摘要:

SUMMARYTwo main types of canker on the shoulders and crowns of parsnips are described, (a) black canker, caused byItersoniliaorPhoma, or both together, and (b) orange‐brown canker, of unknown cause. Black canker is the more common.A large number of isolates ofItersoniliawere obtained from diseased parsnip roots and leaves and from the air within parsnip crops in widely separated localities. The dicaryophase only of these isolates was studied. The majority possessed many chlamydospores and agreed with the descriptions by Olive and by Sowell&Korf of isolates obtained from and pathogenic to parsnips. Although these authors identified such isolates as I.perplexans, the writer considers that they should be regarded as a new species, I.pastinacae.The remainder of the isolates from these sources and a number from other hosts possessed few or no chlamydospores and more closely resembled I.perplexansDerx. Tests showed that I.pastinacaewas pathogenic to parsnip roots and leaves, but not to chrystanthemum flowers, while an isolate of I.perplexanspathogenic to chrysanthemums, did not attack parsnips. Of the other isolates resembling I.perplexans, only those obtained from cankered roots were pathogenic to parsnip roots.APhomasp. causing black canker was isolated from parsnips in four out of thirteen localities. In laboratory pathogenicity tests it attacked only parsnips (both seedlings and mature roots), and may thus be different from otherPhomaspp. Parsnip foliage was readily infected artificially, but natural leaf infection has not been observed in the field.Attack by both I.pastinacaeandPhomasp. was enhanced by wounding of the parsnip root

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1963.tb03670.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

SUMMARYHaulm susceptibility toPhytophthora infestans(Mont.) de Bary of fourteen widely differing potato varieties was compared in laboratory and field tests with the maincrop variety Majestic as a standard. These two tests gave similar results except that the early varieties Viola and Arran Pilot were more resistant in the laboratory than in the field.The sequence of infection within the crop canopy was the same in susceptible and resistant varieties, starting first mainly on the lowest leaves on the stem, then the middle and finally the uppermost. This sequence was lost when haulm became prostrate. Varieties differed in the rate that infection spread and leaves were destroyed, some being attacked more rapidly, and others more slowly, than Majestic.In the field the fungus spored on different varieties as in the laboratory test; the annulus was wide and sporulation intense on susceptible varieties, but narrow and sparse on resistant ones.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1963.tb03671.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

SUMMARYThe external symptoms of a hitherto undescribed leaf‐spot disease of young Lacatan bananas are described. The name ‘eyespot’ is suggested since the mature lesion has a white or grey centre and a narrow, well‐defined, brown border.Drechslera gigantea(Heald&Wolf) Ito was consistently isolated from eyespot lesions and, in pathogenicity tests, conidia of the fungus caused typical spots to develop within 48 hr.Conidia ofD. giganteagerminated after 30–60 min. in a film of water on the leaf surface, one to five germ tubes being produced from each terminal cell. After 12 hr., germ tubes were up to 75 μ long and swollen at the tip into appressorium‐like bodies. Penetration of the host occurred within 24 hr. Similar stages in the infection process were observed on naturally infected leaves. Sometimes, one conidium caused two distinct lesions as a result of bipolar germination and infection.Air‐borne conidia ofD. giganteawere caught by means of a Hirst spore trap. They displayed regular diurnal periodicity, being maximal between 08.00 and 14.00 hr. E.S.T. and practically absent at all other times. Conidia were violently discharged under drying conditions. Highest conidium concentrations were recorded after rain. In the vicinity of the trap, the major source of conidia was Bermuda grass(Cynodon dactylonL.) which was bearing zonate eyespot lesions caused byD. gigantea.This appears to be the first record ofD. giganteain Jamaica. In addition toMusaspp., the grassAnthephora hermaphrodita(L.) Kuntze is now added to Drechsler's host list

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1963.tb03672.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

SUMMARYSteeping sugar‐beet seed in ethyl mercury phosphate solution controlledPleospoya betaeand increased the emergence of seedlings in the field more than did ‘short‐wet’ fungicide treatments, spraying EMP solution on to the seed, or steeping in other fun

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1963.tb03673.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

SUMMARYA method is described for the artificial inoculation of large numbers of potted apple rootstocks or barley seedlings with conidia of the appropriate powdery mildew, using settling towers large enough to hold 100 pots, and blowing spores via a central pipe into the upper part of the tower and allowing them to settle on the foliage.Plants are put in the tower some 24 hr. before introducing the spores, left enclosed for a further 24 hr., and then placed on the bench in a greenhouse with forced ventilation until lesions are clear enough for recording, usually 9 days after inoculation for apple mildew and 7 for barley mildew.Rooted shoots from stoolbeds of M. III apple rootstock provided suitable material for apple mildew experiments. The largest numbers of lesions per leaf were usually found on the third and fourth leaves down the shoots; records were usually taken on leaves 3 to 5.For barley mildew, the variety Plumage Archer was found to be suitable. Conidia can be collected and weighed as required, facilitating control over the inoculum load applied in each test. Seedlings are preferred before the second leaf emerges, i.e. before bending or twisting interferes with inoculation.The method is successful for the study of both the protective and curative effects of chemicals applied by a dipping technique.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1963.tb03674.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

SUMMARYApple rootstocks placed in the settling‐tower 24 hr. before introduction of spores ofPodosphaera Zeucotrichadeveloped more lesions than those placed in position immediately before inoculation; a period of 24 hr. in the tower after introduction of spores induced more infections than one of 48 hr.Rootstocks kept at high temperature for a few hours immediately on removal from the tower (24 hr. after inoculation) developed only half as many lesions as those maintained at normal temperatures. This effect declined steadily as the heating was applied on successively later days until the 8th day when such heating had no effect.Plants kept at about 20°C. and a relative humidity not exceeding 70% grew satisfactorily and developed very similar numbers of lesions to those inoculated in the same tower but subsequently incubated in a greenhouse where R.H. reached saturation every night. High humidity therefore is unnecessary for the inoculation and development of apple mildew.The leaves initially produced by rootstocks potted in John Innes No. I compost and watered daily with ammonium nitrate solution, were no more susceptible to powdery mildew than those on similar plants given water only. However, when such rootstocks were grown for several weeks, cut back to a few buds, and allowed to break again, the leaves were larger and more susceptible if ammonium nitrate was given as a 0·005 to 0·015 M solution.The susceptibility of leaves on M. III rootstocks decreased with age by about 50% per leaf‐position down to the fourth and even faster below that position, so that the youngest leaf that is just unrolling is by far the most susce

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1963.tb03675.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

SUMMARYStrawberry green petal, clover witches' broom, stolbur and Delphinium yellows viruses were distinguished from one another and from aster yellows, tomato big bud (lucerne witches' broom) and cranberry false blossom viruses by vector species, host range, host symptoms and reactions to heatin vivo.Euscelis plebejus(Fall.) leafhoppers transmitted green petal virus from, but not to, strawberry plants.Aphrodes bicinctus(Schrank) was an efficient vector and is probably chiefly responsible for green petal disease in strawberry crops.Green petal virus did not protect clover plants from the effects of witches' broom virus, but the latter seemed to interfere with the transmission of green petal virus byE. plebejus.The witches' broom virus also retarded the development ofE. plebejusvectors and apparently reduced their longevity. This virus was not transmitted byA. bicinctus.Strawberry plants did not become infected with stolbur virus, but did with Delphinium yellows virus, which caused a bronze‐leaf‐wilt syndrome indistinguishable from that caused by clover witches' broom virus. Stolbur and Delphinium yellows viruses both killed clover; stolbur was occasionally transmitted byE. plebejusand frequently byA. bicinctus, neither of which transmitted Delphinium yellows.Cuscuta campestrisYunck. transferred Delphinium yellows virus fromVinca roseaL. to strawberry andV. Yoseabut not to clover or aster; only a single white clover plant was infected byMacrosteles sexnotatus(Fall.). Delphinium yellows virus was inactivated inV. Yoseaplants kept at 42°C. for 3 weeks, whereas green petal virus was not, although virus‐free cuttings were propagated from heat‐treate

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1963.tb03676.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

SUMMARYSap‐transmissible viruses were obtained from grapevines affected by fanleaf, yellow mosaic, distorting mosaic, witches' broom or fasciation diseases. Virus isolates from American, Australian, French and Portuguese grapevines did not differ with country of origin but those from any one country varied in virulence. Herbaceous hosts of isolates originally obtained from grapevines with fanleaf or with yellow mosaic included thirty‐two species in five plant families; yellow mosaic isolates usually caused distinctive symptoms in systemically infected leaves ofChenopodium amaranticolor, but in many other hosts could not be distinguished from fanleaf isolates. Yellow mosaic and fanleaf diseases were each reproduced by transmitting the respective isolates back to grapevine fromC. amaranticolor.Grapevine fanleaf and grapevine yellow mosaic viruses were both transmitted through seed ofC. amaranticolor; both were precipitated without inactivation by ethanol, by acetone, by ammonium sulphate and at pH 5. Preparations of each, partially purified from systemically infected leaves ofNicotiana clevelandii, contained polyhedral particles about 30 mp in diameter. Phenol‐disrupted virus was 1–5% as infective as its parent virus susp

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1963.tb03677.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

SUMMARYPlant protection and serological tests showed that the viruses causing the grapevine fanleaf and grapevine yellow mosaic diseases occurring in Portugal, Switzerland and the United States are closely related strains. These strains and arabis mosaic virus cause similar symptoms in many herbaceous species, but arabis mosaic virus is more virulent and more often becomes systemic. Attempts to transmit arabis mosaic virus to grapevine failed. Arabis mosaic virus shares only few antigenic determinants with the viruses obtained from grapevine, and these viruses do not protect plants against it. In a virus classification, the grapevine virus isolates and arabis mosaic virus can be considered two distinct serotypes of one virus.The nematodeXiphinema diversicaudatrimacquired arabis mosaic virus and transmitted it to herbaceous plants but did not transmit the grapevine viruses. AsX. indexis known to transmit grapevine fanleaf virus and probably transmits grapevine yellow mosaic virus, this suggests specific transmission of virus serotypes by different species of nematodes.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1963.tb03678.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

SUMMARYIn a series of four pot experiments single plants of kale and sugar beet or wheat were grown alone and with sixteen plants of several different weed species for from 7 to 11 weeks. Two levels of nitrogen were included.The effects of different weeds on dry‐weight growth of the crop plants were used as a measure of their competitive abilities. The results from each experiment were corrected on the basis of the effects ofChenopodium album, which was included as a standard in all experiments. The order of competitive abilities obtained was: with kale, firstSinapis arvensis, thenPolygonum convolvulusandAlopecurus myosuroides, thenChenopodium album, Polygonum uviculureandP. persicaria, followed byMatricaria maritimassp.inodora, and finallyStellaria media, Capsella bursa‐pastoris, Veronica perszcaandAnagallis arvensis;with wheat, a similar order, butPolygonum convolvulushad less competitive ability thanAlopecurusand about the same asChenopodiumandP. aviculure, andMatricariahad about the same value asVeronica.The effect of nitrogen on kale and on sugar beet was statistically significant, but on wheat it was significant in only one experiment. Weed effects generally were not significantly decreased by high nitrogen; the effects ofSinapison kale, and ofChenopodiumon wheat were increased, The leaf nitrogen percentage of kale and sugar beet was greatly increased by high nitrogen, but usually only slightly affected by weeds; nitrogen deficiency seems not to have been the sole cause of the weed effects. In two experiments with wheat, although high soil nitrogen increased the leaf nitrogen percentage of plants with weeds, it had little effect on their leaf dry weight, so that competition for nitrogen appeared non‐effective. In a third experimentAlopecurusandSinapisboth appeared to compete with wheat for nitrogen.In spite of the greater number of weeds per pot, their yields were usually decreased by adding a single indicator plant to their pots. Those weeds were least affected which themselves most reduced the growth of the indicators.The method used is judged to give results similar to those that might be found in the field, and to have advantages over alternative methods for estimating the relative importance of weeds as competitors of

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1963.tb03679.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY