Resistance of Grape Rootstocks to Plant-parasitic Nematodes

Abstract

Candidate grape rootstocks were selected through a rigorous screening program initiated with important sources of resistance to Meloidogyne pathotypes and to Xiphinema index in Muscadinia rotundifolia and Vitis species native to North America. Based on their rooting capability and horticultural characteristics, 200 candidates were selected from 5,000 progeny of multiple crosses between commercial grape rootstocks and wild grape species that exhibited resistance to nematodes. After a 15-year screening process, 13 selections emerged with either almost complete or complete combined resistance to M. incognita Race 3, M. incognita pathotype Harmony C, M. arenaria pathotype Harmony A, and X. index, important nematode pests of grapevines. Durability of this broad resistance was tested by challenging the selections with the target nematodes in combination and with the target nematodes in combinations with species not included in the screening process. Durability of resistance of the candidate rootstocks was also tested by exposure to the nematode communities of infested field soils from different locations. Breadth of resistance was determined on the basis of their host status to non-target nematodes, including Mesocriconema xenoplax, Pratylenchus vulnus, Tylenchulus semipenetrans and Paratylenchus hamatus. After a total of 204 separate trials, the rootstocks were released to the grape industry as UCD GRN1, UCD GRN2, UCD GRN3, UCD GRN4, and UCD GRN5. We provide a compilation of current knowledge of the host status of these five newly released rootstocks and of 27 other rootstock cultivars to plant-parasitic nematodes.

Keywords: Screening; broad resistance; durable resistance; host status; selection.

Fig. 1

The succession of events in creating hybrid progeny of interspecies crosses among Vitis and Muscadinia species, and the sequence of screening and testing that has resulted in the release of five rootstocks with broad and durable resistance to nematodes.

Fig. 2

Relative numbers of egg masses/g root (in relation to the maximum observed on cv Colombard) on parent genotypes of the UCD-GRN rootstocks after 3 months of exposure to Xiphinema index, Meloidogyne incognita race 3, M. arenaria pathotype Harmony A and M. incognita pathotype Harmony C. Data are means of two experiments for M. incognita race 3 and M. arenaria pathotype Harmony A, one for M. incognita pathotype Harmony C across a range of soil temperatures.