Apple rootstock evaluation trials at Hortgro

Prof. Wiehann Steyn, General Manager of Hortgro Science, explains their approach to rootstock evaluation.

New rootstocks offer the exciting prospect of enhancing the productivity and profitability of orchards. But a poor rootstock choice can be a costly mistake. Hortgro funds rootstock evaluation trials that empower growers with information to select the right rootstock for their situation.

Previous rootstock trials saw all vigour classes planted together in the same orchard. This meant suboptimal management for some — or all — the trees. So the newer and future trials will focus on one of the ten vigour classes per site, and only rootstocks in that class and the adjacent classes will be planted. For example, if the spotlight is on class 3, then rootstocks from classes 2, 3 and 4, but not 1 or 5, can be included.

New rootstocks will be compared to a standard for their vigour class. For example, G.778 is the standard for vigorous rootstocks, and M.9 is the standard for dwarfing rootstocks. The standard is the best representative of the vigour class — it sets the bar for the performance of new rootstocks.

Another change to the Hortgro Science trials is that all rootstocks will be evaluated on three sites. More evaluation data improve the odds of growers picking rootstocks matched to their own soil types, microclimates, orchard systems, and management practices.

When a rootstock is tested on only one site, its performance will relate to site-specific conditions such as soil or climate. Multiple sites help tease out environmental and genetic effects and show which rootstocks adapt more readily to different conditions.

Sites for the evaluation of apple rootstocks are in the EGVV, the Koue Bokkeveld, and the Langkloof. New dwarfing-rootstock trials are also underway on the Highveld.

In the past, trials were fully funded by Hortgro, but licence holders are now co-funders, paying for evaluating their rootstocks at one of the three sites. Hortgro carries the cost associated with the other two sites, as well as the cost of the standards.

Hortgro Science rootstock evaluation trials are run by independent cultivar-evaluation company Provar, with input from Hortgro, a rootstock and nursery-tree quality workgroup, and a rootstock evaluation committee.

In addition to evaluation, Hortgro funds research on specific rootstock-related topics, including the susceptibility of different rootstocks to drought stress and major soil-borne pests and diseases like replant disease, nematodes, Phytophthora, and woolly apple aphids.

For more information, please visit the Rootstocks and Nursery Tree Quality page on the Hortgro Science website.