Diagnosis of apple replant disease (ARD)

Microscopic evidence of early symptoms in fine roots of different apple rootstock genotypes

authored by

Gisela Grunewaldt-Stöcker, Felix Mahnkopp, C. Popp, Edgar Maiß, Traud Winkelmann

Abstract

Apple replant disease (ARD) is a problem of high economic relevance in tree nurseries and apple orchards worldwide. After replanting, plants show growth reduction, reduced yield, and damaged root systems. The disease's decade-long persistence in soil exacerbates the situation where alternative cultivation areas and ecologically safe soil decontamination measures are lacking. The etiology is still unclear and there are neither clear causal factors nor reliable parameters (except growth data from plant bioassays) for the early detection of the disease in plants or from samples from potentially affected soils. We report on greenhouse pot trials with the susceptible rootstock Malus domestica ‘M26’ grown in soils of ARD-affected as well as grass plots from three different field sites. Both gamma-irradiated ARD soils and grass soils served as control soils. The aim was to develop a diagnostic tool for the early detection of ARD. In fine roots of first to third order, we assessed the root structure, the root hair density, the cellular damages in the outer layers, and the cell vitality. After only two weeks in ARD soil, ‘M26’ reacted with cell necroses and blackening in a characteristic pattern, impaired root hair development, and low cell vitality. These symptoms were confirmed in Malus domestica ‘Bittenfelder’ and Malus-hybrid B63. Root systems grown in gamma-irradiated soils were almost symptom-free while those from grass soils showed different and only minor alterations. Thus, we suggest selected fine root symptoms to be used for an early diagnosis of ARD, e.g. in plant breeding selections and soil surveys.

Organisation(s)

Phytomedicine Section
Section Reproduction and Development

Type

Article

Journal

Scientia horticulturae

Volume

243

Pages

583-594

No. of pages

12

ISSN

0304-4238

Publication date

03.01.2019

Publication status

Published

Peer reviewed

Yes

ASJC Scopus subject areas

Horticulture

Electronic version(s)

https://doi.org/10.1016/j.scienta.2018.09.014 (Access: Closed)