Detection of three major RNA viruses infecting sugarcane by multiplex reverse transcription–polymerase chain reaction (multiplex-RT-PCR)

Historical Review of Sugarcane Streak Mosaic Virus that Has Recently Emerged in Africa

Sugarcane streak mosaic virus (SCSMV), now assigned to the genus Poacevirus of the family Potyviridae, was reported for the first time in 1932 in Louisiana and was believed to be strain F of sugarcane mosaic virus (SCMV) for more than six decades. SCMV-F was renamed SCSMV in 1998 after partial sequencing of its genome and phylogenetic investigations. Following the development of specific molecular diagnostic methods in the 2000s, SCSMV was recurrently found in sugarcane exhibiting streak mosaic symptoms in numerous Asian countries but not in the Western hemisphere or in Africa. In this review, we give an overview of the current knowledge on this disease and the progression in research on SCSMV. This includes symptoms, geographical distribution and incidence, diagnosis and genetic diversity of the virus, epidemiology, and control. Finally, we highlight future challenges, as sugarcane streak mosaic has recently been found in Africa, where this disease represents a new threat to sugarcane production.

Identification of resistance to Sugarcane mosaic virus, Sugarcane streak mosaic virus, and Sugarcane bacilliform virus in new elite sugarcane accessions in India

Sugarcane mosaic and leaf fleck diseases are significant viral diseases affecting sugarcane crops in India. The use of resistant sugarcane varieties is considered the most economical and effective approach to manage viral diseases, especially in vegetatively propagated crops such as sugarcane. Sugarcane mosaic virus (SCMV) and Sugarcane streak mosaic virus (SCSMV) are the primary pathogens responsible for mosaic disease in sugarcane-growing regions of India. Sugarcane bacilliform virus (SCBV), causing leaf fleck disease, is also often found in mixed infections with mosaic symptoms. The study aimed to identify new sources of resistance by screening sugarcane germplasm for resistance to SCMV, SCSMV, and SCBV. The screening was carried out under high inoculum using the infector row method in both plant and ratoon crops. Out of 129 genotypes tested, only 8 were found to be free of mosaic viruses, indicating a rare occurrence of resistant sources. The study revealed that mosaic disease is widespread, with nearly 95% of tested varieties/genotypes being infected with mosaic viruses. SCMV, SCSMV, and SCBV were detected in 121 out of 129 genotypes using the RT-PCR and PCR assays. Based on their response to the viruses, the tested genotypes were categorized into different resistance grades: highly resistant (grade 1), resistant (grade 2), moderately resistant (grade 3), susceptible (grade 4), and highly susceptible (grade 5). The results of the study provide valuable information about elite resistance resources that can be used for the prevention and control of mosaic disease. These resistant genotypes could also serve as potential donors for mosaic and leaf fleck disease resistance in breeding programs.

Analysis of Wheat Virome in Korea Using Illumina and Oxford Nanopore Sequencing Platforms

Wheat (Triticum aestivum L.) is one of the most important staple crops in the world, along with maize and rice. More than 50 plant viruses are known to infect wheat worldwide. To date, there are no studies on the identification of viruses infecting wheat in Korea. Therefore, we investigated virome in wheat from three different geographical regions where wheat is mainly cultivated in Korea using Oxford Nanopore Technology (ONT) sequencing and Illumina sequencing. Five viral species, including those known to infect wheat, were identified using high-throughput sequencing strategies. Of these, barley virus G (BVG) and Hordeum vulgare endornavirus (HvEV) were consistently present in all libraries. Sugarcane yellow leaf virus (SCYLV) and wheat leaf yellowing-associated virus (WLYaV) were first identified in Korean wheat samples. The viruses identified by ONT and Illumina sequencing were compared using a heatmap. Though the ONT sequencing approach is less sensitive, the analysis results were similar to those of Illumina sequencing in our study. Both platforms served as reliable and powerful tools for detecting and identifying wheat viruses, achieving a balance between practicality and performance. The findings of this study will provide deeper insights into the wheat virosphere and further help improve disease management strategies.

Present Status and Future Management Strategies for Sugarcane Yellow Leaf Virus: A Major Constraint to the Global Sugarcane Production

Sugarcane yellow leaf virus (SCYLV) is a distinct member of the Polerovirus genus of the Luteoviridae family. SCYLV is the major limitation to sugarcane production worldwide and presently occurring in most of the sugarcane growing countries. SCYLV having high genetic diversity within the species and presently ten genotypes are known to occur based on the complete genome sequence information. SCYLV is present in almost all the states of India where sugarcane is grown. Virion comprises of 180 coat protein units and are 24-29 nm in diameter. The genome of SCYLV is a monopartite and comprised of single-stranded (ss) positive-sense (+) linear RNA of about 6 kb in size. Virus genome consists of six open reading frames (ORFs) that are expressed by sub-genomic RNAs. The SCYLV is phloem-limited and transmitted by sugarcane aphid Melanaphis sacchari in a circulative and non-propagative manner. The other aphid species namely, Ceratovacuna lanigera, Rhopalosiphum rufiabdominalis, and R. maidis also been reported to transmit the virus. The virus is not transmitted mechanically, therefore, its transmission by M. sacchari has been studied in different countries. SCYLV has a limited natural host range and mainly infect sugarcane (Sachharum hybrid), grain sorghum (Sorghum bicolor), and Columbus grass (Sorghum almum). Recent insights in the protein-protein interactions of Polerovirus through protein interaction reporter (PIR) technology enable us to understand viral encoded proteins during virus replication, assembly, plant defence mechanism, short and long-distance travel of the virus. This review presents the recent understandings on virus biology, diagnosis, genetic diversity, virus-vector and host-virus interactions and conventional and next generation management approaches.