Prestorage heat treatment reduces pathogenicity of Penicillium expansum in apple fruit

Penicillium expansum is one of the main postharvest pathogens of apples in Israel. Heating apple fruit inoculated with P. expansum for 96 h at 38°C completely inhibited decay development. Fruit held for 24 h at 42°C or 12 h at 46°C had significantly reduced decay after an additional 14 days incubation at 20°C, compared with unheated inoculated control fruit. Mycelial growth and percentage spore germination in vitro were inversely proportional to length of time of exposure to various temperatures. The ET₅₀ for spore germination was 42, 34 and 20 h at 38, 42 and 46°C, respectively, while the ET₅₀ for mycelial growth was 48, 44 and 36 h at those temperatures. When Penicillium spores were incubated on crude extract prepared from the peel of apple fruits held 4 days at 38°C, germ tube elongation was significantly reduced, while the walls of the tubes were thicker, compared with germ tubes from spores incubated on crude extract prepared from peel of non-heated fruit. The evidence presented here supports the hypothesis that the effect of heating on the decay of apples caused by P. expansum is not only the result of direct inhibition of fungal germination and growth by high temperature, but is also partly due to the formation of an inhibitory substance in the heated peel.     

Non-deep simple morphophysiological dormancy in seeds of the weedy facultative winter annual Papaver rhoeas

Embryos in freshly matured seeds of the facultative winter annual Papaver rhoeas are underdeveloped and physiologically dormant; thus, seeds have morphophysiological dormancy (MPD). Seeds lost physiological dormancy during 12 weeks of burial in moist soil at 12 h/12 h daily alternating temperature regimes of 15/5°C, 20/10 °C and 25/15 °C but not at 1 °C. Physiological dormancy was not broken in seeds stored dry at room temperature for 12 weeks. After physiological dormancy was broken, seeds required light for embryo growth (i.e. for loss of morphological dormancy) and consequently for germination. After a 12-week period of burial in soil at 25/15 °C, seeds that matured in 1997 germinated to 100% in light at 25/15 °C, demonstrating that cold stragification temperatures (≈ 0.5–10 °C) are not required for embryo growth. Thus, seeds have non-deep simple MPD. During exposure to low winter temperatures (5/1 °C, 1 °C), 52% of the seeds with physiologically non-dormant embryos entered conditional dormancy and thus lost the ability to germinate at 25/15 °C but not at 15/5 °C or 20/10 °C. The peak of germination for seeds sown in southern Sweden was in autumn, but some also germinated in spring. A higher percentage of seeds that matured in a relatively warm, dry year (1997) came out of MPD and germinated than did those that matured in a relatively cool, wet year (1998) at the same site.     

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.     

The effectiveness of postharvest hot water dipping on the control of grey and black moulds in sweet red pepper (Capsicum annuum)

The effectiveness of hot water dipping on the control of grey mould, caused by Botrytis cinerea , and black mould, caused by Alternaria alternata on sweet red pepper quality was investigated. Dipping naturally infected or artificially inoculated fruit at 508C for 3 min completely inhibited, or significantly reduced, decay development caused by B. cinerea and A. alternata , respectively. Heat damage was observed on fruit dipped for 5 min at 50°C, or at 55°C for 1 min or longer. Damage appeared as cracks and pitting on the fruit surface. Spore germination and germ tube elongation in vitro was inversely related to the duration of exposure or to the range of temperature used. The ET₅₀ for spore germination for B. cinerea was 3.2, 1.5 and 0.8 min, and for A. alternata 8.8, 4.2 and 1.4 min, at 45, 50 and 55°C, respectively. The ET₅₀ for germ tube elongation for Botrytis was 2.6, 0.9 and 0.5 min, and for Alternaria , 7.2, 2.5 and 1.6 min, at 45, 50 and 55°C. The mode of action of hot water dips on decay of pepper appears to be by direct interaction with the fungi.     

The effect of thermal time and soil water on emergence of Ranunculus repens

The effect of temperature and soil available water (AW) on the emergence of Ranunculus repens ␣L. was examined in artificial media in growth chambers. Two seed populations, `arable type' and `wild type', were investigated. Moisture levels were 20%, 40%, 60% and 80% AW, and temperatures were 10/5 °C, 15/7 °C, 20/10 °C and 25/15 °C. Time to onset of emergence varied from 11 to 28 days for both seed populations, primarily as a result of mean temperature. Mean thermal time (TT) required for the onset of emergence of both populations was 251 ± 45 TT. Total emergence of the `arable type' R. repens varied from 3% at 10/5 °C and 20% AW to 30% at 25/15 °C and 60% AW. Total emergence of the `wild type' was greater, ranging from 4% at 10/5 °C and 20% AW to 57% at 25/15 °C and 80% AW. Temperature and AW significantly affected total emergence. A logistic response was displayed for the cumulative emergence of both populations. Seedling emergence models based on TT were developed for both populations at each of the four levels of AW.     

Factors affecting mummification and sporulation of pome fruit infected by Monilinia fructigena in Dutch orchards

A 2-year field experiment (1997–98, 1998–99) was conducted to study mummification and subsequent sporulation in spring of apple (cvs James Grieve, Golden Delicious) and pear (cv . Conference) fruits infected by Monilinia fructigena . Most mummified fruits were found in James Grieve and Conference, whereas in late-infected Golden Delicious, fruits were still soft when examined in April. In the first year, these late-infected fruits had a significantly higher sporulation intensity per sporulating fruit ( P  = 0·05) compared with Golden Delicious fruits infected 9 and 5 weeks before harvest maturity, which were partly mummified. It was concluded that early- and late-infected fruits contributed to primary inoculum in the next season. In a postinfection regime of 25°C and 65–75% relative humidity under controlled conditions, the number of Conference fruits sporulating decreased rapidly, and after 12 weeks' incubation sporulation had completely ceased. After 8 weeks' incubation, sporulation intensity in the postinfection regime at 10°C was significantly higher than that at 20 and 25°C in a first experiment with inoculated unripe fruit ( P  = 0·05). Results of a second experiment with ripe fruit were less clear. These results are discussed in relation to orchard disease management.     

Variation in the response of melon genotypes to Fusarium oxysporum f.sp. melonis race 1 determined by inoculation tests and molecular markers

Screening of genotypes of melon ( Cucumis melo ) for resistance to wilt caused by Fusarium oxysporum f.sp. melonis is often characterized by wide variability in their responses to inoculation, even under carefully controlled conditions. The variability at the seedling stage of 17 genotypes susceptible to race 1 was examined in growth-chamber experiments. Disease incidence varied from 0 to 100% in a genotype-dependent manner. Using four combinations of light (60 and 90  µ E m⁻² s⁻¹) and temperatures of (27 and 31°C), only light intensity showed a statistically significant effect. Marker-assisted selection for fusarium resistance breeding using cleaved amplified polymorphic sequence (CAPS) and sequence-characterized amplified region (SCAR) markers were compared using a single set of genotypes that included 24 melon accessions and breeding lines whose genotype regarding the Fom-2 gene was well characterized. The practical value of the markers for discriminating a range of genotypes and clarifying the scoring of phenotypes was also tested using a segregating breeding population which showed codominant SCAR markers to be useful in marker-assisted selection.     

Effect of temperature on head blight of wheat caused by Fusarium culmorum and F. graminearum

The effect of small temperature differentials (16 vs. 20°C) on the pathogenicity of deoxynivalenol producing single isolates of Fusarium culmorum and F. graminearum and on the fusarium head blight (FHB) response of eight wheat cultivars was examined. Fusarium culmorum inoculation caused greater visual disease symptoms at 20°C than at 16°C, both overall and on an individual cultivar basis (overall AUDPC = 13·5 and 9·6, respectively) ( P  < 0·05). In contrast, F. graminearum inoculation caused greater overall visual disease symptoms at 16°C than at 20°C, both overall and at the individual cultivar level (overall AUDPC = 12·8 and 10·9, respectively) ( P  < 0·05). Results showed both F. culmorum and F. graminearum inoculations caused a greater loss in yield at 20°C (54·3 and 46·9% relative 1000-grain weight, respectively) compared with 16°C (73·3 and 66·9% relative 1000-grain weight, respectively) ( P  < 0·05). Fusarium culmorum -inoculated heads contained similar amounts of fungal DNA at both 16 and 20°C (1·9 and 1·7 ng mg⁻¹ of plant material, respectively) (not significant), while for F. graminearum inoculation, plants contained higher amounts of fungal DNA at 20°C (2·0 and 1·0 ng mg⁻¹ of plant material, respectively) ( P  < 0·05). Overall, there was a significant negative correlation between AUDPC and percentage relative 1000-grain weight at both 16 and 20°C ( r  =−0·693 and −0·794, respectively, P  < 0·01).     

Effect of soil temperature on disease development in melon plants infected by Monosporascus cannonballus

The effect of soil temperature on melon collapse induced by Monosporascus cannonballus was studied in the laboratory and in the field. In the laboratory, ascospore germination and hyphal penetration into melon roots were enhanced by increasing the temperature from 20 to 32°C. The optimum temperature for mycelial growth of five isolates of M. cannonballus was 30°C. In the field, the effect of temperature was studied in experiments conducted during the winter and autumn cropping seasons from 1995 to 1998. Disease progress was much faster in the autumn than in the winter crop seasons. Disease incidence reached 100% in the three consecutive autumn seasons studied. In the winter seasons, however, planting date influenced disease incidence. Early planting, at the beginning of January, resulted in a low disease incidence (6–26%, 125 days after planting), whereas planting at the end of January resulted in higher disease incidence (72–88%, 95–119 days after planting). In plots in which the soil was artificially heated to 35°C during the winter season, disease incidence reached 85%, as in the autumn season. Plants grown during the winter in unheated soil, or in artificially heated soil disinfected with methyl bromide, did not collapse. Root colonization by the pathogen was higher in the autumn and in heated soil than in the winter season in nonheated soil. Fifty per cent of root segments were colonized 35, 42 and 67 days after planting in the winter-heated, autumn and winter-unheated plots, respectively. A high correlation was found between soil temperatures above 20°C during the first 30 days after planting and disease severity. It is suggested that soil temperature during the early stages of plant development is an important factor in disease development and the expression of melon collapse caused by M. cannonballus.     

Cucumis metuliferus is resistant to root‐knot nematode Mi1.2 gene (a)virulent isolates and a promising melon rootstock

Pot experiments were carried out to characterize the response of two Cucumis metuliferus accessions (BGV11135 and BGV10762) against Mi1.2 gene (a)virulent Meloidogyne arenaria, M. incognita and M. javanica isolates and to determine the compatibility and the effect on physicochemical properties of fruit melons. In addition, histopathological studies were conducted. One week after transplanting, plants were inoculated with one J2 cm^?3 of sterilized sand (200 cm³ pots) and maintained in a growth chamber at 25 °C for 40 days. The susceptible cucumber cv. Dasher II or melon cv. Paloma were included for comparison. The number of egg masses and number of eggs per plant were assessed, and the reproduction index (RI) was calculated as the percentage of eggs produced on the C. metuliferus accessions compared to those produced on the susceptible cultivars. The compatibility and fruit quality were assessed by grafting three scions, two of Charentais type and one of type piel de sapo, under commercial greenhouse conditions. The resistance level of both C. metuliferus accessions ranged from highly resistant (RI < 1%) to resistant (1% ≤ RI ≤ 10%) irrespective of Meloidogyne isolates. Melon plants grafted onto C. metuliferus accession BGV11135 grew as self‐grafted plants without negatively impacting fruit quality traits. Giant cells induced by Meloidogyne spp. on C. metuliferus were in general poorly developed compared to those on cucumber. Furthermore, necrotic areas surrounding the nematode were observed. Cucumis metuliferus accession BGV11135 could be a promising melon rootstock to manage Meloidogyne spp., irrespective of their Mi1.2 (a)virulence, without melon fruit quality reduction.     

Influence of water management, application timing and temperature on efficacy of MTB-951, a mycoherbicide using Drechslera monoceras to control Echinochloa crus-galli L.

MTB-951 is a potential mycoherbicide using a fungal plant pathogen ( Drechslera monoceras ) isolated from native Echinochloa species in Japan. Conidia of this pathogen were used as the active ingredient and its herbicidal performance was examined in a greenhouse. The efficacy of MTB-951 on Echinochloa crus-galli L. was higher in deep water (7–9 cm) than in relatively shallow water (3–5 cm). In a postemergence application, the efficacy decreased as the leaf stage of E. crus-galli proceeded between the 1 and 2.5 leaf stage. For example, the control ratio (%) of E. crus-galli was 95% when applied at the 1 leaf stage, and 72% at the 2.5 leaf stage in 5 cm water. Generally, mycoherbicidal efficacy was less when applied pre-emergence rather than postemergence. Efficacy was also influenced by the duration of submergence in deep water. For example, when water depth was kept at 5 cm for more than 7 days after application and then decreased down to 3 cm, the efficacy was high. However, when the water depth was kept at 5 cm for less than 7 days, the efficacy was low. Efficacy was lower under high temperatures (35°C/25°C, day/night) than under low temperatures (25°C/15°C, day/night). Water management, application timing and temperature are important factors on herbicidal efficacy of MTB-951 to control E. crus-galli .     

Seed transmission of Melon necrotic spot virus and efficacy of seed-disinfection treatments

Rates of seed transmission of Melon necrotic spot virus (MNSV) were estimated in seedlings grown from commercial melon ( Cucumis melo ) cv. Galia F₁ seeds. Seedlings at the cotyledon stage and adult plants were assayed for MNSV by DAS-ELISA and RT-PCR. None of the seedling groups tested positive for MNSV by ELISA. The proportion of seedlings infected with MNSV was at least 7 and 8% in seed lots 05 and 06, respectively, as estimated from RT-PCR analysis of grouped seedlings. Fourteen and eight grouped samples (10 seedlings per group), of a total of 200 and 100 seedlings, respectively, grown from infected seeds were MNSV-positive in seed lots 05 and 06, respectively, corresponding to seed-to-seedling transmission rates of 11·3 and 14·8%, respectively. Several seed-disinfection treatments were evaluated for their ability to prevent seed transmission of MNSV. The results suggest that a treatment of 144 h at 70°C can be used to eradicate MNSV in melon seeds without hindering germination.     

The effects of soil solarization and soil fumigation on Fusarium wilt of watermelon grown in plastic house in south-eastern Spain

The effects of pre-planting solarization or fumigation with metham-sodium of sand-mulched soil on fusarium wilt of watermelon in plastic house culture were investigated at Almeria, south-eastern Spain. In two trials, 2 months' solarization increased the average maximum soil temperature by c. 5°C to 44-48° C at 10 cm depth and by 4-5° C to 40-42° C at 20-30 cm. The amount of Fusarium oxysporum in the upper 15 cm of a naturally infested soil was reduced by solarization and by fumigation. During the 9 months following treatment, the F. oxysporum population stabilized at a low level in soil solarized for 2 months, but fluctuated in soil solarized for 1 month and increased in fumigated soil. The amount of wilt in watermelon sown into this soil after treatment was generally low; plants growing in solarized or fumigated soil suffered less wilt than plants in untreated soil but the differences were not significant. In a soil artificially infested with the highly pathogenic race 2 of F. oxysporum f. sp. niveum, F. oxysporum populations were greatly reduced following solarization or fumigation, and fluctuated erratically thereafter. Solarization for 2 months completely controlled wilt in watermelon and gave a fruit yield almost five times that of plants in untreated soil. Solarization for 1 month only slowed disease development slightly but gave a yield more than twice that in untreated soil. Fumigation with metham-sodium retarded disease development considerably and tripled fruit yield. Plant performance was significantly better in soil solarized for 2 months than in uninfested control soil, suggesting beneficial effects of this treatment additional to wilt control.     

Eradication of Plasmodiophora brassicae during composting of wastes

Survival of infectious inoculum of the clubroot pathogen Plasmodiophora brassicae was assessed following bench-scale flask composting experiments and large-scale composting procedures. Clubroot-affected material was provided by artificial inoculation of Chinese cabbage or naturally infected Brussels sprout and cabbage roots. Both sets of diseased material were used in flask experiments, and the latter in large-scale windrow and aerated tunnel experiments. Municipal green wastes, onion waste and spent mushroom compost were evaluated in flask experiments with varying temperature, aeration and moisture conditions. Green wastes were used in larger-scale composts. Within the limits of a Chinese cabbage seedling bioassay, both temperature and moisture content were critical for eradication of P. brassicae spores extracted from composted clubroot-affected residues. Incubation in compost at 50°C for 7 days or 1 day at 60°C with high moisture levels (= −5 kPa matric potential or 60% w/w moisture content) eradicated inoculum from artificially inoculated Chinese cabbage roots. In large-scale windrows and aerated tunnels, the pathogen was eradicated from naturally infected brassica wastes after 6–7 days at 54–73°C.     

Enhanced field control of wheat take-all using cold tolerant isolates of Gaeumannomyces graminis var. graminis and Phialophora sp. (lobed hyphopodia)

Cold tolerant isolates of Gaeumannomyces graminis var. graminis ( Ggg ) and Phialophora sp. (lobed hyphopodia), which produced at least comparable growth rates at 5°C to those of pathogenic G. graminis var. tritici ( Ggt ), were shown to control take-all disease in wheat effectively in 2 years of field experiments in New South Wales, Australia. The addition of oat inoculum of these fungi at the rate of 60 kg/ha to the seeding furrow significantly ( P  ≤ 0.05) reduced disease and increased grain yields by 33–45% compared to the Ggt alone treatment. The use of 30 kg/ha of oat inoculum also significantly ( P  ≤ 0.05) reduced disease and increased grain yields by 21–44%. These high levels of take-all control were obtained consistently from four field experiments on three different soil types with different pHs. A treatment inoculated with Ggg alone showed no disease symptoms and produced grain yields similar to that of untreated wheat. This fungus is, therefore, non-pathogenic to wheat. At high rates of inoculation of Ggg and Phialophora sp. (lobed hyphopodia), 65–80% of tillering wheat plants (GS 32) had root systems colonized by these fungi. In contrast, two Pseudomonas spp. and an isolate each of Ggg and Phialophora sp. (lobed hyphopodia), which did not grow at 5°C, were ineffective in controlling take-all. Take-all assessments during heading (GS 61-83) were highly correlated ( R ²=0.6047, P ≤0.0005) with the relative yield increase or decrease of inoculated treatments compared to the Ggt alone treatment. The use of a Ggg isolate (90/3B) and a Phialophora sp. (lobed hyphopodia) isolate (KY) for take-all control has been patented. These fungi are being developed for commercial use.     

Inter-population variation in seed longevity for two invasive weeds: Chrysanthemoides monilifera ssp. monilifera (boneseed) and ssp. rotundata (bitou bush)

Seed longevity has a major influence on the success of weed management and eradication programmes. A correlation between responses to a controlled aging test performed at 45°C, 60% relative humidity (RH) and seed persistence in the field has recently been suggested. Here we investigated whether collections of differing quality of two closely related invasive weeds, Chrysanthemoides monilifera ssp. monilifera and ssp. rotundata (boneseed and bitou bush, respectively), had different seed longevity using the controlled aging test. Chrysanthemoides monilifera ssp. monilifera fruits were collected from across five Australian states, and C. monilifera ssp. rotundata from one state, covering their invasive ranges. Seed quality was assessed visually and using tetrazolium staining, and a series of germination tests established appropriate germination conditions. The controlled aging test was run for a subset of collections. Chrysanthemoides monilifera ssp. rotundata seeds died more quickly (time to lose 50% viability, P ₅₀ = 16 days) than the C. monilifera ssp. monilifera collections ( P ₅₀ = 47 days) when aged at 45°C and 60% RH. This difference was significant even considering the large differences in longevity between C. monilifera ssp. monilifera populations ( P ₅₀ = 35–61 days; probably due to differences in maturity at collection). Based on a published correlation, we predict that mature C. monilifera ssp. monilifera may have a long-lived (>3 years) seed bank and C. monilifera ssp. rotundata may have a transient (<1 year) seed bank. This suggests the two sub-species should be considered separately when designing effective control measures.     

The effect of inoculation temperature on the reaction of potato cultivars to Synchytrium endobioticum

The reactions of potato cultivars to inoculation with germinating winter spores of Synchytriuum endobioticum at 10, 15 and 20°C were compared. The classification of wart reactions for cultivars at the Resistant Grade 1/Resistant Grade 2 (RG1/RG2) and RG2/susceptible borderlines was found to depend on the inoculation temperature. For RG2 cultivars, there was a clear increase in the proportion of more resistant reactions with increase in inoculation temperature. The borderline cultivars 'Teena' and 'Alhamra' reacted as RG2 when inoculated at 10°C and as RG1 when inoculated at higher temperatures. However the inoculation temperature is unlikely to influence the outcome of tests on cultivars that produce a higher percentage of RG2 reactions. An inoculation temperature of 10–15°C more readily identified cultivars that are slightly susceptible. The slightly susceptible cultivars 'Apache', 'Morven' and 'Hassia' reacted as susceptible at 10 and 15°C and as RG2 at 20°C. However, cultivars known to produce wart tissue, including the very slightly susceptible 'Altena', were found readily to produce susceptible reactions when inoculated at all the temperatures tested.     

Factors affecting the efficacy of post-harvest fungicide applications for the control of blue mould (Penicillium expansum) in stored apples

The effects of apple fruit maturity, temperature of fruit or dip solution, period of time in fungicidal dip, storage conditions, and spore inoculum concentration, on the efficacy of fungicides for control of blue mould ( Penicillium expansum ) were examined in various experiments.
Iprodione and imazalil were only effective when inoculum concentration was low, whilst prochloraz was highly effective in controlling rot on fruit inoculated with 3 × 10⁶ spores/ml. There was no consistent effect of dip temperature or fruit maturity on the efficacy of the fungicides. Iprodione was more effective on warm fruit (19°C) than cold fruit (6°C) whilst the reverse was true of imazalil. Extended periods of immersion in the fungicides slightly reduced the incidence of rotting but not to any useful degree.
The incidence of rotting in fruit treated with prochloraz and etaconazole was less in fruit stored under controlled-atmosphere cold storage conditions than in fruit stored in air cold-storage. Both fungicides were also effective for short-term storage at 20 C in air. Captan, benomyl, captan plus benomyl or vinclozolin were either ineffective or of poor efficacy under all storage conditions.     

Effect of soil solarization on the control of Phytophthora root rot in avocado

Phytophthora root rot is of paramount importance in avocado orchards of southern Spain. Soil solarization has been demonstrated to control the pathogen in infested areas from which infected trees had been removed. We aimed to determine whether soil solarization in established avocado orchards controls the disease. Soil solarization increased average maximum hourly soil temperatures by 6.5–6.9°C in unshaded areas of avocado orchards in coastal areas of southern Spain, depending on depth and year. The corresponding temperatures in shaded areas were c. 2–3°C lower. P. cinnamomi in soil, on infected avocado rootlets, and in a nutrient substrate buried at 30–60 cm depth was reduced to negligible amounts after 6–8 weeks of solarization in both unshaded and shaded locations of avocado orchards. P. cinnamomi could not be detected in avocado rootlets up to 14 months later, suggesting a long-term effect. Soil solarization did not affect growth of the trees, and fruit yields were increased as compared with control plots. Following soil solarization for 3 weeks from mid-July 1994, when maximum hourly temperatures reached 33–36°C, P. cinnamomi could not be recovered from a depth of up to 45 cm in unshaded areas or from a depth of up to 30 cm in shaded areas after the initial 10-day period. The viability of inoculum of the pathogen buried at depths between 15 and 60 cm in bare soil was determined by sequential sampling in two solarization experiments starting 12 June and 4 July 1995, respectively. In the first experiment, P. cinnamomi could not be detected at any depth after 4–8 weeks of solarization in unshaded areas but could be recovered at all depths except 15 cm in shaded areas. In the second experiment, where temperatures were higher and the soil surface not shaded, P. cinnamomi could not be recovered after 2 weeks at 15 and 30 cm.     

Effect of temperature on symptom expression and accumulation of tomato spotted wilt virus in different host species

The effect of two temperature regimes (daytime, 29 ± 2°C, night-time, 24 ± 3°C; and daytime, 23 ± 1°C, night-time, 18 ± 2°C) on the symptoms caused by tomato spotted wilt virus (TSWV), and the accumulation of TSWV virions, was compared in Datura stramonium , Nicotiana tabacum cv. White Burley and Physalis ixocarpa . Tobacco plants were more severely affected by TSWV at the high temperature regime, but the incidence (percent of plants with symptoms) was 100% for both regimes. In P. ixocarpa and D. stramonium the higher temperature caused an increase in both incidence and rate of development of symptoms. At high temperature, all three species showed both local and systemic symptoms; however, at low temperature only P. ixocarpa consistently developed systemic symptoms. In general, virus accumulation in the inoculated leaves (presumably the combined effect of virus replication and local movement) of all plants was higher at the lower temperature. Long distance movement in tobacco, leading to virion accumulation in other plant organs, was favoured by high temperature; but there was relatively little effect in P. ixocarpa and D. stramonium .