STUDIES ON SEED HEALTH

An account is given of the survey made in 1940-55 to determine the incidence of the seed-borne fungal parasites of flax. It was shown that fibre flax seed produced in eastern and south-eastern England was relatively free from contamination with Colletotrichum linicola, Polyspora lini and Phoma sp. and that there was no build-up of infection in seed stocks in these areas. In the wetter and cooler regions west and north of the Pennines, conditions were more favourable for these fungi, and seed contamination tended to increase.
Seed contamination with Botrytis cinerea was general throughout the United Kingdom, with a tendency to be higher in coastal and upland areas. The incidence of Fusarium lini and Alternaria linicola in fibre flax seed produced in the United Kingdom was negligible.
The examination of seed samples from other countries indicated the possible importance of P. lini in Denmark, of B. cinerea and C. linicola in the Netherlands, of A. linicola as a contaminant of oil flax seed in Sweden, and of C. linicola in parts of Canada.
Seed disinfection, using a thiram product, proved useful for the control of flax diseases in general, but should be used as an ancillary to the method of avoiding seed infection by limiting the production of seed flax to areas where the risk of contamination is slight or absent. Where there is any risk of a build-up of contamination, seed disinfection should be carried out as a routine practice each season.     

Survival and seed to seedling transmission of Alternaria linicola on linseed

Alternaria linicola survived as thick-walled chlamydospores in hyphal or conidial cells on infected linseed stem debris, either on the soil surface or buried in the soil, during the period between the harvest of linseed and sowing of the following crop (September - April). Conidia produced on these debris under favourable conditions were not only viable but also pathogenic to young linseed seedlings. Infected stem debris increased the incidence of infected seedlings which emerged from infected seed (incidence of A. linicola 1% to 28%), especially if the debris was on the soil surface rather than buried. A. linicola also survived between successive linseed crops on infected volunteer linseed plants which survived the low temperatures in winter and on the weed Veronica persica. A. linicola was more effectively transmitted from infected seeds to seedlings at temperatures 15–25°C than at 10°C. The incidence of the disease on seedlings which emerged from infected seed was positively correlated with the amount of seed-borne inoculum, whereas the proportion of seedlings which emerged was negatively correlated with the incidence of A. linicola on the seed.     

紫花苜蓿种子对逆境贮藏条件的反应

以陇东紫花苜蓿 (MedicagosativaL .cv .“Longdong”)种子为材料 ,在室温、35℃和 35℃ +10 %的种子含水量 (SMC) 3种贮藏、接种或不接种燕麦镰刀菌 (Fusariumavenaceum (Fr.)Sacc .)的条件下 ,1年贮藏期内对各逆境处理的种子每隔 6 0d进行 1次标准发芽试验 ,2 0℃恒温、第 10d统计种子的发芽率和死亡率 ,试验结束时计测种子幼苗的长度和感病率 ;在大田条件下观测各处理种子的出苗率 ,确定催腐 (CD)与各种贮藏条件下的苜蓿种带真菌种类和检出率 .结果表明 ,随着贮藏温度和种子含水量等逆境贮藏条件胁迫的加剧 ,苜蓿种带真菌检出率逐渐增高 ,从室温、35℃条件下的 10 %上升到CD +35℃ +10 %SMC条件下的 2 9% ;抗病性逐渐减弱 ,35℃ +10 %SMC条件下幼苗的感病率和种子死亡率显著 (P <0 .0 5 )高于室温和 35℃下的感病率和种子死亡率 ;室内种子发芽率和田间出苗率逐渐下降 ,35℃ +10 %SMC条件下的种子的发芽率和田间出苗率显著 (P <0 .0 5 )低于在室温和 35℃下的发芽率和田间出苗率 ;幼苗生长受到抑制 ,35℃ +10 %SMC条件下的苗长和根长显著 (P <0 .0 5 )低于在室温和 35℃下的幼苗长度 .随着贮藏时间的延长 ,种子真菌检出率和田间出苗率下降 ,幼苗感病率增加 .与未接种的对照相比 ,接种燕麦镰刀菌的种子     

Observations on the maintenance and measurement of soil water in simple pot experiments and its effects on seed-borne Fusarium culmorum seedling blight of winter wheat

A simple method for maintaining and measuring soil water and the relationship between soil water and seed-borne Fusarium culmorum seedling blight of wheat was investigated under controlled environmental conditions to develop reproducible assay conditions for epidemiological studies and the testing of fungicide seed treatments. For reproducibility, soil matric potential (ψ_m) was used to define soil water, and a range of watering regimes were tested. Treatments were watered to either a maximum ψ_m or to maintain a mean ψ_m in order to establish which parameter best described the effect that soil water had on the incidence of disease symptoms. The severity of disease symptoms was closely related to the mean soil water status and not the maximum ψ_m value. Watering intervals, ranging from three times a day to once every three days, did not affect this relationship. The percentage of seedlings showing symptoms after emergence (i.e. localised or extensive necrotic lesions) was inversely related to the mean ψ_m. With increasing soil dryness (mean ψ_m from -0.14 MPa to -0.17 MPa) the percentage of seedlings with post-emergence symptoms decreased from 50% to 20%. However, as the mean ψ_m changed from -0.14 MPa to -0.17 MPa the percentage of seedlings dying before emergence increased from 25% to 55% in direct proportion to ψ_m. Overall the incidence of infection as indicated by the total number of seedlings showing symptoms either before or after emergence remained relatively constant, and was not significantly related to mean ψ_m.     

Low temperature during infection limits Ustilago bullata (Ustilaginaceae, Ustilaginales) disease incidence on Bromus tectorum (Poaceae, Cyperales)

Ustilago bullata is frequently encountered on the exotic winter annual grass Bromus tectorum in western North America. To evaluate the biocontrol potential of this seedling-infecting pathogen, we examined the effect of temperature on the infection process. Teliospore germination rate increased linearly with temperature from 2.5 to 25°C, with significant among-population differences. It generally matched or exceeded host seed germination rate over the range 10-25°C, but lagged behind at lower temperatures. Inoculation trials demonstrated that the pathogen can achieve high disease incidence when temperatures during infection range 20-30°C. Disease incidence was drastically reduced at 2.5°C. Pathogen populations differed in their ability to infect at different temperatures, but none could infect in the cold. This may limit the use of this organism for biocontrol of B. tectorum to habitats with reliable autumn seedling emergence, because cold temperatures are likely to limit infection of later-emerging seedling cohorts.     

Effects of Temperature on Germination of Peronospora parasitica Conidia and Infection of Brassica oleracea

The effect of temperature on germination of a South African isolate of Peronospora parasitica , and infection of Brassica oleracea was studied. The optimum condition for germination was 20° C at 100% relative humidity. The percentage germination obtained was 80–98% and 70–80% between 15 and 25° C at 100% relative humidity, after a 12 and 6h incubation period, respectively. Optimum temperature for germ tube growth was also 20° C. The temperature range for maximum infection of seedlings of a highly susceptible cabbage cultivar and subsequent disease development in vitro was 15–25° C and 90–100% infection was achieved after 48 h of incubation. At<15°C and 26–30° C infection percentage was decreased to 40–50% and 35–40%, respectively. No disease incidence was recorded at temperatures above 35° C. A scanning electron microscope study of the infection process showed that penetration of cotyledons by germ tubes was mostly via stomata and occasionally directly through the cuticle. Results are discussed in relation to the need for future studies of P. parasitica in South Africa.     

The performance of carrot seeds in relation to their viability

The germination and emergence characteristics, and early seedling growth, of carrot seeds cv. Chantenay red-cored from different sources with a range of germination from 54–94%, was compared. Seeds from protected crops (mean temperature of growth 21°C, r.h. 45–70%) gave higher percentage germination than those from crops grown outdoors (mean temperature 15°C, 70–100% r.h.). Germination was also higher from mature (seed moisture content at harvest 20% or lower) than immature seed (seed moisture content at harvest between 20 and 60%). High percentage germination (>90%) was associated with low mean germination times and low spreads of germination times whilst the reverse was true for low percentage germination. Similar relationships were found for seedling emergence characters in the field although a lower proportion of the viable seeds produced seedlings from slowly than rapidly germinating seed lots. In general, seed lots having a low percentage germination gave greater variability in plant weight than those of higher percentage germination. There was no effect of seed source on radicle or shoot relative growth rates or on post-emergence seedling growth rates.     

鄂尔多斯高原4种主要沙生植物种子萌发与出苗对水分和沙埋的响应

 羊柴 (Hedysarum leave)、柠条 (Caragana korshinskii)、籽蒿 (Artemisia sphaerocephala)与油蒿 (Artemisia ordosica)为鄂尔多斯高原广泛分布的植物种,也是该地区飞播选用的主要植物种。由于飞播为鄂尔多斯高原植被恢复的重要手段,而飞播后植物种子的出苗率与土壤水分及沙埋密切相关。因此,上述植物种子萌发与出苗对水分和沙埋反应的研究对当地退化生态系统的恢复具有重要意义。通过温室控制实验,对4种植物萌发特性及出苗与水分和沙埋深度的关系进行研究,阐明了种子萌发最适合的水分条件和沙埋深度。结果表明,4种植物种子萌发与出苗最适宜的供水量都接近于当地种子萌发时期的平均降水量, 最适宜的沙埋深度为0.5～1 cm, 过多的水分和过深的沙埋会降低种子萌发与出苗,反映了4种植物对沙区环境的生态适应。4种植物最适宜的供水量均为123 ml,羊柴、柠条、籽蒿和油蒿的最适沙埋深度分别为：0.5、1.0、0.5和0.5 cm。根据实验结果及当地气候特点,鄂尔多斯地区的飞播时间应由6月初提前至5月中下旬,以提高飞播植物的出苗率。     

Hoary cress (Cardaria draba (L.) Desv.) seed germination ecology,longevity and seedling emergence

The effects of gibberellic acid (GA₃), potassium nitrate (KNO₃), prechilling, temperature, salt stress and osmotic potential on seed germination and sowing depth on seedling emergence and burial depth on seed viability of hoary cress (Cardaria draba (L.) Desv.), were studied in a series of laboratory, glasshouse and outdoor experiments. The optimal temperature for hoary cress seed germination was 20°C, both in light/dark and darkness regimes. Seed germination of hoary cress at 400 ppm concentration of GA₃ in a light/dark regime was maximal. Potassium nitrate concentrations increased the percentage of germination in comparison with the control treatment. Increasing the duration of dry prechilling to 30 and 45 days promoted the seed germination of hoary cress. Germination of hoary cress markedly decreased as salt and drought stress increased. Seed germination of hoary cress occurred at a range of pH from 3 to 11. Seedling emergence significantly decreased as planting depth increased. Total seed viability decreased with increasing burial depth. The maximum increase in mortality occurred in seeds that were buried at 5‐cm depth.     

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.     

Varietal Resistance of Flax to Disease

Field experiments, using contaminated seed, have been carried out from 1941 to 1947 to study the reaction of a wide range of both fibre and oil varieties of Linum usitatissimum to attack by Polyspora Lini Laff., Colletotrichum linicola Pethybr. & Laff., Phoma sp. and Melampsora Lini (Ehrenb.) LéV. The tests made with Colletotrichum linicola were supplemented by direct inoculation experiments with young seedlings grown under greenhouse or laboratory conditions.
None of the varieties tested proved to be immune to attack by Polyspora Lini, Colletotrichum linicola or Phoma sp. Herkules, Concurrent, Hindi, La Plata, Saginaw x Ottawa 770 B and Winona x Ottawa 770 B were resistant to the stem-break and browning phases of attack by Polyspora Lini ; Bison, Hindi and La Plata were resistant to attacks by Colletotrichum linicola , while Hindi and La Plata showed some resistance to Phoma sp. Immunity or a 'high' measure of resistance to attack by Melampsora Lini was exhibited by Formosa, Stakhanovets, Textilshchik, U.S.S.R. No. 2 (ex Dugejheshchya), Wada, Argentine Selection (C.I. 112), Baladi, Bolley Golden (C.I. 644), Bombay (C.I. 42), Hindi, Italia Roma (C.I. 1005–2), J.W.S. (C.I. 708–1), Koto (C.I. 872), Kenya (C.I. 709–1), La Plata, Newland (C.I. 188), Ottawa 770B (C.I. 355), Pale Blue Crimped (C.I. 647), Tammes Pale Blue (C.I. 333–1), Williston Golden (C.I. 25–1) and C.I. 836.
All varieties did not show the same reactions to stem-break as to the browning phase of attack by Polyspora Lini and similar differences were noted in the case of the uredospore and teleutospore stages of Melampsora Lini. In certain varieties the stems showed a greater resistance to attack by Polyspora Lini or Melampsora Lini than the leaves.
Seeds of all varieties tested in the field experiments became heavily attacked with Polyspora Lini (except in La Plata), Colletotrichum linicola and Phoma sp.     

Relationships between position on the parent plant and germination characteristics of seeds of parsley (Petroselinium crispum Nym.)

The percentage germination of seeds of parsley cv. Imperial Curled was higher in the light than in the dark, the high temperature limits for germination being 30 and 28°C for light and dark respectively. At the higher temperatures, the germination rate was slower in the dark. At 30°C, treatment with a gibberellin A_4/7 mixture at 2 × 10^–4 M partially alleviated the inhibiting effect of darkness on the germination percentage. Pre-incubation of parsley seeds at 35°C in the dark for 30 h increased the rate, but decreased the percentage, of germination of seeds incubated at 15°C in the light. Germination and seedling emergence studies were made on seed harvested from four different umbel positions. Although heavier seeds were produced from primary umbels than from other umbel orders, they were less viable as measured by seedling emergence in the glasshouse. The rate of emergence was decreased with increasing umbel order i.e. with later seed development: this was reflected in subsequent seedling weights, with seedlings from quarternary umbel seeds being about half the weight of those from primary umbel seeds. The upper temperature limit for dark germination was only slightly affected by umbel order, with quarternary umbel seeds being the most thermo-inhibited.Abbreviations BA N⁶-benzyladenine - GA_4/7 a mixture of gibberellins A₄ and A₇ - SD8339 6-benzyl-amino-9-(tetrahydropyran-2-yl)-9H-purine     

Effects of altitude and seed size on germination and seedling survival of heathland plants in north Spain

The effects of altitude and seed size on germination and seedling survival were studied in Calluna vulgaris, Erica cinerea and Erica vagans. Experiments were carried out in the laboratory over a one year period. Seeds collected from heathlands of different altitudes were divided in two size classes. They were sowed on moist filter paper inside Petri dishes which were placed in chambers at 20 °C and a photoperiod of 12 h light/12 h darkeness. The seeds of Calluna vulgaris were the first to begin germination and had the highest rate and percentage of germination. The germination of Erica vagans was moderate, while seeds of Erica cinerea germinated later and the germination was very low. Seeds of Calluna vulgaris and E. cinerea collected at the highest altitudes had the highest germination percentages. Seed size in Calluna vulgaris and E. cinerea did not affect germination. However, large seeds of Erica vagans had higher germination rates and percentages than small seeds. The large seed size of Calluna vulgaris contributes to a better survival and growth of its seedlings.     

Some effects of temperature during seed development on carrot (Daucus carota) seed growth and quality

The growth and development of carrot seeds cv. Chantenay Red-cored Royal Chantenay at day/night temperatures of 20/10°C, 25/15°C and 30/20°C and subsequent seed performance were examined in 1984 and 1985. An increase in temperature from 20/10°C to 30/20°C reduced mean weight per seed by 20% in 1984 and by 13% in 1985. There were no effects of temperature on endosperm + embryo weight, or on endosperm cell number but the weight of pericarp decreased with an increase in temperature. Seeds grown at the highest temperature had the largest embryos and the highest nitrogen, DNA and rRNA content; they germinated and emerged earlier, and gave higher percentage seedling emergence than those grown at the lowest temperature. There were no effects of temperature during seed growth on the rate of imbibition of water by seeds during the germination process.     

Impact of two soil-applied herbicides on damping-off of cowpea caused byRhizoctonia solani

Summary Alachlor was more inhibitory toRhizoctonia solani growth than fluchloralin in potato dextrose broth (PDB). Infective capacity of the pathogen was not altered by growing it in a medium containing either of the herbicides. Cowpea seedlings grown in alachlor-treated soil were more susceptible toR. solani than those treated with fluchloralin and the untreated seedlings. Pre-sowing application of alachlor in soil (5 l a.i./kg) aggravated damping-off whereas fluchloralin decreased the disease incidence to nearly half of that in untreated soil in greenhouse pot tests (av. temperature 31±5°C). Both herbicides reduced damping-off in pots kept at constant temperature of 30°C and increased the disease incidence at 20°C. Fungus growth in culture was stimulated at 20° but was strongly inhibited at 30°C by both herbicides. Growth inhibition by herbicides was maximum in PDB of pH 8 and decreased steadily up to pH 5.Impact of fluchloralin and alachlor onR. solani damping-off of cowpea appears to be due to the predisposing effect by the herbicides on the susceptibility of the host and is influenced by atmospheric temperature.     

A study of the longevity of the seed-borne parasites of flax in relation to the storage of the seed

From 1939 to 1947 observations were made on the longevity of Colletotrichumlinicola Pethybr. & Laff., Polyspora Lini Laff., Botrytis cinerea F t ., and Phoma sp. occurring to different extents as seed-borne parasites of naturally contaminated samples of flax seed held under ordinary conditions of storage. The results obtained, together with the germination capacity of the seed estimated on different occasions during storage, are given and show that the longevity of the fungi considered varies within the following limits: Colletotrichum linicola , 26–69 months, Polyspora Lini , 16–55 months, Botrytis cinerea , 16–40 months and Phoma sp. 27–43 months. The data provide grounds for suggesting that the higher the percentage number of seeds contaminated with Polyspora Lini the longer will be the time taken for the death of the parasite to occur. As the time taken for the deactivation of the parasites is normally much longer than that for which flax seed for sowing purposes can be safely stored, prolonged storage of the seed does not commend itself as a likely method for securing the control of the diseases caused by seed-borne fungi. The germination capacity of the seed was normally found to be seriously impaired by the time all the parasites had died.     

沙埋对花棒种子萌发和幼苗生长的影响

为探讨花棒(Hedysarum scopariium)种子萌发和幼苗生长对沙埋的响应,并为固沙造林、水土保持提供理论基础,研究了6种沙埋深度(0、1、2、3、4和5cm)对花棒种子萌发和幼苗生长的影响.结果表明,埋深对花棒幼苗出土率、首次出苗时间、单株叶片数、幼苗生长高度以及生物量的分配均有极显著影响(P<0.001).种子出苗率在2 cm沙埋下达到最高(95.6%),在5cm沙埋下最低(43.4%);幼苗最大高度(11.6cm)、绝对株高(13.9cm)和最大地上生物量(26.7mg)均出现在2cm的埋深,幼苗最小高度(3.3cm)、最小根长(4.3cm)和最小地上生物量(5.3mg)出现在5cm的埋深;生物量分配随沙埋深度增大而更多地分配给地下部分.2cm的沙埋是花棒种子萌发和幼苗生长的最佳深度.     

The effects of soil conditions, soil sterilisation and seed treatmen on the emergence of cabbage in controlled temperature cabinets and the field

Previous cropping history of the soil and the changes that occurred in soil moisture content and temperature were the major factors determining the emergence of cabbage seedlings from pathogen-free seeds. Seedling losses caused by soil-borne pathogens could be high but these losses were prevented by seed treatment with metalaxyl or soil sterilisation with methyl bromide prior to sowing. The beneficial effects of metalaxyl and methyl bromide treatments were confirmed in field experiments involving repeated sowings of cabbage seeds. In experiments with sterilised soil and cabbage seed infected with Alternaria brassicicola emergence at – 0·2 bars soil moisture potential was reduced by 7·8–23.5% at 5, 10, 20, and 25°C. In the field, losses due to A. brassicicola were greatest when the soil became capped after sowing. The results show that recently developed fungicides may facilitate emergence under conditions extremely favourable for seed- and soil-borne pathogens. For maximum benefit, selection of seed treatments should be based on knowledge of the range of pathogens likely to reduce emergence.     

The effect of fruit age on seed germinability of a heterocarpic species, Atriplex sagittata

Atriplex sagittata is an annual heterocarpic plant that produces three different fruit types (termed A, B, and C). To examine the consequence of heterocarpy on germinability patterns over long time periods, we compared seed germinability of different fruit types that had been stored for up to 8 years. While germinability of non-dormant type C fruits in distilled water was high (up to 100 %) in the first 2 years, it rapidly decreased over time. Dormant fruit types A and B showed increased germinability up to 7 years, though loss of germinability was lower for type B than for type A fruits. Eight-year-old fruits of all types had significantly lower germinability than younger fruits, probably due to loss of viability. Heterocarpy, therefore, ensures that emergence rates for seedlings of A. sagittata will be maintained over relatively long periods, even in years of strong disturbance when all adult plants may be destroyed. The experiment further showed that germinability of all fruit types in high concentrations of salt, as compared with water treatment, changed over the course of 8 years. Whilst dormant types (A and B) of A. sagittata show increased germinability with age of the seed in water treatment, they significantly lose germinability over time with salinity treatment. Type C fruit was not influenced by salt in the first year, but germinability rapidly decreased with time. It follows that the species is able to germinate under high salt concentration in the first year, but this advantage gradually disappears.