Limited Evidence for Accumulation of Latent Infections of Canker-Causing Pathogens in Shoots of Stone Fruit and Nut Crops in California

Abstract

Prevalence of latent infections of the canker-causing fungi Botryosphaeria dothidea and species of Cytospora, Diplodia, Lasiodiplodia, Neofusicoccum, and Phomopsis in young shoots of almond, prune and walnut trees in California was studied to test the hypotheses that 1) latent infections accumulate from current-season shoots to 1-year-old shoots in the orchard and 2) there are distinct associations among pathogen taxa present as latent infections in the same shoot. Samples of newly-emerged and 1-year-old shoots were periodically collected in each almond, prune, and walnut orchard for two growing seasons. A real-time quantitative PCR assay was used to quantify latent infection with three parameters: incidence, molecular severity and latent infection index. Diplodia spp. were absent from most samples. For almond, Lasiodiplodia spp. and Cytospora spp. were detected with a maximum incidence >90%, while B. dothidea and Neofusicoccumspp. incidence was <20% in most cases. In prune orchards, the incidence levels of B. dothidea were >50% in most cases, while those of Cytospora spp. and Lasiodiplodia spp. were 30 - 60% and 30 - 100%, respectively. For walnut, many samplings showed higher incidence in 1-year-old (30 – 80%) than in newly-emerged shoots (10 – 50%). Accumulation of latent infection between the two shoot age classes was detected in only few cases. The percentages of samples showing coexistence of two, three and four pathogen taxa in the same shoot were 20 – 25%, <10% and <5%, respectively. Pairwise associations among pathogen taxa in the same shoot were significant in many cases.

Exploring the Efficacy of Biocontrol Microbes against the Fungal Pathogen Botryosphaeria dothidea JNHT01 Isolated from Fresh Walnut Fruit

“…dothidea is one of the main pathogens for controlling postharvest diseases of walnut. This species frequently infects wounds on young almond and mature walnut and can be found year-round on diseased branches [ 15 ]. Hence, this fungus has been isolated from a large number of blighted shoots of walnut and causes walnut canker [ 8 ].…”

“…Branch dieback, brown blight, and canker diseases caused by Bot. dothidea were widely observed in walnut trees all over the world, including China [ 8 ], Turkey [ 12 ], South Korea [ 13 ], Japan [ 14 ], and the USA [ 15 ], etc. In order to effectively reduce postharvest decay and extend the storage time, preservation technologies should be proposed to inactivate mold fungi, especially Bot.…”

A New Disease for Europe of Ficus microcarpa Caused by Botryosphaeriaceae Species

“…From this and previous studies conducted in Sicily, it emerged that Botryosphaeriaceae spp., and especially the species described in this study, are easily encountered in different hosts and landscapes. Regarding the ecology of these fungi, it is well known that they are also endophytes on many hosts [ 11 ], often coexisting in the same tissues [ 39 ] and forming long latent infections [ 40 , 41 ]. This must be taken into serious consideration, since many infections can spread from nurseries (as latent infections) to open fields.…”

Potential Role of Biocontrol Agents for Sustainable Management of Fungal Pathogens Causing Canker and Fruit Rot of Pistachio in Italy

“…Most of the canker-pathogens, such as Botryosphaeriaceae spp. occur in complexes [ 19 ], and produce spores in flask-like structures, both asexual (pycnidia) or sexual (pseudothecia) embedded in the outer layers of the infected host tissue, making the penetration of the fungicides difficult [ 12 , 13 ]. Although many bioformulates have been tested among different key pathogens in pre-and postharvest, few studies are available regarding biological control of pistachio diseases.…”