Soybean sudden death syndrome (SDS), caused by Fusarium virguliforme (FV), is a root disease that results in severe foliar symptoms during the reproductive stage. In a regular growing season, an epidemic of SDS is highly correlated with the planting date and the disease tends to be more severe in earlier planted soybeans. Occurrence of infection early in the season is likely to result in colonization in the xylem and phloem tissues, a process essential for foliar symptom expression because xylem tissues are upward pathways in soybean plants. To demonstrate the biology of this infection, we used an effective and quantifiable seedling inoculation technique in which germinated seeds in a Petri dish were spray-inoculated with conidial suspension before being transplanted. Plants that had foliar symptoms showed both external and internal discolored taproots and basal stems, while plants with no foliar symptoms had only superficial discoloration. Microtome sectioning of taproots of plants that had foliar symptoms revealed the presence of fungal structures in both xylem and phloem tissues, while plants that had no foliar symptoms revealed fungal structures only in phloem tissue. A scanning electron microscope study showed a higher penetration frequency of FV near the root-cap zone where few or no root hairs of the radicle were found. These results indicate that fungal penetration into the xylem tissue plays a role in foliar symptom expression. Accepted for publication 10 December 2007. Published 22 February 2008.

Grain mold caused by a complex of fungi is an economically important disease of sorghum worldwide. Little is known about the epidemiology of sorghum grain mold, which is essential for its management. Studies were conducted to quantify the effects of wetness duration on grain mold development under controlled conditions at ICRISAT. Six major sorghum grain mold fungi determined from previous field experiments,Curvularia lunata, Cladosporium oxysporum, Bipolaris australiensis, Fusarium moniliforme, F. pallidoroseum, and Phoma sorghina, were used. Panicles of a pot-grown mold-susceptible sorghum line, IS 10513, were spray inoculated with each fungus at five growth stages: flowering (F), milk (M), soft dough (S), hard dough (H), and physiological maturity (P), and were incubated in dew chambers for 0,16, 24, 40, 48, and 72 h. Then, the plants were placed on greenhouse benches at 25 ± 1°C to allow grain mold infection to develop. Eight days after treatments, grains from F, M, and S stages were plated onto potato dextrose agar, while those from H and P stages were incubated in blotter paper humid chambers at 28 ± 1°C. Fungal colonization of grains were scored after 7 days. Results indicated a significant (P < 0.01) correlation between wetness duration and grain mold development at different stages of inoculation. Generally, with increasing wetness duration, there was an increase in grain infection by all six fungi. However, infection frequency varied among fungi and grain development stages, indicating that individual fungi might have different windows for maximum infection during the grain development stages. In many regions of the world where sorghum (Sorghum bicolor (L.) Moench) is produced, grain mold is a serious disease that reduces grain quality and utilization. The term "grain mold" is used to describe the diseased appearance of sorghum grain resulting from infection by one or more parasitic fungal species (21). Grain mold is most commonly caused by Fusarium moniliforme J. Sheld. and Curvularia lunata (Wakk.) Boedjin, although many other fungal species are also associated with the mold complex (9,16). It is a major biotic constraint to sorghum improvement and production worldwide, especially when grain development coincides with wet and warm weather conditions (10). It is estimated that annual economic losses in Asia and Africa as a result of grain mold are in excess of US $130 million (13). In some cases, yield losses can reach 100% in highly susceptible cultivars (12). Apart from yield reduction, grain mold also reduces seed quality, with effects ranging from cosmetic deterioration of the pericarp to substantial deterioration of the endosperm and embryo with reduction in acceptability by food and feed processors (17). In addition to reducing the nutritional value, fungi that cause grain mold in sorghum may also produce mycotoxins (7), thus limiting the use of sorghum grain as food and feed (16). Molded sorghum grain fetches lower market prices and therefore affects the income of sorghum farmers (2).Ce...

Macrophomina phaseolina, the causal agent of soybean charcoal rot, is widely present in soil and has been reported to cause yield losses of 30 to 50%, mainly in southern soybean production regions of the United States. (2). Charcoal rot was first reported in North Dakota during 2002, suggesting a range expansion for M. phaseolina (1). Charcoal rot has been occasionally observed in Iowa in individual soybean plants, but epidemics of the disease have not been recorded. During the 2003 growing season, a severe epidemic of charcoal rot was observed throughout the state. Diseased plants were first noticed in late July and by late August, patches of diseased plants wilted and died prematurely in many fields. The pith of diseased plants had a brown discoloration in taproots and lower stems. Symptoms were observed up to the 4th or 5th nodes, typical of charcoal rot. In some plants, no discoloration was evident. In discolored plants, microsclerotia of M. phaseolina were commonly observed in the epidermis, just beneath the epidermis, and inside taproots and lower stems of wilted plants. A systematic survey was conducted between late August and early September, 2003 to determine the prevalence and severity of charcoal rot in Iowa. The disease was observed in 60% of fields surveyed in northern Iowa (north of latitude 42.5°N), 90% in central Iowa (latitude 41.6 to 42.5°N), and 20% in southern Iowa (south of latitude 41.6°N). Incidence in surveyed fields ranged from 10 to 80%. One 80-ha field in Hampton (northern Iowa) had 50% disease incidence. An incidence of 80%, with extensive premature death prior to growth stage R6 (full seed), was observed in a 16-ha field east of Huxley (central Iowa). The fungus was isolated by splitting open the tap roots of a few representative symptomatic plants from 18 fields. Tissue colonized with microsclerotia of M. phaseolina was scraped, collected in sterile petri dishes, surface sterilized in 1% sodium hypochlorite, washed in distilled sterile water, and transferred to potato dextrose agar. The plates were incubated for 2 weeks at 22 ± 1°C on laboratory benches with a 12-h photoperiod. All resulting cultures produced abundant microscleorotia of M. phaseolina similar to those described by Smith and Wyllie (3). Pycnidia were observed in two cultures. August 2003 was the driest month on record in Iowa, which may have contributed to the outbreaks of this disease. Statewide, yield in Iowa soybean during 2003 was 1,976.1 kg/ha (2,798 kg/ha in 2002). The largescale epidemic of charcoal rot may have contributed to the overall reduction in soybean productivity in Iowa in 2003 (4). Since M. phaseolina also infects corn (2), and corn/soybean rotation is the most common cropping system in Iowa, efforts are needed to address the future risk of M. phaseolina to corn and soybean. References: (1) C. A. Bradley and L. E. del Rio. Plant Dis. 87:601, 2003. (2) D. C. McGee. Soybean Diseases: A Reference Source for Seed Technologists. The American Phytopathological Society, St. Paul, MN, 1992; (3) G. S. Smith and T. D. Wyllie. Charcoal rot. Pages 29–31 in: Compendium of Soybean Diseases. 4th ed. G. L. Hartman et al., eds. The American Phytopathological Society, St. Paul, MN, 1999. (4). X. B. Yang et al. Biology and management of soybean charcoal rot. Pages 55–60. in: Proc. 15th Integrated Crop Management Conf. Iowa State University, Ames. 2003.

Effect of temperature and humidity regimes on grain mold sporulation and seed quality in sorghum (Sorghum bicolor (L.) Moench) Abstract Grain mold, induced by a number of non-specific fungi, causes substantial loss to seed/grain yield and quality in sorghum (Sorghum bicolor (L.) Moench). Fungal sporulation and grain mold severity are greatly influenced by temperature and relative humidity (RH) levels. We studied the effects of three incubation temperatures (25, 27 and 288C) and two sets of RH levels (first set: 85, 90, 95, 98, and 100%, second set: 95, 96, 97, 98, 99 and 100%) on sporulation and grain mold severity in three major mold fungi (Curvularia lunata, Fusarium moniliforme, and Bipolaris australiensis) and on four each of resistant, moderately resistant and susceptible sorghum genotypes for sporulation and mold severity of major fungi. Results indicated that both fungal sporulation and grain mold severity increased on most sorghum genotypes with increasing incubation temperature from 25 -288C and RH levels from 95 -98%. A linear relationship was observed among RH levels, grain mold severity and fungal sporulation. The highest sporulation of all the three fungi occurred at 288C and 98% RH after 5 days of incubation. Among the three fungi, C. lunata grew and sporulated faster than B. australiensis and F. moniliforme, in that order. Among the sorghum genotypes, IS 25017 supported the least sporulation and had the lowest mold severity, followed by IS 8545 and PVK 801. Seed quality parameters, such as seed germination, seedling vigor index, field emergence potential, dehydrogenase and þ-amylase activities declined significantly with increasing temperature and RH levels that supported heavy sporulation and grain colonization.

Soybean (Glycine max) seedlings with symptoms of Pythium damping-off were collected in northeastern Iowa soybean fields and processed for isolation of the causal agents on both potato dextrose agar (PDA) and pimaricin-, ampicillin-, rifampicin-, and pentachloronitrobenzene (PARP)-containing media. Isolates were identified based on morphological characteristics, growth rates, along with sequence data for the nuclear rDNA ITS1-5.8S-ITS2 region (ITS barcode). Nine isolates were identified via NCBI BLASTn search of sequences available in GenBank: one isolate of Pythium orthogonon; three isolates of P. inflatum; two isolates of P. ultimum var. ultimum; one isolate of P. torulosum; and two isolates of P. ultimum var. ultimum or P. ultimum var. sporangiferum. Pathogenicity of all the nine isolates, along with a positive control (P. irregulare), was tested in greenhouse conditions on soybean variety Pioneer 22T61R. Soybean seeds were planted in potting mixture inoculated with Pythium inoculum fermented on sterilized proso millet grains. The Pythium spp. were subsequently re-isolated from symptomatic plants. Average incidence of Pythium damping-off across isolates was 27.4% but varied among isolates, ranging from 1.2 to 79.8%. Among the Pythium spp. collected in this single location, the most aggressive isolate was selected to test the efficacy of seed treatments using foliar fungicides in artificially-inoculated field conditions. Out of the eight tested foliar fungicides, six of them significantly suppressed damping-off compared with the untreated control. The average yield advantage of foliar fungicides as seed treatments was 0.23 mt (metric ton)/ha (ranged from 0.15 to 0.31 mt/ha

Sudden death syndrome (SDS) caused by Fusarium virguliforme is one of the major yield-limiting soil borne diseases of soybean (Glycine max). The SDS has been reported from 21 U.S. states and is known to occur in Africa, North America, and South America. In the U.S. the losses due to SDS was estimated at $3.06 billion for a period from 1988 to 2010. Since 1983, several management approaches have been investigated to reduce SDS and yet, continued efforts are necessary to develop long term disease management programs and to sustain disease below economic threshold levels. Integrating available control measures is an option, but adaptability and real-world assessments are equally important. Support of several funding agencies to better understand the disease in identifying suitable control measures to reduce yield losses in commercial cultivations has been indispensable in accomplishing these goals. In spite of sustained efforts, SDS continued to spread within the U.S. and reported in seven other countries since its first report in 1971.Comprehensive reviews have previously been published on this disease by Roy et al. [98], Leandro et al. [58], and Hartman et al. [32]. In this review, updated information on geographic distribution and economic significance of SDS, epidemiology, factors affecting SDS, and management options for SDS including screening techniques have been compiled. Also, discussed significant gaps in use of plant, fungi and bacteria based biocontrol agents in addressing management of SDS.Keywords: Soybean sudden death syndrome, SDS, Fusarium virguliforme, biocontrol, global reports, yield losses due to SDS, epidemiological factors, greenhouse and field screening. ______________________________________________________________________________This is a manuscript of an article from CAB Reviews 11 (2016): 039, doi: 10.1079/PAVSNNR201611039. Navi, S. S.; Yang, X. B. 2016. Sudden death syndrome -a growing threat of losses in soybeans. CAB International, Wallingford, UK. Aoki et al., and F. virguliforme,90] is an economically significant soil-borne disease, and a risk to many soybean production areas worldwide. The disease was first observed by H.J. Walters in Arkansas, United States in 1971[100], but it was only in 1983 that the disease was named as sudden death syndrome (SDS) of unknown etiology [40]. As of this review, the disease has been reported in three continents, North America (Canada and United States), South America (Argentina, Bolivia, Brazil, Paraguay, and Uruguay), and Africa (South Africa), and within the United States 21 states (Fig. 1) Whether the pathogens causing SDS have been introduced in to new regions or if they have been present in the soil in production fields of these countries for some time without being detected is unknown. After the SDS was detected in Iowa [150], Scherm and Yang [114] developed a risk assessment model to determine potential geographic range of development of this disease, which was considered a southern disease by then, in North America. They predi...

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