Harley Smith, Team Leader – Research Scientist, at CSIRO Agriculture and Food shares an update on the CSIRO rootstock breeding program.

There is a pressing need in Australia to develop new rootstocks with durable resistance to root knot nematode and phylloxera, especially for use in replant situations and/or in Phylloxera Infested Zones.

The CSIRO Rootstock Breeding Program is focused on developing durable resistant rootstocks to allow growers to maintain production in the presence of these damaging soil pests.

Rootstocks provide a direct means to improve scion and vineyard performance. The CSIRO rootstock-breeding program, which was initiated almost 50 years ago when seeds from specific crosses produced under the direction of Dr Allan Antcliff, were imported from the USA in the late 1960s.

In the mid 1980s, the Australian wine industry recognised that adoption of high vigour, nematode resistant rootstocks, such as Ramsey, for production in hotter regions was having a negative impact on wine quality, particularly for red wine due to high potassium uptake leading to high pH and poor colour development. Hence, CSIRO breeding activities were primarily focused on the development of rootstocks with reduced potassium uptake to limit the impact on juice pH.

In 2005, CSIRO released three rootstocks of low to medium vigour, which have reduced potassium uptake, and produce wines with enhanced colour and flavour attributes. To improve rootstocks further, focus of breeding efforts was then shifted towards improving water use efficiency and salt tolerance.

Subsequently, near to release varieties with improved water use efficiency and salt tolerance are being evaluated in field trials in Sunraysia (hot climate) and Padthaway (saline soil conditions) with further regional cool climate trials have been established in the Mornington Peninsula and the Adelaide Hills.

To increase the efficiency of the rootstock development, the CSIRO Breeding Program has been subdivided into two groups, one focused on developing rootstocks with durable resistance to soil borne pests (root knot nematode and grape phylloxera) and the other program focused on salinity and drought tolerance.

Root knot nematode and grape phylloxera are major soil-borne pests that limit viticulture production. Most of the commercially available rootstocks used for grapevine production were bred more than 100 years ago in Europe and are not adapted to Australian conditions. For example, performance of the popular 1103 Paulsen rootstock rapidly declines in replant situations where root knot nematodes are present. And given that a majority of the wine grape production occurs in sandy soil environments where root knot nematodes thrive, it is essential that for the industry to have access to rootstocks with durable resistance to root knot nematode, as well as phylloxera for maintaining production in Phylloxera Infested Zones.

The goal of the CSIRO Rootstock Breeding team is to improve vineyard performance through the development of new rootstocks with durable root knot nematode and grape phylloxera resistance selected for Australia conditions. The development of rootstocks with single pest resistance loci can provide a high level of resistance when first deployed; however, new virulent pest(s) can emerge, which are capable of overcoming these single resistance loci. For example, widespread usage of Freedom and Harmony grapevine rootstocks in California resulted in the emergence of two virulent root-knot nematode pathotypes. As a result, Freedom and Harmony, as well as other rootstocks with a similar pedigree including Ramsey, breakdown in the presence of these virulent root knot nematodes.

To breed rootstocks with durable pest resistance, different genetic sources of root knot nematode and grape phylloxera resistance must be first identified using standard glasshouse pot assay screens. In these assays, a genetic strain(s) of root knot nematode or phylloxera is propagated on susceptible plant material then added to the soil containing the rootstock breeding material. After 8-10 weeks, the roots are evaluated for gall and egg mass production or gall and insect number for root knot nematode and phylloxera, respectively. As each vine is screened in triplicate, a limited number of individuals can be screened each year in the glasshouse. Once resistant material is identified, genetic studies are performed to map the location of the resistant trait to a particular chromosome. Molecular markers, which specifically recognise DNA signatures linked to the resistant trait, are used to follow the inheritance of root knot nematode and grape phylloxera resistance in new rootstock breeding lines without having to undertake the laborious screening procedures. In this way, marker assisted selection enables larger numbers of breeding lines to be screened at the seedling stage of development and facilitates the identification of lines with multiple resistance traits. Rootstock breeding lines harboring multiple resistant traits are expected to provide durable resistance. After selecting for durable resistant lines, field trials will be performed to evaluate the new rootstocks for viticultural traits including rooting ability, graft compatibility, vigour, yield, fruit and wine quality prior to commercial release.

A recent article from the CSIRO Rootstock Breeding Team in the international journal PLOS ONE describes the identification of a root knot nematode resistance trait in Vitis cinerea designated MELOIDOGYNE JAVANICA RESISTANCE 1 (MJR1). This root knot nematode resistance trait provides complete resistance to the aggressive M. javanica ‘pt 1103P’ isolate, which effectively parasitizes the popular 1103 Paulsen rootstock. The MJR1 trait was identified using a next generation sequencing approach for molecular marker discovery. These markers were then used in genetic- and marker-association approaches to map the MJR1 trait to chromosome 18.

Molecular markers tightly linked to the MJR1 trait will be used in the future for breeding new nematode resistant rootstocks by marker-assisted selection. Lastly, results in the manuscript showed that MJR1-mediated resistance involves the induction of cell necrosis in the root meristem, which inhibits the formation of the nematode feeding site.

This paper is the first step for developing durable resistant rootstocks to root knot nematode. Other genetic sources of root knot nematode resistance have been identified and genetic studies are underway to map these traits and identify linked molecular markers. Lastly, phylloxera resistant traits are being targeted for genetic mapping and molecular marker development.

Through this research, CSIRO aims to develop durable resistant rootstocks to allow growers to maintain production in the presence of these soil pests.