摘要:

SUMMARYThe longevity ofSitobion avenaevaried inversely with temperature from 25 to over 100 days when reared outdoors on barley under lantern jars, being longest between December and April–May. This was due mainly to changes in the length of the pre‐ and post‐reproductive periods rather than the length of the period of reproduction. Fecundity varied directly with temperature, from eight to sixty‐seven nymphs per female. When reared on winter wheat and sheltered from wind, rain and snow,S. avenaesurvived best,Metopolophium dirhodumsurvived less well andRhopalosiphum padiworst; when exposed in the open none of the three species survived.Close relationships were not demonstrable between the numbers of alateM. dirhodum, S. avenaeandRhopalosiphumspp. trapped in any year, between the abundance of these aphids and weather conditions between January and April, or between the numbers of these alatae and the size of crop infestations. This was probably because insufficient information was available about their biology, both inside and outside t

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1974.tb01351.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYThe inheritance of resistance to lettuce root aphid,Pemphigus bursarius, was studied in lettuce using the Wellesbourne cultivars Avondefiance and Avoncrisp as resistant parents and Borough Wonder and Webb's Wonderful as aphid‐susceptible parents. All four cultivars were crossed in all possible combinations including reciprocals and the response to root aphid of plants in theP1F1F2and BC generations was assessed using apterae ofP. bursariusfrom the lettuce cv. Iceberg. Resistance to attack was clearly inherited and the parents appeared to be homozygous for their resistance or susceptibility. In theF1generation, however, in all crosses between resistant and susceptible parents, segregation into susceptible, resistant and some slightly less resistant plants occurred. This and the highly significant differences in segregation between pairs of reciprocal crosses in theF1and other generations indicate that the inheritance of resistance to root aphid is controlled by extra‐nuclear factors. Modifying genes might also be involved but there appears to be no linkage of root aphid resistance with resistance to downy mildew, for which the Wellesbourne lettuces were b

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1974.tb01352.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYIn the field, caged potato plants of King Edward and Majestic cultivars infested with the potato aphidMacrosiphum euphorbiaedeveloped top‐roll symptoms, the proportion of affected plants increasing with the size and persistence of the aphid population. Yield of tubers from plots in which 90% of the plants had top‐roll symptoms was 40% less than that from control plots; yield of saleable ware was even less. Foliage produced after the aphids had been killed was symptomless even when it arose from the axil of an affected leaf. Caged field plants treated with phorate granules to prevent aphid attack did not develop top‐roll.Prolonged infestation of Pentland Crown, Majestic and King Edward plants byM. euphorbiaein a glasshouse induced rolling of upper leaves similar to top‐roll of field plants. Experimental results suggest that rolling was directly attributable to heavy attack byM. euphorbiae, not to an aphid‐transmitted

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1974.tb01353.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYA wilt disease of garden pea (Pisum sativum) caused byVerticillium dahliaeis described and the range of pathogenicity of the isolate investigated. It is pathogenic to potato, sweet pea, antirrhinum and broad bean and isolates ofV. dahliaefrom potato, lucerne and sweet pea andV. albo‐atrumfrom lucerne are pathogenic to pea.Since the most common disease symptoms, acropetal progression of chlorosis and necrosis of the leaves followed by premature defoliation are indistinguishable from natural senescence, it is probable that disease and senescence symptoms are confused in the field.The premature defoliation results in marked reduction in green leaf area, leaf dry weight and pod yiel

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1974.tb01354.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYThe influence of a non‐cultivation (herbicide) regime on wilt incidence was compared with that of normal tillage in three observation trials on commercial hop farms. Non‐cultivation resulted, on average, in 28% wilt control when wilt incidence was high. When wilt incidence was low there was a tendency for more wilt to occur with non‐cultivation.The reduction in wilt under non‐cultivation was probably mainly due to the virtually complete eradication throughout the year of alternative weed host plants, but other possible influential factors were: (i) the absence of root severance which could result in increased inoculum potential, (ii) changes in the pattern of hop root distribution, and (iii) the inhibiting action of simazine on root growth in surface soil resulting in reduced contact between roots and surface‐borne inoculum.The lack of disease control with non‐cultivation when wilt incidence was low was attributed to differential effects of the treatments on nitrogen metabolism or availability.The factors contributing to disease control under non‐cultivation were considered to represent aspects of the process of sanitation, and the data were interpreted in terms of the sanitation ratio (sensuvan der Plank). When wilt incidence was high the sanitation ratios at the three sites were similar.Modified cultural practices provide an important supplement to genetic resistance in the control of hop wilt. These practices (restricted use of nitrogen fertilizers and efficient sanitation with respect to the crop plant as well as to weeds) have proved economical and beneficial for hop culture in presence of wilt, under the threat of wilt, and in the ab

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1974.tb01355.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYLaboratory methods are described for the culture and observation ofBremia lactucaeon lettuce.Mycelial growth of the fungus within the cotyledons of the cultivar Cheshunt Early Giant progressed to a minimum density at which sporulation occurred, and then continued to a maximum density coinciding with peak sporulation. The timing and intensity of sporulation was influenced by the concentration of the inoculum. Seedlings often became systemically infected and this, together with intensity of sporulation, was a good indicator of fungal growth and hence host susceptibility.The severity of disease development on four susceptible lettuce cultivars (Cheshunt Early Giant, Paris White, Trocadero Improved and Crackling Ice) decreased with age and development of the seedlings at inoculation. The reasons for this are discussed.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1974.tb01356.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYWhen fresh sugar‐cane bagasse containing about 50% water and 3% sugar was baled and stacked, it quickly heated to over 50°C and remained hotter than 40°C for 50 days. The residual sucrose was utilized by microbial growth and the content of fungal, bacterial and actinomycete spores increased to more than 108/g dry wt. The spores in heated bagasse were mostly of thermophilic actinomycetes and fungi, and included two actinomycetes implicated in bagassosis.Thermoactinomycetes saccharioccurred in 40% of samples examined, some of which yielded up to 5 × 106colonies/g, whileT. vulgarisoccurred in 80% of samples, but these rarely yielded more than 105colonies/g. Other organisms were cellulolytic and caused fibre deterioration. Heating and moulding could be much decreased either by drying to about 25% water content, which halved the spore content after storage, mostly at the expense of the actinomycetes, or by adding 2% by weight of propionic acid, which decreased the spore content to 4 × 106spores/g or less even after 18 months' storage. Sometimes adding only 0·6% of propionic acid or 2% of propionic acid applied as a 50% aqueous solution had a similar effect. Treatment with propionic acid thus decreased the deterioration of bagasse, permitted its storage between harvests and prevented the hazard of bagassosis to w

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1974.tb01357.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYLoss of the water droplet above inoculation sites during the first day after inoculation inhibited lesion formation byBotrytis cinereaand prevented the development of spreading lesions ofB. fabae.With droplets present two general patterns of infection byB. cinereawere determined; in one, few or no symptoms were produced and in the other, limited lesions developed with marked browning of the inoculation site. Where few or no symptoms were produced, germination and germ‐tube growth were inhibited on the leaf surface.B. cinereawas inhibited within the leaf at sites bearing limited lesions; invading hyphae were restricted to brown epidermal cells. Fungal growth on the leaf surface was greatest at sites with most browning beneath the droplet area. Variation in lesion development byB. cinereacould not be related to droplet position or leaf damage during normal preparation for inoculation. Plants differed in their susceptibility to lesion formation byB. cinerea.B. fabae, with droplet present, was not inhibited on the leaf surface and spread inter‐ and intra‐cellularly beneath the inoculum drop and then into surrounding tissues. Delay in spread until the inoculation site was completely necrotic and colonized suggested thatB. fabaeis partially inhibited during the initial phase of infection. The rate of lesion spread varied in different plants and was most rapid in the youngest l

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1974.tb01358.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYStolons attached to developing potato tubers were inoculated with the soft rot bacteriumErwinia carotovoravar.atroseptica.Almost all the stolons rotted, but soft rots developed in less than 10% of new tubers; the bacterium was isolated later from these tubers. No rots developed in the other tubers but the bacterium was later isolated from about half of them. It could not be isolated from tubers attached to inoculated stolons where the rot on them did not extend to the tuber or from tubers attached to stolons that were not inoculated though many of these rotted.The bacterium was reisolated from almost all arrested lesions in tubers inoculated 8 month earlier withE. carotovoravar.atroseptica.Blackleg did not develop from plants grown fom these tubers under various soil conditions. It did develop in a large proportion of plants from tubers inoculated shortly before planting and grown in cool, wet soil.Less than 1% blackleg developed in plants grown from tubers from plants with blackleg or from plants immediately adjacent.The presence of pectolytic bacteria andE. caratovoravar.atrosepticain seed and new tubers was investigated during June, July and August. AlthoughE. caratovoravar.atrosepticawas obtained fromc.40% tubers, onlyc.0·3% ofc.8400 plants developed blackleg. The bacterium was isolated from only three of 160 new tubers sampled during the summer

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1974.tb01359.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYThere was a significant inverse correlation (P= 0=001) between concentrations of mushroom viruses 1 and 2 in sporophores and amounts of mycelial growth on malt agar of isolates taken from them. Increasing virus concentrations decreased linear growth of one mushroom strain from 76 mm (healthy) to 35 mm (mildly infected) and 7 mm (severely infected) when incubated at 25°C for 3 wk.Mycelial growth rates of isolates from healthy and from virus‐infected mushrooms were compared on eleven agar media. All media clearly differentiated between healthy and severely infected isolates, but fewer separated healthy from mildly infected isolates. Those that did contained maltose, sucrose or starch as carbon source. Media containing peptone usually gave better differentiation than those with other sources of nitrogen, but the best differentiation was obtained with malt agar.Growing healthy and infected isolates on a range of media affected their subsequent growth on malt agar, the growth of some isolates apparently being changed permanently after 2 months on some of the different media. Whereas none of the infected isolates grew less rapidly after this treatment, the growth of some of the mildly infected isolates improved to such an extent that they could no longer be distinguished from healthy isolates.After heat‐treatment (1–6 wk at 33°C), mycelial growth rates of infected isolates were increased, but viruses 1 and 2 were not always eliminated unless the heat‐treatment was begun immediately after subculture.Mycelial growth rate and colony characters are not infallible criteria of the presence or absence of virus, a feature of particular significance when checking the health of mushr

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1974.tb01360.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY