Effect of Arbuscular Mycorrhizal Fungi Combined with Exogenous Calcium on Papaya (Carica papaya L.) Plant Growth

Abstract

The pawpaw (Carica papaya L.) is a very productive fruit tree but is not widely exploited on the international market due to rapid deterioration of the fruits after harvest. This deterioration is due to a nutritional dysfunction related to the deficiency of nutrients, especially calcium, which is involved in the firmness of fruits in general and the papaya in particular. The symbiotic capacity of arbuscular mycorrhizal fungi (AMF) has been profiled to enhance uptake and regulation of exchangeable calcium ions in the soil. The aim of this study was to reduce losses and improve post-harvest quality of papaya fruits through the potential of arbuscular mycorrhizal fungi (AMF) in calcium uptake for international exploitation. A composite of AMF species identified of papaya rhizosphere in two study sites, combined with different calcium doses (0 µM, 100 µM, 200 µM, 300 µM and 1000 µM) was applied to two papaya varieties (calcium deficiency-resistant V1 Calina papaya IPB9 and calcium deficiency-sensitive V2 Solo N°8) and the effect was evaluated in greenhouse. The frequency and intensity of root colonization were evaluated. The AMF/calcium 1000 µM combination significantly influenced (P = .05) the number of plant height (44%, 68%), leaves (71%; 122%), fresh biomass of leaves (3,3%; 596.3%), roots (159.2%, 265.3%), and stems (910%;4075%) in both varieties V1 and V2 respectively compared to AMF/ calcium 0 µM. Increased absorption of calcium ions (150%) and phytochemicals were recorded in the leaves. The frequency (81%; 85%) and intensity (15%; 21%) of root colonization by AMF respectively was not significantly different (P>.05) in both two varieties (V1 and V2). However, the presence of AMF spores was observed on the roots of papaya plants mycorrhized with the calcium 1000 µM. Inoculation with AMF combined with the high calcium dose (1000 µM) promoted mycorrhizal infectivity of roots, colonization of mycorrhizal spores in the soil and increased roots absorption surface area.