Possible Role of High Temperature and Soil Biological Fertility on Kiwifruit Early Decline Syndrome

Laura Bardi,Luca Nari,Chiara Morone,Maria Giulia Faga,Eligio Malusà

doi:10.3389/fagro.2020.580659

Abstract

Kiwifruit early decline is a disorder widespread worldwide in kiwifruit orchards, worsened in the last few years, seriously affecting economic sustainability of several rural areas where kiwifruit is an important crop. The symptoms include leaf epinasty, chlorosis, desiccation and abscission, reduced fruit production, anomalous root morphology and anatomy, followed by the plant collapse and death, usually in the same or the following year after symptoms occurrence. Even though several phytopathological or agronomical studies have been carried out, a clear and univocal explanation of the causes and the possible remedies are yet to be understood. A field trial has been carried out in an experimental kiwifruit orchard, in which several soil management practices (ridging, amendment with compost, bioinoculation with selected rhizospheric microorganisms) were tested to evaluate their effect on early decline symptoms occurrence. The analysis of plant growth parameters, root morphology and anatomy, and symptoms onset were related to environmental data (air and soil temperature, soil water tension). The results pointed to a possible role and interaction between agronomic soil management and climatic conditions as the triggering factors of kiwifruit early decline syndrome.

Highlights

Kiwifruit is an economically important fruit crop, totaling more than 4 million tons of fruits produced annually world-wide, 14% of which are produced in Italy (Ferguson, 2016; FAO, 2018)
On the third year (2019), at mid July (53 days after mid bloom (DAMB)) initial symptoms of kiwifruit early decline syndrome (KEDS) were visible only on 8.3% of plants grown on ridged plots with (RI) or without (R) inoculation of microorganisms, while no symptoms were observed in plants grown on ridged plots with the compost addition (RC) (Figure 1)
A general worsening of symptoms was observed throughout the season, and collapsed plants appeared: in the not ridged plots (C and CC), dead plants (16.7%) were observed already in August (82 DAMB), and after a month (123 DAMB) they were more than 40%

Summary

Introduction

Kiwifruit is an economically important fruit crop, totaling more than 4 million tons of fruits produced annually world-wide, 14% of which are produced in Italy (Ferguson, 2016; FAO, 2018). In the last decade, kiwifruit cultivation has been challenged by several threats. Serious damages to kiwifruit orchards arose from the bacteria Pseudomonas syringae pv. A syndrome resulting in an early decline of the plant occurred, hereafter called kiwifruit early decline syndrome (KEDS). The plants affected by KEDS suddenly collapse and die (Montanaro et al, 2014; Tacconi et al, 2014; Tosi et al, 2015; Sorrenti et al, 2016; Nari and Vittone, 2017; Bardi, 2020; Spigaglia et al, 2020).

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