Factors influencing infection of the tomato by Verticillium albo-atrum. II

Tomato plants receiving adequate supplies of mineral nutrient acquired great resistance to infection by Verticillium albo-atrum if the leaf-shoot ratio was reduced; this effect is attributed to reduction in carbohydrate content of the host. Wide variation in potash manuring did not affect susceptibility of tomatoes to Verticillium .     

Growth Regulator Changes in Cotton Associated with Defoliation Caused by Verticillium albo-atrum

Cotton plants, variety Acala 4-42 family 77 (Gossypium hirsutum L.,), were stem puncture-inoculated with either a defoliating isolate (T9) or a nondefoliating isolate (SS4) of Verticillium albo-atrum (Reinke and Berth.). As symptoms developed, growth regulators were assayed in diseased plants to discern their importance in the disease syndrome.     

Factors influencing infection of the tomato by Verticillium albo-atrum

Infection of tomato plants by Verticillium albo-atrum was encouraged by application of nitrogenous manures. Application of phosphate had no significant effect on the progress of the disease, but a deficiency of potash tended to encourage it. Steam-sterilized soil inoculated with Verticillium immediately after treatment produced a very high total of infected plants. When inoculation of the steamed soil by Verticillium was delayed for 17 days or longer after steaming, the steamed soil was no more favourable for development of the disease than untreated soil. Spread of Verticillium from the roots of an infected plant to those of neighbouring healthy plants was hastened by killing the infected plant.     

Properties of wilt-toxins produced by Verticillium albo-atrum Reinke & Berth.

Cultures of Verticillium albo-atrum grown in a liquid, mineral salts/sucrose medium, were harvested at daily intervals and subjected to gel-filtration on Sephadex G-25 columns eluted with demineralized water. Ultraviolet scanning of the eluate indicated a broad division into high and low molecular weight fractions (HMW and LMW). The HMW material was found to be a variable mixture of a protein component (M.W. c. 100,000) possessing mild cellulase activity, and fructosan (M.W. 5,000–10,000). Both components produced wilting in a lucerne detached-leaf bioassay. Heat denaturation resulted only in the loss of the protein component with a corresponding reduction in wilt-toxicity. A number of LMW components were found to produce leaf necrosis, but only in high concentrations and long-duration assays. These were considered to be of doubtful significance in the wilt syndrome. The possible action mechanisms and the basis of resistance are discussed.     

Changes in Amino-acid Content of Tomato Xylem Sap Following Infection with Strains of Verticillium albo-atrum

Xylem exudates of four tomato cultivars showing resistance andsusceptibility to the vascular pathogen Verticillium albo-atrum,were analysed for amino acids and amides by column chromatography42 days after inculation with different isolates of the fungus.Analysis of the exudate from healthy, resistant Loran Bloodshowed a substantial reduction in amino compounds compared withthe healthy, susceptible Potentate and Bonny Best. ResistantMoscow, however, gave similar results to Potentate. Infectionin all cultivars except Moscow led to a general increase inthe concentration of amino acids and predominantly in asparticand glutamic acids, threonine, serine, proline, tyrosine, ornithine,lysine, histidine, and phenylalanine. A reduction in prolinecontent of up to 90 per cent occurred in the resistant plantsin both pathogenic and non-pathogenic combinations. The resultsare discussed in relation to previously published data on vascularcolonization and disease development with the same tomato cultiversand fungal strains.     

Verticillium albo－atrum激发子诱导的番茄组织培养细胞的反应性氧迸发

从对Ｖｅｒｔｉｃｉｌｌｉｕｍａｌｂｏ－ａｔｒｕｍ感抗性不同的两株近等位基因番茄获得细胞悬浮培养物Ｓ－ＧＣＲ２６和Ｒ－ＧＣＲ２１８。用．ａｌｂｏ－ａｔｒｕｍ激发子处理后,敏感性的Ｓ－ＧＣＲ２６未表现出明显的反应性氧改变。抗性的Ｒ－ＧＣＲ２１８则响应以反应性氧迸发。反应性氧迸发中的细胞,其反应性氧累积量与激发子浓度的关系呈近Ｓ形。悬浮介质、某些无机离子、培养物的生长状况和培养日龄等因素均影响细胞对激发子的反应性氧迸发响应。     

Verticillium wilt of the hop: the survival of V. albo-atrum in soil

Verticillium albo-atrum was apparently eradicated from soil in which dicotyledonous plants were suppressed. In one field experiment V. albo-atrum was not recovered after 4 years of weed-free grass cover; in the same period soil infectivity reduced to very low levels under two bare fallow treatments. Where weeds developed after single annual cultivations soil infectivity declined from the initially high level but finally increased. In three observation trials in which hop plants were used to detect V. albo-atrum after grass-cover treatments, soil infectivity was very low after 2 years and apparently nil after 3–5 years. Grass cover effectively stabilizes infested soil; it may be used for limiting spread from primary disease outbreaks, and also as a short-term treatment to reduce the infectivity of soil to be re-planted with resistant varieties. The frequent incidence of V. dahliae hop infections in one trial indicated that this fungus was not amenable to control by grass cover treatment and hence may be ecologically distinct from V. albo-atrum.     

Studies on the nature of resistance in tomato plants to Verticillium albo-atrum

Extracts of healthy resistant and of healthy susceptible plants of tomato had the same effect on growth of Verticillium albo-atrum in vitro. Tracheal saps from resistant and from susceptible plants showed no difference in their effect on spore germination and mycelial growth of V. albo-atrum. Cuttings from resistant plants, inoculated with V. albo-atrum and fed with low concentrations of casamino acids, or glucose, at first wilted more than controls but soon recovered. Continuous treatment with dilute ethanol solutions for 2 weeks induced marked wilting in inoculated cuttings of resistant plants: treatment for shorter periods caused less severe symptoms, from which cuttings recovered slowly. Metabolic inhibitors did not break resistance of cuttings, but the pathogen survived longer in cuttings treated with sodium diethyldithiocarbamate, salicylaldoxime or 8-hydroxyquinoline than in controls. When one end of segments of stems of resistant plants was inoculated with the pathogen, and 48 h later the uninoculated end was placed near a colony of V. albo-atrum on agar, growth of the fungus colony towards the stem segment was sometimes inhibited. There was no such inhibition when segments from susceptible plants were used. Both tracheal sap and diffusates from segments of inoculated resistant plants supported less growth of germ tubes of V. albo-atrum than sap and diffusates from uninoculated plants. These differences were not obtained with the susceptible variety and production of fungitoxic substances in resistant plants after infection is inferred.     

Contribution to the study of the chemical composition of Verticillium albo-atrum secretions in liquid media

Slower growth at temperatures ranging from 15 to 32.5 °C and high tolerance of three fungicides, benomyl, carbendazim and thio- phanate methyl, were shown to be reliable characteristics in distinguishing rubber isolates of Colletotrichum acutatum from Colletotrichum gloeosporioides in addition to the characteristics reported previously. This revised version was published online in June 2006 with corrections to the Cover Date.     

The response of tomato seedling roots to infection by Verticillium albo-atrum or Fusarium oxysporum f. sp. lycopersici

The response of seedling roots of near-isogenic tomato varieties to infection by Verticillium albo-atrum or Fusarium oxysporum f. sp. lycopersici was investigated. Studies of the infection of seedling roots not artificially damaged indicated that there was an extra-vascular expression of resistance towards V. albo-atrum but not to F. oxysporum. Roots of resistant tomato seedlings infected by V. albo-atrum contained the fungus in the epidermis and outer cortex while susceptible roots became heavily colonised. Observations made by transmission electron microscopy showed that the fungus appeared to be abnormal in growth and appearance in the epidermal and cortical cells of resistant seedling roots but normal in susceptible roots. Two preformed antifungal terpenoids were detected in seedling roots in greater amounts in resistant that in susceptible varieties. The possible mechanisms of seedling root resistance to vascular wilts are discussed.     

Effects of temperature and rainfall on the incidence of wilt (Verticillium albo-atrum) in hops

Wilt incidence in certain hop cultivars recorded during 15 years of experiments on a plot infested with a virulent strain of V. albo-atrum, and over shorter periods on various infested farm sites, was studied by multiple regression analysis in relation to rainfall and soil temperature at various periods during the growing season. In the least-resistant cultivar, Fuggle, the incidence of wilt was always high, and was independent of rainfall and soil temperature. Wilt incidence in other cultivars showed a negative correlation with mean soil temperature at 20 cm for the period mid-April to late June; no other single or multiple regression was consistently significant. It was concluded that the commonly observed association of high wilt incidence with wet weather in early summer is attributable to low soil temperature rather than to high rainfall.