Pollen mimicry during infection of blueberry flowers by conidia of Monilinia vaccinii-corymbosi

Infection of blueberry flowers by Monilinia vaccinii-corymbosi, which causes mummy berry disease, occurs via the gynoecium and involves conidial germination on the stigmatic surface followed by hyphal ingress into the stylar canal and subsequent colonization of the ovary. The extent to which these events mimic pollen–pistil interactions during pollination was investigated. Similar to blueberry pollen tubes, conidial germ tubes of M. vaccinii-corymbosi adhered selectively to imprints of stylar transmitting tract tissue on nitrocellulose membrane, with adhesion in both cases occurring at the tips of the tubes. By contrast, hyphae of the related Monilinia fructicola, which is nonpathogenic on blueberry and does not cause gynoecial infection, adhered indiscriminately to the entire membrane. Using monoclonal antibodies, the presence of epitopes of esterified and unesterified pectins and of arabinogalactan proteins (AGPs), which have been implicated in adhesion and pollen tube guidance in other plant species, was documented on blueberry pollen tubes in vitro. Epitopes of certain AGPs, but not of pectins, were also localized on conidia and hyphae of M. vaccinii-corymbosi. However, such epitopes were also detected on M. fructicola, suggesting that they are unlikely to be a discriminatory factor between fungi capable or not capable of gynoecial infection. Microscopic observation of inoculated pistils showed that similar to pollen tubes, hyphae of M. vaccinii-corymbosi tracked the lobes of the stylar lumen, grew directionally (i.e. with very limited branching) in close proximity to cells of the stylar adaxial epidermis and to one another, and were surrounded by extracellular matrix. By contrast, hyphae of M. fructicola, while being able to ingress into the style, branched profusely within the stylar canal, showing no directional growth or affinity to specific regions of the lumen. We propose these results as evidence of specialized opportunism by M. vaccinii-corymbosi, whereby fungal hyphae appear to mimic host pollen tubes and take advantage of an infrastructure intended to support host reproduction in order to facilitate infection of the ovary.     

Infection of Cranberry Flowers by Monilinia oxycocci and Evaluation of Cultivars for Resistance to Cottonball

ABSTRACT Infection of cranberry flowers by conidia of Monilinia oxycocci, the cottonball pathogen, was investigated using a squash-mount histological method. Conidia germinated on anthers, nectaries, petals, and stigmata, but not styles. The stigma was the only flower part penetrated by the fungus, but no specialized infection structures were noted. Both fungal and pollen germ tubes grew through the stylar canal and made contact with ovules and nucellar tissue by 72 h after inoculation and pollination. Cottonball incidence was greatest when stigmata were inoculated; the low level of cottonball that resulted from inoculation of other flower parts and in noninoculated flowers was attributed to contamination of stigmata. In greenhouse tests, cottonball incidence was 25, 28, 31, and 38% for cvs. Searles, Pilgrim, Ben Lear, and Stevens, respectively, and was greater for M. oxycocci isolate 593 than isolate 591. We conclude that the stigma is the sole floral infection court for conidia of M. oxycocci and that the most popular cranberry cultivars in Wisconsin do not differ in inherent resistance to cottonball. The relevance of these findings to the long-term management of cottonball is discussed.     

Temporal Dynamics of the Biocontrol Agent Pseudomonas fluorescens Strain A506 in Flowers in Inoculated Pear Trees

ABSTRACT The colonization of individual flowers in mature pear orchards by Pseudomonas fluorescens strain A506 applied at different times during bloom was measured to determine the receptivity of flowers to colonization and the extent of intra-tree movement over time. Strain A506 populations in flowers open at inoculation were initially about 10(4) cells per flower and increased to approximately 10(6) cells per flower in flowers that were inoculated within about 5 days of opening. However, eventual populations decreased with further increases in flower age at inoculation to as few as about 10(3) cells per flower when inoculated flowers were more than 10 days old. Populations of strain A506 on flowers that opened after inoculation was initially very low at the time of petal expansion (<100 cells per flower) but increased rapidly with time after flower opening. The maximum population of strain A506 that developed on such flowers decreased with increasing time between inoculation and petal expansion; 10(4) to 10(5) cells of strain A506 eventually colonized flowers that opened within 7 days of inoculation, whereas fewer than 100 cells colonized flowers that opened 24 days or more after inoculation. Large total bacterial populations on A506-treated trees were associated with significant reductions in populations of Erwinia amylovora and reduced incidence of fire blight and severity of fruit russet.     

Infection of plum and nectarine flowers by Botrytis cinerea

The ability of Botrytis cinerea to infect plum and nectarine flowers was studied in moist chambers and in the orchard. Within 36 h of inoculation, the pathogen penetrated and colonized the stamens, styles and petals on shoots placed in moist chambers, causing blossom blight. Similar lesion development was observed following inoculation with dry and wet conidia, Hyphae were usually distorted in stylar tissue, but grew normally in petals and filaments. Growth of the fungus through filaments into the sepals or floral tubes, or through the transmitting tissue of the style into the ovary, was never observed. Symptoms of blossom blight were not observed on inoculated shoots in the orchard. The floral tube, bearing the sepals and stamens, dehisced within 14 days of fruit set and infected floral parts did not remain attached to young developing fruit. No relation was found between post-harvest decay and flower infection. Losses following post-harvest decay might have been caused by direct penetration of ripening fruit and not by flower infection. The importance of infected floral parts as a source of secondary inoculum on ripening fruit is discussed.     

Temperature and Pomaceous Flower Age Related to Colonization by Erwinia amylovora and Antagonists

ABSTRACT Fire blight of apple and pear is initiated by epiphytic populations of Erwinia amylovora on flower stigmas. Predicting this disease and managing it with microbial antagonists depends on an understanding of bacterial colonization on stigmas. Detached 'Manchurian' crab apple flowers were inoculated with E. amylovora and subjected to a range of constant temperatures or various fluctuating temperature regimes. Results may have application to disease risk assessment systems such as the Cougarblight model, which now are based on in vitro growth of the pathogen. In other experiments, detached crab apple flowers and attached 'Gala' apple flowers were maintained at different temperatures for various periods before inoculation with E. amylovora or antagonists (Pseudomonas fluorescens strain A506 and Pantoea agglomerans strains C9-1 and E325). Maximum stigma age supporting bacterial multiplication decreased as temperature increased, and was reduced by pollination. Stigmas were receptive to bacteria at ages older than previously reported, probably due to less interference from indigenous organisms. The study revealed antagonist limitations that possibly affect field performance (e.g., the inability of strain A506 to grow on relatively old stigmas conducive to the pathogen). Such deficiencies could be overcome by selecting other antagonists or using antagonist mixtures in the orchard.     

Pollination of chasmogamous flowers and the effects of light and emergence time on chasmogamy and cleistogamy in Monochoria vaginalis

Monochoria vaginalis is one of the most serious weeds of rice fields in Asia. The species has both chasmogamous (CH) and cleistogamous (CL) flowers on individual plants. The objective of this study is to clarify the reproductive characteristics that affect the selfing rate of M. vaginalis. An emasculation experiment revealed that the CH flowers emasculated just after flower opening produced seeds. The seed production in the flowers emasculated just after flower opening was less than that of the flowers emasculated and hand‐pollinated with pollen from another plant. These results indicate that, although self‐pollination before anthesis occurs, cross‐pollination also can produce seeds. An experimental manipulation of light and the emergence time of the plants revealed that more than half of the flowers produced were CL flowers and the CH/CL ratio decreased with reduced light availability. The plants that emerged later produced as many CH flowers as those that emerged earlier. There was no significant difference between the CH and CL flowers in the seed number per fruit and the seed mass. These results suggest that M. vaginalis has reproductive characteristics that make the selfing rate high; however, outcrossing also can occur. Under favorable light intensity conditions, such as on the edges of paddy fields or in fallow fields, M. vaginalis will produce more CH flowers and will have a higher outcrossing rate than in shaded conditions.     

The infestation of tomato seed by Fusarium oxysporum f.sp. radicis-lycopersici

The infestation of seed by Fusarium oxysporum f.sp. radicis-lycopersici occurred at rates of 0-1 to 0-01 % in fruit on stem-infected plants. Direct infection of fruit in the flower or young developing fruit stage resulted in a grayish-brown lesion on the stylar end of the fruit or mummification. F. oxysporum f.sp. radicis-lycopersici was isolated from all seeds in such fruit. Picked fruit inoculated on the stem scar also became infected but 96 h after inoculation of the fruit, the seed was not infested or infected. The contact of clean seed with hands that had previously handled F. oxysporum f.sp. radicis-lycoperisid-infesied sawdust resulted in a high level of seed infestation. The fungus survived on seed sent across Canada and stored for up to 12 weeks. Treatment with NaOCl or 0·1 N HCl did not completely disinfest infested seed.     

The Role of Water in Epiphytic Colonization and Infection of Pomaceous Flowers by Erwinia amylovora

ABSTRACT Detached crab apple flowers were used as an experimental model to investigate the effect of relative humidity (RH), free moisture, and water potential Psi(w) on the interaction between Erwinia amylovora and pomaceous flowers. Flowers were maintained at 24 degrees C with the cut pedicel submerged in a sucrose solution. The bacterium multiplied on inoculated flower stigmas at between approximately 55 and 100% RH but not in the floral cup (hypanthium) until the RH was higher than 80%. To study the effect of free moisture, stigma-inoculated flowers were kept wet for different periods. Flowers became diseased only with wetting, and incidence was high (77%) even when water application was immediately followed by a 52-min drying period. In other experiments with hypanthium-inoculated flowers, RH or sucrose concentration in holding vials was varied to affect Psi(w) of flower nectar and ovary tissue. Population size of E. amylovora in the hypanthium increased with nectar Psi(w) following a sigmoidal curve (R(2) = 0.99). Disease incidence and severity, however, were more closely related to ovary Psi(w) (R(2) = 0.85 and 0.91, respectively) than to bacterial population size (R(2) = 0.25 and 0.67, respectively) as fitted to the quadratic equation. Maximum disease incidence and severity occurred at an ovary Psi(w) above -2.0 MPa, and disease severity continued to increase above -1.0 MPa. These results were confirmed with detached flowers of Delicious apple and d'Anjou pear. A practical implication is that disease might be partly managed in arid climates by limiting soil irrigation water during bloom and early fruit set.     

Factors influencing internal fruit rot of cucumber caused by Didymella bryoniae

Several factors influencing the incidence of internal fruit rot of cucumber caused byDidymella bryoniae were studied.Internal infection of fruits is achieved via the flower. However, in most cases the majority of the fruits escaped infection after flower inoculation. It took more than two days for the fungus to reach the fruit after infection of the style. A mechanical barrier was not detected in the fruit tip within three days after inoculation of the open flower.Inoculation of wilted flowers resulted in 60% less infection than inoculation of fresh flowers. Blossom excision reduced fruit infection with ca 75%. Growing plants under drought stress markedly increased the incidence of internal fruit rot.Neither the method of inoculation, nor the composition of the inoculum, nor the relative humidity influenced the incidence of internal fruit rot. Fruit thinning, duration of fruit growth, flowering period and the removal of parts of the flower had no effect either on fruit infection.Cultivars resistant to powdery mildew were also resistant to internal fruit infection. The resistance was associated with a long style and a short flowering period.Growing cultivars in which the flowers quickly fall away from the fruitlets or in which the flowers have no style may solve the problem of internal fruit rot in cucumber.Samenvatting Factoren die van invloed kunnen zijn op het ontstaan van inwendig vruchtrot van komkommer, veroorzaakt doorDidymella bryoniae, werden onderzocht.Inwendige vruchtinfectie vindt plaats via het bloempje. Bijna altijd ontsnapte echter het grootste deel van de vruchten aan een aantasting als de bloem werd geïnoculeerd. Het duurde meer dan twee dagen voordat de schimmel via de stijl de vrucht had geïnfecteerd. In de punt van de vrucht werd binnen drie dagen na inoculatie van de open bloem geen mechanische barrière gevonden.Na inoculatie van verwelkte bloemen kwam 60% minder aantasting voor dan na inoculatie van bloemen die pas open waren. Het verwijderen van het bloempje reduceerde de aantasting met ca. 75%. Het optreden van inwendig vruchtrot nam aanzienlijk toe door de planten onder droge omstandigheden te telen.Noch de methode van inoculatie, noch de samenstelling van het inoculum, noch de relatieve luchtvochtigheid beïnvloedden het optreden van inwendig vruchtrot. Vruchtdunning, duur van de vruchtgroei, bloeiduur en het verwijderen van delen van de bloem hadden ook geen effect op de aantasting.Cultivars die resistent waren tegen echte meeldauw vertoonden ook resistentie tegen inwendige vruchtaantasting. De resistentie was gecorreleerd met een lange stijl en met een korte bloeiduur.De teelt van cultivars waarvan de bloemdelen snel van de vruchtbeginsels afvallen, of waarvan de bloempjes geen stijl hebben, zou het probleem van inwendig vruchtrot bij komkommer kunnen oplossen.     

绿盲蝽对冬枣不同生长期的为害

为了解绿盲蝽对其重要果树寄主冬枣的为害特点,通过对各生长期叶、蕾、花、幼果等易受害部位接虫试验,研究绿盲蝽对冬枣的为害规律及其对冬枣坐果的影响。结果显示,不同生长期各部位的被害率和刺点数均随着接虫数的增加而增大。嫩叶期最幼嫩的部位顶芽和第1片叶被害率均为100%,第4、5片叶的被害率均为0;相同接虫密度下,花的刺点数显著高于蕾和幼果;花蕾并存时,花的刺点数显著高于蕾,而被害率无显著差异。花期受害后,坐果数显著降低,其中接1、2、3、4、5头绿盲蝽坐果数分别降低了49.49%、59.60%、84.85%、94.95%、94.87%。研究表明,绿盲蝽对冬枣的为害有明显趋嫩和趋花性,花期受害后对产量的影响最大,应加强对花、幼果期绿盲蝽种群的控制。     

Effects of temperature,relative humidity and age of conidia on the incidence of spotting on gerbera flowers caused by Botrytis cinerea

In recent years, spotting of ray florets of gerbera flowers has become an important problem. This type of small necrotic lesions may occur before, but especially shortly after harvesting the flowers.Botrytis cinerea was easily isolated from such lesions. Inoculation withB. cinerea only gave typical necrotic lesions, when dry conidia were dusted on the flowers with a short period of high rh after inoculation. At 18–25 °C a high rh for at least 5 hours was necessary. Rotting of ray florets and receptacles byB. cinerea occurred when inoculated flowers were kept wet for a few days. Spots consist of one to several necrotic, usually epidermal cells. A single conidium could give rise to a necrotic lesion after germination. Germination of conidia and lesion formation occurred between 4 and 25 °C; at 30 °C, germination and lesion formation did not occur. Between 18 and 25 °C, many lesions became visible within 1 day after inoculation; at 4 °C it took 2 to 3 days before lesions could be seen. If kept dry, conidia ofB. cinerea remained ungerminated on ray florets of gerbera flowers and could be removed from the ray florets. Within 1 day at high rh, germination occurred and lesions were produced. Conidia ofB. cinerea, stored dry, were able to survive much longer than the lifetime of a gerbera flower. Even after storage at room temperature for up to 14 months, some conidia were able to germinate in vitro and on ray florets and induce the formation of lesions. Addition of gerbera pollen diffusate stimulated germination and lesion formation.     

Limitations on the recruitment of the rare sand shrubby legume Eremosparton songoricum (Fabaceae) in Gurbantunggut Desert, China

Eremosparton songoricum,a rare and endemic sand dune plant,appears to be experiencing recruitment failure.The structure of five populations from the Gurbantunggut Desert,China,was investigated for recruitment patterns,and two of them were examined for flowering,pollination and seed germination limits on regeneration.The results showed that total 150 seedlings only occurred on line transects in riverside Dure population,but they all died half a month later;no seedlings occurred in other four hinterland desert populations indicating recruitment was a failure at all populations although flowers were plentiful.Reproductive success depends on pollinators.Nectar is 'reward' for pollinators,with 0.06 μL-0.12 μL and 0.15 μL-0.35 μL per flower in Dure and Kabu populations,respectively,in continuously two secreting days.Spontaneous self pollination is rare with nearly zero fruit production.Geitonogamous self pollination is predominant with 14.47% fruit set.Seed mass in the riverside Dure population was significantly greater than that in other hinterland desert populations.Consequently,the Dure population exhibited a significantly higher germination rate(about 90%) than those in other populations(about 30%).Results suggested that recruitment failure of E.songoricum is not due to flower shortage,pollination limitation,or poor seed germination but environmental pressure and/or human disturbance.     

Pathways of bacterial invasion and watermelon seed infection by Acidovorax citrulli

This study explored the pathways of ingress of Acidovorax citrulli, the causal agent of bacterial fruit blotch of cucurbits, into watermelon seeds. Up until 7 days post‐inoculation (DPI), a significantly higher percentage of watermelon seeds was infected with A. citrulli when the bacteria were applied (c. 1 × 10⁶ colony‐forming units) to stigmas versus ovary pericarps of female flowers. Immunofluorescence microscopy showed that, with stigma inoculation, A. citrulli colonized style and ovary tissues by 1 DPI, and the bacteria co‐localized with pollen germ tubes in these tissues. With ovary pericarp inoculation, A. citrulli cells penetrated the epicarp and mesocarp tissues by 1 DPI but did not reach endocarp until 4 DPI. Finally, manual pollination followed by stigma inoculation led to >53% A. citrulli‐infected seed lots, while A. citrulli was not detected in seeds/ovules generated by stigma inoculation without pollination (chemically induced parthenocarpy). These results show that stigma inoculation results in faster colonization of watermelon ovules by A. citrulli than pericarp inoculation, even though there is no difference in the levels of infection in mature seeds. The data also indicate that pollen germ tubes play an important role in A. citrulli ingress into watermelon seeds via stigmas.     

Management of strawberry anthracnose by choice of irrigation system,mulching material and host resistance

We studied, by means of field experiments, the combined effects of irrigation system, mulching material and genetic resistance on the incidence of strawberry anthracnose caused by Colletotrichum acutatum. All trials involved artificial inoculation with fruits colonized by the pathogen. One experiment examined the effects of drip irrigation, overhead sprinkler irrigation, and localized low-pressure tape irrigation, and the effects of grass (Brachiaria sp.) and plastic (polyethylene) mulches, in a split plot, randomized complete block design with four replicates. Lower disease incidence, indicating lower pathogen dispersal, was verified with low-pressure tape and drip irrigation. Flower blight and fruit rot incidence in drip-irrigated plots was minimal (ca. 2% of the disease levels in the plots otherwise irrigated). Grass mulch reduced flower blight in the sprinkler system (up to 80%), but had no significant effect when disease levels were already low due to use of other irrigation systems. A second experiment compared the effects of grass mulch, pine (Pinus elliotti) mulch, and plastic mulch with overhead sprinkler irrigation on strawberry cultivars partially resistant (‘Dover’) and susceptible (‘Campinas’) to the disease in a factorial completely randomized design (CRD). Both organic mulches reduced flower blight and diseased fruit incidence by up to 76% compared to the plastic mulch treatment, especially in the early stages of the epidemics. ‘Dover’ had 70% lower incidence of flower blight than ‘Campinas’, and the effects of organic mulches were more pronounced in ‘Campinas’. A third experiment, with all three irrigation systems combined with inoculated and non-inoculated plots, estimated yield effects due to disease and irrigation system. All plots were covered with plastic mulch in a CRD with six treatments. This experiment clearly confirmed the higher flower blight and fruit rot incidences when sprinkler irrigation was used. In inoculated treatments, fruit yield was significantly reduced in tape-irrigated plots, and more so in sprinkler-irrigated plots. In drip-irrigated plots yield was reduced by only 1%. Overall, our results confirm the importance of cultural and genetic factors as valuable means of strawberry anthracnose management. Adoption of localized irrigation systems, the use of organic mulches and choice of a partially resistant cultivar significantly reduced disease levels in field plots. The importance of water splash for C. acutatum dispersal and its dependency on the soil mulch characteristics are the likely causes for the results observed.     

Fruit set and the diurnal pollinators of the invasive Lantana camara and the endemic Lantana peduncularis in the Galapagos Islands

Fruit set is highly relevant to a plant's reproductive success. Fruit set can vary due to predation on flowers, pollinator services and/or resource availability. Reproductive success, measured as the fruit set of the invasive Lantana camara and the endemic Lantana peduncularis in the cool–dry season and the warm–wet season of the Galapagos Islands, was studied. Also, autonomous self‐pollination ability and seed viability were probed for both species. Furthermore, flower visitors and their activity were registered for both species during the warm–wet season. Lantana peduncularis produced fewer flowers per inflorescence, but had a higher fruit set in the cool–dry season, compared to the warm–wet season. In contrast, the fruit set in L. camara did not change seasonally. The fruit set in L. camara was higher than in L. peduncularis in the warm–wet season. Moreover, ～18% of the bagged flowers of the invasive Lantana produced fruits by autonomous self‐pollination, while for the endemic Lantana, the rate of autonomous self‐pollination was very low. More than 80% of the fruits for both species had at least one viable seed per fruit. The number of pollinators and their frequency, inflorescence‐ and flower‐visiting rates and the duration of the visit per flower were higher in the invasive Lantana than in the endemic one. The endemic Lepidoptera Urbanus galapagensis (the main pollinator of both Lantana species) and the introduced Hymenia perspectalis were observed pollinating both Lantana species. These results indicate that the alien L. camara is more attractive to pollinators and it has reproductive advantages regarding fruit set in comparison with L. peduncularis, factors that contribute to the colonization pattern of this invasive species.     

Evaluation of sorghum germplasm used in US breeding programmes for sources of sugary disease resistance*

Ergot or sugary disease of sorghum has become an important constraint in North and South American countries that rely on F₁ hybrid seeds for high productivity. The objective of this research was to determine the vulnerability of various germplasm sources and publicly bred sorghum lines to sugary disease ( Claviceps africana ) in the United States. Flower characteristics associated with sugary disease resistance were also studied. A-/B-line pairs, R-lines, putative sources of resistance and their hybrid combinations with an A₃ cytoplasmic male-sterile source were evaluated using a disease incidence, severity, and dual-ranking system. Trials were planted in a randomized complete block design with three replications and repeated in at least two planting dates. Planting dates and pedigrees had significant effects on overall ranking for resistance. A-lines were most susceptible to sugary disease. R-lines were more susceptible than B-lines with respect to incidence and severity of the disease. Newer releases of A- and B-lines were more susceptible to sugary disease than older releases. Sugary disease reaction of A-lines was a good indicator of disease reaction of B-lines. Tx2737, a popular R-line, was highly susceptible to sugary disease in spite of being a good pollen shedder because the stigma emerged from glumes 2–3 days before anthesis. The combination of flower characteristics associated with resistance were least exposure time of stigma to inoculum before pollination, rapid stigma drying after pollination, and small stigma. An Ethiopian male-fertile germplasm accession, IS 8525, had good levels of resistance. Its A₃ male-sterile hybrid had the highest level of resistance in the male-sterile background. IS 8525 should be exploited in host-plant resistance strategies.     

Infection of citrus pollen grains by Colletotrichum acutatum

Postbloom fruit drop (PFD), an important disease caused by Colletotrichum spp., affects citrus yields in Brazil. PFD is characterised by the presence of necrotic lesions on the petals and stigmas of citrus flowers and by the subsequent abscission of young fruit. PFD epidemics have high disease progress rates, which is unusual for a pathogen that produces acervuli and is dispersed by rain. It is possible that other dispersal agents, such as insects and pollen, are involved in the spread of this disease. The objective of this work was to test whether citrus pollen grains can be colonised by Colletotrichum acutatum. Studies using light and electron microscopy showed that the pollen of Citrus sinensis can be infected by C. acutatum. This pathogen can penetrate and colonise citrus pollen grains 24 h after inoculation with the pathogen. The germ tube of conidia either penetrates the pollen sporodermis directly or passes through pollen germ pores. A single hypha can colonise more than one pollen grain. On the surface of the stigma, conidium formation can be observed. This study shows that Citrus sinensis pollen may, in fact, play a role in the spread of C. acutatum in citrus orchards.     

Colonization of red raspberry flowers and fruit by Botrytis cinerea under commercial production conditions in northwestern Washington,USA

Colonization of red raspberry flowers and fruit by Botrytis cinerea was determined during 2017–2018 growing seasons under commercial fungicide application programmes used for grey mould management in northwestern Washington, USA. Colonization of flowers and fruit was assessed qualitatively (incidence, %) and quantitatively (abundance, number of colonies) by recovering B. cinerea from surface-disinfested samples. Both incidence and abundance of flower colonization were significantly lower than fruit colonization in both untreated and fungicide-treated plots. Incidence of flower colonization did not differ significantly between untreated and fungicide-treated plots (43% vs. 45%, respectively). In contrast, significantly greater colonization incidence was detected at green fruit stage in untreated compared to fungicide-treated plots (96% vs. 77%, respectively). Ripe fruit had the greatest colonization incidence among the three stages sampled and colonization was not significantly different between untreated and fungicide-treated plots (100% vs. 92%, respectively). Similarly, colonization abundance of flowers did not differ significantly between untreated and fungicide-treated plots (1.0 colonies per colonized flower in both treatments), but colonization abundance of green and ripe fruit was decreased 2.3- and 2.1-fold, respectively, in fungicide-treated plots. DNA fingerprinting analysis of the pathogen revealed that different multilocus genotypes colonized flowers and fruit within the same inflorescence and that genotypic diversity increased through time, suggesting independent infection events. Overall, our results demonstrate that under current environmental conditions, raspberry flowers may not be the exclusive or major route of infection for grey mould of red raspberry in northwestern Washington. Implications of current findings for management and further research are discussed.     

湖北省设施番茄灰霉病发生规律及流行因子分析

为探索湖北省设施番茄灰霉病的发生规律,揭示不同流行因子与番茄灰霉病发生的关系。于2013-2016年在湖北省武穴市吴谷英村番茄种植基地选取代表性番茄大棚进行调查和取样检测,结果表明:湖北省设施番茄叶片和花朵带菌率变化起伏较大,带菌率分别为0～90.0%和0～100.0%;叶片带菌率在3月下旬到4月中下旬和5月中下旬是高峰期;花朵带菌率在4月中旬和5月中下旬达到高峰期,总体上花朵带菌率较高。番茄不同组织灰霉病的发病时间不同,叶片首先开始发病,花、果实、茎秆再逐渐发病,花朵和果实的发病率相对较高,叶片和茎秆发病率较低;花朵和果实发病率均在5月中旬至6月初达到最大值,茎秆发病率于5月下旬至6月上旬达到最高值,叶片无明显发病高峰期。果实、叶片、花朵和茎秆的发病率分别为0～42.0%、0～24.7%、0～100.0%和0～32.0%。番茄叶片发病率、花朵发病率、茎秆发病率和相对湿度均与果实发病率呈显著相关;通过预测模型检验表明相对湿度和叶片发病率所建模型预测值和实际值符合程度较好。在湖北省设施番茄大棚中,叶片发病率、花朵发病率、茎秆发病率和相对湿度对番茄果实发病影响最为显著,在防治过程中应及时摘除发病组织,调控棚内环境条件,预防灰霉病发生。     

Leaf and Flower Blight Caused by Monilinia vaccinii-corymbosi on Lowbush Blueberry: Effects on Yield and Relationship to Bud Phenology

ABSTRACT Naturally established lowbush blueberry clones in four fields were evaluated for the incidence of leaf and flower blight, proportion of mummy berries, and yield reductions caused by Monilinia vacciniicorymbosi. The relationship between the phenology of flower and leaf bud development and susceptibility also was examined. Three fields were examined over one crop year and one field was studied in two subsequent crop years. The incidence of stems with blight was correlated to incidence of leaf blight in all fields and to incidence of flower blight in one field. Incidence of leaf and flower blight and the proportion of mummy berries produced were not correlated. Lowbush blueberry clones with higher incidence levels of leaf blight had reduced fruit set and lower berry weights. For healthy stems, leaf-to-fruit ratios had no effect on berry weight in most fields. In contrast, blighted stems with higher leaf-to-fruit ratios had higher berry weights in three fields. Stems with slowerdeveloping leaf and flower buds had less leaf and flower blight, respectively, than stems with faster bud development. Some blueberry clones may avoid infection by delaying production of susceptible tissue until after ascospore release by M. vaccinii-corymbosi.