Molecular, serological and biological variation among chickpea chlorotic stunt virus isolates from five countries of North Africa and West Asia

Chickpea chlorotic stunt virus (CpCSV), a proposed new member of the genus Polerovirus (family Luteoviridae), has been reported only from Ethiopia. In attempts to determine the geographical distribution and variability of CpCSV, a pair of degenerate primers derived from conserved domains of the luteovirus coat protein (CP) gene was used for RT-PCR analysis of various legume samples originating from five countries and containing unidentified luteoviruses. Sequencing of the amplicons provided evidence for the occurrence of CpCSV also in Egypt, Morocco, Sudan, and Syria. Phylogenetic analysis of the CP nucleotide sequences of 18 samples from the five countries revealed the existence of two geographic groups of CpCSV isolates differing in CP sequences by 8–10%. Group I included isolates from Ethiopia and Sudan, while group II comprised those from Egypt, Morocco and Syria. For distinguishing these two groups, a simple RFLP test using HindIII and/or PvuII for cleavage of CP-gene-derived PCR products was developed. In ELISA and immunoelectron microscopy, however, isolates from these two groups could not be distinguished with rabbit antisera raised against a group-I isolate from Ethiopia (CpCSV-Eth) and a group-II isolate from Syria (CpCSV-Sy). Since none of the ten monoclonal antibodies (MAbs) that had been produced earlier against CpCSV-Eth reacted with group-II isolates, further MAbs were produced. Of the seven MAbs raised against CpCSV-Sy, two reacted only with CpCSV-Sy and two others with both CpCSV-Sy and -Eth. This indicated that there are group I- and II-specific and common (species-specific) epitopes on the CpCSV CP and that the corresponding MAbs are suitable for specific detection and discrimination of CpCSV isolates. Moreover, CpCSV-Sy (group II) caused more severe stunting and yellowing in faba bean than CpCSV-Eth (group I). In conclusion, our data indicate the existence of a geographically associated variation in the molecular, serological and presumably biological properties of CpCSV

Two distinct nanovirus species infecting faba bean in Morocco

Using monoclonal antibodies raised against a Faba bean necrotic yellows virus (FBNYV) isolate from Egypt and a Faba bean necrotic stunt virus (FBNSV) isolate from Ethiopia, a striking serological variability among nanovirus isolates from faba bean in Morocco was revealed. To obtain a better understanding of this nanovirus variability in Morocco, the entire genomes of two serologically contrasting isolates referred to as Mor5 and Mor23 were sequenced. The eight circular ssDNA components, each identified from Mor5- and Mor23-infected tissues and thought to form the complete nanovirus genome, ranged in size from 952 to 1,005 nt for Mor5 and from 980 to 1,004 nt for Mor23 and were structurally similar to previously described nanovirus DNAs. However, Mor5 and Mor23 differed from each other in overall nucleotide and amino acid sequences by 25 and 26%, respectively. Mor23 was most closely related to typical FBNYV isolates described earlier from Egypt and Syria, with which it shared a mean amino acid sequence identity of about 94%. On the other hand, Mor5 most closely resembled a FBNSV isolate from Ethiopia, with which it shared a mean amino acid sequence identity of approximately 89%. The serological and genetic differences observed for Mor5 and Mor23 were comparable to those observed earlier for FBNYV, FBNSV, and Milk vetch dwarf virus. Following the guidelines on nanovirus species demarcation, this suggests that Mor23 and Mor5 represent isolates of FBNYV and FBNSV, respectively. This is the first report not only on the presence of FBNSV in a country other than Ethiopia but also on the occurrence and complete genome sequences of members of two nanovirus species in the same country, thus providing evidence for faba bean crops being infected by members of two distinct nanovirus species in a restricted geographic area

Bread wheat x Agrotricum crosses as a source of immunity and resistance to the PAV strain of barley yellow dwarf luteovirus

The Agrotricum line OK7211542 (2n=56) was immune to the Cloutier isolate, which belongs to the PAV serotype of barley yellow dwarf luteovirus (BYDV). Through a process of selection for BYDV resistance and threshable phenotypes with wheat-like seeds, wheat-like F7-derived lines were obtained from Triticum aestivum\OK7211542 crosses. Some of these were immune to BYDV and had 44 chromosomes. Resistant lines with 2n=42 chromosomes or slightly higher chromosome numbers were also obtained. The low frequency of expression of immunity in the bread wheat background over many generations suggests that more than one gene is involved. These results are a first step towards the creation of wheat cultivars immune to BYDV. However, successful introgression will necessitate a transfer of immunity associated with a smaller amount of alien chromatin in the wheat genome.Croisements blé tendre x Agrotricum comme sources d'immunité et de résistance à la souche PAV du lutéovirus de la jaunisse nanisante de l'orge. La lignée d'Agrotricum OK7211542 (2n = 56) est immune à l'isolat Cloutier, un isolat de sérotype PAV du virus de la jaunisse nanisante de l'orge (VJNO). Après une sélection pendant plusieurs générations pour la résistance au VJNO et pour un phénotype semblable au blé tendre quant à la facilité de battage et à la forme du grain, on a obtenu des lignées visuellement semblables au blé. Certaines lignées à 2n = 44 furent classées immunes au VJNO. Des lignées à 2n = 42 ou possédant quelques chromosomes de plus ont été classées résistantes au virus. La rareté des phénotypes immuns semblables au blé, au fil des générations, suggère que plus d'un gène est impliqué. Ces résultats sont une première étape vers la création de cultivars immuns au VJNO. L'introgression ne sera cependant complètement réussie qu'avec un transfert d'immunité associée à des quantités plus faibles de chromatine étrangère dans le génome du blé