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

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.

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

Silverleaf is an important trunk disease of fruit crops, like Japanese plum. It is known that Chondrostereum purpureum produces wood discoloration, leaves silvering and tree decline, however, the information about the effects on fruit production is scarce. Therefore, the objectives of this study were to determine C. purpureum pathogenicity on Prunus salicina and 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 plating wood sections from the necrosis margin on culture media. Isolates colonies morphological and molecular characteristics accorded to C. purpureum (98%). Representative isolates were inoculated on 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, water potential, and fruit yield and quality were measured in healthy and Silverleaf diseased plum plants cv. ‘Angeleno’. Water potential was altered on diseased trees, and their yield was reduced in 51% (2019) and 41% (2020), compared to fruit from healthy plants. 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.

Managing orchard pathogens and disorders.

This chapter provides information on the various pathogens causing damage to cherry production, such as Pseudomonas syringae pv. syringae, Podosphaera clandestina, Chondrostereum purpureum and Little cherry virus 1 and 2, among others. Details on their symptoms, transmission and disease cycle are discussed and the efficacy of various methods in their management are pointed out.

Role and function of Chondrostereum purpureum in biocontrol of trees

A decay fungus, Chondrostereum purpureum (Pers. Ex Fr.) Pouzar, has been investigated in Europe, Northern America and New Zealand for its ability to decay hardwood stumps and thus prevent sprouting. The aim of these investigations has been to find an alternative to mechanical (cutting only) and chemical sprout control (cutting and applying chemicals to stumps in order to prevent sprouting). Mechanical sprout control is not an efficient option due to hardwood tree species’ ability to re-sprout efficiently after cutting, and therefore management costs are high. Chemicals would be efficient but due to their harmful effects on the environment, alternatives are needed. The fungal treatment, i.e., cutting accompanied with C. purpureum inoculum is an environmentally friendly and efficient option for sprout control. This mini-review comprises the role and function of C. purpureum in biocontrol of trees: the ecology of C. purpureum, its sprout control efficacy, factors affecting sprout control efficacy, devices in biological sprout control, potential risks, and the future perspectives of biological sprout control. Key points • A fungus Chondrostereum purpureum is efficient in preventing sprouting of hardwoods • C. purpureum is not sensitive to environmental conditions • Devices should be developed for cost-efficient biological sprout control

A PCR-Based Method for the Rapid Detection of Chondrostereum purpureum in Apple

Silverleaf caused by the basidiomycete Chondrostereum purpureum affects numerous woody species, including fruit tree crops like apple, resulting in wood necrosis and foliar silvering. There are no curative alternatives for this disease, and its management is by prevention methods. Therefore, the aim of this study was to develop a rapid diagnostic tool for the detection and identification of C. purpureum directly from woody tissues to help distinguish the pathogen from other basidiomycetes that are commonly found on apple. The silverleaf pathogen was isolated from different hosts and locations, and Koch’s postulates were performed by inoculating the isolates on apple cuttings and measuring internal necrosis. A previously described APN 1 pair of primers specificity was also tested against 25 C. purpureum isolates in this study, using other wood rotting species as negative controls. Seven virulent isolates were inoculated on apple cuttings, and DNA was extracted from the cuttings’ sawdust and amplified using APN 1, after 22 days of incubation. To prove the efficiency of the method in the field, DNA from healthy nursery plants inoculated with two virulent isolates, and naturally infected plants showing different levels of foliar symptoms, were tested. Presence of the fungus was verified by reisolation on APDA in all assays. Koch’s postulates indicated that all C. purpureum isolates were pathogenic, showing different virulence levels, and APN 1 primers were able to discriminate them from other basidiomycetes. The method was also able to detect C. purpureum from artificially inoculated plants as well as naturally infected ones, demonstrating that the protocol may become a rapid minimally destructive diagnostic tool to detect the pathogen without the need to isolate it from tissues, and thus taking measures to prevent its dissemination.

The efficacy of Chondrostereum purpureum in sprout control of birch during mechanized pre-commercial thinning

The efficacy of mechanized pre-commercial thinning (PCT) done by a lightweight mini-harvester Tehojätkä together with the Chondrostereum purpureum (Pers. ex Fr.) Pouzar fungal treatment (dilutions 1:100, 1:200, 1:400) and control (cutting only) was studied for three years. The efficacy of the fungal treatment was defined as capability to prevent sprouting of birch (Betula pendula Roth. and B. pubescens Ehrh.). The fungal treatment resulted in higher stump mortality and lower number of sprouts but it did not have a clear effect on the maximum height of stump sprouts. However, mortalities obtained in this study (34.1%, 26.8%, and 25.6% for dilutions 1:100, 1:200, and 1:400, respectively) were notably lower compared to previous studies which indicate that the accuracy of the spreading mechanism was not satisfactory. We conclude that it is possible to decrease stump sprouting with the fully mechanized fungal treatment but putting this implementation into practice needs more testing to increase efficacy.