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The Northeastern Cape is a potato producing region where approximately 2.3% of South Africa’s commercial potatoes are produced on approximately 1 160 ha.
The most prominent cultivars produced in the region for table consumption are Mondial, Hertha, and Panamera.
Ugie is located south of the Drakensberg Mountains, just below Lesotho, and falls within South Africa’s summer rainfall region (Figure 1). Over the past ten to 26 years, the area has recorded an average annual rainfall of between 670 and 930 mm, depending on the weather station consulted and its altitude above sea level. The region is characterised by mild summers and very cold winters.
Trial design and details
The Ugie cultivar trial was laid out in a randomised block design with three replications per cultivar. Table 1 contains relevant technical information regarding the trial.
Cultivars with short and long growing periods were included in the cultivar trial, which means growing periods can influence the eventual yield of certain cultivars. The length of growing periods is subject to the nature of a given season but is regarded as the time that passes from emergence to natural leaf senescence.
Table 2 outlines how growing periods can differ from one cultivar to the next. Table 2 also illustrates the plant readiness of tubers at the time of planting, as well as the haulm count later in the growing season.
The evaluation of new cultivars, as in the case of the Ugie cultivar trial, provides results relating to yield and 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 are then compared to market prices obtained at the time of harvest.
However, the performance of cultivars cannot be based solely on the results of a single specific season, as climate differs from one year to the next. Therefore, cultivars are preferably tested across several seasons.
Rainfall and climate trends
As with any crop, factors such as temperature, water availability (whether good irrigation scheduling or rainfall), as well as heat units have a significant influence on the potato plant during its growth period.
These factors are considered when evaluating the performance of cultivars. Applicable daily and long-term weather data is obtained from an Agricultural Research Council (ARC) weather station located as close as possible to the trial site.
The 2024/25 season (Figure 2) experienced lower rainfall compared to the cumulative long-term average.
The month preceding the planting date (21 November) saw substantial rainfall up to approximately two weeks before planting. After that, rainfall was unusually low for the area, except during the final stages of the growing period when significant rainfall was recorded in March.
Minimum and maximum temperatures are presented in Figure 3. During the season, considerable fluctuations in maximum temperatures were recorded. The collection of heat units during a growing period is an important factor in the development of a potato plant. The trend of heat units available for this season’s Ugie cultivar trial appears to be significantly higher than the long-term data trend of heat units (Figure 4).
Yield and cultivar effect
Yield data recorded during harvesting is statistically processed 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), but the coefficient of variation (CV) was very high (25.9%).
The high CV value indicates that substantial variability occurred during the trial due to several factors, and the results are therefore not necessarily as reliable as desired.
The yield of each of the cultivars is divided by the trial average, with the average of all cultivars taken as 100%. This is used to determine a yield index, and each cultivar’s performance in terms of yield is read as a percentage of the trial average.
The average yield of the trial in the 2024/25 season was 21.78 t/ha, which is a significant below-average yield due to poor plant density. During the first month after planting, the trial faced dry and hot conditions, as well as hail damage, and weed control was consistently inadequate. As a result of these challenges, the trial did not show any significant statistical differences. However, Lilly and Noya achieved the highest marketing index. A good marketing index can be ascribed to a higher yield of large potatoes and/or potatoes of good quality.
Size group distribution and grading evaluations in potatoes are essential for determining a cultivar’s marketability (Figures 6 and 7). Given the nature of the seasons, cultivar performance will vary from one season to the next, simply because climate varies from one season to the next. Therefore, it is important to consider consistent cultivar performance across a number of seasons. As this was the first season of the trial, it wasn’t possible to determine the stability of the cultivars yet.
Internal quality
Lastly, when looking at the internal quality of potatoes, it is possible to also evaluate cooking and processing traits. In order to meet processing requirements, cultivars must meet the chip colour norm of >50 and specific gravity (SG) of ≥1.075. None of the cultivars met the prescribed SG. Baking quality at a specified standard oil temperature is illustrated in Table 3. – Enrike Verster, Potatoes SA
Special thanks to the collaborator, Vuyani Kama, as well as the participating seed houses and their representatives: Martin Smith and Johann Botes (GWK), and Michelle Lombard (RSA).
For more information, send an email to enrike@potatoes.co.za.