Dr. Jakkie Stander, Commercial Head Products & Services & Dr. Elmi Lötze, Head of ITEST™ CARBOHYDRATES and ITEST™ LEAF
In South Africa, the months from March to June mark the most critical, yet least visible stage of the citrus production cycle: the period of flower induction. During this time, buds on the current season’s vegetative shoots decide whether they will become flowers the following spring.
Although hormones initiate this developmental shift (Moss, 1970), the ultimate success of induction depends on adequate carbohydrate reserves, balanced mineral nutrition and the quality of the new vegetative shoots that carry these buds. When any of these are lacking, even optimal hormonal cues cannot produce a strong or uniform bloom (Goldschmidt, 1999). This is why TRY ME™ (K9552), CITRUS-TO-GROW LMO™ (B4732) and ZINC PHLOEM™ (B5734) play essential roles during this window, reinforcing the physiological foundation required long before the first blossoms appear.
Strong bloom starts with strong shoots
Flowering potential is determined by the new vegetative shoots that emerge prior to induction, because these shoots carry next season’s flowers (Embleton et al., 1973). Their age, number and nutritional status strongly influence future flower intensity, uniformity and fruit set.
Once induction begins, the tree cannot correct poor shoot quality or nutrient imbalances, as immobile and essential elements, such as zinc (Zn), can’t be translocated from old leaves behind fruit, to new potential floral units for the next season. Nutrient evaluation must therefore be performed specifically on the leaves of the flower-bearing shoots, as older or unrelated leaves provide values that do not reflect the physiology of the tissues committing to flowering (Koo, 1985).
Outdated norms plus wrong leaves leads to wrong decisions
Across the industry, nutrient samples are often collected incorrectly from sampling the wrong organs, at the wrong time to interpreting them using outdated norms developed decades ago. These conventional norms do not reflect the requirements of modern cultivars, contemporary crop-load expectations or regional climatic variation (Reuther et al., 1973). Sound decisions require sampling the correct shoots at the correct time and interpreting measurements using current, cultivar- and region-specific benchmarks.
The data advantage: Agri Technovation leads the industry
Agri Technovation currently maintains the largest and most advanced integrated/complete citrus dataset available in South Africa. This includes nutrient profiles of flower-bearing shoots, cultivar- and region-specific nutrient patterns, carbohydrate behaviour across phenological stages and shoot-quality markers directly linked to induction success.
This uniquely detailed dataset allows interpretation accuracy unmatched in the industry.
The carbohydrate truth: 1,6 tons of sugar and the real driver of floral development
Although phytohormones initiate the floral transition the developmental switch that determines whether a bud will become a flower (Bangerth, 2009) they do not provide the physical materials required to build floral structures or sustain their development. While hormones act as the regulatory signal, carbohydrates supply the structural building blocks, metabolic energy and carbon skeletons essential for floral organ formation, ovule development, pollen tube growth and the early stages of fruit set (Goldschmidt & Koch, 1996; Martínez-Fuentes et al., 2013).
The magnitude of carbohydrate demand during flowering is extraordinary. Citrus flowering removes approximately 1,6 tons of sugar over a three-month period (Mehouachi et al., 1995). No citrus tree can meet this demand through current photosynthesis alone, especially during early spring when leaf area is limited, weather is variable and respiration remains high (Syvertsen & Lloyd, 1994). The tree must therefore rely heavily on carbohydrate reserves built during the April-June induction period. Trees entering spring with insufficient reserves cannot sustain the metabolic requirements of flowering, resulting in weak bloom, poor fruit set, early fruit drop and a greater risk of alternate bearing (Goldschmidt, 1999). Thus, hormones determine whether a bud becomes a flower, but carbohydrates determine whether that flower can develop fully and transition successfully into fruit.
Hormone levels are difficult and expensive to determine and thus not a grower-friendly service. In contrast, commercial services to determine carbohydrate levels in plants are available and affordable.
Once the carbohydrate levels are quantified, interpretation depends on context. Because sugar and starch levels vary during the season and actual values vary between organs, norms must be developed for specific
phenological stages (Figure 1).
Figure 1: Seasonal and type variation in citrus leaf carbohydrate levels in the Southern Hemisphere, from
more than 45,000 ITEST™ Carbohydrate samples.
What Agri Technovation brings to the Carbohydrate table
Agri Technovation remains the only commercial carbohydrate laboratory for growers that can provide an interpretation of the data. Agri Technovation have processed more than 45,000 ITEST™ CARBOHYDRATE samples.
At Agri Technovation, we have identified four critical action times where we can act on undesirable carbohydrate levels in leaves and/ or roots to improve the carbohydrate status for specific physiological responses.
Our extensive carbohydrate database also allowed us to refine our sugar and starch norms on a regional and recently, also cultivar basis. Thus, we can manage upregulation of photosynthesis, sugar conversion to starch and/or translocation of sugar to the main sink/s on an orchard level by adjusting specific inputs.
The strong relationship between leaf tissue mineral analyses and carbohydrate dynamics is well documented and one of the main drivers, in addition to irrigation, to support carbohydrate levels at critical action times to ensure hormonal signals are fully executed.
ZINC PHLOEM™
Zinc nutrition in citrus leaves plays a central role in flower induction through its influence on hormone regulation, photosynthesis, and carbohydrate metabolism (Chapman, 1968; Alloway, 2008). Adequate zinc supports auxin synthesis and enzymatic activity, enhancing carbohydrate production and translocation from leaves to developing buds during the critical induction period, thereby improving flowering intensity and return bloom (Erner & Reuveni, 1981; Goldschmidt, 2013).
However, not all zinc formulations are safe or effective across phenological stages; inappropriate sources or poorly timed applications can damage sensitive tissues or disrupt carbohydrate partitioning (Swietlik, 2002). Consequently, advanced zinc formulation technologies, combined with a clear understanding of citrus phenology, are essential to ensure safe uptake during flower induction while maximising carbohydrate availability and floral initiation.
TRY ME™: The foliar boost that builds carbohydrate reserves
TRY ME™ is a foliar application designed to increase leaf carbohydrate levels (Figure 2), reduce the tree’s energy expenditure by supplying readily usable amino acids and biopeptides (Kavi Kishor & Sreenivasulu, 2014) and stabilise photosynthetic and hormonal processes under winter stress (Bangerth, 2009). This ensures that flower-bearing shoots possess the necessary carbohydrate reserves to meet the enormous energy cost of flowering.
Figure 2: Change in carbohydrate status after two foliar applications of TRY ME™️ on citrus (200 ml/100 L of water) applied at flower induction and balloon stage, applied in 2,500 to 3,000 L of water per hectare.
CITRUS-TO-GROW LMO™: Foliar protection for the carbohydrate engine
CITRUS-TO-GROW LMO™ protects the tree’s carbohydrate-producing capacity and enhances and simultaneously improves the uptake of nitrogen, phosphorus, magnesium, iron, zinc and manganese nutrients fundamental to chlorophyll formation, energy metabolism and sugar synthesis (Lado & Zacarías, 2016). By stabilising cell membranes and maintaining osmotic balance, CITRUS-TO-GROW LMO™ ensures effective translocation of carbohydrates and minerals into developing floral primordia (Ito & Hayama, 2010).
The induction blueprint for a strong crop
Successful flowering is the predictable outcome of strong carbohydrate reserves, nutritionally balanced flower-bearing shoots and effective stress protection during the March-June induction window.
TRY ME™ and CITRUS-TO-GROW LMO™ provide precise foliar support for carbohydrate accumulation, nutrient uptake and photosynthetic resilience, while ZINC PHLOEM™ provides an essential immobile element in a critical period.
Because no citrus tree can meet the enormous sugar demand of flowering, approximately 1,6 tons, without reserves built during this period, integrating these products with Agri Technovation’s diagnostic capabilities gives producers the strongest possible foundation for a productive, uniform bloom.
References:
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2. Bangerth, F. (2009). Flower induction in perennial fruit trees: Still an unsolved puzzle. Acta Horticulturae.
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flowering. Journal of the American Society for Horticultural Science, 106, 448–452.
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