Influence of environmental conditions in a glasshouse on conidia ofBotrytis cinerea and on post-harvest infection of rose flowers

Quantification and horizontal distribution of air-borne inoculum ofBotrytis cinerea in a rose crop in a glasshouse of 300 m² was studied in 1991 and 1992. Conidia ofB. cinerea were caught in spore traps consisting of an agar medium selective forB. cinerea in Petri dishes placed within the crop, at flower height 1 m above the ground. Spore catches were counted as colonies, after incubation. Lesions due to conidial infection were counted on petals of rose flowers, also after incubation. Relative humidity (RH) and temperature within the glasshouse and global radiation and windspeed outside were recorded during the experiments. The horizontal distribution ofB. cinerea in a rose crop grown under glass was fairly uniform in both years. In 1991 a clear seasonal pattern in the number of colonies could not be found. In 1992 the number of colonies were high in August, September and October. The number of lesions on rose flowers showed a distinct pattern in both years. In August, September and October many lesions were counted whereas in the other months few lesions appeared. In linear regression analysis, variation in numbers of colonies (spore catches) could not be explained by environmental factors recorded during the experiments. Linear regression accounted for 76 and 63% of the variation in the number of lesions on rose flowers in 1991 and 1992, in terms of relative humidity (positively correlated), global radiation outside the glasshouse (negatively correlated) and, numbers of colonies on spore traps (positively correlated). The results in the rose crop suggest that RH, global radiation and spore density in glasshouses are important variables in regulating the numbers of lesions during storage and transport. The numbers of spores in glasshouses are dependent on the production system. A glasshouse with a system resulting in wet dead tissue on the ground give higher amount of spores in the glasshouse air and through that high numbers of lesions on flowers. On roses outside the glasshouses very high numbers of lesions were counted sometimes, mostly during and after rain showers, as a result of rain-deposition of spores onto the flowers.     

Horizontal and vertical distribution of airborne conidia of Botrytis cinerea in a gerbera crop grown under glass

The horizontal and vertical distribution of airborne conidia ofBotrytis cinerea in a gerbera crop in two glasshouses (100 m² and 350 m²) was studied during 18 months in 1988 and 1989. Conidia ofB. cinerea were caught in simple spore traps consisting of agar in Petri dishes placed in a regular pattern at three different heights in the glasshouse and counted as colonies, after incubation. Lesions due to conidial infection were counted on gerbera petals. The horizontal and vertical distribution of conidia ofB. cinerea in a gerbera crop grown under glass was fairly uniform in both distinct glass-houses. Conidia ofB. cinerea trapped in a glasshouse can originate from sources inside and outside the glasshouse. No significant interaction was found between location and time for the colony counts and for the log transformed (ln(N+1)) lesion counts. The results of this study suggest that spore trapping at one height and at a limited number of locations and dates is sufficient for efficient monitoring ofB. cinerea in a glasshouse.     

Effects of temperature,vapour pressure deficit and radiation on infectivity of conidia ofBotrytis cinerea and on susceptibility of gerbera petals

The effect of vapour pressure deficit, temperature and radiation on the postharvest susceptibility of gerbera flowers toB. cinerea, on the water relations of gerbera flowers and on the lesion formation after conidial infection ofB. cinerea was studied. The temperature range in whichB. cinerea could germinate and growin vitro is 5–30 °C. In climate chamber experiments flowers had more lesions ofB. cinerea at temperatures of 20 and 25 °C than at 10 and 15°C. At 15, 20 and 25°C the infectivity ofB. cinerea conidia was negatively affected during a storage-period of 7 days. At a vapour pressure deficit (VPD) of 200 Pa significantly more conidia ofB. cinerea were infective than at 800 Pa. At a VPD of 800 Pa the susceptibility of gerbera flowers forB. cinerea was not significantly different than at 200 Pa. High radiation levels in glasshouses in spring and summer negatively influenced the infectivity of conidia ofB. cinerea on the flower surface, but did not affect the susceptibility of gerbera flowers forB. cinerea. In spring and early summer conidia lost their infectivity at high radiation levels, high temperatures and high levels of VPD. In summer gerbera flowers could be more susceptible toB. cinerea because of high temperatures in glasshouses, but the negative effect of radiation on the conidia ofB. cinerea seemed to overrule the temperature effect. Thus, the numbers of lesions in spring and summer can be low compared with the numbers in other seasons, although the numbers ofB. cinerea colonies on spore traps can be high. The effect of temperature on the susceptibility of gerbera flowers can probably be explained by changes of water status in the petals. At higher temperatures the number of lesions and the turgor (=water potential—osmotic potential) in the petals increased. Temperatures <10°C during lesion formation (RH>95% and VPD<50 Pa) had a temporary negative effect on the number of lesions. After 3 days of incubation the numbers of lesions were about equal (30 lesions/cm²) from 5 to 20°C. At 30°C no lesion formation was observed even after 3 days.     

Components of resistance of apple to powdery mildew (Podosphaera leucotricha)

Components of resistance of apple to Podosphaera leucotricha were assessed in the glasshouse by spraying shoot tips of cultivars with conidia. Disease incidence (proportion of leaf surfaces with mildew) and colony numbers were higher and incubation periods correspondingly shorter on the older leaves. unrolled at the time of inoculation. Numbers of colonies were higher on the lower surface. Spore production per colony was higher on the younger leaves. In general, a short incubation period on a cultivar was associated with a high disease incidence, many colonies and high spore production. For some cultivars the association between these components permitted resistance to be classified as very high (cv. Discovery), very low (cv. Golden Delicious), or intermediate(cvs Bramley's Seedling. Suntan). The effects of inoculum concentration and post-inoculation environment (glasshouse or outdoors) on components of resistance were assessed in a further study. No interactions between cultivar and inoculum concentration were detected. There was generally an associated variation in components between cultivars within an environment, but inconsistencies in cultivar rankings were noted between the two environments and the two studies. Mean incubation period was shorter and colony area larger in the glasshouse than outdoors. There were significant differences in conidia/cm² colony between cultivars only in the glasshouse. Components conferring high resistance in cv. Discovery and low resistance in cv. Golden Delicious were confirmed in both environments and in both studies.     

Relations between glasshouse climate and dry weight of petals,epicuticular wax,cuticle, pre-harvest flowering period and susceptibility toBotrytis cinerea of gerbera and rose flowers

Studies were conducted on the effects of seasonal levels of relative humidity, temperature, and total radiation, on dry weight of petals, on fresh weight of epicuticular wax and of cuticle of petals, on numbers ofBotrytis cinerea lesions in petals, and on preharvest flowering periods in gerbera and rose. No temporal relationships or significant correlations were found among dry weight of petals, weight of wax and cuticle of petals, and numbers of lesions on the petals. Temperature, relative humidity and total radiation did not correlate significantly with dry weight of petals, or with fresh weights of wax and cuticle of petals, except for a positive correlation between relative humidity and cuticle weight in the gerbera cultivar Delphi. No relation was found between weight of epicuticular wax and cuticle of petals and susceptibility of gerbera and rose petals toB. cinerea. The thickness of wax and cuticle on flowers did not seem to be an important factor influencing the susceptibility of flowers toB. cinerea. The seasonal pattern in number of lesions produced on the flowers byB. cinerea was related to the effects of relative humidity and radiation on infectivity of conidia of the pathogen on the flower surface but not to the effects on the susceptibility of flowers.     

Costs and Benefits of Quarantine Measures against Liriomyza trifolii in Finland1

In order to prevent the entry of Liriomyza trifolii into Finland the importation of rooted chrysanthemum, gerbera, cucumber, tomato and lettuce plants is prohibited, as well as the importation of chrysanthemum cut flowers and leaves of gerbera. Unrooted chrysanthemums and gerberas must be cultivated in quarantine for two weeks before they are approved. During 1982 the total costs of this quarantine survey were 70,000 Fmk. Eradication of the pest has been more expensive; in 1980 its eradication from eight glasshouses caused total costs of 380,000 Fmk to the government, and in 1982 the corresponding figure with four glasshouses was 280,000 Fmk. The range of costs of chemical control in glasshouses growing vegetables and chrysanthemums while « living with >> L. trifolii are estimated to be 0.8–8.8 million Fmk depending on whether 10 or 100 % of the growing area is to be treated. When all the costs caused by exclusion measures are summed (eradication + quarantine) and compared with the costs of « living with >> the pest, the ratio will be 1: 3 to 1: 13 depending on the use of insecticides. The secondary effects of additional use of insecticides on biological control or marketing difficulties because of residues are not included in this comparison. In this case the most economical way of avoiding problems caused by L. trifolii is to invest in pre-entry quarantine measures and prevent its spread into the country.     

Epidemiological aspects of Didymella bryoniae,the cause of stem and fruit rot of cucumber

The survival ofDidymella bryoniae and the incidence of ascospores in glasshouses, outdoors and under controlled conditions were studied. The fungus was able to overwinter in the open as dormant mycelium. Dry and undecomposed crop residues remained a source of infection for more than one year. Moisture and a minimum temperature between 5 and 10°C were needed for fructification. For ascospore release a high relative humidity was not sufficient, the substrate had to be moist during a short period. Ascospores could be trapped throughout day and night both outdoors and in glasshouses, but there was a marked peak during a period of 3 h in the evening. Both on days with and without rain about the same numbers of ascospores were trapped from crop residues in the open. Ascospore release was favoured by watering the plants in the glasshouse. Under controlled conditions the release of ascospores was determined by humidity and not by light or darkness. In a cucumber crop in the glasshouse the first ascospores were trapped at about the same time the first symptoms on the plants appeared. In the glasshouse with introduced diseased plant debris, particularly when the debris became wet when the plants were watered, the disease was more severe and yield was less than in a glasshouse without introduced plant debris. Airborne ascospores may cause the primary infection of a cucumber crop. Therefore, hygienic measures must be taken to eliminate plant debris as source of infection, both in glasshouses and outdoors.     

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

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

Potential for a sticky trap monitoring system for the diamondback moth (Lepidoptera: Yponomeutidae) on cabbages in Indonesia

Experiments on the development of a sticky trap monitoring system for the diamondback moth, Plutella xylostella (L.), were carried out in six cabbage fields (two in each of three villages) in North Sulawesi, Indonesia. This region is characterized by small, closely‐situated, fields. Yellow cardboard traps with a sticky upper surface were placed 10 cm below the crop canopy, four traps per field, and were maintained throughout the 1991 growing season. Larvae were sampled weekly in quadrats centred around each trap. One village where continuous cabbage growing occurred had higher P. xylostella populations than the other two villages, where growing is discontinuous. Although the relationship between trap catches and larval populations for individual fields was weak, the relationship between catches in all fields pooled and larval populations 2 weeks later was very strong, suggesting that a region‐wide predictive system would be feasible. An increase in larval numbers as distance from the traps increased further suggests that sticky traps may have potential for use in mass trapping.     

Epidemiology and control of Botrytis cinerea in tomato crops grown under cover in Greece

Out-of-season tomatoes grown in unheated glasshouses in Greece annually suffer considerable losses from grey mould induced by Botrytis cinerea. Characteristic soft rots of young fruit by the calyx end, flower abortions and stem lesions or cankers are the most commonly occurring symptoms of the disease. Severe ghost spots on fruit only appear when fungicides inhibiting spore germination are not applied. Conidia produced on plant debris of the previous year's crop serve as primary inoculum. Disease starts in late autumn, increases rapidly during the winter period and ceases abruptly at the end of April. Infections caused by isolates resistant to dicarboximides or to both dicarboximides and benzimidazoles are uncommon at the beginning of each new crop cycle. These increase substantially as the season progresses and decline after cessation of fungicide sprays. By contrast, infections caused by benzimidazole-resistant strains are stable throughout the growing season. Efficient disease control implies use of proper glasshouse covering material, adequate indoor air circulation, partial night heating, strict indoor and outdoor hygiene and regular fungicide sprays. When disease pressure is low, application only of conventional compounds like dichlofluanid and chlorothalonil is recommended. Under conditions favourable to Botrytis infections, mixtures of conventional compounds with reduced strength specific botryticides should preferably be applied. Such regimes efficiently minimize losses from fungicide resistance development and ghost spot.     

Effectiveness of Some Insecticides on Wheat Blossom Midges in Winter Wheat

Orange wheat blossom midge damage can impart serious loss of quantity and quality of winter wheat. Wheat midges were evaluated in large scale field in winter wheat in Bad Lausick (Leipzig, Saxsony) central Germany. The present study aimed at studying the activity of wheat blossom midges WBM, Sitodiplosis mosellana (Géhin) and Contarinia tritici (Kirby) using pheromone, sticky traps and two types of water traps. Management of midges with different treatments was studied; Karate (pyrethroid), Biscaya (neonicotinoid) and NeemAzal T/S (botanical insecticide) were sprayed on wheat at heading stage (GS 55). Monitoring was conducted before the treatment and continued for 4 weeks after the treatment. Pheromone traps were used for forecasting midge adult population and determine the control date. Water traps were used to assess midge larvae, while midge adults were surveyed using sticky traps. A strong correlation between midge catches and weather conditions was obtained; as well a coincidence between pheromone catches and wheat midge infestation in the susceptible growth stages (GS 47–65) was recorded. Insecticide applications to fields of midge-infested winter wheat significantly reduced the wheat midge damage. There were significant differences in wheat midge numbers between treated and untreated; wheat midge numbers were lower in the treated than in control. The results proved that both Karate and Biscaya caused more mortality to wheat midges than NeemAzal T/S.     

Wind dispersal of conidia of Botrytis spp. pathogenic to Vicia faba

Increasing numbers of conidia were blown from sporulating cultures of Botrytis fabae and B. cinerea as windspeed increased up to 10 m/s. Partial drying of cultures increased the number of spores blown away at low and intermediate windspeeds. Release of spores at a constant windspeed was sustained over a prolonged period. Different patterns of release from colonies of the two species when windspeed was gradually increased, or at a constant windspeed. may be related to differences in spore size affecting the drying rate. Many conidia of both species were released as clumps. A higher proportion of B. cinerea than B. fabae conidia were clumped, partly because the mean number of spores per clump was greater. Individual conidia fell more slowly in still air than did clumps. The humidity in a bean crop was more favourable to development of Botrytis lesions than that above the crop. Low windspeeds measured within crops may restrict dispersal of conidia and may result in uneven distribution of chocolate spot lesions.     

Seasonality of the common cutworm Spodoptera litura in a soybean ecosystem

Seasonal occurrence of the common cutworm Spodoptera litura (Fab.) (Lepidoptera: Noctuidae) moths captured in synthetic sex pheromone traps and associated field population of eggs and larvae in soybean were examined in India from 2009 to 2011. Male moths of S. litura first appeared in late July or early August and continued through October. Peak male trap catches occurred during the second fortnight of September, which was within soybean reproductive stages. Similarly, the first appearance of S. litura egg masses and larval populations were observed after the first appearance of male moths in early to mid-August, and were present in the growing season up to late September to mid-October. The peak appearance of egg masses and larval populations always corresponded with the peak activity of male moths recorded during mid-September in all years. Correlation studies showed that weekly mean trap catches were linearly and positively correlated with egg masses and larval populations during the entire growing season of soybean. Seasonal means of male moth catches in pheromone traps during the 2010 and 2011 seasons were significantly lower than the catches during the 2009 season. However, seasonal means of the egg masses and larval populations were not significantly different between years. Pheromone traps may be useful indicators of the onset of numbers of S. litura eggs and larvae in soybean fields.     

Spore traps need improvement to fulfil plant biosecurity requirements

Spore traps are widely used in plant pathology, but less so in plant biosecurity. Potentially they can be used to determine the geographical extent of a plant pathogen incursion, to track the active spread of an incursion, and to declare area freedom following an eradication program. This review discusses the abilities and constraints of spore traps in the context of plant biosecurity, and highlights the problems that need to be overcome before spore traps can be routinely used for detection and eradication of plant pathogen incursions. To meet biosecurity requirements, spore traps must be efficient, mechanically reliable and any spores captured must be rapidly identified and quantified. At present, there is significant variation in types of spore traps, and in the methods used to capture and identify spores. Standard spore traps are generally inefficient for surveillance because they do not sample large volumes of air or capture samples that are representative of entire crop growing regions. If spore traps are to become routinely used for plant biosecurity purposes, improved designs, novel applications and standard operating protocols must be developed. A better understanding of background atmospheric data and the spatial and temporal characteristics of pathogen spores will be required to design trapping systems and protocols so that incursions can be readily detected, and presence/absence data can be confidently reported.     

Identification of W-type and R-type isolates of Pseudocercosporella herpotrichoides

W-type isolates of Pseudocercosporella herpotrichoides grown on a maize-based agar and exposed to near- ultra-violet radiation at c . 13°C produced a greenish black colour, whilst R-type isolates produced a pink or pale brown colour in the agar medium. More colonies from directly plated lesions or from spore suspensions could be recognized as P. herpotrichoides and could be more easily differentiated as W-type or R-type or as mixtures of both by colour production on maize agar (MA) than by colony morphology on potato dextrose agar (PDA), despite the presence of other fungi. Isolates with intermediate morphology on PDA were positively identified as W-type or R-type on MA; their pathogenicities to wheat and rye seedlings were usually similar to those of W-type or R-type isolates with typical colony morphology, confirming their identification on MA. Drops of mixed suspensions of W-type and R-type spores on PDA formed fast-growing colonies with smooth margins which sometimes had slow-growing sectors with feathery margins. Drops of the same mixtures on MA formed greenish black colonies which sometimes had pink or pale brown sectors. However, when these mixtures were spread onto MA, W-type and R-type colonies could easily be differentiated by colour.     

Some biological observations on pale fruit,a viroid-incited disease of cucumber

A viroid-incited disease characterized by pale fruits, crumpled flowers, and rugosity and chlorosis on the leaves of cucumber, occurs occasionally in cucumber crops grown in glasshouses in the Netherlands. The disease is found primarily in crops planted in spring, rarely in those planted in summer but not in those planted in late summer. The pathogen can be transmitted with sap, during pruning, by grafting and with dodder to cucumber and a number of other cucurbitaceous species, but not withM. persicae. There is no evidence for seed or nematode transmission. The incubation period is 21 days at high temperatures (30°C) but shorter after inoculation by razorbalade slashing. The number of glasshouses with the disease has increased since 1965, but the number of diseased plants is usually low. The initial distribution of diseased plants in the glasshouses suggests that the pathogen is introduced by an insect.     

First report of Rhizopus stolonifer causing inflorescence and fruit rot of Rauvolfia serpentina in India

Inflorescence and fruit rot caused by Rhizopus stolonifer has appeared for the first time on Rauvolfia serpentina (sarpgandha) in North Indian plains during July–September, 2003. Disease incidence was very high under high humidity and moderate temperature and posing threat to the commercial cultivation of the crop. The initial disease symptoms appear in the form of water-soaked lesions on the flowers and flower buds which later produce slimy wet rot symptoms leading to premature death and drying of infected parts including the leaves. Pathogenicity of R. stolonifer was established artificially under glasshouse conditions.     

Relationship between Concentrations of Botrytis Cinerea Conidia in Air, Environmental Conditions, and the Incidence of Grey Mould in Strawberry Flowers and Fruits

Atmospheric concentrations of Botrytis cinerea conidia were monitored for two seasons in a strawberry crop in Moguer (Huelva, southwestern Spain). Concentrations of conidia were estimated using a Burkard volumetric spore sampler. A diurnal pattern of conidial release was observed. Airborne conidial concentration was significantly and positively correlated with the average solar radiation and mean temperature, and negatively with rainfall and relative humidity. Among the weather variables considered, solar radiation showed the most consistent results in the regression analysis, explaining over 40% of airborne conidial concentration variability. Correlation between Botrytis fruit rot incidence and accumulated number of conidia over seven days was significant and positive. Two regression models containing three variables explained over 62 and 52% of the fruit rot incidence variability. A positive but non-significant correlation was established between B. cinerea incidence in flowers and airborne conidial concentration. It was not possible to fit a consistent regression model to relate flower infection incidence to conidial concentration or weather variables.     

Comparison of different positions and heights of yellow sticky traps for sampling populations of the leafminerLiriomyza trifolii

A study was carried out to determine the optimal height, position (angle) and direction of yellow sticky traps for maximum attraction ofLiriomyza trifolii flies above gerbera plants. Catches at 30 cm above the plant tops were greater than at 70 cm above the tops. Horizontal and 45° angle traps caught larger numbers on the upper side, whereas with vertical traps there was no effect of side. Catches on vertical traps were greater than those on horizontal and 45° angle traps. Free-hanging vertical traps caught more flies than fixed traps facing north and south. Publication of the Agricultural Research Organization. No. 2437-E, 1988 series.     

孢子捕捉仪在植物病害监测中的应用

作为一种孢子取样和监测工具,孢子捕捉仪的应用实现了空气中病原菌孢子的捕捉、计数和识别等功能,使许多流行性病害得以提前预警,及时精准施策,从而为作物高产稳产起到了关键性作用。本文在对各种类型孢子捕捉仪自身特点和实际应用效果对比分析的基础上,以孢子捕捉技术的发展为主线,详细介绍了常见孢子捕捉仪的原理、特点、应用范围和捕捉后分析方法,综述了孢子捕捉仪在植物病害流行研究和生产实践中的应用情况,以及如何量化与鉴定所捕捉病原菌孢子的方法。为更好地实现田间病害监测及防治策略制订提出了孢子捕捉仪今后改进的方向,旨在使该类仪器在病害监测方面更好地服务于农林生产。