FERTILISATION GUIDELINES FOR THE TABLE GRAPE INDUSTRY

new cells is concerned. A deficiency of Ca during the cell division phase of the berry will thus lead to sub-optimal berry development (e.g. small berries). Furthermore, Ca is also involved in the functioning of cell membranes, i.e. to stimulate the movement of K through cell membranes and to exclude detrimental compounds. However, accumulation of Ca slows down closer to veraison and stops completely as soon a as the berries start to soften, after veraison (Figure 29). This related to reduced sap flow in the xylem (Possner & Kliewer, 1985; Creasy et al ., 1993). Due to berry growth there is therefore a reduction in the Ca concentration of the berry tissue (Figure 29) – this is the result of dilution that happens as the berry cells expand (Donèche & Chardonnet, 1992). During ripening drastic changes in the cells of the berry tissue also take place, as far as cell structure is concerned. These changes are brought about on account of pectin becoming increasingly insoluble as the Ca concentration in the berry declines. As discussed above for potassium, this is the result of collapse of cell walls to allow continued berry growth (through expansion of individual cells) (Poovaiah et al ., 1988). Therefore, Ca does not contribute physiologically to the enhancement of berry firmness, or to significant improvement of storage ability. Consequently, wide-spread research found no evidence that additional foliar or bunch applications, or a focus on Ca fertilisation, will improve the storage ability of table grapes.

Calcium content of the berry

Calcium concentration of berry tissues

0.7

700

0.6

600

Deurslaan V rai on

Skin Pulp

0.5

500

0.4

400

0.3

300

0.2

200

Ca-concentration

(mg/100g dry mass)

Ca-content (mg/berry)

0.1

100

Deurslaan V raison

0

0

0

20

40 60

80 100

0

20

40 60

80 100

Days after anthesis (full bloom)

Days after anthesis (full bloom)

Figuur 4. Verandering van kalsiuminhoud en -konsentrasie in Prime Seedless-korrels vanaf blom tot oes (Raath, 2012). FIGURE 29: Changes of calcium content and concentration in Prime Seedless berries from bloom to harvest (Raath, 2012).

The development of the so called “calcium ring” (Figure 30), a term generally used in Chile, has nothing to do with a higher Ca concentration in the berries. It appears to be better connected to the effectiveness and rate of accumulation of sugar and electrolytes, that enhance the turgidity of the cells in the flesh (Du Plessis, 2008). Die ontwikkeling van die sogenaamde “kalsiumring” (Figuur 5), ‘n term wat algemeen in Chili gebruik word, het egter niks met ‘n hoër Ca-konsentrasie/inhoud in die korrels te doen nie. Dit blyk meer verband te hou met die effektiwiteit en tempo van opgaring van suiker en elektroliete wat die turgiditeit van die selle in die vleis bevorder (Du Plessis, 2008).

100 | THE RELATIONSHIP BETWEEN FERTILISATION, THE NUTRITIONAL STATUS OF A VINEYARD AND GRAPE QUALITY