Rootstock Screening for Phylloxera Resistance under Controlled Conditions Using Selected Phylloxera Clonal Lineages

The primary long-term management option for grape phylloxera (Daktulosphaira vitifoliae Fitch) worldwide has been to graft cultivars of Vitis vinifera L., European grapevine, onto resistant rootstocks. These resistant rootstocks are hybrids of American Vitis species including V. cinerea var. helleri (L. H. Bailey) M.O. Moore, V. riparia Michx, V. rupestris Scheele, V. cinerea Engelm and V. candicans Engelm. Resistant rootstocks are relatively limited in their usage in Australia where phylloxera is regarded as a quarantine pest and is restricted to phylloxera infested zones located in only two states (Victoria and New South Wales). So far 83 genotypic clones of phylloxera have been identified in Australia of which six have been selected for screening, based on genetic diversity and geographical distribution, against conventional and newly developed rootstock hybrids for resistance traits. A three-tiered rootstock screening approach has been developed in Australia to test the resistance of commonly used rootstocks in Australia against selected phylloxera genetic strains. Rootstock screening is conducted initially in the laboratory on excised roots and under glasshouse conditions on potted grapevines and finally in the field on commercially-grown grapevines. The development and survival of six phylloxera clones and associated root damage over an eight to ten-week trial period was compared on five commercially available rootstocks belonging to five hybrid crosses: '5BB Kober' (V. cinerea var. helleri x V. riparia), 'Schwarzmann' (V. riparia x V. rupestris), 'Brner' (V. cinerea x V. riparia), 'Ramsey' (V. rupestis x V. candicans) and '140 Ruggeri' (V. cinerea var. helleri x V. rupestris). Results from laboratory and glasshouse rootstock screening are presented which highlight the importance of developing a robust screening program for phylloxera resistance based on genetic traits of both host plant and target pest.