A major QTL located in chromosome 8 of Cucurbita moschata is responsible for resistance to tomato leaf curl New Delhi virus (ToLCNDV)

Tomato leaf curl New Delhi virus (ToLCNDV) is a bipartite whitefly transmitted begomovirus, responsible since 2013 of severe damages in cucurbit crops in Southeastern Spain. Zucchini (Cucurbita pepo) is the most affected species, but melon (Cucumis melo) and cucumber (Cucumis sativus) are also highly damaged by the infection. The virus has spread across Mediterranean basin and European countries, and integrated control measures are not being enough to reduce economic losses. The identification of resistance genes is required to develop resistant cultivars. In this assay, we studied the inheritance of the resistance to ToLCNDV previously identified in two Cucurbita moschata accessions. We generated segregating populations crossing both resistant pumpkins, an American improved cultivar Large Cheese (PI 604506) and an Indian landrace (PI 381814), with a susceptible C. moschata genotype (PI 419083). The analysis of symptoms and viral titers of all populations established the same monogenic recessive genetic control in both resistant accessions, and the allelism tests suggest the occurrence of alleles of the same locus. By genotyping with a single nucleotide polymorphism (SNP) collection evenly distributed along the C. moschata genome, a major quantitative trait locus (QTL) was identified in chromosome 8 controlling resistance to ToLCNDV. This major QTL was also confirmed in the interspecific C. moschata × C. pepo segregating populations, although C. pepo genetic background affected the resistance level. Molecular markers here identified, linked to the ToLCNDV resistance locus, are highly valuable for zucchini breeding programs, allowing the selection of improved commercial materials. The duplication of the candidate region within the C. moschata genome was studied, and genes with paralogs or single-copy genes were identified. Its synteny with the region of chromosome 17 of the susceptible C. pepo revealed an INDEL including interesting candidate genes. The chromosome 8 candidate region of C. moschata was also syntenic to the region in chromosome 11 of melon, previously described as responsible of ToLCNDV resistance. Common genes in the candidate regions of both cucurbits, with high- or moderate-impact polymorphic SNPs between resistant and susceptible C. moschata accessions, are interesting to study the mechanisms involved in this recessive resistance

Natural occurrence of begomovirus recombinants associated with tomato yellow leaf curl disease co-existing with parental viruses in tomato crops and weeds in Tunisia

Tomato yellow leaf curl virus disease (TYLCVD) is the main limiting factor for tomato production in the Mediterranean Basin, and particularly in Tunisia where climatic and crop production conditions, as well as the occurrence of many weeds, provide suitable conditions for the presence and spread of TYLCVD all year round. In Tunisia, epidemics in tomato-growing regions have been associated with two begomoviruses: Tomato yellow leaf curl virus (TYLCV) and Tomato yellow leaf curl Sardinia virus (TYLCSV) but the presence of recombinants between them has never been investigated. A large-scale survey was conducted on leaves sampled from late-season tomato crops exhibiting severe curling symptoms, from beans, and from nine nearby weed species in the South and Sahel regions of Tunisia to investigate: (i) the natural occurrence of the TYLCV and TYLCSV species; (ii) the presence of the two recombinant types, RecA and RecB, derived from these species. Identification of TYLCV and TYLCSV was based on a multiplex PCR with primers generating a typical pattern on gels (750 bp and 366 bp fragments, respectively). Recombinants were identified by simplex PCR, which amplified the intergenic region, the most common recombination site described for begomoviruses, and sequencing. The occurrence of TYLCSV and TYLCV was confirmed in both Tunisian regions. Their co-existence was shown on tomato and in new weed species. This is the first time that recombinants between TYLCV and TYLCSV species showing 93% to 95% nucleotide identity with tomato yellow leaf curl recombinant viruses, are reported in Tunisia in tomato and black nightshade