Cherry rasp leaf virus. [Distribution map].

A new distribution map is provided for Cherry rasp leaf virus. Picornovirales: Secoviridae: Cheravirus. Hosts: Prunus spp., Malus spp. Information is given on the geographical distribution in Asia (China, Liaoning, Shandong) and North America (Canada, British Columbia, Quebec, USA, California, Colorado, Minnesota, Montana, Nebraska, New Mexico, Oregon, Utah, Washington, Wisconsin).

First Detection and Molecular Characterization of Apple Stem Grooving Virus, Apple Chlorotic Leaf Spot Virus, and Apple Hammerhead Viroid in Loquat in Spain

Loquat (Eriobotrya japonica) is an important crop in Spain. To date, only one viral species, apple stem pitting virus (ASPV), has been detected in Spanish loquat orchards. In this study, the presence of additional viruses infecting this crop in Spain was investigated. RT-PCR and high-throughput sequencing (HTS) of symptomatic loquat plants led to first-time detection and characterization of apple stem grooving virus (ASGV), also known as citrus tatter leaf virus (CTLV), and apple chlorotic leaf spot virus (ACLSV) from Spain with description of nearly complete genomic sequences. The frequency of ACLSV infection was the highest, with over 30% of the samples testing positive and were also detected as coinfections with ASGV and ASPV, although most of the samples infected were symptomless. Studies on all the full-length sequences available in the databases were performed in order to establish the phylogenetic relationships of the Spanish isolates of these two viral species. Moreover, apple hammerhead viroid (AHVd) was also detected to infect loquat, the first host different from apple reported for this viroid to date.

Effect of Sugarcane Cultivars Infected with Sugarcane Yellow Leaf Virus (ScYLV) on Feeding Behavior and Biological Performance of Melanaphis sacchari (Hemiptera: Aphididae)

Sugarcane yellow leaf virus (ScYLV), Polerovirus, Luteoviridae, is one of the main viruses that infect sugarcane worldwide. The virus is transmitted by the aphid Melanaphis sacchari in a persistent, circulative manner. To better understand the interactions between ScYLV, sugarcane genotypes and M. sacchari, we explored the effect of sugarcane cultivars on the feeding behavior and biological performance of the vector. The number of nymphs, adults, winged, total number of aphids and dead aphids was assayed, and an electrical penetration graph (EPG) was used to monitor the stylet activities. Multivariate analysis showed changes in the vector’s behavior and biology on cultivars, identifying specific groups of resistance. In the cultivar 7569, only 5.5% of the insects were able to stay longer on sustained phloem ingestion, while in the other seven cultivars these values varied from 20% to 60%. M. sacchari showed low phloem activities in cultivars 7569 and Bio266. Overall, cultivar 7569 showed the worst biological performance of aphids, with the insects presenting mechanical difficulties for feeding and a shorter duration of the phloem period, and thus being considered the most resistant. We conclude that ScYLV virus infection in different sugarcane cultivars induced specific changes in the host plant, modifying the behavior of its main vector, which may favor or impair virus transmission.

Survey of Sugarcane Yellow Leaf Virus in the Canal Point Breeding and Cultivar Development Program

Sugarcane yellow leaf virus (SCYLV), a Polerovirus in the family Luteoviridea, causes yellow leaf disease (YLD). Yield losses from YLD have been reported from several countries in both symptomatic and asymptomatic sugarcane cultivars. The breeding nursery at Canal Point (CP) in 2016 and primary and secondary seed increases in the CP cultivar development program at grower’s farm from 2015 to 2019 were surveyed for SCYLV infection by the tissue-blot immunoassay using polyclonal antibodies raised against SCYLV. More than 32% of varieties in the CP breeding nursery were infected with SCYLV in 2016. The SCYLV data of primary and secondary seedcane increases from 2015 to 2019 showed that out of 54 varieties screened at different locations, 12 had no SCYLV-positive plants, 24 had less than 5%, 5 had 6% to 12%, and 13 had 20% to 75% of the plants infected with SCYLV. The SCYLV screenings in varieties in the primary and secondary seed increase plantings provide growers an opportunity to acquire virus-free clean seedcane by apical meristem propagation to minimize the spread of the SCYLV and avoid yield losses.

Potential Targets for Evaluation of Sugarcane Yellow Leaf Virus Resistance in Sugarcane Cultivars: In silico Sugarcane miRNA and Target Network Prediction

The Sugarcane yellow leaf virus (SCYLV) is associated with sugarcane yellow leaf disease (SCYLD) and is considered to be the most economically deleterious emerging pathogen that represents a potential threat and danger to sugarcane cultivation in China. Over the last two decades, high genetic diversity in the SCYLV genotypes was observed worldwide, with a greater chance of YLD incidence for sugarcane injury. SCYLV infection has significantly damaged its economic traits and is responsible for substantial losses in biomass production in sugarcane cultivars. This study aims to identify and comprehensively analyze sugarcane microRNAs (miRNAs) as therapeutic targets against SCYLV using plant miRNA prediction tools. Mature sugarcane miRNAs are retrieved and are used for hybridization of the SCYLV. A total of seven common sugarcane miRNAs were selected based on consensus genomic positions. The biologically significant, top ranked ssp-miR528 was consensually predicted to have a potentially unique hybridization site at nucleotide position 4162 for targeting the ORF5 of the SCYLV genome; this was predicted by all the algorithms used in this study. Then, the miRNA–mRNA regulatory network was generated using the Circos algorithm, which was used to predict novel targets. There are no acceptable commercial SCYLV-resistant sugarcane varieties available at present. Therefore, the predicted biological data offer valuable evidence for the generation of SCYLV-resistant sugarcane plants.

Genome-wide approaches for the identification of markers and genes associated with sugarcane yellow leaf virus resistance

Sugarcane yellow leaf (SCYL), caused by the sugarcane yellow leaf virus (SCYLV) is a major disease affecting sugarcane, a leading sugar and energy crop. Despite damages caused by SCYLV, the genetic base of resistance to this virus remains largely unknown. Several methodologies have arisen to identify molecular markers associated with SCYLV resistance, which are crucial for marker-assisted selection and understanding response mechanisms to this virus. We investigated the genetic base of SCYLV resistance using dominant and codominant markers and genotypes of interest for sugarcane breeding. A sugarcane panel inoculated with SCYLV was analyzed for SCYL symptoms, and viral titer was estimated by RT-qPCR. This panel was genotyped with 662 dominant markers and 70,888 SNPs and indels with allele proportion information. We used polyploid-adapted genome-wide association analyses and machine-learning algorithms coupled with feature selection methods to establish marker-trait associations. While each approach identified unique marker sets associated with phenotypes, convergences were observed between them and demonstrated their complementarity. Lastly, we annotated these markers, identifying genes encoding emblematic participants in virus resistance mechanisms and previously unreported candidates involved in viral responses. Our approach could accelerate sugarcane breeding targeting SCYLV resistance and facilitate studies on biological processes leading to this trait.

The identification of Tautoneura mori as the vector of mulberry crinkle leaf virus and the infectivity of infectious clones in mulberry

Mulberry crinkle leaf virus (MCLV) is a novel geminivirus identified from mulberry. The pathogenicity and the natural vector of transmission have remained unknown for MCLV. Here, the infectious clones which consisted of the complete tandem dimeric genome of MCLV in a binary vector were constructed and agro-inoculated into mulberry seedlings. The results showed that the infectious clones of MCLV were systemically infectious to mulberry, but the infected mulberry plants did not show any virus-like symptoms. The natural transmission vectors of MCLV were also identified from possible vector insects occurring on the MCLV-infected mulberry plants. The vector ability of Tautoneura mori Matsumura was identified through inoculation assay. Three of 21 (14.3%) seedlings inoculated with T. mori collected from MCLV-infected mulberry plants grown naturally were detected to be MCLV-positive 50 days post-inoculation. These MCLV-positive mulberry plants did also not show any virus-like symptoms. Collectively, it is suggested that MCLV is infectious to mulberry plants, but MCLV alone does not induce symptoms. The leafhopper T. mori was for the first time determined experimentally to be a transmission vector of MCLV.