Presence of Tomato yellow leaf curl virus Infecting Squash (Curcubita pepo) in Cuba

Flue-cured tobacco confirmed as a reservoir host plant for Tomato yellow leaf curl virus by agro-inoculation and Bemisia tabaci MED-mediated transmission

Tomato yellow leaf curl virus (TYLCV) causes great losses in tomato production. In addition to tomato, TYLCV infects many crops or weeds as alternative hosts. These alternative hosts may serve as reservoirs for TYLCV survival and spread. Here, we tested the capability of cultivated, flue-cured tobacco to act as a reservoir host plant for TYLCV. TYLCV DNA was detected in nine flue-cured tobacco cultivars inoculated with an infectious TYLCV clone, although no visible symptoms developed on TYLCV-infected tobacco plants. The percentage of whiteflies with viral DNA increased with an increasing acquisition access period (AAP) and reached 100% after a 12 h AAP on infected tobacco plants. Using infected tobacco plants as virus resources, TYLCV was capable of being transmitted to tobacco and tomato plants by whiteflies, and typical symptoms of TYLCV infection were observed on infected tomato plants but not on infected tobacco plants. Our results suggest that flue-cured tobacco can serve as a reservoir host plant for TYLCV and may play an important role in the spread of TYLCV epidemics in China.

Ongoing geographical spread of Tomato yellow leaf curl virus

Tomato yellow leaf curl virus (TYLCV) seriously impacts tomato production throughout tropical and sub-tropical regions of the world. It has a broad geographical distribution and continues to spread to new regions in the Indian and Pacific Oceans including Australia, New Caledonia and Mauritius. We undertook a temporally-scaled, phylogeographic analysis of all publicly available, full genome sequences of TYLCV, together with 70 new genome sequences from Australia, Iran and Mauritius. This revealed that whereas epidemics in Australia and China likely originated through multiple independent viral introductions from the East-Asian region around Japan and Korea, the New Caledonian epidemic was seeded by a variant from the Western Mediterranean region and the Mauritian epidemic by a variant from the neighbouring island of Reunion. Finally, we show that inter-continental scale movements of TYLCV to East Asia have, at least temporarily, ceased, whereas long-distance movements to the Americas and Australia are probably still ongoing.

Eugenol confers resistance to Tomato yellow leaf curl virus (TYLCV) by regulating the expression of SlPer1 in tomato plants

Tomato yellow leaf curl virus (TYLCV) is one of the most devastating plant diseases, and poses a significant agricultural concern because of the lack of an efficient control method. Eugenol is a plant-derived natural compound that has been widely used as a food additive and in medicine. In the present study, we demonstrated the potential of eugenol to enhance the resistance of tomato plants to TYLCV. The anti-TYLCV efficiency of eugenol was significantly higher than that of moroxydine hydrochloride (MH), a widely used commercial antiviral agent. Eugenol application stimulated the production of endogenous nitric oxide (NO) and salicylic acid (SA) in tomato plants. The full-length cDNA of SlPer1, which has been suggested to be a host R gene specific to TYLCV, was isolated from tomato plants. A sequence analysis suggested that SlPer1 might be a nucleobase-ascorbate transporter (NAT) belonging to the permease family. The transcript levels of SlPer1 increased markedly in response to treatment with eugenol or TYLCV inoculation. The results of this study also showed that SlPer1 expression was strongly induced by SA, MeJA (jasmonic acid methyl ester), and NO. Thus, we propose that the increased transcription of SlPer1 contributed to the high anti-TYLCV efficiency of eugenol, which might involve in the generation of endogenous SA and NO. Such findings provide the basis for the development of eugenol as an environmental-friendly agricultural antiviral agent.

Emerging virus diseases transmitted by whiteflies

Virus diseases that have emerged in the past two decades limit the production of important vegetable crops in tropical, subtropical, and temperate regions worldwide, and many of the causal viruses are transmitted by whiteflies (order Hemiptera, family Aleyrodidae). Most of these whitefly-transmitted viruses are begomoviruses (family Geminiviridae), although whiteflies are also vectors of criniviruses, ipomoviruses, torradoviruses, and some carlaviruses. Factors driving the emergence and establishment of whitefly-transmitted diseases include genetic changes in the virus through mutation and recombination, changes in the vector populations coupled with polyphagy of the main vector, Bemisia tabaci, and long distance traffic of plant material or vector insects due to trade of vegetables and ornamental plants. The role of humans in increasing the emergence of virus diseases is obvious, and the effect that climate change may have in the future is unclear.

A multiplex PCR method discriminating between the TYLCV and TYLCV-Mld clades of tomato yellow leaf curl virus

Tomato yellow leaf curl virus (TYLCV) is one of the causal agents of tomato yellow leaf curl disease (TYLCD) and can cause up to 100% yield losses in tomato fields. As TYLCV continues to spread, many isolates have been described in different parts of the world. Recently two closely related but distinct TYLCV clades, called TYLCV and TYLCV-Mld, have been identified. Isolates from those two clades differ mainly in the nucleotide sequences of their replication associated protein genes but do not display significantly different symptomatology. In order to improve monitoring of the rapidly expanding worldwide TYLCD epidemic, a multiplex polymerase chain reaction assay (mPCR) was developed. A set of three primers were designed to detect and characterize the TYLCV and TYLCV-Mld clade isolates. The specificity and sensitivity of the mPCR were validated on TYLCV infected tomato plants and Bemisia tabaci whiteflies. Being cheap, fast and highly sensitive this new diagnostic tool should greatly simplify efforts to trace the global spread of TYLCV.