Search

Aim: We assessed the effect of exposing apple orchard soil to different temperatures and CO2 levels on the resident microbiome of soils from a conventionally managed and an organically managed apple orchard. The key difference between these two orchards was that synthetic fertilizers and pesticides are routinely used in the former one., Methods and Results: To investigate the effect of CO2 and temperature, soil samples from each site at two depths were exposed to either elevated temperature (29°C) at either 5000 or 10 000 ppm for five weeks or control conditions (25°C + 400 ppm). Both bacterial and fungal communities were profiled with amplicon-sequencing. The differences between the two orchards were the most significant factor affecting the bacterial and fungal communities, contributing to 53.7-14.0% of the variance in Bray-Curtis β diversity, respectively. Elevated CO2 concentration and increased temperature affected organic orchard microbial diversity more than the conventionally managed orchard. A number of candidate beneficial and pathogenic microorganisms had differential abundances when temperature and CO2 were elevated, but their effect on the plant is unclear., Conclusions: This study has highlighted that microbial communities in bulk soils are most significantly influenced by crop management practices compared to the climate conditions used in the study. The studied climate conditions had a more limited effect on microbial community diversity in conventionally managed soil samples than in organically managed soils., (© The Author(s) 2023. Published by Oxford University Press on behalf of Applied Microbiology International.)

Botryosphaeria dothidea causes severe disease of apple trees in China. The process of conidium germination, colonization, and infection of apple fruit and branches was examined on 'Fuji' apple and the effect of temperature, surface wetness and relative humidity (RH), and host surface washates on these processes was studied in controlled environments. Initial germ tube development and hyphal growth resulted in the colonization of the host surface without forming an infection structure. Hyphae expanded radially across the host surface and, after entering lenticels, developed into a dense mycelium mass or differentiated pseudoparenchyma. Hyphae from the bottom of the pseudoparenchyma either directly penetrated the lenticel surface intercellularly through the cell layer, or formed an undifferentiated hypha that invaded the lenticel through cracks formed during the lenticel development. Conidial germination and hyphal colonization occurred at 10 to 40°C, with an optimum of approximately 28°C. Conidial germination required an RH > 95% or surface wetness but, for hyphal colonization, an RH > 90% was sufficient. Conidia germinated and formed germ tubes within 1 h under optimum conditions. However, the pathogen required a longer period at RH > 90% or surface wetness for hyphae to colonize and form pseudoparenchyma or dense mycelia on the host surface. Hyphal colonization is a crucial stage for infection of apple tissues by B. dothidea .

Pollinators face multiple pressures and there is evidence of populations in decline. As demand for insect-pollinated crops increases, crop production is threatened by shortfalls in pollination services. Understanding the extent of current yield deficits due to pollination and identifying opportunities to protect or improve crop yield and quality through pollination management is therefore of international importance. To explore the extent of "pollination deficits," where maximum yield is not being achieved due to insufficient pollination, we used an extensive dataset on a globally important crop, apples. We quantified how these deficits vary between orchards and countries and we compared "pollinator dependence" across different apple varieties. We found evidence of pollination deficits and, in some cases, risks of overpollination were even apparent for which fruit quality could be reduced by too much pollination. In almost all regions studied we found some orchards performing significantly better than others in terms of avoiding a pollination deficit and crop yield shortfalls due to suboptimal pollination. This represents an opportunity to improve production through better pollinator and crop management. Our findings also demonstrated that pollinator dependence varies considerably between apple varieties in terms of fruit number and fruit quality. We propose that assessments of pollination service and deficits in crops can be used to quantify supply and demand for pollinators and help to target local management to address deficits although crop variety has a strong influence on the role of pollinators., (© 2021 The Authors. Ecological Applications published by Wiley Periodicals LLC on behalf of Ecological Society of America.)

European apple canker, caused by Neonectria ditissima, is a severe disease of apple. Achieving effective control is difficult with the currently available pesticides. Specific apple endophytes associated with cultivars may partially contribute to the cultivar response to the pathogen and thus could be used for disease management. We sought to determine whether the overall endophyte community differed among cultivars differing in their susceptibility to N. ditissima and to identify specific microbial groups associated with the susceptibility. Using Illumina MiSeq meta-barcoding, we profiled apple tree endophytes in 16 scion-rootstock combinations at two locations and quantified the relative contribution of scion, rootstock and location to the observed variability in the endophyte communities. Endophyte diversity was primarily affected by the orchard location (accounting for 29.4% and 85.9% of the total variation in the PC1 for bacteria and fungi, respectively), followed by the scion genotype (24.3% and 19.5% of PC2), whereas rootstock effects were small (<3% of PC1 and PC2). There were significant differences in the endophyte community between canker-resistant and -susceptible cultivars. Several bacterial and fungal endophyte groups had different relative abundance between susceptible and resistant cultivars. These endophyte groups included putative pathogen antagonists as well as plant pathogens. Their possible ecological roles in the N. ditissima pathosystem are discussed., (© The Author(s) 2021. Published by Oxford University Press on behalf of FEMS.)

Until recently, the causal agent of Botryosphaeria canker was assumed to differ from that causing ring rot on fruit and warts on branches on apple trees in China and East Asia. However, recent research documented that Botryosphaeria dothidea caused both disease symptoms on apple. Inoculations with strains isolated from cankers and warts on branches were conducted to investigate symptom progression caused by B. dothidea and conditions inducing the two symptom types. The results confirmed that both cankers and warts are caused by B. dothidea. Warts are the results of hyperplasia and suberization of bark tissues induced by fungal infection, whereas cankers result from the rapid growth of hyphae from inside warts, lenticels, or wounds. Resistance to B. dothidea exists in living apple branches. When a living branch is infected via lenticels, the pathogen induces proliferation and suberization of cortical cells that restricts the growth and expansion of the hyphae, leading to warts. However, under certain stress conditions such as drought, the hyphae inside host tissues expand rapidly and kill cortical cells, leading to canker development. Host resistance may recover during active growth periods, which suppresses or even stops rapid expansion of the hyphae, leading to the intermediate symptom of canker warts. Abiotic factors, such as drought or high temperature in early spring, can result in rapid extension of colonized hyphae in branches and conversion of warts to cankers. Preventing this transition can be an important measure in managing Botryosphaeria canker on apple.

Botryosphaeria dothidea is a fungal pathogen causing canker, dieback, and fruit rot of apple trees worldwide. Ascospores are an important source of inoculum of Botryosphaeria canker in China. Experiments were conducted under both controlled and natural conditions to study perithecium formation in relation to environmental conditions. Perithecia of B. dothidea were detected on cankered lesions throughout the apple growing season except in July and in some years including August under natural conditions. On newly formed canker lesions, the first perithecium was detected as early as August, about 1 week after rainfall. Perithecia matured successively, lasting from early August to June of the next year, with a peak in late September or early October. Temperature and rainfall are two key environmental factors affecting perithecium formation. Under controlled conditions, perithecia were produced only on cankered shoots incubated at test temperatures of 20 and 25°C and wetted by >3 days of simulated rainfall per week. The number of perithecia produced on canker lesions increased with the increase in rainfall duration. Perithecia were formed on canker shoots exposed to rainfall only in June, July, and August but not in September. Rainfall of >3 days per week can be used to predict the initial formation of perithecia in the main apple production areas in China to assist disease management.

Apple scab, caused by Venturia inaequalis , is a major fungal disease worldwide. Cultivation of scab-resistant cultivars would reduce the chemical footprint of apple production. However, new apple cultivars carrying durable resistances should be developed to prevent or at least slow the breakdown of resistance against races of V. inaequalis . One way to achieve durable resistance is to pyramid multiple scab resistance genes in a cultivar. The choice of the resistance genes to be combined in the pyramids should take into account the frequency of resistance breakdown and the geographical distribution of apple scab isolates able to cause such breakdowns. In order to acquire this information and to make it available to apple breeders, the VINQUEST project (www.vinquest.ch) was initiated in 2009. Ten years after launching this project, 24 partners from 14 countries regularly contribute data. From 2009 to 2018, nearly 9,000 data points have been collected. This information has been used to identify the most promising apple scab resistance genes for developing cultivars with durable resistance, which to date are: Rvi5 , Rvi11 , Rvi12 , Rvi14 , and Rvi15. As expected, Rvi1 , together with Rvi3 and Rvi8 , were often overcome, and have little value for scab resistance breeding. Rvi10 may also belong to this group. On the other hand, Rvi2 , Rvi4 , Rvi6 , Rvi7 , Rvi9 , and Rvi13 are still useful for breeding, but their use is recommended only in extended pyramids of ≥3 resistance genes.

Tetranychus urticae is a widespread polyphagous mite, found on a variety of fruit crops. Tetranychus urticae feeds on the underside of the leaves perforating plant cells and sucking the cell contents. Foliar damage and excess webbing produced by T. urticae can reduce fruit yield. Assessments of T. urticae populations while small provide reliable and accurate ways of targeting control strategies and recording their efficacy against T. urticae. The aim of this study was to evaluate four methods for extracting low levels of T. urticae from leaf samples, representative of developing infestations. These methods were compared to directly counting of mites on leaves under a dissecting microscope. These methods were ethanol washing, a modified paraffin/ethanol meniscus technique, Tullgren funnel extraction and the Henderson and McBurnie mite brushing machine with consideration to: accuracy, precision and simplicity. In addition, two physically different leaf morphologies were compared; Prunus leaves which are glabrous with Malus leaves which are setaceous. Ethanol extraction consistently yielded the highest numbers of mites and was the most rapid method for recovering T. urticae from leaf samples, irrespective of leaf structure. In addition the samples could be processed and stored before final counting. The advantages and disadvantages of each method are discussed in detail.

Background: The amount and structure of genetic diversity in dessert apple germplasm conserved at a European level is mostly unknown, since all diversity studies conducted in Europe until now have been performed on regional or national collections. Here, we applied a common set of 16 SSR markers to genotype more than 2,400 accessions across 14 collections representing three broad European geographic regions (North + East, West and South) with the aim to analyze the extent, distribution and structure of variation in the apple genetic resources in Europe., Results: A Bayesian model-based clustering approach showed that diversity was organized in three groups, although these were only moderately differentiated (FST = 0.031). A nested Bayesian clustering approach allowed identification of subgroups which revealed internal patterns of substructure within the groups, allowing a finer delineation of the variation into eight subgroups (FST = 0.044). The first level of stratification revealed an asymmetric division of the germplasm among the three groups, and a clear association was found with the geographical regions of origin of the cultivars. The substructure revealed clear partitioning of genetic groups among countries, but also interesting associations between subgroups and breeding purposes of recent cultivars or particular usage such as cider production. Additional parentage analyses allowed us to identify both putative parents of more than 40 old and/or local cultivars giving interesting insights in the pedigree of some emblematic cultivars., Conclusions: The variation found at group and subgroup levels may reflect a combination of historical processes of migration/selection and adaptive factors to diverse agricultural environments that, together with genetic drift, have resulted in extensive genetic variation but limited population structure. The European dessert apple germplasm represents an important source of genetic diversity with a strong historical and patrimonial value. The present work thus constitutes a decisive step in the field of conservation genetics. Moreover, the obtained data can be used for defining a European apple core collection useful for further identification of genomic regions associated with commercially important horticultural traits in apple through genome-wide association studies.