Inoculation of cucumber, melon and zucchini varieties with Tomato leaf curl New Delhi virus and evaluation of infection using different detection methods

Abstract

The disease caused by Tomato leaf curl New Delhi virus (ToLCNDV), which is naturally transmitted by the whitefly Bemisia tabaci, causes important economic losses in cucurbit crops. The availability of simple and efficient inoculation protocols and detection methods is necessary for screening varieties and germplasm collections as well as for breeding populations. We evaluated the infectivity of ToLCNDV inocula prepared using three different buffers for mechanical sap inoculation in a susceptible variety of zucchini. We found that inoculum prepared with buffer III, which contains polyvinylpyrrolidone, is highly efficient for mechanical inoculation, with 100% of plants displaying severe symptoms 21 days post-inoculation. Using this buffer, we mechanically inoculated 19 commercial varieties of cucurbit crops (six of cucumber, six of melon and seven of zucchini), evaluated the evolution of symptoms and diagnosed infection using nine different ToLCNDV detection methods (four based on serology, four based on molecular hybridization and one based on PCR detection). The results revealed that all varieties are susceptible, although cucumber varieties display less severe symptoms than those of melon or zucchini. All detection methods were highly efficient (more than 85% of plants testing positive) in melon and zucchini, but in cucumber, the percentage of positive plants detected with serology and molecular hybridization methods ranged from 20.4% with Squash leaf curl virus (SLCV) antiserum, to 78.5% with DNA extract hybridization. Overall, the best detection results were obtained with PCR, with 92.6%, 92.4% and 98.4% cucumber, melon and zucchini plants, respectively, testing positive. When considering the overall results in the three crops, the best serology and molecular hybridization methods were those using Watermelon chlorotic stunt virus (WmCSV) antiserum and DNA extract, respectively. The inoculation methodology developed and the information on detection methods are of great relevance for the selection and breeding of varieties of cucurbit crops that are tolerant or resistant to ToLCNDV.

Seed Transmission of Tomato Leaf Curl New Delhi Virus from Zucchini Squash in Italy

“…Unlike most other begomoviruses, ToLCNDV is known for its mechanical transmission [7,31,32]. Such transmission can occur naturally by infected plants in farms, and sap of ToLCNDV-infected leaves can be a good inoculum for artificial inoculation [32,33]. To identify whether seed-borne ToLCNDV can be transmitted from infected zucchini squash seedlings to other healthy plants by sap, homogenized sap was spread on healthy plant leaves.…”

Genetic Differentiation and Migration Fluxes of Viruses from Melon Crops and Crop Edge Weeds

“…ToLCNDV is limited to the plant phloem and is transmitted in a circulative persistent manner by the whitefly Bemisia tabaci ( 20 , 21 ). This virus has a wide host range with 43 different plant species identified so far, mainly belonging to the families Solanaceae and Cucurbitaceae ( 22 – 25 ). The Mediterranean population of ToLCNDV is genetically very homogeneous with no clustering patterns identified thus far ( 8 ).…”

Natural Hosts and Genetic Diversity of the Emerging Tomato Leaf Curl New Delhi Virus in Spain

“…This virus is limited to the plant phloem and is transmitted in a circulative persistent manner by the whitefly Bemisia tabaci (Fondong, 2013; Zaidi et al, 2017), although it should be noted that experimental host plants have also been infected by mechanical inoculation (Ruiz et al, 2017). ToLCNDV has a wide host range with 43 different plant species identified thus far (Pratap et al, 2011; Sayed et al, 2013; Kushwaha et al, 2015; Yazdani-Khameneh et al, 2016; Zaidi et al, 2016, 2017; Figàs et al, 2017; Ruiz et al, 2017), mainly belonging to the Solanaceae and Cucurbitaceae families, which comprise economically important crops such as potato (Usharani et al, 2004) and aubergine (Pratap et al, 2011), as well as to several weed species. However, since the emergence of ToLCNDV in some Mediterranean countries, it has only been described to infect cucurbit and tomato plants (Juárez et al, 2014; Mnari-Hattab et al, 2015; Fortes et al, 2016; Panno et al, 2016; Yazdani-Khameneh et al, 2016; Sifres et al, 2017; Zaidi et al, 2017), while other plant hosts can also be involved in the distribution and prevalence of this virus (Ruiz et al, 2017).…”