O. A. Abdalla

Response of greenhouse-grown cucumber cultivars to an isolate of Zucchini yellow mosaic virus (ZYMV)

Mechanical inoculation of 12 greenhouse-grown cucumber (Cucumis sativus) cultivars at the three- to four-leaf stage with an isolate of zucchini yellow mosaic virus (ZYMV) from Saudi Arabia resulted in various symptoms in 11 cultivars. Significant differences in plant height, fruit numbers, and fruit weight were observed between the inoculated and the control plants of the 11 affected cultivars. The cultivar Dina was asymptomatic, and no significant differences were observed between the inoculated and control plants for any of the parameters tested. Virus recovery test from cultivar Dina performed on the susceptible cultivar, Farol, together with lack of virus detection by enzyme-linked immunosorbent assay (ELISA) indicated that this ZYMV isolate did not infect Dina. However, inoculation of Dina at the cotyledon stage revealed minor symptoms that were confined to a few of the lower leaves, suggesting that Dina is resistant but not immune to this ZYMV isolate. Virus titer in Dina was low and the virus was restricted to the older leaves; whereas in Farol virus titer was considerably higher and the virus spread to all leaves.

Detection of new viruses in alfalfa, weeds and cultivated plants growing adjacent to alfalfa fields in Saudi Arabia

A total of 1368 symptomatic plant samples showing different virus-like symptoms such as mottling, chlorosis, mosaic, yellow mosaic, vein clearing and stunting were collected from alfalfa, weed and cultivated plant species growing in vicinity of alfalfa fields in five principal regions of alfalfa production in Saudi Arabia. DAS-ELISA test indicated occurrence of 11 different viruses in these samples, 10 of which were detected for the first time in Saudi Arabia. Eighty percent of the alfalfa samples and 97.5% of the weed and cultivated plants samples were found to be infected with one or more of these viruses. Nine weed plant species were found to harbor these viruses namely, Sonchus oleraceus, Chenopodium spp., Hibiscus spp., Cichorium intybus, Convolvulus arvensis, Malva parviflora, Rubus fruticosus, Hippuris vulgaris, and Flaveria trinervia. These viruses were also detected in seven cultivated crop plants growing adjacent to the alfalfa fields including Vigna unguiculata, Solanum tuberosum, Solanum melongena, Phaseolus vulgaris, Cucurbita maxima, Capsicum annuum, and Vicia faba. The newly reported viruses together with their respective percent of detection in alfalfa, and in both weeds and cultivated crop plant species together were as follows: Bean leaf roll virus (BLRV) {12.5 and 4.5%}, Lucerne transient streak virus (LTSV) {2.9 and 3.5%}, Bean yellow mosaic virus (BYMV) {1.4 and 4.5%}, Bean common mosaic virus (BCMV) {1.2 and 4.5%}, Red clover vein mosaic virus (RCVMV) {1.2 and 4%}, White clover mosaic virus (WCIMV) {1.0 and 5%}, Cucumber mosaic virus (CMV) {0.8 and 3%}, Pea streak virus (PeSV) {0.4 and 4.5%} and Tobacco streak virus (TSV) {0.3 and 2.5%}. Alfalfa mosaic virus (AMV), the previously reported virus in alfalfa, had the highest percentage of detection in alfalfa accounting for 58.4% and 62.8% in the weeds and cultivated plants. Peanut stunt virus (PSV) was also detected for the first time in Saudi Arabia with a 66.7% of infection in 90 alfalfa samples collected from the surveyed regions during the last visit that tested negative to all the previously detected viruses.

IDENTIFICATION AND CHARACTERIZATION OF COWPEA APHID-BORNE MOSAIC VIRUS ISOLATES IN SAUDI ARABIA

SUMMARY Cowpea (Vigna unguiculata subsp. unguiculata) plants showing mosaic, and other virus‐like symptoms, were noticed in May 2009 in a field located in the Alahsa Governorate (eastern Saudi Arabia). Systemic infections were observed on mechanically inoculated V. unguiculata subsp. unguiculata, V. unguiculata subsp. sesquipedalis, and Nicotiana benthamiana plants, while local infections developed on inoculated leaves of Chenopodium quinoa, C. amaranticolor, and N. occidentalis. Latent infections were detected in inoculated Ocimum basilicum and Cajanus cajan. DAS-ELISA from the above plants gave positive reactions with Cowpea aphid-borne mosaic virus (CABMV) antibodies. The virus was transmitted by Aphis craccivora Koch. in a non-persistent manner and by infected cowpea seeds at a rate of ca. 5%. Electron microscopic examination of leaf-dip preparations from symptomatic cowpea leaves revealed flexuous particles, 750x12 nm. The virus was also identified molecularly by dot-blot hybridization and RT-PCR assays. The coat protein gene of each of the Saudi virus isolates was partially sequenced and compared with those of 18 CABMV strains from different countries. Phylogenetic analysis indicated that the Saudi virus isolates are virtually identical and had the highest nucleotide sequence identity (93.5%) with two CABMV strains from Morocco and one strain from Nigeria, and the lowest identity with two strains from Zimbabwe and a strain from Brazil. The partial nucleotide sequence of only one of these Saudi isolates was deposited in the GenBank under the accession number JQ638520 to represent all other isolates. This is the first report of the presence of CABMV in Saudi Arabia whose strain is denoted CABMV-SA.

Lucerne transient streak virus; a Recently Detected Virus Infecting Alfafa (Medicago sativa) in Central Saudi Arabia

A survey was conducted to determine the status of Lucerne transient streak virus (LTSV) in three high-yielding alfalfa regions in central Saudi Arabia (Riyadh, Qassim, and Hail) during 2014. Three hundred and eight symptomatic alfalfa, and seven Sonchus oleraceus samples were collected. DAS-ELISA indicated that 59 of these samples were positive to LTSV. Two isolates of LTSV from each region were selected for molecular studies. RT-PCR confirmed the presence of LTSV in the selected samples using a specific primer pair. Percentage identity and homology tree comparisons revealed that all Saudi isolates were more closely related to each other but also closely related to the Canadian isolate-JQ782213 (97.1–97.6%) and the New Zealand isolate-U31286 (95.8–97.1%). Comparing Saudi isolates of LTSV with ten other sobemoviruses based on the coat protein gene sequences confirmed the distant relationship between them. Eleven out of fourteen plant species used in host range study were positive to LTSV. This is the first time to document that Trifolium alexandrinum, Nicotiana occidentalis, Chenopodium glaucum, and Lathyrus sativus are new host plant species for LTSV and that N. occidentalis being a good propagative host for it.