Increase cherry production potential through adaptability indexing of new genotypes in different South African growing areas

Lacking the ability to accurately quantify the chilling requirements and adaptability of new cherry  cultivars (‘genotypes’), the ultimate aim of this project was to develop an index based on phenotypic data collected from a range of tree and fruit characteristics and by applying designated statistical models to quantify and qualify stability and performance of ten different cherry genotypes planted in three diverse growing areas (‘environments’}

After accumulating sufficient winter chilling, twelve trees of ten cherry genotypes representing low to high chill requiring range were planted in a randomised complete block design. Planting was done in three climatic environments representing low, medium, and high chill winters. An extended list of characteristics was collected and explored which could assist in defining an ideal sweet cherry tree. Data was collected from trees that were treated and untreated with a rest breaking agent. The data collected from the different environments was analysed using combined multi-environment trial (MET) ANOVA, Additive Main, and Multiplicative Interaction (AMMI) and Genotype plus GxE (GGE) statistics to explore the main effect variability and Genotype x Environment interactions (GxE). Statistical analysis tools including principal component analysis (PCA) and stepwise discriminant analysis (SDA), were applied to identify drivers from the various traits measured which are most indicative for genotypic adaptability and stability.

Both genotype and environment (chill and heat accumulation) influenced bud break patterns. High and medium chill environments favoured increased bud break and improved bud break synchronisation. All genotypes succeeded in filling their vertical space in all environments due to strong vertical growth and basal dominance did not hinder this. Genotype influenced tree vigour but also growth habits and basal dominance. Genotype primarily influenced branching in the first season (total growth, shoot numbers, crotch angle). In the second season, chill and heat accumulation surpassed genotype’s influence with warmer environments favouring longer internode extension, whilst colder environments promoted more spur formation. It was shown that the genotype had limited influence on operational costs of the Tall Spindle Axis system in both seasons. Warmer conditions however, required more intensive pruning due to increased vegetative growth. In the third and fourth season, despite diverse environments and genotypes with varying chilling needs, nearly all buds (97%) exhibited growth. Results showed both high and medium chill environments displayed optimal bud break timing, rate, and maximum percentage, along with growth habits characterised by abundant flowering spurs. The warm environment exhibited variable performance across seasons and between shoots and spurs. Shoots were less affected, but spurs displayed prolonged dormancy symptoms.In the warm environment, despite bud break unaffected, low yields resulted due to limited flowering positions caused by extinction and minimal spur formation, probably due to high temperatures during floral induction. Despite genotype, warmer climates brought risks associated with poor bud break, flowering, and fruit set, ultimately leading to reduced yields. The medium chill environment emerged as a promising growing environment for cherries prospect with sufficient chill accumulation.

Initial observations revealed genotype as the primary driver of key adaptability traits, evident in tree vigour, growth habits, branching patterns, and spur formation. This emphasises the inherent potential encoded within specific genotypes for adaptation. Following overwintering, environmental factors became the dominant influence underscoring the crucial role of chill accumulation in allowing sweet cherries to express their full genetic potential. Low chill conditions posed a significant challenge, restricting canopy development and fruit-bearing potential, highlighting the need for understanding GxEl limitations and exploring alternative options for success in such regions. Additionally, moderate tree vigour in the high chill area reduced pruning and maintenance needs. The high chill environment promoted reproductive potential, evidenced by superior bud break synchronicity, increased flowering, and more bearing positions. This environment proved to be the most ideal for early cherry growth. Despite favourable bud break and flowering conditions across genotypes in the medium chilling environment, the yield was not as high as in a high chilling environment. This suggests that inhibitory factors likely affected yield after bud break, possibly during pollination, fertilisation, or fruit differentiation and needs further investigation.

Throughout the study, findings consistently displayed the significant influence of GxE, emphasising that a genotype’s performance cannot be evaluated in isolation from the environmental effect. Different genotypes displayed varying levels of adaptability across three diverse environments. This reinforces the critical role of selecting genotypes based on their compatibility with the specific production area’s climate, soil conditions, and other environmental factors. By strategically matching genotypes to their optimal environments, growers can unlock full genotypic potential, optimise growth and development, and ensure long-term orchard sustainability. An index for performance and stability will aid in optimal selection of stable and high performing genotypes to specific growing environments.