Assessment of a Postharvest Treatment with Pyrimethanil via Thermo-Nebulization in Controlling Storage Rots of Apples

Apples are very susceptible to infections from various fungal pathogens during the growing season due to prolonged exposure to environmental influences in the field. Therefore, a strict and targeted fungicide strategy is essential to protect fruit and trees. Increased environmental and health concerns and pathogen resistance have resulted in a rising demand to reduce fungicide usage and residues on marketed fruit. Thus, producers must develop new plant protection strategies to conform to the legal and social demands while still offering high-quality apples. This study assessed the efficacy of a post-harvest fungicide treatment with pyrimethanil via thermo-nebulization for controlling storage rots and compared the results to those of standard pre-harvest fungicide strategies. The results showed that a single post-harvest application of pyrimethanil successfully controlled storage rots and is comparable to strategies using multiple pre-harvest fungicide applications. The control of fungal rot was sustained even after 5 months of storage and 2 weeks of shelf life. Thermo-nebulization into the storage facility allowed for a lower dosage of fungicide to be used compared to pre-harvest applications, while still maintaining optimal rot control. Residue analyses showed that the post-harvest fungicide treatment did not exceed legal or retailer’s standards.

Diplodia seriata (grapevine trunk disease).

Diplodia seriata is a cosmopolitan and plurivorous fungal species occurring on woody hosts belonging to many plant genera and families (Punithalingam and Waller, 1973; Phillips et al., 2007; Slippers et al., 2007). The fungus is encountered in many habitats, but has a primarily temperate distribution and is present on most continents. D. seriata causes canker, dieback, fruit rot and leaf spot diseases on economically important forest and horticultural species (Farr and Rossman, 2020). Reports of the virulence of this pathogen vary depending upon the crop, varieties and hosts involved and it is often regarded as a stress-related pathogen taking advantage of weak or stressed plants. In common with other members of the Botryosphaeriaceae, D. seriata is capable of living endophytically inside plants (Crous et al., 2006; Slippers and Wingfield, 2007) and latent infections of fruits can result in storage rots. The pathogen is dispersed through both pycnidia and ascospores with conidia regarded as the most important inoculum source for short-distance spread. Infection is through wounds, natural openings, or direct penetration of the host tissue. There is no evidence that this species is seedborne although some members of the Botryosphaeriaceae have been shown to be present in seeds (Gure et al., 2005). The extensive host range of this species means that it is more likely to become established in new areas, as establishment will not depend on the presence of specific hosts. The widespread distribution of this species is presumably as a result of the word-wide movement agricultural, forestry and ornamental plants.

Diplodia seriata (grapevine trunk disease).

Diplodia seriata is a cosmopolitan and plurivorous fungal species occurring on woody hosts belonging to many plant genera and families (Punithalingam and Waller, 1973; Phillips et al., 2007; Slippers et al., 2007). The fungus is encountered in many habitats, but has a primarily temperate distribution and is present on most continents.D. seriata causes canker, dieback, fruit rot and leaf spot diseases on economically important forest and horticultural species (Farr and Rossman, 2020). Reports of the virulence of this pathogen vary depending upon the crop, varieties and hosts involved and it is often regarded as a stress-related pathogen taking advantage of weak or stressed plants. In common with other members of the Botryosphaeriaceae, D. seriata is capable of living endophytically inside plants (Crous et al., 2006; Slippers and Wingfield, 2007) and latent infections of fruits can result in storage rots. The pathogen is dispersed through both pycnidia and ascospores with conidia regarded as the most important inoculum source for short-distance spread. Infection is through wounds, natural openings, or direct penetration of the host tissue. There is no evidence that this species is seedborne although some members of the Botryosphaeriaceae have been shown to be present in seeds (Gure et al., 2005). The extensive host range of this species means that it is more likely to become established in new areas, as establishment will not depend on the presence of specific hosts. The widespread distribution of this species is presumably as a result of the word-wide movement agricultural, forestry and ornamental plants.

Review of the Impact of Apple Fruit Ripening, Texture and Chemical Contents on Genetically Determined Susceptibility to Storage Rots

Fungal storage rots like blue mould, grey mould, bull’s eye rot, bitter rot and brown rot destroy large amounts of the harvested apple crop around the world. Application of fungicides is nowadays severely restricted in many countries and production systems, and these problems are therefore likely to increase. Considerable variation among apple cultivars in resistance/susceptibility has been reported, suggesting that efficient defence mechanisms can be selected for and used in plant breeding. These are, however, likely to vary between pathogens, since some fungi are mainly wound-mediated while others attack through lenticels or by infecting blossoms. Since mature fruits are considerably more susceptible than immature fruits, mechanisms involving fruit-ripening processes are likely to play an important role. Significant associations have been detected between the susceptibility to rots in harvested fruit and various fruit maturation-related traits like ripening time, fruit firmness at harvest and rate of fruit softening during storage, as well as fruit biochemical contents like acidity, sugars and polyphenols. Some sources of resistance to blue mould have been described, but more research is needed on the development of spore inoculation methods that produce reproducible data and can be used for large screenings, especially for lenticel-infecting fungi.

Effect of Environment and Sugar Beet Genotype on Root Rot Development and Pathogen Profile During Storage

Storage rots represent an economically important factor impairing the storability of sugar beet by increasing sucrose losses and invert sugar content. Understanding the development of disease management strategies, knowledge about major storage pathogens, and factors influencing their occurrence is crucial. In comprehensive storage trials conducted under controlled conditions, the effects of environment and genotype on rot development and associated quality changes were investigated. Prevalent species involved in rot development were identified by a newly developed microarray. The strongest effect on rot development was assigned to environment factors followed by genotypic effects. Despite large variation in rot severity (sample range 0 to 84%), the spectrum of microorganisms colonizing sugar beet remained fairly constant across all treatments with dominant species belonging to the fungal genera Botrytis, Fusarium, and Penicillium. The intensity of microbial tissue necrotization was strongly correlated with sucrose losses (R2 = 0.79 to 0.91) and invert sugar accumulation (R2 = 0.91 to 0.95). A storage rot resistance bioassay was developed that could successfully reproduce the genotype ranking observed in storage trials. Quantification of fungal biomass indicates that genetic resistance is based on a quantitative mechanism. Further work is required to understand the large environmental influence on rot development in sugar beet.

Control of sooty blotch and black rot of apple through removal of fruit mummies

Several popular apple cultivars retain their aborted fruits as mummies on the tree. In laboratory conditions, overwintered fruit mummies collected from a Northern German apple orchard under organic management released inoculum, which caused black rot due to Diplodia seriata and sooty blotch due to Peltaster cerophilus on ripe apples. In a field trial conducted over four years in another organic orchard, the manual removal of fruit mummies in winter and again in late June of each year significantly reduced the incidence of both these diseases. However, fruit mummy removal did not significantly affect the development of storage rots due to Neofabraea alba and N. perennans. The potential, limitations and costs of this phytosanitary measure are discussed in the context of organic apple production.