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Podosphaera xanthii is the main causal agent of powdery mildew (PM) on Cucurbitaceae. In Cucumis melo , the Pm - w resistance gene, which confers resistance to P . xanthii, is located on chromosome 5 in a cluster of nucleotide-binding leucine-rich repeat receptors (NLRs). We used positional cloning and transgenesis, to isolate the Pm-w WMR 29 gene encoding a coiled-coil NLR (CC-NLR). Pm-w WMR 29 conferred high level of resistance to race 1 of PM and intermediate level of resistance to race 3 of PM. Pm-w WMR 29 turned out to be a homolog of the Aphis gossypii resistance gene Vat-1 PI 161375 . We confirmed that Pm-w WMR 29 did not confer resistance to aphids, while Vat-1 PI 161375 did not confer resistance to PM . We showed that both homologs were included in a highly diversified cluster of NLRs, the Vat cluster. Specific Vat-1 PI 161375 and Pm-w WMR 29 markers were present in 10% to 13% of 678 accessions representative of wild and cultivated melon types worldwide. Phylogenic reconstruction of 34 protein homologs of Vat-1 PI 161375 and Pm-w WMR 29 identified in 24 melon accessions revealed an ancestor with four R65aa-a specific motif in the LRR domain, evolved towards aphid and virus resistance, while an ancestor with five R65aa evolved towards PM resistance. The complexity of the cluster comprising the Vat/Pm-w genes and its diversity in melon suggest that Vat homologs may contribute to the recognition of a broad range of yet to be identified pests and pathogens., (© The Author(s) 2024. Published by Oxford University Press on behalf of Nanjing Agricultural University.)

Cucumber vein yellowing virus (CVYV) is an emerging virus on cucurbits in the Mediterranean Basin, against which few resistance sources are available, particularly in melon. The melon accession PI 164323 displays complete resistance to isolate CVYV-Esp, and accession HSD 2458 presents a tolerance, i.e., very mild symptoms despite virus accumulation in inoculated plants. The resistance is controlled by a dominant allele Cvy - 1 1 , while the tolerance is controlled by a recessive allele cvy - 2 , independent from Cvy - 1 1 . Before introducing the resistance or tolerance in commercial cultivars through a long breeding process, it is important to estimate their specificity and durability. Upon inoculation with eight molecularly diverse CVYV isolates, the resistance was found to be isolate-specific because many CVYV isolates induced necrosis on PI 164323, whereas the tolerance presented a broader range. A resistance-breaking isolate inducing severe mosaic on PI 164323 was obtained. This isolate differed from the parental strain by a single amino acid change in the VPg coding region. An infectious CVYV cDNA clone was obtained, and the effect of the mutation in the VPg cistron on resistance to PI 164323 was confirmed by reverse genetics. This represents the first determinant for resistance-breaking in an ipomovirus. Our results indicate that the use of the Cvy - 1 1 allele alone will not provide durable resistance to CVYV and that, if used in the field, it should be combined with other control methods such as cultural practices and pyramiding of resistance genes to achieve long-lasting resistance against CVYV.

Melon is an economically important fruit crop that has been cultivated for thousands of years; however, the genetic basis and history of its domestication still remain largely unknown. Here we report a comprehensive map of the genomic variation in melon derived from the resequencing of 1,175 accessions, which represent the global diversity of the species. Our results suggest that three independent domestication events occurred in melon, two in India and one in Africa. We detected two independent sets of domestication sweeps, resulting in diverse characteristics of the two subspecies melo and agrestis during melon breeding. Genome-wide association studies for 16 agronomic traits identified 208 loci significantly associated with fruit mass, quality and morphological characters. This study sheds light on the domestication history of melon and provides a valuable resource for genomics-assisted breeding of this important crop.

Thirty-one melon accessions were screened for resistance to the begomoviruses Melon chlorotic mosaic virus (MeCMV) and Tomato leaf curl New Delhi virus (ToLCNDV). Five accessions presented nearly complete resistance to both viruses. Accession IC-274014, showing the highest level of resistance to both viruses, was crossed with the susceptible cultivar Védrantais. The F 1 , F 2 , F 3 /F 4 , and both backcross progenies were mechanically inoculated with MeCMV. Plants without symptoms or virus detection by enzyme-linked immunosorbent assay and/or PCR were considered as resistant. The segregations were compatible with two recessive and one dominant independent genes simultaneously required for resistance. Inheritance of resistance to ToLCNDV in the F 2 was best explained by one recessive gene and two independent dominant genes simultaneously required. Some F 3 and F 4 families selected for resistance to MeCMV also were resistant to ToLCNDV, suggesting that common or tightly linked genes were involved in resistance to both viruses. We propose the names begomovirus resistance-1 and Begomovirus resistance-2 for these genes (symbols bgm-1 and Bgm-2 ). Resistance to MeCMV in IC-274014 was controlled by bgm-1 , Bgm-2 , and the recessive gene melon chlorotic mosaic virus resistance ( mecmv ); resistance to ToLCNDV was controlled by bgm-1 , Bgm-2 , and the dominant gene Tomato leaf curl New Delhi virus resistance ( Tolcndv ).