Inheritance of Resistance to Race 5 of Powdery Mildew fungus Podosphaera xanthii in Melon and development of Race 5-Specific High Resolution Melting Markers

Abstract

Powdery mildew (PM), caused by the biotrophic fungus Podosphaera xanthii, drastically reduces the yield and quality of melon (Cucumis melo L.). Knowledge on the genetic control and high throughput molecular markers linked with resistance against this disease are essential for breeding programs. The bioassay study of the F1 and F2 populations derived from the parents, ‘PMR 5’ (♂) and ‘SCNU1154’ (♀) revealed a monogenic dominant nature of resistance to the devastating race, race 5. Besides, we developed three SNP based high resolution melting markers, PMm-HRM-1, PMm-HRM-2, and PMm-HRM-3 based on the previously identified SNPs on chromosome 12 and validated those using 10 melon lines and 137 F2 population. Among these, the SNP of marker PMm-HRM-1 causes a missense mutation (Lysine → Glutamic acid) in the LRR region of MELO3C002393 and were able to distinguish the resistant vs susceptible genotypes from 10 diverse melon population and the segregating F2 population with more than 90% genotyping efficiency. Other two markers were based on intergenic SNPs and had more than 80% genotyping efficiency F2 population. These markers will be helpful to melon breeders to develop melon cultivars resistant to P. xanthii race 5 via marker assisted breeding programs.

Advanced Genetic Studies on Powdery Mildew Resistance in TGR-1551

“…Nevertheless, the phenotyping and genotyping of the advanced backcrossed lines allowed us to narrow the resistance interval to a region of approximately 400 kb between HRM markers Oidio3 (chr12: 21,870,304 bp) and Oidio2 (chr12: 22,251,703 bp) ( Table 3 ). This narrowed region is not located within the previously proposed resistance QTL and is also outside the boundaries proposed for other resistance sources such as Edisto27, MR-1, PMR5, WM6, PI 124112, and PI 134198 [ 17 , 19 , 24 , 25 , 26 , 30 , 35 , 36 , 63 ] ( Figure 1 ). Nevertheless, the recessive gene present in TGR-1551 is unique, since no recessive genes conferring resistance to more than one Px race have been reported previously in melons, and this resistance could be conferred by a gene different from those derived from other accessions.…”

“…This QTL from Fukino et al [ 17 ] was strongly linked to the microsatellite markers associated with the QTL derived from TGR-1551 (TJ29, CMBR111, and CMBR150) [ 33 ]. This candidate interval proposed by Fukino et al [ 17 ] has recently been confirmed by Hong et al [ 35 ] and the resistance of MR-1 to race 1 has recently been mapped to the same region [ 19 , 24 ]. More recently, Howlader et al [ 36 ] described three SNP markers associated with specific resistance to race 5 of Px in chromosome 12, in close proximity to the microsatellite markers previously described by Fukino et al [ 17 ] and Beraldo-Hoischen et al [ 33 ].…”

“…As the dominant resistances of powdery mildew identified so far have been easily broken by newly emerging races [ 47 ], it has been postulated that many of the QTLs detected could encode PRRs that would be manipulated by the secreted fungal effectors [ 48 , 49 ]. It has recently been proposed that several dominant resistances against powdery mildew in melon could be caused by missense mutations in different LRR-receptor like kinases and TIR-NBS-LRR genes [ 19 , 35 ]. In this sense, two SNPs with a predicted modifier impact were detected within the sequence of a gene coding TMV resistance protein N-like ( MELO3C004311 ) ( Supplementary Table S4 ), which could play a potential role in an eventual protein product and thereby confer resistance against Px .…”

“…The effect of the detected SNPs was calculated with SNPeff ( Supplementary Table S4 ). Regarding other accessions, different candidate resistance genes have recently been proposed using a similar approach [ 19 , 24 , 25 , 35 ]. There were SNPs affecting the coding region of 19 genes located within the candidate region on chromosome 12.…”

“…A similar phenomenon occurs with serine/threonine-protein kinases, which play a key role in the transduction of the internal and external signals. Some genes coding these kinds of receptors, and located in chromosome 12, have already been proposed as candidate resistance genes derived from MR-1 and PMR5 [ 19 , 26 , 35 ]. Nevertheless, other candidate genes have been proposed within the same region [ 24 , 25 ].…”