Whitefly Control Strategies against Tomato Leaf Curl New Delhi Virus in Greenhouse Zucchini

Advances and Prospects of Virus-Resistant Breeding in Tomatoes

Plant viruses are the main pathogens which cause significant quality and yield losses in tomato crops. The important viruses that infect tomatoes worldwide belong to five genera: Begomovirus, Orthotospovirus, Tobamovirus, Potyvirus, and Crinivirus. Tomato resistance genes against viruses, including Ty gene resistance against begomoviruses, Sw gene resistance against orthotospoviruses, Tm gene resistance against tobamoviruses, and Pot 1 gene resistance against potyviruses, have been identified from wild germplasm and introduced into cultivated cultivars via hybrid breeding. However, these resistance genes mainly exhibit qualitative resistance mediated by single genes, which cannot protect against virus mutations, recombination, mixed-infection, or emerging viruses, thus posing a great challenge to tomato antiviral breeding. Based on the epidemic characteristics of tomato viruses, we propose that future studies on tomato virus resistance breeding should focus on rapidly, safely, and efficiently creating broad-spectrum germplasm materials resistant to multiple viruses. Accordingly, we summarized and analyzed the advantages and characteristics of the three tomato antiviral breeding strategies, including marker-assisted selection (MAS)-based hybrid breeding, RNA interference (RNAi)-based transgenic breeding, and CRISPR/Cas-based gene editing. Finally, we highlighted the challenges and provided suggestions for improving tomato antiviral breeding in the future using the three breeding strategies.

Tomato leaf curl New Delhi virus: an emerging plant begomovirus threatening cucurbit production

Tomato leaf curl New Delhi virus (ToLCNDV), a bipartite begomovirus, was first reported to infect tomato and has recently spread rapidly as an emerging disease to Cucurbitaceae crops. To date, the virus has been reported to infect more than 11 cucurbit crops, in 16 countries and regions, causing severe yield losses. In autumn 2022, ToLCNDV was first isolated from cucurbit plants in Southeastern coastal areas of China. Phylogenetic analysis established that these isolates belong to the Asian ToLCNDV clade, and shared high nucleotide identity and closest genetic relationship with the DNA-A sequence from the Chinese tomato-infecting ToLCNDV isolate (Accession no. OP356207) and the tomato New Delhi ToLCNDV-Severe isolate (Accession no. HM159454). In this review, we summarize the occurrence and distribution, host range, detection and diagnosis, control strategies, and genetic resistance of ToLCNDV in the Cucurbitaceae. We then summarize pathways that could be undertaken to improve our understanding of this emerging disease, with the objective to develop ToLCNDV-resistant cucurbit cultivars.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42994-023-00118-4.

Development of an In-Field Real-Time LAMP Assay for Rapid Detection of Tomato Leaf Curl New Delhi Virus

Tomato leaf curl New Delhi virus (ToLCNDV) represents a threat to economically important horticultural crops. A real-time loop-mediated isothermal amplification (LAMP) assay for in-field ToLCNDV detection was developed, coupled to a rapid sample preparation method, and tested both in field and laboratory conditions on zucchini squash, tomato, and pepper samples. A set of six LAMP primers was designed for specific ToCLNDV detection, targeting a 218-nucleotide sequence within the AV1 gene. The sensitivity, specificity and accuracy of the real-time LAMP assay and comparison with canonical PCR were evaluated. The real-time LAMP assay developed was about one-thousand times more sensitive than the conventional PCR method, detecting a total of 4.41 × 10² genome copies as minimum target; no cross-reactivity was detected with the other geminiviruses used as the outgroup. The rapid sample preparation method allows for a reliable detection with a low reaction delay (≈2-3 min) compared to canonical DNA extraction, providing results in less than 45 min. Lastly, an increase in ToLCNDV-positive sample detection was observed compared to PCR, in particular for asymptomatic plants (85% and 71.6%, respectively). The real-time LAMP assay developed is a rapid, simple, specific, and sensitive technique for ToLCNDV detection, and it can be adopted as a routine test, for both in-field and laboratory conditions.

Grafting to Manage Infections of the Emerging Tomato Leaf Curl New Delhi Virus in Cucurbits

Tomato leaf curl New Delhi virus (ToLCNDV) is an emerging begomovirus (Geminiviridae family) listed in the EPPO Alert List 2, present in the Mediterranean area and in Italy, where it was reported in 2015 in Sicilian courgette. The virus is widespread in cucurbits where it causes up to 100% production losses. In 2018, ToLCNDV was isolated in Apulia (southern Italy) in commercial fields of zucchini squash and since then its recurrent outbreaks generated justified concern among growers. Thus, a sustainable and environmentally friendly approach must be adopted. Genetic resistances have been identified in Cucurbita moschata and Luffa cylindrica but, compared to genetic resistance, grafting could provide a faster and more flexible solution because the graft wounding induces tolerance rather than resistance against airborne virus infection. Compared to tolerance, the up-regulation of resistance genes requires energy resources mobilized at the expense of primary metabolism, plant growth, and development. Results of screening among twenty-one local cucurbit cvs. ecotypes and accessions to evaluate tolerance levels against rub-inoculation of ToLCNDV led to the identification of potential rootstocks to attain suitable levels of tolerance against the virus in commercial cucurbit varieties. Cucurbit plants were challenged by a ToLCNDV isolated in Apulia denoted ToLCNDV-Le and evaluated for disease symptoms development and viral DNA accumulation up to 28 days after inoculation. On the basis of disease symptoms developed, plants were classified as tolerant, moderately tolerant, moderately susceptible, and susceptible. Cucumis melo cv. Barattiere did not show any detectable disease symptoms and very low levels of viral DNA accumulation was recorded; thus, it was used as rootstock for some of the remaining cucurbit genotypes that were used as scions. The tolerance trait was transmitted to the otherwise susceptible and moderately susceptible cucurbit genotypes grafted onto the cv. Barattiere. The results of this study suggest practical implications of the approach described.

Review: Presence, distribution and current pesticides used in Spanish agricultural practices

To guarantee an adequate food supply for the world's growing population, intensive agriculture is necessary to ensure efficient food production. The use of pesticides helps maintain maximum productivity in intensive agriculture by minimizing crop losses due to pests. However, pesticide contamination of surface waters constitutes a major problem as they are resistant to degradation and soluble enough to be transported in water. In recent years, all groups of pesticides defined by the World Health Organization have increased their use and, therefore, their prevalence in the different environmental compartments that can have harmful effects. Despite this effort, there is no rigorous monitoring program that quantifies and controls the toxic effects of each pesticide. However, multiple scientific studies have been published by specialized research groups in which this information is disseminated. Therefore, any attempt to systematize this information is relevant. This review offers a current overview of the presence and distribution of the most widely-used pesticides (insecticides, herbicides, and fungicides) by crop type and an evaluation of the relationships between their uses and environmental implications in Spain. The data demonstrated that there are correlations between the presence of specific pesticides used in the main crops and their presence in the environmental compartments. We have found preliminary data pointing to existing associations between specific pesticides used in the main crops and their presence in environmental compartments within different geographical areas of Spain; this should be the subject of further investigation.

Host Species-Dependent Transmission of Tomato Leaf Curl New Delhi Virus-ES by Bemisia tabaci

The tomato leaf curl New Delhi virus (ToLCNDV) is a bipartite, single-stranded begomovirus that was first identified in India in 1995 affecting solanaceous crops. A different strain, named ToLCNDV-ES, was introduced in Spain in 2012 and causes severe symptoms in zucchini crops. Virus transmission experiments with the whitefly Bemisia tabaci, were used to compare the transmission parameters in zucchini and tomato plants. The minimum acquisition access period and inoculation access period of ToLCNDV-ES transmission was similar in zucchini and tomato. However, the transmission efficiency was significantly higher in zucchini (96%) compared to tomato (2%). The maximum retention of the virus in the vector was 16 days. B. tabaci feeding on, or recently emerged from infected zucchini plants, accumulated more virus than those from infected tomato, as determined by real-time PCR. A total of 20% of B. tabaci that were recently emerged from infected zucchini, and none from infected tomato, were able to transmit the virus to virus-free zucchini. The results may explain the different incidences of ToLCNDV-ES in zucchini and tomato crops in Spain. But they are also relevant for ToLCNDV-ES management of crops and the role of the trade and transport of infected plant material, when small-sized immature stages of B. tabaci could be a source of infection.

Occurrence, Distribution, Evolutionary Relationships, Epidemiology, and Management of Orthotospoviruses in China

Orthotospoviruses are responsible for serious crop losses worldwide. Orthotospoviral diseases have spread rapidly in China over the past 10 years and are now found in 19 provinces. Currently, 17 Orthotospovirus species have been reported in China, including eight newly identified species from this genus. The number of new highly pathogenic Orthotospovirus strains or species has increased, likely because of the virus species diversity, the wide range of available hosts, adaptation of the viruses to different climates, and multiple transmission routes. This review describes the distribution of Orthotospovirus species, host plants, typical symptoms of infection under natural conditions, the systemic infection of host plants, spatial clustering characteristics of virus particles in host cells, and the orthotospoviral infection cycle in the field. The evolutionary relationships of orthotospoviruses isolated from China and epidemiology are also discussed. In order to effectively manage orthotospoviral disease, future research needs to focus on deciphering the underlying mechanisms of systemic infection, studying complex/mixed infections involving the same or different Orthotospovirus species or other viruses, elucidating orthotospovirus adaptative mechanisms to multiple climate types, breeding virus-resistant plants, identifying new strains and species, developing early monitoring and early warning systems for plant infection, and studying infection transmission routes.

A Review of the Biology and Control of Whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae), with Special Reference to Biological Control Using Entomopathogenic Fungi

Simple Summary

The whitefly, Bemisia tabaci, is considered one of the most destructive insect pests of vegetables and ornamental crops globally. Synthetic chemical pesticides are mainly used to control B. tabaci, however, their extensive usage has led to a series of detrimental concerns to human health and environmental contamination. It is therefore of significant interest to develop a safer and eco-friendly alternative for controlling B. tabaci. Here, we review the use of entomopathogenic fungi as a proven, biologically sustainable method to effectively control B. tabaci. The development of entomopathogenic fungi in an integrated pest management strategy against B. tabaci can reduce our reliance on chemical pesticides, and help us to secure food safety while preserving nature.

Abstract

Whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), consists of genetically diverse species known to cause significant destruction in several crops around the world. Nymphs and adults of B. tabaci cause damage to plants during feeding, and they can act as a virus vector, thus causing significant yield loss to crops in the tropical and subtropical regions. Chemical pesticides are widely used to control B. tabaci due to their immediate action, but this approach has several drawbacks including food safety issues, insecticide resistance, environmental pollution, and the effect on non-target organisms. A biological control agent using entomopathogenic fungi (EPF) has therefore been developed as an alternative against the conventional use of chemical pesticides in an integrated pest management (IPM) system to effectively control B. tabaci. It is apparent from this review that species of hyphomycetes fungi are the most common EPF used to effectively control B. tabaci, with the second instar being the most susceptible stage of infection. Therefore, this review article focuses specifically on the control of B. tabaci with special emphasis on the use of EPF as biological control agents and their integration in IPM.