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Decline of Mediterranean Fruit Crops and Forests Associated with Fungal Trunk Pathogens

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A special issue of Plants (ISSN 2223-7747). This special issue belongs to the section "Plant Protection and Biotic Interactions".

Deadline for manuscript submissions: closed (31 March 2021) | Viewed by 44554

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Dr. Carlos Agustí-Brisach

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Agroforestal Pathology Research Group, Department of Agronomy, ETSIAM, University of Cordoba, 14071 Cordoba, Spain
Interests: biocontrol; etiology; epidemiology; fungi; integrated pest management; Mediterranean fruit crops; phytopathology; plant–pathogen–environment interactions; fungal trunk and vascular diseases
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Dear Colleagues,

Tree decline has been a growing syndrome in agriculture and forest ecosystems in recent decades, causing major economic losses worldwide. This syndrome has been categorized as a complex disease due to the wide diversity of symptoms expression, as well as the multiple fungal species associated with the disease. Tree decline can express itself in a broad diversity of symptoms, including chlorotic and necrotic leaves, shoot blight, branch dieback, cankers in the tree trunk, crown rot, gummosis, internal wood discoloration, and/or reduction in root biomass and root necrosis. When the disease progresses, the tree shows general debilitation and eventually dies. Symptoms vary depending on the biology of the causal agent, the affected host, the environmental and agronomical conditions, and all their interactions. A broad diversity of Mediterranean fruit crops (grapevine, olive, and tree nuts) and forest trees (Pinus spp., Quercus spp., etc.), have been described as susceptible hosts. Botryosphaeriaceae, Diaporthaceae, and Diatrypaceae fungi have been identified as the main causal agents of this disease syndrome. However, there are hundreds of fungal species associated with tree decline. For all these aspects, the diagnosis of the disease is difficult, and elucidating its etiology is essential for the establishment of effective management strategies.

On the other hand, to date, the role of the different fungi associated with the disease is dynamic and still uncertain due to taxonomic revisions. In fact, there is major controversy within the scientific community because some experts think that fungal trunk pathogens are the primary causal agents of this complex disease; meanwhile, others support the hypothesis that most of the fungal trunk pathogens are characterized by a prolonged latent infection or endophytic phase, changing to pathogenic phase when stress conditions occur in the host plant. Thus, elucidating the role of biotic and abiotic factors in the infection of fungal trunk pathogens as well as the interactions among fungal trunk pathogens to determine synergistic or antagonistic effects among them will provide important challenges for research.

This Special Issue on the “Decline of Mediterranean Fruit Crops and Forests Associated with Fungal Trunk Pathogens” in Plants brings together a collection of research papers on applied plant pathology and targeted reviews of the etiology, epidemiology, ecology, and control of fungal trunk diseases worldwide. It provides a snapshot of the current knowledge of this complex disease syndrome, with the goal of targeting hot areas of discussion and investigation such as the role of biotic and abiotic factors, and their interaction in the disease development. A better understanding of tree decline syndrome diseases will build a strong foundation for developing effective management approaches to reduce losses from the tree decline syndrome.

Dr. Carlos Agustí-Brisach
Guest Editor

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Keywords

ecology
etiology
epidemiology
disease development (latent vs. endophytic)
control
fungal trunk pathogens
Mediterranean fruit crops
forest trees
plant–pathogen interactions

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Published Papers (10 papers)

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Research

22 pages, 3086 KiB

Open AccessArticle

Investigations on Fungi Isolated from Apple Trees with Die-Back Symptoms from Basilicata Region (Southern Italy)

by Stefania Mirela Mang, Carmine Marcone, Aurel Maxim and Ippolito Camele

Plants 2022, 11(10), 1374; https://doi.org/10.3390/plants11101374 - 21 May 2022

Cited by 14 | Viewed by 3703

Abstract

Val d’Agri is an important orchard area located in the Basilicata Region (Southern Italy). A phenomenon affecting cv. “Golden Delicious” apples which lead to tree death has been observed in the past several years in this area. This phenomenon has already been detected in about 20 hectares and is rapidly expanding. The symptoms observed were “scaly bark” and extensive cankers, mainly located in the lower part of the trunk, associated with wood decay. Dead plants ranged from 20% to 80% and, in many cases, trees were removed by farmers. In order to identify the causes of this phenomenon, investigations were started in autumn/winter 2019. In order to determine the possible causal agents, fungal and bacterial isolations, from symptomatic tissues, were performed in laboratory. Bacterial isolations gave negative results, whereas pure fungal cultures (PFCs) were obtained after 3–4 passages on potato dextrose agar (PDA) media. Genetic material was extracted from each PFC and amplified by PCR using three pairs of primers: ITS5/4, Bt2a/Bt2b and ACT-512F/ACT-783R. The amplicons were directly sequenced, and nucleotide sequences were compared with those already present in the NCBI GenBank nucleotide database. All isolated fungi were identified based on morphological features and multilocus molecular analyses. Neofusicoccum parvum, Diaporthe eres and Trametes versicolor were most frequently isolated, while Pestalotiopsis funerea, Phomopsis spp. and Diaporthe foeniculina were less frequently isolated. All nucleotide sequences obtained in this study have been deposited into the EMBL database. Pathogenicity tests showed that N. parvum was the most pathogenic and aggressive fungus, while Phomopsis sp. was demonstrated to be the less virulent one. All the investigated fungi were repeatedly reisolated from artificially inoculated twigs of 2-year-old apple trees, cv. “Golden Delicious”, and subsequently morphologically and molecularly identified. The role played by the above-mentioned fungi in the alterations observed in field is also discussed. Full article

(This article belongs to the Special Issue Decline of Mediterranean Fruit Crops and Forests Associated with Fungal Trunk Pathogens)

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14 pages, 3814 KiB

Open AccessArticle

Silverleaf (Chondrostereum purpureum) Effects on Japanese Plum (Prunus salicina)

by Daina Grinbergs, Javier Chilian, Carla Hahn, Marisol Reyes, Mariana Isla, Andrés France and Jorunn Børve

Plants 2021, 10(12), 2777; https://doi.org/10.3390/plants10122777 - 16 Dec 2021

Cited by 4 | Viewed by 4685

Abstract

Silverleaf is an important fungal trunk disease of fruit crops, such as Japanese plum (Prunus salicina). It is known that infection by Chondrostereum purpureum results in discolored wood, “silvered” foliage, and tree decline. However, effects on fruit yield and quality have not been assessed. Therefore, the objectives of this study were to determine C. purpureum pathogenicity on P. salicina and the effects on physiology, fruit yield, and quality, in Chile, in 2019 and 2020. Wood samples from affected plum trees were collected in the Chilean plum productive area. Fungi were isolated by plating wood sections from the necrosis margin on culture media. Morphological and molecular characteristics of the isolates corresponded to C. purpureum (98%). Representative isolates were inoculated from healthy plum plants and after 65-d incubation, wood necrotic lesions and silver leaves were visible. Fungi were reisolated, fulfilling Koch’s postulates. To determine Silverleaf effects, xylem water potential and fruit yield and quality were measured in healthy and Silverleaf-diseased plum trees ‘Angeleno’. Water potential was altered in diseased trees, and fruit yield was reduced by 51% (2019) and by 41% (2020) compared to fruit from healthy trees. Moreover, cover-colour, equatorial-diameter, and weight were reduced, and fruit were softer, failing to meet the criteria to be properly commercialized and exported to demanding markets. Full article

(This article belongs to the Special Issue Decline of Mediterranean Fruit Crops and Forests Associated with Fungal Trunk Pathogens)

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14 pages, 552 KiB

Open AccessArticle

Cultivar Susceptibility to Natural Infections Caused by Fungal Grapevine Trunk Pathogens in La Mancha Designation of Origin (Spain)

by Juan L. Chacón-Vozmediano, David Gramaje, Maela León, Josep Armengol, Juan Moral, Pedro M. Izquierdo-Cañas and Jesús Martínez-Gascueña

Plants 2021, 10(6), 1171; https://doi.org/10.3390/plants10061171 - 9 Jun 2021

Cited by 12 | Viewed by 3187

Abstract

Grapevine trunk diseases (GTDs) are one of the main biotic stress factors affecting this crop. The use of tolerant grapevine cultivars would be an interesting and sustainable alternative strategy to control GTDs. To date, most studies about cultivar susceptibility have been conducted under controlled conditions, and little information is available about tolerance to natural infections caused by GTD fungi. The objectives of this study were: (i) to identify tolerant cultivars to GTD fungi within a Spanish germplasm collection, based on external symptoms observed in the vineyard; and (ii) to characterize the pathogenic mycoflora associated with symptomatic vines. For this purpose, a grapevine germplasm collection including 22 white and 25 red cultivars was monitored along three growing seasons, and their susceptibility for esca foliar symptoms was assessed. Fungi were identified by using morphological and molecular methods. Cultivars such as, ‘Monastrell’, ‘Graciano’, ‘Cabernet Franc’, ‘Cabernet Sauvignon’, ‘Syrah’, ‘Moscatel de Alejandría’, ‘Sauvignon Blanc’, and ‘Airén’ displayed high susceptibility to GTDs, whereas others such as ‘Petit Verdot’, ‘Pinot Noir’, ‘Chardonnay’, and ‘Riesling’ were considered as tolerant. The prevalent fungal species isolated from symptomatic vines were Phaeomoniella chlamydospora (27.9% of the fungal isolates), Cryptovalsa ampelina (24.6%), and Dothiorella sarmentorum (21.3%). Full article

(This article belongs to the Special Issue Decline of Mediterranean Fruit Crops and Forests Associated with Fungal Trunk Pathogens)

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21 pages, 1198 KiB

Open AccessArticle

Factors Involved on Tiger-Stripe Foliar Symptom Expression of Esca of Grapevine

by Francesco Calzarano, Giancarlo Pagnani, Michele Pisante, Mirella Bellocci, Giuseppe Cillo, Elisa Giorgia Metruccio and Stefano Di Marco

Plants 2021, 10(6), 1041; https://doi.org/10.3390/plants10061041 - 21 May 2021

Cited by 8 | Viewed by 2993

Abstract

Esca of grapevine causes yield losses correlated with incidence and severity symptom expression. Factors associated with leaf symptom mechanisms are yet to be fully clarified. Therefore, in 2019 and 2020, macro and microelement analyses and leaf reflectance measurements were carried out on leaves at different growth stages in a vineyard located in Abruzzo, central Italy. Surveys were carried out on leaves of both never leaf-symptomatic vines and different categories of diseased vine shoots. Never leaf-symptomatic and diseased vines were also treated with a fertilizer mixture that proved to be able to limit the symptom expression. Results showed that untreated asymptomatic diseased vines had high calcium contents for most of the vegetative season. On the contrary, treated asymptomatic diseased vines showed higher contents of calcium, magnesium, and sodium, at berries pea-sized, before the onset of symptoms. These vines had better physiological efficiency showing higher water index (WI), normalized difference vegetation index (NDVI), and green normalized difference vegetation index (GNDVI) values, compared to untreated asymptomatic vines, at fruit set. Results confirmed the strong response of the plant to symptom expression development and the possibility of limiting this response with calcium and magnesium applications carried out before the symptom onset. Full article

(This article belongs to the Special Issue Decline of Mediterranean Fruit Crops and Forests Associated with Fungal Trunk Pathogens)

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17 pages, 2961 KiB

Open AccessArticle

Production of Phytotoxic Metabolites by Botryosphaeriaceae in Naturally Infected and Artificially Inoculated Grapevines

by Pierluigi Reveglia, Regina Billones-Baaijens, Jennifer Millera Niem, Marco Masi, Alessio Cimmino, Antonio Evidente and Sandra Savocchia

Plants 2021, 10(4), 802; https://doi.org/10.3390/plants10040802 - 19 Apr 2021

Cited by 10 | Viewed by 3253

Abstract

Grapevine trunk diseases (GTDs) are considered a serious problem to viticulture worldwide. Several GTD fungal pathogens produce phytotoxic metabolites (PMs) that were hypothesized to migrate to the foliage where they cause distinct symptoms. The role of PMs in the expression of Botryosphaeria dieback (BD) symptoms in naturally infected and artificially inoculated wood using molecular and analytical chemistry techniques was investigated. Wood samples from field vines naturally infected with BD and one-year-old vines inoculated with Diplodia seriata, Spencermartinsia viticola and Dothiorella vidmadera were analysed by cultural isolations, quantitative PCR (qPCR) and targeted LC-MS/MS to detect three PMs: (R)-mellein, protocatechuic acid and spencertoxin. (R)-mellein was detected in symptomatic naturally infected wood and vines artificially inoculated with D. seriata but was absent in all non-symptomatic wood. The amount of (R)-mellein detected was correlated with the amount of pathogen DNA detected by qPCR. Protocatechuic acid and spencertoxin were absent in all inoculated wood samples. (R)-mellein may be produced by the pathogen during infection to break down the wood, however it was not translocated into other parts of the vine. The foliar symptoms previously reported in vineyards may be due to a combination of PMs produced and climatic and physiological factors that require further investigation. Full article

(This article belongs to the Special Issue Decline of Mediterranean Fruit Crops and Forests Associated with Fungal Trunk Pathogens)

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14 pages, 2560 KiB

Open AccessArticle

Early Season Symptoms on Stem, Inflorescences and Flowers of Grapevine Associated with Botryosphaeriaceae Species

by Pedro Reis, Ana Gaspar, Artur Alves, Florence Fontaine, Inês Lourenço, José Saramago, Mariana Mota and Cecília Rego

Plants 2020, 9(11), 1427; https://doi.org/10.3390/plants9111427 - 24 Oct 2020

Cited by 16 | Viewed by 3978

Abstract

Botryosphaeria dieback caused by several Botryosphaeriaceae species is one of the most important grapevine trunk diseases affecting vineyards worldwide. These fungi cause wedge-shaped perennial cankers and black streaking of the wood and have also been associated with intervein leaf chlorosis, dried or mummified berries, and eventually, the death of the plant. Early season symptoms may sometimes be disregarded by growers, being mistaken with symptoms from other diseases such as downy mildew or botrytis rot. Currently, few studies are available to determine what species may be causing these early season symptoms in grapevines. During the 2018 season, during the flowering period, grapevine samples showing necrosis on green shoots, dried inflorescences, and flowers, were collected in vineyards throughout the central regions of Portugal. Isolations were performed from symptomatic organs, and twenty-three isolates of Botryosphaeriaceae were selected. An analysis of the ITS and part of the translation elongation factor 1-α sequences was performed, revealing that the two main species apparently responsible for these symptoms were Diplodia seriata and Neofusicoccum parvum. In pathogenicity tests conducted on 1-year-old plants grown under controlled conditions in a greenhouse and on field-grown clusters, symptoms were reproduced, confirming the pathogenic behavior of the selection of isolates. Full article

(This article belongs to the Special Issue Decline of Mediterranean Fruit Crops and Forests Associated with Fungal Trunk Pathogens)

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26 pages, 12409 KiB

Open AccessArticle

Water Stress Enhances the Progression of Branch Dieback and Almond Decline under Field Conditions

by Carlos Agustí-Brisach, David Moldero, María del Carmen Raya, Ignacio J. Lorite, Francisco Orgaz and Antonio Trapero

Plants 2020, 9(9), 1213; https://doi.org/10.3390/plants9091213 - 16 Sep 2020

Cited by 18 | Viewed by 3901

Abstract

Branch dieback and tree decline have been described as a common complex disease worldwide in woody crops, with Botryosphaeriaceae and Diaporthaceae being considered the most frequent fungi associated with the disease symptoms. Their behaviour is still uncertain, since they are considered endophytes becoming pathogenic in weakened hosts when stress conditions, such as water deficiency occur. Therefore, the main goal of this study was to determine if water stress enhances general decline on weakened almond trees subjected to different irrigation treatments under natural field conditions. In parallel, the occurrence of fungal species associated with almond decline was also determined in relation to disease progression by fungal isolation, and morphological and molecular based-methods. The symptoms of branch dieback and general decline were observed over time, mainly in the experimental plots subjected to high water deficiency. Botryosphaeriaceae were the most consistently isolated fungi, and Botryosphaeria dothidea was the most frequent. Collophorina hispanica was the second most frequent species and Diaporthe and Cytospora species were isolated in a low frequency. Most of them were recovered from both asymptomatic and symptomatic trees, with their consistency of isolation increasing with the disease severity. This work reveals the need to elucidate the role of biotic and abiotic factors which increase the rate of infection of fungal trunk pathogens, in order to generate important knowledge on their life cycle. Full article

(This article belongs to the Special Issue Decline of Mediterranean Fruit Crops and Forests Associated with Fungal Trunk Pathogens)

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20 pages, 3859 KiB

Open AccessArticle

A Survey of Trunk Disease Pathogens within Citrus Trees in Iran

by Nahid Espargham, Hamid Mohammadi and David Gramaje

Plants 2020, 9(6), 754; https://doi.org/10.3390/plants9060754 - 16 Jun 2020

Cited by 30 | Viewed by 6196

Abstract

Citrus trees with cankers and dieback symptoms were observed in Bushehr (Bushehr province, Iran). Isolations were made from diseased cankers and branches. Recovered fungal isolates were identified using cultural and morphological characteristics, as well as comparisons of DNA sequence data of the nuclear ribosomal DNA-internal transcribed spacer region, translation elongation factor 1α, β-tubulin, and actin gene regions. Dothiorella viticola, Lasiodiplodia theobromae, Neoscytalidium hyalinum, Phaeoacremonium (P.) parasiticum, P. italicum, P. iranianum, P. rubrigenum, P. minimum, P. croatiense, P. fraxinopensylvanicum, Phaeoacremonium sp., Cadophora luteo-olivacea, Biscogniauxia (B.) mediterranea, Colletotrichum gloeosporioides, C. boninense, Peyronellaea (Pa.) pinodella, Stilbocrea (S.) walteri, and several isolates of Phoma, Pestalotiopsis, and Fusarium species were obtained from diseased trees. The pathogenicity tests were conducted by artificial inoculation of excised shoots of healthy acid lime trees (Citrus aurantifolia) under controlled conditions. Lasiodiplodia theobromae was the most virulent and caused the longest lesions within 40 days of inoculation. According to literature reviews, this is the first report of L. theobromae and N. hyalinum on citrus in Iran. Additionally, we report several Phaeoacremonium species, S. walteri, Pa. pinodella and C. luteo-olivacea on citrus trees for the first time in the world. Full article

(This article belongs to the Special Issue Decline of Mediterranean Fruit Crops and Forests Associated with Fungal Trunk Pathogens)

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17 pages, 4120 KiB

Open AccessArticle

Macrophomina Crown and Root Rot of Pistachio in California

by Mohamed T. Nouri, Daniel P. Lawrence, Craig E. Kallsen and Florent P. Trouillas

Plants 2020, 9(2), 134; https://doi.org/10.3390/plants9020134 - 21 Jan 2020

Cited by 12 | Viewed by 6377

Abstract

In this study, declining pistachio rootstocks were detected in newly planted commercial pistachio orchards in Kern County, California. Symptoms were characterized by wilted foliage combined with crown rot in the rootstock. From diseased trees, 42 isolates were obtained, and all had similar cultural and morphological characteristics of Macrophomina phaseolina. Analyses of nucleotide sequences of three gene fragments, the internal transcribed spacer region (ITS1–5.8S–ITS2), partial sequences of β-tubulin, and translation elongation factor 1-α (TEF1) confirmed this identification, and 20 representative isolates are presented in the phylogenetic study. Testing of Koch’s postulates showed that M. phaseolina, when inoculated to stems and roots of the pistachio rootstocks using mycelial plugs or a microsclerotial suspension, is indeed pathogenic to this host. The widely used clonal University of California Berkeley I (UCBI) rootstock appeared highly susceptible to M. phaseolina, suggesting that this pathogen is an emerging threat to the production of pistachio in California. This study confirmed the association of M. phaseolina with the decline of pistachio trees and represents the first description of this fungus as a crown rot-causing agent of pistachio in California. Full article

(This article belongs to the Special Issue Decline of Mediterranean Fruit Crops and Forests Associated with Fungal Trunk Pathogens)

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19 pages, 1840 KiB

Open AccessArticle

Exhibition of Local but Not Systemic Induced Phenolic Defenses in Vitis vinifera L. Affected by Brown Wood Streaking, Grapevine Leaf Stripe, and Apoplexy (Esca Complex)

by Piebiep Goufo, Ana C. Marques and Isabel Cortez

Plants 2019, 8(10), 412; https://doi.org/10.3390/plants8100412 - 14 Oct 2019

Cited by 11 | Viewed by 4499

Abstract

Balance between constitutive and induced responses provides plants flexibility to cope with biotic stresses. This study tested the hypothesis that invasion of grapevine wood by esca-associated fungi induces the production of defensive compounds as part of locally- and systemically-induced responses. In a vineyard, different symptomatic expressions of “Esca complex” in Vitis vinifera L. ‘Malvasia’ were evaluated in annual inspections. Then, levels of phenolics and fatty acids were determined in asymptomatic leaves of brown wood streaking (BWS) and grapevine leaf stripe (GLSD) vines, and in symptomatic leaves of GLSD and apoplectic vines; the results were compared with levels in healthy vines. In asymptomatic leaves of BWS and some GLSD vines, levels of phenolics decreased, independent of the total phenolic group. Such responses were usually associated with an increase in levels of linoleic, γ-linolenic and arachidonic acids, well-known signal transduction mediators. In symptomatic leaves, levels of phenolics increased, which is consistent with a locally-induced response; the onset of symptoms coincided with the highest increases e.g., 35% for quercetin-3-O-glucuronide. Thus, the long latency period between trunk invasion by fungi and visible foliar damage and the year-to-year fluctuation in symptomatic expressions observed with “Esca complex” might be partially attributed to a better utilization of constitutive defenses. Full article

(This article belongs to the Special Issue Decline of Mediterranean Fruit Crops and Forests Associated with Fungal Trunk Pathogens)

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