Effects of humidity, leaf wetness, temperature and light on conidial production by Phaeoisariopsis personata on groundnut

Controlled-environment studies of conidial production by Phaeoisariopsis personata on groundnut are described. With constant relative humidity (RH), conidia were only produced above a threshold (94·5% RH) and there was a linear increase between 94·5% RH and 100% RH. Conidial production was less with continuous leaf wetness (resembling heavy dew) than with continuous 98–99% RH, but it was similar with intermittent leaf wetness and intermittent 98–99% RH (8 h at 70% RH each day). With alternate high (≥97% RH) and low humidity, daily conidial production depended both on the duration of high RH and on the low RH value. With 99% RH at night (12 h), night-time conidial production decreased with the previous daytime RH. After conidial production had started, small numbers of conidia were produced even when the RH was well below the threshold (94·5%). Conidia were produced in continuous light when the photon flux density was 2 μmol/m²/s, but production was completely inhibited with 60 μmol/m²/s. With constant RH, more conidia were produced with a 12 h photoperiod than in continuous darkness. However, more than 75% of the conidia were produced in the dark. With continuous darkness, more conidia were produced during the night (18.00–06.00 h) than during the day, but this biological rhythm was overcome with a (light-night)/(dark-day) regime. With constant 98–99% RH there was a linear increase in conidial production with temperature between 10 and 28°C, and virtually no conidia were produced at 33°C. The daily production of conidia increased with time for 2 to 6 days, depending on the treatment.     

Effects of temperature, wetness duration and leaf age on incubation and latent periods of black leaf mold (Pseudocercospora fuligena) on fresh market tomatoes

Black leaf mold (BLM), caused by Pseudocercospora fuligena is a serious threat to tomato production in the humid tropics. Accurate information about the incubation (IP) and latent period (LP) under various host susceptibility and weather favourability circumstances will help to formulate holistic approaches to manage this disease. In this study, effects of temperature, wetness duration, and leaf age on the monocyclic components (IP and LP) of BLM were studied from growth chamber (GC) and greenhouse (GH) experiments as well as detached leaf assays in growth cabins. Linear interpolation and inflection point (of logistic regression model) methods were used to determine IP and LP. These two methods were highly correlated in GC (r ²?=?0.89; P?<?0.0001) and GH experiments (r ²?=?0.90; P?<?0.0001) except when the epidemics were not asymptotic. Thus, IP and LP were estimated according to inflection point method. There was a delay of at least 5 days of IP and LP when plants were left in non-humid open environment than when exposed to wetness durations of 1, 2 or 3 days after inoculation. In general, IP and LP became shorter as the temperature increased from 20–24 and then to 28 °C. In growth chambers, there was more disease and consequently shorter IP and LP on young and unfolded tomato leaves that were 1-, 3-, or 5-week old at the time of inoculation than 7-week old leaves. In the greenhouse, there was about 50 % more disease incidence and sporulation on 1-week than 3-week old leaves. The shortest IP (8–11 days) and LP (12–13 days) were recorded from two out of three GH experiments on 1-week old leaves at an ambient mean temperature of 28.5 °C. This study implicated that fresh market tomatoes planted during warm temperatures in 50-mesh greenhouses and exposed to extended periods of wetness are highly prone to BLM infection at their young stages of growth.     

Modelling the effects of temperature and leaf wetness on monocyclic infection in a tropical fungal pathosystem

Modelling the epidemiology of water yam anthracnose (Dioscorea alata) caused by the fungus Colletotrichum gloeosporioides is an important research goal, as it will allow the investigation of a wide range of scenarios of new practices to reduce the disease impact before experimentation in the field. Developing such a model requires a prior knowledge of the fungus’s response to the environmental conditions, which will be affected by pest management. In this work, we first measured the response of the fungus to the main physical environmental factors controlling its development, namely temperature (ranging from 18 °C to 36 °C) and wetness duration (from 2 h to 72 h). As response variables, we measured the percentage of formed appressoria (relative to the total number of spores), the length of the latent period (time lag between inoculation and first symptoms observed), and the rate of necrotic lesion extension (percentage of diseased leaf surface at different time steps). These variables allow us to estimate the effects of temperature and wetness duration on the success of infection (appressoria formation) and the subsequent rate of disease development (latent period length and lesion extension rate). The data were fitted to non-linear models chosen for their ability to describe the observed patterns. From our data and model analyses, we were able to estimate parameters such as the optimal and maximal temperatures (25–28 °C and 36 °C, respectively), the required wetness duration to reach 20 % of infection success and the time to reach 5 % disease severity as a function of temperature.     

Effects of host resistance, temperature, leaf wetness, and leaf age on infection and lesion development of pecan scab

ABSTRACT The effects of partial host resistance, temperature, leaf wetness duration, and leaf age on infection and lesion development of pecan scab were evaluated. Trees of cultivars Wichita (susceptible) and Sumner (resistant) were inoculated with conidia of Cladosporium caryigenum and placed in mist chambers set at 15, 25, or 35 degrees C. The trees were removed from the chambers after 3, 6, 12, 24, 36, or 48 h of leaf wetness and placed in a greenhouse to allow disease development. After 8 to 16 days, disease began to develop on both 'Wichita' and 'Sumner'. Logistic regression analysis showed that the probability of a leaf becoming infected was greatest for 'Wichita' it decreased with increasing leaf age and temperature and increased with increasing leaf wetness. Leaves on 'Wichita ' were susceptible to infection between 2 and 23 days after budbreak, while leaves on 'Sumner' were susceptible to infection from 2 to 18 days after budbreak. Infection frequency, lesion size, and conidia production decreased proportionately with increasing leaf age. The magnitude of this effect was greatest on 'Sumner'. Conidia production was positively correlated with lesion size, and both were positively correlated with infection frequency on both cultivars.     

不同湿润持续时间及叶片温度对温室黄瓜霜霉病发生的影响

为探明不同湿润持续时间及叶片温度与黄瓜霜霉病发生的关系,通过观察不同湿润条件下黄瓜霜霉病的初显症时间,计算逐日显症率及累积显症率,并利用热红外成像仪对显症后叶片温度进行连续监测。结果显示,不同湿润持续时间对黄瓜霜霉病的初显症时间、逐日显症率产生影响。叶片湿润持续4 h,黄瓜霜霉病在接种后7.00 d显症;叶片湿润持续12 h,黄瓜霜霉病初显症时间最早,仅为3.25 d。叶片湿润持续时间不同,黄瓜霜霉病初显症时的叶片温度存在显著差异。回归分析表明,初显症时间与最大温差呈显著正相关,与平均温度呈显著负相关。叶片湿润持续4、6 h的病斑出现高峰在显症后第2、3天,逐日显症率分别是37.50%和41.18%,比叶片湿润持续10、12 h的早。显症后期,湿润持续时间4、6、8、10、12 h的病斑累积显症率分别是87.94%、93.71%、90.25%、84.24%和88.36%,差异不显著。表明接种黄瓜霜霉菌Pseudoperonospora cubensis后叶片湿润持续时间越长,潜育期越短,叶片最大温差越小,叶片平均温度越大。     

Effects of leaf wetness and temperature on late leaf-spot infection of groundnut

Experiments are described to quantify the effects of temperature and leaf wetness duration on infection of groundnut by Phaeoisariopsis personata. Temperature response curves for conidial germination and infection were similar, with optima close to 20°C and minimum and maximum temperatures of about 8°C and 34 C, respectively. The effect of temperature on infection between 15°C and 26°C was slight. Lesions developed only if the leaf wetness period exceeded about 20 h, and the total wetness period necessary for maximum infection exceeded 160 h. The number of lesions resulting from a fixed amount of inoculum was several times greater if leaves were exposed to alternate wet and dry periods (intermittent wetness), compared with continuous wetness. With intermittent wetness the length of the dry period had little effect on the number of lesions, providing it exceeded 2 h. The response curve relating total wetness periods to lesion density was an exponential asymptote.     

Requirements of leaf wetness and temperature for infection of groundnut by rust

Experiments are described to quantify the effects of temperature and duration of leaf wetness on infection of groundnut by Puccinia arachidis. After inoculation, a minimum period of leaf wetness, m. was necessary for infection. When leaf wetness duration was greater than m, lesion density increased with increasing wetness duration to an asymptote, D_max. The principal effects of temperature were on m and D_max- The value of m decreased linearly from 6 h, as temperature increased from 15 to 25 C and increased slightly at temperatures greater than 25 C D_max increased with temperature from zero at 8 C to a maximum at 22 C. and decreased to zero again at about 30 C. The experimental results were used to produce a set of curves relating an infection index to leaf wetness duration at different temperatures. The implications for infection of groundnut crops are discussed in relation to the climate at Patancheru in southern India.     

Effects of temperature, leaf wetness and cultivar on the latent period of Mycosphaerella graminicola on winter wheat

After inoculation of winter wheat cv. Longbow at a single time, lesions of M. graminicola were produced over a long interval starting 15–35 days after inoculation, dependent on temperature. There was no evidence that a single infection gave rise to more than one lesion. After the initial infection period at 100% relative humidity (r.h.), keeping leaves wet for c. 10 h per day did not shorten latent period on seedlings. Experiments in controlled-environment chambers demonstrated a minimum latent period at approximately 17°C Variation in the latent period of individual lesions was also minimum at this temperature. The latent period varied among the cultivars tested, cv. Longbow having the shortest, cv. Avalon having almost the longest. Field observations broadly confirmed the results of experiments in constant-environment chambers.     

Effects of temperature and leaf wetness on Pyrenophora teres growing on barley cv. Sonja

Conidia of Pyrenophora teres germinated only in the presence of liquid water and at temperatures above 2°C. The speed with which germination occurred was inversely proportional to temperature measured from a base of 2°C, up to the maximum temperature tested of 21°C. Once conidia on leaves had been wetted, about 40% of all infections that would eventually occur were established within 100°C-hours. Subsequent lesion extension was rapid, with area doubling times of about 1 day between 10 and 20°C.
If conidia germinated, up to 80% formed successful infections on young, susceptible leaves. On older leaves fewer spores germinated and the proportion that then infected was smaller.
The latent period, defined as the time before which sporulation did not occur under any wetness conditions, ranged from about 25 days at 5°C to 11 days at 20°C under dry conditions. Under continuously wet conditions it was about 20% shorter at all temperatures. Its inverse had a curvilinear relation to temperature.
Spores were produced after one to several days of humidity above 95%. The precise period decreased with increasing temperature, but at 25°C spores never appeared. The drier a dead leaf was, the longer the pathogen in it look to produce spores.     

Effects of temperature and continuous and interrupted wetness on the infection of pear leaves by conidia of Venturia nashicola

Experiments were conducted to determine: (i) the effects of temperature and duration of continuous wet periods on the infection of pear seedlings by conidia of Venturia nashicola , the causal agent of pear scab; and (ii) the effects of the length and temperature of dry interrupting periods on the mortality of infecting conidia. Average number of scab lesions per leaf increased with increasing duration of wetness. Logistic models adequately described the change in the average number of scab lesions per leaf at 5, 10, 15, 20 and 25°C over the wetness duration. At 30°C, only a few lesions developed. Simple polynomial models satisfactorily described the relationship of the three logistic model parameters (maximum number of lesions, rate of appearance and the time to 50% of the maximum number of lesions) with temperature. The optimum temperature for infection was found to be approximately 20°C. The relationship between mortality and the length of a dry period interrupting an infection process can be satisfactorily described by an exponential model. The rate of mortality at 10, 16 and 22°C did not differ significantly, but was significantly less than that at 28°C.     

Effects of leaf wetness duration, relative humidity, light and dark on infection and sporulation by Didymella rabiei on chickpea

No infection occurred at less than 95% relative humidity (r.h.) when chickpea plants were dried after inoculation with conidia of Didymella rabiei. Infection was significant when the dry leaves were exposed to 98% r.h. for 48 h. When inoculated plants were subjected to different leaf wetness periods, some infection occurred with 4 h wetness, and disease severity increased with wetness duration according to an exponential asymptote, with a maximum value after about 18 h. Germination of conidia and germ tube penetration increased linearly with increasing wetness periods when recorded 42 h after inoculation. With a 24-h wetness period, germination of conidia was first observed 12 h after inoculation and increased linearly with time up to 52 h (end of the experiment). Dry periods immediately after inoculation, followed by 24-h leaf wetness, reduced disease severity; as the dry period increased the severity decreased. Disease severity increased with increasing periods of darkness after inoculation. The number of pycnidia and the production of conidia on infected leaves increased only slightly with high r.h. (either in the light or in the dark), but large increases occurred over an 8-day period when the leaves were kept wet.     

Early development of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape (Brassica napus) in relation to temperature and leaf wetness.

In controlled environment experiments to study early development of light leaf spot, lesions developed with leaf wetness durations of 16 to 48 h after inoculation of oilseed rape with conidial suspensions of Pyrenopeziza brassicae at 12 or 18°C, but not with leaf wetness durations of 0 to 13h. The incubation period was 21 to 22 days at 12°C and 14 to 18 days at 18°C for leaf wetness durations of 16 to 48 h. The latent period was 21 to 23 days at 12°C and 18 to 19 days at 18°C, and the total number of lesions increased with increasing leaf wetness duration at both temperatures. In field experiments, light leaf spot always developed on oilseed rape with a leaf wetness duration of 48 h after inoculation in both 1990/1991 and 1991/1992, but the percentage leaf area affected was less on plants placed in an oilseed rape crop than on those placed in a glasshouse. Plants moved to an oilseed rape crop immediately after inoculation nearly always developed light leaf spot symptoms when they were inoculated between 19 October 1990 and 1 March 1991 or between 27 September 1991 and 14 February 1992, but plants inoculated between 31 August and 16 October 1990 or on 20 September 1991, when estimated leaf wetness duration was less than 16 h for several days after they were placed in crops, did not develop symptoms. The latent period of light leaf spot on plants transferred to the oilseed rape crop was 15 to 40 days, and there was an approximately linear relationship between 1 (latent period) and mean temperature during this period. The accumulated temperature during the latent period ranged from c. 150 to 250 day-degrees. The severity of lesions on these plants increased with increasing temperature from 5 to 15°C.     

Modelling the progress of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape (Brassica napus) in relation to leaf wetness and temperature

A compartmental model was developed to describe the progress with time of light leaf spot ( Pyrenopeziza brassicae ) on leaves of winter oilseed rape ( Brassica napus ) during the autumn in the UK. Differential equations described the transition between the four compartments: healthy susceptible leaves, infected symptomless leaves, sporulating symptomless leaves and leaves with necrotic light leaf spot lesions, respectively. The model was fitted to data on the progress of light leaf spot on winter oilseed rape at a single site during the autumn of the 1990–1991 season. Model parameters were used to describe rates of leaf appearance, leaf death, infection by airborne ascospores (primary inoculum) and infection by splash-dispersed conidiospores (secondary inoculum). Infection was dependent on sufficient leaf wetness duration. The model also included delay terms for the latent period between infection and sporulation and the incubation period between infection and the appearance of necrotic light leaf spot lesions. This modified SEIR model formulation gave a reasonable fit to the experimental data. Sensitivity analysis showed that varying the parameter accounting for the rate of infection by ascospores affected the magnitude of the curves after the start of the epidemic, whilst including a parameter for conidiospore infection improved the fit to the data. Use of ascospore counts from different sites and different years showed variation in spore release patterns sufficient to affect model predictions.     

Sporulation of Pyrenopeziza brassicae (light leaf spot) on oilseed rape (Brassica napus) leaves inoculated with ascospores or conidia at different temperatures and wetness durations

In controlled environment experiments, sporulation of Pyrenopeziza brassicae was observed on leaves of oilseed rape inoculated with ascospores or conidia at temperatures from 8 to 20°C at all leaf wetness durations from 6 to 72 h, except after 6 h leaf wetness duration at 8°C. The shortest times from inoculation to first observed sporulation ( l ₀), for both ascospore and conidial inoculum, were 11–12 days at 16°C after 48 h wetness duration. For both ascospore and conidial inoculum (48 h wetness duration), the number of conidia produced per cm² leaf area with sporulation was seven to eight times less at 20°C than at 8, 12 or 16°C. Values of Gompertz parameters c (maximum percentage leaf area with sporulation), r (maximum rate of increase in percentage leaf area with sporulation) and l ₃₇ (days from inoculation to 37% of maximum sporulation), estimated by fitting the equation to the observed data, were linearly related to values predicted by inserting temperature and wetness duration treatment values into existing equations. The observed data were fitted better by logistic equations than by Gompertz equations (which overestimated at low temperatures). For both ascospore and conidial inoculum, the latent period derived from the logistic equation (days from inoculation to 50% of maximum sporulation, l ₅₀) of P. brassicae was generally shortest at 16°C, and increased as temperature increased to 20°C or decreased to 8°C. Minimum numbers of spores needed to produce sporulation on leaves were ≈25 ascospores per leaf and ≈700 conidia per leaf, at 16°C after 48 h leaf wetness duration.     

Effects of inoculum density, leaf age, moisture, temperature, and wetness duration on black streak of edible burdock

Inoculum density, temperature, leaf age, and wetness duration were evaluated for their effects on the development of black streak (Itersonilia perplexans) on edible burdock (Arctium lappa L.) in a controlled environment. The effect of relative humidity (RH) on ballistospores production by I. perplexans was also evaluated. Symptoms of black streak on leaves increased in a linear fashion as the inoculum density of I. perplexans increased from 10² to 10⁶ ballistospores/ml. Rugose symptoms on young leaves were observed at densities of ≥10⁴ ballistospores/ml. Disease severity of I. perplexans in relation to leaf age followed a degradation curve when the leaves were inoculated with ballistospores. Disease severity was high in newly emerged leaves up to 5 days old, declined as leaf age increased to 29 days, and was zero when leaf age increased from 30 to 33 days. Disease development of edible burdock plants exposed to ballistospores of I. perplexans was evaluated at various combinations of temperature (10°, 15°, 20°, 25°C) and duration of leaf wetness (12, 24, 36, 48, and 72 h). Disease was most severe when plants were in contact with the ballistospore sources at 15° or 20°C. The least amount of disease occurred at 25°C regardless of wetness duration. Ballistospores required 24–36 h of continuous leaf wetness to cause visible symptoms by infection on edible burdock. Ballistospores production in infected lesions required at least 95.5% RH.     

A temperature and leaf wetness duration-based model for prediction of gray leaf spot of perennial ryegrass turf

ABSTRACT Gray leaf spot is a serious disease of perennial ryegrass (Lolium perenne), causing severe epidemics in golf course fairways. The effects of temperature and leaf wetness duration on the development of gray leaf spot of perennial ryegrass turf were evaluated in controlled environment chambers. Six-week-old Legacy II ryegrass plants were inoculated with an aqueous conidial suspension of Pyricularia grisea (approximately 8 x 10(4) conidia per ml of water) and subjected to four different temperatures (20, 24, 28, and 32 degrees C) and 12 leaf wetness durations (3 to 36 h at 3-h intervals). Three days after inoculation, gray leaf spot developed on plants at all temperatures and leaf wetness durations. Disease incidence (percent leaf blades symptomatic) and severity (index 0 to 10; 0 = leaf blades asymptomatic, 10 = >90% leaf area necrotic) were assessed 7 days after inoculation. There were significant effects ( alpha = 0.0001) of temperature and leaf wetness duration on disease incidence and severity, and there were significant interactions ( alpha = 0.0001) between them. Among the four temperatures tested, 28 degrees C was most favorable to gray leaf spot development. Disease incidence and severity increased with increased leaf wetness duration at all temperatures. A shorter leaf wetness duration was required for disease development under warmer temperatures. Analysis of variance with orthogonal polynomial contrasts and regression analyses were used to determine the functional relationships among temperature and leaf wetness duration and gray leaf spot incidence and severity. Significant effects were included in a regression model that described the relationship. The polynomial model included linear, quadratic, and cubic terms for temperature and leaf wetness duration effects. The adjusted coefficients of determination for the fitted model for disease incidence and severity were 0.84 and 0.87, respectively. The predictive model may be used as part of an integrated gray leaf spot forecasting system for perennial ryegrass turf.     

Effect of temperature and leaf wetness duration on infection of sweet oranges by Asiatic citrus canker

Asiatic citrus canker, caused by Xanthomonas smithii ssp. citri , formerly X. axonopodis pv. citri , is one of the most serious phytosanitary problems in Brazilian citrus crops. Experiments were conducted under controlled conditions to assess the influence of temperature and leaf wetness duration on infection and subsequent symptom development of citrus canker in sweet orange cvs Hamlin, Natal, Pera and Valencia. The quantified variables were incubation period, disease incidence, disease severity, mean lesion density and mean lesion size at temperatures of 12, 15, 20, 25, 30, 35, 40 and 42°C, and leaf wetness durations of 0, 4, 8, 12, 16, 20 and 24 h. Symptoms did not develop at 42°C. A generalized beta function showed a good fit to the temperature data, severity being highest in the range 30–35°C. The relationship between citrus canker severity and leaf wetness duration was explained by a monomolecular model, with the greatest severity occurring at 24 h of leaf wetness, with 4 h of wetness being the minimum duration sufficient to cause 100% incidence at optimal temperatures of 25–35°C. Mean lesion density behaved similarly to disease severity in relation to temperature variation and leaf wetness duration. A combined monomolecular-beta generalized model fitted disease severity, mean lesion density or lesion size as a function of both temperature and duration of leaf wetness. The estimated minimum and maximum temperatures for the occurrence of disease were 12°C and 40°C, respectively.     

Germination of Peronospora farinosa f. sp. spinaciae conidia: a two-topped temperature curve

Samenvatting Bij verschillende herkomsten vanP. farinosa f. sp.spinaciae werden twee optima geconstateerd in de curve welke het verband aangeeft tussen conidiënkiemingspercentage en temperatuur.     

Effects of temperature,inoculum concentration,leaf age,and continuous and interrupted wetness on infection of olive plants by Spilocaea oleagina

Experiments were conducted on olive plants in controlled environments to determine the effect of conidial concentration, leaf age, temperature, continuous and interrupted leaf wetness periods, and relative humidity (RH) during the drier periods that interrupted wet periods, on olive leaf spot (OLS) severity. As inoculum concentration increased from 1·0 × 10² to 2·5 × 10⁵ conidia mL^?1, the severity of OLS increased at all five temperatures (5, 10, 15, 20 and 25°C). A simple polynomial model satisfactorily described the relationship between the inoculum concentration at the upper asymptote (maximum number of lesions) and temperature. The results showed that for the three leaf age groups tested (2–4, 6–8 and 10–12 weeks old) OLS severity decreased significantly (P < 0·001) with increasing leaf age at the time of inoculation. Overall, temperature also affected (P < 0·001) OLS severity, with the lesion numbers increasing gradually from 5°C to a maximum at 15°C, and then declining to a minimum at 25°C. When nine leaf wetness periods (0, 6, 12, 18, 24, 36, 48, 72 and 96 h) were tested at the same temperatures, the numbers of lesions increased with increasing leaf wetness period at all temperatures tested. The minimum leaf wetness periods for infection at 5, 10, 15, 20 and 25°C were 18, 12, 12, 12 and 24 h, respectively. The wet periods during early infection processes were interrupted with drying periods (0, 3, 6, 12, 18 and 24 h) at two levels of RH (70 and 100%). The length of drying period had a significant (P < 0·001) effect on disease severity, the effect depending on the RH during the interruption. High RH (100%) resulted in greater disease severity than low RH (70%). A polynomial equation with linear and quadratic terms of temperature, wetness and leaf age was developed to describe the effects of temperature, wetness and leaf age on OLS infection, which could be incorporated as a forecasting component of an integrated system for the control of OLS.     

Infection of Linseed by Alternaria linicola; Effects of Inoculum Density, Temperature, Leaf Wetness and Light Regime

Controlled environment studies were conducted to determine the effects of inoculum density, temperature, leaf wetness and light regime on the infection of linseed by Alternaria linicola. The % cotyledons and leaves with symptoms, and the disease severity (% leaf area with symptoms) increased linearly when the inoculum density increased from 1×10³ to 1×10⁵ conidiaml^–1. The first symptoms appeared on cotyledons and leaves 4 and 6 days after inoculation, respectively. Eight hours of leaf wetness were sufficient to initiate the disease at 25°C but not at 15°C, when 10-h periods of leaf wetness were required. % leaf area with symptoms was lower at 15°C than that at 25°C irrespective of the leaf wetness periods tested. Interruption of a continuous leaf wetness period by a 12-h dry period, occurring at any time between 1 and 18h after inoculation, decreased the % cotyledons with symptoms and the disease severity, with the greatest reductions (60% and 100%, respectively) being observed when the dry period began 6h after inoculation. A. linicola conidia were able to exploit successive 12-h periods of leaf wetness cumulatively to infect linseed plants. Disease incidence and severity were positively correlated with the dark period following inoculation, but they were negatively related to the length of the initial light period. Our findings suggest that infection of linseed by A. linicola and further development of symptoms can occur under unfavourable environmental conditions.