Occurrence Of Rust Research Articles

Seedling resistance to stem rust race Ug99 and marker analysis for Sr2, Sr24 and Sr31 in South African wheat cultivars and lines

The appearance and spread of races of Puccinia graminis f. sp. tritici with virulence for the Sr31 resistance gene has renewed interest in breeding for durable resistance to stem rust of wheat. Since the occurrence of stem rust has been low in South Africa until the detection of race TTKSF in 2000, breeding for resistance to this disease has not been a primary objective. The aim of this study was to test bread wheat cultivars and lines at the seedling stage for their infection response to stem rust, thus determining their level of resistance or vulnerability. A collection of 65 bread wheat entries was tested with one USA race, two Eastern African races, and three South African races of P. graminis f. sp. tritici. The Eastern African and South African races all belong to the Ug99 lineage. The cultivars Duzi, Caledon, Elands, PAN 3364, PAN 3191, SST 047, SST 399, and Steenbras produced resistant infection types (IT < 3) to all races. The molecular marker Sr24#50 indicated the presence of Sr24 in 12 entries. In cultivars resistant to TTTTF, TTKSF, and TTKSP but susceptible to TTKSK and PTKST, the iag95 DNA marker indicated the presence of Sr31 in five wheat lines. Using the cleaved amplified polymorphic sequence marker csSr2, Sr2 was detected in PAN 3377, Inia, and Steenbras. Few South African wheat cultivars appear to have a broad-based resistance to stem rust, as 88% of the entries were susceptible as seedlings to at least one of the races tested. Diversification of resistance sources and more directed breeding for stem rust resistance are needed in South Africa.

Association of Faba Bean Rust (Uromyces viciae-fabae) with Environmental Factors and Cultural Practices in the Hararghe Highlands, Eastern Ethiopia

Disease survey was conducted in Hararghe highlands of Ethiopia during the 2009 cropping season to determine the incidence and severity of faba bean rust (Uromyces viciae-fabae) in major growing districts of Hararghe highlands, and its association with environmental factors and cultural practices. A total of 90 faba bean fields were surveyed in six districts. Sample plants were systematically selected in an “X” fashion. In each field, 10 plants were sampled for disease assessment. During the survey, altitude, type of cropping system, weed management practices, crop growth stage, previous crop in the field and sowing date were recorded. Significant differences among locations were indicated with respect to altitude, sowing date, crop growth stage and field management practices. The mean incidence of the disease varied from 44.6% in Bedeno to 98% in Tullo, while severity of the disease varied from 12.7% in Bedeno to 65% in Gorogutu and Kurfachale districts. Logistic regression analysis for the association of rust incidence and severity with environmental factors and cultural practices as independent variables showed rust incidence below 80% had a high probability of association with Deder district, areas with altitude above 2450 m.a.s.l. and when faba bean was planted after July 25. Rust incidence above 80% had a high probability of association with Gorogutu, Kurfachale, Tullo districts; altitudes below 2450 masl, and when faba bean was planted from the end of June up to July 25. Similarly, disease severity below 40% had a high probability of association with Bedeno district, flowering growth stage, altitude above 2450 m.a.s.l., and when weeds were managed properly. Disease severity greater than 40% had a high probability of association with Gorogutu, Kurfachale, Tullo, Deder and Metta districts, altitudes below 2450 m.a.s.l., podding and late podding growth stages, and where poor weed management was practiced. The survey revealed high occurrence and distribution of faba bean rust in the study area and the need for effective and feasible management options to be developed. Keywords : Disease Incidence; Disease Severity; Faba Bean Rust; Uromyces viciae-fabae; Weed Management

Intensidade da ferrugem e da cercosporiose em cafeeiro quanto à face de exposição das plantas

Knowledge of coffee leaf diseases related to sun exposition can contribute to better sampling techniques to evaluate diseases and reduce agricultural losses. This work evaluated the coffee rust (Hemileia vastatrix Berk. & Broome) and cercospora leaf spot (Cercospora coffeicola Berk. & Cooke (= Mycosphaerella coffeicola (Cooke) Stev. & Wellman)) intensity on coffee leaves (Coffea arabica L.) exposed to North or South. The disease intensity was evaluated at coffee leaves of cultivar Rubi, at average interval of 23 days, from April 2004 to June 2006. The experimental design was randomized blocks at the factorial scheme of 6 water depths x 2 plant sides and 3 replicates, being the plant sides related to North or South direction exposition. The area below the disease progress curve (AACPD) was evaluated and compared through analysis of variance. It was found that the exposition side presented significant differences related to rust occurrence and intensity on both agricultural years 2004/2005 and 2005/2006. Larger increase on rust occurrence was observed on leaves exposed to South compared to North direction. Larger occurrence of shading on plant side turned to South direction and longer leaf wetting periods on this side may have caused the rust progression. For cercospora leaf spot occurrence, significant influence was observed according to plant side only at agricultural year 2004/2005, with larger incidence on those leaves turned to North direction. Larger solar radiation incidence on this side may have been the cause for cercospora leaf spot progress on these leaves. Thus, in order to get more representative leaf samples for rust and cercospora investigation, this study suggests considering plant orientation in relation to suns trajectory.

リンドウにさび胞子世代を有するヌマガヤさび病菌 Puccinia moliniae , 特にリンドウが自生しないヌマガヤ湿原における発生特徴について

リンドウにさび胞子世代を有するヌマガヤさび病菌 Puccinia moliniae , 特にリンドウが自生しないヌマガヤ湿原における発生特徴について

Effect of Melampsora larici-populina on growthand biomass yield of eight clones of Populus nigra

This study evaluates the effect of the identified pathogenic races E1, E2 and E3 of the leaf rust Melampsora larici-populina on some growth traits and biomass yield in the species Populus nigra. A field trial was conducted with 8 clones of P. nigra using fungicide-sprayed and unsprayed treatments in 3 replications of 4 plants. In the course of three years the occurrence of the rust was evaluated on a six-point scale. The plant height and stem diameter were measured during the trial. In the last year the plants were harvested and the dry weight was determined. In the untreated plants a significant negative correlation was found between the intensity of rust occurrence and the values of stem diameter and dry matter yield (P &amp;lt; 0.05). A decline in dry matter yield caused by the rust was low (below 9%) or zero in a half of the clones while it ranged between 19% and 28% in the other half of clones. In some clones the yield decline was relatively low although the expression of rust symptoms was rather high which could be attributed to a tolerance to the given pathogen.

化成処理鋼板の白錆の定量的外観評価技術

In relation to the evaluation of corrosion resistance of zinc-coated steel sheets with chemical conversion coatings, evaluation of white rust occurrence is commonly conducted by visual observation of the specimens. However, because large individual variation exists in evaluation by visual observation and minute white rust is generated on the specimen surface, it is difficult to evaluate corrosion resistance objectively. An evaluation method was developed to appropriately evaluate the corrosion resistance of zinc-coated steel sheets with chemical conversion of coatings. It can visualize minute white rust accurately using low-angle lighting, a line scan camera, and a linear stage. Furthermore, the corrosion area ratio of the white rust can be evaluated quantitatively using image analysis. Good correlation was found between the developed quantitative analysis method and evaluation by visual observation.The developed quantitative analysis method is applicable to various corrosion tests such as the exposure test, the salt spray test (SST), the combined cyclic corrosion test (CCT), and a new accelerated corrosion test (ACTE: Accelerated Corrosion Test for Electrical appliances). Superior correlation was found between the ACTE results and corrosion in actual environments. The ACTE test can estimate the influence of the amount of deposited sea salt on corrosion resistance of materials. The ACTE test and the developed quantitative analysis method enable appropriate evaluation of the corrosion resistance of zinc-coated steel sheets with chromate-free coatings.

Influences of the biophysical environment on blister rust and mountain pine beetle, and their interactions, in whitebark pine forests

Aim To understand how the biophysical environment influences patterns of infection by non-native blister rust (caused by Cronartium ribicola) and mortality caused by native mountain pine beetles (Dendroctonus ponderosae) in whitebark pine (Pinus albicaulis) communities, to determine how these disturbances interact, and to gain insight into how climate change may influence these patterns in the future. Location High-elevation forests in south-west Montana, central Idaho, eastern and western Oregon, USA. Methods Stand inventory and dendroecological methods were used to assess stand structure and composition and to reconstruct forest history at sixty 0.1-ha plots. Patterns of blister rust infection and mountain pine beetle-caused mortality in whitebark pine trees were examined using nonparametric Kruskal–Wallis ANOVA, Mann–Whitney U-tests, and Kolmogorov–Smirnov two-sample tests. Stepwise regression was used to build models of blister rust infection and mountain pine beetle-related mortality rates based on a suite of biophysical site variables. Results Occurrence of blister rust infections was significantly different among the mountain ranges, with a general gradient of decreasing blister rust occurrence from east to west. Evidence of mountain pine beetle-caused mortality was identified on 83% of all dead whitebark pine trees and was relatively homogenous across the study area. Blister rust infected trees of all ages and sizes uniformly, while mountain pine beetles infested older, larger trees at all sites. Stepwise regressions explained 64% and 58% of the variance in blister rust infection and beetle-caused mortality, respectively, indicating that these processes are strongly influenced by the biophysical environment. More open stand structures produced by beetle outbreaks may increase the exposure of surviving whitebark pine trees to blister rust infection. Main conclusions Variability in the patterns of blister rust infection and mountain pine beetle-caused mortality elucidated the fundamental dynamics of these disturbance agents and suggests that the effects of climate change will be complex in whitebark pine communities and vary across the species’ range. Interactions between blister rust and beetle outbreaks may accelerate declines or facilitate the rise of rust resistance in whitebark pine depending on forest conditions at the time of the outbreak.

Occurrence of leaf rust of canna in Singapore caused by Puccinia thaliae

Occurrence of leaf rust of canna in Singapore caused by <i>Puccinia thaliae</i>

Occurrence and expansion of wheat stripe rust under mixed-cultivar planting

在田间分别设计6个小麦品种单播及其9个组合混播小区, 研究条锈病在小麦混播群体中的发生、扩展情况及品种混播对条锈病的控制效果。结果表明, 苗期品种混播小区发病中心的数量明显减少, 条锈病发病中心越冬率达77.78%, 单片病叶也可越冬。品种混播降低了条锈病传播距离, 条锈病在各小区呈中心式分布。品种混播在孕穗期的相对防效为16.25%~58.89%, 平均为35.31%。相对防效以“陕138”和“西农979”品种混播及“陕138”、“小偃22”和“西农889”品种混播最高, 分别达58.89%和52.19%。品种混播对小麦条锈病有较好的控制效果, 可作为生态防病措施之一。

Modelos de pontos críticos para relacionar o rendimento de grãos de aveia branca com a intensidade de doença no patossistema múltiplo ferrugem da folha: helmintosporiose

A ferrugem da folha e a helmintosporiose são as principais doenças fúngicas foliares de aveia branca. Em cultivares suscetíveis, o controle químico não considera o limiar de dano econômico (LDE). O objetivo deste trabalho foi obter funções de dano, por modelos de ponto crítico, ao relacionar o dano pela ocorrência simultânea da ferrugem da folha e a helmintosporiose com o rendimento de grãos nas safras de 2006 e 2007, em Lages, Santa Catarina (SC). O gradiente da intensidade das doenças foi gerado por número de aplicações e doses de fungicidas nas cultivares 'UPFA 20' e 'UPFA 22'. Os ensaios consistiram de 10 tratamentos, distribuídos em blocos casualizados, com quatro repetições. As doenças foram avaliadas nos estádios de alongamento, emborrachamento e florescimento. Os modelos de ponto crítico foram obtidos por regressão linear entre rendimento de grãos e incidência (I) e severidade (S). Em 2006, funções significativas foram obtidas para 'UPFA 20' no emborrachamento (R=6.345-22,07I), enquanto para a 'UPFA 22' foi obtida no alongamento (R=5.726-17,96I; R=5.160-541,5S), emborrachamento (R=5.961-21,85I; R=5.433-966,8S) e florescimento (R=6.217-36,41I; R=5.539-1.185S). Em 2007, para 'UPFA 20', no alongamento (R=6.369-55,61I; R=4.965-2.911S), emborrachamento (R=6.620-40,91I; R=5.181-1.702S) e florescimento (R=6.129-32,34I; R=5.252-638,6S), e para 'UPFA 22', no alongamento (R=5.201-41,96I; R=4.977-657,8S), emborrachamento (R=5.329-60,51I; R=4.238-798,1S) e florescimento (R=5.604-32,83I; R=4.680-588,5S). A produção na cultivar 'UPFA 22' foi mais afetada pela ocorrência das doenças, e a intensidade das doenças no estádio de florescimento apresentou maior relação com o rendimento de grãos. As funções geradas permitem obter o coeficiente de dano para uso no cálculo do LDE em patossistema múltiplo ferrugem da folha e helmintosporiose.

Predicting the risk of soybean rust in Minnesota based on an integrated atmospheric model

To minimize crop loss by assisting in timely disease management and reducing fungicide use, an integrated atmospheric model was developed and tested for predicting the risk of occurrence of soybean rust in Minnesota. The model includes a long-range atmospheric spore transport and deposition module coupled to a leaf wetness module. The latter is required for spore germination and infection. Predictions are made on a daily basis for up to 7 days in advance using forecast data from the United States National Weather Service. Complementing the transport and leaf wetness modules, bulk (wet plus dry) atmospheric deposition samples from Minnesota were examined for soybean rust spores using a specific DNA test and sequence analysis. Overall, the risk prediction worked satisfactorily within the bounds of the uncertainty associated with the use of modeled 7-day weather forecasts, with more than 65% agreement between the model forecast and the DNA test results. The daily predictions are available as an advisory to the user community through the University of Minnesota Extension. However, users must take the actual decision to implement the disease management strategy.

Precipitation and dew in a soybean canopy: Spatial variations in leaf wetness and implications for Phakopsora pachyrhizi infection

With the occurrence of soybean rust ( Phakopsora pachyrhizi) now a seasonal problem in the United States, increased research is needed to ascertain the potential transmission of this disease among soybean ( Glycine max L.) in major growing regions throughout the nation. The fungal disease spores are deposited on leaves in the lower region of the canopy through rain events or wind transport from nearby plants during the growing season and must then have moist conditions on the lower trifoliolates for several hours in order to infect the plant. These moist conditions can be achieved through any form of wetness. This wetness was measured in a soybean canopy at West Lafayette, IN, during the summer of 2007 using resistance-grid wetness sensors located at three heights representative of the top, mid-level, and lowest trifoliate of the canopy. Temperature, relative humidity, wind speed, and precipitation measurements were used to determine the cause of wetness. Over the course of the experiment, wetness events were classified as dew, rain, or neither. The dew events were then compared to rain events with an emphasis on differences in vertical and horizontal duration of wetness. Dew events were found to be the dominant wetness source in the upper canopy. Rain events were the most dominant cause of wetness in the lower canopy. Upper canopy wetness events had the longest duration. Horizontal variation in wetness and wetness duration was large.

Widespread Occurrence of the Aecial Stage of Sunflower Rust Caused by Puccinia helianthi in North Dakota and Minnesota in 2008.

Sunflower rust caused by Puccinia helianthi (Schw.) is widespread in North America and occurs annually on cultivated sunflower (Helianthus annuus L.) and wild annual and perennial Helianthus spp., although severity on the U.S. sunflower crop has been increasing in recent years (2). P. helianthi is a autoecious, macrocyclic rust, but the aecial stage is rarely observed in the field (1,3,4). In most years, the earliest appearance of sunflower rust in North Dakota (ND) and surrounding states usually occurs in early August as the uredinial stage. Initial inoculum can result from urediniospores that overwinter in the Northern Great Plains, urediniospores blown in from areas south of North Dakota, or basidiospores completing the life cycle. However, aecia have been noted very infrequently and never widespread, indicating initial inoculum is usually urediniospores. Aecia of P. helianthi were first observed on 24 June 2008 in a commercial sunflower field (confection hybrid CHS 3126) near Mohall, ND. Aecia cups measuring 0.2 to 0.3 mm in diameter were observed in clusters that were 1 to 7 mm wide in diameter and containing as many as 150 cups. Aecia cups were bright orange but turned brown-black as they senesced. As many as 15 aecial clusters occurred on individual leaves or cotyledons. Aeciospores were ellipsoid, hyaline, and measured approximately 20 μm in diameter. On 4 July 2008, uredinia were first observed in the same Mohall, ND field. At that time, uredinia, aecia, and senesced aecia could all be found on the same leaves. In a non-fungicide-treated strip of the field, pustule coverage on the lower leaves was 10 to 20% by mid-July, pustule coverage on the upper four leaves of plants in the untreated strip was 56% by 27 August, and yield at harvest was less than 200 kg/ha. The rest of the field was sprayed twice with fungicides and yielded 1,571 kg/ha, which is similar to the statewide yield average of 1,573 kg/ha in 2008. To determine the prevalence of aecia in the primary growing regions of ND and Minnesota (MN), surveys were conducted in 75 sunflower fields in 18 counties between 22 and 24 July in ND and 34 fields in 8 counties between 17 and 31 July in MN. Incidence of aecia and uredinia were determined by visual observation of a minimum of 20 plants scouted in a 'W' pattern in the field. Rust was found in 31 and 53% of fields in ND and MN, respectively. In fields where rust was found, both aecia and uredinia were observed in 37% of the fields, aecia only in 29% of the fields, and uredinia only in 34% of the fields. Although it is uncertain why aecia were widespread in 2008, night temperatures in Mohall, ND, where aecia were first observed, reached the dew point temperature on 51 of 61 days in June and July, suggesting that dew or fog likely formed. Thus, favorable conditions for germination and infection early in the growing season indicate widespread occurrence of rust was likely a result of local inoculum sources. The early appearance of aecia is cause for concern for two reasons: significant yield loss can occur when rust appears early in the growing season; and the presence of aecia suggest that the pathogen completed its sexual cycle. When P. helianthi completes its life cycle it is likely that a greater diversity of races will result (4).

Rust severity in bioenergy willow plantations treated with additional nutrients

SummaryA 3‐year field study was carried out to determine the effect of wastewater irrigation and previous differences in mineral fertilization on the occurrence of willow leaf rust (Melampsora epitea). The experiment was conducted in two energy forest plantations: one designed for wastewater purification and the other as a mineral fertilization experiment. The severity of leaf rust on different clones and sites with different treatments was assessed by counting the number of uredinia per leaf unit area. Generally, plants irrigated with wastewater consistently had more leaf rust, irrespective of the study years or willow clones. Previous mineral fertilization had mixed effects on different clones 2 years after the last application. Three years after the last fertilizer application, however, no impact of the treatment on rust disease development was detected. In general, the rust levels differed from year to year probably due to climate. In this study, no correlation was detected between shoot age and rust severity, whereas climate and treatments strongly influenced leaf rust levels on some willow clones.

Tiny Terrors: The Soybean Aphid

known how these other hosts may playa role in the over-wintering of the fungus, and if they will provide a broader geographic base than that currently known for kudzu. Because the introduction of soybean rust is relatively new to the continental United States, much remains unknown about the potential in-season and overwintering distribution of the fungus. It seems likely, as it is with most invasive species, that it may take a decade to fully understand the distribution of the fungus and its capacity to cause economic losses to the U.S.soybean crop. References Cited Harmon, P. F.,M. T.Momol, J. J. Marios, H. Dankers, and C. L.Harmon. 2005. Asian soybean rust caused by Phakopsora pachyrhizi on soybean and kudzu in Florida. Online. Plant Health Progress:doi:10.1094/PHP2005-0613-01-RS. Hartman, G. L., R. A. Hines, C.D. Faulkner, T. N. Lynch, and N. Pataky. 2007. Late season occurrence of soybean rust caused by Phakopsora pachyrhizi on soybean in Illinois. Plant Dis. 91: 466. Killgore, E.,and R.Heu. 1994. First report of soybean rust in Hawaii. Plant Disease 78: 1216. Lynch, T.N., J. J. Marios, D. L.Wright, P. F.Harmon, C.L. Harmon, M. R. Miles, and G. L. Hartman. 2006. First report of soybean rust caused Phakopsora pachyrhizi on Phaseolus species in the United States. Plant Dis. 90: 970. Miles, M.R.,G.L.Hartman, and R.D.Frederick. 2003. Soybean rust: Is the U.S.crop at risk? [Online] http://www.apsnet.org/online/feature/rust Ono, Y.,P. Buritica, and J. F.Hennen. 1992. Delimitation of Phakopsora, Physopella and Cerotelium and their species on Leguminosae. Mycol. Res. 96: 825-850. Schneider, R.W.,C.A Hollier, H. K.Whitman, M.E.Palm, J.M.McKemy, J. R.Hernandez, L.Levy,and R.DeVries-Paterson. 2005. First report of soybean rust caused by Phakopsora pachyrhizi in the continental United States. Plant Dis. 89: 774. Sinclair, J. B., and G.L.Hartman, [Eds.] 1995. Proceedings of the soybean rust workshop, 9-11 Aug.1995, pp. i-vii, 68. National Soybean Research Laboratory, Urbana, IL.

Occurrence of wheat leaf rust (Puccinia triticina) races and virulence changes in Slovakia in 1994–2004

In 1995–2004 we investigated leaf rust virulence in Slovakia on Thatcher near isogenic lines (NILs) with genes Lr1, Lr2a, Lr2b, Lr2c, Lr3a, Lr9, Lr10, Lr11, Lr15, Lr17, Lr19, Lr21, Lr23, Lr24, Lr26 and Lr28. According to reaction of leaf rust isolates resistance genes Lr9 and Lr19 were completely effective to all examined pathotypes in all years. The resistance genes Lr24 and Lr28 were also completely effective to all examined pathotypes till the year 2001. In the year 2001 we detected 20% and 10% virulent isolates on NILs Lr24 and Lr28, respectively. According to the reaction of investigated isolates from the territory of Slovakia on NILs, resistance genes Lr2c, Lr3a, Lr11, Lr17, Lr21, Lr23 and Lr26 were mostly ineffective.

PUCREC/PUCTRI – a decision support system for the control of leaf rust of winter wheat and winter rye*

During a three‐year project from 2003 to 2006, two models have been developed to predict leaf rust (Puccinia recondita and P. triticina) occurrence and to simulate disease incidence progress curves on the upper leaf layers of winter rye (PUCREC) and winter wheat (PUCTRI). As input parameters the models use air temperature, relative humidity and precipitation. PUCREC and PUCTRI firstly calculate daily infection favourability and a cumulative infection pressure index and, in a second step, disease incidence is estimated. An ontogenetic model (SIMONTO) is used to link disease predictions to crop development. PUCREC and PUCTRI have been validated with data from 2001 to 2005. Both models give satisfactory results in simulating leaf rust epidemics and forecasting dates when action thresholds for leaf rust control are exceeded.

Occurrence of Rust Caused by Puccinia carthami on Snow Lotus in China.

Snow lotus (Saussurea involucrata (Kar. & Kir.) Sch. Bip.) is an economically important medicinal herb increasingly grown in China in recent years. In August 2005, a rust disease on snow lotus plants commercially grown was found in the Tianshan mountain area of Xinjiang at 2,100 m above sea level. Disease incidence was approximately 15% of the plants observed in a commercial field in 2006. At the initial stage, tiny (1 to 2 mm long), orange brown pustules are formed on leaves. Later in the season, pustules turned chestnut brown to form bigger rust patches. Severely attacked leaves may die prematurely. During the growing season, rust pustules broke open to release reddish brown spores that cause secondary infection. The infected snow lotus plants were sampled, and the urediniospores and teliospores were observed for identification with a light microscope (4). Urediniospores were globose or broadly ellipsoid, 22 to 28 × 22 to 25 μm; teliospores were slightly or not constricted at the septum, 31.5 to 41.5 × 21.5 to 26.5 μm, wall was sienna to fulvous, occasionally chestnut colored, and pedicels were basal or oblique, verrucose, hyaline, and fragile. The pathogenicity test of the fungus was done by burying five leaves bearing telia around the roots of healthy safflower seedlings grown in a greenhouse under controlled conditions (25°C and 70% relative humidity) and healthy snow lotus seedlings grown under natural conditions with five replications. Symptoms were evaluated 60 days after inoculation. Similar rust symptoms were observed on both the snow lotus and safflower seedlings (1). The pycnidial and aecial stages of this autoecious rust were not observed in nature or the pathogenicity tests. The teliospores were reisolated and deposited at the Key Oasis Eco-Agriculture Laboratory of Xinjiang Production and Construction Group, Xinjiang and the Institute of Biotechnology, Zhejiang University. The causal organism of rust of snow lotus was identified as Puccinia carthami Corda on the basis of the morphology and pathogenicity test. To our knowledge, this is the first report of this rust on snow lotus (S. involucrata) (1-4).

Genetic control of Asian rust in soybean

The objective of this study was to investigate the genetic mechanisms of soybean resistance to Asian rust (Phakopsora pachyrhizi Syd. & P. Syd). F2 and F3 generations from 15 diallel crosses involving six soybean cultivars, FT-2, EMBRAPA 48, BRS 154, BRS 184, BRS 214, BRS 231, were used to analyze the genetic control of Asian rust resistance in the soybean parents tested. Genetic models were fitted to means and variances of the generations tested in a completely randomized field experiment with 5,700 hill plots. The experiment was spray-inoculated twice with an isolate that was first detected during the 2002/03 season in Mato Grosso (MT) State and presently prevail in Central Brazil, at a six-day interval, on borders rows and on the useful area, respectively, with a 104 spores/ml distilled H2O suspension. Assessments were made using a diagrammatic scale for disease severity at seven and 39 days after the first detection of Asian rust in the experiments. Evaluations made in the second assessment (39 days) discriminated better between genotypes. Selection at early plant developmental stages may not result in adult resistant plants. Cultivar FT-2, which had presented monogenic resistance to a rust isolated that prevailed in the first two years of rust occurrence in Brazil, showed no resistance to the MT State rust strain used in this experiment, but eleven crosses showed genetic variability for resistance in the second assessment. Soybean rust resistant genes showing predominantly additive effects are dispersed among parents. Narrow sense heritability values ranging from 0.42 to 0.74 at the F3 family level in the second assessment suggested that selection of resistant genotypes is feasible.

Occurrence of Asian Soybean Rust Caused by Phakopsora pachyrhizi in Mississippi

Asian soybean rust (ASR) caused by Phakopsora pachyrhizi Sydow is one of the most destructive diseases of soybean. The first detection of ASR in Mississippi on soybean was in Adams Co. on 16 November 2004. As of November 2006, ASR was found in Claiborne, George, Issaquena, Jackson, Jefferson, Lee, Warren, Washington, and Yazoo counties in 20 locations. Accepted for publication 22 May 2007. Published 17 September 2007.