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.     

The control of fungal seed–borne diseases by means of a thiram seed soak

A method of soaking seeds in an 0·2% aqueous suspension of thiram for 24 h at 30 °C, which had previously been shown to eradicate infection by several fungi, was tested against a further thirteen seed-borne pathogens. Eleven of these were completely controlled, one was almost completely controlled and one was not adequately controlled by the treatment. The thiram soak treatment was much more effective than dust treatments with fungicides for the control of many internal fungal pathogens. It was also generally more effective and less damaging than hot-water treatment. The ways of applying the method commercially have been investigated and it is being adopted for the treatment of celery, brassicas and red beet.     

Pathogenicity of fungi associated with wheat and barley seedling emergence and fungicide efficacy of seed treatment

Presented study focused on the influence of Cochliobolus sativus isolates origin on pathogenicity towards wheat and barley seedlings in comparison with pathogenicity of certain Fusarium species and Microdochium nivale. The efficacy of fungicide seed treatment against C. sativus was estimated. The C. sativus isolates were collected from different locations and were isolated from wheat, barley and sunflower seeds. The pathogenicity of C. sativus, Fusarium species and M. nivale towards germinating seedlings were expressed as germination (GA) retardation and coleoptile growth rate retardation (CGR). Of wheat only, the CGR was significantly influenced by the isolate origin. The C. sativus isolates obtained from sunflower seeds were the most aggressive. Of the barley seeds, the barley isolates were the most aggressive. Barley was significantly more susceptible to damage by C. sativus isolates than wheat. The pathogenicity of tested fungal species declined in the order: F. culmorum, F. graminearum, C. sativus, F. avenaceum, M. nivale, F. poae for both barley and wheat. The results highlighted high pathogenicity potential of C. sativus equal to that of F. avenaceum and M. nivale. The symptoms of C. sativus on coleoptile and roots were very similar or the same as the symptoms caused by Fusarium species and M. nivale, except of white, pink or red colours. Of wheat sprouts, the fungicide efficacy (FE) against C. sativus declined in the order: tebuconazole + thiram, carboxin + thiram, quazatine, difenoconazole, iprodione + triticonazole (in term of GA) and carboxin + thiram, iprodione + triticonazole, tebuconazole + thiram, difenoconazole, quazatine (in term of CGR). In barley, the FE declined in the order: carboxin + thiram, iprodione + triticonazole, tebuconazole + thiram, difenoconazole, quazatine (in term of GA) and carboxin + thiram, tebuconazole + thiram, difenoconazole, iprodione + triticonazole, quazatine (in term of CGR).     

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 water potential on soil-borne diseases of wheat seedlings

Under glasshouse conditions, Fusarium culmorum caused more injury to wheat seedlings in soil at 33% saturation (approximately – 1 bar) than at 66% (–0·1 bar). The same effect occurred with inoculated seeds raised on soil moisture tension tables at –0·1 and –0·5 bar, at 20° and at 15°C. In controls, spontaneous infection by soil-borne F. culmorum was unaffected by soil water potential. Inoculated F. nivale, at 127deg; and at 15°C, showed a similar, but smaller, effect to that with inoculated F. culmorum. Water potential in this range did not affect disease incidence with inoculated Gaeumannomyces graminis, but disease was more severe in the drier soil. On tension tables, seedlings did not consistently develop faster under wetter conditions, and factors other than host growth rate probably played a part in limiting fungal attack.     

The reproductive behaviour of Metopolophium festucae (Theobald) at different temperatures and on different host plants

Metopolophium festucae is a cold-hardy species: on young oat seedlings nymphs are produced from apterae at temperatures below 6 °C. Alatae are less well adapted to low temperatures: in a laboratory experiment the average daily production of nymphs from apterae was 0·96 at 10·2 °C and 2·71 at 22·8 °C; the corresponding figures for alatae were 0·42 and 1·81. Aphids on oats, wheat and Italian ryegrass have a slightly higher progeny production than on barley, timothy and cocksfoot: the adults produced on the cereals are heavier than those on the grasses. It is postulated that the aphids require a perennial crop on which to overwinter as nymphs or parthenogenetic adults; consequently successful colonization of cereal crops is rare.     

Respiration in barley seeds treated with mutagenic methyl methanesulphonate and stored at different water contents

In water soaked barley seeds the respiration rate (QO₂) at 25 °C is about 100 times higher at 30% than at 20% water content. The treatment of seeds with mutagenic methyl methanesulphonate led to the depression of the respiration rate in dependence on the applied mutagenic dose. Seed storage at 30% water content resulted in a recovery from the inhibition of seed respiration caused by methyl methanesulphonate. In contrast, at 20% seed water content the respiration rate either slightly decreased or remained unchanged in the course of storage. The results are discussed in relation to the previously described changes in the yield of induced mutagenic effects in barley seeds treated with monofunctional alkylating agents and stored at 30% and 20% seed water content.     

Comportamento Alla Germinazione Delle Cariossidi Delle Linee Primaverile e Invernale del Triticum Esaploide «Denti de Cani»

Abstract

The germination of spring and winter wheat lines of exaploid Triticum « Denti de Cani ». — The dormancy in the seeds of two lines of Triticum « Denti de Cani » (which is spontaneous in Sardinia), one with solid stem (CP line), a spring line, the other with hollow stem (CV line), an winter line, has been studied. Germination was carried out in the dark, in Petri dishes at the constant temperatures of 5°, 10°, 20°, 23°, 26°, 30° and 35°C, using full ripe seeds, and seeds in different stages of after-ripening up to one year of age. The increase in % germination, for increasing temperatures above 5°C, is clearly conditioned by the progress of after-ripening in the seeds. In fact it was seen that, in general for the two lines, percentages over 50% of seeds germinated at 3 days were reached: at 10° and 20° after 15 days from the full ripening; at 23°C after 30 days; at 26°C after 50 days; at 30°C after about 100 days and at 35°C only after about 4–5 months from the harvest. During the experiment at 5°C it was observed that, during the first year of life of seeds and especially in the CP line, this temperature produces a clear slowing down in germinations after first year from the ripening, only the CV seeds — not the CP which remain very much inhibited — reach germination values over 50% at 3 days. It has also been demonstrated that the CV are more sensitive than the CP, in the first initial period of after-ripening (15 and 30 days), to the non-inhibiting activity of low temperatures (5° and 10°C) and that, between these, the 10°C temperature promotes the germination more clearly than the 5°C temperature. The results obtained have shown that the dormancy wears off in the spring CP-line much more slowly than in the winter CV-line. The CP-seeds remain in a relative dormancy condition for a long time, which causes a significative delay in germination, up to 100 days from the full ripening stage.     

Some properties of cocksfoot mottle virus

Cocksfoot mottle virus (CFMV) was transmitted by manual inoculation of sap to cocksfoot (Dactylis glomerata L.), wheat, oats and barley, but not to nineteen other monocotyledonous and thirteen dicotyledonous plant species. The virus was also transmitted by cereal leaf beetles (Lema melanopa L.). Adult beetles infected plants more frequently than larvae, and remained infective for up to 2 weeks after they had fed on infected plants. Seed from infected cocksfoot and oat plants produced virus-free seedlings. The infectivity of sap was lost during 10 min. at 65° C., and 2 weeks at 20° C., but survived many months at — 15° C. Purified virus preparations, made by various methods, contained numerous nearly spherical particles, about 30 mμ in diameter. In electron micrographs some of the particles were penetrated by negative stain though most appeared intact. However, all the particles migrated together in a centrifugal (sedimentation coefficient = 118 S) or electrophoretic field. The ultraviolet absorption spectrum, and the phosphorus and nitrogen contents of the virus preparations, were typical of a nucleoprotein containing about 25 % nucleic acid. Serological tests failed to show any relationship between CFMV and eleven other viruses with particles of similar shape and size.     

The Survival of Germinating Orthodox Seeds after Desiccation and Hermetic Storage

Seeds of barley (Hordeum vulgare L.) and mung bean (Vigna radiata(L.) Wilczek), with orthodox seed storage behaviour, were imbibedfor between 8 h and 96 h at 15 °C and 25 °C, respectively,while barley seeds were also maintained in moist aerated storageat 15 °C for 14 d. These seeds and seedlings, together withcontrols, were then dried to various moisture contents between3% and 16% (wet basis) and hermetically stored for six monthsat —20°C, 0°C or 15°C. In both species, neitherdesiccation nor subsequent hermetic storage of the control lotsresulted in loss in viability. The results for barley seedsimbibed for 24 h were similar to the control, but desiccationsensitivity increased progressively with duration of imbibitionbeyond 24 h in barley or 8 h in mung bean; these treatmentsalso reduced the longevity of the surviving seeds in air-drystorage. Loss in viability in barley imbibed for 48 h was mostrapid at the two extreme seed storage moisture contents of 3·6%and 14·3%, and in both these cases was more rapid at15 °C than at cooler temperatures. Similarly, for mung beanimbibed for 8 h, loss in viability was most rapid at the lowest(4·3%) moisture content, but in this case it was morerapid at –20 °C than at warmer temperatures. Thus,these results for the storage of previously imbibed orthodoxseeds conform with the main features of intermediate seed storagebehaviour Key words: Barley, Hordeum vulgare L., mung bean, Vigna radiata (L.) Wilczek, desiccation sensitivity, seed longevity, seed storage behaviour     

Reduction of Escherichia coli O157:H7 on radish seeds by sequential application of aqueous chlorine dioxide and dry‐heat treatment

Aims: To assess the effectiveness of sequential treatments of radish seeds with aqueous chlorine dioxide (ClO₂) and dry heat in reducing the number of Escherichia coli O157:H7. Methods and Results: Radish seeds containing E. coli O157:H7 at 5·5 log CFU g^?1 were treated with 500 μg ml^?1 ClO₂ for 5 min and subsequently heated at 60°C and 23% relative humidity for up to 48 h. Escherichia coli O157:H7 decreased by more than 4·8 log CFU g^?1 after 12 h dry‐heat treatment. The pathogen was inactivated after 48 h dry‐heat treatment, but the germination rate of treated seeds was substantially reduced from 91·2 ± 5·0% to 68·7 ± 12·3%. Conclusions: Escherichia coli O157:H7 on radish seeds can be effectively reduced by sequential treatments with ClO₂ and dry heat. To eliminate E. coli O157:H7 on radish seeds without decreasing the germination rate, partial drying of seeds at ambient temperature before dry‐heat treatment should be investigated, and conditions for drying and dry‐heat treatment should be optimized. Significance and Impact of the study: This study showed that sequential treatment with ClO₂ and dry‐heat was effective in inactivating large numbers of E. coli O157:H7 on radish seeds. These findings will be useful when developing sanitizing strategies for seeds without compromising germination rates.     

The effect of the weight of the seedling-derived tuber on subsequent clonal generations in a potato breeding programme

Cultures of Polymyxa graminis were maintained in roots of barley plants grown in sand at different temperatures using Wisconsin soil temperature tanks. At 17 – 20°C, the minimum time from inoculation with cystosori to the production of zoospores from the inoculated roots was 2 – 3 wk. At 11 – 20°C many zoospores were produced but the incubation period was longer at the lower temperatures. Above 20°C little fungal development occurred. The duration of motility of zoospores ranged from c. 1 h to > 24 h. Bovine serum albumen (BSA) prolonged motility but glycine and glucose had no effect or, at higher concentrations, were toxic. Zoospores were rapidly immobilised by zinc ions in solution at or above 10μg/ml. In some experiments BSA added to the zoospore suspension greatly increased transmission of barley yellow mosaic virus (BaYMV) while glucose, glycine and ovalbumen decreased it. When seedlings were incubated with zoospore suspensions for 24 h at different temperatures, BaYMV transmission was high (> 60%) at 10, 15 and 20°C but there was little at 5 or 25°C. In experiments to determine the time taken for zoospore penetration, seedlings were incubated in suspension for different periods of time and then rinsed in zinc sulphate solution to kill free zoospores. Between 3 and 3·5 h was needed for zoospores to establish infection. Transmission occurred equally to plants of various ages between 3 days and 7·5 wk.     

A study of the optimum drying conditions for cabbage seed following selection on the basis of a newly-emerged radicle

A series of experiments were carried out to study the effects of different drying regimes on the survival of newly-germinated (radicle emerged 0·5-1·5 mm through the seed coat) cabbage seeds and to establish a treatment for reducing the moisture content of these germinated seeds. A preliminary surface-drying step proved necessary to avoid seed agglutination during the main drying stage. Of the drying regimes compared both viability and vigour were most effectively maintained in air, conditioned to between 20 and 30°C and with 80% r.h., flowing through the seeds at 0·25 m s^-1. Under these conditions, the viability and vigour of newly-germinated seed was maintained during drying to an equilibrium moisture content of c. 14%. At this moisture content further radicle growth was prevented and seeds remained free-flowing and separate for sowing or for further treatment.     

Influence of post-flowering temperature on seed development, and subsequent performance of crisp lettuce

Crisp lettuce plants cv. Saladin were grown from the time they started flowering, at 20/10°C (16 h day, 8 h night), 25/15°C and 30/20°C in glasshouses on two occasions in 1985. Yields of seed increased from, on average, 15 g to 27 g and then fell to 20 g per plant with progressive increases in temperature. The number of mature florets per plant increased with temperature but the number of seeds per mature floret was lower at 20/10°C and 30/20°C than at 25/15°C. An increase in temperature reduced mean seed weight by up to 45%, seed volume by 15%, cell numerical volume density (N_v) by 27% and the number of cells per seed by 39%. Percentage seed germination reached a maximum early in seed development at the stage when the pappus appeared through the involucral bracts. Differences in percentage germination and vigour of seeds (slope test) from different temperatures were accounted for largely by the effects on mean seed weight. However, when germinated at 30°C seeds produced at 30/20°C germinated more readily than those produced at 25/15°C or 20/10°C. Seed vigour gradually increased with an increase in the length of storage after harvest, reaching a maximum after 260 days. In general, seeds produced at 25/15°C exhibited a greater variation in numbers of seeds per floret, N_v, seed weight, times of seedling emergence, seedling and mature head weight than seeds produced at lower or higher temperatures.     

Control of Botrytis cinerea and Botrytis squamosa in overwintered salad onions by fungicide sprays

In 1974/75, 13 sprays of 0·2% a.i. thiram applied at 14 day intervals to overwintered salad onions reduced the incidence of Botrytis cinerea and significantly increased onion yields. In 1977/78 both B. cinerea and B. squamosa occurred, and 12 iprodione sprays at 0·1% a.i. applied at 14-day intervals or 6 sprays at 0·2% a.i. applied at 28-day intervals gave good control of B. cinerea and B. squamosa and significantly increased onion yields. Benomyl (0·1% a.i. at 14-day intervals, or 0·2% a.i. at 28-day intervals) failed to control either pathogen because of the development of carbendazim-insensitive strains of the fungi. Effective control of both pathogens and increased yields were obtained with an application of 0·4% a.i. thiram in October and November followed by an application of 0·2% a.i. iprodione in December and January.     

Effects of temperature, light, storage conditions, sowing time, and burial depth on the seed germination of Cardiocrinum cordatum var. glehnii (Liliaceae)

In this study, we conducted experiments to accumulate practical information on the propagation and establishment of a population of Cardiocrinum cordatum var. glehnii by seed sowing. C. cordatum var. glehnii seeds require approximately 19 months from seed dispersal to cotyledon emergence in the field. However, the period from seed dispersal to radicle emergence was shortened to approximately 7–8 months by the temperature transition of 25/15°C (60 days) → 15/5°C (30 days) → 0°C (120 days) → 15/5°C (i.e., 15/5°C represents alternating temperature treatment wherein the seeds were placed at 15°C for 12 h during the day and then at 5°C for 12 h during the night). More than 90% of the seeds, which were stored dry at 5°C for 12 months and sown in pots in the field, showed cotyledon emergence, whereas in seeds stored dry at 25°C, dry at room temperature, and non-dry at room temperature, cotyledon emergence was decreased by less than 1%. More than 88% of the seeds that were stored dry at 5°C and sown in the field in October 2002 immediately after collecting, November, and from April to July 2003 showed cotyledon emergence in spring 2004. However, seeds sown in August, September, and October 2003 showed cotyledon emergences of 57.6%, 0%, and 0% in spring 2004, respectively. Seeds collected in October 2002 and sown until July 2003 in the field received adequate high temperature in summer, moderate temperature in autumn, and cold temperature in winter; therefore, the percentage of cotyledon emergence was high in spring 2004. On the other hand, seeds sown in August 2003 or later could not receive enough high temperature; thus, cotyledons emerged from only a few seeds.     

Effect of hot water and ultra violet radiation on the incidence of seedborne fungi of okra

Seed samples of okra (Abelmoschus esculentus (L.) Moench) variety Arka anamika were subjected to hot water treatment at 42, 52 and 62°C for a period of 30 min and UV light treatment for 10, 20, 30 min at 28 ± 2°C. Their efficacy was tested against some seedborne fungal species. Among them, seeds under hot water treatment at 52°C for 30 min and UV light at 20 min were found to be more effective in the improvement of crop, both in greenhouse and field conditions. Ultimately, there was increase in the total number of leaves, fruits, length of the fruit, girth and biomass of the plants. Apart from these the total number of seeds per fruit, 1000 seed weight and ascorbic acid content were also found to be enhanced. These treatments also reduced the incidence of mycoflora in the seeds and thereby enhanced the seed germination percentage and vigour index of the seedlings.     

Storage of ethyl methanesulphonate-treated barley seeds with low moisture contents

Barley seeds were treated with ethyl methanesulphonate (EMS) for 3 h at 25° C, washed with tap water for 24 h at 25° C, redried at 40° C to different moisture contents below 15% and stored at 25° C in desiccators or in sealed plastic bags. The criteria used for expressing the effect of storage were the M₁ seedling height and the frequency of chromosomal aberrations. With 14·9% seed moisture a strong increase of biological injury occurred in the course of a 2-week storage, while storage of seeds having an initial moisture content of 11·7% led to a significant increase of injury only after 6 weeks. Superdry EMS-treated seeds with 5% or less moisture can be stored at 25° C without any changes in the biological effects. A method is recommended to avoid the EMS-storage effects.     

Effects of Photoperiod on Germination of Seeds of Talinum triangulare (Jacq.) Willd

Seed germination in Talinum triangulare as affected by photoperiod,with or without previous incubation in the dark in water at25 or 4 °C, was studied. The time course and quantity ofseed germination in photoperiods of 1 h and above were similarwith or without dark pretreatment, but the time to half maximumgermination was reduced from 12 days in non-dark pretreatedseeds to 4 days in seeds given 20 days in the dark at 25°C.A photoperiod of 0·25 h gave a lower rate and total germinationthan photoperiods of 1 h and above. Un-pretreated seeds required17 cycles of 24 h photoperiod for maximum germination as comparedwith 7 or less cycles if the seeds received more than 10 daysdark pretreatment at 25 °C. Both the rate and total germinationin light increased as the length of dark pretreatment at 25°C was increased from zero to 30 days. Incubation of theseeds in water in the dark at 4 °C for 5 to 30 days priorto illumination at 21 °C, reduced both the rate and quantityof seed germination in light as compared with those similarlyincubated in the dark at 25 °C. However, previous incubationin the dark for 30 days at 4 °C partially substituted forthe light requirement. The possible mechanism of breakage ofseed dormancy in Talinumis discussed in relation to these andother findings. Talinum triangulare (Jacq.), Willd, light, photoperiod, seed germination     

Aerated-steam treatment for control of Alter nana tenuis on lobelia seed

Alternaria tenuis may cause severe seedling blight, damping-off and leaf spotting of the bedding plant lobelia. Disease transmission from seed naturally and artificially infected by A. tenuis was demonstrated and the pathogenicity of four isolates established. Soaking of lobelia seed in 0–2% thiram suspension at 30 ^oC for 12 h adversely affected the rate of germination and did not consistently reduce infection to acceptable levels. Treatment with aerated steam at 50–51 ^oC for 15–20 min reduced seed infection to undetectable or insignificant levels and caused only slight damage to the seed. In glasshouse trials seed treated with aerated steam performed significantly better than seed soaked in thiram suspension both in terms of germination and foliage production.