Seed and Pollen Transmission of Tomato Leaf Curl New Delhi Virus, Tomato Leaf Curl Taiwan Virus, and Tomato Yellow Leaf Curl Thailand Virus in Cucumbers and Tomatoes

Abstract

Understanding the seed-borne nature of plant viruses is essential for developing disease control strategies and is impactful to the seed market. Here, we investigated seed transmissibility of tomato leaf curl New Delhi virus-cucumber isolate (ToLCNDV-CB) and -oriental melon isolate (ToLCNDV-OM) in cucumber and seed transmissibility of tomato leaf curl Taiwan virus (ToLCTV) and tomato yellow leaf curl Thailand virus (TYLCTHV) in tomato. Parent plants were inoculated using agroinfiltration with virus infectious clones, and virus infection was confirmed by PCR with virus-specific primers. ToLCNDV-CB and ToLCNDV-OM were detected in different parts of the female and male flowers and the fruits of cucumbers. ToLCNDV-CB and ToLCNDV-OM were also detected in cucumber seed coats and seedlings with an infection rate higher than 79%. Similar results were observed with ToLCTV and TYLCTHV as they were detected in different parts of the female and male flowers and fruits of three tomato cultivars. ToLCTV and TYLCTHV were also detected in tomato seed coats and seedlings with an infection rate higher than 36%. In addition, pollen-mediated transmission assays of these four begomoviruses were conducted with pollen derived from virus-infected plants to healthy plants. Results showed that ToLCNDV-CB and ToLCNDV-OM were detected in cross-pollinated cucumber progenies with an infection rate higher than 70%. ToLCTV and TYLCTHV were [also] detected in cross-pollinated tomato progenies with an infection rate higher than 77%. Our results indicated that ToLCNDV, ToLCTV, and TYLCTHV can be transmitted via seeds or pollens of cucumber and tomato plants. To our knowledge, this is the first report documenting the pollen-mediated transmission of begomoviruses.

Further Molecular Diagnosis Determines Lack of Evidence for Real Seed Transmission of Tomato Leaf Curl New Delhi Virus in Cucurbits

“…With ToLCNDV, most reports that describe transmission through seeds have focused on the Asiatic strains of the virus [33][34][35][36]. Before the present work, only two research works had studied the seed transmission of ToLCNDV-ES in cucurbits, of which only one described that this mode transmission is possible in zucchini plants [37].…”

“…Likewise, recent studies on tomato have reported the absence of TYLCV and tomato yellow leaf curl Sardinia virus (TYLCSV) transmission through infected seeds in tests performed at different locations [39,40]. Finally, the seed transmission of SPLCV was not detected after the recent large-scale screening of sweet potato plants [33][34][35][36]41]. The analysis of melon seedlings germinated from the ToLCNDV-ES-infected seeds did not support vertical transmission [42].…”

“…and sweet pepper (Capsicum annuum L.) [31,32]. Indian isolates of ToLCNDV were reported as being seed-transmitted for Indian isolates in chayote (Sechium edule L.) in Tamil Nadu, India [33], in cucumber in Taiwan [34], in bitter gourd (Momordica charantia L.) in Coimbatore, India [35] and in sponge gourd (Luffa cylindrica L.) in Varanasi, India [36]. In cucurbits, the seed transmission of the Spanish ToLCNDV isolate has also been investigated in Mediterranean regions.…”

Two Novel Geminiviruses Identified in Bees (Apis mellifera and Nomia sp.)

“…Some plant-infecting viruses, especially RNA viruses, have been identified in pollen, reviewed in Fetters and Ashman [ 29 ] and Mink [ 82 ]; thus, it is not surprising that many of these viruses are detected and identified from plant pollinators. Within the context of geminiviruses, there are only a handful of reports of the identification of viruses in the genus Begomovirus in floral parts including pollen and seeds [ 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 ]. Thus, it is likely that we have sampled the apiscitlodal virus and nomiamastrel virus that are in floral tissue, including pollen, carried on the honeybee and solitary bees during pollination.…”

Global Scenario of Begomovirus Diseases in Vegetable Crops

“…Most of the experimental evidence shown was the amplification by PCR of Begomovirus genomes from the seeds of infected plants, and in some cases from the asymptomatic grow-out seedlings. ToLCNDV, ToLCTV, and TYLCTHV can be transmitted via seeds or pollens of cucumber and tomato plants to an extend of 70-77% (Chang et al, 2023). Pérez-Padilla et al (2020) reported that TYLCV-IL is seed-borne but is not seed transmitted in tomatoes or N. benthamiana, suggesting that transmission through seed is not a general property of TYLCV.…”