Molecular characterization of a new recombinant brassica yellows virus infecting tobacco in China.

Brassica yellows virus (BrYV), prevalently distributed throughout mainland China and South Korea while triggering serious diseases in cruciferous crops, is proposed to be a new species in the genus Polerovirus within the family Luteoviridae. There are three distinct genotypes (BrYV-A, BrYV-B and BrYV-C) reported in cabbage and radish. Here, we describe a new BrYV isolate infecting tobacco plants in the field, which was named BrYV-NtabQJ. The complete genome sequence of BrYV-NtabQJ is 5741 nt in length, and 89% of the sequence shares higher sequence identities (about 90%) with different BrYV isolates. However, it possesses a quite divergent region within ORF5, which is more close to Beet western yellows virus (BWYV), Beet mild yellowing virus (BMYV) and Beet chlorosis virus (BChV). A significant recombination event was then detected among BrYV-NtabQJ, BrYV-B Beijng isolate (BrYV-BBJ) and BWYV Leonurus sibiricus isolate (BWYV-LS). It is proposed that BrYV-NtabQJ might be an interspecific recombinant between BrYV-BBJ and BWYV-LS, and the recombination might result in the successful aphid transmission of BrYV from cruciferous crops to tobacco. And it also poses new challenges for BrYV diagnosis and the vegetable production.

[Effects of Trichoderma longbrachitum and Streptomyces jingyangensis combination on the growth and disease resistance of tobacco seedlings].

An agar plate antagonism experiment in combining with in vivo screening experiment was conducted to study the affinity and bacteriostasis spectrum of the combination of biocontrol agents Trichoderma longbrachitum and Streptomyces jingyangensis to Nicotiana tabacum seedlings, with the effects of each agent and their combination on the N. tabacum seedlings growth, induced resistance, and resistance to Phytophthora nicotianae analyzed. The two agents had no interactive inhibitory effect and showed higher affinity to N. tabacum, and the agents themselves as well as their metabolites had higher bacteriostasis activities and wider bacteriostasis spectrum to P. nicotiaonae, Pythium aphanidermatum, and Alternaria alternate in different habitats. The combination of the two agents affected the morphological characteristics of the seedlings underground and aboveground parts, promoted the growth of root, stem, and leaf, and increased the root volume, total surface area, length, and average diameter as well as the stem height and size and the leaf length, width, and biomass, with these promotion effects being superior than those of the single-agent treatment. The combination of the two agents also increased the activities of the defensive enzymes superoxide dismutase, catalase, phenylalanine ammonia lyase, and peroxidase in the seedlings root significantly, with the relative control efficiency against P. nicotianae reached 69.3%, as compared to the conventional treatment. This study showed that the combination of T. longbrachitum and S. jingyangensis was a compatible combination with higher affinity and efficiency. This combination showed a synergistic effect of the two agents in plant disease control and in promoting plant growth, being able to promote the tobacco seedlings growth and control the P. nicotianae effectively.