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Limpopo is a major potato production area where roughly 24.8% of the country’s total commercial potatoes are produced by 121 producers on approximately 12 760 ha. The most prominent cultivars produced for table and processing purposes are Mondial, Panamera, and Sifra.
Dendron is located in South Africa’s tropical summer rainfall region (Figure 1) and has recorded an average annual rainfall of 375 mm over the past 23 years, according to the nearest Agricultural Research Council (ARC) weather station. The winters in this region are cool and short, whereas the summers are warm and long.
In the winter months (May to July), the region’s long-term temperatures average between 6°C and 24°C, with a few days dipping below 0°C. Two production seasons are therefore possible: an early planting from January to March, and a main planting from April to July. Because of the two planting seasons, this region is one of the largest contributors to the South African potato industry.
Trial design and details
The Dendron cultivar trial is laid out in a random block design with three replications per cultivar. Table 1 contains additional information relating to the trial. Soil samples were taken prior to planting in order to determine the soil nutrient profile of the trial site (Table 2).
The cultivar trial includes cultivars with short and long growing periods, which can influence the final yield of certain cultivars. The length of growing periods is subject to the nature of the seasons but is generally regarded as the time that passes from emergence to natural leaf senescence. Table 3 sets out how these growing periods differ among cultivars. The plant readiness of tubers at the time of planting, as well as the density and haulm count observed later in the growing season, are also presented in Table 3.
Marketing-related results
The evaluation of new cultivars, as in the Dendron cultivar trial, provides results on yield and the marketing index. The marketing index of the cultivars involved is calculated by classing and sorting each cultivar based on quality and size groups (for example, Class 1 large or Class 2 large-medium).
Prices were then compared to market prices obtained at the time of harvest. However, the performance of cultivars cannot be based solely on a single season’s results, as climate varies from year to year. Therefore, cultivars are preferably tested across several seasons.
Impact of climate conditions
As with any crop, factors such as temperature, water availability (whether through good irrigation scheduling or rainfall), and heat units influence the potato plant during its growing period. These factors are considered when evaluating cultivar performance.
Applicable daily weather data for the relevant season is obtained from a weather station near the trial, whereas long-term weather data is obtained from the nearest ARC weather station. The rainfall data is presented in Figure 2. When considering long-term data, the season recorded below-average rainfall, except for October, when slightly higher rainfall was recorded. Proper irrigation scheduling is essential, especially during key growing periods when temperatures are high.
Minimum and maximum temperatures are illustrated in Figure 3. Large fluctuations in maximum temperatures were observed during the last three months of the season. The collection of heat units during a growing period is a key factor in the development of a potato plant. The trend of heat units available for this season’s Dendron cultivar trial appears to be higher than the long-term data trend of heat units (Figure 4).
Yield and cultivar effect
Yield data recorded during harvesting were processed statistically using the GenStat® program. The Tukey test of least significant differences (LSD) was used to separate the mean. The cultivar effect during this trial (Figure 5) was statistically significant (p<0.05), and the coefficient of variation was very good (7.1%). These factors indicate that the trial was well executed and that the results are therefore reliable.
Each cultivar’s yield is divided by the trial average, with the average across all cultivars set to 100%. This is used to determine a yield index, with each cultivar’s yield performance read as a percentage of the trial average.
The average yield of the trial in the 2025 season is 60.25 t/ha, which is higher than the previous five seasons’ trial average of 58.5 t/ha. Foxy statistically produced the highest yield and, along with Moonlight and Sound, also achieved the best marketing index. A good marketing index can be attributed to higher yields of large potatoes and/or a high percentage of good-quality potatoes. Size group distribution and grading are important evaluations when assessing a potato cultivar’s marketability (Figures 6 and 7).
The main reasons for downgrading are set out in Table 4. Malformation appears to be the leading cause of downgrading of potatoes in this trial.
Cultivar performance
Given the nature of the seasons, cultivar performance will vary from one season to the next. This is simply because the climate is never the same from one season to the next. Thus, it is important to consider cultivar performance across multiple seasons. The variation in participating cultivars over the past five seasons is illustrated in Figure 8.
Processing characteristics can also be evaluated when considering the internal quality of potatoes. To adhere to processing requirements, cultivars must meet a chip colour standard of >50 and a specific gravity (SG) of ≥1.075 (Table 5). According to ARC analyses, almost all cultivars met the correct chip colour, but only Palace and Satin King achieved both the correct SG and chip colour.
During the internal quality evaluation, none of the cultivars showed signs of hollow heart.
Special thanks to Mossie Jongbloed (producer), Schalk Grobbelaar (working group chairperson), participants FPD, GWK, RSA and Provision Agri, Ané du Plessis, and other Potatoes SA staff. – Enrike Verster, Potatoes SA