Evaluation of apricot rootstocks

The aim of this project was to identify rootstocks for apricot trees to optimise the performance of the scion cultivar and broaden the rootstock base available to apricot producers. Breakage at the bud union is an important aspect when selecting rootstocks for apricots. Currently only apricot seedling (Royal and Soldonne) are compatible with apricot scion cultivars used in South Africa. This puts a limitation on the choice of rootstocks available to cover aspects like high pH, nematode infested soil and horticultural traits.

Four trials using a randomised complete-block design with 10 replications were planted. Two were planted in Bonnievale and Montagu during 2012 using Solitaire and Rustic as scion cultivars as well as two in Bonnievale and McGregor during 2013 using Rustic as scion cultivar. The first two plantings were done using seedlings that may help to broaden the rootstock base. The last two were planted on rootstocks used in the peach and plum industry (Atlas, Viking, Cadaman and GF 677 at Bonnievale site and added to these, Guardian, SAPO 778 and Tskuba 4 at McGregor site) with Royal interstems to ensure compatibility. Royal seedling was used as the industry standard.

During the 2014 season growers who planted Solitaire and Rustic during 2011 expressed their discontent about these new releases that did not set fruit. The ARC, who released these cultivars concluded that ˈRusticˈ does not appear to be self-compatible and based on their results, ˈBulidaˈ, ˈRoyalˈ, ˈCape Babecoˈ and ˈPalsteynˈ could be used as cross-pollinators. Most producers decided to remove their orchards. Our first two plantings were removed during the 2014/15 season by the land owners and the third one during the 2015/16 season. Only trunk circumferences were measured.

Four years after planting trees at Thornvilla, on Cadaman, Guardian and Royal seedling had the biggest trunk circumference, but it was not statistically bigger compared to trees on Atlas, Viking and SAPO 778.  No signs of breakage at the bud-union occurred over this period. Moderate to high numbers of ring, root-lesion and spiral nematodes are present in this soil. The orchard at Thornvilla was successfully worked over to Bulida during January 2017 and new growth reach an average of 40 cm at the end of March 2017. All trees had three to four new Bulida shoots to form the new leaders. Unfortunately, the owners decided to remove this orchard during the winter of 2017.

The cultivar Rustic was highly recommended, but unfortunately it was a disaster under commercial conditions due to pollination problems that was experience in orchards during 2014. Cross-pollinators and flower bouquets were introduced in the Thornvilla, McGregor orchard. No fruit-set occurred during the 2015 and 2016 seasons. Over a four-year period, trees grew excellent and no incompatibility occur. Trees were successfully worked over to Bulida during January 2017. However, the owners decided to remove the apricot orchard during July 2017. An article was written for Die Krat to make recommendations for the apricot producers.