Fruit yellow-shoulder disorder as related to mineral element uptake of tomatoes grown in high temperature

In order to reduce yellow-shoulder (YS) disorder by regulating nutrient solution in high temperature, effects of potassium (K) and phosphorus (P) supplementation on YS index were investigated. Experiments were conducted in an optimum temperature condition under 20 °C, and in a high temperature condition under 31 °C. Nutrient solution of EC 0.9 dS m−1 (PO4-P 1.5 me L−1, K 3.0 me L−1), EC 0.9 + P (PO4-P 4.6 me L−1, K 3.0 me L−1), EC 0.9 + K (PO4-P 1.5 me L−1, K 5.8 me L−1), and EC 0.9 + P + K (PO4-P 4.6 me L−1, K 5.8 me L−1) were used. Each tomato (Solanum lycopersicum L. 'CF Momotaro York') plant was grown in 250 mL pot combining three trusses and high-density planting. Results showed that K uptake amount was significantly higher at EC 0.9 + P + K than at EC 0.9, EC 0.9 + P and EC 0.9 + K. K uptake efficiency was higher at EC 0.9 + P than that at EC 0.9, although the application concentraiton of K were identical in them. YS disorder was more severe in 31°C than 20°C temperatures condition in the case of nearly similar uptake of K per plant. The YS index showed a significantly negative linear correlation with K uptake (R2 = 0.81, P < 0.01) in 31 °C, which was not found in 22 °C or other mineral elements. These results indicated that the K uptake was significantly improved. YS disorder was correspondingly reduced by increasing P or/and K concentration in 31 °C high temperature condition. In conclusion, we recommended the nutrient solution formula (EC 0.9 + P)/(EC 0.9 + P + K) to reduce the YS disorder in high temperature growing season, because its K uptake efficiency was improved as compared with EC 0.9 + P + K.