Resistant dwarf apple trees
From the December 2007 edition of Agriculture Today.
The trend in apple growing in Australia towards closer planting using smaller compact trees poses a challenge for breeders.
This is because fewer rootstocks resistant to woolly apple aphid are available when dwarfing stocks are required.
Many intensive plantings in Australia are based on a rootstock known as M9, which has excellent production efficiency and produces a tree of suitable size.
However, it is not resistant to woolly aphid and at times can be difficult to propagate.
A breeding program initiated by the NSW Department of Primary industries is seeking to develop a dwarfing apple rootstock with woolly apple aphid (WAA) resistance.
The use of resistant rootstocks is one of the most effective methods of controlling this pest.
The project, initiated by NSW DPI, and funded by Apples and Pear Australia, started in 1996 and has used resistant parent material from around the world.
The program has used the Malling-Merton (MM) series of rootstocks and its MM derivatives. Other sources of resistance include Malus seiboldii and Malus robusta.
The Malus robusta component has been introduced through the CG (Cornell University, Geneva) series which have M.robusta as one parent.
It has been important to incorporate a diversity of species into the program for both WAA resistance and dwarfing characteristics.
The program is now split into two parts.
Following an expansive culling program for material with non desirable horticultural traits, enough productivity data is now available from the first group of crosses to select a group of elite stocks.
The second group of crosses were planted to the evaluation orchard in 2004 and require further evaluation although some stocks were eliminated due to excessive vigour.
It is anticipated that within three more seasons an elite group will emerge.
The Australian apple industry has acknowledged the significance of woolly aphid as a key pest and now the program enters the critical stage of elite stock selection.
The implication for the commercial apple industry, tree nursery industry and other breeders is that a more sustainable and profitable rootstock will be available to meet Australian conditions.
Contact Roy Menzies, Bathurst, (02) 6330 1213, Lester Snare, Orange, (02) 6391 3982.
