Early Kiwifruit Decline: A Soil-Borne Disease Syndrome or a Climate Change Effect on Plant–Soil Relations?

Laura Bardi

doi:10.3389/fagro.2020.00003

Abstract

Kiwifruit early decline is a physiological disorder whose appearance was reported for the first time in New Zealand, following a cyclone that caused a heavy and prolonged flooding of kiwifruit orchards. Following studies on kiwifruit vine physiology and anatomy demonstrated that this plant has a significant water demand, but is also extremely sensible to roots waterlogging and soil anoxic conditions. Pathogenic microorganisms were sometimes identified in soil and root samples of declining plants, but they were not considered the primary cause of kiwifruit decline, and their presence in roots was considered a consequence of waterlogging and plant weakening. Agronomic practices have been developed and adopted to deliver water in amounts adequate to plant needs, but avoiding excess and stagnation in soil, and to improve soil aeration. However, in recent years early decline is spreading worldwide and is affecting even orchards in which waterlogging is prevented or is only occasionally caused by intense local rainfall. A global overview of the knowledge on botanical, physiological and ecological traits of kiwifruit, along with the examination of phenomena concomitant to early decline appearance, can help to identify the causes and the possible actions to prevent its occurrence. Some assumptions and possible solution attempts are proposed.

Highlights

The kiwifruit, a spontaneous plant native to China whose fruits were widely harvested from the wild, was introduced in New Zealand, Europe, and America at the beginning of twentieth century, and its cultivation rapidly spread through temperate regions in the second half of the century
The anatomy and histochemistry of the root system of A. deliciosa var. deliciosa has been extensively described by Lemon and Considine (1993); it is crucial to summarize their findings in view of the implications with the kiwifruit early decline
It is widely accepted that the main cause of early kiwifruit decline is an insufficient oxygen availability to roots

Summary

Laura Bardi*

Research Centre for Engineering and Agro-Food Processing, CREA Council for Agricultural Research and Economics, Turin, Italy. Kiwifruit decline is a physiological disorder reported for the first time in New Zealand following a cyclone that caused a heavy and prolonged flooding of kiwifruit orchards. Following studies on kiwifruit vine physiology and anatomy demonstrated that this plant has a significant water demand but is extremely sensible to root waterlogging and soil anoxic conditions. In recent years, early decline has seen worldwide spread, affecting even orchards in which waterlogging is prevented or is only occasionally caused by intense local rainfall. A global overview of the knowledge on botanical, physiological, and ecological traits of kiwifruit, along with the examination of phenomena concomitant to early decline appearance, can help to identify the causes and the possible actions to prevent its occurrence.

INTRODUCTION

Kiwifruit Ecology

Kiwifruit Root System

Root Symptoms and Possible Causes Explored in Kiwifruit Decline

Findings

DISCUSSION