The leaflet addresses organic farmers who are cultivating green peas. The first article is about crop management from growing to harvesting. Afterwards, an overview about pests, diseases and biological pest control is provided, followed by a specific description of viruses and strategies to reduce nanoviruses. The last topics are aphid attacks and biological aphid control.
The recent identification of a new nanovirus, pea necrotic yellow dwarf virus, from pea in Germany prompted us to survey wild and cultivated legumes for nanovirus infections in several European countries. This led to the identification of two new nanoviruses: black medic leaf roll virus (BMLRV) and pea yellow stunt virus (PYSV), each considered a putative new species. The complete genomes of a PYSV isolate from Austria and three BMLRV isolates from Austria, Azerbaijan and Sweden were sequenced. In addition, the genomes of five isolates of faba bean necrotic yellows virus (FBNYV) from Azerbaijan and Spain and those of four faba bean necrotic stunt virus (FBNSV) isolates from Azerbaijan were completely sequenced, leading to the first identification of FBNSV occurring in Europe. Sequence analyses uncovered evolutionary relationships, extensive reassortment and potential remnants of mixed nanovirus infections, as well as intra- and intercomponent recombination events within the nanovirus genomes. In some virus isolates, diverse types of the same genome component (paralogues) were observed, a type of genome complexity not described previously for any member of the family Nanoviridae. Moreover, infectious and aphid-transmissible nanoviruses from cloned genomic DNAs of FBNYV and BMLRV were reconstituted that, for the first time, allow experimental reassortments for studying the genome functions and evolution of these nanoviruses.
In a survey of 14 processing crops and 7 pea seed crops throughout Canterbury Cucumber mosaic virus (CMV) was the most widespread with crop incidences of up to 20 Alfalfa mosaic virus (AMV) up to 11 Pea seedborne mosaic virus (PSbMV) up to 9 Soybean dwarf virus (SDV) up to 2 Turnip yellows virus (TuYV) up to 2 and Bean yellow mosaic virus (BYMV) up to 35 Red clover vein mosaic virus (RCVMV) was detected in peas for the first time in New Zealand with incidences of up to 35 Pea necrotic yellow dwarf virus (PNYDV) Faba bean necrotic yellows virus (FBNYV) and Broad bean stain virus (BBSV) were not detected In a survey of 8 beetroot crops TuYV was detected in Auckland at 1 incidence but not in Hawkes Bay Beet mosaic virus was detected at 1 incidence in both regions Fungal leaf spotting pathogens appear a greater concern in beetroot In 12 dwarf bean processing crops throughout Canterbury virus was only detected in early sown crops AMV and RCVMV were most widespread with incidences of up to 9; CMV with up to 7 incidence; then BYMV TuYV and SDV each with 1 incidence No Bean common mosaic virus was detected
Pea necrotic yellow dwarf virus (PNYDV) ist ein neuer Nanovirus in Mitteleurope, der verschiedene Leguminosen befallt und persistent durch Blattlause ubertragen wird. In dieser on-farm Studie untersuchten wir sechs Ackerbohnen-Felder mit PNYDV-symptomatischen Nestern mittels multispektraler Drohnen-Aufnahmen, die mit ground-truth Pflanzenwachstumsparametern korreliert werden. Symptomatische Pflanzen zeigten einen signifikanten Ruckgang der Sprosslange, oberirdische Trockenmasse, Hulsenzahl sowie Anzahl und Trockenmasse N-fixierender Wurzelknollchen. Im Gegensatz zu gesunden Pflanzen hatten symptomatische Pflanzen keine rosa oder rot gefarbten Knollcheninhalte, stattdessen hohere Anteile zerfallender und inaktiver Knollchen. Verschiedene Indices der multispektralen Aufnahmen zeigten einen deutlichen Unterschied in der spekteralen Information von symptomatischem Infektionsherd gegenuber der umgebenden Referenz.
Pea necrotic yellow dwarf virus (PNYDV), a member of the Nanovirus genus, has been reported from numerous European countries causing yield loss in peas, faba beans, vetches and lentils (Grigoras et al., 4; Grigoras et al., 3; Gaafar et al., 2; Gaafar et al., 1). In July and August 2016, five faba bean (Vicia faba) samples were received from five fields in different regions of Denmark, in which 2 to 25% plants were diseased. Affected plants displayed leaf-rolling, yellowing, and symptoms of severe stunting (Figs. 1-2). The samples reacted positively when analysed with ELISA using antibodies against PNYDV (Gaafar et al., 2). DNA was extracted and PNYDV infection was confirmed by PCR using primer pairs specific for components R and S (Gaafar et al., 1). Additionally, the full genomes of these Danish PNYDV isolates were determined. Rolling circle amplification was performed using a TempliPhiTM 100 Amplification Kit (GE Healthcare Limited, UK). Libraries were prepared from the products and submitted for high-throughput sequencing on two Illumina platforms, three samples on HiSeq (2*150) and two on MiSeq (2*301). The paired-end reads were analysed using Geneious 11.0.4 software (Biomatters Limited, NZ). The reads were trimmed, error corrected and normalised, then used for de novo assembly. Assembled contigs were compared with the GenBank non-redundant nucleotide and protein databases using BLASTn and BLASTx, respectively. The results confirmed the presence of all eight PNYDV components in all samples. Additionally, an alphasatellite 3 sequence was found associated with the DK HZ16-572 and DK HZ16-582 isolates, and a satellite DNA-X sequence was found associated with DK HZ16-572. The PNYDV genome Drohndorf-15 (Germany; GenBank Accession Nos. NC_023154 to NC_023161) was used to assemble the eight components of the Danish isolates and Austrian sequences (Gross-Enzernsdorf_1) for alphasatellite 3 and satellite DNA-X (KC979052 and KC979053, respectively) by mapping to reference. The sequences of the Danish PNYDV isolates can be accessed on GenBank (MH000227 to MH000269). A neighbour-joining tree (Jukes-Cantor genetic distance model and 1000 bootstrap replicates) was created using Geneious Tree Builder (Fig. 3) and the alignment (ClustalW 2.1) of the concatenated genome components (DNA-R, -S, -C, -M, -N, -U1, -U2 and -U4) from the Danish PNYDV isolates as well as the Austrian, Dutch and German isolates. Additionally, a pairwise comparison between the associated alphasatellite 3 of DK HZ16-572 and DK HZ16-582 showed 99% nucleotide identity to each other, and 99.1% and 99.3% identity when compared with the Gross-Enzersdorf_1 isolate, respectively. Finally, DNA-X of DK HZ16-572 shared 98.8% identity with Gross-Enzersdorf_1. The tree and the sequence alignments indicate that the Danish isolates are very closely related to other European isolates of PNYDV. To our knowledge, this is the first report of a nanovirus disease in Denmark demonstrating that PNYDV is also widespread throughout Denmark. This is further evidence that PNYDV (and possible other nanoviruses) is an emerging threat for legumes not only in Denmark which has an increasing area of legume production (Table 1) but also in other European countries. The authors are thankful to the technical staff for their excellent technical support. This research was funded from the Euphresco network project (2015-F-172). Y. Gaafar was supported by the German Egyptian Research Long-Term Scholarship.
Red clover vein mosaic virus (RCVMV) is an important virus of leguminous crops that can cause devastating losses. During a routine survey of legumes conducted on the South Island of New Zealand, RCVMV was found in mixed infections in clover plants with Alfalfa mosaic virus and White clover mosaic virus. The full-length sequence of the New Zealand isolate RCVMV-NZ from clover shared 96% nucleotide sequence identity with a chickpea isolate previously described from Washington (United States). Targeted surveys of pea, faba bean, and pasture crops showed that RCVMV-NZ is widespread on the South Island in New Zealand. This isolate is causing mild if any symptoms on experimental hosts and naturally infected plants.
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