Inoculation Of Flowers Research Articles

Nectar microbes may indirectly change fruit consumption by seed-dispersing birds

An increasing number of recent studies show that nectar-inhabiting microorganisms influence plant fitness by mediating interactions between plants and pollinators. However, whether the effects of nectar microbes extend beyond pollination to affect subsequent stages of plant reproduction remains largely unknown. This study aims to explore whether nectar microbes can indirectly affect fruit consumption by birds, which can be essential for seed dispersal and germination. Wild flowers of Eurya japonica trees were experimentally inoculated with the nectar-inhabiting yeast Metschnikowia reukaufii and the nectar-inhabiting bacterium Acinetobacter boissieri, both of which had been previously isolated frequently from E. japonica flowers. In this experiment, I examined whether these microbes changed female reproductive success of the understory tree. Experimental inoculation of flowers with yeasts decreased fruit and seed set compared to those inoculated with bacteria, and the control. Furthermore, fruits with higher seed set tended to be larger, and larger fruits were more likely to be consumed by seed-dispersing birds, including the Japanese white-eye Zosterops japonica, the brown-eared bulbul Hypsipetes amaurotis, and the Daurian redstart Phoenicurus auroreus. These results suggest that nectar-inhabiting microorganisms have the potential to affect plant reproduction by influencing not only plant-pollinator interactions, but also by indirectly modifying plant-frugivore interactions via changes in plant-pollinator interactions.

Influence of the degree of ergot damage on the productivity elements of winter rye varieties

Under the conditions of the Kirov region in 2020-2022 there were studied 21 varieties of winter rye bred by Russian scientific institutions according to the nature of the relationship in the patho-system "Secale cereale L. – Claviceps purpurea (Fr.) Tul.". Under artificial inoculation of flowers with a suspension of the pathogen all the studied varieties were affected by ergot in the range from 3.17 (Graphite FP) to 34.69 % (Saratovskaya 10), with grain contamination with sclerotia – from 0.13 (Graphite FP, Quail) up to 1.87 % (Amber), which indicates their susceptibility to the disease. However, taking into account the signs of "damage by ergot", "contamination of grain with sclerotia" and "yield" for further breeding for ergot resistance, it is possible to recommend varieties Perepel, Lika and Graphite FP (bred by the Federal Agricultural Research Center of the North-East named N. V. Rudnitsky. The influence of the genotype on the biometry of sclerotia has been revealed. This is indirectly evidenced by the significant variability of their parameters in different varieties of rye, which should be taken into account during the mechanical cleaning of grain. Using the Graphite variety as an example, a significant (P ≥ 095) decrease in the grain content and productivity of an ear has been established when more than two sclerotia are formed in it, and four sclerotia form 1000 grains. With an increase in their number to 11 pieces, this pattern remained unchanged, and the harmfulness of ergot reached 64.05 % (ear grain size), 79.60 % (ear productivity) and 46.32 % (grain size). In the process of regression analysis, it has been established that with an increase in infection of the ear by 1-2 sclerotia, the number of grains in the ear decreases by 4.96 pieces, the mass of grain per ear – by 0.26 g, the grain size – by 2.49 g. The similar calculations with a preliminary analysis of the degree of plant damage can be of prognostic value in assessing the potential harmfulness of ergot.

Etiology of Colletotrichum diseases on Sastuma mandarin in Croatia

During the last decade anthracnose has become a major disease of Satsuma mandarin, the most important citrus crop in Croatia. The aim of this study was to determine Colletotrichum species associated with different symptoms and to identify the origin of inoculum. From 2013 to 2016, 437 samples of plant material were collected. Colletotrichum spp. was isolated from 93% of dried twigs, 35% of dropped flowers, 89% of leaf spots, all fruit (100%) with anthracnose or calyx-end rot symptoms, 12% of fruit with post-harvest soft rot and from 40% of fruit showing spots remaining on trees after harvest. Out of 258 Colletotrichum isolates, 253 has been morphologically identified as C. gloeosporioides (Penz.) Penz. & Sacc. species complex. Twenty-seven representative isolates were selected for phylogenetic analysis. Sequencing the inter-spacer gene region of ribosomal DNA confirmed the identity of the species. Artificial inoculation of flowers led to more than 2-fold higher young fruit drop compared to control. Pathogenicity tests on green fruit induced typical anthracnose symptoms on 82% of inoculated fruit two months after inoculation. Inoculation of mature fruit caused the appearance of typical anthracnose symptoms on 87% of inoculated fruit. These results showed that C. gloeosporioides species complex is responsible for different disease types on Satsuma mandarin, and that the fungus is present throughout the year on different plant organs.

Blossom blight resistance in peach: heritability and segregation in progenies from reciprocal crosses

Blossom blight and brown rot caused by Monilinia fructicola is the most important peach disease in Brazil. Genetic resistance is a control strategy that is gaining importance in breeding programs worldwide. This study aimed to identify genotypes with higher levels of blossom blight resistance to estimate the heritability of this character; study the frequency distribution in populations; and test the possibility of maternal effect. Blossom blight susceptibility was tested in reciprocal hybridizations seedlings, as well as their parents. The detached flower technique was used in a randomized complete block design, considering each genotype as a treatment. Flower inoculation was made by spraying a M. fructicola suspension and evaluations were carried out after 72 and 120 hours using a scale of five severity levels. The studied populations presented low phenotypic variability regarding the flower resistance/susceptibility to M. fructicola, being most of them susceptible or very susceptible. Among the tested genotypes, the cultivars Maciel and Cerrito showed less blossom blight susceptibility, transmitting this character to their progenies. Heritability estimates of the blossom blight resistance were medium to low. The low heritability and its distribution in the progenies suggest that the character has additive inheritance, without detecting deviations associated with maternal effects.

Inoculation of pear flowers with Metschnikowia reukaufii and Acinetobacter nectaris enhances attraction of honeybees and hoverflies, but does not increase fruit and seed set.

Currently, one of the most important challenges is to provide sufficient and affordable food and energy for a fast-growing world population, alongside preserving natural habitats and maintaining biodiversity. About 35% of the global food production depends on animals for pollination. In recent years, an alarming worldwide decline in pollinators has been reported, putting our food production under additional pressure. Therefore, there is an urgent need to find sustainable ways to ensure this crucial ecosystem service. Recent studies have shown that floral nectar is generally colonized by microorganisms, specifically yeasts and bacteria, which may alter nectar chemistry and enhance attraction of pollinators. In this study, we investigated changes in pollinator foraging behavior and pollination success in European pear (Pyrus communis L.) cultivars ‘Regal Red’ and ‘Sweet Sensation’ (red sports of ‘Doyenné de Comice’) after flower inoculation with the typical nectar-inhabiting microorganisms Metschnikowia reukaufii and Acinetobacter nectaris, and a combination of both. Pollination success was monitored by measuring the number of flower visits, fruit set and seed set in two consecutive years, 2019 and 2020. Results revealed that application of a mixture of M. reukaufii and A. nectaris resulted in significantly higher visitation rates of honeybees and hoverflies. By contrast, no effects on flower visits were found when yeasts and bacteria were applied separately. Fruit set and seed set were not significantly affected by any of the inoculation treatments. The only factors affecting fruit set were initial number of flower clusters on the trees and the year. The absence of treatment effects can most likely be attributed to the fact that pollination was not a limiting factor for fruit set in our experiments. Altogether, our results show that inoculation of flowers with nectar microbes can modify pollinator foraging patterns, but did not lead to increased pollination success under the conditions tested.

Aspergillus niger, the causal agent of black mould disease in date fruits, infects and colonizes flowers and young fruitlets

AbstractBlack mould, caused by Aspergillus niger, is the main fungal disease affecting date fruits. Symptoms develop inside the fruit, at the inner space between the pulp and the seed. This study focuses on the aetiology of black mould disease in Medjoul fruit. We followed symptom appearance naturally and after artificial A. niger inoculation at different development and maturity stages. Symptoms developed in only a short period during early fruit ripening. However, fruits were commonly colonized at earlier stages of development. Artificial inoculation of flowers and setting fruitlets increased the level of fruit colonization, while fungicide spraying at these stages decreased colonization. Several weeks following flower inoculation by A. niger, mycelium could be detected on degenerating stigmas and carpels as well as between the fruit and the calyx. Following inoculation with an A. niger strain expressing green fluorescent protein (A. nigerGFP), the pathogen was detected on stigmas of setting fruitlets but not within the stigmatic tissue or the transmitting tract of the carpel. The A. nigerGFP strain was detected during fruit development below the base of the large fruitlets and above the calyx surrounding the vascular bundle leading into the fruit. The results suggest that A. niger can infect and colonize flowers and setting fruitlets, grows on the degenerating carpels, and remains latent at a protected site at the base of the fruit until ripening. It then induces the typical black mould symptoms. The significance of these results for developing means to cope with the disease is discussed.

Epidemiology and Management of Bacterial Spot of Almond Caused by Xanthomonas arboricola pv. pruni, a New Disease in California.

Bacterial spot caused by Xanthomonas arboricola pv. pruni was first detected on almond in California in 2013, and it is reported herein as a new disease in California based on fulfilling Koch's postulates and identification of the pathogen using species-specific PCR primers. Infected mummified fruit from the previous growing season and their peduncles were identified as primary overwintering sites of the bacterium on the tree. Twig cankers were not observed, and the pathogen was not recovered from dormant buds. Isolation from flowers and emerging leaves was only successful when they were collected within 20 cm of an infected, mummified fruit on the tree. Inoculation of flowers and immature fruit as well as immature and mature leaves resulted in disease development, indicating a long period of host susceptibility in the spring, but disease incidence was highest in fruit inoculations. In split-plot trials over 3 years, dormant applications in December or January with copper or copper-mancozeb significantly reduced the disease compared with untreated controls in seasons with high rainfall, but they had no effect in seasons with low rainfall. In-season applications of copper-mancozeb at petal fall or at full bloom and petal fall were also effective in reducing the disease. Phytotoxicity was observed after repeated applications of copper bactericides, especially in low-rainfall seasons. Dormant and in-season treatments of copper-mancozeb mixtures integrated with removal of mummified fruit are currently the best management strategies for bacterial spot of almond in California.

Mapping of fire blight resistance in Malus \xd7robusta 5 flowers following artificial inoculation

BackgroundAlthough the most common path of infection for fire blight, a severe bacterial disease on apple, is via host plant flowers, quantitative trait loci (QTLs) for fire blight resistance to date have exclusively been mapped following shoot inoculation. It is not known whether the same mechanism underlies flower and shoot resistance.ResultsWe report the detection of a fire blight resistance QTL following independent artificial inoculation of flowers and shoots on two F1 segregating populations derived from crossing resistant Malus ×robusta 5 (Mr5) with susceptible ‘Idared’ and ‘Royal Gala’ in experimental orchards in Germany and New Zealand, respectively. QTL mapping of phenotypic datasets from artificial flower inoculation of the ‘Idared’ × Mr5 population with Erwinia amylovora over several years, and of the ‘Royal Gala’ × Mr5 population in a single year, revealed a single major QTL controlling floral fire blight resistance on linkage group 3 (LG3) of Mr5. This QTL corresponds to the QTL on LG3 reported previously for the ‘Idared’ × Mr5 and an ‘M9’ × Mr5 population following shoot inoculation in the glasshouse. Interval mapping of phenotypic data from shoot inoculations of subsets from both flower resistance populations re-confirmed that the resistance QTL is in the same position on LG3 of Mr5 as that for flower inoculation. These results provide strong evidence that fire blight resistance in Mr5 is controlled by a major QTL on LG3, independently of the mode of infection, rootstock and environment.ConclusionsThis study demonstrates for the first time that resistance to fire blight caused by Erwinia amylovora is independent of the mode of inoculation at least in Malus ×robusta 5.

Floral Traits Predict Frequency of Defecation on Flowers by Foraging Bumble Bees.

Flowers may become inoculated with pathogens that can infect bees and other critical pollinators, but the mechanisms of inoculation remain unclear. During foraging, bees may regurgitate or defecate directly onto flower parts, which could inoculate flowers with pollinator pathogens and lead to subsequent disease transmission to floral visitors. We tested if captive eastern bumble bees (Bombus impatiens) (Cresson) (Hymenoptera: Apidae) defecate on floral surfaces during foraging and if flower shape played a role in the probability of defecation and the quantity of feces deposited on floral surfaces. Captive Bombus impatiens were fed a solution of fluorescent dye and sucrose, then allowed to forage freely on flowers of a variety of shapes in a flight cage. Flowers were then examined under ultraviolet light for fluorescing fecal matter. We found that bumble bees did defecate on floral surfaces during foraging and that composite flowers with a large area of disk flowers were the most likely to have feces on them. Our results point to defecation by bumble bees during foraging as a potential mechanism for inoculation of flowers with pollinator pathogens and suggest that flower shape could play a significant role in inoculation.

Influence of weather factors on separate periods of fungus Claviceps purpurea (Fr.) Tul development and level of ergot harmfulness in Kirov region

In 2001-2017 in the conditions of Kirov region 36 winter rye varieties were assessed according to the character of interrelation in a "Secale cereale - Claviceps purpurea" pathosystem. The article provides the results of this research. For assessment of the change in meteorological conditions and their influence on ergot development the average daily air temperature and amount of precipitations from May 1 to May 31 (the period of screrotia germination) and from June 5 to June 15 (the period of plants infection) were used. The study of varieties was carried out by artificial inoculation of flowers with pathogen suspension. The ergot recording was carried out at a phase of milk-wax ripeness of grain according to infection of biocenoses (quantitative trait) and on contamination of grain mass with sclerotia (qualitative trait). At an artificial inoculation all rye varieties under study were infected by ergot in limits from 8.3 up to 100% that demonstrated their strong susceptibility to disease. Only 6 varieties (Falenskaya 4, Kirovskaya 89, Rada, Flora, Dymka, and Volkhova) were infected at the level of 8.3-27.3%, contamination of grain mass by sclerotia – 0.4-1.9%. The standard variety Falenskaya 4 had a high productivity and efficiency of plants (660 g/m2 and 11.0 g), which was characterized by a high degree of re-growth after infestation with a snow mold (100%), the smallest distribution of an ergot in sowing and contamination of grain mass with sclerotia. During the correlation analysis a close relation between the infestation of plants with an ergot and contamination of grain mass with sclerotia (r = 0.76) was established. The same immunological traits significantly influenced on the productivity (r = -0.67 and -0.55) and insignificantly - on plants efficiency. The positive dependence between immunological traits and 1000-grain mass was revealed. Possibly, sterilization of an ear leads to formation of a larger grain in fertile flowers (r = 0.42 and 0.37). The regression equations between the amount of sclerotia in an ear, mass of grain per ear and a number of grains in it have proved with 95-97% probability that with 1 sclerotium increase in contamination per ear, the grain mass per ear decreases by 0.18 grams, and the amount of grains per ear – by 4.7 pieces.

BREEDING FOR HOST RESISTANCE TO FIRE BLIGHT

Breeding for fire blight resistance in apple and pear has a long tradition. It was primarily related to the importance of the disease in the area where breeding programs are located. The main sources of resistance are wild species with low quality fruits. To introgress these sources of resistance, several breeding generations are required to develop resistant varieties with commercial fruit quality. Different methods are currently applied to speed up the generation cycle. However, also commercial cultivars and modern breeding material show considerable differences in susceptibility. Genotypes carrying a high level of resistance can be used as parents in breeding. Phenotypic scoring of resistance is mainly done by shoot inoculation tests on grafted plants in greenhouses. These tests can be complemented by outdoor flower inoculation tests to achieve a more comprehensive resistance evaluation. Progress in the development of molecular markers closely linked to fire blight resistance loci allow breeders for more efficient selection.

Histopathology of Sclerotinia sclerotiorum infection and oxalic acid function in susceptible and resistant soybean

The success of the necrotrophic fungus Sclerotinia sclerotiorum is largely dependent on its major virulence factor, oxalic acid (OA). Virulence is lost in transgenic plants that express OA degrading enzymes, e.g. oxalate oxidase (OxO). The histopathology of S. sclerotiorum infection and OA accumulation was examined in a transgenic soybean line over‐expressing OxO (OxO‐OE) and its isogenic parent (WT). In situ flower inoculation showed that the OxO‐OE plants were highly resistant to the pathogen while the WT parents were susceptible. This difference in resistance was not apparent in the floral tissues, as aggressive hyphal activity was similar on both hosts, showing that high OxO activity and low OA accumulation in OxO‐OE was not a deterrent. However, the process of fungal infection on excised leaf tissue differed on the two hosts. Primary lesions developed and showed similar severe ultrastructural damage on both hosts but rapid lesion expansion (colonization) proceeded only on the WT, concomitant with OA accumulation. Oxalic acid rose in OxO‐OE 1 day post‐inoculation and did not change over the following 3 days, showing that colonization can be blocked by maintaining low levels of OA. However, OxO degradation of OA did not deter initial host penetration and primary lesion formation. This shows that OA, the major virulence factor of S. sclerotiorum, is critical for host colonization but may not be required during primary lesion formation, suggesting that other factors are contributing to the establishment of the primary lesion.

Identification of a molecular dialogue between developing seeds of Medicago truncatula and seedborne xanthomonads

Plant pathogenic bacteria disseminate and survive mainly in association with seeds. This study addresses whether seeds are passive carriers or engage a molecular dialogue with pathogens during their development. We developed two pathosystems using Medicago truncatula with Xanthomonas alfalfae subsp. alfalfae (Xaa), the natural Medicago sp. pathogen and Xanthomonas campestris pv. campestris (Xcc), a Brassicaceae pathogen. Three days after flower inoculation, the transcriptome of Xcc-infected pods showed activation of an innate immune response that was strongly limited in Xcc mutated in the type three secretion system, demonstrating an incompatible interaction of Xcc with the reproductive structures. In contrast, the presence of Xaa did not result in an activation of defence genes. Transcriptome profiling during development of infected seeds exhibited time-dependent and differential responses to Xcc and Xaa. Gene network analysis revealed that the transcriptome of Xcc-infected seeds was mainly affected during seed filling whereas that of Xaa-infected seeds responded during late maturation. The Xcc-infected seed transcriptome exhibited an activation of defence response and a repression of targeted seed maturation pathways. Fifty-one percent of putative ABSCISIC ACID INSENSITIVE3 targets were deregulated by Xcc, including oleosin, cupin, legumin and chlorophyll degradation genes. At maturity, these seeds displayed decreased weight and increased chlorophyll content. In contrast, these traits were not affected by Xaa infection. These findings demonstrate the existence of a complex molecular dialogue between xanthomonads and developing seeds and provides insights into a previously unexplored trade-off between seed development and pathogen defence.

First Report of Fusarium succisae Causing Flower Rot on Thread-leaf Coreopsis.

In July 2010, flower rot of thread-leaf coreopsis (Coreopsis verticillata) was found in a garden in the Icheon City, Korea. The disease affected about 20 to 50% of a 100 m2 area. The disease was characterized by the appearance of pinkish mycelia on the stigmata and inflorescences of flowers. In some cases, flowers failed to bloom or turned brown before opening fully. Fragments (each 5 × 5 mm) of the symptomatic tissue were surface-sterilized with 1% NaOCl for 1 min, and then rinsed twice in sterilized distilled water. The tissue pieces were placed on water agar (WA) and incubated at 25°C for 4 to 6 days. Twenty-two isolates of Fusarium species were obtained from the diseased flowers. All isolates were identified as Fusarium succisae based on their morphological characteristics on carnation leaf agar (CLA) medium and DNA sequences of the translation elongation factor 1-alpha gene (1). Macroconidia and sporodochia were sparsely produced on CLA medium. Microconidia were abundant, borne in false heads, oval or allantoid and sometimes pyriform, and measured 4.2 to 13 × 2.2 to 5.4 μm. Chlamydospores were absent. The EF-1α gene was amplified from three isolates by PCR assay and the amplification products were sequenced (2). The nucleotide sequences obtained were deposited in GenBank with accession numbers KF514658, KF514659, and KF514660. BLASTn analysis showed 99% homology with the EF-1α sequence of F. succisae NRRL13613 (GenBank Accession No. AF160291). Pathogenicity tests were conducted with inoculation of flowers on Coreopsis verticillata. Spore suspension was prepared by flooding 7-day-old cultures on potato dextrose agar with sterilized 2% (w/v) sugar solution. When the plants started to have buds, the isolates were inoculated by placing one drop (20 μl) of spore suspension (1 × 106 spores ml-1) into the buds. Fifteen buds of the plants were arranged into three replications. The control was treated with sterilized 2% sugar solution. Inoculated plants were kept in a greenhouse at 25/20°C (12 h/12 h). Three weeks after inoculation, the symptoms were observed on buds with mycelial production. Control plants had no mycelia on buds. F. succisae was re-isolated from the inoculated flowers. To our knowledge, this is the first report of flower rot of thread-leaf coreopsis caused by F. succisae.

EVALUATION OF LIKELIHOOD OF CO-OCCURRENCE OF ERWINIA AMYLOVORA WITH MATURE FRUIT OF WINTER PEAR

Phytosanitary concerns about fire blight prohibit export of U.S.-grown pears to some countries without this disease. To examine these concerns, we evaluated the potential for co-occurrence of Erwinia amylovora with mature, symptomless winter pear fruit by inoculation experiments and by survey of commercial orchards. Immature pear and apple fruit were inoculated in orchards with E. amylovora strain 153N as resuspended lyophilized cells or as ooze from diseased tissues. Regardless of inoculum source, population size of Ea153N on fruit declined by an order of magnitude every 3 to 4 days during the first 2 weeks after inoculation; at 56 days after inoculation, Ea153N was not detected, except on 1 of 450 fruit with 4 colony forming units (CFU). After inoculation of flowers, calyx-end survival of Ea153N on pear and apple fruit declined from high populations at petal fall to a few cells at harvest, with no detection of the pathogen after a 7-week cold storage. Migration of Ea153N into symptomless pear fruit from diseased branches was evaluated by enrichment assay and nested polymerase chain reaction of internal fruit core tissues; these assays failed to detect the pathogen in healthy fruit from diseased trees. At harvest, E. amylovora could not be detected on 5,599 of 5,600 fruit of d'Anjou pear sampled from commercial orchards in major production areas of the Pacific Northwest; one fruit yielded 32 CFU of the pathogen. Postharvest, mature pear fruit contaminated with Ea153N and subsequently wounded required a dose of >10,000 cells at the wound site to allow for persistence of the pathogen through a 7-week-cold storage. We conclude that epiphytic E. amylovora shows similar survival characteristics on both pear and apple fruit, this pathogen is not an endophyte within mature symptomless pear fruit, its presence is exceptionally rare on commercially produced fruit, and that epiphytic survival of E. amylovora through a postharvest chilling period is unlikely given the unrealistically high population size required for persistence.

MÉTODOS DE INOCULAÇÃO DE PLÂNTULAS DE FEIJOEIRO PARA AVALIAÇÃO DE GERMOPLASMA QUANTO A RESISTÊNCIA A Sclerotinia sclerotiorum (Lib.) De Bary

The development of a reliable method of inoculation of dry bean ( Phaseolus spp. ) with Sclerotinia sclerotiorum is of great importance for evaluation of genotypes for resistance to white mold. The objective of this study was to test three inoculation methods in different parts of 11-day-old Phaseolus spp seedlings. The plant was inoculated with a suspension of ascospores at the blossom stage as a reference for comparing the efficiency of the methods tested, since it simulates field infections. The methods consisted of the inoculation of leaves or axils with disks of PDA containing mycelia; and inoculation of the stems with a toothpick colonized by the pathogen. Nine dry bean genotypes of Phaseolus spp . and two isolates of S. sclerotiorum (UnB 1541 and UnB 1547) were used to test the methods. The inoculated plants were incubated in a fog room, with 100% humidity, a temperature of 21±2oC and a photoperiod of 12 hours. The incubating period varied from two days for the PDA disk leaf inoculation, four days for the axil inoculation and ten days for stems inoculation with toothpicks colonized by the pathogen and flowers inoculation with ascospores. Disease assessment was accomplished by using a key ranging from 1 to 9 (1= no symptoms; 9= plant dead). Inoculation of seedlings in the axils using PDA disks containing mycelia was the best method to differentiate the genotypes, it also presented similar results to the inoculation of flowers with ascospores. The isolate UnB 1541 was more virulent than UnB 1547, and discriminated better the genotypes for resistance or susceptibility to S. sclerotiorum. KEY-WORDS: White mold; genetic resistance; Phaseolus spp ; inoculation method.

Evaluation of Likelihood of Co-Occurrence ofErwinia amylovorawith Mature Fruit of Winter Pear

ABSTRACT Phytosanitary concerns about fire blight prohibit export of U.S.-grown pears to some countries without this disease. To examine these concerns, we evaluated the potential for co-occurrence of Erwinia amylovora with mature, symptomless winter pear fruit by inoculation experiments and by survey of commercial orchards. Immature pear and apple fruit were inoculated in orchards with E. amylovora strain 153N as resuspended lyophilized cells or as ooze from diseased tissues. Regardless of inoculum source, population size of Ea153N on fruit declined by an order of magnitude every 3 to 4 days during the first 2 weeks after inoculation; at 56 days after inoculation, Ea153N was not detected, except on 1 of 450 fruit with 4 colony forming units (CFU). After inoculation of flowers, calyx-end survival of Ea153N on pear and apple fruit declined from high populations at petal fall to a few cells at harvest, with no detection of the pathogen after a 7-week cold storage. Migration of Ea153N into symptomless pear fruit from diseased branches was evaluated by enrichment assay and nested polymerase chain reaction of internal fruit core tissues; these assays failed to detect the pathogen in healthy fruit from diseased trees. At harvest, E. amylovora could not be detected on 5,599 of 5,600 fruit of d'Anjou pear sampled from commercial orchards in major production areas of the Pacific Northwest; one fruit yielded 32 CFU of the pathogen. Postharvest, mature pear fruit contaminated with Ea153N and subsequently wounded required a dose of >10,000 cells at the wound site to allow for persistence of the pathogen through a 7-week-cold storage. We conclude that epiphytic E. amylovora shows similar survival characteristics on both pear and apple fruit, this pathogen is not an endophyte within mature symptomless pear fruit, its presence is exceptionally rare on commercially produced fruit, and that epiphytic survival of E. amylovora through a postharvest chilling period is unlikely given the unrealistically high population size required for persistence.

Monilia mumecola, a new brown rot fungus on Prunus mume in Japan

In 1982, an anamorphic fungus in the genus Monilia was first isolated as the causal agent of brown rot disease of Japanese apricot or mume (Prunus mume) in Oita Prefecture, Kyushu, Japan. Inoculation of flowers, shoots, and fruit of P. mume with the fungus reproduced brown rot disease symptoms similar to those found in nature. The fungus somewhat resembled the colony appearance of Monilinia (anamorph Monilia) laxa, the apricot brown rot fungus, on PSA plates, but it differed from the latter and the other two brown rot fungi, M. fructigena and M. fructicola, in terms of growth rate, temperature optima for mycelial growth and sporulation, morphology and germination pattern of conidia, nuclear number in the conidium, and nucleotide sequences in the ITS region of ribosomal DNA. It is newly described as Monilia mumecola Y. Harada, Y. Sasaki & T. Sano. A key to anamorphic states of four brown rot fungi of fruit trees is provided.

Internal fruit rot caused by Fusarium subglutinans in greenhouse sweet peppers

Experiments were conducted to isolate the causal organism of internal fruit rot in greenhouse sweet pepper (Capsicum annum), confirm its identity, and elucidate its transmission mode and host range. The effects of inoculum concentration, growth stage of the plant, and cultivar of sweet pepper on disease development were also determined. The causal organism was identified as Fusarium subglutinans. Inoculum concentrations of 104 to 106 conidia/mL resulted in a higher incidence of fruit infection compared with 103 conidia/mL when just-opened and fully opened flowers were inoculated. Inoculation of flowers at different stages with F. subglutinans resulted in more diseased fruits than fruit inoculations. None of the seeds from infected pepper fruits germinated, and 92% of those yielded typical F. subglutinans colonies. No evidence of root infection of pepper plants by F. subglutinans was observed, and no disease developed on fruits of greenhouse tomato, cucumber, or eggplant. Fruits of Capsicum annuum ‘Bison’ and ‘Mazurka’ were less susceptible to F. subglutinans than those of ‘Sympathy’ and ‘444’.

Greenhouse and field assessments of resistance in soybean inoculated with sclerotia, mycelium, and ascospores of Sclerotinia sclerotiorum

Thirty-five soybean lines were evaluated for sclerotinia stem rot (SSR) resistance using stem inoculations with mycelium in the field and greenhouse, flower inoculations with mycelium or ascospores in the field and greenhouse, and soil infestation with sclerotia in the field, between 1997 and 2000. Symptoms were evaluated by stem lesion length (SLL, mm) and lesion extension (LE, mm) after stem inoculations; infected flowers (IF, %) and a disease severity index (DSI, %) after flower inoculations with ascospores and mycelium; and a DSI after soil infestation with sclerotia. Results show significant differences among lines for SLL and LE in the greenhouse and for IF and DSI in the field and greenhouse. Significant correlations were found between stem inoculation and sclerotia method and between all trials with flower inoculation using either ascospores or mycelium. Maple Donovan and Frisquet were the least susceptible genotypes after flower inoculations with ascospores, whereas OAC Bayfield was the most susceptible. Maple Donovan was also the least susceptible genotype after mycelium stem inoculation in the trials in 2000, while OAC Bayfield was again the most susceptible. Nattosan was the most susceptible genotype in trials conducted in the fields infested with sclerotia. In this study, flower inoculations provided better discrimination than stem inoculations in the assessment of soybean genotypes for SSR resistance, and the results suggested two phenotypes of partial or incomplete resistance, one occurring in the flower, and the other in the stem. Key words: Sclerotinia sclerotiorum, soybean, mycelium, ascospores, inoculation, resistance