Stemphylium botryosum f. lactucae- its developmentjn vifro and its pathogenicity to lettuce leaves

Stemphylium botryosum f. lactucae, incitant of a leaf-spot disease of stored lettuce, was found to be relatively restricted in its host range. Cross-inoculations with spore suspension of this fungus failed to induce symptoms in any of the host plants tested, except carrot. Among isolates of S. botryosum from various hosts, only the isolate from carrot induced slight symptoms on lettuce. While mycelial growth of the lettuce isolate was confined to the range 13–37 ^oC spores germinated at more extreme temperatures. The optimum temperature for germination and for radial growth on PDA was found to be between 25 and 30 ^oC. Wet spores were quickly inactivated at 50 ^oC, whereas more than 40 % of dry spores withstood a 24 h exposure to that temperature. Only the outer leaves of lettuce responded readily to inoculation with a spore suspension, the required incubation period being 3 days at 25 ^oC. Symptoms developed less readily on bruised leaves. Relative humidity approaching saturation was necessary for prompt and typical infection, notably during the 24 h following inoculation. Short dry periods (60 % r.h.) interposed at a later stage, while somewhat inhibitory, did not prevent infection.     

The effect of temperature on viability of imbibed weed seeds

Imbibed seed of 10 common arable weeds were placed in trays in initially moist soil and, after imbibing for 2h, heated in ovens/incubators set to 31^oC, 42^oC, 56^oC, 75^oC or 100^oC for 0.5, 1, 2, 4, 8 or 16 days or at 102^oC, 155^oC, 204^oC or 262^oC for 0.5, 1, 2, 5, 7.5 or 10 min. After heating, seeds were incubated for 28 days at 10/20^oC or 20/30^oC on a 12 h dark/light regime, depending on species, and germination recorded. At the lower temperatures, germination of all species was prevented by temperatures of 75^oC or higher for periods of 0.5 days or more. Germination was lower after treatment at 56^oC than at 31^oC or 42^oC for all species except Rumex obtusifolius. The maximum temperature required to prevent germination varied among species and was of greater importance than the duration of heating. Germination was variable with duration of heating. At the higher temperatures, there was very little germination of any species after heating at 204^oC for 7.5 min or 262^oC for 5 min or more. Seeds were greatly buffered from the air temperature by 3 mm of soil, throughout the shorter duration of heating. The average temperature of the soil, over the 10 min heating required to prevent over 90% germination, varied among species and ranged from 48^oC for Avena fatua to 65^oC for R. obtusifolius. This work implies that composting systems maintained at 65^oC are unlikely to provide an efficient method of weed control. Recommendations for improvement of the laboratory technique are suggested.     

Pea seed infection by Mycosphaerella pinodes and Ascochyta pisi and its control by seed soaks in thiram and captan suspensions

Apparently normal pea seeds from pods bearing lesions of Mycosphaerella pinodes were often internally infected with the fungus. When infected seeds were sown in sterile grit almost all the seedlings showed disease lesions, at or below soil level, 4–6 weeks after sowing. Seed infected with Ascochyta pisi gave only 40% infection of seedlings: these showed lesions on the stem and first two leaves within 4 weeks of sowing. Infection of seeds by both pathogens could be eradicated by soaking the seeds for 24 hr. in 0.2% suspensions of thiram or captan at 30d?C. In laboratory or greenhouse tests these treatments did not check germination, but in the field the captan treatment reduced emergence. The treated seeds became fully imbibed but could be dried and stored: the thiram treatment was used for semi-commercial treatment of quantities of seed up to 3 cwt.     

The effect of elevated temperatures and their duration on the incidence of hollow heart in pea seeds

Plants of Pisum sativum cv. Pania were exposed to high temperature (35 ^oC day/25 ^oC night) at three stages in development. These were: (i) at process crop maturity, when the seed moisture content (m.c.) was 80%, i.e. about 10 days prior to pod wrinkle, (ii) at a seed m.c. of 70 to 80%, about the onset of pod wrinkle, and (iii) when the seed m.c. was 50 to 60%, 10 days after the onset of pod wrinkle. At each stage of development the high temperature treatment was imposed for 2,4,6, 8 or 10 days. Plants exposed to high temperature at seed m.c. of 70 to 80% produced seed with the highest incidence of hollow heart and at all stages of development the incidence increased with the length of exposure to the high temperature. Where plants at the development stage of pod wrinkle (seed m.c. 70–80%) were exposed to a range of temperature regimes for 5 days, over 20% of the seeds had hollow heart when the mean day/night temperature was 25 ^oC. Above a mean temperature of 25 ^oC, the percentage of affected seed increased with increasing day or night temperature. Over 80% of the seeds had hollow heart symptoms after 5 days exposure to a daily mean temperature of 32-5 ^oC. The severity of symptom development was not related to the proportion of seeds with the disorder and, under laboratory conditions, seed germination was not affected.     

Harnessing Candida tenuis and Pichia stipitis in whole-cell bioreductions of o-chloroacetophenone: Stereoselectivity,cell activity,in situ substrate supply and product removal

Generally, recombinant and native microorganisms can be employed as whole-cell catalysts. The application of native hosts, however, shortens the process development time by avoiding multiple steps of strain construction. Herein, we studied the NAD(P)H-dependent reduction of o-chloroacetophenone by isolated xylose reductases and their native hosts Candida tenuis and Pichia stipitis. The natural hosts were benchmarked against Escherichia coli strains co-expressing xylose reductase and a dehydrogenase for co-enzyme recycling. Xylose-grown cells of C. tenuis and P. stipitis displayed specific o-chloroacetophenone reductase activities of 366 and 90 U g_CDW^–1, respectively, in the cell-free extracts. Fresh biomass was employed in batch reductions of 100 mM o-chloroacetophenone using glucose as co-substrate. Reaction stops at a product concentration of about 15 mM, which suggests sensitivity of the catalyst towards the formed product. In situ substrate supply and product removal by the addition of 40% hexane increased catalyst stability. Optimisation of the aqueous phase led to a (S)-1-(2-chlorophenyl)ethanol concentration of 71 mM (ee > 99.9%) obtained with 44 g_CDW L^–1 of C. tenuis. The final difference in productivities between native C. tenuis and recombinant E. coli was < 1.7-fold. The optically pure product is a required key intermediate in the synthesis of a new class of chemotherapeutic substances (polo-like kinase 1 inhibitors).     

Effect of temperature, light and host on prepenetration development of Puccinia graminis avenae and Puccinia coronata avenae

The influence of temperature and light on prepenetration development of single and mixed isolates of Puccinia graminis avenae and Puccinia coronata avenae was studied on 0–2% water agar and on leaves of three oat cultivars and on three non-cultivated species of Avena. Germination of uredospores of P. graminis avenae and P. coronata avenae occurred best at 10–30^oC and at 20^oC respectively. The optimum temperature for germ-tube growth and for appressorial formation was 20^oC for both rusts. An inverse relationship was observed between light intensity and prepenetration development with maximal germination of uredospores, germ-tube growth and appressorial formation occurring in darkness. Under optimum conditions maximum percentage germination and appressorium formation of both rusts was attained within 4 and 12 h after inoculation respectively. The proportion of germinated uredospores of crown rust which gave rise to appressoria was about twice that observed for stem rust. No significant differences were observed in prepenetration development between the single and mixed race inocula of the two rusts. Although germination of uredospores was significantly greater on water agar than on oat leaves, there were no significant differences in prepenetration development of the rusts on the various oat cultivars and species examined. Consequently, the data failed to indicate the presence of resistance mechanisms operating during the prepenetration phase of the infection process on the cultivars and species examined.     

Effects of virus genotype and temperature on seed transmission of nepoviruses

Transmission of different nepoviruses through chickweed (Stellaria media) seed was differently affected by ambient temperature during seed production. Raspberry ringspot and tomato black ring (Scottish isolate) viruses were similarly and frequently transmitted at 14 , 18 and 22 ^oC, whereas arabis mosaic virus was transmitted most frequently at 14 ^oC, and strawberry latent ringspot and tomato black ring (German isolate) viruses at 22 ^oC. When infected by seed-borne nepoviruses, seedlings of S. media and other species were symptomless at 15–25 ^oC, and the viruses were therefore detected by inoculating sap to Chenopodium quinoa indicator plants. However, typical symptoms of arabis mosaic and tomato black ring viruses were induced by growing Nicotiana tabacum, N. clevelandii and C. quinoa seedlings infected with seed-borne virus at 33–37 ^oC during the third and fourth weeks after sowing, preceded and followed by periods at 15–25 ^oC. The proportion of N. tabacum seedlings developing symptoms was the same as that of untreated seedlings yielding sap-transmissible virus. Seed transmissibility of pseudo-recombinant isolates of raspberry ringspot and tomato black ring viruses, containing RNA-i from one virus strain and RNA-2 from another strain, depended greatly on the transmissibility of the strain contributing RNA-i. The source of RNA-2 had an additional but smaller influence. The satellite RNA (RNA-3) of tomato black ring virus was seed-transmitted in S. media and its occurrence in cultures did not affect the frequency of transmission of the virus. Results of testing the infectivity of extracts of seed from infected mother plants suggested that failure of seed transmission reflected failure to become established in the seed, not subsequent inactivation. Whereas seed transmissibility of raspberry ringspot virus is primarily dependent on information carried in RNA-i, transmissibility by nematode vectors, another property of major ecological importance, is determined by RNA-2. In the field, selection pressures presumably can act independently on the two parts of the genome but evidence was also obtained of selection for mutual compatibility of RNA-i and RNA-2.     

Studies on the etiology of black rot, Stemphylium radicinum (Meier, Drechsl. & Eddy) Neerg., and leaf blight, Alternaria dauci (Kühn) Groves & Skolko, on carrot crops; and on fungicide control of their seed-borne infection phases

Of nineteen commercial samples of carrot seed in use at Wellesbourne in 1963, eight were found to be infected with both Stemphylium radicinum and Alternaria dauci and five with S. radicinum alone. Both fungi caused damping-off of seedlings and when carrots were grown at high densities A. dauci caused severe foliar infection. Neither fungus gave rise to marked infection of ware crops at normal spacings but, when seed infected with S. radicinum was sown in the autumn, the resulting seed crop was heavily infected by the succeeding autumn. Spring-sown carrots grown in soil that had borne infected crops or contained debris infected with either fungus showed little or no infection in the autumn or after storage for 3 1/2 months; autumn-sown or spring-planted (steckling) carrots put into ground infected with S. radicinum showed severe infection in the following autumn. This suggested that ware-crop carrots were resistant to infection from the soil whereas the seed crop was not. Both fungi were eradicated from seed by a 24 hr. soak at 30d? C. in a 0.2% thiram suspension, but were not completely eliminated by seed dust treatments with a range of fungicides.     

Effect of high soil temperatures on nodulation of cowpea, Vigna unguiculata

Cowpeas, inoculated with one of five effective strains of Rhizobium isolated from African soils, were grown at root temperatures of 30 ^oC continuously or at 36, 38, 40, 42 and 44 ^oC for 5 h/day and returned to glasshouse ambient for the intermediate period. Growth was best at 30 and 36 ^oC; above 40 ^oC growth was poor and no nodules formed. At 40 ^oC two strains failed to nodulate. Symbiotic performance was not dependent only on nodule production as nodule efficiency varied inversely with temperature. The number of nodules formed by strain R5000 after exposure of inoculated seed or seedlings to 40,42 or 44 ^oC for 5 h/day on each of 3 or 6 days depended on the age of plant and the duration of exposure to stress. When exposed to 42 or 44 ^oC during the first 3 days after sowing nodulation was reduced from 18 to 1–3 nodules/plant even after a further 40 days growth at ambient (30 day, 20 ^oC night). Nodulation was unaffected when 10–15-day-old seedlings were exposed to the same conditions. Numbers of strain R5000 on seed declined rapidly following three daily exposures of 5 h at 39 and 42 ^oC; at 45 ^oC less than three bacteria survived on each seed. Other rhizobia of the cowpea group varied greatly in their toleration of high temperatures, some survived well at 45 ^oC whereas others behaved like R5000.     

In vitro and In vivo Effects of Some Fungicides against the Chickpea Blight Pathogen, Ascochyta rabiei

The effects of various fungicides on mycelial growth and spore germination of Ascochyta rabiei were determined by incorporating them into potato dextrose agar and measuring colony diameter and observing colony growth and spore germination at 20 ± 2°C. Eight fungicides prevented spore germination of the pathogen at concentrations of 0.125–2 μg/ml, three hindered mycelial growth at 2–4 μg/ml and seven failed to inhibit mycelial growth even at 128 μg/ml. The reference fungicide for the pathogen, chlorothalonil, stopped conidial germination at low rates but did not prevent mycelial growth at 128 μg/ml. Thirteen fungicides were tested against seed infections of the pathogen, and benomyl + thiram, carbendazim and carbendazim + chlorothalonil seed treatments gave more than 85% inhibition on both vacuum‐infiltrated and naturally infected seeds. Coating the seeds with polymers did not increase the effectiveness of fungicides. Three fungicides; (azoxystrobin, chlorothalonil and mancozeb), gave the highest protection in the field but protection decreased with increased inoculum pressure. Addition of humic acid to fungicide suspensions did not affect their performance.     

Tree fine root Ca/Al molar ratio – Indicator of Al and acidity stress

Many Aloe species are exploited as natural products. Generally, the leaves are unsustainably picked from wild plants to meet the market demand. Basic scientific information on seed biology and the ways of increasing levels of secondary metabolites in seedlings is still lacking for Aloe species. This study investigated seed germination requirements and evaluated levels of secondary metabolites in seedlings of Aloe arborescens, an important species in traditional medicine. The highest percentage germination (78%) and the fastest germination rate (GR) (10% d^? 1) with a mean germination time (MGT) of 9 days were achieved at 20°C under a 16-h photoperiod. At 25°C, maximum percentage germination (67%) (P < 0.05), higher GR (13% d^? 1) and shorter MGT (6 days) were obtained under constant light. These results indicate that temperature and light play a significant role in germination of A. arborescens seeds. Increasing osmotic pressure on seeds decreased percentage germination, whereas buffering the solution to a range of pH values (4–10) did not significantly affect germination. Smoke–water (1:500 v/v), smoke-isolated karrikinolide (10^? 8 and 10^? 9 M) and potassium nitrate (10^? 3 and 10^? 4 M) significantly promoted germination compared with the control at 25°C (supra-optimal temperature) under a 16-h photoperiod. These treatments were also effective in increasing secondary metabolite levels (flavonoids and phenolics) in A. arborescens seedlings.     

Infection of the flowers and seed of parsnip by Itersonilia pastinacae

Seeding parsnip plants on four commercial holdings in Essex showed not only the root cankers and leaf spots associated with infection by Itersonilia pastinacae, but also extensive lesions on the petioles and necrosis of the inflorescences. These last-named symptoms were proved to be caused by I. pastinacae which could also be found on some of the seeds. Seed infection, though largely superficial, was sometimes more deep-seated. It could be eliminated by soaking the seed in an aqueous suspension of 0·2% thiram at 30 °C for 24 h. Heavily infected seed gave a low percentage of seedlings bearing cotyledon lesions: it is uncertain whether hypocotyl lesions, which also occurred, were caused directly by the fungus. An outdoor test failed to show that infected seed gave rise ultimately to roots bearing Itersonilia cankers: the significance of this and other possible sources of infection is discussed.     

Growth and ion relations in response to combined salinity and waterlogging in the perennial forage legumes Lotus corniculatus and Lotus tenuis

Lotus tenuis (Wadst. & Kit.) is a perennial legume widely grown for pasture in the flood-prone and salt affected Pampa region of Argentina. The physiology of salt and waterlogging tolerance in L. tenuis (four cultivars) was evaluated, and compared with Lotus corniculatus (three cultivars); the most widely cultivated Lotus species. Overall, L. tenuis cultivars accumulated less Na⁺ and Cl⁻, and more K⁺ in shoots than L. corniculatus cultivars, when exposed to 200 mM NaCl for 28 days in aerated or in stagnant solutions. Root porosity was higher in L. tenuis cultivars due to greater aerenchyma formation. In a NaCl dose–response experiment (0–400 mM NaCl in aerated solution), L. tenuis (cv. Chaja) accumulated half as much Cl⁻ in its shoots than L. corniculatus (cv. San Gabriel) at all external NaCl concentrations, and about 30% less shoot Na⁺ in treatments above 250 mM NaCl. Ion distributions in shoots were determined for plants at 200 mM NaCl. L. tenuis (cv. Chaja) again accumulated about half as much Cl⁻ in old leaves, young leaves and stems, compared with concentrations in L. corniculatus (cv. San Gabriel). There were not, however, significant differences between the two species for Na⁺ concentrations in the various shoot tissues. The higher root porosity, and maintenance of lower shoot Cl⁻ and Na⁺ concentrations in L. tenuis, compared with L. corniculatus, contributes to the greater tolerance to combined salt and waterlogging stress in L. tenuis. Moreover, significant variation for tolerance to combined salinity and waterlogging stress was identified within both L. tenuis and L. corniculatus.     

Germination and Dormancy of Reed Canary-Grass Seeds (Phalaris arundinacea)

Effects of various chemical and physical factors on the germination of several seed lots of reed canary-grass (Phalaris arundinacea L.) have been studied. Germination at the optimum constant temperatures of 24 to 27°C was significantly stimulated by the following treatments: moist chilling in light, red light given during the first 3 days of imbibition, three 2-h periods at 12°C given during the second day of imbibition, ethylene, increased oxygen tension and soaking in aerated water for 4 days. Dry storage at 20–30°C had no effect on the germination ability of the seeds. No significant quantities of germination inhibitors were found either in water or methanol extracts of seed dispersal units. By comparing three cultivars with various degrees of seed dormancy, respiration measurements showed that there was a significant positive correlation between oxygen uptake prior to visible germination and germination capacity. Similarly, germination-stimulating treatment significantly enhanced oxygen uptake prior to visible germination.     

FACTORS AFFECTING GERMINATION IN GREENHOUSE-PRODUCED SEEDS OF OXALIS CORNICULATA,A PERENNIAL WEED

A study was conducted to investigate the physiological responses of greenhouse-produced Oxalis corniculata seeds to light, temperature, moist heat treatment, aging, and season of production. Fresh seeds exhibited over 90% germination and required low levels of light (5 μmol m^-2 s^-1, 400–700 nm) to germinate. Seeds germinated over a broad, yet seasonally-dependent range of incubation temperatures. Seeds produced in winter had the narrowest temperature range of germination (15 to 25 C) and the lowest germination percent (44% at 2 wk) at optimum temperature (17 C); seeds produced in summer had the widest temperature range of germination (10 to 30 C) and the highest germination percent (93% at 2 wk) at optimum temperature (17 C). Incubation at non-optimum temperatures between 5 and 40 C suppressed or slowed the rate of germination until seeds were placed at optimum temperature, where full germination subsequently occurred. Moist heat treatment at temperatures over 40 C resulted in varying degrees of inhibition of subsequent germination. When seeds were stored dry in laboratory conditions, three of four seed lots examined retained over 80% germination capacity until ca. 8 months; 50% capacity remained after ca. 15 months. These results indicate that the seasonal temperature and daylength effects on maternal plants in the greenhouse environment are major determinants of seed germination characteristics of O. corniculata.     

Germination and emergence of Sorghum bicolor. genotypic and environmentally induced variation in the response to temperature and depth of sowing

Abstract The germination of Sorghum bicolor seeds of 9 genotypes was tested at temperatures between 8°C and 48°C on a thermal gradient plate. Samples were tested from three regions of the panicle expected to differ in temperature during grain filling. Seeds of a tenth genotype, SPV 354, produced in controlled-environment glasshouses at different panicle temperatures, were tested similarly. In addition, the emergence of SPV 354 was measured from planting depths of 2 and 5 cm at mean soil temperatures of 15, 20 and 25°C. Four methods of calculating mean germination rate for the nine genotypes were compared. Germination characters like base, optimum and maximum temperature (T_b, T_o, T_m), thermal time (θ)and the germination rate at T_o(R_max showed only small differences between methods. There was a range of genotypic variation in all characters: T_b 8.5–11.9°C; T_o, 33.2–37.5°C; T_m, 46.8–49.2°C; θ, 23.4–38.0°Cd; R_max, 0.69–1.14-d_-1. In contrast, mean germinability (G) was between 90% and 100% over the temperature range 13–40°C. Panicle temperature had no effect on any germination character in SPV 354. However, deeper burial increased θ for emergence and decreased G, irrespective of soil temperature except at 5 cm. Increasing panicle temperature, by reducing seed size, reduced G and increased θ by about 10% only at 15°C and 5 cm depth.     

Root nitrogen concentration of sorghum above 2% produces least Striga hermonthica seed stimulation

A series of pot and laboratory experiments was carried out to assess the effects of N status of sorghum roots and timing of N application (as NH₄NO₃) on the germination of Striga hermonthica seeds. Root N concentrations varied from 10 to 26 mg N g^?1. The cut root and the root exudates technique used in assaying S. hermonthica seed germination gave similar results. However, the cut root technique was easier to handle and more discriminating at low germination levels. S. hermonthica seed germination per unit sorghum root mass followed a broken‐stick model. It decreased with increasing root N concentrations, reaching lowest levels at a root N concentration of 19.5 mg N g^?1, after which no further reduction occurred. It was not possible to reduce S. hermonthica seed germination to a zero level. Timing of N application influenced the time a higher N concentration is reached, not the S. hermonthica seed germination. Both timing and rate of N application are important in maintaining root N concentrations above 19.5 mg N g^?1, thereby potentially reducing S. hermonthica germination in the field. Translation of results to reductions in infection levels and yield losses is hampered by density‐dependent relations after the S. hermonthica germination stage.     

Effect of temperature and cold stratification on seed germination of the Mediterranean wild aromatic Clinopodium sandalioticum (Lamiaceae)

A germination study was carried out on seeds of Clinopodium sandalioticum (Bacch. & Brullo) Bacch. & Brullo ex Peruzzi & Conti (Lamiaceae), a wild aromatic plant endemic to Sardinia. Seeds were incubated at a range of constant (5–25°C) and an alternating temperatures regime (25/10°C), with 12 hours of irradiance per day. The results achieved at 10°C were also compared with those obtained after a period of cold stratification at 5°C for three months. Final seed germination ranged from ca. 28% (5°C) to ca. 72% (25/10°C). A base temperature for germination (T_b) of ca. 5°C and a thermal constant for 50% germination (S) of 89.3°Cd were identified and an optimal temperature for germination (T_o) was estimated to be comprised between 20 and 25°C. Cold stratification negatively affected seed viability and germination at 10°C. Although a typical “Mediterranean germination syndrome”, could not be detected for C. sandalioticum seeds, these results were coherent with those previously reported for other Mediterranean Lamiaceae species.     

Fungitoxicity of acetaldehyde vapour to some major post-harvest pathogens of citrus and subtropical fruits

In laboratory trials, fumigation with acetaldehyde vapour at 0–75 to 20 % concentration (v/v) for 0–5 to 120 min at 21 ^oC killed six species of post-harvest citrus pathogens grown on agar media. The fungicidal effect of acetaldehyde vapour at this temperature was a function of concentration and exposure. Penicillium digitatum and P. italicum were not as susceptible to inhibition of spore germination as Alternaria citri, A. tenuis, Colletotrichum gloeosporioides and Glomerella cingulata. A concentration of 10 % acetaldehyde vapour at 21 ^oC for 10 min was fungitoxic to all the pathogens tested.     

Hirsutella thompsonii, a fungal pathogen of mites. I. Biology of the fungus in vitro

Hirsutella thompsonii, a moniliaceous fungus pathogenic to mites, grew and sporulated on sterilised wheat bran. The effects of environmental factors were studied on the fungus grown on potato-dextrose-agar (PDA). The fungus was mesothermophilic. Growth, sporulation and conidial germination were best at 25^o-30 ^oC. Conidia kept at 37 ^oC for 5 days on PDA died, but those held at 5 ^oC germinated upon a subsequent removal to 25 ^oC. Almost all conidial germ tubes survived an 8 h exposure to 3–5% r.h. and to 60% r.h., but subsequently the former grew poorly at 100% r.h. H. thompsonii sporulated equally well in continuous darkness or light, and produced typical chlorinous to light olive-green mycelium and conidia under all conditions. A 2 h exposure of naked mycelium and conidia (which have melanised walls) to u.v. irradiation failed to kill the fungus.