Electrical conductivity of the nutrient solution: implications for flowering and yield in day-neutral cultivars

The influence of EC on the developmental behavior of June-bearing cultivars, particularly during flower bud initiation and differentiation has been well documented. The influence of nutrient solution EC on the growth and behavior of day-neutral cultivars however is less well established. In this trial three commercial day-neutral cultivars 'Portola', 'Murano' and 'Verity' were grown under tunnels on raised substrate beds. Plants were given nutrient solutions with either a high (1.6 mS cm(-1)), standard (1.2 mS cm(-1)) or low (0.7 mS cm(-1)) EC. Assigned nutrient solutions were given continuously from planting until the end of harvest. Total yield, fruit number, fruit size and truss number were assessed. At high EC none of the cultivars displayed a difference in the number of trusses per plant, however, truss architecture was more complex. Truss development at high EC led to more quaternary and quinary fruits. The resulting percentage of class one fruit (>31 mm diameter) compared with class two (<31 mm diameter) decreased. In the case of 'Murano' and 'Portola', the shift in production towards smaller fruit led to an increase in total yield but a total net decline in marketable fruit. Truss development in 'Verity' at high EC like 'Murano' and 'Portola' also resulted in more complex trusses. Despite the similar shift in production towards smaller fruit, 'Verity' had an inherent ability to more evenly distribute fruit weight across its truss compared to 'Murano' and 'Portola'. This coupled with a significantly greater number of fruit per plant resulted in maximized yields of class one fruit in 'Verity' grown at EC 1.6 mS cm(-1) (indicating potential financial gains). These results suggest that day-neutral cultivars have varying sensitivity to high and low EC and thus differ in their EC optimum. It is also suggests that EC plays an important role in regulating the frequency and complexity inflorescence architecture in day-neutral cultivars and thus the total number of fruit. It might also be concluded that the ability of a cultivar to evenly distribute fruit weight across all berries on a truss is an important characteristic for establishing a suitable EC regime.