摘要:

SummaryTo test the hypothesis that early maturation of barley affords it some resistance to cereal aphids, the colonisation, survival, growth, reproduction and emigration of M. dirhodum on barley was measured and compared with previously published results for this aphid on wheat.Barley plants were colonised as readily as wheat plants. Survival to maturity was similar on both hosts. Relative growth rate was higher on wheat than on barley for most of the season while reproduction was similar on both. Emigration, measured alate production, was significantly higher on mature wheat than on mature barley.It is proposed that the increase of M. dirhodum populations on barley is normally terminated early in the year directly plant maturation and consequent drying out of the leaves, resulting in the death of aphids. This is different to the situation on wheat, which matures later, and where emigration following plant induced alate induction has been shown to be the major factor affecting the decline in population growth.These results support the hypothesis that early maturation of barley provides some resistance to M. dirhodum.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1995.tb06646.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryAmong the 12 varieties of tea tested against three isolates of Pestalotiopsis theae, causal agent of grey blight disease, Teen Ali‐17/1/54 and TV‐23 were found to be highly susceptible while CP‐1 and TV‐26 were resistant under identical conditions. Leaf antigens were prepared from all the tea varieties, three isolates of P. theae and a non‐pathogen of tea (Bipolaris tetramera). Polyclonal antisera were raised against mycelial suspensions of P. theae (isolate Pt‐2) and leaf antigens of Teen Ali‐17/1/54 and CP‐1. These were compared an immunodiffusion test and enzyme‐linked immunosorbent assay to detect cross reactive antigens (CRA) shared the host and the parasite. CRA were found among the susceptible varieties and isolates of P. theae (Pt‐1, 2 and 3). Such antigens were not detected between isolates of P. theae and resistant varieties, B. tetramera and tea varieties or isolates of P. theae. Indirect staining of antibodies using fluorescein isothiocyanate (FITC) indicated that in cross sections of tea leaves, the CRA was concentrated in the epidermal cells and mesophyll tissues. CRA was present in the young hyphal tips of the mycelia and on the setulae and appendages of the

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1995.tb06647.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryThis study investigates the structural aspects of cavity spot pathogenesis. Different Pythium spp. isolated from infected carrots, apples and melons were cultured on agar in Petri dishes and used for inoculation of uninfected carrots. Only slow‐growing Pythium spp. (<15 mm day‐1), such as P. violae and P. sulcatum caused cavity spot lesions. It is suggested that slow‐growing species are able to penetrate, albeit slowly, into the plant tissue for 3 to 4 days before a hypersensitive reaction develops. Fast‐growing species, however, did not cause lesions. Based on ultrastructural observations, we suggest that the following sequence of events occurs between the plant and the pathogen: The fungus infects the walls and grows for several days, during which time small amounts of wall‐degrading enzymes are secreted. Phenylalanine ammonia lyase (PAL) activity and phenols increase linearly immediately upon inoculation. There was a lag phase of about 5 days before lignin began to increase linearly for about a month. Dissolution of wall components decreases the solute potential and water potential in the apoplast. Thus, water moves from the symplast into the apoplast, the turgor pressure gradually dissipates, and the cells shrink and event

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1995.tb06648.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryAlternaria 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

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1995.tb06649.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryIn August 1994 verticilliosis‐like symptoms were noticed in a maturing crop of sunflower at IACR‐Rothamsted. Wilting plants with chlorotic areas on some leaves, and dark areas of microsclerotia at the base of stems, were first observed on 11 August. As the plants matured, dark stripes were also observed on the stems. Many stems became brittle and later collapsed. Infected xylem showed a brown discolouration, later turning to black, and microsclerotia developed. Verticillium dahliae was isolated from all parts of the plant.In general, once symptoms were present, the incidence of verticilliosis‐affected plants increased, and the disease developed, more rapidly in early maturing varieties than in the later maturing types. At harvest, incidence ranged between 24.5% and 89.8%, depending on variety. Early maturing varieties appeared to be more susceptible than later maturing types.Isolates of V. dahliae were cultured in the laboratory. Sunflower plants were artificially inoculated with these isolates and developed verticilliosis symptoms when grown under controlled environmental condi

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1995.tb06650.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummarySeed tubers of cvs Désirée and Pentland Crown with different severities of black dot were planted in 1988 and 1989 at Rothamsted in fields in 4– or 7‐course rotations, respectively. Tubers treated with prochloraz (1988) or imazalil (1989) were planted in some plots, and in others Colletotrichum coccodes inoculum was added to the soil at planting. In further experiments at Mepal, Cambridgeshire in 1989 and 1990 and at Rothamsted in 1990 on sites where potatoes had not been grown for more than 15 years, large amounts of inoculum were added to the soil around disease‐free seed tubers of two (1989) or three (1990) cultivars at planting. In all experiments plants were sampled during the season and the effects of treatments on disease development, growth and yield were recorded.Disease on roots, stem bases and tubers was found early in the season and was more severe on Désirée than on Pentland Crown plants from fields in 4– or 7‐course rotations. Severity increased throughout the season and with increasing amounts of disease on the seed tubers, especially with Desiree. Disease was also found on plants from disease‐free tubers and was more severe in 1988 than 1989. At harvest, black dot on tubers was significantly more severe from severely affected than from disease‐free seed, and was most severe where inoculum, especially large amounts, had been added at planting. Fungicide treatment decreased disease early in the season but had no effect on tuber infection at harvest. In 1989 the weight loss of seed tubers during sprouting increased with increasing amounts of black dot, but the disease had little effect on plant size through the season. At harvest the yield of ware tubers (>50 mm) decreased with severe disease but total tuber yields were not significantly affected. However, at harvest in 1988 severely affected seed yielded significantly less than healthy seed.Plants grown from mini‐tubers were free from disease on sites where potatoes had not been grown for at least 15 years. Inoculum applied at planting caused severe disease on all cultivars in both years, whereas disease was slight on uninoculated plants. Inoculated plants senesced early at Mepal in 1990, but there were no significant differences in total tuber yield in any experiment. However, yields of ware tubers (>50 mm) were sometimes decreased and the total tuber number

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1995.tb06651.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryThe effects of different seed sizes, planting densities and planting patterns on the transmission of silver scurf (Helminthosporium solani) and black scurf (Rhizoctonia solani) diseases of potatoes were examined in five field experiments with cv. Estima in 1991–93.In all experiments, silver scurf was more severe with increase in seed size and planting density. At high planting density, silver scurf was less severe from a square planting pattern than from planting in wide rows. The incidence of black scurf also tended to increase with increase in seed size and was increased markedly high planting densit

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1995.tb06652.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryFour mouse monoclonal antibodies (MAbs) specific for the Andean strain of potato virus S (PVSA) were produced. The MAbs reacted with four isolates of PVSAbut did not react with four isolates of ordinary strain of PVS (PVSO). The MAbs did not react with six other members of the Carlavirus group including potato virus M. A MAb‐based ELISA, using MAbs (IEB‐1 and IEB‐4‐AP), was devised and shown to specifically dete

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1995.tb06653.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryEight major dsRNA species ranging from 1.0 to 19.5 kbp were detected in a low‐yielding clone of Sultana (Thompson seedless) grape (Vitis vinifera L., cv. Sultana, clone B4L) affected leafroll disease. Using total dsRNA from this Sultana line as template, a number of cDNA clones were produced. The clones were used as probes for northern blot analysis of dsRNA extracted from Sultana B4L, and from six other grapevine leafroll‐infected Sultana sources differing in yield performance. Based on the hybridisation of each probe with dsRNA bands from various Sultanas, the cDNA clones could be divided into three groups. One group of cDNA clones hybridised to high molccular weight dsRNA (19.5 kbp) from two low‐yielding Sultanas, another group hybridised to high MrdsRNA from three low‐yielding Sultanas and the third group hybridised to a number of smaller dsRNA species ranging in size between 1.15 and 6.5 kbp. Using the latter cDNA clones, the sequence of 965 nucleotides at the 5′‐end of a 1.15 kbp dsRNA (dsRNA 6) of B4L Sultana was determined. This RNA contains an open reading frame encoding a putative protein of M, = 33 441 with no homology to known protein sequences. The sequence of dsRNA 6 was found to overlap larger dsRNAs of sizes between 2.2 to 6.5 kbp. This allowed us to determine the sequence upstream of the 5′‐end of the positive strand of dsRNA 6. The nucleotide sequence neighbouring the 5′‐end of the positive strand of dsRNA 6 conforms to a consensus sequence proposed as a subgenomic promoter element for the coat protein gene of positive strand RNA plant viruses. The results indicate that more than one virus was present in Sultana B4L and that dsRNA 6 may be a subgenomic spec

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1995.tb06654.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryA new strain of cassava common mosaic virus, designated CsCMV‐ve, was isolated from cassava (Manihot esculenta Crantz) plants growing in Venezuela. The 520 nm long semi‐flexuous virus particles sedimented in sucrose gradients as one component and contained a single coat protein molecule of c. 28 kDa, and a ssRNA of c. 2.1 times 106. A single dsRNA species of c. 4.2 times 106kDA was isolated from virus‐infected cassava leaves. In double antibody sandwich enzyme‐linked immunosorbent assay, CsCMV‐ve reacted strongly with antisera to CsCMV and potato virus X, but not with those to other typical members of the potexvirus group. Ultrastructural studies of CsCMV‐ve infected cells showed the presence of large bundles of inclusion bodies in the cytoplasm, a proliferation of the rough endoplasmic reticulum, and large crystals in the peroxisomes. CsCMV‐ve in crude buffered sap or in purified preparations was not mechanically transmitted to known hosts of the Chaya and Brazilian strains of CsCMV. Isolated virus RNA also failed to infect a range of test‐plant species. This is the first report of the presence of CsC

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1995.tb06655.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY