Transplant depth, irrigation, and soilless media effect on "elephant's foot" plant disorder in a hydroponic greenhouse sweet pepper crop

Abstract

A physiological disorder in greenhouse hydroponic sweet pepper (Capsicum annuum L.), where the base of the plant's stem becomes swollen below the cotyledon level and wounds develop at the base of the stem's epidermis has been named "Elephant's Foot". The disorder might predispose the plant to a localized rot and result in sudden plant wilt. Factors that might cause the disorder are not known; however salt accumulation at the base of the stem could be a possible cause of the epidermal wounds. The effects of soilless media (perlite, coconut coir, pine bark, and peat-perlite-vermiculate mix), transplant depth, and amount of nutrient solution applied per day were studied to evaluate the development of "Elephant's Foot" on a summer-fall sweet pepper (cv. Kelvin) greenhouse crop in Gainesville, FL, USA. Seedlings in 370 cm 3 cell polyethylene containers were transplanted (29 June, 1999) into 11.4-liter pots at three transplant depths: a) at half of the cell height, discarding only the bottom of the container, b) at the cotyledons level, and c) at the 2nd stem node. Plants were irrigated with the same frequency but with different irrigation periods in order to give per day volumes of solution of 2, 2.5, 3, 3.5, and 4 liters per plant. Salt accumulation at the base of the stem level was determined indirectly by measuring the electrical conductivity (EC) on a solution obtained from washing the stem epidermis. The percentage of plants with epidermal wounds at the base of the stem was highest (82.6%) on plants transplanted at half of the cell height, compared to plants transplanted to the cotyledonary level (5.8%) and the 2nd stem node (0%). Plants transplanted at half of the cell height had higher values of EC than plants transplanted to the cotyledon level and to the 2nd node. There was a positive linear relationship (r = 0.82) between the percentage of plants with epidermis wounds and the EC. The EC increased with the amount of nutrient solution applied per day. The type of soilless media did not influence in salt accumulation at the base of the stem. The practice of transplanting sweet pepper with the cotyledonary node under the surface of the soilless media could minimize salt accumulation and epidermal damage at the base of the stem level and avoid the development of the "Elephant's Foot" disorder.