Excess Phosphorus Reduces the Pungency and Expression of Capsaicinoid Biosynthesis Genes in Chili Pepper (Capsicum annuum L.)

抄録

The present study was conducted to determine the effects of excess phosphorus fertilizer application on number of seeds, placental septum weight, and capsaicinoid content in ‘Takanotsume’, ‘Sapporo Oonaga Namban’ and ‘Shishito’ (only used in 2020) chili pepper varieties under different phosphorus fertilizer treatments in 2020 (60, 300 and 600 g·m^-2) and in 2021 (100 and 600 g·m^-2). Furthermore, this research is also to determine the relative expression levels of capsaicinoid biosynthesis genes in 2021. With the increasing amount of P fertilizer added, the number of seeds and placenta dry weights did not change, but the capsaicinoid content was significantly lower in all varieties except for the ‘Shishito’. Relative expression levels of 18 capsaicinoid biosynthesis genes were tested using a quantitative reverse transcription-polymerase chain reaction (qRT-PCR) in 2021. The genes were divided into four groups based on their expression patterns. Group 1 showed a higher gene expression of Pun1, pAMT, ACL and CaKR1 genes in plants grown in 100 g·m^-2 P-treated soil for both cultivars at 20 days after flowering (DAF). Group 2 genes, WRKY9, BCKDH, KAS I, CaMYB31, HTC, KAS III and BCAT showed a higher expression in ‘Takanotsume’ under the 100 g·m^-2 P fertilizer treatment at 20 DAF. Group 3 comprised ACS, FAT and COMT, showed higher expression in at least one variety grown in 100 g·m^-2 P fertilizer at 30 DAF. The increased expression of groups 1, 2 and 3 genes induced increases in the pungency of chili peppers grown in 100 g·m^-2 P fertilizer.