A Low Temperature Therapy and Meristem-Tip Culture for Eliminating four Viroids from Infected Plants

Viroid-free potato and chrysanthemum plants were obtained from meristem-tips cut from potato spindle tuber viroid-infected potato plants and from chrysanthemum plants infected with chrysanthemum stunt, chrysanthemum chlorotic mottle or cucumber palefruit viroids after 6 months therapy in a growth chamber at 5 °C and 16 hours daily light of 5.000 lx intensity. Chrysanthemum plants survived quite well the conditions of therapy while potato plants grown from stem cuttings survived these conditions much worse and potato plants grown from tubers did not survive these conditions. PSTV-free plants were obtained from meristem-tips cut from sprouts grown from potato tubers infected with severe (s-PSTV) or mild (m-PSTV) strains of potato spindle tuber viroid after 6 months therapy at 6–7 °C in the dark. The tubers survived these conditions quite well. The 3 months therapy period was found too short for any plant material. The efficiency of 6 months therapy in viroid elimination varied for different viroids and different plant material from 18.5 to 80.0 %.     

Some properties of chrysanthemum stunt, a virus with the characteristics of an uncoated ribonucleic acid

Grafting to virus-free Mistletoe chrysanthemums was the most reliable method of detecting the chrysanthemum stunt agent, but specific light and temperature conditions were required for the diagnostic ‘measles’ symptoms to develop. Although stunt agent was highly infectious, leaf-rubbing inoculations with chrysanthemum sap gave erratic results. Colorimetric and electrophoretic tests were unreliable for indexing chrysanthemums. Stunt agent infected eight of twenty-nine species in the family Compositae, but none of 116 species in forty-seven other families. Stunt spread rapidly by foliage contact and by handling plants, but dipping the hands in 2% trisodium orthophosphate when handling plants increased the amount of spread. Stunt agent was not transmitted by four species of aphids, the glasshouse redspider mite, dodder (Cuscuta campestris) or through chrysanthemum seed. Stunt agent withstood 10 min at c. 98 °C and dilution to 10^-4, was not pelleted by ultracentrifugation, and was inactivated by RNase in weak, but not strong, buffer, suggestive of an uncoated RNA ‘viroid’. Partially purified preparations were made by homogenizing frozen chrysanthemum leaves in 0.5 m phosphate buffer with antioxidant at c. 2 °C, and clarification by n-but-anol and chloroform, followed by centrifugation. Highly infective RNA was precipitated from the supernant fluid by 2.5 vol. cold ethanol, and resuspended in a small volume of buffer. The u.v. absorption spectra of infective preparations and the u.v. absorbance profiles of density-gradients, were very similar to those of preparations from healthy chrysanthemum. Infective partially purified preparations of stunt agent withstood exposure to 2% formaldehyde or tri-sodium orthophosphate, u.v. irradiation, and sonication. Stunt preparations contained no virus particles recognizable by electron microscopy, gave no distinct peak on analytical ultracentrifugation, and did not consistently contain any specific antigen. Although similar to the ‘viroids’ potato spindle tuber and citrus exocortis, stunt agent did not infect Citrus limon, Gynura aurantiaca or tomato.     

Studies on the occurrence of tomato bushy stunt virus in English rivers

Tomato bushy stunt virus (TBSV) of unknown source was isolated from water of the River Thames, near Oxford. The isolate designated TBSV-T was mechanically transmissible to several tomato (Lycopersicon esculentum) cvs and to other species including Petunia hybrida, pepper (Capsicum annuum). eggplant (Solanum melongena), Nicotiana clevelandii, Chenopodium amaranticolor and C. quinoa in which it caused systemic symptoms. It caused no infection of globe artichoke (Cynara scolymus) or Pelargonium domesticum. The virus was not adsorbed to soil and could be isolated from leachate of soil in which systemically-infected tomato or C. quinoa plants were grown. Tomato plants became infected when grown in soil watered with virus suspensions. TBSV-T was infective after 10 min at 80°C but not at 90°C and when diluted to 10^-5 but not to 10^-6. Purified virus preparations contained C. 30 nm isometric particles. In gel-diffusion serological tests, TBSV-T reacted with homologous anti-serum and with antiserum to petunia asteroid mosaic virus but not to pelargonium leaf curl virus. Seed-borne infection (50–65%) of TBSV was demonstrated in plants grown from seed of symptomlessly-infected tomato fruit. TBSV was isolated from symptomlessly-infected tomato fruit imported from Morocco during October-April 1981. One of the isolates (TBSV-M) was indistinguishable from TBSV-T in host range, symptomatology and serological reactions. TBSV was also found in tomato plants growing extraneously in primary settlement beds at sewage works; such plants having been derived from undigested seeds in sewage. Because of its ‘alimentary-resistance’ in man, it is possible that one ecological route whereby TBSV enters rivers is by man's consumption of TBSV-infected tomatoes and eventual sewage dispersal into rivers.     

Viruses Associated with a Mosaic Disease of Crotalaria juncea in Nigeria

Cowpea mosaic virus was one of the viruses isolated from Crotalaria juncea showing mosaic, distortion and puckering symptoms. The virus induced local necrotic lesions in Canavalia ensiformis, Cassia occidentalis, Nicotiana debneyi, N. occidentalis, N. repanda and N. sylvestris and some cultivars of Phaseolus vulgaris 4–6 days after inoculation. It induced local chlorotic spots, which later became necrotic, as well as systemic chlorotic spots, vein chlorosis, distortionand puckering in Chenopodium amaranticolor. Sap from systemically infected cowpea cv. ‘C20-55’was infective after dilution to 10^?5 but not 10^?6, after 10 min at 65°C but not 70°C, or after 4 days, but not 5 days, at a room temperature of 15–25°C. Infectious virus was recovered from fresh reproductive tissues of infected cowpea cvs ‘C20-55’and ‘Ife Brown’ plants but not after dehydration.     

Phytophthora cryptogea root rot of tomato in rock woo] nutrient culture. II. Effect of root zone temperature on infection, sporulation and symptom development

The effect of root-zone temperature on Phytophthora cryptogea root rot was studied in tomato cv. Counter grown under winter and summer conditions in rockwool culture. A nutrient temperature of 25°C resulted in increased root initiation and growth, higher in winter-grown than in summer-grown plants. Rhizosphere zoospore populations were greatly reduced at 25°C and above. Growth of P. cryptogea in vitro was optimal between 20°C and 25°C and completely suppressed at 30°C. Encystment was enhanced by increased temperatures above 20°C. Zoospore release in vitro occurred in cultures maintained at constant temperatures in the absence of the normal chilling stimulus. Optimal release was at 10°C; no zoospores were released at 30°C. Inoculated, winter-grown tomato plants maintained at 15°C developed acute aerial symptoms and died after 21 days. Comparable plants grown at a root-zone temperature of 25°C remained symptomless for the 3-months duration of the experiment. Summer-grown infected plants at the higher root temperature wilted but did not die. Enhanced temperature was ineffective as a curative treatment in summer-grown plants with established infection. Aerial symptoms of Phytophthora infection are seen as a function of the net amount of available healthy root. With high root zone temperatures this is determined by new root production and decreased inoculum and infection.     

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.     

Growth at 37°C of the EGs strain of the amoeboflagellate Naegleria gruberi containing viruslike particles. II. Cytoplasmic changes

The EG_s strain of the amoeboflagellate Naegleria gruberi contains viruslike particles (VLP) apparently responsible for the development of cytoplasmic structures in infected cells. Growth of amoebae at 37°C produced changes in the normal pattern of development of the cytoplasmic units. Structures referred to as bacterium-like bodies, which developed in infected amoebae grown at 21°C, did not form at the elevated temperature. Amoeba cytoplasm at the elevated temperature exhibited regions of varying densities and bundles of microtubule-like fibrils. Presumed transmissive stages which were seen in cells grown at 21°C were not formed at 37°C. These changes are of significance in that they parallel cytoplasmic changes in cytopathic chick embryo fibroblasts exposed to lysates made from VLP-infected cultures of amoebae.     

Carnation Italian ringspot virus

Carnation Italian ringspot virus (CIRV) was obtained only twice in tests on several thousand carnations in Britain during 15 yr. The two isolates, from cultivars ‘Dusty Sim’ imported from Italy and ‘Orchid Beauty’ from the U.S.A., were indistinguishable serologically and in host reactions. CIRV was cultured in Nicotiana clevelandii and assayed in Chenopodium amaranti-color; it was readily transmitted by leaf-rubbing inoculation to 62 of 104 plant species tested. Virus-free carnations were infected only by injecting purified preparations into the stem, and developed chlorotic spots and oval rings in the younger leaves. CIRV was eliminated from Nicotiana clevelandii plants grown for 8 weeks at 36°C. CIRV presents no threat to carnation growing in Britain. In N. clevelandii sap, CIRV was infective at a dilution of 1/50000 to 1/100000, after heating 10 min at 85 °C (but not 90 °C), and after 16 weeks at 16 °C or 23 weeks at 2 °C. After freeze-drying, the virus survived at least 7 yr storage under vacuum at room temperature. CIRV was still infective and antigenic after treatment for 30 min at 18 °C with ultraviolet radiation (750 μW/cm²), ultrasound, 2% formaldehyde or 0.2% tri-sodium ortho-phosphate (TSP). Infectivity was not wholly abolished in 30 min by 2% TSP. The virus was readily purified by overnight maceration of N. clevelandii leaves extracted in phosphate buffer + butanol, followed by differential centri-fugation. Purified preparations contained abundant isometric particles c. 29 nm diameter, and like other serotypes of the tomato bushy stunt-pelargonium leaf curl group, gave three or four specific bands in density-gradient centri-fugation. The bands corresponded to four Schlieren peaks in analytical centrifugation. Virus from the lower bands was usually less invasive in N. clevelandii than from the upper bands, although the material in the different bands contained similar amounts of nucleic acid. Only one antigenic component was found by Immunoelectrophoresis; different serotypes of the TBSV-PLCV group differed widely in immunoelectrophoretic behaviour. The present cryptogram of CIRV is */*:*/*:S/S:S/*.     

Nuclear DNA content as an indicator of inflorescence colour stability of in vitro propagated solid and chimera mutants of chrysanthemum

In chrysanthemum, breeders seek for desirable characteristics of the inflorescence, which can first be established once the plant is mature. The present study aims to determine whether measurement of DNA content can be useful in the detection of somaclonal variants and/or separation of chimera components in chrysanthemum at the early in vitro multiplication stage. Eleven Chrysanthemum?×?morifolium (Ramat.) Hemsl. cultivars of the Lady group (a mother cultivar and ten of its radiomutants obtained by X-ray- or γ-irradiation; solid and periclinal chimeras) were propagated in vitro. Single-node explants were cultured in Murashige and Skoog (MS) medium, either without plant growth regulators (PGRs) or supplemented with 6-benzyladenine (BA) and indole-3-acetic acid (IAA). The nuclear DNA content was measured by flow cytometry (FCM) in the shoots produced in vitro. After acclimatization and growth of the plants in a glasshouse, inflorescence colour was recorded. The addition of PGRs to the medium almost doubled the mean number of shoots produced in vitro per explant, but caused a change in inflorescence colour of all (‘Lady Apricot’; periclinal chimera) or part of the plants (‘Lady Amber’; solid mutant and ‘Lady Salmon’; periclinal chimera). All radiomutants contained less DNA than the mother cultivar ‘Richmond’. There were significant differences in DNA content between plants of the same cultivar grown in media with or without PGRs for ‘Lady Apricot’ and ‘Lady Salmon’, but no phenotype alternation occurred in chrysanthemums produced in PGR-free medium compared to the original cultivars. Conversely, in medium with PGRs, chimeras produced flowers different from the original colour. In all except one cultivar (‘Lady Amber’; solid mutant) a lack of differences in genome size between plants grown in either medium coincided with a stable inflorescence colour. The occurrence of some plants of ‘Lady Amber’ with different inflorescence colour may be due to small DNA changes, undetectable by FCM. It can be concluded that FCM analysis of DNA content in young plantlets can be indicative of the stability of inflorescence colour in chrysanthemum, especially chimeric cultivars, and for mutant detection.

     

Elimination of Mycoplasma-like Organisms from Witches' Broom Infected Sweet Potato

The witches' broom disease of sweet potato has so far been reported only from Asia and the South Pacific. To insure safe distribution of germplasm it is important that vegetative material introduced from regions in which this disease is present has to be free of this pathogen. Meristem tip culture was found to be effective in eliminating MLO from infected sweet potato tissue. On the other hand, all plantlets originating from 1 cm long stem tips immediately below the meristems developed typical witches' broom symptoms as early as 5 weeks after excision of the stem tips. A high percentage of stem tips originating from cuttings previou.sly treated with 25, 50 and 100 mg tetracycline for 3 days developed into healthy plants. Similarly, more than 90 % of plants derived from stem tips excised from cuttings which had received a one-month heat treatment at 37°C remained without symptoms for 9 months.     

Induction of male sterility in transgenic chrysanthemums (Chrysanthemum morifolium Ramat.) by expression of a mutated ethylene receptor gene, Cm-ETR1/H69A, and the stability of this sterility at varying growth temperatures

Chrysanthemum (Chrysanthemum morifolium Ramat.) is one of the most popular ornamental flowers in the world, and many agronomic traits have recently been introduced to chrysanthemum cultivars by gene transformation. Concerns have been raised, however, regarding transgene flow from transgenic plants to wild plants. In early studies, ethylene receptor genes have been used for genetic modification in plants, such as flower longevity and fruit ripening. Recently, overexpression of ethylene receptor genes from melon (CmETR1/H69A) caused delayed tapetum degradation of the anther sac and a reduction in pollen grains. We therefore introduced the ethylene receptor gene into chrysanthemums to induce male sterility and prevent transgene flow via pollen. The chrysanthemum cultivar Yamate shiro was transformed using a disarmed strain of Agrobacterium tumefaciens, EHA105, carrying the binary vector pBIK102H69A, which contains the CmETR1/H69A gene. A total of 335 shoots were regenerated from 1,282 leaf discs on regeneration medium (26.1%). The presence of the Cm-ETR1/H69A gene was confirmed in all of the regenerated plantlets by Southern blot analysis. These genetically modified (GM) plants and their non-GM counterparts were grown in a closed greenhouse and flowered at temperatures between 10 and 35°C. In 15 of the 335 GM chrysanthemum lines, the number of mature pollen grains was significantly reduced, particularly in three of the lines (Nos. 91, 191 and 324). In these three lines, pollen grains were not observed at temperatures between 20 and 35°C but were observed at 10 and 15°C, and mature pollen grains were formed only at 15°C. In northern blot analyses, expression of the CmETR1/H69A gene was suppressed at low temperatures. This phenomenon was observed as a result of both the suppression of CmETR1/H69A expression at low temperatures and the optimal growth temperature of chrysanthemums (15–20°C). Furthermore, the female fertility of these three GM lines was significantly lower than that of the non-GM plants. Thus, the mutated ethylene receptor is able to reduce both male and female fertility significantly in transgenic chrysanthemums, although the stability of male and/or female sterility at varying growth temperatures is a matter of concern for its practical use.     

The Effect of Temperature on Symptom Expression and Colonization in Resistant and Susceptible Carnation Cultivars Infected with Fusarium oxysporum f. sp. dianthi

Six commercial carnation cultivars were inoculated with Fusarium oxysporum f. sp. dianthi race 2, and grown under three different temperature regimes. Colonization by the pathogen and development of wilt symptoms were assessed at intervals up to 40 days. No symptoms and very little colonization were seen in any of the cultivars at 14–15°C. At a temperature of 22°C, the cultivars were clearly differentiated into three groups: those with resistance, partial resistance or susceptibility to the pathogen depending on the severity of symptoms and the extent of fungal colonization. Symptom severity was associated with the extent of colonization. This differentiation was not seen at 26°C, when all cultivars except the most resistant, cv.‘Carrier 929′, rapidly became diseased and died by 23 days after inoculation. ‘Carrier 929’ also showed some wilt symptoms at this temperature and was colonized throughout the height of the stem after 40 days. The pathogen caused disease at 26°C by a combination of vascular wilting and stem base and root rotting. Fungal colonization was assayed at 22°C by the dilution plate/homogenization method and by estimation of fungal chitin in a highly resistant (‘Carrier 929′) and in a highly susceptible (‘Red Baron’) cultivar. Both methods of assay gave similar results. In ‘Red Baron’, colonization increased slowly up to 20 days after inoculation then progressed rapidly, closely following the development of severe wilt symptoms. In ‘Carrier 929’, colonization remained very low. The low level of fungal biomass in ‘Carrier 929’ compared with ‘Red Baron’ indicated that the former cultivar showed true resistance as opposed to tolerance to the disease.     

A Comparative Study of Four Viroids of Plants

The host-ranges and the reactions of particular plant hosts to inoculation with severe (s-PSTV) and mild (m-PSTV) strains of potato spindle tuber viroid, as well as with chrysanthemum stunt viroid (CSV) and cucumber pale fruit viroid (CPFV) were quite similar. Some minor differences did not exceed the limits of differences noted for the strains of the same plant viroid. Two-directional crossprotection was noted for each viroid pair when s-PSTV, m-PSTV, CSV and CPFV were tested on chrysanthemum cv., ‘Bonnie Jean’ plants. Finally, the relative mobility of RNAs of s-PSTV, m-PSTV, CSV and CPFV on 5% polyacrylamide gel was identical, no matter what extraction method from plant material was used. We postulate that these four plant viroids may be regardedas the strains of the same plant viroid “species”. On the other hand, chrysanthemum chlorotic mottle viroid (ChCMV) appeared to be a quite different plant pathogen. This viroid infected and caused symptoms only in chrysanthemum plants, and was able to infect and induce symptoms on plants which had already been infected with any other viroid studied, and it did not protect chrysanthemum cv. ‘Bonnie Jean’ plants against any of the other viroids. We were not able to locate a ChCMV-RNA band on polyacrylamide gel.     

Temperature interactions with transpiration response to vapor pressure deficit among cultivated and wild soybean genotypes

A key strategy in soybean drought research is increased stomatal sensitivity to high vapor pressure deficit (VPD), which contributes to the ‘slow wilting’ trait observed in the field. These experiments examined whether temperature of the growth environment affected the ability of plants to respond to VPD, and thus control transpiration rate (TR). Two soybean [Glycine max (L.) Merr.] and four wild soybean [Glycine soja (Sieb. and Zucc.)] genotypes were studied. The TR was measured over a range of VPD when plants were growing at 25 or 30°C, and again after an abrupt increase of 5°C. In G. max, a restriction of TR became evident as VPD increased above 2.0 kPa when temperature was near its growth optimum of 30°C. ‘Slow wilting’ genotype plant introduction (PI) 416937 exhibited greater TR control at high VPD compared with Hutcheson, and only PI 416937 restrained TR after the shift to 35°C. Three of the four G. soja genotypes exhibited control over TR with increasing VPD when grown at 25°C, which is near their estimated growth optimum. The TR control became engaged at lower VPD than in G. max and was retained to differing degrees after a shift to 30°C. The TR control systems in G. max and G. soja clearly were temperature‐sensitive and kinetically definable, and more restrictive in the ‘slow wilting’ soybean genotype. For the favorable TR control traits observed in G. soja to be useful for soybean breeding in warmer climates, the regulatory linkage with lower temperatures must be uncoupled.     

Effects of high temperature on nodulation and nitrogen fixation by Phaseolus vulgaris L.

Screening of Rhizobium leguminosarum bv. phaseoli strains showed some that were able to nodulate common beans (Phaseolus vulgaris L.) at high temperatures (35 and 38°C/8 h/day). The nodulation ability was not related to the capability to grow or produce melanin-like pigment in culture media at high temperatures. However, nodules formed at high temperatures were ineffective and plants did not accumulate N in shoots. Two thermal shocks of 40°C/8 h/day at flowering time drastically decreased nitrogenase activity and nodule relative efficiency of plants otherwise grown at 28°C. Recovery of nitrogenase activity began only after seven days, when new nodules formed; total incorporation of N in tops did not recover for 2 weeks. Non-inoculated beans receiving mineral N were not affected by the thermal shock, and when growing continuously at 35 or 38°C had total N accumulated in shoots reduced by only 18%.     

Effects of Temperature on Disease Severity in Plants of Subterranean Clover Infected Singly or in Mixed Infection with Bean yellow mosaic virus and Kabatiella caulivora

Many epidemics involve plants infected with more than one pathogen, but few experiments address climate change scenarios that influence mixed infections. This study addresses the interactive effects of co‐infection and temperature on disease development in plants of the annual pasture species subterranean clover (Trifolium subterraneum), which is widely sown in different world regions. Bean yellow mosaic virus (BYMV) and the fungus Kabatiella caulivora are two important pathogens causing considerable production losses in pastures containing this species. Both occur together in such pastures causing a severe necrotic disease when mixed infection occurs. Effects of temperature on symptom expression were investigated in subterranean clover plants infected singly or in mixed infection with these pathogens. Plants were maintained in controlled environment rooms at 18°C, 20°C or 22.5°C after sap inoculation with BYMV. K. caulivora conidia suspensions were inoculated to plants once systemic BYMV symptoms developed. Plants were assessed for three disease assessment parameters, dead petioles numbers, marginal leaflet necrosis and overall plant damage. In general, mixed infection caused most severe symptoms, K. caulivora least severe symptoms, and BYMV symptoms of intermediate severity. In single infections, effects of temperature on disease severity differed between pathogens: BYMV symptoms were most pronounced at 18°C, but K. caulivora induced more severe symptoms at 20°C and 22.5°C. In mixed infections, disease severity generally followed the pattern developed with BYMV alone as temperature increased. Also, synergistic increase in disease severity sometimes occurred at 18°C, but increases were only additive at 20°C and 22.5°C. These results reflected the greater BYMV multiplication detected in infected leaves at 18°C compared with 20°C or 22.5°C. Our findings indicate that in rainfed subterranean clover pastures, as global warming progresses disease severity from infection with BYMV and K. caulivora alone may decline or increase, respectively, and mixed infection with them may become less damaging.     

The effect of temperature on the uptake and loss of anions by seedling roots ofZea mays L

Intact maize seedlings were examined for the uptake and leakage of labelled sulphate and phosphate anions affected by temperature. Control plants, grown at 25 °C were compared from the aspects of uptake capacity and leakage with plants incubated in nutrient solutions cooled to 15 °C and 5 °C, respectively. Short time intervals as well as 1–7 d exposure to cooling were used. Already after 1 h exposure at 5 °C and 5 h cooling at 15 °C and at 5 °C, considerable changes were manifested in anion uptake and leakage. The uptake of³²P declined more than that of³⁵S. So, after a 30 min uptake interval the uptake of³⁵S decreased at 15 °C to 49.84% and at 5 °C to 6.05% comparing with the uptake at 25 °C, while the uptake of³²P declined to 28.64% at 15 °C and to 4.45% at 5 °C. The leakage of both anions was the highest at 25 °C in absolute rates, but relatively most of the uptaken³⁵S and³²P was released at 5 °C. Longer exposure to a chilling temperature of 5 °C (1–7 days) resulted in two patterns of sulphate and phosphate uptake.     

Temperature effects on the response to sulphur of barley,peas and rape

Summary The effects of temperature and sulphur nutrition on the growth, yield and mineral composition (N, NO₃-N, S and SO₄-S) ofHordeum vulgare L. cv Olli,Pisum sativum L. cv Dark Skin Perfection, andBrassica campestris L. cv Arlo, were investigated in controlled environments. When barley and rape plants were grown at O ppm S, deficiency symptoms developed in about two weeks, whereas peas at the same level developed deficiency symptoms in about three weeks. The location of the deficiency symptoms varied between species. Plant weight increased with increasing S levels, but the shoot had a greater growth response than did the root. Optimum day/night growing temperature regimes for barley and peas were found to be near 24/16 at four weeks from seeding and near 18/10°C at the mature stage as evident from weights, maximum fruit set and mineral uptake. Optimum temperature for rape plants was near 29/21°C at both stages of growth. Mineral concentration was higher at four weeks after seeding than at the mature stage in pea and rape plants, while in barley the mineral concentration was similar at both stages of growth. With increase in S supply there was an increase in concentration of both total S and SO₄-S. Concentrations also increased with increasing temperatures. S deficient plants had increased total N and NO₃-N concentrations in all three species. NO₃-N concentration also increased with an increase in temperature while total N concentration was not appreciably influenced. These experiments indicated that the effects of S nutrition on growth, development and mineral composition of plants depends on the species, temperature regime and growth stage     

Some effects of time,temperature and feeding on infection rates with Babesia bovis and Babesia bigemina in Boophilus microplus larvae

Dalgliesh R. J. and Stewart N. P. 1982. Some effects of time, temperature and feeding on infection rates with Babesia bovis and Babesia bigemina in Boophilus microplus larvae. International Journal for Parasitology12: 323–326. Percentages of larval ticks in which Babesia bovis and B. bigemina parasites could be detected (infection rates) were determined after the larvae had been exposed to temperatures between 9°C and 27°C for periods of 1–35 days and then either fed on calves or heated at 37°C to stimulate babesial development. Infection rates with both species increased during 2–4 weeks after the larvae hatched, regardless of the temperature of exposure. Infection rates with B. bovis were higher after exposure of larvae to 14°C than to 27°C. This effect was less pronounced with B. bigemina. Infection rates were higher in fed larvae than in unfed, ‘heat stimulated’ larvae. The findings indicate that infected larval ticks become more efficient vectors of Babesia during the first 2–4 weeks after hatching and that repeated sampling of a tick population is necessary to determine valid infection rates.