Pathogenic Fungi Diversity of ‘CuiXiang’ Kiwifruit Black Spot Disease during Storage

Kiwifruit black spot disease has become increasingly widespread in many ‘CuiXiang’ kiwifruit plantings regions. This research was aimed at the pathogenic microorganisms of black spot of the ‘CuiXiang’ cultivar. Physiological, morphological and transcriptional characteristics between black spot fruit and healthy fruits were evaluated. Then, it applied a high-throughput internal transcribed spacer (ITS) sequencing to analyze the black spot disease microbial community. The cell structure showed that mycelium was attached to the surface of the kiwifruit through black spot, and that consequently the mitochondria were damaged, starch particles were reduced, and shelf life was shortened. Transcriptome revealed that different genes in kiwifruit with black spot disease were involved in cell wall modification, pathogen perception, and signal transduction. ITS sequencing results described the disease-causing fungi and found that the microbial diversity of black spot-diseased fruit was lower than that of healthy fruit. We predict that candidate pathogenic fungi Cladosporium cladosporioides, Diaporthe phaseolorum, Alternaria alternata, and Trichothecium roseum may cause black spot. This study was to explore the pathogenic fungal community of ‘CuiXiang’ kiwifruit black spot disease and to provide essential information for field prevention.

Mitigating Grapevine Red Blotch Virus Impact on Final Wine Composition

Grapevine red blotch virus (GRBV), the causative agent of red blotch disease, causes significant decreases in sugar and anthocyanin accumulation in grapes, suggesting a delay in ripening events. Two mitigation strategies were investigated to alleviate the impact of GRBV on wine composition. Wines were made from Cabernet Sauvignon (CS) (Vitis vinifera) grapevines, grafted onto 110R and 420A rootstocks, in 2016 and 2017. A delayed harvest and chaptalization of diseased grapes were employed to decrease chemical and sensory impacts on wines caused by GRBV. Extending the ripening of the diseased fruit produced wines that were overall higher in aroma compounds such as esters and terpenes and alcohol-related (hot and alcohol) sensory attributes compared to wines made from diseased fruit harvested at the same time as healthy fruit. In 2016 only, a longer hangtime of GRBV infected fruit resulted in wines with increased anthocyanin concentrations compared to wines made from GRBV diseased fruit that was harvested at the same time as healthy fruit. Chaptalization of the diseased grapes in 2017 produced wines chemically more similar to wines made from healthy fruit. However, this was not supported by sensory analysis, potentially due to high alcohol content masking aroma characteristics.

First Report of Colletotrichum fructicola Causing Anthracnose on Indian Jujube (Ziziphus mauritiana) in Taiwan

Ziziphus mauritiana Lamarck known as Indian jujube is one of the most popular and delicious fruit crops in Taiwan. This crop is mainly planted in southern Taiwan and their fruit are harvested for providing fresh fruit. In March 2015, an anthracnose-like disease was observed on Indian jujube fruit (cv. Candied date) planted in an orchard in Yanchao District (22°46'33" N, 120°21'37" E) in Kaohsiung City. The disease was quickly distributed around the orchard after rain and caused great loss (around 40% of fruit infected). The diseased fruit would completely rot and lose its market value. Symptoms could be observed on all the developmental stages of fruit. On ripe fruit, symptoms were round, brown, water-soaked lesions covered with salmon-colored spore masses. Four fungal isolates from diseased fruit in the same orchard were collected by single spore isolation with hand-made glass needle. They were grown on potato dextrose agar (PDA) at 24 to 28°C with diffused light. All four strains produced white to gray, aerial, and cottony mycelia scattered with abundant salmon-colored conidial mass on the center of the colony on PDA. The conidia were hyaline, single celled, round cylindrical on both ends, thin walled, and the contents guttulate. The sizes of conidia were 15.2 (17.5 to 13.0) × 5.0 (5.5 to 4.5) μm (length/width ratio = 3.03, n = 40). DNA was isolated from JC1 and used for amplification of partial sequences of the internal transcribed spacer (ITS), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), actin (ACT), β-tubulin 2 (TUB2), chitin synthase 1 (CHS-1), manganese-superoxide dismutase (SOD2) and the intergenic region of apn2 and MAT1-2-1 gene (ApMat) genes (Silva et al. 2012; Weir et al. 2012). A BLAST search against the NCBI database revealed that JC1 gene sequences [GenBank accession nos. MT197188 (ITS), MT199871 (GAPDH), MT199872 (ACT), MT199870 (TUB2), MT815918 (CHS-1), MT815919 (SOD2) and MT221653 (ApMat)] displayed 100.0, 100.0, 99.1, 100.0, 99.7, 99.5 and 99.8% nucleotide identity to the respective gene sequences of Colletotrichum fructicola ICMP 18581 (JX010165, JX010033, FJ907426, JX010405, JX009866, JX010327, and JQ807838). Conidial suspension (1 × 106 conidia/mL) was prepared from JC1 isolate of C. fructicola and inoculated by spraying onto detached, ripe, healthy, non-wounded and surface-disinfected jujube fruit (cv. Candied date, n = 4). Four control fruit were sprayed with sterile water. Fruit were kept in a moist chamber (greater than 90% relative humidity, 24 to 28°C) for 24 h and maintained in the lab for additional 5 days. The inoculated fruit initially showed small light-colored spots in 5 to 7 days, which eventually developed into brown, sunken, water-soaked lesions 8 to10 days after inoculation, similar to the symptoms in the orchard. C. fructicola was re-isolated from symptomatic fruit showing similar morphological characteristics to those collected from the field, thus fulfilling Koch’s postulates. No symptom was observed on fruit treated with water and no pathogen was re-isolated. The experiment was performed twice. The JC1 isolate of C. fructicola with the identification number BCRC FU31437 has been deposited at Taiwan Bioresource Collection and Research Center. This pathogen has been found in many plant species in various countries (Weir et al. 2012). To our knowledge, this is the first report of C. fructicola causing Indian jujube fruit anthracnose in Taiwan and worldwide.

Identification, pathogenicity and effects of plant extracts on Neopestalotiopsis and Pseudopestalotiopsis causing fruit diseases

Pestalotiopsis and related genera, including Neopestalotiopsis and Pseudopestalotiopsis have damaged many plants for many decades; however, there is little available information about the fungi on tropical fruit in Thailand. This study isolated and characterized pestalotioid fungi on tropical fruit, investigated host specificity, and screened whether plant extracts could control the fungi. In total, 53 diseased fruit samples were sampled from eight types of fruit trees (jackfruit, rose apple, mangosteen, plum, snake fruit, rambutan, strawberry, and avocado). Based on morphological characteristics, 44 isolates were classified as belonging to pestalotioid taxa. Of these isolates, seven with distinct characteristics were selected for identification using molecular analysis, and six isolates were identified as Neopestalotiopsis and one as Pseudopestalotiopsis. In the cross-inoculation experiment, the isolates exhibited nonhost specificity and could infect at least two host plants. The isolates were used to screen for a potential biocontrol resource using six crude plant extracts (clove, ginger, lemongrass, mangosteen, roselle, and turmeric). All crude extracts except mangosteen could inhibit the growth of Neopestalotiopsis and Pseudopestalotiopsis. Application of crude plant extracts could be a potential treatment to control these diseases on tropical fruit.

Impact of Rootstock and Season on Red Blotch Disease Expression in Cabernet Sauvignon (V. vinifera)

Grapevine red blotch virus (GRBV), the causative agent of grapevine red blotch disease, is widespread across the United States and causes a delay in ripening events in grapes. This study evaluates the effects of GRBV on Cabernet Sauvignon grape berry composition, grafted on two different rootstocks (110R and 420A) in two seasons (2016 and 2017). Total soluble solids, acidity, and anthocyanin concentrations were monitored through ripening and at harvest. Phenolic and volatile compounds were also analyzed at harvest to determine genotypic and environmental influences on disease outcome. Sugar accumulation through ripening was lower in diseased fruit (RB (+)) than healthy fruit across rootstock and season. GRBV impact was larger in 2016 than 2017, indicating a seasonal effect on disease expression. In general, anthocyanin levels and volatile compound accumulation was lower in RB (+) fruit than healthy fruit. Total phenolic composition and tannin content was higher in RB (+) fruit than healthy fruit in only 110R rootstock. Overall, GRBV impacted Cabernet Sauvignon grape composition crafted on rootstock 110R more than those crafted on rootstock 420A.

Under-Vine Vegetation Mitigates the Impacts of Excessive Precipitation in Vineyards

Excessive precipitation events have greatly increased in several grape growing regions due to human-caused climate change. These heavy downpours result in a myriad of problems in the vineyard including soil aggregate breakdown, soil runoff, nutrient leaching, excessive vine vegetative growth, and diseased fruit. The negative impacts of excessive precipitation events on vineyards are exacerbated by the maintenance of bare soil under the vines. Exposure of bare soil results in soil erosion and runoff which pollutes nearby watersheds; raindrops weaken and break apart soil aggregates, leading to increased soil erosivity and contributing to the formation of surface crusts. In addition to excessive precipitation events, some grape growing regions can be characterized by fertile soils. The availability of ample water and nutrients can lead to highly vigorous vines with shoot growth continuing through harvest. Long shoots and large leaves result in shaded fruit, a humid vine microclimate, and excessive cluster rot. In this review, we examined how either natural (i.e., resident) or seeded under-vine vegetation (UVV) can help mitigate many of the problems associated with excessive precipitation. Through providing vegetative coverage to reduce the force of raindrops, increasing soil organic matter and enhancing soil microbial diversity, UVV can reduce the soil degradation and off-site impacts caused by excessive precipitation events. Through competition for soil resources, UVV can reduce excessive vegetative growth of vines and decrease cluster rot incidence and severity, although grapevine response to UVV can be highly variable. We discussed recent advances in understanding below and aboveground vine response and acclimation to UVV and presented current evidence of factors influencing the impact of UVV on vine growth and productivity to assist practitioners in making informed decisions and maximize the ecosystem services provided by UVV.

Identification and Detection of Botryosphaeria dothidea from Kiwifruit (Actinidia chinensis) in China

Kiwifruit is very popular among consumers due to its high nutritional value. The increasing expansion in kiwifruit cultivation has led to the spread of rot diseases. To identify the pathogens causing kiwifruit ripe rots in China, 24 isolates were isolated from the diseased fruit and wart in trees. Botryosphaeria dothidea was recognized as the pathogen causing kiwifruit ripe rot and wart in the tree through internal transcribed spacer (ITS) sequencing, pathogenicity testing, morphological and microscopic characteristics. The rapid and accurate detection of this pathogen will lead to better disease monitoring and control efforts. A loop-mediated isothermal amplification (LAMP) method was then developed to rapidly and specifically identify B. dothidea. These results offer value to further research into kiwifruit ripe rot, such as disease prediction, pathogen rapid detection, and effective disease control.

Spray Volume and Rate Based on the Tree Row Volume for a Sustainable Use of Copper in the Control of Citrus Canker

Copper is the most efficient pesticide for the control of citrus canker (Xanthomonas citri subsp. citri). To mitigate the environmental impacts and costs, the copper sprays in citrus orchards are being optimized based on the tree row volume (TRV). A previous investigation allowed for significant reductions of the spray volume and copper rates. Nevertheless, the results also indicated the need for additional studies. The aim of this work was to assess whether both the spray volume and the metallic copper rate based on the TRV may be further reduced. A field trial was carried out during two seasons in a 3-year-old commercial orchard of Pera sweet orange located in the municipality of Paranavaí, Paraná, Brazil. The volumes of 20 and 40 ml of spray mixture per m3 of the tree canopy were assessed in combination with the metallic copper rates of 10.5, 21.0, 36.8, or 52.5 mg/m3. Disease was measured as the temporal progress of canker incidence on leaves, cumulative dropped fruit with canker, and incidence of diseased fruit at harvest. The quality of sprays was assessed by measuring the copper deposition and leaf coverage. The treatment with the highest citrus canker control for the lowest use of water and copper was the combination of 40 ml and 36.8 mg/m3. Regression analyses indicated that the minimum threshold deposition of copper was ∼1.5 µg Cu2+/cm2 leaf area. In addition, the lowest spray volume and copper rate necessary to achieve this deposition are 35 ml/m3 and 30 mg/m3. The use of 20 ml/m3 did not efficiently control the disease due to the deficient coverage of treated surfaces. This study demonstrated that it is possible to use even lower amounts of copper and water without interfering with the efficiency of control of citrus canker.

The Effect of Erwinia amylovora Infection in Apple Saplings and Fruit on the Behavior of Delia platura (Diptera: Anthomyiidae)

The Vector Manipulation Hypothesis (VMH) posits that phytopathogens develop strategies to enhance dissemination by mediating behavior change in insect vectors. The VMH is poorly studied in phytopathogenic bacteria, especially in systems with numerous, occasional vectors. Erwinia amylovora is a bacterial pathogen of pome fruit that produces a bacterial ooze and is mechanically vectored by insects after they feed on ooze. The blossom blight phase of the disease exhibits manipulation of honeybees, leading to enhanced transmission, but whether the same occurs during the shoot blight phase of the disease is unknown. The goal of this study was to evaluate the effect of E. amylovora on the behavior of Delia platura, a fly with a worldwide endemic presence that may transmit E. amylovora. We show that D. platura prefer infected, oozing fruit to uninfected fruit in choice tests and that preference subsides when bacterial ooze is removed from the infected fruit. Flies did not exhibit a preference between infected saplings and uninfected saplings. The volatiles of infected fruit did not attract D. platura, indicating that diseased fruit odor is not responsible for the observed preference for infected fruit. Flies did not differentiate between sapling odors until infected trees had died, at which point they preferred uninfected tree odors. This study supports previous hypotheses suggesting that E. amylovora takes advantage of existing plant–insect interactions, though it is not fully understood how significantly behavioral changes affect transmission. Additional pathosystems with occasional, nonspecific vectors should be studied to further understanding of the VMH.

Characterization of Botrytis cinerea and B. prunorum from Healthy Floral Structures and Decayed ‘Hayward’ Kiwifruit During Post-Harvest Storage

Gray mold is the primary post-harvest disease of ‘Hayward’ kiwifruit (Actinidia deliciosa) in Chile, with a prevalence of 33.1% in 2016 and 7.1% in 2017. Gray mold develops during postharvest storage, which is characterized by a soft, light to brown watery decay that is caused by Botrytis cinerea and B. prunorum. However, there is no information related to the role of B. prunorum during the development and storage of kiwifruit in Chile. For this purpose, asymptomatic flowers and receptacles were collected throughout fruit development and harvest from five orchards over two seasons in the Central Valley of Chile. Additionally, diseased kiwifruits were selected after storage for 100 days at 0°C plus 2 days at 20° C. High (HCP) and low conidial production (LCP) colonies of Botrytis sp. were consistently obtained from apparently healthy petals, sepals, receptacles, styles, and diseased kiwifruit. Morphological and phylogenetic analysis using three partial gene sequences encoding glyceraldehyde-3-phosphate dehydrogenase (G3PDH), heat shock protein 60 (HSP60), and DNA-dependent RNA polymerase subunit II (RPB2) were able to identify and separate B. cinerea and B. prunorum species. Consistently, B. cinerea was predominantly isolated from all floral parts and fruit in apparently healthy tissue and diseased kiwifruit. During full bloom, the highest colonization by B. cinerea and B. prunorum was obtained from petals followed by sepals. In storage, both Botrytis species were isolated from the diseased fruit (n=644), of which 6.8% (n=44) were identified as B. prunorum. All Botrytis isolates grew from 0°C to 30°C in vitro and were pathogenic on kiwifruit leaves and fruit. Notably, B. cinerea isolates were always more virulent than B. prunorum isolates. This study confirms the presence of B. cinerea and B. prunorum colonizing apparently healthy flowers and floral parts in fruit and causing gray mold during kiwifruit storage in Chile. Therefore, B. prunorum plays a secondary role in the epidemiology of gray mold developing in kiwifruit during cold storage.