Assessment of the Current Status of Potyviruses in Watermelon and Pumpkin Crops in Spain: Epidemiological Impact of Cultivated Plants and Mixed Infections

Abstract

Viral infections on cucurbit plants cause substantial quality and yield losses on their crops. The diseased plants can often be infected by multiple viruses, and their epidemiology may depend, in addition to the agro-ecological management practices, on the combination of these viral infections. Watermelon mosaic virus (WMV) is one of the most prevalent viruses in cucurbit crops, and Moroccan watermelon mosaic virus (MWMV) emerged as a related species that threatens these crops. The occurrence of WMV and MWMV was monitored in a total of 196 apical-leaf samples of watermelon and pumpkin plants that displayed mosaic symptoms. The samples were collected from 49 fields in three major cucurbit-producing areas in Spain (Castilla La-Mancha, Alicante, and Murcia) for three consecutive (2018–2020) seasons. A molecular hybridization dot-blot method revealed that WMV was mainly (53%) found in both cultivated plants, with an unadvertised occurrence of MWMV. To determine the extent of cultivated plant species and mixed infections on viral dynamics, two infectious cDNA clones were constructed from a WMV isolate (MeWM7), and an MWMV isolate (ZuM10). Based on the full-length genomes, both isolates were grouped phylogenetically with the Emergent and European clades, respectively. Five-cucurbit plant species were infected steadily with either WMV or MWMV cDNA clones, showing variations on symptom expressions. Furthermore, the viral load varied depending on the plant species and infection type. In single infections, the WMV isolate showed a higher viral load than the MWMV isolate in melon and pumpkin, and MWMV only showed higher viral load than the WMV isolate in zucchini plants. However, in mixed infections, the viral load of the WMV isolate was greater than MWMV isolate in melon, watermelon and zucchini, whereas MWMV isolate was markedly reduced in zucchini. These results suggest that the impaired distribution of MWMV in cucurbit crops may be due to the cultivated plant species, in addition to the high prevalence of WMV.

Aphid‐borne viruses infecting cultivated watermelon and squash in Spain: Characterization of a variant of cucurbit aphid‐borne yellows virus (CABYV)

“…In conclusion, despite the extent of this new yellowing disease in watermelon and other cucurbit crops being unknown, our findings suggest that this novel CABYV variant may be currently threatening cucurbit crops. It is thus fundamental to consider that plant viral epidemics are often initiated and spread through different host plants and varieties, along with different agroecological practices that may alter the viral disease epidemiology (Moya‐Ruiz et al, 2021; Jeger, 2020; Juárez et al, 2019; Valverde et al, 2020). This exchange of viral diseases between overlapping crops at spatial/temporal scales could play an important role, as it may hinder the early detection of the disease.…”

“…Additionally, potyviruses, such as watermelon mosaic virus (WMV), zucchini yellow mosaic virus (ZYMV), and papaya ringspot virus (PRSV), as well as cucumber mosaic virus (CMV, genus Cucumovirus), among others, have been reported to affect cucurbit crops (Bertin et al, 2020;Desbiez et al, 2020;Juárez et al, 2013), with a relatively high importance in Spain (De Moya-Ruiz et al, 2021;Juárez et al, 2013). Furthermore, the number of multiple viral infections is comparatively high in cucurbit plant species in Spain, and CABYV and WMV are often found in mixed virus combinations (Juárez et al, 2013;Kassem et al, 2007Kassem et al, , 2013.…”

“…These factors provide genetic plasticity that may allow for the rapid evolution and adaptation of viruses to new agricultural conditions and may therefore be contributing to the creation of new CABYV variants that could challenge the prevailing control strategies. Heterogeneous host genotype populations (i.e., different host plants and varieties of cucurbits along with particular agroecological practices) may alter the epidemiological patterns of viral diseases (De Moya-Ruiz et al, 2021;Juárez et al, 2019;Valverde et al, 2020). Hence, the systematic monitoring of the occurrence of viral diseases and their causative agents, combined with ecological and quantitative epidemiological approaches, is essential to understand and mitigate their consequences on crops and natural ecosystems (Jeger, 2020;McLeish et al, 2020).…”

Occurrence, Distribution, and Management of Aphid-Transmitted Viruses in Cucurbits in Spain

“…Within the Mediterranean basin, Spain is among the largest producer of cucurbits, with a total of 67,500 ha cultivated in the central and southeastern areas and over 3 million tonnes harvested a year [ 31 ]. Our current observations in these crops suggest that the incidence of aphid-transmitted viruses has increased in the last few seasons [ 32 , 33 , 34 ], concurrently with an increase in the aphid population in the early stages of crop cultivation. Thus, a better understanding of the intricate epidemiology of cucurbit viral diseases will allow the improvement of the management strategies utilized for these pests and the aphid-transmitted viruses in crops [ 35 , 36 ].…”

Special Issue: “Plant Virus Epidemiology”

“…However, a monitoring of crops revealed the different presence of WMV and MWME which could be explained on host plant species, but also on the different ranges of plant host species, and of aphid vector species between the two virus species. In addition, experimental infections suggest that mixed infections with both virus species in the same host also determines the viral loads, and may explain impaired distribution of one of the viruses [12].…”