Distinct Genomic Loci Underlie Quantitative Resistance to Meloidogyne enterolobii Galling and Reproduction in Citrullus amarus

Abstract

Meloidogyne enterolobii is a virulent species of root-knot nematode that threatens watermelon (Citrullus lanatus) production in the southeast United States. There are no known sources of root-knot nematode resistance in cultivated C. lanatus. Specific genotypes of a wild watermelon relative, C. amarus, are resistant against Meloidogyne incognitaM. incognita, but the genetics that underly this resistance are still unknown and it is not clear that this same resistance will be effective against M. enterolobii. To identify and characterize new sources of resistance to M. enterolobii, we screened 108 diverse C. amarus lines alongside a susceptible C. lanatus cultivar (‘Charleston Gray’) for resistance against M. enterolobii. Different C. amarus genotypes ranged from resistant to susceptible for the three resistance phenotypes measured; mean percent root system galled ranged 10 - 73%, mean egg mass counts ranged 0.3 - 64.5, and mean eggs per gram of root ranged 326 - 146,160. We used each of these three resistance phenotypes combined with whole-genome resequencing data to conduct a genome wide association scan that identified significant associations between M. enterolobii resistance and 11 SNPs (single nucleotide polymorphisms) within the C. amarus genome. Interestingly, SNPs associated with reduced galling and egg masses were located within a single quantitative trait locus (QTL) on Chromosome Ca03, while reductions in nematode eggs per gram of root were associated with separate QTL on chromosomes Ca04 and Ca08. The results of this study suggest multiple genes are involved with M. enterolobii resistance in C. amarus and the SNPs identified will assist with efforts to breed for M. enterolobii resistance in watermelon.

Reactions of Citrullus amarus and Cucumis metuliferus to Meloidogyne chitwoodi, Meloidogyne enterolobii and Meloidogyne luci

“…The main objective of this study was to determine host suitability of C. metuliferus BGV11135 and C. amarus BGV5167 for the nematodes M. chitwoodi, M. enterolobii and M. luci, to provide insights into the potential use of these rootstocks for melon and watermelon crops, and to provide this information to assist management of RKN species. Previous studies have reported resistance of some C. metuliferus accessions to M. incognita, M. arenaria, M. hapla, M. javanica and M. enterolobii (Walters et al, 2006;Ye et al, 2017;Pinheiro et al, 2019), and that of C. amarus to M. arenaria, M. enterolobii, M. incognita and M. javanica (García-Mendívil et al, 2019;Waldo et al, 2023). The present paper is the first report on levels of resistance of C. metuliferus and C. amarus to M. chitwoodi and M. luci.…”

“…has been attributed to its high root fibrosity in comparison with that of other cucurbits (Thies and Levi, 2007;Thies et al, 2015;García-Mendivil et al, 2019). Waldo et al (2023) suggested that resistance to M. enterolobii is modulated by 11 single-nucleotide polymorphisms. Those in the locus QTL 3.1 influence root galling and egg mass formation, while those in QTL 4.1, 4.2, and 8.1 are associated with nematode egg production.…”

“…In addition, virulent isolates of M. luci able to overcome resistance conferred by the tomato Mi1.2 gene have been reported (Aydinli et al, 2019). In cucurbits, the experimental melon rootstocks Cucumis metuliferus BGV11135 display resistance to M. arenaria, M. incognita and M. javanica (Expósito et al, 2018, and, as well as Citrullus amarus, a commercial watermelon rootstock (García-Mendívil et al, 2019;Waldo et al, 2023). Additionally, three accessions of C. metuliferus 'Kino' exhibit resistance to M. enterolobii, M. incognita race 1, and M. javanica (Pinheiro et al, 2019).…”

“…Additionally, three accessions of C. metuliferus 'Kino' exhibit resistance to M. enterolobii, M. incognita race 1, and M. javanica (Pinheiro et al, 2019). Waldo et al (2023) also evaluated 108 different accessions of C. amarus, and some of these were resistant to M. enterolobii. Nevertheless, there is currently no available knowledge about the host suitability of C. metuliferus and C. amarus for the emerging RKN species M. chitwoodi and M. luci.…”

Characterization of resistance responses to Meloidogyne enterolobii in Capsicum annuum landraces from Mexico

“…Some plant species such as guava (Psidium spp. ), acerola (Malpighia emarginata), sweet potato (Ipomoea batatas), and wild watermelon (Citrullus amarus) have been reported as possible candidates with resistance to M. enterolobii (Freitas et al, 2014;Santos et al, 2021;Schwarz et al, 2021;Waldo et al, 2022). In chili pepper, mainly the species C. chinense, C. frutescens, and C. baccatum have been reported as highly resistant to M. enterolobii (Gonçalves et al, 2014;Marques et al, 2019;Pinheiro et al, 2020); however, few studies have investigated the sources of resistance in C. annuum genotypes (Marques et al, 2019;Carrillo-Fasio et al, 2020;Pinheiro et al, 2020).…”