Effect of pea canopy architecture on microclimate and consequences on ascochyta blight infection under field conditions

In order to investigate the impact of pea canopy architecture and development on microclimate and infection by Mycosphaerella pinodes, two field experiments were conducted in 2009 and 2010 at Le Rheu (France) to obtain canopies contrasted in height, closure dynamic, leaf area index (LAI) and leaf area density (LAD). Three pea cultivars (Athos, Antares, Gregor) were sown at two (80 and 40 seeds/m² in 2009) and three densities (80, 40 and 30 seeds/m² in 2010) and microclimatic sensors were located inside the canopy (at the bottom and in the middle) and outside. Two main sources of wetness were identified: rainfall and dew. During rainfall periods, average daily leaf wetness duration (LWD) was about 15 h, and 3 to 10 h longer inside than outside the canopies. LWD was positively correlated with LAI until canopy closure during these periods. During dry periods when dew was the only source of leaf wetness, average daily LWD was short, decreasing as the canopy developed. Shorter LWDs were observed at the base than at the mid-level of the canopies and longer LWDs were observed outside the canopy and inside the less dense canopies irrespective of the cultivar. LWD was negatively correlated with canopy height and LAI during these periods. Slow wind speeds were recorded inside the canopies (less than 0.5 km/h) and no significant canopy effect was observed on air temperature. An infection model was developed and showed that only rainfall periods which induced long LWDs inside the canopy, were favourable to M. pinodes infection under our climatic conditions and suggested a more favourable microclimate inside dense canopies.     

Effect of interrupted leaf wetness periods on suppression of sporulation ofBotrytis allii andB. cinerea by antagonists on dead onion leaves

Saprophytic antagonists were evaluated for suppression of sporulation ofBotrytis allii andB. cinerea on artificially killed segments of onion leaves that were pre-inoculated with the pathogens. During incubation of the antagonisttreated leaf segments in moist chambers, periods of leaf wetness and leaf dryness were alternated to simulate conditions in the field. Interruption of humid conditions with dry periods had a differential effect on antagonists.Alternaria alternata, Chaetomium globosum, Ulocladium atrum andU. chartarum suppressed sporulation ofB. allii almost completely under continuously wet conditions, and when the leaf wetness periods were interrupted with drying periods of 9h imposed 16, 40, and 64 h after the antagonists were applied. When leaf wetness was interrupted 16 h after antagonist application, the number of conidia ofB. allii produced cm^–2 leaf surface after eight days was under the detection limit of 5.2 × 10³ conidia on leaves treated with these antagonists compared to 3.7 × 10⁵ conidia on leaves that were not treated. On the other hand,Gliocladium roseum, G. catenulatum andSesquicillium candelabrum, all highly efficient under continuously wet conditions, were of low to moderate efficiency when leaf wetness periods had been interrupted 16 h after application of the antagonists. The antagonists showed the same differentiation and sensitivity to interrupted wetness periods when tested withB. cinerea.     

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.     

Scientific critique of the paper “Climatic distribution of citrus black spot caused by <Emphasis Type="Italic">Phyllosticta citricarpa</Emphasis>. A historical analysis of disease spread in South Africa” by Martínez-Minaya et al. (2015)

The global distribution of citrus black spot (CBS) disease, caused by Phyllosticta citricarpa, is climatically constrained, which is evident from its occurrence in citrus growing areas with warm, summer rainfall and its absence from areas with cooler, Mediterranean-type winter rainfall. Various epidemiological and modelling studies have supported this observation, predominantly estimating unsuitability for P. citricarpa in Mediterranean type climates, with no more than marginal suitability estimated at a few localities within some regions with Mediterranean type climates. The study by Martínez-Minaya et al. (European Journal of Plant Pathology, 143, 69–83, 2015), describes an historic sequence of recorded CBS occurrence in parts of South Africa, conducts an autocorrelation analysis and a correlative analysis with Köppen-Geiger climate zones and makes observations about the occurrence of certain Köppen-Geiger climate zones in the European Union. The study suggests that significant portions of the European Union and the broader Mediterranean basin are climatically similar to warm, summer rainfall areas in South Africa where P. citricarpa persists and causes CBS disease and concludes that the potential distribution of P. citricarpa is less constrained by climatic factors than spatial contagion. However, in this critique we expose methodological shortcomings in the Martínez-Minaya et al. (European Journal of Plant Pathology, 143, 69–83, 2015) study and conclude that the study grossly overestimated the extent of the geographical area that could support P. citricarpa, thereby rendering the findings scientifically unreliable.     

Production of Didymella rabiei Pseudothecia and Dispersal of Ascospores in a Mediterranean Climate

ABSTRACT Temperature and wetness conditions required for development and maturation of Didymella rabiei pseudothecia were determined in a series of experiments conducted in controlled-environmental conditions. Initial stages of pseudothecium formation occurred at temperatures ranging from 5 to 15 degrees C. Incubation at low temperatures was essential for subsequent pseudothecium maturation. This requirement was satisfied for chickpea stem segments incubated at 5 or 10 degrees C for three consecutive weeks or during periods of 3 or 5 days, separated by periods at higher temperatures. Following the low-temperature requirement, subsequent pseudothecium development was independent of temperature in the range tested (5 to 20 degrees C). Wetness was essential for pseudothecium production: pseudothecia formed and matured on stem segments maintained continuously wet but also on those exposed to periods of three or five wet days, separated by dry periods. The dispersal of D. rabiei ascospores was studied using chickpea plants as living traps in the field. Trap plants were infected mainly when exposed during rain but also in rainless periods. Results of this study enabled us to describe the developmental events leading to the production of the teleomorph stage and the dispersal of ascospores by D. rabiei in the Mediterranean climate of Israel.     

Witches' broom disease on cocoa in Rondonia, Brazil: pod infection in relation to pod susceptibility, wetness, inoculum, and phytosanitation

Infection of cocoa pods by Crinipellis perniciosa was examined in the field in relation to pod susceptibility and variations in inoculum and climate over 2 years. The disease was incubated for 13 or 14 weeks in pods inoculated when 2 and 4 weeks old, and for 12 weeks in pods inoculated 6-12 weeks old. Pods were uniformly susceptible to natural infection during the 12 weeks after pollination. Over 75% of rain showers started between 12.00 and 02.00 h, providing sufficient water to rehydrate basidiocarps as well as to wet pods. Pods remained wet after rainfall for decreasing periods when rain occurred after 13.00 h. Incidence of pod disease was shown to be related to the number of wetness periods longer than 4 h, and to the number of open turgid basidiocarps occurring 12 weeks earlier. Wetness periods had a greater influence on disease. Pod infection was modelled by assuming that infection was limited by either wetness periods or turgid basidiocarp numbers; critical numbers of wetness periods when both factors were of equal weight were defined by an exponential equation. The model was used to predict reductions in pod disease associated with different amounts of broom removal in each year.     

Release and recovery ofMetaphycus spp. (Hymenoptera: Encyrtidae) imported for the control of the mediterranean black scale,Saissetia Oleae (Olivier), in Israel

During 1972–1976 four species of African encyrtid wasps were introduced into Israel and released against the Mediterranean black scale,Saissetia oleae (Olivier), in citrus and olive groves.Metaphycus helvolus (Compere) andM. aff. stanleyi Compere were recovered in small numbers.M. bartletti Annecke and Mynhardt andM. lounsburyi (Howard), which were found in large numbers on citrus during the release season, seem to be promising for the biological control of the black scale.     

Modelling the progress of Asiatic citrus canker on Tahiti lime in relation to temperature and leaf wetness

The combined effect of temperature (15°C, 20°C, 25°C, 30°C, 35°C, 40°C and 42°C) and leaf wetness duration (0, 4, 8 12, 16, 20 and 24 h) on infection and development of Asiatic citrus canker (Xanthomonas citri subsp. citri) on Tahiti lime plant was examined in growth chambers. No disease developed at 42°C and zero hours of leaf wetness. Periods of leaf wetness as short as 4 h were sufficient for citrus canker infection. However, a longer leaf duration wetness (24 h) did not result in much increase in the incidence of citrus canker, but led to twice the number of lesions and four times the disease severity. Temperature was the greatest factor influencing disease development. At optimum temperatures (25–35°C), there was 100% disease incidence. Maximum disease development was observed at 30–35°C, with up to a 12-fold increase in lesion density, a 10-fold increase in lesion size and a 60-fold increase in disease severity.     

Influence of Weather Conditions on Infection of Peach Fruit by Taphrina deformans

ABSTRACT The effect of environment on the infection of peach fruit by Taphrina deformans was investigated using orchard observations under natural conditions (in 2001 to 2004) or in trees managed in such a way to exclude rainfall. These conditions were then validated using pot-grown peach plants exposed to single infection events and independent orchard observations. Leaf curl incidence was related to rainfall, length of wet periods, and the temperature during wetness and during the incubation period, as well as to the developmental stage of flowers and fruit. Weather conditions before petal fall did not influence fruit infection. After petal fall, rainfall and the duration of the wet period triggered by rainfall played a key role in infection occurrence. The minimum rainfall required for infection was 12 mm, with at least 24 h of wetness interrupted by no more than 4 h. No infection occurred when temperature was >/=17 degrees C during the wet period or >19 degrees C during incubation. Disease symptoms appeared on fruit after approximately 3 weeks of incubation, which is equivalent to 240- to 290-degree-days (base 0 degrees C). The period for fruit infection was relatively short being from petal fall until air temperature remained greater than 16 degrees C. During this period, the incidence of fruit that developed symptoms was closely related to the number of favorable events and the total wetness duration during such events.     

Influence of environmental factors on conidial germination and survival of Sphaeropsis pyriputrescens

Sphaeropsis pyriputrescens is the cause of Sphaeropsis rot in apples and pears. In this study, effects of temperature, wetness duration, relative humidity (RH), dryness, and interrupted wetness duration on conidial germination of the fungus were evaluated. Conidial germination and germ tube elongation occurred at temperatures from 0°C to 30°C. The optimum temperature for germination and germ tube elongation appeared to be 20°C, at which a minimum wetness period of 5 h was required. Conidia germinated at RH as low as 92% after 36 h at 20°C, but not at 88.5% RH. The effect of dry periods on germination depended on RH. Conidial germination at 85% RH was higher than that at 25% RH within a 4-h dry period, after which time no difference was observed. Less than 10% conidia germinated after a 10-day dry period at both 20°C and 28°C. Conidial germination decreased as the wetness duration prior to dryness increased. Conidia wetted for 6 h prior to dryness died within a 1-h dry period. After a 12-h dry period, no or few conidia germinated at 25% RH, whereas 3% to 10% of the conidia germinated at 85% RH and no further decrease was observed as the dry period increased. The results contribute to our understanding of conditions required for conidial germination of S. pyriputrescens and infection of fruit leading to Sphaeropsis rot.     

Infection criteria,inoculum sources and splash dispersal pattern of <Emphasis Type="Italic">Colletotrichum acutatum</Emphasis> causing bitter rot of apple in New Zealand

Infection of Malus x domestica cv. Royal Gala fruit by Colletotrichum acutatum causing bitter rot was studied in the temperate climate of New Zealand. Temperatures above 15 °C were required for lesions to develop on detached apple wound-inoculated or inoculated without wounding with C. acutatum spores, regardless of maturity. A wetness period of 72 h was required for infection of mature detached apple fruit without wounding. On wound-inoculated detached apple fruits, sporulation was related to temperature and followed a similar pattern. In the field, a mean temperature above 15 °C for 72 h after wound-inoculation was required for lesions to develop. Buds were a more important source of inoculum than twigs, and it was shown that C. acutatum could be isolated more frequently from outer bud scales than from inner scales. Asymptomatic infection of vegetative and reproductive buds was detected. C. acutatum was detected on asymptomic surface-sterilised petals and fruit, more commonly during summer than spring. Symptomless sterilised leaves generally yielded C. acutatum throughout the season, but isolations were more frequent in summer. Recovery of inoculum using a splash meter to detect vertical dispersal showed that in summer inoculum was primarily splashed up from the ground. In spring, inoculum was recovered in similar quantities from all heights up to a metre, suggesting that splash dispersal occurs from the canopy as well as from the ground. A disease cycle for C. acutatum infecting apples and causing bitter rot in New Zealand is suggested.     

Conidial production and viability of Calonectria pseudonaviculata on infected boxwood leaves as affected by temperature,wetness, and dryness periods

Calonectria pseudonaviculata causes lesions on boxwood leaves and twigs. Controlled-environment experiments were conducted to determine the effects of temperature and leaf wetness period on C. pseudonaviculata sporulation on diseased (cv. Suffruticosa) leaves and of dryness periods and high temperature on conidial survival. Infected leaves were incubated in moist chambers and subjected to six temperatures (9, 13, 17, 21, 25, and 29°C) and six leaf wetness periods (0, 12, 24, 40, 48, and 72 h). Spore production was influenced significantly by wetness period, temperature, and their interaction. Increasing duration of leaf wetness and increasing temperature generally increased sporulation, with no sporulation occurring at 29°C or 9 and 13°C, except at 72 h of wetness exposure, while it was optimal at 21°C. Detached leaves with profuse conidia were subjected to a range of drying (relative humidity at 65%) times (0, 2, 4, 6, and 8 h) at two temperatures of 21 and 29°C. Conidia were then harvested and plated on water agar. Germinating conidia were counted to measure the spore viability. Spore mortality increased with increasing dryness duration at both temperatures but occurred more quickly and severely at 29 than 21°C. Overall, this study extended biological knowledge of conditions required for crucial stages of the C. pseudonaviculata disease cycle and the obtained results will be vital for developing boxwood blight forecasting and management tools.     

Survival of strawberry-pathogenic fungi Fusarium oxysporum f. sp. fragariae, Phytophthora cactorum and Verticillium dahliae under anaerobic conditions

The growth and survival of three strawberry pathogens, Fusarium oxysporum f. sp. fragariae (FOF), Phytophthora cactorum, and Verticillium dahliae, were examined in anaerobic (anoxic) conditions at several temperatures (10–40 °C). The growth and survival of these fungi were suppressed by anaerobic conditions in comparison with those in cultured aerobically. Under anaerobic conditions at 22.5 °C, tested isolates of FOF and P. cactorum grew slightly, but V. dahliae did not grow. The three fungi survive for markedly shorter time in the anaerobic conditions compared with the aerobic conditions at all tested temperatures except 40 °C for FOF and P. cactorum. Moreover, survival periods shortened as the cultivation temperature increased. These results demonstrate that anaerobic conditions contribute to eradicating these pathogens during flooding or reductive soil disinfestation.     

Influence of Environmental Conditions on Infection of Peach Shoots by Taphrina deformans

ABSTRACT The effect of weather conditions on the infection of peach shoots by Taphrina deformans was investigated both under orchard conditions and in controlled-environment experiments. Leaf curl incidence and severity were related to rainfall, length of wet periods, and temperature during wetness and during the incubation period, as well as to the development stage of shoots. Surface wetness was more important than rainfall for infection to occur. Minimum rainfall for infection was 3 mm, with a wet period of at least 12.5 h; higher amounts of rainfall did not cause infection when the wet period they triggered was shorter. Wet periods initiated by dew or fog were too short for infection to occur. Infection occurred only when air temperature was <16 degrees C during the wet period and <19 degrees C during incubation. Logistic equations relating relative disease incidence and either duration of wetness or temperature were developed under controlled-environment conditions, with asymptotes at >/=48 h of wetness and 相似文献   

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.     

Plant diseases in the mediterranean region

The Mediterranean region is a well-defined ecological unit with hot and dry summers and relatively cold and rainy winters. Its climate is very changeable and the seasonal irregularity renders agriculture particularly hazardous. Some characteristics of plant diseases or the behavior of pathogens in the Mediterranean region are discussed briefly, with particular reference to some important crops such as olive, grapevine, citrus, date palm and cereals, as well as certain woody trees like chestnut, elm and cypress. 1 Lecture presented at the First Israeli-Italian Phytopathological Symposium, Bet Dagan, Israel, February 13–15, 1989.     

Vertical dispersal of plant pathogens by splashing. Part I: the theoretical relationship between rainfall and upward rain splash

The theoretical relationship between rainfall intensity, raindrop size distribution and the upward transport of splash droplets is examined to establish a better understanding of the natural rainfall characteristics that can cause upward movement of plant pathogens in a crop. The theory suggests that splash transport is determined by the rain splash intensity index, which is defined as the intensity of the rainfall with raindrops greater than a threshold size. Ulbrich's (1983) empirical model of the size distribution of raindrops is used to calculate the relationship between rainfall intensity and rain splash intensity index. The calculations show that rainfall intensity is not a reliable indicator of the rain splash intensity index, particularly in convective showers. Therefore, a correlation between rainfall volume and upward disease progress is unlikely to provide a reliable basis for forecasting sudden disease outbreaks associated with short-duration convective showers during the summer. Finally, we consider the instruments that have the capability to measure the rain splash intensity index.     

Characteristics and pathogenicity of six Phytophthora isolates from pot plants

From several greenhouse plants showing foot and root rot symptomsPhytophthora isolates were gathered. Isolates fromPeperomia, Saintpaulia andSinningia were identified asP. nicotianae van Breda de Haan var.nicotianae and an isolate fromBegonia asP. cryptogea Pethybr. & Laff. Cardinal temperatures for the various isolates were determined. The specific and non-specific pathogenicity of the isolates was studied by inoculating the different crops with the different isolates, including aP. cryptogea isolate fromGerbera and aP. nicotianae var.nicotianae isolate from carnation. TheP. nicotianae var.nicotianae isolates appeared to be morphologically identical. Some of the isolates were similar in host range, but others exhibited differences in host specificity at 20°C as well as 25, 30 or 35°C. The same applies for the twoP. cryptogea isolates.     

Some diseases of agricultural crops and their control in the land of Israel during biblical,mishnaic and talmudic times

Plant diseases that were widespread during Biblical, Mishnaic and Talmudic times are reviewed. They include biotic and abiotic diseases such asshidaphon ,yerakon,kemachin (in wine), rotten fruits,beushim andmeyablin. Some optional identifications of the diseases discussed are suggested, according to modern nomenclature.     

Potential distribution of citrus black spot in the United States based on climatic conditions

Citrus black spot (CBS), caused by Phyllosticta citricarpa McAlp Van der Aa, was recently detected in southern Florida in the US. In addition to infected plant propagation materials, movement of infected citrus fruit poses a concern for potential spread of the disease out of the current quarantine zone, because lesions with pycnidia and conidia could develop after harvest. The conditions conducive for mycelial growth and development of pycnidia and conidia are not well known. Therefore, effects of temperature and relative humidity on growth and conidial production of P. citricarpa were determined and used as parameter inputs in CLIMEX to predict potential establishment of CBS in North America. Colony growth and conidial production in vitro were optimal at 27 °C, whereas there was no growth below 4 °C and above 37 °C. On fruit, lesion development and conidial production were observed at 4 °C, though at a low rate, indicating a greater versatility of the fungus on fruit. More full pycnidia were produced on the CBS lesions at 91 % RH compared to 84 %. Input parameters for CBS risk in CLIMEX obtained from literature, which reflected conditions for infection in spring/summer in Florida, predicted potential establishment in Florida but not in California. However, altering the parameter values to account for survival of the pathogen in leaf litter in winter predicted potential establishment in California as well as Florida. Thus, P. citricarpa could possibly establish beyond Florida if this organism is transported outside of the current quarantine zone to other citrus production areas.