Influence of NPK fertilizer rates on growth flower abortion, concetration of secondary metabolites and quality of field and greenhouse grown pepino melons (salanum muricatum Aiton)

Abstract

Pepino melon (Solanum muricatum Aiton) is a plant that was originally grown in South America, mainly for its juicy fruits. It was introduced in Kenya in 2013 and is gaining a lot of popularity due to its high nutritive, medicinal and economic value. Despite its popularity and multiple uses, production of pepino is constrained by flower abortion and inadequate knowledge on the effect of nutrients on growth, yield, quality, nutritional composition and concentration of secondary metabolites. The main objective of this study was to investigate the effects of NPK fertilizer rates on growth, concentration of secondary metabolites, nutritional composition, flower abortion, yield and postharvest quality of field and greenhouse grown pepino melons. The study was conducted in the open field and greenhouse at the Horticulture Training Field three of Egerton University, Njoro in two trials. The experimental design in the field and greenhouse was Randomized Complete Block Design (RCBD) with five treatments (0, 100, 200, 300 and 400 kg NPK ha‘l) with three replications. Results indicated that at 100 Days after planting (DAP) plants grown in the greenhouse and supplied with 200 kg NPK ha" had a stem diameter of 14.01 mm which was significant (p 5 0.05) compared to a stem diameter of 1l.7lmm obtained from open field grown plants supplied with 300 kg NPK ha'l in trial two. Application of 300 kg NPK ha" for field grown pepino melons gave the highest yield of 1102.48 kg ha" and 1060.55 kg ha" in trial one and two respectively. Application of 200 kg NPK ha" favoured accumulation of lutein, lycopene and B-carotene in both growing environments and trials. Fruits from greenhouse grown plants which were not supplied with fertilizer (control) had a Total phenolic content (TPC) content of 174.3 and 145.5 mg Gallic acid equivalent (GAE) l00g'l fresh weight (FW) in trial one and two, respectively. Application of 200 and 300 kg NPK ha" enhanced copper (Cu), manganese (Mn), molybdenum (Mo) and iron (Fe) content of greenhouse and field grown pepino melon fruits respectively. Application of 200 kg NPK ha" enhanced vitamin C content in field and greenhouse grown pepino melon fruits. Application of 200 and 300 kg NPK ha'1 to greenhouse and field grown pepino melons increased the number of flowers per truss, reduced flower abortion, increased pollen viability and in vitro pollen germination in both trials. Field grown fruits from the control treatment stored at room temperature had the highest TSS of 8.67 °Brix and 8.13 °Brix in trial one and two, respectively after 28 days of storage. Application of 100 kg NPK ha'1 to both field and greenhouse grown pepino melon plants and storage at low temperature (7°C) enhanced the quality and shelf life of pepino melon fruits. It is concluded that NPK fertilizer rates and growing environment have an effect on growth, secondary metabolites, flower abortion, yield and postharvest quality of pepino melon.