Relationship between Colour, Phenolic Content and Impermeability in the Seed Coat of various Trifolium subterraneum L. genotypes

The relationship between seed colour, phenol content of thetesta and water impermeability in dark and light seeded genotypesof Trifolium subterraneum L. was investigated. The developmentof water impermeability and catechol oxidase activity in expandingseeds of two genotypes was monitored. The results show catecholoxidase activity decreases as seed colour changes from greento purple, but the potential to become impermeable with dehydrationis not acquired until later in seed development. Both waterpermeable and impermeable seeds of dark coloured genotypes containsubstantial amounts of phenol in the lumen of the Malpighiancells; light coloured testas do not. It is concluded that the darkening of the testa of Trifoliumsubterraneum is associated with oxidation of phenol by catecholoxidase but that development of impermeability is independentof this process. Trifolium subterraneum L., subterranean clover, seed coat impermeability, catechol oxidase, phenol, testa colour     

Effects of Some Metabolic Phosphorus Compounds on Rates of Photosynthesis of detached Phosphorus-deficient Subterranean Clover Leaves

Rates of photosynthesis (net CO₂ uptake in saturating light)of leaves sampled from phosphorusdeficient subterranean cloverplants (Trifolium subterraneum L. cv. Mt. Barker) were lowerthan those of non-deficient leaves. When comparable deficientleaves were placed in solutions containing 0.13 mM P_i¹, therewere no responses in photosynthesis, even though earlier resultshad established these solutions as optimal for responses forintact deficient plants. Deficient leaves, placed for the first12 h after detachment in solutions of increasing P_i¹ concentrations(0.15, 0.70, 2.0, and 6.0 mM) and then in distilled water, showedmarked increases in photosynthesis in the three higher phosphatetreatments on the first day after detachment. During the following6 d the decline in photosynthesis was less the higher the initialphosphate treatment. By contrast, non-deficient leaves in thesame treatments showed a decline in photosynthesis with increasingphosphate levels, due to leaf damage in the two highest treatments(phosphorus toxicity). Rates of photosynthesis of deficient leaves kept for 3 h in3 or 6 mM FDP¹ or G-6-P¹ increased within 24 h and remainedhigher than those for corresponding leaves in 0.13 mM P_i ordistilled water. There were no differences between the sametreatments for non-deficient leaves, thus enabling a clear distinctionbetween leaves that were deficient and those that were not.There was no leaf damage in these solutions, even after 48 h.AMP¹ or ADP¹ had no effect. ATP¹ and 3-PGA¹ caused toxicitysymptoms. Fructose itself (6 mM) had no effect on photosynthesis.     

Functional Manganese Requirement and its use as a Critical Value for Diagnosis of Manganese Deficiency in Subterranean Clover (Trifolium subterraneum L. cv. Seaton Park)

The effects of manganese supply on plant growth and on photosynthesisand manganese concentrations in young leaves were examined inSeaton Park subterranean clover in three glasshouse water cultureexperiments. Plants werc grown initially with a copious supply of manganese,and transferred to solutions either with or without manganese.Sequential harvests were taken to determine the effects of developingmanganese deficiency on dry matter (DM) yield of whole plantsand selected characteristics [manganese, chlorophyll and photosyntheticoxygen evolution (POE)] of youngest open leaf blades (YOL).In addition, the deffect of leaf age and iron supply on POEwerc examined. Manganese concentrations and POE in YOL declined markedly andrapidly in plants transferred to solutions without manganese,while chlorophyll concentrations of YOL and plant DM yield respondedmore weakly and more slowly. As a result, a level of manganesedeficiency which depressed POE in young leaves by more than50 per cent had no effed on DM production. In youngleaves (YOL, YOL + 1, YOL–1), POE declined whentheir manganese concentrations were < 20 µg g^–1DM. Iron supply did not affect this rdationship. When learnwith < 20 µg Mn g^–1 DM were detached and incubatedfor 24 h in solutions containing high concentrations of manganese,their POE increased to normal rates; leaves with higher manganeseconcentrations did not respond. It is suggested that the valueof 20 µg Mn g^–1 DM is the functional manganese requirementfor POE in young subterranean clover leaves It is also suggestedthat this value may be used as a critical value for indicatingmanganese deficiency in subterranean clover. Functional nutrient requirements determined in this way by correlationof nutrient concentrations in young leaves with their biochemicalor physiological activities appear to offer more accurate andconsistent standards for use an critical values for diagnosisof plant nutrient status than do the critical values determinedin the usual way by correlation with plant dry weight. Trifolium subterraneum L. subterranean clover, manganese, functional requirements, deficiency diagnosis, nutrient requirements, critical values, photosynthetic oxygen evolution     

Some Effects of Potassium and Magnesium on the Growth of Subterranean Clover (Trifolium subterraneum)

Subterranean clover plants (Trifolium subterraneum L., cv. Mt.Barker) were grown in culture solutions at optimum nutrientlevels and on the 23rd day after sowing transferred to solutionswithout magnesium or potassium. A third group remained at thesame nutrient levels as before (controls). Magnesium deficiency caused a particularly rapid decline inroot growth, followed later by a net loss of root dry matter.This, and the fact that leaf expansion declined relatively morethan the increase in laminae dry matter, resulted in an accumulationof assimilates per unit leaf area. Transfer of magnesium-deficientplants to complete solutions on day 35 caused a preferentialdistribution of dry matter to the roots, then to petioles andrelatively less to the laminae. These changes caused a pronouncedfall in the root: shoot ratio as the deficiency became moresevere and a rise in the ratio during recovery. Plants in solutions without potassium showed no marked shiftsin dry matter distribution between plant parts. The root: shootratio remained close to that for control plants, except duringthe recovery, when there was a decrease in the ratio. Net rates of CO₂ uptake by laminae from potassium-deficientplants showed little change during the first 10 days of thedeficiency although values were somewhat lower than those forcorresponding control laminae. After transfer to complete solutionsthere was a marked response in photosynthesis, rising to a finalvalue close to that for control laminae. Laminae of plants placedin solutions without magnesium showed a rapid decline in photosynthesisonly 4 days later; there was little response when plants weretransferred to complete solutions a week later. Trifolium subterraneum L., subterranean clover, growth, root: shoot ratio, potassium deficiency, magnesium deficiencies     

Regrowth by Swards of Subterranean Clover after Defoliation. 1. Growth, Non-structural Carbohydrate and Nitrogen Content

Swards of subterranean clover (Trifolium subterraneum L.) atLAl 6 grown in N-free nutrient solution were subjected to threedefoliation treatments which removed 30, 70 and 80% of shootdry weight. Subsequent regrowth and changes in the concentrationsof carbohydrate and nitrogen in plant components were measuredat 0, 1, 5, 9 and 13 d after defoliation and compared with thosein uncut swards. The rate of shoot regrowth declined with increasing severilyof defoliation. In all defoliation treatments, growth was confinedto leaves for up to 5 d. Root growth ceased in all treatmentsfor a longer period. Reestablishment of the leaf area in severely-defoliatedswards was facilitated by the rapid opening of developing leavesand by changes in the allocation of carbon which favoured leafover branch and root, and lamina over petiole growth. Loss of carbohydrate and nitrogen from roots and branches lasting5–9 d was observed in the more severe defoliation treatments.Loss of protein (N x 6.25) exceeded that of total non-structuralcarbohydrate, and could have accounted for the nitrogen contentof new leaf during this period. Branches lost 62% of their initialcarbohydrate content compared with 25% from roots in the 80%cut swards. In contrast, roots, by virtue of their greater mass,were the principle source of mobilized nitrogen. Nitrogen accumulationceased in 80% cut swards for 9 d. However, carbohydrate levelsin the crown nodules were not severely depleted. It was concluded that partitioning of growth to lamina and themobilization of carbohydrates and nitrogen were important forrecovery from defoliation. Carbohydrates, carbon partitioning, defoliation, nitrogen, mobilization, regrowth, subterranean clover, Trifolium subterraneum L     

The effects of copper nutrition and developmental state on the biosynthesis of diamine oxidase in clover leaves

The biosynthesis of diamine oxidase (DAO; EC 1.4.3.6) in leaf blades of subterranean clover (Trifolium subterraneum L. cv Seaton Park) was followed by labeling whole plants with ¹⁴CO₂. A pulse-chase experiment where DAO was immunoprecipitated with anti-DAO antibodies showed that only leaf primordia and the youngest emerged leaves were able to synthesize the enzyme. The amount of DAO in young leaves of clover grown with a range of Cu treatments was determined by its enzymic activity and by single radial immunodiffusion against anti-DAO antibodies; both parameters were highly correlated with the Cu concentration of the leaf. Further, anti-DAO antibodies reacted against apo-DAO prepared in vitro indicating that apo-DAO was absent from Cu-deficient leaves. These results suggest that the biosynthesis of DAO in young clover leaves is controlled by the Cu concentrations of the leaves. Poly(A) mRNA purified from leaf primordia and young emerging leaves of plants with either a high Cu or low Cu supply was translated in wheat germ and rabbit reticulocyte cell-free systems. No differences between the two Cu treatments could be seen in the sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles of the translation products after fluorography. However, anti-DAO antibodies did not detect any DAO synthesized in vitro from either treatment.     

Flowering Sequence and the Ordering of Impermeability Breakdown in Seed of Subterranean Clover (Trifolium subterraneum L.)

The pattern of breakdown of seed coat impermeability of seedwithin the burrs of two cultivars of subterranean clover (Trifoliumsubterraneum L.) was closely associated with relative differencesin flowering sequence within the inflorescence. The patternof seed weight variation showed very little relationship withthe pattern of breakdown, while that for seed moisture contentshowed no relationship. Within a burr it was almost invariably the seed which developedfrom the latest flower within the inflorescence which was thefirst to become permeable. An ordering of the timing of breakdownwas evident only within the burr; there was no evidence fora pattern of breakdown of impermeability between the differentburrs along the runner. Trifolium subterraneum L., subterranean clover, seed coat impermeability, seed weight, seed moisture, hardseededness     

Water Relations of Red Clover Trifolium pratense L. as Affected by VA Mycorrhizal Infection and Phosphorus Supply Before and During Drought

Red clover Trifolium pratense L. plants were grown in a factorialdesign with four levels of added P and with and without a mycorrhizalinoculum, to test the separate effects of P nutrition and infectionon plant water relations. Under well-watered conditions, onlyuninfected plants on very low P soil showed reduced stomatalconductance and these had the lowest leaf P concentrations.During droughting, only plants with very high leaf P concentrationsmaintained high conductance. There was no evidence of increasedwater uptake by mycorrhizal plants. This and other evidencesuggests that mycorrhizal effects on water relations are secondaryconsequences of changes in P nutrition which are, in any case,inconsistent. Key words: Trifolium pratense, VAM, water relations, concentration, drought     

The Distribution of Mg, P and K in the Split Roots of Subterranean Clover

The aim of these experiments was to determine whether uninhibitedroot growth is possible in a soil lacking Mg, provided thatthe plant is adequately supplied with Mg from another regionwithin the soil. Two experiments were undertaken using splitroot systems in free-draining sand or gravel irrigated dailywith nutrient solution. Magnesium supply to one half of theroot system was varied and root growth in the deficient partof the system was measured. Magnesium redistribution was comparedto that of calcium, phosphorus and potassium. Magnesium content of the roots grown in the compartment withno Mg supply increased, but only when the shoots had an adequateto luxury Mg status. Even under these conditions root growthwas inhibited compared to roots with an adequate external supplyin both compartments. Similarly potassium was transferred tothe roots with no external supply, but root growth was retardedin this compartment. Roots proliferated in the compartment suppliedwith phosphate and did so at the expense of growth in the non-supplycompartment. The shoots had a barely adequate phosphorus statusand there was no transfer of phosphorus to the root with noexternal supply. Magnesium, phosphorus, potassium, root growth, split root systems, subterranean clover, Trifolium subterraneum L.     

Male Sterility and Anther Wall Structure in Copper-deficient Plants

Anther development and pollen sterility were followed in plantsof wheat, oat, barley, sweetcorn, sunflower, petunia and subterraneumclover grown at a range of copper supplies. Copper-deficientplants had increased pollen sterility. Lignified wall thickenings were reduced or absent in the endotheciaof anthers from Cu-deficient plants. Reduced seed set may resultboth from reduced pollen fertility or failure of the stomiato rupture due to decreased lignification of anther walls. Triticum aestivum L., wheat, Hordeum vulgare L., barley, Avena sativa L., oat, Zea mays L., corn, sweetcorn, maize, Helianthus annuus L., sunflower, Petunia hybrida L., Trifolium subterraneum L., subterranean clover, male sterility, anther development, copper deficiency     

The Effects of Rootzone Salinity and Hypoxia on Shoot and Root Growth in Trifolium Species

The effect of concurrent salinity (0-60 mM NaCl) and rootzonehypoxia (flooding for up to 15 d) on shoot and root growth andshoot ion concentrations of six species of Trifolium (T. subterraneumL., T. fragiferum L., T. michelianum Savi., T. isthmocarpumBot., T. purpureum Lois., and T. repens L.), was studied intwo greenhouse experiments. There was a significant salinityx flooding effect for shoot yield but no significant salinityx flooding x species interaction although individual speciesdiffered significantly (P < 0·001) in their growthresponse to the saline or flooded conditions separately. Concentrationsof Na and Cl in the shoots of all species increased with increasingperiods of saline flooding and there was a significant salinityx flooding interaction. Sodium and Cl concentrations were significantlyhigher (P < 0·001) in T. purpureum, the species inwhich shoot growth was most depressed by saline flooding, thanother species. In T. michelianum, T. fragiferum and T. repens,fresh and dry weight of roots increased with flooding underboth saline and non-saline conditions while in T. subterraneumroot growth decreased. A significant proportion of the increasedroot growth in the first three species occurred as new adventitiousroots. These roots had higher percentages of internal gas spaceswithin the root tissue even in the presence of salinity comparedwith roots from non-flooded conditions. There were also significantlymore gas spaces in the total root tissue in T. fragiferum andT. repens under saline-flooding than in roots of T. subterraneum.Electron micrographs of the root cross sections illustratedthe presence of these gas spaces or aerenchyma. Trifolium fragiferum, T. repens and T. michelianum are morelikely to be suited to growth in soils prone to high salinityand to flooding than are T. subterraneum, T. purpureum and T.ishmocarpum.Copyright 1993, 1999 Academic Press Trifolium subterraneum, Trifolium fragiferum, Trifolium michelianum, Trifolium isthmocarpum, Trifolium purpureum, Trifolium repens, salinity, flooding, hypoxia, adventitious roots, aerenchyma, subterranean clover, white clover, strawberry clover, purple clover, balansa clover     

Determining the effectiveness of grazing and trampling by livestock in transmitting white clover mosaic and subterranean clover mottle viruses

Glasshouse and mini-sward experiments were done to determine the relative roles of grazing and trampling by livestock in transmitting white clover mosaic (WC1MV) and subterranean clover mottle (SCMoV) viruses between clover plants in pastures. Wounding due to grazing was simulated by repeatedly cutting plants with serrated scissors (glasshouse) or mowing (mini-swards), while wounding due to trampling was simulated by repeatedly bashing plants with the flat end of a wooden hammer handle (glasshouse) or rolling (mini-swards). In glasshouse experiments, cutting was more effective than bashing in transmitting WC1MV to white clover (Trifolium repens) plants but cutting and bashing transmitted it to subterranean clover (T. subterraneum) plants at similar rates. In an experiment with white clover mini-swards, mowing was more effective than rolling in transmitting WC1MV, and when both were combined, initially spread exceeded that obtained when the spread from mowing and rolling alone was added together. In glasshouse experiments, bashing was more effective than cutting in transmitting SCMoV to subterranean clover plants. In one experiment, neither mowing nor rolling spread SCMoV in mini-swards of subterranean clover. When transmission to subterranean clover cultivars which were ‘susceptible’ or ‘moderately susceptible’ to SCMoV was compared in glasshouse experiments, repeated bashing spread the virus more slowly to the ‘moderately susceptible’ cultivars. When mixed with ruminant saliva, infective sap containing WC1MV or SCMoV was still infective to clover plants after 4 wk storage at room temperature. When infective sap was allowed to dry naturally on a metal surface, SCMoV still infected clover plants when the dried sap was taken up in tap water after 4 but not 14 days, while WC1MV was infective after 24 h but not 4 days. These results suggest that grazing and mowing are more effective than trampling at transmitting WC1MV to white clover plants in pastures, while trampling is more effective at spreading SCMoV to subterranean clover. However, both transmitted WC1MV to subterranean clover at similar rates. Possible reasons for these differences are discussed in relation to differences in clover plant morphology and virus-specific factors.     

Effect of Phosphorus Deficiency on Phosphatase Activity of Cell Walls from Roots of Subterranean Clover

Clover (Trifolium subterraneum L. cv. Mt. Barker) was grownin solution culture with adequate (+P) or no phosphate (–P).Cell walls were extracted from roots in such a way that theywere uncontaminated by other cellular materials. Phosphataseactivity was assayed using p-nitro-phenylphosphate (NPP). Phosphatasebound to cell walls had a pH optimum between 5.0 and 6.0, irrespectiveof the P supply to the plants. Activity of phosphatase boundto cell walls increased with electrolyte concentration of theassay medium at pH 6.5 but not at pH 5.5. This increase in activitywas probably due to a higher degree of ionization of the cellwall at pH 6.5 than at pH 5.5, and to effects of high ionicstrength in decreasing the mutual repulsion of negatively chargedNPP from negative charges on the cell walls. Cell wall-boundphosphatase did not exhibit Michaelis-Menten kinetics: the concentrationof NPP at which activity was half the maximum rate (S_0.5) was0.7 mM for cell walls extracted from roots of both +P and –Pplants. Up to 30% of the phosphatase activity bound to cellwalls could be removed using buffer solutions of high pH andhigh ionic strength which contained Triton X100. Both soluble and cell wall-bound phosphatase(s) of roots increasedin activity with P deficiency. The phosphatase activity of cellwalls increased 1.5 fold as the P concentration in the rootsfell from 0.4–0.2% dry weight. Experiments with sterileroots of clover showed that increases in cell wall-bound phosphataseactivity associated with P deficiency were not due to microbialcontamination. It is argued that phosphatase(s) in cell wallsof roots could make a substantial contribution to the P nutritionof clover in soils deficient in inorganic phosphate by hydrolysingorganic phosphate compounds in the soil. Key words: Phosphatase, Clover, Roots, Phosphorus deficiency, Cell walls     

A Dynamic Equation for Plant Interaction and Application to Yield-density-time Relations

A model for plant interaction is developed based on a definitionof space in terms of actual and potential amount of growth factorsabsorbed per unit of time. The resulting equation is a second-orderdifferential equation which is solved by dynamic simulation.Five data sets on yield-density relations are used to demonstratethe model's excellent predictive power. Competition model, plant interaction, yield-density relations, Richards function, subterranean clover (Trifolium subterraneum L.), Wimmera ryegrass (Lolium loliaceum Hand-Mazz.), lettuce (Lactuca sativa L.), maize (Zea mays L.), lucerne (Medicago sativa L     

The Effect of Shade During Leaf Expansion on Photosynthesis by White Clover Leaves

In three experiments measurements of photosynthesis were madeon single leaves of white clover (Trifolium repens L.) on threecultivars grown in a controlled environment. Plants which had grown under an irradiance of 30 J m^–2s^–1, or in shade within a simulated mixed sward, producedleaves with photosynthetic capacities some 30 per cent lowerthan did plants grown at 120 J m^–2 s^–1 without shade.There were no differences between treatments either in photosynthesismeasured at 30 J m^–2 s^–1, or in respiration ratesper unit leaf dry weight. Respiration per unit leaf area washigher in the plants grown at 120 J m^–2 s^–1, reflectingthe lower specific leaf area of these leaves. There were nodifferences between the three cultivars examined. Leaves which were removed from the shade of a simulated swardshortly after becoming half expanded achieved photosyntheticcapacities as high as those which were in full light throughouttheir development. It is suggested that it is this characteristicwhich enables clover plants growing in an increasingly densemixed sward to produce a succession of leaves of high photosyntheticcapacity, even though each lamina only reaches the top of thesward at a relatively late stage in its development. Trifolium repens L., white clover, photosynthesis, leaf expansion, shade, specific leaf area, stomatal conductance     

Transpiration efficiency of three Mediterranean annual pasture species and wheat

Attempts to improve water use efficiency in regions with Mediterranean climates generally focus on increasing plant transpiration relative to evaporation from the soil and increasing transpiration efficiency. Our aim was to determine if transpiration efficiency differs among key species occurring in annual pastures in southern Australia. Two glasshouse experiments were conducted with three key pasture species, subterranean clover (Trifolium subterraneum L.), capeweed [Arctotheca calendula (L.) Levyns] and annual ryegrass (Lolium rigidum Gaudin), and wheat (Triticum aestivum L.). Transpiration efficiency was assessed at the levels of␣whole-plant biomass and water use (W), leaf gas exchange measurements of the ratio of CO₂ assimilation to leaf conductance to water vapour (A/g), and carbon isotope discrimination (Δ) in leaf tissue. In addition, Δ was measured on shoots of the three pasture species growing together in the field. In the glasshouse studies, annual ryegrass had a consistently higher transpiration efficiency than subterranean clover or capeweed by all methods of measurement. Subterranean clover and capeweed had similar transpiration efficiencies by all three methods of measurement. Wheat had W values similar to ryegrass but A/g and Δ values similar to subterranean clover or capeweed. The high W of annual ryegrass seems to be related to a conservative leaf gas exchange behaviour, with lower assimilation and conductance but higher A/g than for the other species. In contrast to the glasshouse results, the three pasture species had similar Δ values when growing together in mixed-species swards in the field. Reasons for these differing responses between glasshouse and field-grown plants are discussed in terms of the implications for improving the transpiration efficiency of mixed-species annual pasture communities in the field. Received: 6 March 1997 / Accepted: 23 December 1997     

Virus diseases of subterranean clover

Subterranean clover (Trifolium subterraneum) is grown as a pasture legume in several temperate regions of the world where the soils are acidic and infertile, and the rainfall is winter dominant and less than 600 mm annually. It is particularly important in southern Australia where more than 16 million ha have been sown with this species as the pasture legume component. Nine viruses have been recorded infecting subterranean clover in the field. These are alfalfa mosaic, bean yellow mosaic (pea mosaic), beet western yellows, clover yellow vein, cucumber mosaic, pea enation mosaic, soybean dwarf (subterranean clover red leaf), subterranean clover mottle and white clover mosaic. In addition there is an important problem referred to as subterranean clover stunt that was assumed to be caused by a virus but whose aetiology is still unknown. The importance of these diseases is reviewed and details on their epidemiologies are outlined together with details on progress towards their control and some comments on matters worthy of attention in the future. Reference is also made to several exotic viruses known to infect subterranean clover experimentally that could possible cause problems if introduced into Australia.     

Photosynthesis by White Clover Leaves in Mixed Clover/Ryegrass Swards

Measurements of rates of net photosynthesis were made on singleBlanca white clover leaves on plants taken from a field-grown,mixed clover/perennial ryegrass sward during two regrowth periods. Net photosynthesis fell by 20 per cent in the first measurementperiod as leaf area index increased and the grass componentof the crop flowered, but did not change significantly in thesecond measurement period during which the grass remained vegetative. Leaves which had been artificially protected from shading inthe sward did not have significantly different photosyntheticcapacities from leaves in the undisturbed sward, even in thefirst measurement period. As leaf area index and sward height increased, successive cloverpetioles were longer, keeping the newly expanded leaves nearthe top of the sward where they received full light. It is suggestedthat it is this which allows successive clover leaves, unlikethose of vegetative grasses, to attain a high photosyntheticcapacity throughout a growth period. Trifolium repens, Lolium perenne, Photosynthetic capacity, shading, growth     

Increased damage by western flower thrips Frankliniella occidentalis in chrysanthemum intercropped with subterranean clover

Suppressive effects of intercropping on Frankliniella occidentalis (Pergande) infestations have been reported in several crops. However, this study demonstrates that in year-round chrysanthemum, Dendranthema grandiflora Tzvelev, undersowing with subterranean clover, Trifolium subterraneum L., results in an increased thrips feeding damage. In a pot experiment, performed with chrysanthemum plants (cultivars Reagan and Tiger) grown with or without subterranean clover, significantly more leaves with silver and growth damage were found in the chrysanthemum plants with subterranean clover in comparison with the monocropped chrysanthemum plants. Similarly, the degree of deformation of leaf perimeter and leaf surface was higher in the top leaves of the intercropped chrysanthemum plant. In the soil experiment (only performed with Tiger and plants were grown in the soil in the greenhouse) intercropped chrysanthemum plants suffered a higher feeding damage as well. Analysis of the relation between silver or growth damage and the thrips pressure demonstrates that at similar thrips pressure in the intercropped chrysanthemum plants suffered significantly more damage. The higher thrips pressure in the intercropped chrysanthemum only explains the differences in damage partly. Changes in the reaction of chrysanthemum plants to thrips feeding or in the behaviour of the thrips, mediated by the presence of the non-host crop, are discussed. Our explanation is that chrysanthemum plants grown with clover are more susceptible to thrips feeding than monocropped plants. We conclude that undersowing with clover does not contribute to reduce damage by F. occidentalis in year-round chrysanthemum. Also, the influence of crop diversification on a pest cannot be foreseen until the specific characteristics of each individual crop – pest system are studied.     

Effects of Temperature on Growth and Nitrogen Fixation by Swards of Subterranean Clover

Subterranean clover (Trifolium subterraneum L.) cv. ‘Woogenellup’ swards were grown at 10, 15, 20 and 25 Cwith a 12 h photoperiod of 500 or 1000 µmol m^–2s^–1 [low and high photosynthetic photon flux density (PPFD)].Nitrogen-fixing swards received nutrient solution lacking combinednitrogen while control swards received a complete nutrient solution.Growth was measured by infra-red analysis of carbon dioxideexchange and by accumulation of dry matter. Swards were harvestedat intervals between 95 and 570 g d. wt m^–2 for estimationof nitrogenase activity by acetylene reduction and hydrogenevolution assays. Nitrogen fixation was also measured by increasein organic nitrogen. The growth rate was highest at 10 C at low PPFD, and at 10–15C at high PPFD. Nitrogen-fixing swards grew slower than thosereceiving combined nitrogen. Nitrogen fixation measured by increasein organic nitrogen responded similarly to the growth rate,as did acetylene reduction between 10 and 20 C. At 25 C therelationship between acetylene reduction and nitrogen fixationwas distrupted. The difference between the rates of acetylenereduction and hydrogen evolution, theoretically proportionalto nitrogen fixation, was not a reliable indicator of nitrogenfixation because hydrogen uptake developed. Trifolium subterraneum L, subterranean clover, growth, nitrogen fixation, temperature, acetylene reduction