Occurrence, Distribution, and Transmission of Alfalfa Viruses in China

Abstract

Alfalfa (Medicago sativa L.) is one of the most important quality forages worldwide and is cultivated throughout China. Alfalfa is susceptible to a variety of viral diseases during its growth, which has caused huge amounts of commercial losses. However, the profile of the alfalfa virus in China remains ambiguous and the viruses transmitted by Odontothrips loti (Haliday), dominant insect pests in alfalfa, are also poorly understood. In the present study, virus diversity was investigated in the primary alfalfa-growing areas in China. A total of 18 alfalfa viruses were identified through RNA-sequencing (RNA-seq) and reverse transcription-polymerase chain reaction (RT-PCR). Two new plant viruses, Medicago sativa virus 1 (MsV1) and Medicago sativa luteovirus 1 (MsLV1), were detected for the first time. Another four viruses, including the Alfalfa ringspot-associated virus (ARaV), Alfalfa virus F (AVF), Alfalfa enamovirus 1 (AEV1), and Alfalfa deltaparitivirus (ADPV), were reported in China for the first time as well. Both Alfalfa mosaic virus (AMV) and Medicago sativa alphapartitivirus 2 (MsAPV2) are the dominant pathogens, with an infection incidence of 91.7–100%, and 74.4–97.2%, respectively. Additionally, O. loti with first- and second-instar nymphs were shown to acquire the AMV within 0.25 h of feeding on a virus-infected alfalfa. Transmission by thrips to healthy alfalfa plants was also demonstrated. Additionally, we clarified the dynamic changes in the AMV in pre-adult stages of O. loti, which indicated that the AMV is propagated in the nymph stage of O. loti. These findings provide valuable information for understanding the alfalfa virome, confirm the role thrips O. loti plays in alfalfa virus transmission, and improve our fundamental knowledge and management of diseases in China.

The Complex World of Emaraviruses – Challenges, Insights and Prospects

“…In China, AcCRaV and Actinidia virus 2 (AcV-2), both infecting kiwifruits, have been found in several provinces [52,54]. Further emaraviruses including JYMaV [55], PerMV [110], LiCRaV [62], Camellia chlorotic ringspot virus 1 (CaCRSV-1) and Camellia chlorotic ringspot virus 2 (CaCRSV-2) [59], PCLSaV [31], chrysanthemum mosaic-associated virus (ChMaV) [64,111], Japanese star anise ringspot-associated virus (JSARaV) [71], Vitis emaravirus (VEV) [67,68], alfalfa ringspot-associated virus (ARaV) [66], Ailanthus crinkle leaf-associated emaravirus (ACrLaV) [74] and PloAEV that infect important commercial fruits, ornamental crops and trees have been described in China and Japan. From other parts of the world there is limited information on emaraviruses diversity and distribution.…”

“…Beyond the four core segments, most emaraviruses possess additional genome segments. The only exceptions are PVBV [53], CjaV-2 [58], ARaV [65,66] and ACrLaV [74], however, overlooked segments might await discovery (see chapter 6.2.6). The number of additional segments differs considerably among species, from 1 for RYRaV to 6 for PerMV [61].…”

Transmission from seed to seedling and elimination of alfalfa viruses

“…Viral diseases are one of the most significant biological threats to alfalfa ( Medicago sativa ). Currently, more than 50 viral species have been reported that can infect alfalfa, causing severe symptoms such as enation, streak, yellowing, and mosaic, and inhibiting the normal growth and development of the alfalfa ( Han et al., 2019 ; Jiang et al., 2019 ; Li et al., 2021 ; Guo et al., 2022 ; Li et al., 2022 ). Viral diseases have become a vital factor hindering the development of the alfalfa industry.…”

“…At present, twenty-one species of alfalfa viruses have been detected in China ( Guo et al., 2022 ; Li et al., 2022 ). In our previous study, we found six viruses with a high incidence rate and virus loads in alfalfa were alfalfa mosaic virus (AMV), Medicago sativa alphapartitivirus 1 (MsAPV1), Medicago sativa alphapartitivirus 2 (MsAPV2), Medicago sativa deltapartitivirus 1 (MsDPV1), Medicago sativa amalgavirus 1 (MsAV1), and cnidium vein yellowing virus 1 (CnVYV1) ( Li et al., 2022 ). As a worldwide spread vital alfalfa virus that has drawn extensive attention, AMV may cause alfalfa biomass loss by up to 30% ( Han et al., 2019 ).…”

“…AMV particles are attached to the seed coats in a stable form, highly resistant to potential damages caused by storage temperature and location changes ( Frosheiser, 1964 , Frosheiser, 1974 ). By contrast, the other five viruses, MsAPV1, MsAPV2, MsDPV1, MsAV1, and CnVYV1, were recently detected in the main alfalfa cultivation region in China ( Li et al., 2022 ), but whether and how they were transmitted by seeds remained to be investigated. Moreover, virus accumulation in plants and the dynamic process vary among different viral species ( Ryabinina et al., 2020 ; Xu et al., 2023 ).…”