Rot Developed Research Articles

The effect of Busseola fusca infestation, fungal inoculation and mechanical wounding on Fusarium ear rot development and fumonisin production in maize

Fusarium verticillioides and Busseola fusca are among the most significant biotic constraints to maize production in South Africa. In this study, the effect of B. fusca damage and mechanical wounding to maize ears on Fusarium ear rot development and fumonisin production was investigated. The effect of the interaction on Fusarium ear rot and B. fusca damage was studied by inoculating maize ears with F. verticillioides isolate MRC826 and infesting plant whorls with aliquots of 10–15 neonate larvae at the 12th leaf stage prior to tasselling. To simulate hail damage, maize ears were mechanically wounded at the blister stage with cork borers of different sizes and number of wounds, with and without F. verticillioides inoculation. Uninoculated, uninfested and undamaged control treatments were included. Field trials were conducted over three seasons using a randomised complete block design with six replicates per treatment. In all seasons, most Fusarium ear rot developed on ears inoculated with F. verticillioides. This study indicated that B. fusca infestation was not associated with higher Fusarium ear rot incidence in two of the three seasons. Moreover, B. fusca infestation was not associated with high fumonisin production in any season. This indicates that the presence of B. fusca was not highly associated with Fusarium ear rot or fumonisin production, possibly due to its characteristic feeding nature that causes sporadic wounds on maize ears, but also the strong impact of weather variability. Fusarium ear rot development and fumonisin production by F. verticillioides inoculum varied seasonally indicating the importance of environmental conditions on Fusarium ear rot and fumonisin production. Fusarium ear rot and fumonisin production significantly increased with the severity of cork borer wounding in both naturally infected and artificially inoculated maize ears. Therefore, the prevention of severe injuries to kernels, whether by mechanical damage or insects, should be considered as important in reducing Fusarium ear rot and fumonisin production in maize.

Infection Courts and Timing of Infection of Apple Fruit by Phacidiopycnis washingtonensis in the Orchard in Relation to Speck Rot During Storage.

Phacidiopycnis washingtonensis is the cause of speck rot, a recently reported postharvest fruit rot disease of apple. The pathogen is believed to incite infections in the field, and disease symptoms become evident only during storage. To determine the timing of apple fruit infection in relation to development of speck rot in storage, 'Red Delicious' and 'Fuji' apple fruit were inoculated in the orchard with P. washingtonensis at different times during the growing season, harvested, and monitored for decay development during storage at 0°C. Fruit inoculated in both field and laboratory also were used to identify the infection courts and mode of apple fruit penetration by P. washingtonensis. In all 3 years, stem-end speck rot and calyx-end speck rot developed during cold storage on fruit inoculated during the growing season, regardless of inoculation time; and the incidence of total speck rot in storage increased as the fruit inoculation time approached harvest. On fruit floral parts, the pathogen colonized sepals at higher rates than stamens. Availability of naturally occurring necrotic tissues favored the colonization of the fungus on sepals. Histological studies indicated that infection occurred through micro-cracks on the surfaces of pedicels and sepals of the fruit, and invasion of these tissues was restricted between the cuticle and epidermis. Findings of this study will assist in the development of effective control strategies for speck rot.

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

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

Influence of the kind and age of the inoculum on the development of rot caused by Penicillium expansum (Link) Thom on stored apples

The influence of the kind and age of the inoculum on development of rot on 'Bankroft' and 'Mcintosh' apples was tested. The inoculum consisted of spore suspension and disks of culture of <i>Penicillium expansum</i> (Link) Thorn. Spores were taken from cultures 3, 7, 14, 28 and 52 days old. Disks were prepared from 3- and 7-day-old cultures. The mother cultures in both cases were inoculated with spore suspensione from 7-day-old culture. The influence of the kind and age of cultures was significant, particularly after longer storage period. The rot developed faster after inoculation with the disks of culture than with the spore suspension. The speed of rot development on the four cvs of apples was compared; the rot developed fastest on 'Mcintosh'.

Effects of Environmental Factors and Cultural Practices on Bull's Eye Rot of Pear.

Bull's eye rot of pome fruits caused by Neofabraea spp. is characterized by infection occurring in the orchard throughout the growing season whereas rot lesions develop during long-term storage after harvest. Bull's eye rot was observed on pear fruit exposed to natural infection for any of six to nine sequential 1-to-2-week exposure periods during two growing seasons. Highest infection levels were associated with exposure closest to harvest. Over-tree irrigation and late harvest resulted in higher bull's eye rot incidence than under-tree irrigation and early or mid-season harvest. Fruit were inoculated prior to harvest with Neofabraea perennans to determine the effect of environmental factors on the development of bull's eye rot. The effect of temperature was inconsistent; disease was greatest at 10°C in one year of study but greatest at 30°C in the second year. Bull's eye rot developed independently of wetness durations longer than 0.5 h.

Quantitative Relationships Between Different Injury Factors and Development of Brown Rot Caused byMonilinia fructigenain Integrated and Organic Apple Orchards

In a 4-year study, the incidence of various types of injuries (caused by insects, birds, growth cracks, mechanical wounding, and other, unidentified factors) was assessed in relation to brown rot development (caused by Monilinia fructigena) on fruit of three apple cultivars (Prima, Jonathan, and Mutsu) in integrated and organic blocks of two apple orchards in Hungary. In addition, populations of male codling moths (Cydia pomonella) were monitored with pheromone traps season-long in both management systems. On average, injury incidence on fruit at harvest was 6.1 and 19.2% in the integrated and organic treatments, respectively. Insect injury, which was caused primarily by C. pomonella, had the highest incidence among the five injury types, accounting for 79.4% of the total injury by harvest in the organic blocks and 36.6% in the integrated blocks. Levels of all other injury types remained close to zero during most of the season, but the incidence of bird injury and growth cracks increased markedly in the final 3 to 5 weeks before harvest in both production systems. Brown rot developed more slowly and reached a lower incidence in the integrated (6.4% final incidence on average) compared with the organic blocks (20.1% average incidence). In addition, the disease developed later but attained higher levels as the cultivar ripening season increased from early-maturing Prima to late-maturing Mutsu. Overall, 94.3 to 98.7% of all injured fruit were also infected by M. fructigena, whereas the incidence of brown-rotted fruit without visible injury was very low (0.8 to 1.6%). Correlation coefficients (on a per plot basis) and association indices (on a per-fruit basis) were calculated between brown rot and the various injury types for two selected assessment dates 4 weeks preharvest and at harvest. At both dates, the strongest significant (P < 0.05) relationships were observed between brown rot and insect injury and between brown rot and the cumulative number of trapped C. pomonella. At the harvest assessment, two additional significant correlations were between brown rot and bird injury and between brown rot and growth cracks. In every case, correlation coefficients were larger in organic than in integrated blocks. Although it is well established that brown rot in pome fruits is closely associated with fruit injuries, this is the first study to provide season-long progress data on different injury types and quantitative analyses of their relative importance at different times in the growing season and across two distinct management systems.

Development of Gibberella Ear Rot on Processing Sweet Corn Hybrids Over an Extended Period of Harvest

Gibberella ear rot, caused by Gibberella zeae, has increased in prevalence recently on lateseason processing sweet corn grown in North America. Little information is available about the development of Gibberella ear rot on processing sweet corn hybrids over extended periods of harvest. In five trials from 2003 to 2005, 12 processing sweet corn hybrids were inoculated with G. zeae and evaluated for severity of Gibberella ear rot on sequential harvest dates from 19 to 27 days after midsilk. Ear rot severity was assessed using a rating scale based on the percentage of kernels with visible symptoms of G. zeae colonization including kernel rot and mycelial growth. Severity ranged from 1.6 to 47.8% over the five trials. None of the hybrids was highly resistant to Gibberella ear rot, although some appeared to be less susceptible. Gibberella ear rot was less severe on three hybrids (GH 2690, GG 147, and Sprint) and more severe on three hybrids (GG 42, GG 145, and Jubilee). Other hybrids had moderate levels of ear rot or responses that varied among years. The relative response of hybrids did not change substantially during the extended period of harvest; however, the rate at which Gibberella ear rot developed on hybrids differed in 2003 and 2005 as reflected by a significant hybrid by harvest interaction. The interaction was primarily the result of Gibberella ear rot developing more severely on susceptible hybrids than on the less susceptible hybrids. The difference in Gibberella development could be exploited to limit losses due to this disease under certain circumstances. If a sweet corn processor had several fields ready to harvest at the same time, and some fields were planted with hybrids that are more susceptible while other fields were planted with hybrids that are less susceptible, losses due to Gibberella ear rot might be minimized by harvesting the most susceptible hybrids first. Other hybrids that might be best suited for early or late harvest can be identified from Gibberella ear rot ratings 28 days after silk channel inoculation at the midsilk growth stage.

Influence of temperature and bark injuries on the development of Phytophthora cactorum and P. Citrophthora on peach trees

The effect of temperature and bark injuries on the occurrence of crown rot of peach trees caused by P. cactorum and P. citrophthora were examined in field and laboratory. Lesions developed at 35 °C (the complete range of temperatures tested) but maximum development occurred at 20–25 °C. Greatest growth of these fungi on cornmeal agar (CMA) also occurred between 15 and 30 °C. Both pathogens could infect injured trees up to 20 days after wounding, but could not infect uninjured plants or plants wounded 40 and 30 days before inoculation, respectively. This study showed that temperature is a critical factor for the development of Phytophthora crown rot of peach trees. In addition, crown rot developed from recent wounds inoculated with agar plugs of Phytophthora.

Seasonal variations in populations of Fusarium species in wheat-field soil

Populations in soil of the fungus Fusarium culmorum, a cause of brown foot rot in wheat, and of other Fusarium spp. were monitored in two successive crops of autumn-sown wheat on each of three sites. The occurrence of fluctuations in populations, within and between crop-growing seasons, was confirmed. Smaller populations of F. culmorum occurred on the site that had not grown a cereal crop in the previous year. There was usually a decrease in F. culmorum in late autumn or early winter as temperature decreased and soil moisture increased. Its populations then increased in spring or summer, sometimes following rainfall, but with variations among sites in amount and timing. Conditions in each year were unsuitable for the development of brown foot rot or for rapid increases in populations of F. culmorum as foot rot developed. This led to populations that were generally smaller in the second year. The significance of these fluctuations for the development of disease on wheat from inoculum in the soil is discussed.

Phytophthora Brown Rot of Citrus: Temperature and Moisture Effects on Infection, Sporangium Production, and Dispersal.

Sporadic epidemics of Phytophthora brown rot occur in citrus orchards in Florida and are caused primarily by Phytophthora palmivora and secondarily by P. nicotianae. With P. palmivora, fruit wetness durations of 3 h or more resulted in maximum infection at favorable temperatures. The optimum temperature range for fruit infection and brown rot development was 27 to 30°C. No brown rot developed at 22°C or less. The optimum temperature for sporulation in culture and on the fruit surface was 24°C, with sporangium production decreasing rapidly at higher or lower temperatures. A few sporangia were produced with 18 h of fruit wetness, and numbers increased as duration of wetness increased up to 72 h. Propagules were splash-dispersed by single droplets of water from infested peel disks horizontally about 350 to 450 mm and vertically about 30 to 45 mm with most isolates. Sporangia were not dispersed by air currents alone. Few sporangia of P. nicotianae were produced on fruit surfaces, and they were not readily dispersed by falling water droplets. Brown rot caused by P. palmivora can become epidemic in Florida from July to October during the rainy season because of its high temperature optimum and prolific sporulation on the fruit surface.

EFFECT OF PEELING OF TULIP BULBS ON PYTHIUM TRANSMISSION FROM FIELD INTO GREENHOUSE

A cultural practice which is becoming more common in Dutch tulip-bulb production is peeling of the bulbs by machine. If this method is not used properly old roots can be left on the base of the bulb. An experiment was conducted to investigate if this might be hazardous with respect to development of root rot, caused by Pythium spp., during tulip-flower forcing in the greenhouse. Severe root rot developed in case old roots from bulbs collected from the field were not removed properly. No clear difference was observed between root rot severity of bulbs harvested from patches with above-ground Pythium symptoms and bulbs from a part of the field without above-ground symptoms. Removal of the old roots reduced root rot severity. Treatment of the poorly peeled bulbs with formaldehyde could not prevent root rot completely. Combination of proper peeling of the bulbs and formaldehyde dip gave a crop with a healthy root system.

Differences in tuber rot development for North American clones ofPhytophthora infestans

The relative aggressiveness ofPhytophthora infestons clones in potato tubers was compared in three trials using 7 to 24 isolates of 2 to 4 clones. Visible rot developed slowly at 13C with isolates of the US-1 genotype, the only significant clone found in North America prior to 1979, but substantially faster with most isolates of the newer clonal genotypes US-6, US-7 and US-8. Certain US-7 isolates were similar to US-1, and US-6 isolates also had a broad range of aggressiveness. Secondary infection byFusarium sp. increased rot development in many instances, but this effect was not clone-related. Differences in rot development may affect potato storage or late blight disease transmission.

Etiology of Root and Stalk Rots of Maize in North Queensland. Disease Development and Associated Fungi.

The etiology and development of mesocotyl, root and stalk rots of maize on the Atherton Tableland in north Queensland were investigated in two seasons. The identities and relative isolation frequencies of fungi from the mesocotyls, roots and stalks were determined at different stages of growth at two sites. Mesocotyl rot was first observed ca. 40 days after planting, and by ca. 80 days most of the mesocotyls and seminal roots were dead. Trichoderma spp., Penicillium spp., Pyrenochaeta indica, Fusarium moniliforme and F. oxysporum were isolated most frequently from the mesocotyls. Maize root rot developed in two distinct phases, in the first phase, it was independent of stalk rot and occurred on the lower nodal roots during vegetative growth from ca. 40 days. P. indica, recorded for the first time on maize, was the major fungus isolated from root lesions before maturity (ca. 130 days) but was uncommon thereafter. The second phase developed after physiological maturity and was associated with senescence and stalk rot. Fusarium graminearum, F. moniliforme and F. oxysporum prevailed at this stage. Stalk rot developed after physiological maturity and was most severe at the wetter site where pathogens caused severe defoliation and harvest was delayed by high humidity. A sequence of fungi occurred in maize stalks; Colletotrichum graminicola was prevalent immediately after maturity, while F. graminearum and F. moniliforme predominated at harvest.

Relationship of Soil Temperature and Moisture to Development of Phytophthora Root Rot of Azalea

Temperature and moisture effects on development of Phytophthora root rot of azalea caused by Phytophthora cinnamomi was compared for plants growing in containers and a landscape bed in both sun and shade environment. Symptoms of Phytophthora root rot developed earlier and disease severity was greater on plants grown in the landscape bed where soil temperature and moisture in the root zone of infected plants favored disease development. Disease severity was similar for plants in the bed regardless of exposure to the sun or shade. In container culture, disease severity was greater on plants in the shade where medium temperature was lower and moisture was greater, than on similar plants exposed to the sun.

Biological factors influencing stem deterioration rates and salvage planning in balsam fir killed after defoliation by spruce budworm

Balsam fir (Abiesbalsamea (L.) Mill.) trees dead between 0 and 5 years were sampled in three widely separated areas that had distinctly different population levels of the secondary, stem-attacking, balsam fir bark beetle (Pityokteinessparsus (Lec.)). The percentage of stem volume affected by sap rot increased significantly with the number of years since tree death. The wood volume lost in debarking tests, simulating pulp mill conditions, averaged 23% in trees dead 4–5 years in the two areas with the most sap rot, and in individual trees, debarking losses were significantly correlated with the extent of sap rot. Sap rot developed most quickly where stems had the most bark beetle activity, whereas where the bark beetle population was very low, sap rot development was significantly slower. These results are consistent with those of many earlier studies and observations in which a close relationship has been noted between the extent of sap rot and the intensity of bark beetle attack in stands of budworm-killed balsam fir. Evidence is presented indicating that stem deterioration rates and beetle activity frequently change with time in specific regions during any one budworm outbreak. It is postulated that inoculum levels of Polyporusabietinus (Dicks ex Fr.), the fungus responsible for the sap rot, and population levels of the balsam fir bark beetle are similarly and greatly affected by earlier occurrences of balsam fir mortality in a region. The average density of bark holes, caused by bark beetle tunneling in recently killed trees, can be used as a nondestructive and quick indicator of the average rate of development and probable extent of stem sap rot in budworm-damaged balsam fir stands. This information can be useful in assessments of the economic feasibility of proposed salvage operations.

The effect of some fleece characters on the skin wax layer and fleece rot development in Merino sheep following wetting

This paper describes changes occurring on the skin surface following wetting and during the development of fleece rot and examines the effect of some fleece characters on these changes. One day of wetting reduced the average thickness of the skin wax layer from 7.82 to 4.90 �m, but there was little change In the proportion of the skin surface covered by wax. When hyperaemia of the skin was first noted the proportion of the skin surface covered by wax had decreased from 97.8 to 47.5% and the average thickness of skin wax had decreased to 3.64 �m. Cholesterol content of the skin wax increased steadily from the first day of wetting as fleece rot developed, whereas lanosterol content increased only in the early stages of fleece rot. Suint content of the fleece, measured before wetting commenced, was positively correlated with fleece rot score at all times during wetting. Suint also showed significant correlations with moisture content of the proximal portion of the staple, percentage of the skin surface covered by wax and cholesterol and lanosterol content of the wax. No relationship was observed between fleece rot score and fleece wax content, wettability, staple formation, tip formation, crimp definition or initial thickness of the skin wax layer.

Effect of Constant Moisture Levels on Pythium Rot of Peanut Pods

Different constant levels of topsoil moisture were established by upward capillary movement of water from a basin through soil columns of different heights and were used to determine the influence of soil moisture on development of rot of peanut pods by Pythium myriotylum. Roots obtained water from a wet subsoil, whereas pods developed in a Pythium-infested, sandy, well-aerated topsoil. The wetter the topsoil, the higher the incidence of infected pods. However, some pod rot developed even in soil drier than the wilting range for mesophytes.

Accumulation of Respiratory Co2 around potato tubers in relation to bacterial soft rot

Bacterial soft rot of freshly harvested potatoes was associated with the exhaustion of O2 and the accumulation of CO2 in the atmosphere surrounding the tubers. The rates of depletion of O2 and accumulation of CO2 were correlated with the temperature of the respiring potatoes. When potatoes were held at temperatures near 30 C and aerated with humidified air, little decay developed during 3-day test periods. By contrast, when potatoes were placed in sealed containers at the same temperature O2 was depleted, CO2 exceeded 30% and soft rot developed in nearly all potatoes. The rate of CO3 accumulation in trucks being loaded with warm potatoes in consumer packages paralleled that found in experimental containers under controlled conditions. These results suggest that O2 depletion and CO2 accumulation may occur in loads of potatoes during loading and transit and accelerate the development of bacterial soft rot. The rapidity of CO2 accumulation would depend on the temperature of the potatoes and the rapidity of air movement through the load. The experimental results indicate that soft rot can be greatly reduced if the loaded potatoes are cooled to 13–18 C., or the load is so constructed that humid air circulates around warm potatoes.