Inheritance and genetic mapping of Xiphinema index resistance derived from Vitis arizonica

[摘要] ENGLISH ABSTRACT: Grapevines are one of the most important and diverse crops in the world, but tend to besusceptible for numerous pests and diseases. The dagger nematode, Xiphinema index (X.index) is a well-known soil-borne pest of grapevine and vector of grapevine fanleaf virus.Several Vitis species showed resistance to this pest. Breeding efforts have been underway forseveral decades to create resistant rootstocks. However, conventional breeding efforts are timeconsuming due to grapevines being a perennial crop, its heterozygosity, as well as its longgrowth cycle. Breeding new grapevine varieties are also expensive and work intensive. Thedevelopment of marker-assisted selection introduced a way to overcome some of the abovementionedproblems.The aim of this study was to broaden the genetic evaluation and breeding efforts forimproved X. index resistance in grapevine rootstocks. In 2007 several crosses were made inthe University of California, Davis vineyards. The background for all these crosses consisted ofV. arizonica. These V. arizonica plants are part of a collection obtained by H.P. Olmo during the1960's. In recent studies it was established that X. index resistance is controlled by a singledominant gene. The 0701 (R8916-07 (Wichita Refuge x b40-14) x R8916-32), 0704 (161-49C xb40-14) and 0705 (161-49C x R8916-22) populations were created to confirm the homozygousnature of b40-14, a V. arizonica accession. In addition, several V. arizonica species werescreened to confirm their resistance or susceptibility towards X. index feeding. The 0705population was also used to create a genetic map for X. index resistance.In this study a new and improved screening method was developed to inoculate vinesunder greenhouse conditions. This screening method proved to be quicker and less damagingon the nematodes than traditional systems. Control varieties were used and O39-16, acommercial rootstock showed no damage, even with high nematode pressure, whereas V.rupestris Saint George had severe root damage and decline after eight weeks of exposure.A range of V. arizonica accessions was tested for their resistance to X. index feeding. Ofthe 18 genotypes tested, half showed resistance and the rest were susceptible. It is possiblethat these genotypes are not pure V. arizonica genotypes. Genotypes with V. arizonica in thebackground were also tested. Wichita Refuge was used as a susceptible female parent and theprogeny were expected to be heterozygous resistant. Some of the progeny allowed low levelsof feeding damage, which may have been the result of the more effective inoculation methoddescribed above.The 0701 population confirmed the hypothesized model of 3:1 (Resistance (R):Susceptible(S)) segregation although 13 of the genotypes showed significantly higher gall numbers than thesusceptible female parent. The possibility of transgressive segregation exists, but needs to beconfirmed. All progeny from the 0704 population should be heterozygous resistant, but a 1:1(R:S) segregation pattern was observed. The 0705 population was created as a mappingpopulation to study X. index resistance. This population was also tested in the greenhouse forits X. index resistance and was expected to segregate 1:1 (R:S). The X2 analysis did not fullysupport this model.A genetic map covering all 19 linkage groups, and positioning 175 polymorphic SSRmarkers was created for the 164 progeny in the 0705 population. MapQTL analysis revealed amajor QTL on linkage group 9 and two minor QTL's on groups 13 and 19. The major QTLplaced between markers VMC1c10 and CTG1032918 with a LOD score of 33.4 explaining70.5% of the phenotypic variance for X. index. This QTL is the second major QTL discoveredfor X. index resistance. With the discovery of a second major QTL, the two types of resistance can be pyramided. Workis underway to saturate the area around the major QTL on linkage group 9 and to move towardsphysical mapping of X. index resistance. The b40-14 V. arizonica accession is also known forits resistance to Pierce's disease and the possibility of simultaneous expression of two types ofresistance is created. The 0705 population can also be used to evaluate phenotypicalcharacteristics in the field to determine if useful rootstocks can be selected. Taken together, theresults obtained in this study provide improved methods and highly characterized plantpopulations to support the efforts in obtaining improved X. index resistance in grapevinerootstocks.

[发布机构] Stellenbosch University