Rootstock genetics and improvement: new improved rootstocks with durable resistance to root-knot nematodes and phylloxera
Abstract
Plant Breeders Rights have been lodged for four new CSIRO rootstocks targeted for release. These C-series rootstocks that are adapted to Australian conditions serve as an alternative to major commercial rootstocks bred overseas over 100 years ago. Experimental studies showed that the CSIRO germplasm harbours key traits to develop new rootstocks for a changing climate. Marker-assisted breeding was used to select first-generation rootstocks containing two resistance loci against grape phylloxera and one resistance locus for root knot nematode. Identification of molecular markers linked to the second root knot nematode resistance locus in V. champinii will provide the means to develop second-generation rootstocks with durable resistance to grape phylloxera and root knot nematode for a changing Australian climate.
Summary
The Australian Wine Grape Industry is dependent on commercial rootstocks bred and selected in Europe and California over 100 years ago that are poorly adapted to the major growing climates in Australia. Developing next generation rootstocks adapted to Australian conditions with durable resistance to major soil pests will have a significant impact on safeguarding vineyards from grape phylloxera and root knot nematode. The development of next generation rootstocks aligns with the sustainability and biosecurity risk management strategies for Wine Australia.
The impact of rootstocks on vine performance in two regions with different environments and management practices was stable over time and with vine age. However, the impact of rootstocks on vine performance was not consistent between regions or when grafted with different scions. As a result, rootstock selection will be critical for optimising scion performance in different regions or when grafted with different scions. Further, different management practices may be necessary to optimise the performance of different scion cultivars, particularly in a hot climate. Therefore, developing a single universal rootstock suited for all wine grape varieties under different climate conditions is not feasible. To better equip the wine grape industry with rootstocks adapted to Australian conditions, four rootstocks were targeted for Plant Breeders Rights protection. These genetically diverse rootstocks provide the Wine Grape Industry with alternatives to major commercial rootstocks used in production.
Evaluation of germplasm and experimental rootstock breeding lines showed that the CSIRO Vitis collection has sufficient genetic variation to develop rootstocks for a changing climate, including traits associated with favourable production under deficit irrigation and a limited supply of moderately saline water. Evaluation of commercial rootstocks and new breeding lines also showed that the CSIRO Vitis collection contains traits that maintain root knot nematode resistance at high soil temperatures. Lastly, new sources of grape phylloxera and root knot nematode resistance were identified for future germplasm development and rootstock breeding.
A pathway for the development of next generation rootstocks with durable resistance to grape phylloxera and root knot nematode was generated. First-generation rootstocks with durable resistance to grape phylloxera were developed by marker-assisted selection using DNA-markers tightly linked to RESISTANCE TO DAKTULOSPHAIRA VITIFOLIAE 1 (RDV1) and RDV2 from Börner and Vitis cinerea C2-50, respectively. These experimental rootstocks also contained the root knot nematode resistance locus, MELOIDOGYNE JAVANICA RESISTANCE 1 (MJR1). First-generation rootstocks containing RDV2, RDV2 and MJR1 were established in the field to set up crosses in order to generate second-generation rootstocks with durable resistance to grape phylloxera and root knot nematode. To achieve this goal, we also performed genetic mapping and identified DNA-markers linked the Vitis champinii root knot nematode resistance locus termed MJR2. By crossing first-generation rootstocks harbouring RDV1, RDV2 and MJR1 with Vitis champinii material containing MJR2, the CSIRO Rootstock Breeding Team will be in position to deliver second-generation rootstocks with durable resistance to grape phylloxera and root knot nematode. Interestingly, preliminary results indicate that Vitis cinerea harbours a new grape phylloxera resistance trait specific to an aggressive genotype. In addition, a third root knot nematode resistance trait was identified in Vitis candicans. Future genetic studies aimed at identifying molecular markers linked to the new grape phylloxera and root knot nematode resistance traits from Vitis cinerea and Vitis candicans, respectively, will provide the means to increase the durable resistance in second- and third-generation rootstocks. Moreover, the breeding pathways developed for next generation rootstocks will increase the genetic diversity of future durable pest resistance rootstocks to further safeguard vineyards from these soil pests.
During the project, there has been significant interaction with industry through presentations at conferences and forums, some of which were supported by the tasting of wines produced from new rootstock selections, including the C-series rootstocks. Mother vine plantings of PBR selected C-series rootstocks have been established to ensure that adoption is not limited by the supply of propagation material.
We gratefully acknowledge the valued input of Dr Catherine Clarke (Agriculture Victoria) who undertook the phylloxera screening, Marica Mazza at (Agriculture Victoria) for small-scale wine making and also the financial support of CSIRO. In addition, we thank Inca Lee and Suzanne McLoughlin from VineHealth Australia for support.