Infection of apple fruit by Sphaeropsis pyriputrescens in the orchard in relation to Sphaeropsis rot in storage

Sphaeropsis rot, caused by Sphaeropsis pyriputrescens, is an important postharvest disease of apple in the United States. The objectives of this study were to determine the timing of apple fruit infection in the orchard in relation to development of Sphaeropsis rot in storage and to identify infection courts and mode of penetration by S. pyriputrescens on apple fruit. Fruit of apple cvs Red Delicious, Golden Delicious, and Fuji were inoculated in the orchard from 3 weeks after petal fall to 2 weeks before harvest at 5 to 6-week intervals in three consecutive seasons. All fruit were harvested and stored at 0?ºC to monitor decay development. Light and scanning electron microscopy were used to examine the infection courts and mode of penetration of the fungus on/in the host tissues. At harvest, the fungus was re-isolated from the stem (pedicel), sepal, anther, or filament of the inoculated fruit, but decay did not develop on fruit. Sphaeropsis rot developed on inoculated fruit during cold storage beginning 1–3 months after harvest. Stem-end rot was prevalent on cv. Golden Delicious, whereas calyx-end rot was prevalent on cv. Fuji. Both stem- and calyx-end rots were common on cv. Red Delicious. Infection also occurred at lenticels on fruit skin, particularly on cv. Golden Delicious, but at low incidence. Relationships between the incidence of Sphaeropsis rot in stored apple fruit and the timing of inoculation in the orchard varied with cultivar and year. On cv. Red Delicious apples, the incidence of Sphaeropsis rot generally increased as the timing of infection approached harvest. Histological studies indicated that infection took place through natural openings of plant organs such as stomata on stems and sepals and lenticels on fruit skin. Fungal penetration also was observed at micro-cracks on the stem and sepal and at trichome sockets where mechanical damage occurred in sepals. Direct penetration was observed on the stem and sepal of fruit, but most invasions were restricted between the cuticle and the epidermis. Our results indicate that wounding is not required for infection of apple fruit by S. pyriputrescens, though it may facilitate infections.     

Infection criteria,inoculum sources and splash dispersal pattern of <Emphasis Type="Italic">Colletotrichum acutatum</Emphasis> causing bitter rot of apple in New Zealand

Infection of Malus x domestica cv. Royal Gala fruit by Colletotrichum acutatum causing bitter rot was studied in the temperate climate of New Zealand. Temperatures above 15 °C were required for lesions to develop on detached apple wound-inoculated or inoculated without wounding with C. acutatum spores, regardless of maturity. A wetness period of 72 h was required for infection of mature detached apple fruit without wounding. On wound-inoculated detached apple fruits, sporulation was related to temperature and followed a similar pattern. In the field, a mean temperature above 15 °C for 72 h after wound-inoculation was required for lesions to develop. Buds were a more important source of inoculum than twigs, and it was shown that C. acutatum could be isolated more frequently from outer bud scales than from inner scales. Asymptomatic infection of vegetative and reproductive buds was detected. C. acutatum was detected on asymptomic surface-sterilised petals and fruit, more commonly during summer than spring. Symptomless sterilised leaves generally yielded C. acutatum throughout the season, but isolations were more frequent in summer. Recovery of inoculum using a splash meter to detect vertical dispersal showed that in summer inoculum was primarily splashed up from the ground. In spring, inoculum was recovered in similar quantities from all heights up to a metre, suggesting that splash dispersal occurs from the canopy as well as from the ground. A disease cycle for C. acutatum infecting apples and causing bitter rot in New Zealand is suggested.     

Inhibition on brown rot disease and induction of defence response in harvested peach fruit by nitric oxide solution

Nitric oxide (NO) is an important signal molecule involved in numerous plant responses to biotic and abiotic stresses. The effect of nitric oxide (NO) solution on pathogen infection and defence response of peach (Prunus persica (L.) Batsch) fruit against brown rot disease caused by Monilinia fructicola was investigated. The results showed that 15 μmol l^?1 NO solution did not significantly inhibit spore germination, germ tube length or pathogenicity of M. fructicola, but significantly reduced disease incidence and lesion areas in the fruit. Although 100 μmol l^?1 NO solution effectively inhibited the spore germination, germ tube elongation and pathogenicity of M. fructicola, the high concentration of NO solution caused damage to the fruit. Moreover, 15 μmol l^?1 NO enhanced the activities of chitinase (CHI) and β-1,3-glucanase (GNS) in the fruit. RT-PCR analysis showed that the expression of four genes, CHI, GNS, pathogenesis-related protein 1 and 10 genes (PR-1, PR-10) all increased after NO treatment. Conversely, pretreatment with 100 μmol l^?1 NO scavenger, 2-4-carboxyphenyl-4,4,5,5- tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), rendered the fruit relatively susceptible to pathogen infection and inhibited the defence response of the fruit. These results suggest that NO solution treatment can protect peach fruit from pathogen infection by inducing the activities of the defence enzymes and the expression of PR genes.     

Effects of temperature,zoospore concentration,infection period,and fruit maturity on <Emphasis Type="Italic">Phytophthora palmivora</Emphasis> infection of figs

White powdery rot in figs caused by Phytophthora palmivora is an important disease resulting in severe fruit rot, but is not currently effectively controlled in Japan due to a lack of understanding of its epidemiology. Therefore, the effects of temperature, zoospore concentration, infection period, and fruit maturity on infection of figs were examined by inoculating the fruit with a suspension of P. palmivora zoospores. The zoospores germinated at temperatures from 5 to 35 °C, with the optimum temperature range being 20–35 °C. Germ tube length in zoospore cysts was greatest at 20–30 °C. The disease developed in green figs at temperatures from 20 to 30 °C. Figs inoculated with as few as 10 zoospores per fruit developed severe symptoms at the optimum temperature (25 °C). The minimum infection period required for infection was 2 h at 20–28 °C. All of the figs developed symptoms within an 8 h infection period at 25 or 28 °C, and with a 6 h infection period at 25 °C. All fruit at different stages of development (immature fruit, yellow fruit, and mature fruit) developed symptoms. These results indicate that P. palmivora is capable of infecting figs over a wide range of temperatures, within a short infection period, at a low concentration of zoospores, and at any stage of development. These data could be used to construct forecasting models and develop effective control systems for white powdery rot.     

Characterization of a new Apple dimple fruit viroid variant that causes yellow dimple fruit formation in ‘Fuji’ apple trees

A 303-nucleotide viroid was isolated from an apple tree (Malus × domestica, ‘Fuji’) cultivated in Japan. The viroid had 84.9% overall nucleotide sequence homology to Apple dimple fruit viroid (ADFVd), a member of Pospiviroidae, reported from Italy. This viroid differed from the Italian variant by 47 mutations (38 substitutions, six deletions and three insertions), and most of these mutations occurred on either side of the central conserved region. The leaves and branches of the infected trees did not have any disease symptoms, but the fruits were dimpled and yellow. The infected scions were top-grafted onto a healthy ‘Fuji’ apple tree, which tested positive for this viroid in a northern hybridization analysis, and yellow dimple fruits were produced in the second growing season. We propose that this viroid is a new variant of ADFVd and causes yellow dimple fruit formation in ‘Fuji’ apple trees.     

内生放线菌A-1对苹果果实轮纹病的防效及防御性酶活性的影响

为揭示内生放线菌A-1对苹果果实轮纹病的防效及防病机制,采用平板法和喷雾处理刺伤接种法,测定了其对苹果轮纹病菌的抑制作用及果实内防御性酶活性的影响。结果表明：菌株A-1能显著抑制轮纹病菌菌丝生长,10⁴ CFU/mL菌悬液的抑制率达90%以上;喷施10⁷ CFU/mL A-1菌悬液后,间隔12 h以上接种的各处理,3 d和7 d时防效分别为91.79%~95.67%和77.41%~94.00%,均与对照农药苯醚甲环唑相当。喷施10⁷ CFU/mL A-1菌悬液后接种或不接种轮纹病菌的处理,果实内过氧化物酶、过氧化氢酶、多酚氧化酶和苯丙氨酸解氨酶活性显著升高,且均高于只接种轮纹病菌的处理;喷施A-1菌悬液后接种病原菌的处理酶活性增加最显著,其峰值是对照的2.30~11.00倍。表明内生放线菌A-1可通过产生拮抗物质、提高寄主防御性酶活性等机制实现对苹果轮纹病的有效防治。     

Cytology of infection of apple leaves by Diplocarpon mali

Diplocarpon mali, the causal agent of Marssonina leaf blotch of apple, causes severe defoliation during the growing season. Little information is available on the mode of infection and the infection process. In this study, the infection strategies of D. mali in apple leaves were investigated using fluorescence and electron microscopy. Conidia attached to leaf surface apparently by mucilage and germinated on both sides of leaves 6 h post-inoculation (hpi). The pathogen penetrated the cuticle by infection pegs formed either in germ tubes or appressoria in 6 hpi, and then formed haustoria in host epidermal and mesophyll cells accompanied by extension of subcuticular and intercellular hyphae. Five days post-inoculation (dpi), the intracellular hyphae were observed. At the same time, the subcuticular hyphal strands (SHS) were produced as a means for fast expansion and reproduction. About 7 dpi, acervuli formed on inoculated leaves. This was the first observation that D. mali formed haustoria and SHS as infection strategies. Our results suggest that D. mali may behave like a hemibiotroph, which can use both biotrophic and necrotrophic strategies to establish infections on apple leaves.     

The potential of fludioxonil for anthracnose control on China chili fruit

Anthracnose, caused by Colletotrichum scovillei, is one of the most destructive disease which causes massive yield losses in chili. Our preliminary study has demonstrated that fludioxonil had high activity against mycelial growth and spore germination of C. scovillei but it has not been labeled on chili. The aim of this study was to investigate the impact of fludioxonil on C. scovillei infection. In greenhouse and field trials, fludioxonil was applied to chili plants to determine the duration of protection of fruit provided by this compound against chili anthracnose. Fludioxonil may have impact on the early stage of chili anthracnose infection by inhibiting the germ tube elongation and appressorium formation. Moreover, it inhibited the secondary infection of C. scovillei by inhibiting the sporulation, germination of spores and formation of appressoria. Fludioxonil provided high level of protective activity for up to 96 h, as well as excellent curative activity of within 24 h in vivo tests. In field trials, fludioxonil can reduce the incidence and severity of chili anthracnose while giving a higher chili yield. These results suggest that fludioxonil could be a promising fungicide for anthracnose control in chili production.     

Untersuchungen zur Europäischen Steinobstvergilbung (ESFY) in Deutschland

From 2003 to 2007 surveys have been conducted in different stone fruit growing regions in southwest Germany to detect European stone fruit yellows (ESFY) disease in Germany. Samplings have been done regularly in selected reference orchards in the regions Neuwieder Becken, Rheinhessen, Vorderpfalz and Südpfalz in summer on trees showing ESFY typical symptoms as well as on branches of trees with unspecific symptoms. All samples have been analysed by PCR for infection with Candidatus Phytoplasma prunorum. The phytoplasma could be detected in all investigated regions on the cultivated Prunus species P. armeniaca, P. persica and P. domestica. No infection was found in wild Prunus species. The main spread of the disease appeared on apricot while peach and European plum were less affected. A good correlation between symptoms and molecular detection of the pathogen could be shown for the typical symptoms in summer and winter for apricot as well as for peach. During regular psyllid captures in the reference orchards the population dynamics of Cacopsylla pruni could be described in southwest Germany for several years. By PCR-testing all collected insects individually a yearly natural infection rate of about 1–2% of all individuals of C. pruni could be calculated.     

Modified plant architecture to enhance crop disease control: genetic control and possible value of upright fruit position in cucumber

Plant architectural features can facilitate disease control by creating unfavourable environments for pathogen growth or limiting pathogen contact with the host. In the case of Phytophthora capsici infection of cucumber (Cucumis sativus), the susceptible fruit typically lie in contact with soil under warm, moist conditions of a full canopy, an ideal location for exposure to inoculum and disease development. We have shown that increased row spacing, trellising and architectural variants that allow for more open canopies, such as shorter vines, reduced branching, or smaller leaves, can modify microclimate as assessed by temperature at the location of developing fruits. However, only trellising reduced infection rates (<3 % infection vs. 22 % for control). A cucumber accession PI308916, with extremely short internodes and resulting upright position of young fruit, also exhibited reduced disease. Fruit of PI308916 were susceptible when inoculated with P. capsici, indicating that reduced infection likely resulted from decreased soil contact. The compact trait is inherited as a single recessive gene, cp. Like many architectural traits, cp may be pleiotropic; PI308916-derived breeding lines were reported to have poor seedling emergence. PI308916 exhibited inconsistent apical hook formation that co-segregated with short internodes in F₂ and backcross generations, and disorganized internodal cortical cell arrangement. The combined phenotypes suggest either pleiotropy or very tight linkage of genes affecting hormone balance or cell division. The narrow chromosome region recently defined by QTL analysis includes candidate gene homologs of meristem related genes modulating cell division or spacing of lateral shoot organs and genes associated with brassinosteroid signaling or cytokinin content.     

Development of a method for detection of latent European fruit tree canker (<Emphasis Type="Italic">Neonectria ditissima</Emphasis>) infections in apple and pear nurseries

Fruit tree canker caused by Neonectria ditissima is a serious problem in apple-producing regions with moderate temperatures and high rainfall throughout the year; especially in northwestern Europe, Chile, and New Zealand. Control measures are applied to protect primary infection sites, mainly leaf scars, from invasion by external inoculum. However, latent infections may occur when young apple trees are infected symptomlessly during propagation. This study aimed to develop a method for detection of latent fruit tree canker infections. Inoculations with conidiospore suspensions of N. ditissima were carried out in tree nurseries on the main stems of two-year-old trees of three apple cultivars and one pear cultivar. The inoculations were carried out during the natural abscission period in the autumn. No visible lesion or canker formations were present at the time when the inoculated trees were uprooted. It appeared that the infections may remain latent during the period from infection to uprooting (2 months) and during the subsequent 4 months of cold storage of the trees. Nevertheless, symptoms were generally induced within 8 weeks after transfer of infecting planting material from the nursery field into a climate chamber with high temperature and high relative humidity. The methodology presented is developed to detect latent infections of N. ditissima in nursery trees, prior to planting in the orchards, and it may contribute in reducing the problem with European fruit tree canker in commercial production.     

葡萄座腔菌候选效应子抑制了Bax诱导的PCD反应并促进烟草疫霉的侵染

 轮纹病是苹果生产中发生严重又难以防治的病害。为探究致病机理,本研究选择葡萄座腔菌的3个候选效应子进行研究。农杆菌介导的烟草瞬时表达显示,Bdo_01520、Bdo_11198、Bdo_11545都能够完全抑制Bax诱导的烟草PCD反应。酵母分泌系统测试表明3个候选效应子的信号肽都具有外泌活性。qRT-PCR测定候选效应子在葡萄座腔菌ZY7有伤接种苹果果实后的相对表达量,结果显示3个基因在病菌侵染36~72 h上调表达。在本生烟中瞬时表达Bdo_11198显著促进了烟草疫霉的侵染,并降低了疫霉菌侵染后本生烟中活性氧的积累。结果表明,葡萄座腔菌候选效应子可以通过影响植物的PCD反应和过氧化氢积累促进病原菌的侵染,研究结果为进一步研究葡萄座腔菌的致病机制提供了基础。     

<Emphasis Type="Italic">Colletotrichum acutatum</Emphasis> occurs asymptomatically on apple leaves

Fungi within the Colletotrichum acutatum species complex occur asymptomatically on plant parts of many different plant species. Leaves from apple orchards in southern Norway were sampled, frozen for five hours and incubated for six days to reveal presence of asymptomatic infections of C. acutatum. Number of leaves (incidence) and leaf area covered (severity) with conidial masses of C. acutatum were assessed biweekly on cv. Aroma from late May to late September during three growing seasons. The first finding of conidial masses occurred in the second half of July, and there was a higher incidence occurring in August and September. Sampling of leaves from fruit spurs and vegetative shoots of cvs. Aroma and Elstar showed that conidial masses of C. acutatum developed on leaves on both shoot types, and there was no difference in incidence between these two types. The fungus was detected on leaves from six of eight commercial orchards of cv. Aroma over three years, with a mean incidence of 5.5 %. After storage, bitter rot was found on apple fruit from all eight orchards. There was no correlation between incidence of conidial masses of C. acutatum on leaves and on fruit. In all orchards and seasons investigated, incidence and severity on leaves varied from 0 to 67 % and 0 to 85 %, respectively. The discovery of apple leaves containing conidial masses of C. acutatum clearly indicate for leaves as a potential source of inoculum for fruit infections.     

Incidence and etiology of postharvest fungal diseases of loquat fruit (<Emphasis Type="Italic">Eriobotrya japonica</Emphasis> (Thunb.) Lindl. cv. ‘Algerie’) in Alacant province (Spain)

‘Algerie’ is currently the most important loquat cultivar in Spain. The incidence and etiology of postharvest diseases affecting this cultivar were determined under local conditions. Latent and wound pathogens were evaluated for two consecutive seasons on commercially grown loquats from two orchards. Healthy loquats were either surface-disinfected or artificially wounded in the rind and placed in humid chambers at 20 °C for up to 5 weeks. Additionally, decay was assessed on commercially-handled loquats stored at 5 °C for up to 20 weeks. The most frequent disease was caused by Alternaria alternata, followed by Penicillium expansum. These two pathogens were present on fruit assessed for all types of infection. Moreover, decay caused by Botrytis cinerea was abundantly observed on both wounded and cold-stored fruit, while Colletotrichum gloeosporioides was frequently found on surface-disinfected fruit. Other pathogens that were observed causing latent infection to a lesser extent included Pestalotiopsis clavispora and Diplodia seriata. Common isolates were identified by macroscopic and microscopic morphology and/or DNA amplification and sequencing. Pathogenicity of selected isolates was demonstrated by fulfilling Koch’s postulates and disease development was assessed on artificially inoculated loquats stored at either 20 or 5 °C.     

Ulvan effect on conidial germination and appressoria formation of Colletotrichum gloeosporioides

Ulvan is an algal polysaccharide known for its ability to induce resistance to plant diseases such as the Glomerella leaf spot of apple caused by Colletotrichum gloeosporiodes. This study was aimed at investigating microscopically, in tests in vitro and in vivo, whether ulvan interferes in the development of pre-infective structures of C. gloeosporioides. Conidial germination and appressoria formation were monitored hourly on agar and cellophane, and at 48 h on water- and ulvan-treated susceptible as well as resistant apple leaves. Amendment of agar with ulvan (10 mg ml^?1) enhanced the germination and resulted in longer germ tubes at 7 h of incubation. On cellophane it significantly delayed appressoria formation up to 8 h, but later after 14 h increased the number of appressoria per conidium. Spraying of susceptible leaves with ulvan 6 days before inoculation decreased disease severity by 50%. This was associated with inhibition of appressoria formation and stimulus in growth of germ tubes, without interfering with conidial germination, when compared with both water-treated control and resistant plants. Appressorium formation occurred preferentially on anticlinal walls of epidermal cells and its location was not influenced by host resistance or by ulvan treatment. This study suggests a new mode of action for ulvan interfering with appressorium formation that could protect apple plants against C. gloeosporioides infection.     

Role of Cylindrosporium-type conidia of Mycosphaerella pomi (Pass.) Lindau: cause of Brooks fruit spot of apple, as an infection source in apple orchards

Ascospores of Mycosphaerella pomi, the pathogen of Brooks fruit spot of apple, were produced in pseudothecia on previously infected and overwintered apple leaves from late April through early August in Aomori Prefecture, Japan. In June 2003, the ascospores were germinating and producing Cylindrosporium-type conidia on apple fruit and leaf surfaces in an orchard. After ascospores were sprayed on apple leaves, Cylindrosporium-type conidia developed on the leaf surfaces. Such Cylindrosporium-type conidia caused typical symptoms of Brooks fruit spot on apple trees after inoculations. These results suggested that the Cylindrosporium-type conidia also serve as an infection source, in addition to the ascospores, for Brooks fruit spot in apple orchards.     

Resistance to root-knot nematodes on passion fruit genotypes in Brazil

With the expansion of passion fruit cultivation in Brazil, phytosanitary problems have increased, among them, the occurrence of root-knot nematodes. This research aimed to study the response of passion fruit genotypes to Meloidogyne incognita, M. javanica and M. enterolobii in addition to evaluating the life cycle of M. enterolobii in the passion fruit genotype ‘FB 200’. The genotype response was carried out in a greenhouse. Each pot’s soil was inoculated with 5000 eggs. Gall index, egg mass index and nematode reproduction factors were evaluated at 120 days after inoculation. All genotypes studied were resistant to M. incognita, M. javanica and M. enterolobii, except ‘Roxinho do Kênia’, which was susceptible to the three nematode species. The life cycle of M. enterolobii in “FB 200” passion fruit was studied in a growth chamber at 26 °C with a photoperiod of 12 h. Seven days after transplantation, each plant was inoculated with approximately 400 second-stage juveniles. Evaluations were done at 7, 14, 21, 28, 35, 42 and 49 days post inoculation. The nematode did not complete its life cycle.     

Improving control of crown rot disease and quality of pesticide-free banana fruit by combining Bacillus amyloliquefaciens DGA14 and hot water treatment

The present study aimed at improving the control of crown rot disease and quality of pesticide-free banana banana fruit by integrated approach combining Bacillus amyloliquefaciens DGA14 and hot water treatment (HWT). The efficacy of treatment combination was tested on cultures of crown rot-causing pathogens, Lasiodiplodia theobromae, Thielaviopsis paradoxa, Colletotrichum musae and Fusarium verticillioides, and postharvest application. Combination of DGA14 and HWT inhibited mycelium growth by 82.61 % as compared to 66.68 % by DGA14 and 37.90 % by HWT, as single treatments. Spore germination was totally inhibited in DGA14 with or without HWT. Postharvest application with DGA14 + HWT gave 90 % control of fruit decay comparable to 93 % of synthetic fungicide. Fruit treated alone with hot water or in combination with DGA14 incurred the lowest loss in weight. The over-all quality of fruit with DGA14 + HWT was better appearance and firmer texture which was statistically comparable with fungicide-treated banana. DGA14 + HWT was more consistent in crown rot control i.e., limited variation in severity of disease within a treatment as compared to DGA14 and HWT, as stand-alone treatments.     

Preventive and curative activity of postharvest potassium silicate treatments to control green and blue molds on orange fruit

Preventive and curative antifungal activities of postharvest treatments with potassium silicate (PSi) against green (GM) and blue (BM) molds were evaluated on oranges (cvs. ‘Valencia’ or ‘Lanelate’) artificially inoculated in rind wounds with Penicillium digitatum and P. italicum, respectively. The most effective PSi concentration, the effect of fungal inoculum concentration, and the influence of temporal and spatial factors on antifungal activity were assessed in in vivo primary screenings. After 6 days of incubation at 20 °C, significant preventive (treatment before fungal inoculation) and curative (treatment after inoculation) activities against GM and BM were observed with PSi at 90 mM (GM and BM incidence reductions of 23 and 52 %, and 23 and 40 %, respectively). In preventive tests, the effectiveness of PSi was influenced by inoculum concentration (10³, 10⁴, 10⁵, or 10⁶ spores ml^-1), but not by the distance between treatment and inoculation sites (10, 20 or 30 mm). PSi applied about 2 h before inoculation showed higher preventive activity than applied before 24, 48 or 96 h. In order to determine the best dip treatment conditions, PSi at 90 mM was tested at 20 or 50 °C for 60 or 150 s in small-scale trials with ‘Lanelate’ oranges artificially inoculated before or after the treatment and incubated for 7 days at 20 °C. Dips at 20 °C for 60 s were selected and subsequently applied on inoculated ‘Valencia’ oranges stored at 5 °C and 90 % RH for up to 6 weeks. Curative postharvest dips effectively reduced the incidence and severity of both GM and BM during cold storage, while preventive dips significantly reduced the severity but not the incidence. Overall, postharvest PSi treatments showed potential as a new tool to be part of non-polluting strategies to control penicillium decay of citrus fruit.