Incidence of Blossom-end Rot in Relation to the Water-soluble Calcium Concentration in Tomato Fruits as Affected by Calcium Nutrition and Cropping Season

Abstract

To understand the factors affecting the incidence of blossom-end rot (BER), the effect of the Ca/K ratio (4/12-12/4, in me·L -1 ) in nutrient solutions and Ca concentration in fractions in the distal part of young tomato fruits immediately before BER symptoms appear were investigated for three seasons. The rate of BER incidence increased with a decrease in the Ca/K ratio in the supplied solutions in the summer and spring, but little difference was observed in the winter. Ca concentration was highest in winter and lowest in summer, and the concentration in fractions decreased with a decrease in the Ca/K ratio of the solutions. When the results of all three experiments were pooled, among the fractions, water-soluble Ca concentration was found to have the highest significance in the relationship to BER incidence. The risk of BER incidence in rapidly growing tomato increased to a critical level when water-soluble Ca in the distal part of the fresh fruit decreased to less than 0.20 μmol·g -1 FW. Multiple-regression analysis revealed that the concentration of water-soluble Ca, which is predominantly recovering apoplastic or cytoplasmic Ca 2+ , and total Ca, which has been translocated during fruit development, are significantly affected by solar radiation and Ca concentration in the supplied solution rather than air temperature.

Comparative Analysis on Blossom-end Rot Incidence in Two Tomato Cultivars in Relation to Calcium Nutrition and Fruit Growth

“…Similar to our previous report (Yoshida et al, 2014), increased Ca concentration in the nutrient solution significantly increased Ca absorption but decreased K absorption (Table 3). The varied Ca/K ratios in the nutrient solutions did not affect plant absorption of water and other major elements (data not shown).…”

“…Similar to our data previously described for the cultivar 'House Momotaro' (Yoshida et al, 2014), Ca in nutrient solution indicated a promotive effect on water-soluble Ca in both cultivars. The increase in the order of truss and temperature also had negative effects on water-soluble Ca in both cultivars.…”

“…Similar to our previous reports (Ooyama et al, 2016;Yoshida et al, 2014) ), correspondingly. ** and *** indicate significance at P < 0.01 and P < 0.001, respectively.…”

“…Unlike most works that concern total Ca within fruit tissues (Ho and White, 2005), we found that water-soluble Ca representing apoplastic Ca, cytoplasmic Ca, and loosely wall-bound Ca in the distal part of tomato fruit was potentially most related to the physiological process of BER development in a large sized tomato cultivar, 'House Momotaro' (Yoshida et al, 2014). In a large-sized cultivar, the frequency of BER development increased when water-soluble Ca decreased below 0.20 μmol·g −1 FW in the distal part of the young fruit.…”

“…Ca in the distal part of the fruit was sequentially extracted to water-, sodium chloride (NaCl)-, and hydrochloric acid (HCl)-soluble Ca fractions that served as representatives for (1) apoplastic and cytoplasmic Ca 2+ , loosely wall-bound Ca; (2) Ca pectate in cell wall; and (3) insoluble Ca phosphate and Ca oxalate, respectively. The procedure for fractionated Ca extractions was done as described in Yoshida et al (2014). Ca concentration was determined using atomic absorption spectrometry (SPCA-6210; Shimadzu, Kyoto, Japan) and described as μmol·g ) where y is the incidence of BER, x is the water-soluble Ca concentration, a is the gain coefficient, and b is the value of x at the midpoint (Kent et al, 1972;McDowall and Dampney, 2006).…”