Molecular and Biological Characterization of Spodoptera frugiperda Multiple Nucleopolyhedrovirus Field Isolate and Genotypes from China

The fall armyworm, Spodoptera frugiperda, is a new invading pest in China. The baculovirus Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV) is a pathogenic agent of the fall armyworm and a potential agent for its control in integrated pest management strategies. In this work, we analyze the molecular and biological characteristics of an SfMNPV isolate collected from maize in China (SfMNPV-Hub). Two genotypes were further isolated from SfMNPV-Hub by an in vivo cloning method. The PstI profile of one genotype (SfHub-A) was similar to genotype A of the SfMNPV Colombian isolate, and the other (SfHub-E) was similar to genotype E of the Colombian isolate. The bioactivity of SfHub-A against second-instar S. frugiperda larvae was not significantly different from that of SfMNPV-Hub, whereas SfHub-E was 2.7–5.5 fold less potent than SfMNPV-Hub. The speed of kill of SfHub-E was quicker than SfMNPV-Hub, while SfHub-A acted slower than SfMNPV-Hub. Occlusion body (OB) production of SfHub-A in an S. frugiperda cadaver was significantly higher than that of SfMNPV-Hub, while SfHub-E yielded far fewer occlusion bodies (OBs) in the host larvae. These results provide basic information for developing a virus-based pesticide against the invading pest S. frugiperda.

First Report of Rice stripe necrosis virus Infecting Rice in Burkina Faso

Rice stripe necrosis virus (RSNV) was first described in 1977 as a new virus infecting rice in Cote d'Ivoire (3) and was subsequently observed in Liberia, Nigeria, and Sierra Leone (2). RSNV is a soil-borne virus transmitted by the fungus Polymyxa graminis (1) and belongs to the genus Benyvirus (4). During a survey carried out in April of 2013, severe symptoms characterized by seedling death, severe plant malformation, and foliar striping were observed on rice plants in an experimental field of INERA at Banfora located in western Burkina Faso. Disease incidence in the field was estimated to be 80 ± 5%. The symptoms of disease were successfully transmitted to the susceptible rice (Oryza sativa) cultivar IR64 by soil transmission experiments (1). RSNV was detected by ELISA using a polyclonal antiserum (1), kindly provided by Dr. Denis Fargette, IRD, Montpellier, France. Total nucleic acid was extracted with TRIzol reagent (Invitrogen) from IR64 and field infected samples. The presence of the virus was confirmed by RT-PCR using primers 5′-CATCTTGTCGAGATGAG-3′ and 5′-GCGTTGTCTTTATCAGTG-3′ for specific sequences flanking the RNA2 CP gene. The RT-PCR product was directly sequenced and the sequence was deposited in GenBank (Accession No. LK023710). Sequence analysis showed that the CP gene of the RSNV isolate from Burkina Faso shared the highest nucleotide sequence identity (97.6%) with the known RSNV CP gene sequence from the Colombian isolate (EU099845) available in GenBank, confirming the presence of RSNV in the rice crops in Burkina Faso. To our knowledge, this is the first confirmed report of RSNV in Burkina Faso. Further studies are needed to determine its incidence and spread in the country. Detection of RSNV in Burkina Faso signals the urgent need for adoption of appropriate measures to restrict the spread and impact of this virus within Africa. References: (1) C. Fauquet and J. C. Thouvenel. Proc. Acad. Sci. Ser. D 296:575, 1983. (2) C. Fauquet et al. Develop. Appl. Biol. 2:71, 1988. (3) D. Louvel and J.-M. Bidaux. Agronomie Tropicale 32:257, 1977. (4) I. Lozano and F. Morales. Eur. J. Plant Pathol. 124:673, 2009.

Exclusión de linajes como estrategia para la obtención de resistencia durable en el arroz a Pyricularia grisea Sacc. en Colombia

<p>La durabilidad de la resistencia genética del arroz a <em>Pyricularia grisea </em>Sacc. había estado comprometida en Colombia, por una rápida adaptación aparente del patógeno a los genes dispuestos para contrarrestar su incidencia. Las variedades mejoradas se veían afectadas por la enfermedad en el curso de pocos años y, en ocasiones, a sólo meses de haber sido liberadas. La exclusión de linajes es una estrategia de mejoramiento que propone la identificación y posterior ‘piramidación’ de genes con habilidad para reconocer de manera complementaria las avirulencias de las familias genéticas (linajes) del patógeno. Poblaciones ecológicamente distintitas, caracterizadas molecularmente mediante la sonda MGR-586, exhiben una estructura clonal en la que cada aislamiento del linaje comparte históricamente el mismo espectro de virulencia. La resistencia obtenida con la piramidación de genes complementarios funciona como factor de exclusión hacia la totalidad de la virulencia en la población del patógeno en un ecosistema determinado. Así, en Colombia, los genes <em>Pi-1 (t) </em>y <em>Pi-2 (t) </em>son diferencial y complementariamente excluyentes de la virulencia de las poblaciones de <em>P. grisea</em>. Fueron obtenidas líneas con estos genes piramidados mediante el cruzamiento de dos líneas isogénicas; la presencia y condición homocigota de los genes de resistencia en las nuevas líneas fue establecida a través de marcadores moleculares. El comportamiento de las pirámides fue evaluado en el laboratorio, en cámaras de crecimiento con aislamientos representativos de los linajes colombianos y, en el campo, en una región dedicada tradicionalmente a la producción de arroz donde las epidemias de piricularia son frecuentes.Tanto en las inoculaciones artificiales, como en las áreas de cultivo, las pirámides conservaron la resistencia. La estructura de virulencia entre la población del patógeno en el campo permaneció estable durante tres años, aunque estacional y transitoriamente se identificaron algunos aislamientos virulentos a las pirámides en la estación experimental.</p><p> </p><p><strong><em>Abstract</em></strong></p><p><strong>Lineaje-exclusion, a strategy for breeding rice with durable resistance to </strong><strong><em>Pyricularia grisea </em></strong><strong>Sacc. in Colombia</strong></p><p>Rice blast has challenged plant breeders when they were searching for durable resistance in Colombia. Rapid resistance breakdowns were commonly observed in newly bred cultivars and they are attributed to frequent appearance of new pathotypes. Recent population studies of the rice blast pathosystem have shown that <em>Pyricularia grisea </em>in a given region, typically expresses a phylogenetic organization of distinct lineages (‘genetic families’ as defined by MGR-DNA fingerprinting). Each lineage exhibits a definable virulence spectrum, and the potential for developing new pathotypes appears to be constrained by lineage-specific avirulences. Lineageexclusion is a breeding strategy aimed to enlighten the choosing of genes to obtain more durable resistance in the field. Combining genes that complementary exclude fragments of virulence, will provide complete resistance to known lineages. The resistance of pyramids bearing the major resistance genes <em>Pi-1 (t) </em>and <em>Pi-2 (t) </em>was determined at three sites in a primary rice growing region in Colombia, from 1996 to 1998.The chosen R-genes are individually defeated by common lineages in Colombia, but combined, provide resistance to the complementary spectra of virulence. The pyramids were selected by screening the progeny of a cross of nearisogenic lines with the representative.The presence and homozygosity of both genes were confirmed through molecular markers. Neither single Colombian isolate, nor mixture of isolates infected the pyramids. The pyramids proved to be highly resistant in the field, and no major changes in lineage composition or virulence spectrum were observed. However, some moderately compatible isolates of lineage SRL-6 were transiently observed in the area of Santa Rosa. Resistance breakdown (vulnerability) may depend on within lineage rather than between lineage distributions of virulence.</p>