Fruit Mummies Research Articles

New findings on the effects of different factors involved in fig limb dieback caused by Neoscytalidium dimidiatum in California

The San Joaquin Valley (California, USA) represents an important fig (Ficus carica) production area in the United States. Fig limb dieback represents a serious and emerging disease of fig caused by Neoscytalidium dimidiatum. In the present study we evaluated the effect of tissue age on canker development, the recovery of the fungus from fruit mummies collected in the field, the ability of N. dimidiatum to colonize, under laboratory condition, fig fruits, and the in vitro effects of different water potentials (Ψs) on mycelial growth rate.Results of our study showed that the older branches (> 3-year-old) resulted in longer canker compared to the younger ages. N. dimidiatum was not recovered from the mummies, instead they were colonized by many other fungal saprophytes. Laboratory experiments showed the ability of this species to colonize dried fig fruits from 20 °C to 35 °C. In vitro water potentials experiment showed that the mycelial growth was reduced with the decrease of water potential (from 1–3 -MPa), depending on salt type.

Monitoring Spore Dispersal and Early Infections of Diplocarpon coronariae Causing Apple Blotch Using Spore Traps and a New qPCR Method.

Apple blotch (AB) is a major disease of apple in Asia and recently emerged in Europe and the United States. It is caused by the fungus Diplocarpon coronariae (formerly Marssonina coronaria; teleomorph: Diplocarpon mali) and leads to severe defoliation of apple trees in late summer, resulting in reduced yield and fruit quality. To develop effective disease management strategies, a sound knowledge of the pathogen's biology is crucial. Data on the early phase of disease development are scarce: No data on spore dispersal in Europe are available. We developed a highly sensitive TaqMan qPCR method to quantify D. coronariae conidia in spore trap samples. We monitored temporal and spatial dispersal of conidia of D. coronariae and the progress of AB in spring and early summer in an extensively managed apple orchard in Switzerland in 2019 and 2020. Our results show that D. coronariae overwinters in leaf litter, and spore dispersal and primary infections occur in late April and early May. We provide the first results describing early-season dispersal ofconidia of D. coronariae, which, combined with the observed disease progress, helps to understand the disease dynamics and will be a basis for improved disease forecast models. Using the new qPCR method, we detected D. coronariae in buds, on bark, and on fruit mummies, suggesting that several apple tissues might serve as overwintering habitats for the fungus, in addition to fallen leaves. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Taxonomy, distribution, epidemiology, disease cycle and management of brown rot disease of peach (Monilinia spp.)

Peach is a temperate fruit and is grown in various edaphoclimatic settings worldwide. Brown rot, caused primarily by Monilinia spp. is one of the most destructive peach diseases. The disease results in severe pre-harvest and post-harvest losses. More than half of the world’s post-harvest losses of peach can be attributed to brown rot disease. Despite the widespread adoption of management strategies such as pruning, removing fruit mummies, eliminating wild plums, chemical control remains an effective strategy for managing brown rot disease. However, environmental and human health impacts of chemical control and fungicides resistance consequences, these management tactics tend to be re-evaluated. The aim of this review is to comprehensively sum up the available information on the taxonomy, distribution, epidemiology, symptomology, molecular and morphological characterization of brown rot disease, and to date management approaches. However, fast paced current research on brown rot disease of peach management should be carefully updated for the full-proof control of the fungi. Nevertheless, more research and review of the information regarding various aspects of diseases management exclusively biocontrol agents are needed to exploit their actual potential, which is the salient objective of this review. This review will open new avenues giving future prospects and research agenda to the scientists working on this serious pathosystem of peach.

Identification of inoculum sources of Fusicladium eriobotryae in loquat orchards in Spain

Fusicladium eriobotryae is the causal agent of loquat scab, the main disease damaging fruit, leaves and young twigs of this crop. A two-growing season study (2015–2016 and 2016–2017) was carried out in two loquat orchards (cv “Algerie”) to determine the inoculum sources of F. eriobotryae by direct observation of conidia, pathogen isolation on culture media and detection using a new real time PCR protocol developed in this study. One-year-old twigs, fruit peduncles and fruit mummies were randomly sampled three times per growing season on each orchard, and inflorescences only at flowering. Conidia of F. eriobotryae were not found and the isolation of the pathogen was neither possible from any sample in both seasons. Specific primers FUG2F and FUG2R, were designed to detect and quantify DNA of F. eriobotryae on plant material, with a limit of detection (LOD) established at 48.6 fg/μl. The DNA of the pathogen was not detected by real time PCR in fruit mummies nor inflorescences. It was detected in fruit peduncles and twigs in the season 2016–2017 with concentrations ranging from 50 to 2742 fg/μl, confirming that this two loquat organs might act as potential inoculum sources for F. eriobotryae. The detection of F. eriobotryae only in this season agrees with the predictions of an epidemiological model for this pathogen. Our results indicate that in years with a high disease pressure, fruit twigs and peduncles might act as a source of inoculum of new infections the following year.

A Review of Sooty Blotch and Flyspeck Disease in German Organic Apple Production

Sooty blotch and flyspeck (SBFS) fungi colonise the surface of a range of fruits, especially apple, without penetrating the cuticle. Economic damage results from the exclusion of severely affected fruit batches from being marketed as table apples. A study of SBFS was conducted in 2007–2012 in the two largest German apple production areas, i.e. the Lake Constance and Lower Elbe regions. The absence of this disease complex from orchards under integrated pest management in both regions in all years was explained by the collateral effects of scab and storage-rot sprays with captan and quinone-outside inhibitors (QoI) such as trifloxystrobin. However, SBFS was economically relevant in organically managed orchards, being generally more severe in Southern Germany than in the North. In both regions, Peltaster cerophilus was the most frequently isolated SBFS fungus and was chiefly responsible for crop losses. Cyphellophora sessilis, Microcyclosporella mali and Schizothyrium pomi also contributed to SBFS in some organic orchards, whereas a diversity of additional species was confined to untreated orchards. Evidence was obtained that P. cerophilus overwinters within orchards, fruit mummies being one of presumably several colonised plant organs. Infections of young apple fruits were initiated at any time following the end of flowering, and P. cerophilus was capable of causing several infection cycles per season by means of conidial inoculum. The colonisation of sheets of waxed paper by P. cerophilus indicated that this species does not require fruit leachates for growth. No further expansion of colonies was observed during cold storage; instead, P. cerophilus was gradually displaced by other fungi. Differences in the susceptibility of apple varieties to P. cerophilus were due to fruit ripening, late-maturing cultivars being most heavily colonised, and to surface properties, varieties with a waxy bloom being conspicuously less strongly colonised than others. This fungus was unable to colonise russeted fruit areas. Repeated spray treatments with lime-sulphur and potassium bicarbonate throughout the season were effective and necessary to control SBFS in organic production. This strategy threatens the fungicide-saving potential offered by scab-resistant apple varieties. Cultural measures against SBFS include summer pruning as well as the manual removal of fruit mummies in winter.

Alternative inoculum sources for fire blight: the potential role of fruit mummies and non‐host plants

Fire blight is the most damaging bacterial disease in apple production worldwide. Cankers and symptomless infected shoots are known as sites for the overwintering of Erwinia amylovora, subsequently providing primary inoculum for infection in the spring. In the present work, further potential sources of inoculum were investigated. Real‐time PCR assays covering a 3‐year‐period classified 19·9% of samples taken from fruit mummies as positive. Bacterial abundance in fruit mummies during autumn, winter and spring was up to 109 cells per gram of tissue and correlated well with later infection rates of blossoms. Blossoms of non‐host plants growing close to infected trees were also shown to be colonized by E. amylovora and to enable epiphytic survival and propagation of bacteria. The results indicate a potential role of fruit mummies and buds in overwintering and as a source of primary inoculum for dissemination of the pathogen early in the growing season. Non‐host blossoms may also serve as an inoculum source in the build‐up of the pathogen population. Both aspects may contribute significantly to the epidemiology of E. amylovora. The significance of infected rootstocks as an inoculum source is also discussed. Fruit mummies might be used to determine pathogen pressure in an orchard before the beginning of the blooming period.

Control of sooty blotch and black rot of apple through removal of fruit mummies

Abstract Several popular apple cultivars retain their aborted fruits as mummies on the tree. In laboratory conditions, overwintered fruit mummies collected from a Northern German apple orchard under organic management released inoculum, which caused black rot due to Diplodia seriata and sooty blotch due to Peltaster cerophilus on ripe apples. In a field trial conducted over four years in another organic orchard, the manual removal of fruit mummies in winter and again in late June of each year significantly reduced the incidence of both these diseases. However, fruit mummy removal did not significantly affect the development of storage rots due to Neofabraea alba and N. perennans. The potential, limitations and costs of this phytosanitary measure are discussed in the context of organic apple production.

Sources and Availability of Inoculum and Seasonal Survival of Sphaeropsis pyriputrescens in Apple Orchards.

Sphaeropsis pyriputrescens is the cause of Sphaeropsis rot, a recently reported postharvest fruit rot disease of apple. Infection of apple fruit by the fungus is believed to occur in the orchard, and symptoms develop during storage or in the market. S. pyriputrescens also is the cause of a twig dieback and canker disease of apple and crabapple trees. To determine sources of pathogen inoculum in the orchard, twigs with dieback and canker symptoms, dead fruit spurs, dead bark, and fruit mummies on the trees were collected and examined for the presence of pycnidia of S. pyriputrescens. To monitor inoculum availability during the growing season from early May to early November, dead fruit spurs or twigs from Fuji trees, and twigs with dieback from crabapple trees (as a source of pollen for apple production) in a Fuji orchard as well as dead fruit spurs and dead bark from Red Delicious trees in a Red Delicious orchard were sampled periodically and examined for the presence and viability of pycnidia of S. pyriputrescens. To determine seasonal survival and production of pycnidia of the fungus on twigs, apple twigs were inoculated in early December, sampled periodically for up to 12 months after inoculation, examined for the presence of pycnidia, and subjected to isolation of the fungus from diseased tissues to determine its survival. Pycnidia of S. pyriputrescens were observed on diseased twigs, dead fruit spurs and bark, and mummified fruit on both apple and crabapple trees, suggesting that these tissues were the sources of inoculum for fruit infection in the orchard. With the combined observations from two orchards during three growing seasons, viable pycnidia of the fungus were present throughout the year and observed in 50 to 100% of the Fuji trees, >90% of crabapple trees, and 0 to 50% of the Red Delicious trees. S. pyriputrescens was recovered from diseased tissues of inoculated twigs at all sampling times up to 12 months after inoculation. The results suggest that S. pyriputrescens can survive as mycelium in diseased twigs in north-central Washington State and that availability of viable S. pyriputrescens pycnidia is unlikely a limiting factor for infection of apple fruit in the orchard leading to Sphaeropsis rot during storage.

Overwintering of Monilinia spp. on Mummified Stone Fruit

AbstractMummies were evaluated over the course of four growing seasons to ensure they are source of primary inoculum. The percentage of mummies with presence of conidia and its viability were determined in tree and ground mummies. The number of conidia and its germination were also quantified. Fruit mummies with Monilinia spp. were consistently detected on tree mummies in all studied orchards and growing seasons. However, the percentage of viable mummies over the same sampling periods decreased, and in most cases, it was 0% by October. The percentage of ground mummies with Monilinia spp. was lower and less viable in comparison with tree mummies, tending to decrease faster. The number of overwintering conidia in tree mummies decreased smoothly from 1 × 106 to 1 × 104 conidia/mummy between April and September. On the other hand, the number of conidia in ground mummies rapidly decreased to 0 conidia/mummy at around May–July. The profiles for the percentage of conidia germinated were similar in all cases. The information obtained from this study is a step forward to understanding the epidemiology of Monilinia spp., a useful tool to manage disease development.

Fruit infection and disease cycle of Botrytis cinerea causing cosmetic scarring in persimmon fruit (Diospyros kaki Linn.)

Dark brown, corky spots on the skin of persimmon fruit (Diospyros kaki Linn.) are a cosmetic disorder known as scarring. In New Zealand the disorder causes substantial revenue losses to the persimmon industry. Microscopical examinations showed that the scarring is associated with Botrytis cinerea Pers. In spring, the fungus first colonises the senescent corolla adhering to the juvenile fruit and subsequently attempts to infect the underlying exocarp tissue. Histological and immunolabelling microscopy revealed that the fungus produces mycelial cushions composed of finger-like clusters of hyphae on the fruit surface. Attempted infection triggers a defence response in the fruit which prevents the fungus from establishment, and causes death and discolouration of the surrounding epidermal cells (hypersensitive reaction). Affected areas appear as dark specks to the naked eye and develop into corky scars as the fruit develops. Monitoring in two persimmon orchards suggested that conidia produced from infected senescent corollas infect the corolla of new emerging blossoms, leading to repeated cycles of infection during the flowering period. Conidia from over-wintering sclerotia in calyxes, pedicels and fruit mummies represent likely primary inoculum sources for infection of the corolla in spring. New foliage also often becomes infected by B. cinerea, resulting in necrotic lesions producing large quantities of conidia in spring. Such leaves, as well as aborted fruitlets and wounded fruit, are probable secondary sources of inoculum. A proposed disease cycle for B. cinerea causing fruit scarring in persimmon orchards in New Zealand is presented.

Phacidiopycnis washingtonensis, Cause of a New Storage Rot of Apples in Northern Europe

Phacidiopycnis washingtonensis was identified by morphology and ITS sequence analysis as the cause of rubbery rot, a new storage disease of apples in northern Germany. Infected fruits had an unusually firm texture and pale appearance after storage in ultra-low oxygen conditions, but turned dark brown to black in ambient atmosphere. Ultimately, the surface of rotted fruits became covered by black pycnidia producing cream-coloured conidial exudates. Rubbery rot affected several apple varieties, including the commercially important ‘Jonagold’ and ‘Elstar’. Losses during storage were commonly below 1% but reached 5–10% in a few cases. Fruits of ‘Golden Hornet’ crab apple trees planted as pollinators in commercial orchards became heavily infected by P. washingtonensis in October. Conidia were released throughout the following season from infected fruit mummies, which remained attached to the crab apple tree.

INCIDENCE OF DRY ROT OF POMEGRANATE IN HIMACHAL PRADESH AND ITS MANAGEMENT

Pomegranate is highly susceptible to dry fruit rot caused by Coniella granati (Sacc.) Petrak and Sydow, and the disease has resulted in substantial losses and is threatening the upcoming pomegranate cultivation in Himachal Pradesh. The disease starts on fruits which are half grown or larger. The rot is characterized by softening of the rind and underneath pulp and seed. Ultimately the entire fruit turns brown to black after complete rotting. An extensive and comprehensive survey of various pomegranate orchards was conducted to record the incidence revealed that incidence of dry fruit rot varied from 0.55 to 22.7% with a mean incidence of 8.38% at various locations in Himachal Pradesh. The incidence was higher in Solan district where the infected fruits were often seen in the form of dark brown to black fruit mummies scattered on the orchard floor. The disease appeared maximum during the first week of August after an extended period of warm and foggy weather. Pre-harvest sprays with Bavistin and Stop among systemic fungicides gave significant control whereas, among non systemics, spray of Indofil M-45 showed some promise. Postharvest efficacy of systemic fungicides was better as protectant (pre-inoculation treatment) rather than eradicant (post-inoculation). Attempts have been made to control fruit rot with eco-friendly methods such as wrappers, fumigants, coatings, antagonists, botanicals which included plant oils and plant extracts. Fumigation with sodium or potassium meta bisulphite was superior in checking the disease. Bavistin wrappers and Nipro Fresh coating exhibited significant protection of pomegranate against dry fruit rot. Fungal antagonists, viz., Trichoderma virens, T. harzianum, T. hamatum and T. polysporium gave maximum inhibition of mycelial growth of C. granati. Antagonist protection was higher when applied at a concentration of 108 spores/ml before inoculation. 100% inhibition of mycelial growth of C. granati was obtained with citronella oil at 1000 ppm. Pre-inoculation treatment with plant extracts of darek (Melia azadirach), dedonia (Dedonia viscosa), lantana (Lantana camara) and pepper mint (Mentha piperita) provided significant control of fruit rot of pomegranate.

Primary Inoculum Sources of Monilinia spp. in Spanish Peach Orchards and Their Relative Importance in Brown Rot.

Immediately following the identification of Monilinia fructicola in a Spanish peach orchard in the Ebro Valley in 2006, this orchard and two other orchards in the same valley were intensively sampled for potential tree and ground sources of primary Monilinia inoculum before and during three growing seasons between 2006 and 2008. Overwintered Monilinia spp. produced inoculum from only mycelium, and no apothecia were found in any of the three orchards over the three growing seasons. Mummies on trees were the main source of primary inoculum. More than 90% of Monilinia isolates on all fruit mummies were M. laxa. Positive relationships were found between (i) the number of mummified fruit and the incidence of postharvest brown rot (P = 0.05, r = 0.75, n = 8), and (ii) the number of mummified fruit and nonabscised aborted fruit in the trees and the number of conidia on the fruit surface (P = 0.04, r = 0.71; P = 0.01, r = 0.94, respectively, n = 8) and the incidence of latent infection (P = 0.03, r = 0.75; P = 0.001, r = 0.99; respectively, n = 8). In addition, the numbers of mummified fruit and pruned branches on the orchard floor were correlated with the number of airborne conidia in the orchard. Based on the results of these surveys, the control of brown rot in stone fruit orchards is discussed.

Overwintering of Monilinia fructicola in Stone Fruit Orchards in Northern China

AbstractSurvival of Monilinia fructicola on the surface of mummified fruit and in peduncles and shoots of stone fruit trees infected by M. fructicola in the previous season was studied from 2003 to 2006 in orchards in the agricultural region of Beijing. Viable conidia of M. fructicola were consistently detected on fruit mummies from mid‐March to the end of April. During flowering (in mid‐April), studies in five peach orchards showed that 33–87% of mummified fruit bore viable conidia. The germination rate of conidia on diseased fruit was about 64% in autumn. It decreased to 24% in mid‐winter when the fruit was completely mummified, and in the following year to 2–4% in early spring. Viable M. fructicola was consistently detected in peach and nectarine shoots collected in winter and spring. In general, viable M. fructicola in peduncles was detected from mummified fruit of 11–27% branches and from asymptomatic plant tissues of 3–20% branches. Sporulation of M. fructicola was observed on peduncles in seven of eight surveys, and the percentage of branches containing viable M. fructicola in peduncles in contact with mummified fruits ranged from 18% to 40%. This study demonstrates that the tree‐borne mummified fruit and the peduncles could be the parts of trees where M. fructicola can survive the winter in orchards in suburban Beijing.

Temporal Dynamics of Brown Rot in Different Apple Management Systems and Importance of Dropped Fruit for Disease Development

ABSTRACT Epidemic development of brown rot, caused by Monilinia fructigena, was monitored in integrated and organic apple orchards at two locations in eastern Hungary between 2002 and 2005 on three cultivars with early, midseason, and late ripening periods. Disease incidence and severity measures were affected significantly (P < 0.05) by management system (organic versus integrated) and cultivar, but there was no significant management system-cultivar interaction. Epidemics started 2 to 4 weeks earlier in organic orchards and on the early cv. Prima compared with integrated orchards and the late cv. Mutsu. Disease intensity increased markedly in the final 3 to 5 weeks before harvest and was considerably lower in integrated than in organic orchards. Final brown rot incidence on fruit in the tree was correlated with incidence on dropped fruit on the orchard floor (r > 0.75, P < 0.05), whereby the lag period from the appearance of the first symptomatic fruit on the ground to the occurrence of the first symptomatic fruit in the tree ranged from 2 weeks to 2 months, depending on the cultivar. The inflection point of the disease progress curve was attained first by fruit on the ground, followed successively by fruit in the lower, middle, and upper thirds of the tree canopy. This may indicate that dropped fruit that became infected early provided a source of inoculum for subsequent epidemics by serving as a bridge between sporulation from overwintered fruit mummies in the spring and the first fruit with sporulating lesions in the tree in midsummer. Removal of dropped fruit from the orchard floor resulted in a significantly lower disease incidence on fruit in the tree on all cultivars; thus, drop-removal may be useful as a brown rot management practice in apple orchards.

Epidemiology of apple leaf spot

Apple leaf spot (ALS) caused by Colletotrichum spp. is a major disease of apple (Malus domestica) in Southern Brazil. The epidemiology of this disease was studied in experiments carried out in the counties of Passo Fundo and Vacaria, State of Rio Grande do Sul, from February 1998 to October 2000. The disease was found in all the six apple orchards sampled in the growing seasons of 1997/98 and 1998/99. The fungus isolates associated with ALS fit the characteristics of C. gloeosporioides (75%), C. acutatum (8%), and Colletotrichum sp. (17%). The pathogen overwintered in dormant buds and twigs but not in dropped leaves or fruit mummies. Two sprays of copper oxychloride (at 0.3%) reduced the fungus initial inoculum by 65-84.6% in buds and 85.6-93.7% in twigs, but had no effect on the early season progress of the disease. Disease severity increased proportionally to elevation of temperature from 14 to 26-28 °C. At 34 °C, however, infection was completely inhibited. The duration of leaf wetness required for infection ranged from two hours at 30 °C to 32 h at 16 °C. The relationship of temperature (T) and leaf wetness (W) to disease severity (Y) was represented by the model equation Y = 0.00145[((T-13)1.78)((34.01-T )1.09)] * 25/[1+14 exp(-0.137W)], R² = 0.73 and P &lt; 0.0001. Currently, this information is being used to manage the disease and to validate a forecast system for ALS.

Mycoflora of Stone Fruit Mummies in California Orchards.

Stone fruit mummies infected by Monilinia fructicola were periodically collected in winter from trees and from the ground in eight orchards in 1995-96 and from five orchards in 1996-97. Mycoflora were determined by spreading mummy washings and plating inner tissues onto petri dishes containing acidified potato dextrose agar, then counting colonies of individual fungi after incubation at 23°C for 4 days. Twenty genera, representing 29 fungal species, were isolated from both mummy washings and inner tissues. Aspergillus japonicus, A. terreus, and species of Harknesia, Paecilomyces, and Trichoderma are the first recorded from species of Prunus in the United States, and Aureobasidium pullulans and Epicoccum purpurascens are the first reported for California. The principal mycoflora recovered from mummy washings were species of non-filamentous yeasts (32.1%), Penicillium (28.8%), Cladosporium (11.4%), and Mucor (10.8%). Major mycoflora of mummy inner tissues were species of Penicillium (23.7%), Mucor (19.6%), Cladosporium (17.3%), and Rhizopus (11.1%). The relative recoveries of individual fungi from mummy inner tissues differed with location, Prunus species, and sampling position (tree or ground), and changed as the season progressed. The relative recovery of M. fructicola from mummy inner tissues was negatively correlated with Botrytis (R = -0.53, P = 0.0052), Penicillium (R = -0.58, P = 0.0681), and Rhizopus (R = -0.50, P = 0.0696). These results could help obtain naturally occurring antagonists and maximize their use in biocontrol systems aimed at reducing primary inoculum for blossom blight of stone fruits in California orchards.

Identification of Subpopulations ofColletotrichum acutatumand Epidemiology of Almond Anthracnose in California

ABSTRACT In recent years, almond anthracnose has developed into a major problem for the California almond industry. The identification of the causal pathogen as Colletotrichum acutatum was confirmed using species-specific primers and restriction fragment length polymorphisms of ribosomal DNA in comparative studies with isolates of C. acutatum from strawberry and C. gloeosporioides from citrus. Two distinct clonal subpopulations among the almond isolates of C. acutatum were identified. These two subpopulations differed in their colony appearance (pink versus gray cultures), conidial morphology, virulence in laboratory inoculation studies, temperature relationships for growth, and molecular fingerprints using random and simple-repeat primers in polymerase chain reactions. Both subpopulations were commonly isolated from the same orchard or even the same fruit. In other orchards, one subpopulation predominated over the other subpopulation. Using random, simple-repeat, and species-specific primers, isolates of the almond anthracnose pathogen from Israel were very similar to the California isolates that produce gray colonies. In addition to fruit, the pathogen was isolated from blighted blossoms, water-soaked or necrotic leaf lesions, symptomless peduncles, and spurs and wood from branches showing dieback symptoms, indicating that the amount of tissue that may be infected is more extensive than previously considered. Overwintering fruit mummies were identified as inoculum sources for early spring infections. Growth studies using almond kernels with different moisture contents indicated that postharvest damage of stored kernels likely originates from preharvest field infections.

Springtime dispersal patterns of Monilinia laxa conidia in apricot, peach, prune, and almond trees

Numbers of airborne Monilinia laxa conidia were related to the maturity of the sporodochia, the nature of the host structure bearing them, and the presence or absence of rain or fog. Hirst spore traps collected more airborne conidia during rains and on rainy days than on dry days among prunaceous hosts during the spring of 1966 and 1967. Numbers of conidia were greatest (6440 m−3 h−1) in the first 3–4 h of rain, while in dry periods, numbers were greatest (1200 m−3 h−1) when ambient humidity was lowest and temperature and wind speeds were highest. Fruit mummies, twig cankers, limb cankers, pedicels, and peduncles all bore sporodochia. Rains washed off successive crops of conidia, and with 52 800 conidia cm−2 were collected directly below a sporulating peach fruit mummy. The significance of these dispersal periods in disease development and control is discussed.

The development of stromata of Sclerotinia fructicola and related species : II. In fruits

The development and structure of the stromata of the brown rot fungi were studied using stone fruits, apples and pears. Well-developed stromata were produced inside all the fruits, except apples, inoculated with S. fructicola. The stromata were similar to those formed in agar cultures, except for the inclusion of host cells in the medulla. The inner rind usually developed later than the outer one. On apples and pears, S. laxa forma mali produced only small localized brown areas around the sites of infection. In the other fruits inoculated with the European brown rot species, mummification took place in the outer cells and an outer but no inner rind developed. A thick hyphal mat developed on the outside of pears, nectarines and apricots infected by S. fructicola and this was organized into a structure similar to the stroma that develops in fruits and in agar cultures. Surface mycelium developed on some of the fruits infected by the European brown rot species, but the mats were not as well developed as that produced by S. fructicola. Microconidia were observed on some fruit mummies of all brown rot fungi. They were produced in largest numbers in the cavities between the outer surface of infected fruits and the inner surface of hyphal mats. Some were observed in depressions on the surface of plums and apricots infected with S. laxa and clusters also developed within the loosely interwoven hyphal mat formed on cherries by S. fructigena.