THE INFLUENCE OF TEMPERATURE AND DAYLENGTH ON SPOTTED WILT VIRUS DISEASE OF TOMATO

The responses of young tomato plants to infection with tomato spotted wilt virus were studied at constant temperatures. The plants were grown in nutrient solutions and given three daylength treatments.
The length of the incubation period was positively correlated with temperature and a regression equation for this relationship is given. The calculated temperature at which this period becomes infinite is 6.7°C. The temperature coefficient ( Q ₁₀) varied from 1.7 to 2.9.
Dry-weight determinations were made of stems, leaves and roots. In healthy plants the leaf/stem ratio generally fell with rise of temperature and the shoot/root ratio rose. Infection changed these ratios, which is interpreted as indicating that it interfered with supplies of carbohydrate to the growing regions.
Systemic symptoms are described for plants raised at 11.4°, 18.3°, 23.9°, and 29.4°C.
Changes in daylength did not affect the systemic symptoms or incubation period. With a 9 hr. day at 29.4°C., the virus content of sap was significantly lower than with 12 or 15 hr., and with a 12 hr. day was significantly higher than with a 15 hr. day.     

SOME EFFECTS OF HOST NUTRITION ON THE SUSCEPTIBILITY OF PLANTS TO INFECTION BY CERTAIN VIRUSES

Fertilizer treatments that greatly influenced the growth of tobacco and potato plants in pots had little effect on the number that became infected with potato virus Y when the plants were colonized by equal numbers of infective aphids, though the number was slightly decreased by nitrogen and increased by phosphorus.
The number of local lesions produced on leaves of tobacco and Nicotiana glutinosa by tomato aucuba mosaic and tobacco mosaic viruses was increased by additions of both nitrogen and phosphorus, provided that these also increased growth. The predominant effect of both nutrients in increasing susceptibility was indirect by increasing plant size, but over certain critical ranges both elements also increased the numbers of lesions produced per unit leaf area. Conditions of maximum susceptibility approximated closely to those producing optimal growth, and susceptibility, whether measured by lesions per half-leaf or per unit area, was decreased by a deficiency or excess of either element. Sometimes the addition of nitrogen reduced susceptibility when still increasing plant growth.     

PHYSIOLOGICAL STUDIES ON THE VERTICILLIUM WILT DISEASE OF TOMATO

The water loss per unit leaf area of tomato plants was decreased after inoculation with Verticillium albo-atrum. When diseased plants began to wilt water loss temporarily increased, but then rapidly decreased to become less than that of healthy plants grown under conditions of adequate or restricted water supply.
The transpiration of excised leaves from plants grown with a restricted water supply was reduced, but not so severely as that of comparable leaves from infected plants. Water loss from leaves on infected plants was reduced irrespective of any blocking of the petiolar xylem.
The rate of water loss from turgid leaf disks on mannitol solutions, and the rate of water uptake of leaf disks on water was similar for disks cut from wilting or turgid leaves of diseased plants or healthy plants grown with an adequate or restricted water supply.
Disease or poor water supply reduced leaf growth but had no effect on the rate of leaf initiation. Although the density of stomata was higher on leaves of diseased plants the stomatal area was less than on healthy plants.
The resistance to water flow in diseased stems was high and was correlated with vessel blockage. About half the blocked vessels contained hyphae. The severity and localization of symptoms in inoculated plants growing on susceptible or resistant rootstocks was directly related to the extent of invasion by the pathogen and to vessel blockage.
Experiments on the wilting activity of cell-free filtrates from cultures of the pathogen in vitro indicated that it produced a stable substance, not an enzyme, that caused wilting in cut shoots by blocking the end of the stem. It is suggested that an increasing internal water shortage causes major symptoms of disease.     

THE INFLUENCE OF LIGHT INTENSITY ON THE SUSCEPTIBILITY OF PLANTS TO CERTAIN VIRUSES

Reducing the light intensity under which plants were grown in summer to one-third increased their susceptibility to infection with tobacco necrosis, tomato bushy stunt, tobacco mosaic and tomato aucuba mosaic viruses. With the first two viruses shading increased the average number of local lesions per leaf by more than ten times and by more than five times with the second two.
Reducing the light intensity increased the virus content of sap from leaves inoculated with Rothamsted tobacco necrosis virus by as much as twenty times. As it also reduced the total solid content of sap by about one-half, purification was greatly facilitated; crystalline preparations of the virus were readily made from shaded plants but not from unshaded controls.
Reducing the light intensity also increased the virus content of systemically infected leaves; the greatest effect was with tomato bushy stunt virus with which increases of up to ten times were obtained, but with tobacco mosaic and aucuba mosaic viruses there were also significant increases.
The importance of controlled illumination in raising plants for virus work and the possible mechanisms responsible for the variations in susceptibility are discussed.     

THE PATTERN OF FIELD INFECTION OF POTATO BY THE BEET RINGSPOT STRAIN OF TOMATO BLACK-RING, A SOIL-BORNE VIRUS

The potential importance of the beet ringspot strain of tomato black-ring, a soil-borne virus, was assessed by growing stocks of Kerr's Pink potato for 1 year on infested land and subsequently on uninfested land. The incidence of infection in two stocks was 39 and 8% in the first year on uninfested land, and 29 and 5% after 2 years.
The virus was usually restricted to the roots of plants in the first year of infection, but a few plants showed black rings and spots in their leaves. In the second year, 20–55% of the plants grown from tubers set by symptomless, but infected, mother plants were infected: many of these showed leaf necrosis, others had stunted shoots, and cupped and distorted leaves; some were symptomless although systemically infected. In the third and fourth years, most of the progeny from plants which had symptoms or which were symptomless but systemically infected, contained the virus: nearly all such infected plants were stunted and distorted or were symptomless. Infection decreased the weight of tubers produced by plants with severe necrotic spotting but not the yield of plants with less necrosis. The number and weight of tubers per plant were decreased by 15 and 20% respectively, in symptomless systemically infected plants, and by 20 and 30% in stunted plants.     

THE INHERITANCE AND PHYSIOLOGY OF BORON RESPONSE IN THE TOMATO

Wall , J. R., and C. F. Andrus . (U.S.D.A., U. S. Vegetable Breeding Laboratory, Charleston, S. C.) The inheritance and physiology of boron response in the tomato. Amer. Jour. Bot. 49(7): 758–762. Illus. 1962.—Brittle stem (btl), an abnormal sublethal phenotype in the tomato caused by boron deficiency, was found to be controlled by a single recessive gene. The threshold of boron concentration for brittle-stem expression is not constant but fluctuates and is intimately associated with a number of interrelated environmental factors. Light duration and intensity are especially significant, while temperature and nitrogen, phosphorus, and calcium availability probably contribute to btl expression. It is suggested that when boron supply is limiting, brittle-stem (boron deficiency) symptoms are intensified by any environmental factor or factors which enhance plant growth. Plants of btl/btl genotype contain much less boron in their leaves than do those of the control variety ‘Rutgers’; conversely, these plants contain more boron in their roots when grown in nutrient cultures of high boron content. This finding is discussed in relation to possible modes of gene action.     

The adaptation of tomato mosaic virus to resistant tomato plants

Tomato mosaic virus derived from susceptible tomato plants (the standard virus) was cultured in resistant plants. Sap from non-inoculated leaves of resistant tomato plants infected with virus from the resistant host was more infective and contained more virus particles than leaf sap of resistant plants infected with the standard virus. Leaves of resistant tomatoes infected with virus from the resistant host also showed more obvious symptoms. Susceptible plants infected with virus from resistant plants not only showed fewer symptoms than when infected with standard virus, but samples were less infective and contained less virus up to 26 weeks, when values for infectivity were similar. This modification in activity was not reversible and was obtained with two lines of tomato having different types of resistance. Passage of virus from resistant plants through susceptible plants did not impair its ability to infect resistant plants.     

AN ANALYSIS OF THE GROWTH RESPONSE OF YOUNG TOMATO PLANTS TO INFECTION BY VERTICILLIUM ALBO-ATRUM

Infection of seedling tomatoes with Verticillium albo-atrum checked growth but did not result immediately in leaf yellowing. Localized wilting occurred in some plants 2 weeks after the check to growth was evident. 8 weeks after inoculation, dry weights of leaf, stem and root were decreased by 72, 70, and 65% respectively.
Of the growth attributes studied, leaf area was most reduced by infection and this was due to a failure of the leaves to expand rather than to a fall in the rate of leaf production. Neither water nor nitrogen appeared to be limiting factors in this respect. The water content of infected leaves was not reduced until 6 weeks after inoculation, when leaf yellowing and necrosis had also appeared. The percentage N contents of stem, root and leaf of infected plants exceeded those of the healthy controls 24 days after inoculation. N uptake was not seriously impaired until 21 days later.
The photosynthetic efficiency of the green leaves of infected plants was reduced. The mean values for net assimilation rates were: Healthy 0.47 and infected 0.39 g./dm.²/week.
Plants, in which two-thirds of the root system had been killed by crushing, were placed in contact with mycelium in soil. This initial root injury did not significantly affect the growth of infected plants.
The data accord with a toxin theory of damage to infected plants, but the slow development of chlorosis and wilting symptoms in the young plants suggested a greater tolerance to the toxin than is found in older plants.     

HEAT-THERAPY OF VIRUS-INFECTED PLANTS

Virus-free plants were produced from parents systemically infected with the following five viruses: tomato bushy stunt, carnation ring spot, cucumber mosaic, tomato aspermy and Abutilon variegation. The leaves formed while the infected plants were kept at 36°C. were free from symptoms, and test plants inoculated from these remained uninfected. When cuttings were taken from the infected plants at the end of the treatment most grew into healthy plants. The treated plants themselves usually developed symptoms after varying lengths of time at 20°C, but some that before treatment were infected with tomato aspermy, cucumber mosaic or Abutilon variegation viruses, remained permanently healthy.
The same method failed to cure plants infected with tomato spotted wilt, potato virus X and tobacco mosaic virus, although it decreased their virus content. Heat-therapy seems not to be correlated with the thermal inactivation end point of the virus in vitro.     

THE REACTION OF VIRUS-INFECTED POTATO PLANTS TO PHYTOPHTHORA INFESTANS

The growth of Phytophthora infestans was retarded on leaves of potato plants that had been artificially inoculated with virus X or with virus Y.
Using different virus strains and potato varieties, the effect of virus infection on blight development was found to be greater, the more severe the systemic virus symptoms exhibited on the infected leaves before P. infestans inoculation.
The development of the fungus was never increased by virus infection.
The reduced blight development on virus-infected leaves is partially caused by an increase of resistance to infection. It is also suggested that virus infection alters the nutritional status of leaves to one less favourable for the development of P. infestans.     

番茄曲叶病及其血清学和PCR测定

我国曾报道的番茄病毒病有多种,其中最常见的是黄瓜花叶病毒(CMV)和烟草花叶病毒(TMV)引起的花叶病。柯冲等(1964)在大陆首次报道烟粉虱(Bemisia tabaci)传播的番茄病毒病——番茄黄顶病,此病在50～60年代曾在广州市郊流行,造成大面积减产。Green等(1984)报道台湾发生番茄黄曲叶病,此病与日本的番茄黄矮病(Tomato yellow dwarf)相似,并且与烟草曲叶病毒(TLCV)有血清学关系。印度、委内瑞拉等国也曾报道发生由烟粉虱传播的番茄曲叶病和番茄黄曲叶病。1991和1992年秋,在广西南宁市郊发现一种症状表现为植株矮缩,叶片向上向内卷曲,叶背面产生耳状或杯状增生物,对光看有时可见叶脉呈墨绿色,不结果或少结果的番茄病害。1992年秋广西农业科学院的番茄试验地发病率高达6.8％,对当地秋番茄生产构成了威胁。作者对病害症状、传播、血清学反应及PCR分析等方面与烟草曲叶病毒进行了比较研究,证实了该病的病原与烟草曲叶病毒有很高的同源性。现将研究结果简报如下。     

Effect of nitrogen nutrition on Fusarium wilt of tomato plants

The role of nitrate-nitrogen (NO₃-N) in relation to the development of tomato wilt caused by Fusarium oxysporum f. sp. lycopersici R1 was studied. Plants receiving 284 μg/ml nitrogen in the nutrient solution exhibited the same severe wilt symptoms as the control plants in soil. Disease decreased with increasing nitrogen levels (420, 630 and 1050 μg/ml). Apparently, the plants were also less susceptible to the disease when the concentration of nitrogen was 70 μg/ml, i. e. below the optimal level (284 μg/ml). Protein content in tissues of plants grown with different amounts of nitrogen was also determined. High nitrogen levels, which decreased disease severity, increased the protein content in leaf tissues. Of 17 amino acids only proline content increased with increasing nitrogen supply. High doses of NO₃–N decreased the phenol content and the activity of peroxidase in stem and leaf tissues of tomato plants. It is suggested that phenolic compounds and the activity of peroxidase are not significant in the resistance of tomato to Fusarlum wilt associated with high nitrogen supply.     

THE EFFECT OF SUCROSE SPRAYING ON SYMPTOMS CAUSED BY BEET YELLOWS VIRUS IN SUGAR BEET

When leaves of sugar-beet plants infected with beet yellows virus were sprayed daily with 10% sucrose solution, yellowing symptoms were intensified. When glasshouse plants were shaded so that the light intensity was reduced to less than half of full daylight, yellowing symptoms were suppressed more completely on un-sprayed than on sprayed plants. Spraying with 2–5 % sucrose solution had similar, but slightly smaller effects.
Spraying with sucrose solution increased the carbohydrate content of the leaves, and the effects on symptom intensity and carbohydrate content were closely correlated. The regression coefficients of symptom score on total sugar content were nearly the same for shaded and unshaded plants. As the severity of symptoms was increased by supplying carbohydrate without change in the light conditions, it is concluded that light intensity affects symptom expression by varying the carbohydrate content of the leaves through its influence on photosynthesis.
Sucrose spraying increased the yield of roots of healthy and infected plants, and most of the increase was sucrose. This shows that sprayed sugar was translocated to the roots from the leaves of both healthy and infected plants.
Measurements of changes in carbohydrate content between evening and morning samplings confirmed that movement of carbohydrate out of infected leaves is not stopped by infection.     

STEM ANATOMY AND ASPECTS OF DEVELOPMENT IN TOMATO

Aspects of anatomical development were correlated with internodal growth in tomato plants, variety ‘Yellow Plum,’ grown for more than 3 months. Internodal length was measured weekly in control plants and those harvested for anatomical study. Gross structure indicated progressive development with increasing age. Primary xylem and phloem first mature in distinct strands and the strands are joined laterally by procambium to form a continuous vascular cylinder. Primary phloem occurs on the outer periphery of the procambium between the early-formed vascular strands. Successive periclinal divisions in the procambium during internode elongation give rise to pronounced radial seriations of the cells. Procambial derivatives are included in the cylinder of thick-walled, lignified vascular cells that become prominent after elongation ceases. Secondary xylem is of greater radial width in the stem sectors which include protoxylem. During early secondary growth, vessels develop in the secondary xylem only in these sectors. Nucleate fibers and rays constitute the remainder of the secondary xylem. The rays exhibit an organization noted in other plants of reduced growth habit. Some of these interpretations do not agree with those described for tomato in earlier studies, and they are discussed in relation to pertinent aspects of development.     

AN ANALYSIS OF THE GROWTH RESPONSE OF YOUNG TOMATO PLANTS TO INFECTION BY VERTICILLIUM ALBO-ATRUM: II. THE PRODUCTION OF GROWTH SUBSTANCES

Bioassays on ether-soluble acid extracts from healthy and Verticillium -infected tomato plants, showed the presence of substances inhibiting growth of wheat coleoptiles in both healthy and infected leaves and stems, but the amounts were greater in the infected.
Assays of infected stems and leaves showed increases in growth-promoting activity expressed as indole-3-acetic acid equivalents (IAAe), up to 200% of those for healthy controls.
Similar assays of cultures of V. albo-atrum showed growth-promoting activity. No acid substance capable of inhibiting the growth of wheat tissue was detected in the culture filtrate. IAA was identified by colour test with Ehrlich's reagent on chromatograms from extracts of both infected stems and fungal culture filtrates.
The vertical distribution of IAAe was determined in healthy and infected plants at the eight-leaf stage by assaying individual leaves and four stem segments separately. In healthy plants the IAAe content was greatest in the young leaves (6–8) but no gradient was observed as between leaves 1–5. In infected leaves increases over the controls were found in leaves, 1, 3 and 6 and a decrease in leaf 8.
In healthy stems IAAe was highest in the distal segment and infected stems showed higher values at all four levels, with the relative increase greatest in the distal region.
It is suggested that the major part of the Verticillium syndrome including petiolar epinasty, tylosis, pith hyperplasia and the formation of adventitious roots is the result of an accumulation of growth substances in infected tissue.     

SOME EFFECTS OF HOST-PLANT NUTRITION ON THE MULTIPLICATION OF VIRUSES

The amounts of tobacco mosaic virus present in systemically infected tobacco plants varied greatly with the mineral nutrition of the plants and were related to the effects on plant growth. With plants in soil, supplements of phosphorus produced the greatest increases in plant size, in virus concentration of expressed sap, and in total virus per plant; nitrogen increased plant size only when phosphorus was also added, and only then increased virus concentration and total virus per plant. Combined supplements of phosphorus and nitrogen doubled the virus concentration of sap and increased the total virus per plant by factors up to forty. Potassium slightly reduced the virus concentration of sap, though it usually increased plant size and total virus per plant. From all plants, only about one-third of the virus contained in leaves was present in sap. Virus production seemed to occur at the expense of normal plant proteins, and the ratio of virus to other nitrogenous materials was highest in plants receiving a supplement of phosphorus but not of nitrogen.
The effects of host nutrition on the production of virus in inoculated leaves resembled those in systemically infected leaves, but were more variable.
No evidence was obtained, with plants grown in soil or sand, that host nutrition had any consistent effect on the intrinsic infectivity of tobacco mosaic virus.
The concentration of virus in sap from potato plants systemically infected with two strains of potato virus X was not consistently affected by fertilizers; the chief effect of host nutrition on virus production was indirect by altering plant size.     

Some effects of supplying benzyladenine to leaves and plants inoculated with viruses

With tomato spotted wilt virus in petunia leaf strips, N-6 benzyladenine (BA) was as effective as kinetin in decreasing numbers of local lesions, a result which could not be attributed to an effect on the virus per se. Benzimidazole, adenine and ammonium nitrate were without effect. Benzyladenine was more effective than kinetin when supplied through the petioles of excised whole leaves. Local lesions and infectivity of TSWV in detached leaves of Nicotiana rustica were decreased by supplying BA before and after inoculation. Lesions and infectivity were also decreased in attached leaves when BA was applied 9 days before inoculation. BA supplied to attached leaves after inoculation increased infectivity. Supplying BA to the lower leaves of tomato plants before inoculating with TSWV decreased infectivity of unsprayed, systemically infected tip leaves taken as inoculum; BA supplied after inoculation increased infectivity. Local lesions caused by lucerne mosaic virus in excised leaves of Phaseolus vulgaris were decreased in number by supplying BA. The effects of pre- and post-inoculation sprays of BA are considered in relation to cell metabolism. Since pretreating leaves with kinins did not prevent infection, it is suggested that those which move freely through plants without adverse effects on normal growth may prove of value in increasing the tolerance of plants to virus infection.     

THE PROPERTIES OF TOMATO ASPERMY VIRUS AND ITS RELATIONSHIP WITH CUCUMBER MOSAIC VIRUS*

Chrysanthemum plants infected with tomato aspermy virus (TAV) produce severely distorted and discoloured flowers but show only slight leaf mottle.
TAV infected twenty-five of forty-five species (belonging to seventeen genera) tested and was transmitted by the aphid species Aulacorthum solarti, Macrosiphoniella sanborni and Myzus persicae .
Sap from infected tobacco leaves lost infectivity when diluted more than 1 in 10,000, when heated for 10 min. at above 65°C. and when stored for more than 42 hr. at 16–18°C.
Partial protection was obtained between TAV and two strains of cucumber mosaic virus. Evidence was obtained that this was true protection between related viruses and serological tests confirmed the view that TAV is a strain of cucumber mosaic virus. Evidence was obtained that this was true protection between related viruses and serological tests confirmed the view that TAV is a strain of cucumber mosaic virus.     

Metabolic disturbances innicotiana glauca,a symptomless

Metabolic disturbances inNicotiana glauca, a symptomless carrier of potato witches’ broom were studied. The dry weight content of leaves of diseased plants was slightly decreased, that of the stems increased. The ash content in the dry weight of the whole diseased plant was decreased by 11%. Contrary to tomato plants which had shown considerable disproportions in the distribution of metabolites among the individual organs investigated (ULRYCHOVÁ, LIMBERK 1964), the content of the total nitrogen and of the individual nitrogen fractions of both leaves and stems of diseasedNicotiana glauca were decreased. The content of glutamine was increased in both organs in spite of the decrease of ammonia nitrogen by nearly 30% in both cases. The most striking disturbance found in the diseased plants ofNicotiana glauca was the 67% increase of a low-molecular phosphorus fraction (P extractable with 0-2N HCIO₄) in the leaves. This result agrees with that found in diseased tomato plants and may be primarily associated with the virus infection. The content of all other phosphorus fractions of both leaves and stems was decreased.     

THE RESPIRATION OF TOBACCO LEAVES AFTER SYSTEMIC INFECTION WITH TOBACCO MOSAIC VIRUS

The rate of CO, production per g. dry matter of the younger leaves of tobacco plants systemically infected with tobacco mosaic virus was about 10 yo less than that of comparable healthy leaves. Older infected leaves, showing well-developed mosaic symptoms, had the same respiration rate as comparable healthy leaves. These results were independent of seasonal change in light conditions during the growth of the plants. Older leaves, but not younger leaves, of infected plants had a lower initial water content, and both absorbed less water during the experimental period, than leaves from healthy plants. The effects of TMV infection on water content were so great that the rate of CO, production per g. fresh weight was sometimes significantly increased by infection. This reversal of the apparent effect of infection on respiration rate, depending on the basis of reference may partly account for contradictory results reported previously by other workers. Other causes for contradictory results are discussed.