Soybean-growing Areas Research Articles

Soybean Aphid and Soybean Cyst Nematode Interactions in the Field and Effects on Soybean Yield

How above- and belowground plant pests interact with each other and how these interactions affect productivity is a relatively understudied aspect of crop production. Soybean cyst nematode, Heterodera glycines Ichinohe, a root parasite of soybean, Glycine max (L.) Merr., is the most threatening pathogen in soybean production and soybean aphid, Aphis glycines Matsumura, an aboveground phloem-feeding insect that appeared in North America in 2000, is the key aboveground herbivore of soybean in the midwestern United States. Now, both soybean aphid and soybean cyst nematode co-occur in soybean-growing areas in the Upper Midwest. The objectives of this study were to examine aphid colonization patterns and population growth on soybean across a natural gradient of nematode density (range, approximately 900 and 27,000 eggs per 100 cm3 soil), and to investigate the effect of this pest complex on soybean productivity. Alate (winged) soybean aphid colonization of soybean was negatively correlated to soybean cyst nematode egg density (r = -0.363, P = 0.0095) at the end of July, at the onset of peak alate colonization. However, both a manipulative cage study and openly colonized plants showed that soybean cyst nematode density below ground was unrelated to variation in aphid population growth (r approximately -0.01). Based on regression analyses, soybean aphids and cyst nematodes had independent effects on soybean yield through effects on different yield components. High soybean cyst nematode density was associated with a decline in soybean yield (kg ha(-1)), whereas increasing soybean aphid density (both alate and apterous) significantly decreased seed weight (g 100 seeds(-1)).

Severe Outbreaks of Soybean Frogeye Leaf Spot Caused by Cercospora sojina in the Pampean Region, Argentina.

Frogeye leaf spot of soybean (Glycine max (L.) Merr.) caused by Cercospora sojina Hara was reported to be severe from 1998 to 1999 in northwest Argentina (2). Although the disease was detected at low prevalence (5 to 25%), incidence, and severity in the Pampean Region from 2005 to 2008, no severe outbreaks have been recorded in the provinces of Córdoba, Santa Fe, and Buenos Aires. During the 2008-2009 growing season, disease spread rapidly throughout most soybean-growing areas of the Pampean Region. Disease was observed on almost all varieties of maturity group (MG) III, IV, and V. Symptoms on leaves were circular, reddish brown-to-gray spots (1 to 6 mm) and bordered by typical, narrow, reddish purple margins. Morphology of the fungi was examined on infected tissues. Conidiophores were light-to-dark brown, fasciculate, geniculate, and measured 110 to 203 μm long. Conidia were 1 to 9 septate, hyaline, elongate to fusiform, and measured 26 to 111 (47.3 ± 14.7) × 5.2 to 7.4 μm (6.1 ± 0.7). Pathogenicity tests were conducted on seedlings of a susceptible cultivar by spraying leaves of each of 80 plants at the V3 growth stage with 18 ml of a conidial suspension (3 × 104 conidia/ml) with a hand-held atomizer. Plants were covered with plastic bags and placed in a greenhouse at 28 to 30°C for 48 h. The plastic bags were removed and plants were maintained in high humidity at the same temperature. The same number of noninoculated plants was used as controls. After 10 to 12 days, all inoculated plants showed typical symptoms. Koch's postulates were fulfilled by isolating C. sojina from inoculated plants. Control plants remained healthy. Foliar lesions and morphological characteristics of the pathogen were consistent with C. sojina (1). Disease assessments were made for the middle and upper canopy from 15 arbitrarily collected plants. Soybean plants were in growth stages between R3 and R5 during the survey. Incidence (percentage of plants affected) and severity (percentage of leaf area affected with lesions) were visually estimated from each of the 30 soybean-production fields located in Monte Cristo, Alta Gracia, Jesús María, W. Escalante, Monte Buey, (10 fields, Córdoba Province), Venado Tuerto, Villa Cañás, Cristophersen, María Teresa, (12 fields, Santa Fe Province), Pergamino, Rojas, and Salto (8 fields, Buenos Aires Province). Incidence was 100% in all fields from Córdoba and Santa Fe. Incidence in Buenos Aires was 0 to 100%. Highest severity levels were quantified from fields in Córdoba (severity of 30 to 60%). Lesions also developed on stems and pods. In samples from Buenos Aires, severity levels were ≤10% in the eight soybean fields. Number of lesions per leaflet was recorded from central leaflets in samples from Monte Cristo, Alta Gracia, Venado Tuerto, and María Teresa with 20 to 55 typical lesions per leaflet. Since the disease was always more important in northwest Argentina, genetic resistance is more commonly available in varieties of MG VII to VIII, so most of the varieties of MG III, IV, and V frequently planted in Pampean Region are susceptible. This fact in combination with rainfall, warm temperatures, and high relative humidity in no-till fields during this summer have encouraged the severe outbreak of frogeye leaf spot, especially in the province of Córdoba and in some regions of Santa Fe.

First Report of the Soybean Cyst Nematode, Heterodera glycines, on Soybean in Zhejiang, Eastern China.

The soybean cyst nematode (SCN), Heterodera glycines Ichinohe, is a destructive pest of soybean. Damage to soybean by SCN was first reported from northeastern China in 1899 (1). SCN has been documented in Anhui, Beijing, Hebei, Heilongjiang, Henan, Jiangsu, Jilin, Liaoning, Neimenggu, Shaanxi, Shandong, and Shanxi provinces in mainland China (1). These provinces are situated in the Heilongjiang and Songhuajing valleys in northeastern China and the eastern region of the Yangtze and Yellow rivers in northern China and have cold to temperate climates. In June of 2008, cyst-forming nematodes were detected in two soybean-growing areas of Hangzhou and Xiaoshan in Zhejiang Province, in subtropical eastern China. The soybean plants at the Hangzhou site showed symptoms of stunting and chlorosis, whereas no aboveground or root symptoms were observed on soybean plants at the Xiaoshan site, except for the presence of SCN females on the roots. The two populations had the same morphological and molecular characters. The cysts were lemon shaped with posterior protuberance, ambifenestrate, underbridge and bullae strongly developed, and lateral field of second-stage juveniles consisted of four incisures. The key morphometrics of cysts were fenestra length (41 to 52 μm) and width (33 to 48 μm), vulval silt (47 to 55 μm), and underbridge length (79 to 94 μm), all of which were coincident with that of SCN (2). Amplification of rDNA-internal transcribed spacer (ITS) region using primers TW81 (5'-GTT TCC GTA GGT GAA CCT GC-3') and AB28 (5'-ATA TGC TTA AGT TCA GCG GGT-3') yielded a PCR fragment of approximately 1,030 bp. The digestion patterns of the PCR fragments of the ITS region with AluI, AvaI, CfoI, MvaI, and RsaI showed identical restriction profiles to H. glycines (3), and the sequences exhibited 100% similarity with those of H. glycines isolates, Accession No. AY667456 from GenBank. Morphological and molecular identification confirmed that the two populations of cyst-forming nematodes from Zhejiang are SCN. To our knowledge, this is the first report of SCN in Zhejiang, now the most southern location in mainland China with confirmed infestation of SCN.

Evaluation of glyphosate-tolerant soybean cultivars for resistance to bacterial pustule

Xanthomonas axonopodis pv. glycines causes bacterial pustule of soybean, which is a common disease in many soybean-growing areas of the world and is controlled by a single recessive gene (rxp gene) commonly found in many conventional glyphosate-sensitive soybean cultivars. Since glyphosate-tolerant cultivars are commonly planted today, there has been no information about whether these new cultivars have bacterial pustule resistance. The goal of this study was to screen glyphosate-tolerant soybean cultivars for resistance to X. axonopodis pv. glycines. Three experiments were completed to evaluate resistance. In experiment 1, 525 commercial glyphosate-tolerant cultivars from 2001 were inoculated with X. axonopodis pv. glycines strain UIUC-1. Following inoculation, many of the cultivars were resistant (developed no detectable pustule symptoms) although 152 (~29%) developed bacterial pustule. In experiment 2, the aggressiveness of three strains (UIUC-1, UIUC-2, and ATCC 17915) of X. axonopodis pv. glycines were compared on three bacterial pustule-susceptible, glyphosate-tolerant cultivars. One strain (UIUC-1) was less aggressive than the other two (UIUC-2 and ATCC 17915) on all three cultivars examined. In experiment 3, 45 cultivars from 2005 (all different from 2001) were inoculated with X. axonopodis pv. glycines ATCC 17915. A range of disease severities developed with five cultivars (11%) having disease severity ratings as high as or higher than those on a susceptible check cultivar. Overall, these results suggested that resistance to bacterial pustule occurs in glyphosate-tolerant soybean cultivars, but not at 100% frequency, which means bacterial pustule outbreaks could occur when a susceptible cultivar is planted and conditions are conducive for bacterial pustule development.

New sources of resistance to Soybean mosaic virus in soybean

Soybean mosaic virus (SMV) is one of the most prevalent viral diseases in all major soybean-growing areas worldwide. Seven strain groups of SMV (G1-G7) and three resistance loci (Rsv1, Rsv3, and Rsv4) have been identified in soybean (Glycine max). In our initial study, 209 soybean genotypes were screened for reactions to G1 and G7, 129 of which were resistant to one or two strains. The objective of this research was to screen 127 genotypes with six SMV strains and differentiate specific alleles for resistance in these genotypes. The results demonstrated that 84 genotypes carry alleles at the Rsv1 locus: 42 with Rsv1-y, 5 with Rsv1, 19 with Rsv1-k, 8 with Rsv1-t, 8 with Rsv1-r, 1 with Rsv1-n, and 1 with Rsv1-h. Sixteen genotypes were identified to presumably carry new alleles for SMV resistance at Rsv1, Rsv3, or Rsv4. Nine of these 16 genotypes ('Kosuzu', 'Suzumaru', PI 398877, 'Jitsuka', 'Clifford', and 'Tousan 65', 'Corsica', PI 61944, and PI 61947) may carry new alleles at the Rsv1 locus based on the comparison of their differential reaction patterns against the nine reported Rsv1 alleles. Two genotypes (PI 339870 and PI 399091) may carry new resistance alleles at the Rsv3 locus. Five genotypes (KAERI-GNT-220-7, PI 398593, PI 438307, 'Rhosa', and 'Beeson') may carry new alleles at the Rsv4 locus. In addition, 18 genotypes were resistant to all six strains tested and may carry Rsv1-h, Rsv4, Rsv1Rsv3, Rsv1Rsv4, or Rsv3Rsv4. Research is underway to confirm the new SMV resistance alleles through genetic and molecular approaches. Key words: Glycine max, virus reaction, resistance genes, germplasm, Soybean mosaic virus. Le virus de la mosaïque du soja (VMS) est une des maladies virales les plus répandues dans toutes les principales régions productrices de soja (Glycine max), et ce, à l'échelle de la planète. Sept groupes de souches du VMS (G1-G7) et 3 locus de résistance (Rsv1, Rsv3 et Rsv4) ont été identifiés chez le soja. Au cours de notre étude initiale, 209 génotypes de soja ont été criblés pour évaluer leurs réactions à G1 et G7. Parmi ceux-ci, 129 se sont montrés réfractaires à une souche ou aux deux. Le but de cette recherche était de cribler 127 génotypes avec 6 souches de VMS et d'y différencier les allèles spécifiques de la résistance. Les résultats ont démontré que 84 génotypes portent des allèles au niveau du locus Rsv1 : 42 au Rsv1-y, 5 au Rsv1, 19 au Rsv1-k, 8 au Rsv1-t, 8 au Rsv1-r, 1 au Rsv1-n et 1 au Rsv1-h. Seize génotypes ont été identifiés en tant que porteurs probables de nouveaux allèles de résistance au VMS au niveau des locus Rsv1, Rsv3 ou Rsv4. Si l'on compare leurs schémas différentiels de réaction à ceux des 9 allèles Rsv1 visés, 9 de ces seize génotypes ('Kosuzu', 'Suzumaru', PI 398877, 'Jitsuka', 'Clifford', 'Tousan 65', 'Corsica', PI 61944 et PI 61947) peuvent porter de nouveaux allèles au niveau du locus Rsv1 ; deux génotypes (PI 339870 et PI 399091) peuvent porter de nouveaux allèles au niveau du locus Rsv3 ; et cinq génotypes (KAERI-GNT-220-7, PI 398593, PI 438307, 'Rhosa' et 'Beeson') peuvent porter de nouveaux allèles au niveau du locus Rsv4. De plus, 18 génotypes étaient réfractaires aux 6 souches testées et pourraient porter les locus Rsv1-h, Rsv4, Rsv1Rsv3, Rsv1Rsv4 ou Rsv3Rsv4. Des recherches faisant appel à des protocoles génétiques et moléculaires sont en cours de réalisation afin de confirmer la présence des nouveaux allèles de résistance au VMS. Mots-clés : Glycine max, réaction aux virus, gènes de résistance, plasma germinal, virus de la mosaïque du soja.

New Legume Hosts of Phakopsora pachyrhizi Based on Greenhouse Evaluations.

Phakopsora pachyrhizi, the causal organism of soybean rust, was first found in the continental United States in 2004 and has been found on soybean, kudzu, Florida beggarweed, and three Phaseolus species in the field. The pathogen has been reported to occur on more than 90 legume species worldwide and it is likely to infect native and introduced legume species in the United States. The objective of this study was to determine if 176 species representing 57 genera of legumes, the majority of which are either native or naturalized to soybean-growing areas of the United States, could be hosts of P. pachyrhizi. Between one and three accessions of each species, a total of 264 accessions, were inoculated with a mixture of four isolates of P. pachyrhizi. Severity and sporulation were rated on a 1-to-5 scale at 14 and 28 days after inoculation. P. pachyrhizi was confirmed by the presence of sporulating uredinia and/or immunological assay on 65 new species in 25 genera; 12 of these genera have not been reported previously as hosts. Many of the newly identified hosts grow in the southern United States, and like kudzu, could serve as overwintering hosts for P. pachyrhizi.

Morphologic and Pathometric Characterization of the Asian Soybean Rust (Phakopsora pachyrhizi) on Kudzu (Pueraria lobata) in Argentina.

Asian soybean rust (ASR) is a very important disease caused by Phakopsora pachyrhizi. The disease has emerged as a major threat to soybean production in South America since 2001. During the 2003-2004 growing season, P. pachyrhizi spread rapidly throughout most soybean-growing areas of northwestern and northeastern Argentina (1). One widespread naturalized host in the northeastern part of the country is kudzu (Pueraria lobata). Plants of severely infected kudzu were sampled during January 2005 in Cerro Azul (29°29'S Misiones Province) to quantify P. pachyrhizi infection and morphologically characterize the fungus in leaves. The number of lesions, uredinia per cm2, and uredinia per lesion were recorded from the undersides of 50 leaflets that were visually showing rust symptoms. The average number of lesions and uredinia per cm2 was 14 (4 to 22), and 24 (5 to 78), respectively. The number of uredinia per lesion was 3 (1 to 10). Twenty leaflets from the lower canopy averaged 55 (42 to 78) uredinia per cm2. The average size of urediniospores was 18.4 μm wide (12.5 to 22.5) and 22.7 μm long (17.5 to 26.3). Although important epidemics of ASR have not been registered on soybean crops in January (2) because of adverse conditions, the fungus was observed on kudzu plants. To our knowledge, this is the first report of morphologic and pathometric characterization of P. pachyrhizi on kudzu in Argentina.

Identification of Glycine max Genes Expressed in Response to Soybean mosaic virus Infection

School of Agricultural Biotechnology and Center for Plant Molecular Genetics and Breeding Research, Seoul NationalUniversity, Seoul 151-921, Korea(Received on November 3, 2004; Accepted on December 29, 2004)Identification of host genes involved in disease prog-resses and/or defense responses is one of the mostcritical steps leading to the elucidation of diseaseresistance mechanisms in plants. Soybean mosaic virus(SMV) is one of the most prevalent pathogen of soybean(Glycine max). Although the soybeans are placed one ofmany important crops, relatively little is known aboutdefense mechanism. In order to obtain host genesinvolved in SMV disease progress and host defenseespecially for virus resistance, two different cloningstrategies (DD RT-PCR and Subtractive hybridization)were employed to identify pathogenesis- and defense-related genes (PRs and DRs) from susceptible (Geum-jeong 1) and resistant (Geumjeong 2) cultivars againstSMV strain G7H. Using these approaches, we obtained570 genes that expressed differentially during SMVinfection processes. Based upon sequence analyses,differentially expressed host genes were classified intofive groups, i.e. metabolism, genetic information pro-cessing, environmental information processing, cellularprocesses and unclassified group. A total of 11 differ-entially expressed genes including protein kinase, tran-scription factor, other potential signaling componentsand resistant-like gene involved in host defense responsewere selected to further characterize and determineexpression profiles of each selected gene. Functionalcharacterization of these genes will likely facilitate theelucidation of defense signal transduction and biologicalfunction in SMV-infected soybean plants.Keywords : defense, differential expression, EST analysis,pathogenesis, SMVPlants have developed complicated defense mechanismduring evolution to resist the harmful pathogens they haveencountered. The interaction between a plant and a pathogenoften complies with gene-for-gene model involving plantresistance (R) gene and corresponding pathogen avirulence(Avr) genes (Flor, 1971). These involve changes in ioninflux, generation of reactive oxygen species, production ofpathogenesis-related (PR) proteins and phytoalexins, andreinforcement of the cell wall (Dixon and Lamb, 1990;Dixon et al., 1994). Induction of defense response involvesan initial signal that indicating invasion by a pathogen,followed by transduction of signals activating variousdefense genes (Yang et al., 1997). When plants recognizethe products of Avr genes directly or indirectly from apathogen, the defense-related gene (DR) expression isinduced and the result is resistance to pathogen attack(Keen, 1990; Staskawicz, 2001). However, when plantslack R genes or their products, the plant displaycharacteristics of disease. Based on the advancements ofhost-pathogen interaction at the molecular level, diseaseresistance genes are useful for disease control strategies inagriculture.Soybean mosaic virus (SMV), a member of the genusPotyvirus (Mayo and Pringle, 1998), is one of the mosteconomically important viruses of soybean [Glycine max(L.) Merr]. It cause mosaic and severe necrosis in manysoybean cultivars, and is present in all major soybean-growing areas, where it results in significant reductions inyield and quality. Since the first description of seven groupsof SMV strains (G1-G7) based on the symptoms developedon test cultivars, viral strain variation and the resistancepatterns of different soybean cultivars have been studiedextensively (Cho and Goodman, 1979, 1982; Gunduz et al.,2001, 2002; Lim, 1985). Presence of many SMV strains hasbeen reported and the continual variation is generallybelieved to happen in soybean fields in Korea (Cho et al.,1983). Recently, a new SMV strain, G7H, causing mosaicand necrosis on most recommended soybean cultivars thatare resistant to previously prevalent SMV strains, G5 andG5H, was found in Korea (Kim et al., 2003; Lim et al.,2003).To date, the majority of research in defense signaltransduction has been performed on several model speciessuch as tobacco and Arabidopsis, whereas in economicallyimportant soybean crop, our understanding of the signalingmechanisms leading to disease resistance is largely unknown(Piffanelli et al., 1999). Most characterized R genes can be

Genetic diversity of native Bradyrhizobium populations in soybean-growing areas of Northern Thailand

Native Bradyrhizobium isolates (66 isolates) obtained from traditional soybean-growing areas of northern Thailand were classified using 3 genotypic methods: repetitive extragenic palindromic (REP) sequences, enterobacterial repetitive intergenic consensus (ERIC) sequences together with the polymerase chain reaction (PCR) and mapped restriction site polymorphism (MRSP) analysis of 16S rRNA genes. Sequencing of the 16S rRNA genes was performed for some isolates representing the major REP-ERIC-PCR clusters to acquire data supporting the classifications. The results of the classifications using all these genotypic methods appeared to be consistent, with some minor differences. Five major clusters were obtained by integration of all the classifications: clusters Bj-A (B. japonicum), Bj-B, Brh1, Brh2, and Be (B. elkanii). Two clusters, Brh1 and Brh2 were distantly related to B. japonicum USDA110 and B. japonicum strains, but were genetically close to B. liaoningense. Cluster Bj-B was closer to USDA110 than the Brh-clusters but the phylogenetic positions were clearly separated from each other. The cowpea Bradyrhizobium isolates capable of nodulating soybean were distributed and classified into all of these five clusters. The results revealed unique genetic characters of the Thai soybean-bradyrhizobia. The classification of these native bradyrhizobia using REP and ERIC-PCR as well as the serotype pattern of these isolates reflected well the phylogenetic relationships among isolates based on differences in 16S rDNA sequences. Our results also indicated the existence of a relationship between the genotype of the native isolates and sampling locations. Some genotypicclusters; Brh1, Brh2, and Bj-A were mainly obtained from Chiang Mai Province and a certain cluster, Bj-B from Mae Hong Son Province. This relationship was not observed for cluster Be. In contrast to the sampling locations, no relationship was detected between host cultivars and genotype recovery.

First Report of Charcoal Rot (Macrophomina phaseolina) on Soybean in Minnesota.

In August 1999, soybean (Glycine max (L.) Merr.) plants exhibiting symptoms of charcoal rot were observed near Zumbrota, MN. Symptoms included shrunken, unfilled pods, and brown, wilted leaves attached to dead petioles and stems (1). When stems of symptomatic soybean plants were split, areas of gray-to-black discoloration where present in the stem cortex (1). Black, spherical microsclerotia 77 to 90 µm in diameter and elongated microsclerotia 77 to 120 µm long (1) were found in vascular tissue. Stem tissue placed on potato dextrose agar (PDA) yielded fungal colonies identified as Macrophomina phaseolina (Tassi) Goid. based on gray colony color, colony morphology, and the presence of microsclerotia 70 to 90 µm in diameter. In 2000, M. phaseolina was isolated from plant samples gathered from 11 of 90 fields sampled in a statewide soybean disease survey. More studies are needed to determine the distribution of charcoal rot in Minnesota; however, the occurrence of symptoms at one location and the presence of M. phaseolina in soybean-growing areas of Minnesota suggest that charcoal rot may occur in susceptible soybean cultivars under favorable environmental conditions. Reference: (1) G. S. Smith and T. D. Wyllie. Charcoal rot. Pages 29-30 in: Compendium of Soybean Diseases, 4th ed. G. L. Hartmann, J. B. Sinclair, and J. C. Rupe, eds. The American Phytopathological Society, St. Paul, MN, 1999.

Root Colonization of Soybean Cultivars in the Field by Fusarium solani f. sp. glycines.

Soybean sudden death syndrome (SDS), caused by Fusarium solani f. sp. glycines, is a problem in some soybean-growing areas in the United States. Resistance is an important control strategy. In this study, root colonization of six soybean cultivars by F. solani f. sp. glycines was determined. Cultivars included susceptible P3981, CM497, and Spencer and field resistant LS90-1920, Pharaoh, and Ripley. All cultivars were tested in field experiments at different locations in southern Illinois in 1997 and 1998. Roots were collected at six sampling times and were dried and ground to isolate and enumerate the pathogen on a selective medium. SDS foliar disease index (FDX), the area under the F. solani f. sp. glycines population curve (AUPC), the incidence of colonized roots at 45 days after planting (RCI45), and the root colonization rate (RCR) were used to compare cultivars. FDX on the three resistant cultivars was significantly lower than on the three susceptible cultivars. Means of AUPC on the three resistant cultivars were significantly lower than those on the susceptible CM497 and P3981. RCI45 of Pharaoh was significantly lower than those of P3981 and Spencer. RCRs of all three resistant cultivars were significantly lower than that of P3981, and RCR of Ripley was also significantly lower than that of CM497. Based on combination of all cultivars, AUPC was significantly correlated with RCI45 and RCR.

Changes in the Racial Composition of Phytophthora sojae in Australia Between 1979 and 1996.

Surveys of commercial soybean fields, disease nurseries, and trial plots of soybean were conducted throughout eastern Australia between 1979 and 1996, and 694 isolates of Phytophthora sojae were collected and classified into races. Fourteen races, 1, 2, 4, 10, 15, and 25, and eight new races, 46 to 53, were identified, but only races 1, 4, 15, 25, 46, and 53 were found in commercial fields. Races 1 and 15 were the only races found in commercial fields in the soybean-growing areas of Australia up until 1989, with race 1 being the dominant race. Race 4 was found in central New South Wales in 1989 on cultivars with the Rps1a gene, and it is now the dominant race in central and southern New South Wales. Races 46 and 53 have only been found once, in southern New South Wales, and race 25 was identified in the same region in 1994 on a cultivar with the Rps1k gene. Only races 1 and 15 have been found in the northern soybean-growing regions, with the latter dominating, which coincides with the widespread use of cultivars with the Rps2 gene. Changes in the race structure of the P. sojae population from commercial fields in Australia follow the deployment of specific resistance genes.

Availability of Different Host Plant Species and Changing Abundance of the Polyphagous Bug Nezara viridula (Hemiptera: Pentatomidae)

In soybean-growing areas of SE Queensland, the host plant species available to southern green stink bug during summer were inadequate for egg production by adult females and for nymphal survival and development. However, host plant species available to bugs in spring (the wild crucifers Rapistrum rugosum and Raphanus raphanistrum) and in early autumn (fruiting soybean Glycine max) were suitable. The concentration of bugs on fruiting soybean for feeding and oviposition was not caused by the attractiveness of the plant relative to other host species but may be attributed to the unavailability of other suitable hosts (species and plant growth stage) other than soybean in the area during the time of the season. -from Authors

Native root-nodule bacteria of traditional soybean-growing areas of northern Thailand

Over 1500 root-nodule bacteria were isolated from a range of uninoculated soybeans, and one cowpea, ‘trap-hosts’, sown in 1985 into traditional soybean-growing areas of soybean-growing areas of northern Thailand. Most isolates were slow-growing Bradyrhizobium japonicum. Using a modified ‘bottle-jar’ technique, 586 of the isolates were tested with a range of soybean hosts and one cowpea host. The results indicated:

A ROOT AND STALK ROT OF SOYBEANS CAUSED BY PHYTOPHTHORA MEGASPERMA DRECHSLER VAR. SOJAE VAR. NOV.

Since 1954, a destructive root and stalk rot of soybeans, identical with one reported from several of the soybean-growing areas in the United States, has been prevalent in southwestern Ontario. It is proposed that Phytophthora megasperma Drechsler var. sojae nov. var. replace P. cactorum (Lib. and Cohn) Schroet., and P. sojae Kaufmann and Gerdemann, as the more correct taxonomic designation of the causal fungus. P. megasperma var. sojae comprises strains which though indistinguishable morphologically, differ physiologically and pathologically. Artificial inoculation of varieties and of breeding lines and selections of soybeans with the causal fungus, chiefly by the highly reliable toothpick method, indicated two well-defined types of disease reaction, resistance and susceptibility. Harosoy, the variety which currently is grown most extensively in Ontario, is highly susceptible to the disease. Pathogenicity trials involving many possible wild and cultivated hosts emphasized the marked specificity of P. megasperma var. sojae to Glycine max L. Merrill. The soybean Phytophthora, having been called P. cactorum and thereby associated nomenclaturally with a representative of that species causing a root rot of sweet clover in Ontario, was found to be quite different from the sweet clover pathogen.