Research progress in genetic map construction and QTL mapping for disease resistance in grapevine

Abstract: Grape is one of the most important horticultural crops in the world, which has been cultivated as a source of fresh fruit, raisins, wine and distilled beverages. In recent years, our country's grape production has increased rapidly, ranking first in the world. However, the grape is susceptible to infection by a variety of pathogens during the growth and development process, which affects berry quality and yield and restricts the development of the grape industry. Control of pathogenss requires regular application of fungicides. Nevertheless, the intensive use of chemicals becomes more and more restrictive because of their cost, risk on human health and negative environmental impact. Therefore, plant breeding for disease resistance is the most attractive way to control grapevine pathogens effectively and environment- friendly. The grape has the characteristics of long childhood and high heterozygosity and breeding for disease resistance is a very time-consuming process, because it needs the evaluation of resistance levels of the progeny. Molecular marker assistant selection (MAS) technology can improve the efficiency of directional breeding and accelerate the breeding process. Grape disease resistance is a quantitative trait controlled by multiple genes. QTL mapping is an effective method to study quantitative traits. The construction of a genetic map is the basis for detecting QTLs and cloning genes. Since Lodhi built the first genetic map of grapevines based on RAPD marker and AFLP marker, more than 160 grape genetic maps have been published in the world, of which 40 are related to grape disease resistance. Mapping populations and molecular markers are two key factors in constructing the genetic maps. The QTL mapping study is usually carried out in the crossed F1 generation population, and a feware self-crossed and backcrossed populations. The early grape genetic map was mainly constructed using AFLP and RAPD molecular markers, but different maps could not be compared, and the limitations were large. Subsequently, with the development of sequencing technology, because of its co-dominance and high polymorphism, simple sequence repeat (SSR) markers have high versatility among different grape varieties, and has become the most frequently used marker for constructing the disease resistance genetic maps. However, the limited number of SSR markers and the limited density and precision of genetic maps cannot effectively map candidate genes associated with traits. Single nucleotide polymorphism (SNP) markers are evenly distributed in the genome and have a large number, which can avoid the problem of low map marker density and significantly improve the degree of fine mapping. In recent years, it has been widely used in the construction of genetic maps. Overall, the size of the mapping population in the grape genetic map study was more than 100, and the number and density of disease resistance genetic map markers continued to increase so that the average distance between markers decreased from 12.7 cM to 0.28 cM. Over the years, researchers have identified a series of disease resistance genetic loci. As a global fungal disease, grape downy mildew has the most researched resistance loci. Currently, 28 major or minor resistance loci have been located on chromosomes 4, 5, 6, 7, 8, 9, 10, 12, 14, 17 and 18, which explained phenotypic variation ranging from 3.5% to 86.3%. Grape powdery mildew is a fungal disease caused by the pathogenic fungus Erysiphe necator [synonym Uncinula necator (Schw.) Burr.], which can cause leaves to turn chlorotic and cover with a white powdery layer, resulting in leaf curling, wilting and other symptoms. Grape powdery mildew resistance loci are much more as downy mildew researches are conducted, named Run (Resistance to Uncinula necator) or Ren (Resistance to Erysiphe necator). The current powdery mildew resistance loci are 2 (Ren10), 9 (Ren6), 12 (Run1), 14 (Ren2, Ren5), 15 (Ren3, Ren9), 13 (Ren1), 18 (Run2.1, Run2. 2, Ren4, Ren8) and 19 (Ren7) chromosomes, which are identified, explained phenotypic variation ranging from 14% to 76%. Other grape diseases, such as Pierce ’s disease, crown gall disease, black rot, ripe rot, white rot, etc., also harm grapes, but there are relatively few studies on QTL mapping. These localization results have laid the foundation for the use of molecular markers in breeding. Based on the genomic region of the resistance loci, multiple linkage markers have been developed and applied to the genetic research on grape disease resistance and the grape breeding process has been accelerated. In recent years, the construction of grape disease resistance genetic map has developed rapidly, and some achievements have been obtained, but there are still problems. In this paper, we summarized the research progress in the construction of the genetic linkage map of grapes and the location of QTLs related to disease resistance. Meanwhile, the existing problems in the current research were also analyzed and discussed. This would provide an important reference for future grape disease resistance mapping and molecular marker-assisted selection breeding.