5% in Diyarbakır and 9.8 to 56.8% in Adıyaman. Genotypes G1, G5, G7 and G8 were found to lose less yield, while higher yield loss was observed in G3, G4 (Nurkent), G5 and G9 (Karacadağ‐98). The highest loss in thousand kernel weight was observed in a susceptible cultivar Karacadağ‐98 in Diyarbakır followed by 43.4 and 24.4% in Adıyaman. Test weight loss reached 8.89% in Diyarbakır and 20.8% in Adıyaman. Yield loss and AUDPC had a positive significant relationship. Based on the values of AUDPC, final disease severity and yield loss, three major clusters were formed for 12 wheat genotypes. Partially resistant genotypes were found to lose less grain yield and seemed to be stronger against severe stripe rust pressure.

English

Stem rust (Puccinia graminis f.sp.tritici) of wheat (Triticum aestivum) has caused wheat yield losses in Kenya for years and the trend shows the situation has worsened. The objective of the research was to identify elite genotypes for adult plant and seedling stage resistance. Adult plant resistance study was done under natural conditions in three locations. Scoring was done following the modified Cobbs scale. Seedling stage resistance was done in the greenhouse and scored following the Stakmans scale. Genotype KSL 144, 71, 50, 31 44, 115 were identified as having seedling stage resistance. Area Under Disease Progress Curve (AUDPC) and Final Disease Severity (FDS) when used for adult plant revealed KSL 142, 71, 144, 50, 31, 44, 115, 146, 69 and 76 as having resistance. The variance (Si) and Coefficient of Variation (CVi) was calculated from the FDS and yield values, which distinguished stable genotypes. The stable genotypes for disease severity were KSL 69 (8.8%), 161 (14.9%), 54 (12.4%), 156 (18.24%). The relationship between yield and AUDPC was strong and negative, r=-0. 943 same as yield and FDS relationship r= -0.84. Variation for yield performance was recorded KSL 137 (2.63t/ha), KSL 31 (2.52 t/ha) showing high performance. The thousand kernel weight values were not significant for the three location at (P<0.05). The advanced genotypes that consistently performed better should be released as varieties or used in improving local varieties in the Kenyan wheat stem rust breeding programme or potentially in the Eastern Africa region. Key words: Ug99, disease severity, Area Under Disease Progress Curve (AUDPC), resistance.

Effects of Bacillus subtilis strain QST 713 and storage temperatures on post-harvest disease development on greenhouse tomatoes

Tomato plants in two commercial greenhouses were treated with Rhapsody (Bacillus subtilis strain QST 713, rate of 1.45%) once every 4 weeks during 2012–2013 to determine effects on post-harvest fruit infection. Populations of Bacillus and disease incidence were monitored weekly from harvested fruit over an 18-week period. Population levels of Bacillus ranged from 75 to 110 × 104 colony forming units (cfu) cm−2 of fruit surface area one week after application to 25–30 × 104 cfu cm−2 of fruit surface area 4 weeks after application. Disease incidence on harvested fruit incubated at 21 °C for 7–10 days was variable, due to variation in inoculum levels within the greenhouse as well as variable environmental conditions. Both disease incidence and severity were significantly reduced on Rhapsody-treated fruit, especially in the 1–2 week period following application. Post-harvest storage temperature (13 °C vs. 21 °C) and incubation time (12 vs. 16 days) had a significant effect on final disease severity. Rhapsody-treated fruit incubated at 13 °C had an average of 1–2% fruit infection compared to up to 20% infection on untreated fruit at 21 °C. The most frequent pathogens affecting fruit quality were Penicillium sp. and Rhizopus stolonifer. Rhapsody applications made every 4 weeks maintained sufficiently high populations of Bacillus on the fruit surface to prevent spread of these fungi onto the fruit, resulting in significant post-harvest disease control on fresh market tomatoes. When combined with storage at 13 °C for no more than 12 days, disease was reduced to negligible levels.

Effect of Integrated Climate Change Resilient Cultural Practices on Faba Bean Rust (Uromyces viciae-fabae) Epidemics in Hararghe Highlands, Ethiopia

Climate variability due to increasing temperature and erratic precipitation could affect faba bean rust disease epidemics and the crop productivity. Rust caused by Uromyces viciae-fabae is one of the serious foliar diseases of faba bean in Ethiopia. Field studies were conducted at Haramaya and Arbarakate during 2012 and 2013 to assess effects of integrated climate change resilient cultural practices on rust epidemics in the Hararghe highlands of Ethiopia. Three climate change resilient cultural practices: intercropping, compost application and furrow planting alone and in integration were evaluated using Degaga and Bulga-70 faba bean varieties and Melkassa-IV maize variety. Treatments were factorial arranged in a randomized complete block design with three replications. Faba bean-maize row intercropping and intercropping integrated treatments significantly reduced disease severity, AUDPC and disease progress rate. These treatments reduced rust mean severity by up to 36.5% (2012) and 27.4% (2013) at Haramaya, and up to 27% in 2013 at Arbarakate on both varieties as compared to sole planting. Compost fertilization also led to slow epidemic progression of rust and significantly reduced disease parameters when integrated with maize row intercropping. Compost fertilization in row intercropping recorded the lowest (23.1%) final mean disease severity and the highest (36.5%) percentage reduction in mean disease severity compared to sole cropping at Haramaya in 2012. The trend was similar in 2013 at both locations. Degaga had the lowest rust disease parameters studied compared to Bulga-70 at both locations over years. The overall results indicated that integrated climate change resilient cultural practices were effective to slow the epidemics of rust and to increase faba bean productivity. Hence, integrated climate change resilient cultural practices along with other crop management systems are recommended in the study areas.

Response of some Commercial Strawberry Cultivars to Infection by Wilt Diseases in Egypt and their Control with Fungicides

Isolation trials carried out from naturally infected strawberry plants by wilt diseases grown in three Counties at Qalubiya Governorate resulted in the presence of four fungi with different frequencies. These fungi were identified as Fusarium oxysporum, Verticillium dahliae, Rhizoctonia solani and Pythium sp. Pathogenicity test using the four fungi showed that only F. oxysporum and V. dahliae were able to cause the typical symptoms of wilt. Evaluation of six strawberrycultivars against F. oxysporum and V. dahliae under greenhouse conditions revealed that cvs. Festival, Florida and Sweet Charlie were less susceptible. While under field conditions they exhibited low percentages of final disease severity and low values of area under disease progress curve (AUDPC), low values of relative area under disease progress curve (rAUDPC) and low rates of infection (r-values) during the two tested growing seasons of 2010/11 and 2011/12. On the other hand, cvs. Fortuna and Camarosa exhibited the opposite results in this respect. Six fungicides were evaluated on the susceptiblecv. Camarosa under greenhouse conditions and for two successive seasons under field conditions (2011/12 and 2012/13) where the most effective fungicides were Uniform, Tachigaren and Topsin-M in controlling wilt infection. The highest yield increase percentage was recorded in cv. Camarosa during the two growing seasons (2012/13 and 2013/14) under protective trial by Uniform fungicide.

Genetics of Partial Resistance to Leaf Rust (Puccinia triticina) in Bread Wheat (Triticum aestivum)

The genetics of partial resistance to leaf rust (Puccinia triticina Erikss. & Henn.) in bread wheat (Triticum aestivum L. em Thell) was investigated in a nine-parent diallel (excluding reciprocals) using area under disease progress curve (AUDPC) and final disease severity (FDS) in the F1 and F2 generations. Test material consisted of slow rusting and susceptible lines. The Vr–Wr graphs exhibited partial dominance for FDS and complete dominance for AUDPC (F1 and F2 generations). Parents CPAN1796, HD2329, NW1014 and MACS2496 had preponderance of minor genes for partial resistance, whereas susceptible parents SONALIKA and HS1138-6-4 showed the absence of minor genes for both AUDPC and FDS (F1 and F2 generations). Variations due to additive and dominance genetic variances were significant for both AUDPC and FDS (F1 and F2 generations). The estimate of 1–3 minor gene(s) in the slow rusting parents may be responsible for race non-specific adult plant resistance. Since narrow-sense heritability for both AUDPC and FDS was moderate in both F1 and F2, success in selecting desirable lines with partial resistance to leaf rust in early segregating generations can easily be achieved. The parents CPAN1796, NW1014, HD2329, PBW373 and RAJ3077 with low AUDPC and FDS having partial resistance either due to Lr34 and/or minor genes were identified as good general combiners. The parents identified in the study can be used in breeding program for developing high-yielding cultivars with durable leaf rust resistance.

Integrated management of Ascochyta blight (Didymella fabae) on faba bean under Mediterranean conditions

Integrated disease management options (two sowing dates, three fungicides and 3–6 faba bean genotypes) in managing Ascochyta blight affecting faba bean were evaluated for three cropping seasons (2006/07–2008/09) in northern Syria for their effects on disease parameters, seed infection and dry seed yield. The combined results of the three seasons on disease parameters showed that sowing dates significantly affected final disease severity and area under the disease progress curve (AUDPC); faba bean genotypes significantly affected final disease severity, rate of disease development and AUDPC. The highest AUDPC (255% days) was observed in early than late planted (168% days) faba bean genotypes. The mean AUDPC of faba bean genotypes ranged from 189% days on genotype 1053–1325 to 234% days on ILB-1814. Only faba bean genotypes and fungicides showed significant interactions in affecting final disease severity and AUDPC. Fungicide sprays significantly affected mean percent pod infection and rate of disease development but not mean percent seed infection. Faba bean genotypes showed significant differences in dry seed yield and the yield ranged from 1.7 t ha−1 in cv. Ascot to 2.4 t ha−1 in faba bean genotype 945-105. Improved varieties with Ascochyta blight resistance are not currently released and available for farmers in northern Syria and the integration of early planting (November–December) with one foliar fungicide spray at vegetative stage can help to reduce Ascochyta blight severity, pod and seed infections. Chlorothalonil and azoxystrobin are widely used fungicides to manage Ascochyta blights on food legumes in many countries and one of them could be used depending on their availability and costs to managing faba bean Ascochyta blight in Syria and other Mediterranean type environments.

Effect of silicon on the severity of brown rust of sugarcane in South Africa

Silicon (Si) has been identified as a key element in the management of a wide range of pests and diseases in plants. This study focused on the effect of Si on the severity of brown rust of sugarcane caused by Puccinia melanocephala H & P. Sydow. The trial, repeated twice, consisted of eight treatments which included two different forms of Si and a control to which no Si was added. Plants were naturally infected by spores from brown rust-infected plants within a polytunnel. From three weeks after planting, plants were rated weekly for disease severity and these data were used to calculate an area under disease progress curve (AUDPC). All treatments ≥400 mg Si l−1 had a significantly lower final disease severity rating and AUDPC than the untreated control. No significant difference in disease severity was noted between the 1600 and 2000 mg Si l−1 treatments. A once off application of calcium silicate at a concentration of 1016 mg Si l−1, applied at planting provided the same reduction in disease severity as K2SiO3 applied weekly at a Si concentration of 1200 mg Si l−1. There was a significant negative relationship between the concentration of Si added and disease severity. A similar relationship was noted for the disease severity index and Si accumulation and deposition in the leaf. Results from this study showed a reduction in brown rust severity with an increase in Si content in the plant.

Aspects of the epidemiology and control of powdery mildew (Oidium neolycopersici) on tomato in Ontario, Canada

The epidemiology and control of powdery mildew (Oidium neolycopersici) of tomato (Solanum lycopersicum L.) was studied in greenhouse, growth chamber, and field experiments at Harrow, Ontario. Greenhouse environmental conditions were more favourable for disease development, with higher disease progress rates than in the field. Symptoms were more severe on older, lower leaves where the air temperature was slightly lower and relative humidity higher than on young leaves at the top of the canopy. A temperature of 22°C with 16 or 24 h of leaf wetness was optimal for disease development in a growth chamber experiment. Early inoculation resulted in significantly greater final disease severity and area under the disease progress curve than later inoculations. Disease progress in greenhouse and growth chamber trials was best described by the Gompertz model, while the logistic model was best for disease progress in field studies and for sections of plants in greenhouse studies. No yield loss occurred in field studies. The best disease control was obtained with acibenzolar-S-methyl (Actigard®), trifloxystrobin (Flint®), JMS-Stylet Oil®, azoxystrobin (Quadris®) and sulphur applied as protectants. Some phytotoxicity occurred with Actigard in greenhouse studies. Serenade® (Bacillus subtilis) was less effective while Kaligreen, Sporodex® (Pseudozyma flocculosa), copper octanoate and fumed silica were ineffective. Quinoxyfen was phytotoxic at the rate applied. Several tobacco cultivars, jimsonweed, American and black nightshade were susceptible to infection by O. neolycopersici. Eggplant, hairy nightshade and bittersweet were less susceptible, while no visible symptoms developed on pepper, potato and tomato ‘Grace’, and only trace levels of sporulation occurred on cucumber.

Progresso temporal da cercosporiose da beterraba em diferentes genótipos e épocas de semeadura na primavera

A cultura da beterraba tem se intensificado devido ao consumo in natura e também pelo processamento industrial de conservas. Na região do Alto Vale do Itajaí, SC, grande parte da sua produção vem de agricultores familiares que a usam em sucessão a cultura da cebola, com semeadura na primavera/verão. Entretanto, nesta época do ano a cercosporiose (Cercospora beticola) tem comprometido a produtividade. O objetivo do trabalho foi avaliar o progresso desta doença nos genótipos: All Green, Stays Green, Early Wonder, Cabernet, Boro, Modana e Itapuã e avaliar a severidade em duas épocas de semeadura, na primavera. Os dois ensaios foram conduzidos na Epagri/Estação Experimental de Ituporanga, implantados com 30 dias de diferença entre as semeaduras. O delineamento experimental foi de blocos casualizados com quatro repetições. Para avaliação da severidade da doença foi utilizada uma escala diagramática em dez plantas ao acaso previamente demarcadas. Os dados de severidade foram submetidos à análise de modelos mistos, area abaixo da curva de progresso de doença, taxa de infecção e severidade final. Não houve diferenças no progresso da doença entre os genótipos avaliados nas duas épocas de semeadura de primavera nas condições do Alto Vale do Itajaí, SC.

The effects of temperature and wetness duration on the development of Guignardia psidii in guava fruit naturally infected

A survey conducted in SP state in 2005 and another in 2007 found that black spot (Guignardia psidii) incidence on guava reached 58 %. The aim of this study was to investigate the effects of temperature and wetness duration on the development of black spot symptoms in detached guava naturally infected under controlled conditions. Guava fruit cv. Kumagai from a production field with a history of occurrence of the disease were subjected to different temperatures (10, 15, 20, 25, 30 and 35 °C) with wetness periods of 6 and 24 h. Analyses of variance and nonlinear regression were employed to evaluate the combined effects of temperature and wetness duration on the disease incidence, the final disease severity, the rate of disease progression and incubation period. Black spot symptoms were observed at all temperatures, except at 10 and 35 °C. The first symptoms of black spot in guavas were observed 2 days after incubation at 25 and 30 °C with wetness duration of 6 h. All variables reached their maximum values close to 30 °C, regardless of wetness duration. This temperature combined with 24 h of wetness duration resulted in black spot incidence of 100 %, disease severity of 3.02 cm, progress rate of 6.9 mm/day and incubation period of 6 days, 10 days after incubation. The postharvest storage of fruits at 10 °C and other control methods based on low or high temperature can delay the black spot incidence on ‘Kumagai’ guavas and prolong the fruit shelf life.