摘要:

SUMMARYA form of pea early‐browning virus (PEBV), found in many crops of peas and a few of lucerne on sandy soils in Norfolk and Suffolk, was transmitted by inoculation of sap to many herbaceous species.Chenopodium amaranticolorandPhaseolus vulgariswere useful as indicator plants, andNicotiana clevelandiifor propagating the virus. Its thermal inactivation point was 74–78°C., dilution end‐point about 10‐5, and sap was still infective after 1 year at 20°C. Partially purified preparations contained tubular particles about 20 mμ wide, most of which were about 100 or about 200 mμ long. Isolates from different fields in Britain were closely related serologically, but were only distantly related to a Dutch isolate of PEBV; they seemed serologically unrelated to four other viruses with particles of similar shape and size. Some isolates of PEBV were not readily transmitted using sap as inoculum, but readily with extracts made from leaves using water‐saturated phenol or bentonite. By contrast with other isolates, they caused recurrent necrotic symptoms inN. clevelandii, sap from which did not contain tubular particles.Pea, lucerne, cucumber, tobacco and sugar‐beet seedlings became infected when grown in soil from fields with affected crops. All infested soils contained eitherTrichodorus viruliferusHooper orT. primitivus(de Man), sometimes together with otherTrichodorusspp.;T. viruliferustransmitted the virus in experiments. This contrasts with PEBV in the Netherlands, which is transmitted byT. teresan

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1964.tb01165.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SUMMARYAttempts to find when leaf roll and Y viruses spread within Majestic potato crops, made during 4 years at Harpenden by spraying with aphicides to restrict virus spread during four different periods per season, succeeded with leaf roll but not with virus Y.I n 1957, 1958 and 1961 leaf‐roll virus spread mostly before mid‐July, very little between mid‐ July and early August, but a little more from early August to the season's end. In 1959, when the summer was exceptionally fine, more virus spread during July. Four sprays with persistent aphicides: (I) when 50 yo of the crop has emerged from the ground; (2) 10 days later; and (3) and (4) at fortnightly intervals, will prevent leaf‐roll virus spreading within a potato crop until the end of July and in most seasons will therefore prevent almost all spread; the earliest sprays are usually the most important. Systemic soil insecticides applied to prevent leaf roll virus spreading should make the plants lethal to aphids as early as possible.Little was learned about the time of spread of virus Y because in the experimental conditions the insecticides did not prevent its spread.Further evidence was obtained that leaf roll virus is spread within crops mostly by alatae colonizing the potatoes in spring and early

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1964.tb01166.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SUMMARYSpraying tomato plants infected with tomato mosaic virus (a strain of tobacco mosaic virus) and uninfected ones at weekly intervals with a 0·3% aqueous solution of urea, or this solution with 0·1% mono‐ammonium phosphate and 0·1% potassium sulphate, had little effect on the yield or quality of the fruits, although there was a slight increase in mean weight per fruit in sprayed, early‐infected plants. Steaming the soil did not affect total yield of fruits (weight) but increased fruit number by nearly 6% and also the proportion of good quality fruits. Some severe fruit‐quality disorders were prevalent only on late‐infected plants. A mild tobacco strain of mosaic virus failed to protect inoculated plants from late infection with the tomato strain of

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1964.tb01167.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SUMMARYTomato plants (vars. Moneymaker and Minimonk) inoculated at the cotyledon stage with tomato mosaic virus (TMV) developed about half as much root as did healthy plants, by the time the first trusses were flowering. Although infected plants recovered to some extent, their roots remained 10–25% smaller. Infection at the flowering of the first truss reduced the size of root system by about one‐third after 6 weeks, but the plants then recovered. Infection at later stages of growth did not significantly affect root growth. There was no significant relation between the dry weight of the root system and the fresh weight of the top including fruit.Moneymaker and Potentate tomato plants, sown in November, March, June and September, showed similar seasonal changes in the volume of fruit produced weekly, whether or not the plants were healthy or infected with TMV. Infected plants always produced less than healthy ones, but the decrease varied with time of year and age of plant, being greatest in spring and in young plants; the decrease remained fairly steady in older plants. The initial period of acute decrease in volume of fruit production was greater when ovary swelling began early in the year than when it began later. Fewer fruits were produced by infected plants than by healthy ones, except during the winter in var. Moneymaker. During the winter and spring, mean fruit size was decreased by TMV, and was unaffected or increased during the summer and autumn, especially in older pla

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1964.tb01168.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SUMMARYIt was demonstrated by serial graft transmission experiments that the big‐vein disease of lettuce was caused by lettuce big‐vein virus (LBVV).AnOlpidiumsp., always found in the roots of naturally affected plants, induced the disease when its zoospores were transferred to healthy plants. The fungus was identified asO. brassicae(Wor.) Dang.The same fungus was found in the roots of healthy lettuce, but zoospores from this source would not induce big‐vein when transferred to healthy plants.When a non‐viruliferous isolate ofO. brassicaewas grown in the roots of lettuce affected by big‐vein the fungus acquired LBVV and was able to transmit the disease. Conversely, the viruliferousOlpidiumwas converted to a non‐viruliferous form by culture in the roots ofPlantago majororVeronica persica.These results were not caused by the selection of non‐vector strains of the fungus during its culture in these species, as the fungus reacquired and transmitted LBVV when again cultured in big‐vein affected lettuce roots. The results suggested that LBVV did not multiply inP. majororV. persica, or in the fungus during its growth in them.Attempts to transmit LBVV withCuscuta campestris, C. gronovii, C. reflexaandC. subinclusaand by sap inoculation were unsuccessful.No causal relationship between tobacco necrosis virus (TNV) and big‐vein was found: the reasons for the frequent association of TNV with the dise

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1964.tb01169.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SUMMARYIn field experiments at Wellesbourne, reductions in both black and orange‐brown canker of parsnips were obtained either by late sowing (in May or June), or by singling the plants to a narrow interval (3 in.), or by a combination of both treatments. The treatments reduced mean root size, and small roots had less canker than large ones.It seemed that much of the disease reduction obtained was a consequence of the reduction in mean root weight caused by the treatments. There was evidence, however, that the reductions in black canker obtained by late sowing were also dependent to some extent upon the shorter period that the roots were in the ground.Marketing assessments were made on four occasions in an experiment in which crops were grown from seed sown in March and May and were singled to 3 in. or 6 in. in rows 15 in. apart. They showed that the highest total and highest marketable yields were generally obtained from the earlier‐sown crop at the narrower spac

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1964.tb01170.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SUMMARYIn studies on root‐hair and rhizodermal cell infection of cabbage seedlings byPlasmodiophora brassicaeWoron. seeds were germinated in an incubator at 25°C. on nylon mesh circles placed on glass dishes containing nutrient solution. After 3 days the original nutrient solution was replaced by a similar one containing a known quantity of resting spores of the fungus. After a further 5–7 days in the incubator the roots were removed and stained. The infected plants were counted and the extent of infection on each plant was assessed in grades 0–4.Optimal infection was obtained by using spores from decomposing clubbed roots, by thoroughly washing the resting spores, and by using thirty plants per dish grown from seed of 1·5‐2·0 mm. diam. There was a rapid increase in infection from the 3rd to the 6th day after introduction of the spores.Infection of large numbers of seedlings was easily obtained by this technique, which is now being used for assessing the effects of chemicals in controllin

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1964.tb01171.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SUMMARYSeveral isolates ofRhizoctonia solaniKühn were obtained from wheat stems bearing lesions of sharp eyespot in the summers of 1960 and 1962. Differences in virulence of these isolates, assessed by severity of attack on seedlings, were demonstrated. Isolates taken from different plants in the same crop were shown to differ in virulence. All isolates obtained from wheat‐stem lesions attacked both winter and spring varieties of wheat, barley, oats and rye. Several varieties of spring and winter wheats showed no differences in susceptibility to disease.Infection of the wheat host took place at any time during the growing period, but was most severe in the earlier stages of growth.Sharp eyespot occurs over a wide range of soil types, but the most severe attacks all occurred on lighter soils with neutral to slightly acid pH. Sand‐culture experiments showed no effect of pH on disease development over the range 5·9‐8·1. Disease development in seedling wheat plants was favoured by cool (9·3°C.) dry (ca.20% of the water‐holding capacity) conditions in the greenhouse. Disease incidence in the field over the period 1959‐63 could be correlated with the weather conditions prevailing

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1964.tb01172.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SUMMARYA thoroughly mixed seed sample of Herta barley produced different percentages of smutted ears when grown at several centres throughout the country. From an analysis of the data it was concluded that crop density was not a major factor affecting this variation.The effects of time of sowing, seed size and seed rate on the smut intensity were also examined.By varying the seed rate, differences in the amount of smut were obtained. An examination of the number of infected and non‐infected plants and tillers established from each 100 seeds sown and of the tillering capacity of infected and non‐infected seedlings at each seed rate showed that the differences in smut intensity were the result of competition for establishment between the two kinds of seedli

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1964.tb01173.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SUMMARYPrevious experiments made by the writer showed that scions of tomato varieties that were monogenically resistant to wilt caused byFusarium oxysporumf.lycopersiciwere apparently hypersensitive to toxins produced in infected Bonny Best (susceptible) rootstocks on to which they were grafted. The experiments did not prove conclusively, however, that the toxins were generated in the rootstocks, since they might have arisen from an interaction between the invading fungus and the resistant scion or by the generation of toxic materials when non‐toxic metabolites from the invaded root‐stock entered the resistant scion.In the present study it was demonstrated that the symptoms on the resistant scions arose when the fungus was still confined to the susceptible rootstocks. By double grafts, using resistant or susceptible intermediate stem pieces, it was also shown that the translocation of metabolites from invaded susceptible rootstocks through such stem pieces caused no change in their toxicity.It was concluded that resistant scions were highly sensitive to the direct action of toxins formed in invaded susceptible rootstocks, at concentrations which had no apparent effect on susceptible sci

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1964.tb01174.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY