Effects of growth period and air temperature on the position of the inflorescence on the stem of tomato plants

In the tomato (Solanum lycopersicum), the position of the inflorescence on the stem is known to affect the number of days to first anthesis and has commonly been characterized by the leaf-number (ordinal number from the oldest leaf) of the leaf just below the inflorescence (LEAF-BI) only by the appearance after extension of the stem near the inflorescence. Some examples showing that this evaluation was not suitable were observed by the authors. To confirm the reproducibility of the observation, experiments were conducted in which 4 cultivars were sown in a greenhouse 12 times from Oct. 2008 to Aug. 2010. Based on the vertical positional relationship between the base of the first, second, or third inflorescence and the base of the last initiated leaf before inflorescence primordium on the growing point (L-LEAF, the true guide for determining the inflorescence position), the L-LEAFs of 'My Lock' plants in all growth periods and 'House Momotaro', 'Momotaro 8', and 'Super Fast' plants in the non-high-temperature growth periods were always just above the inflorescences, that is, the LEAF-BIs were always the leaves below the L-LEAFs. In contrast, the L-LEAFs of all cultivars except 'My Lock' in the high-temperature growth periods were often just below the inflorescence, that is, the LEAF-BIs were often the L-LEAFs. Comparing the leaf-number of LEAF-BI and that of L-LEAF demonstrated that the former often overestimated the inflorescence positon among growth periods and cultivars. In temperature treatments with 'House Momotaro', such a positional switch of the L-LEAF was reproducible. External observation indicated that the stem on the L-LEAF side and the stem on the inflorescence side extended non-uniformly and the position of the L-LEAF was determined by which side extended faster. Collectively, the LEAF-BI is not a leaf identified morphogenetically, and to identify the position of the inflorescence, the leaf-number of L-LEAF, not LEAF-BI, should be used.