First Report of Cucurbit yellow stunting disorder virus on Melon in China

Differential Seasonal Prevalence of Yellowing Viruses Infecting Melon Crops in Southern California and Arizona Determined by Multiplex RT-PCR and RT-qPCR

Viruses transmitted by the whitefly (Bemisia tabaci) are an increasing threat to cucurbit production in the southwestern United States and many other cucurbit production regions of the world. The crinivirus cucurbit yellow stunting disorder virus (CYSDV) has severely impacted melon production in California and Arizona since its 2006 introduction to the region. Within the past few years, another crinivirus, cucurbit chlorotic yellows virus (CCYV), and the whitefly-transmitted ipomovirus squash vein yellowing virus (SqVYV) were found infecting melon plants in California's Imperial Valley. CYSDV, CCYV, and an aphid-transmitted polerovirus, cucurbit aphid-borne yellows virus (CABYV), occur together in the region and produce identical yellowing symptoms on cucurbit plants. Mixed infections of these four viruses in the Sonoran Desert and other regions pose challenges for disease management and efforts to develop resistant varieties. A multiplex single-step RT-PCR method was developed that differentiates among these viruses, and this was used to determine the prevalence and distribution of the viruses in melon samples from fields in the Sonoran Desert melon production region of California and Arizona during the spring and fall melon seasons from 2019 through 2021. TaqMan probes were developed, optimized, and applied in a single-step multiplex RT-qPCR to quantify titers of these four viruses in plant samples, which frequently carry mixed infections. Results of the multiplex RT-PCR analysis demonstrated that CYSDV is the predominant virus during the fall, whereas CCYV was by far the most prevalent virus during the spring each year. Multiplex RT-qPCR was used to evaluate differential accumulation and spatiotemporal distribution of viruses within plants and suggested differences in competitive accumulation of CCYV and CYSDV within melon. This study provides the first official report of SqVYV in Arizona and offers an efficient method for virus detection and quantification for breeding and disease management in areas impacted by cucurbit yellowing viruses.

Reverse transcription recombinase polymerase amplification assay for rapid detection of the cucurbit chlorotic yellows virus

The cucurbit chlorotic yellows virus (CCYV) causes severe economic losses in cucurbit plants. Although it has been widely known in various countries for several years, CCYV is rarely recognized due to the lack of rapid and effective detection methods in the early stage of the disease. Recombinase polymerase amplification (RPA) is a new, efficient, and simple technology for nucleic acid detection. In the present study, reverse transcription (RT)-RPA and quantitative RT-RPA were developed and utilized for fast detection of CCYV in field-collected melon samples. The analysis was performed under constant temperature conditions without the necessity for a thermal cycler in just 20 min. Moreover, the detection limit of RT-RPA for CCYV was determined at 10 pg. In the study, 58 field-collected samples were employed to evaluate the performance of the two assays. The positive rates were established at 72.4 % (42/58) and 75.9 % (44/58) by RT-RPA and qRT-RPA, respectively, and were consistent with the RT-PCR results. The successful application of RPA for the detection of CCYV in field-collected melon samples indicated its potential applicability. Thus, the developed RPA assays provide an alternative for fast, efficient, sensitive, and reliable detection of CCYV in diagnostic laboratories, which lack the precise instrumentation, and fields without appropriate equipment.

Tiny Flies: A Mighty Pest That Threatens Agricultural Productivity-A Case for Next-Generation Control Strategies of Whiteflies

Simple Summary

Despite being a pest of global importance, effective management of whiteflies by the implication of environmentally friendly approaches is still a far-reaching task. In this review, we have tried to bring the readers’ attention to next-generation control strategies such as RNA interference and genetic modifications of plants for the expression of anti-whitefly proteins. These strategies offer huge promise to provide an effective and sustainable solution to the problem of whiteflies, either in isolation or in combination with other widely used practices under the regimes of integrated pest management. Focus has also been given to advanced technologies such as nanotechnology and genome editing, with promising prospects for field applications. The importance, applicability, and demand of these technologies for the control of whiteflies have been highlighted. We have also attempted to present the holistic picture of challenges in the path of commercial application of these promising technologies. To underline the pest status of whiteflies concisely, we have enlisted all economically important species of the pest along with their host plants/crops across the world. A comprehensive list of various insecticides of chemical, microbial, and botanical origin, applied in the field for the control of sweetpotato whitefly along with their resistance status, ecotoxicities, and effects on biological control agents, has been provided for readers.

Abstract

Whiteflies are a group of universally occurring insects that are considered to be a serious pest in their own way for causing both direct and indirect damages to crops. A few of them serve as vectors of plant viruses that are detrimental to the crop in question and cause an actual loss in productivity. A lot of attention is focused on pest control measures under the umbrella of IPM. In this review, we attempt to summarize the existing literature on how and why whiteflies are a serious concern for agriculture and society. We reviewed why there could be a need for fresh insight into the ways and means with which the pest can be combated. Here, we have emphasized next-generation strategies based on macromolecules, i.e., RNA interference and genetic engineering (for the expression of anti-whitefly proteins), as these strategies possess the greatest scope for research and improvement in the future. Recent scientific efforts based on nanotechnology and genome editing, which seem to offer great potential for whitefly/crop pest control, have been discussed. Comprehensive apprehensions related to obstacles in the path of taking lab-ready technologies into the farmers’ field have also been highlighted. Although the use of RNAi, GM crops, nanotechnologies, for the control of whiteflies needs to be evaluated in the field, there is an emerging range of possible applications with promising prospects for the control of these tiny flies that are mighty pests.

Melon Genome Regions Associated with TGR-1551-Derived Resistance to Cucurbit yellow stunting disorder virus

Cucurbit yellow stunting disorder virus (CYSDV) is one of the main limiting factors of melon cultivation worldwide. To date, no commercial melon cultivars resistant to CYSDV are available. The African accession TGR-1551 is resistant to CYSDV. Two major quantitative trait loci (QTLs) have been previously reported, both located near each other in chromosome 5. With the objective of further mapping the gene or genes responsible of the resistance, a recombinant inbred line (RIL) population derived from the cross between TGR-1551 and the susceptible cultivar ‘Bola de Oro’ was evaluated for resistance to CYSDV in five different assays and genotyped in a genotyping by sequencing (GBS) analysis. The major effect of one of the two QTLs located on chromosome 5 was confirmed in the multienvironment RIL assay and additionally verified through the analysis of three segregating BC₁S₁ populations derived from three resistant RILs. Furthermore, progeny test using the offspring of selected BC₃ plants allowed the narrowing of the candidate interval to a 700 kb region. The SNP markers identified in this work will be useful in marker-assisted selection in the context of introgression of CYSDV resistance in elite cultivars.

Whitefly-transmitted criniviruses of cucurbits: current status and future prospects

In the past decade, crinviruses have gained interest due to their rapid widespread and destructive nature for cucurbit cultivation. Several members of the genus Crinivirus are considered emerging viruses. Currently, four criniviruses: Beet pseudo-yellows virus, Cucurbit chlorotic yellows virus, Cucurbit yellow stunting disorder virus and Lettuce infectious yellows virus have been reported to infect field- or greenhouse- grown cucurbits. Apart from their cucurbit hosts, criniviruses infect other cash crops and weeds. Criniviruses are exclusively transmitted by whiteflies. The virion titer and the vector genus or species complex are predominant factors affecting virus transmission. These criniviruses maintain genetic stability with limited intra-species variability. They share similar core genome structure and replication strategies with some variations in the non-core proteins and downstream replication processes. Management of the diseases induced by criniviruses relies on integrated disease management strategies and on resistant varieties, when available. This review will cover their epidemiology, molecular biology, detection and management.

Yellowing disease in zucchini squash produced by mixed infections of Cucurbit yellow stunting disorder virus and Cucumber vein yellowing virus

Zucchini squash is host to Cucurbit yellow stunting disorder virus (CYSDV), a member of the genus Crinivirus, and Cucumber vein yellowing virus (CVYV), a member of the genus Ipomovirus, both transmitted by the whitefly Bemisia tabaci. Field observations suggest the appearance of new symptoms observed on leaves of zucchini squash crops when both viruses were present. When infected during controlled experiments with CYSDV only, zucchini plants showed no obvious symptoms and the virus titer decreased between 15 and 45 days postinoculation (dpi), after which it was no longer detected. CVYV caused inconspicuous symptoms restricted to vein clearing on some of the apical leaves and the virus accumulated progressively between 15 and 60 dpi. Similar accumulations of virus followed single inoculations with the potyvirus Zucchini yellow mosaic virus (ZYMV) and plants showed severe stunting, leaf deformation, and mosaic yellowing. However, in mixed infections with CYSDV and CVYV, intermediate leaves showed chlorotic mottling which evolved later to rolling, brittleness, and complete yellowing of the leaf lamina, with exception of the veins. No consistent alteration of CVYV accumulation was detected but the amounts of CYSDV increased ≈100-fold and remained detectable at 60 dpi. Such synergistic effects on the titer of the crinivirus and symptom expression were not observed when co-infected with ZYMV.