The soybean crop is one of the most important crops worldwide.

In 5 March 2001, a severe rust outbreak was recorded at Pitapó, Paraguay, and the causal organism was determined to be Phakopsora pachyrhizi using polymerase chain reaction (PCR) and DNA sequence analysis. In May, rust surveys showed spread throughout most of Paraguay and into western and northern Parana, Brazil. In the 2001-02 season, rust was widespread in Paraguay, but losses were reduced due to severe drought; however, in Brazil it spread to more than 60% of the soybean acreage, causing field losses estimated at 0.1 million metric tons (MMT). In 2003, the disease was observed in more than 90% of the fields in Brazil, and the projected losses in Mato Grosso and Bahia alone are 2.2 MMT (US$487.3 million). Approximately 80% of the soybean acreage in Brazil was sprayed twice with fungicides at the cost of US$544 million. Differences in efficacy have been observed among the commercial strobilurin and triazol fungicides.

The soybean aphid [Aphis glycines Matsumura (Hemiptera: Aphididae)] is an invasive insect pest of soybean [Glycine max (L.) Merr.] that was first reported in North America in 2000. There are currently no reports of soybean aphid biotype diversity and this information is needed before aphid resistance genes are deployed. The objective of this research was to test for aphid biotype variation. The response of two A. glycines isolates, one collected in Ohio and the other in Illinois, were compared by infesting eight soybean genotypes in nonchoice tests. The same genotypes also were tested with the Ohio isolate using a choice test. In the nonchoice test, there was a significant (P < 0.0001) effect of aphid isolate, genotype, and a significant aphid isolate by soybean genotype interaction for the number of aphids per plant 10 and 15 d after infestation. The responses of the eight genotypes to the Ohio isolate in the choice test were similar to their responses in nonchoice tests. PI 200538 and PI 567597C were resistant to both the Ohio and Illinois isolates and will be useful sources of resistance to both isolates. These tests confirm that there are at least two distinct biotypes of A. glycines in North America.

Mycoviruses can have a marked effect on natural fungal communities and influence plant health and productivity. However, a comprehensive picture of mycoviral diversity is still lacking. To characterize the viromes of five widely dispersed plant-pathogenic fungi, Colletotrichum truncatum, Macrophomina phaseolina, Diaporthe longicolla, Rhizoctonia solani, and Sclerotinia sclerotiorum, a high-throughput sequencing-based metatranscriptomic approach was used to detect viral sequences. Total RNA and double-stranded RNA (dsRNA) from mycelia and RNA from samples enriched for virus particles were sequenced. Sequence data were assembled de novo, and contigs with predicted amino acid sequence similarities to viruses in the nonredundant protein database were selected. The analysis identified 72 partial or complete genome segments representing 66 previously undescribed mycoviruses. Using primers specific for each viral contig, at least one fungal isolate was identified that contained each virus. The novel mycoviruses showed affinity with 15 distinct lineages: Barnaviridae, Benyviridae, Chrysoviridae, Endornaviridae, Fusariviridae, Hypoviridae, Mononegavirales, Narnaviridae, Ophioviridae, Ourmiavirus, Partitiviridae, Tombusviridae, Totiviridae, Tymoviridae, and Virgaviridae. More than half of the viral sequences were predicted to be members of the Mitovirus genus in the family Narnaviridae, which replicate within mitochondria. Five viral sequences showed strong affinity with three families (Benyviridae, Ophioviridae, and Virgaviridae) that previously contained no mycovirus species. The genomic information provides insight into the diversity and taxonomy of mycoviruses and coevolution of mycoviruses and their fungal hosts. IMPORTANCEPlant-pathogenic fungi reduce crop yields, which affects food security worldwide. Plant host resistance is considered a sustainable disease management option but may often be incomplete or lacking for some crops to certain fungal pathogens or strains. In addition, the rising issues of fungicide resistance demand alternative strategies to reduce the negative impacts of fungal pathogens. Those fungus-infecting viruses (mycoviruses) that attenuate fungal virulence may be welcome additions for mitigation of plant diseases. By high-throughput sequencing of the RNAs from 275 isolates of five fungal plant pathogens, 66 previously undescribed mycoviruses were identified. In addition to identifying new potential biological control agents, these results expand the grand view of the diversity of mycoviruses and provide possible insights into the importance of intracellular and extracellular transmission in fungus-virus coevolution. R ecent metatranscriptomic and metagenomic studies of animals, fungi, insects, plants, and environmental samples have shown that mycoviruses are ubiquitous in nature (1-10). Analyses of viral metagenomes (i.e., viromes) of environmental samples suggest that the field of virology has discovered less than 1% of the existing viral diversity, and the rate of discovery by metage...

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Asian soybean rust (ASR), caused by Phakopsora pachyrhizi and recently discovered for the first time in continental United States, has been of concern to the U.S. agricultural industry for more than 30 years. Since little soybean rust resistance is known, and resistance is often difficult to detect or quantitate, we initiated a project to develop a better, more quantitative, method. The methodology determined the average numbers and diameters of uredinia in lesions that developed on leaves of inoculated plants 14 days after inoculation. It was used to compare virulence of P. pachyrhizi isolates from Asia and Australia and P. meibomiae from Puerto Rico and Brazil, collected as many as 30 years earlier, with isolates of P. pachyrhizi recently collected from Africa or South America. Susceptible reactions to P. pachyrhizi resulted in tan-colored lesions containing 1 to 14 uredinia varying greatly in size within individual lesions. In contrast, on these same genotypes at the same time of year, resistance to other P. pachyrhizi isolates was typified by 0 to 6 small uredinia in reddish-brown to dark-brown lesions. Using appropriate rust resistant and rust susceptible genotypes as standards, examination of uredinia 14 days after inoculation allowed quantitative comparisons of sporulation capacities, one measure of susceptibility or resistance to soybean rust. The study verified the presence and ability to detect all known major genes for resistance to soybean rust in the original sources of resistance. It demonstrated that soybean lines derived from the original PI sources, and presumed to possess the resistance genes, in actuality may lack the gene or express an intermediate reaction to the rust pathogen. We suggest that a determination of numbers and sizes of uredinia will detect both major gene and partial resistance to soybean rust.

severe aphid infestation . An additional threat posed by the aphid is its ability to transmit certain With an efficient greenhouse screening method, the first resistance plant viruses to soybean such as Alfalfa mosaic virus, Soyto the soybean aphid (Aphis glycines Matsumura) was found in cultivated soybean [Glycine max (L.) Merr.] germplasm. No resistance was bean dwarf virus, and Soybean mosaic virus (Sama et al., found in 1425 current North American soybean cultivars, 106 Maturity 1974; Iwaki et al., 1980; Hartman et al., 2001; Hill et al., Group (MG) 000 through VII Asian cultivars, and in a set of 11 'Clark' 2001; Clark and Perry, 2002). isolines possessing different pubescence traits. Dense pubescence did Aphis glycines and close relative A. gossypii, the cotton not provide protection against the soybean aphid. Resistance was or melon aphid, are the only aphid species found colonizdiscovered and established in three ancestors of North American ing soybean in the USA. In other parts of the world, A. genotypes: 'Dowling', 'Jackson', and PI 71506. Expression of resiscraccivora, Aulacorthum solani, and other species have tance in those genotypes was characterized in choice and nonchoice been found colonizing soybeans (D. Voegtlin, personal tests. In choice tests, significantly fewer aphids occurred on Dowling, communication, 2003). Jackson, and PI 71506 plants compared with susceptible cultivars (P ϭ Aphis glycines has a heteroecious, holocyclic life-cycle 0.05). Aphid populations did not develop on Dowling and Jackson in nonchoice tests, indicating that there was a negative impact on pattern (Guang-xue and Tie-sen, 1982). Rhamnus catharaphid fecundity on those cultivars. That evidence combined with ob-tica (buckthorn) is the primary host of A. glycines (Hartservations of aphid mortality on those cultivars suggested that antibioman et al., 2001) and soybean is a secondary host. In sis-type resistance contributed to the expression of resistance. Possible autumn, when the soybean crop matures, the aphid moves donors of resistance to Dowling and Jackson were identified. In nonto R. cathartica, where mating and oviposition occurs. The choice tests, population development on PI 71506 was not sigegg stage overwinters on R. cathartica. During the follownificantly different from development on susceptible cultivars, indicating spring, the eggs hatch and a few generations are proing that antixenosis was more important in that genotype. Resistance duced before alatae (winged females) fly to soybean. was expressed in all plant stages. Dowling provided season-long pro-Because A. glycines is a recent pest in the USA, a comtection against aphids equal to the use of the systemic insecticide imiprehensive integrated management approach to control dacloprid {1-[(6-Chloro-3-pyridinyl)methyl]-N-nitro-2-imidazolidini-mine} in a field test. Four other germplasm accessions, 'Sugao Zarai',