Survey of Oomycetes Associated with Root and Crown Rot of Almond in Spain and Pathogenicity of Phytophthora niederhauserii and Phytopythium vexans to ‘Garnem’ Rootstock

Francisco Beluzán,Xavier Miarnau,Laura Torguet,Paloma Abad-Campos,Josep Armengol

doi:10.3390/agriculture12020294

Francisco Beluzán, Xavier Miarnau + Show 3 more

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https://doi.org/10.3390/agriculture12020294

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Abstract

From 2018 to 2020, surveys of oomycetes associated with root and crown rot of almond (Prunus dulcis) were conducted on diseased young almond trees in commercial orchards and nurseries in six provinces of Spain. A total of 104 oomycete isolates were obtained from plant and soil samples, which h were identified by sequencing the internal transcribed spacer (ITS) region of the ribosomal DNA. Diverse species belonging to the genera Globisporangium, Phytophthora, Phytopythium and Pythium were found, Phytopythium vexans and Phytophthora niederhauserii being the most frequent. The pathogenicity of these two species to one-year-old almond seedlings of ‘Garnem’ (P. dulcis × P. persica) rootstock was studied. All seedlings inoculated with Pp. vexans and Ph. niederhauserii isolates showed severe symptoms at the late stage of the pathogenicity test (defoliation, wilting and dieback) and several plants died. Some isolates of Ph. niederhauserii significantly reduced the dry weight of the roots compared with the control, but this effect was not observed in seedlings inoculated with Pp. vexans. These results provide new information about the oomycete species present in almond crops in Spain and highlight the importance of carrying out frequent phytosanitary surveys for a better knowledge of potential risks posed by these soil-borne pathogens.

Highlights

In the Mediterranean area, almond crops (Prunus dulcis (Miller) D.A
Pythium species recovered from almond tree samples showing root and crown rot symptoms in six provinces of Spain
This study presents the results of a three-year survey of oomycetes associated with root and crown rot of the almond trees

Summary

Introduction

In the Mediterranean area, almond crops (Prunus dulcis (Miller) D.A. Webb. syn.Prunus amygdalus Batsch) are cultivated mainly in marginal soils and rainfed conditions, quite the opposite to what happens in the USA and Australia, the two major almond producers [1], where almond crop is grown under irrigation conditions. In Spain, this crop has been traditionally planted throughout the Mediterranean coastline, where lighter and poor soils are found and it has been cultivated mainly in dry conditions [2] It was not until about the 2000s that almond crops began to be planted in irrigated lands in new Spanish cropping areas, with heavier and clayey soils, until used to grow other fruit trees or extensive crops [3]. New hybrid rootstocks obtained from crosses of almond or peach with plum species have appeared in recent years to avoid these problems [5,6,7] These new materials have certain tolerance or resistance to soil-borne diseases, but it is important to note that the area planted with them is still reduced

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