Genetic Diversity, Pathogenicity and Pseudorecombination of Cucurbit-Infecting Begomoviruses in Malaysia

Abstract

Cucurbits are important crops in the world. However, leaf curl disease constrains their production. Here, begomovirus diversity and pathogenicity associated with the disease in Malaysia were studied based on 49 begomovirus-detected out of 69 symptomatic plants from seven cucurbit crops in 15 locations during 2016 and 2017. The presence of Squash leaf curl China virus (SLCCNV) and Tomato leaf curl New Delhi virus (ToLCNDV) were confirmed by virus detection by polymerase chain reaction, viral DNA sequence analysis and specific detection of the viral components. ToLCNDV Malaysian isolates were further distinguished into strains A, B, C and D. Virus co-infection was detected in bitter gourd, bottle gourd and squash. Among them, eight bitter gourd samples were detected without SLCCNV DNA-A. However, one bottle gourd and five squash samples were without ToLCNDV DNA-B. Pseudorecombination of ToLCNDV DNA-A and SLCCNV DNA-B was detected in two bitter gourd samples. The pathogenic viruses and pseudorecombinants were confirmed by agroinoculation. The viral DNA-B influencing on symptomology and host range was also confirmed. The results strengthen the epidemic of cucurbit-infecting begomovirus in Malaysia as well as Southeast Asia. Especially, the natural pseudorecombinant of begomovirus that extends host range and causes severe symptom implies a threat to crops.

Genetic Diversity and Geographic Distribution of Cucurbit-Infecting Begomoviruses in the Philippines

“…According to the ICTV taxonomic criteria for begomovirus, viruses with nucleotide identity < 91% of full-length DNA-A are considered as distinct species and those with 91–94% are considered as distinct strains of a virus species [ 13 , 14 ]. More than 17 begomoviruses were associated with CuLCD [ 14 , 15 ], and most of them are bipartite begomoviruses [ 14 ].…”

“…CuLCD has been reported in Southeast Asia, including Indonesia [ 16 , 17 , 18 ], Malaysia [ 15 ], Thailand [ 11 , 19 ], Philippines [ 20 , 21 , 22 ] and Vietnam [ 8 , 23 ]. Furthermore, cucurbit-infecting begomovirus sequences associated with CuLCD were also obtained from Cambodia and Laos [ 24 ].…”

“…Furthermore, cucurbit-infecting begomovirus sequences associated with CuLCD were also obtained from Cambodia and Laos [ 24 ]. Meanwhile, Tomato leaf curl New Delhi virus (ToLCNDV), Squash leaf curl China virus (SLCCNV) and Squash leaf curl Philippines virus (SLCuPV) are three major begomoviruses associated with CuLCD in Southeast Asia [ 15 ]. ToLCNDV was firstly identified in diseased tomato in northern India in 1995, and the host range (associated with more than 43 plant species) and geographical distribution are extending [ 25 , 26 ].…”

“…The wide host range and geographic distribution of ToLCNDV has constrained the cucurbit production in Southeast Asia [ 8 , 26 , 28 ]. So far, ToLCNDV has been reported to be associated with cucumber, luffa and melon in Indonesia [ 16 , 17 , 18 , 29 ], bitter gourd, bottle gourd, cucumber, oriental melon, squash, ridge gourd and wax gourd in Malaysia [ 15 ], and bottle gourd, cucumber, melon, luffa and star gooseberry in Thailand [ 11 , 19 , 30 , 31 ]. In addition, ToLCNDV sequences were also obtained from chilli pepper (JX416185) and wax gourd (MH328257) in Cambodia and from bitter gourd (MH328255) and luffa (MH328254) in Laos [ 24 ].…”

“…SLCCNV was associated with cucurbit disease in Vietnam in 2003 [ 23 ], and then in India, Pakistan, Thailand and the Philippines from 2001 to 2013 [ 22 , 35 , 36 , 37 ]. So far, in Southeast Asia, SLCCNV has been found on cucumber and squash in Indonesia [ 17 , 18 ], on bottle gourd and squash in Malaysia [ 15 ], on chayote in the Philippines [ 22 ], on pumpkin and wax gourd in Thailand [ 11 , 35 ] and on wax gourd and zucchini in Vietnam [ 23 ]. Furthermore, SLCCNV sequences were also obtained from wax gourd (MK064240) in Cambodia and pumpkin (KC857509) in Vietnam [ 24 ].…”