0971-4693/94US $ 5.00 AllelopathyJournal 3 (2): 185- 1 94(1 996) O InternationalAllelopathy Foundation 1996

Differentialphytotoxicity of speciesand their parts

M. AN*, J.E.PRATLEY andT. HAIG Cen(re for ConservationFarming CharlesSturt University,Wagga Wagga.NSW 2678, Australia

(Receivedin revisedform: April 18,1996)

ABSTRACT

The phytotoxicity of silvergrass(It.bromoides L. Gray and l/.myurosL. Gmel) residuesand their planl parts were examined in the laboratory using wheat (Trilicumaestivum cv. Vulcan) as the test species.The germination,elongation ofthe coleoptileand seminal root ofwheat were inhibited by aqueousextracts of l/ulpiaresidues. /.bromoides residuesexhibited stronger allelopathic el'fects thanthat of V.myuros.Phytotoxicity varied with plant parts.fulpi4 shootswere the most phytotoxic and seedsleast phytotoxic. Radicle elongation of wheat wasmore sensitiveto phytotoxicitythan coleoptileand germinationpercentage. Germination inhibition was affected by l'ulpiu species,plant parts and germinatingperiod.

Key words:Allelopathy, phytotoxicity,plant residue,silvergrass, straws, L'ulpia, vtheat

INTRODUCTION

Silvergrasses(Vulpia spp.).originally from the Mediterraneanregion, are naturalisedwinter annual grassesand have become importantweeds of pastures andcereal crops in southernAustralia (17). Theseare consideredundesirable componentsof pasturesdue to their Iorvproductivity in winter and unpalatability duringspring and summer. V. bromoides(L.) Gray and V. myuros (L ) Gmel are ecologicallywidespread and aremost common in mixed standsin southernAustralia (4,l7). There are a few optionsfor their controlby availableherbicides (12).

A differencein phytotoxicity betweanthe residuesof V. bromoidesand V. myuroshasbeen reported,V. bromoirles affects allthe test speciesbut l'. myuros haslittle effect on Iucerne(2 l). The differencesin allelopathicpotential among plantspecies and among accessions of theone species have been well documented *Corresnondenceauthor 186 An, Pratley and Haig

(3,7,11,14)and are attributedto the possibility of geneticcontrol of allelopathy (19,22,25). It is establishedthat the phytotoxic effects of plant residues on succeedingplants are due to phytotoxinsleached from the residuestogether with toxins producedduring microbial decay(10,15,23). Such endogenous phytotoxins, known as secondaryplant metabolites,depends on the plant's genetic make-up and its interactionwith environmentalconditions during growth (1,8,13).

Experimentsunder glasshouse conditions have shown that vulpia residues during decompositionare allelopathicto the germination and growth of wheat, lucerne, phalaris and canola (20,21). The purpose of this paper is to further evaluatephytotoxicity of residuesof different Vulpia speciesand their plant parts.

MATERIALSAND METHODS

Plant residues from pure mature stands of V. bromoides and V. myuros were obtainedin Decemberl99l from the Agricultural ResearchInstitute, Wagga Wagga. Residuematerial was manually harvestedeither I cm abovethe soil surface or as whole including roots. Thesewere oven dried at 40oC for 72 h and stored in dry conditions.Vulpia residueswere cut into l-2 cm lengths and were soakedin lots of l0 g/100 ml distilled water for 6 days in the dark at 20'C. The suspensionwas filtered through one layer of filter paper and centrifugedfor 30 min at 3900 rpm. The supernatantwas decantedand used for bioassays.The volume of aqueous extract recovered from this procedure was about 60Yoof the total originalvolume.

Seedgermination bioassay

Germination was carried out in 9-cm plastic dishes lined with one Whatman number I filter paper. Twenty seedswere used in each dish and 5 ml extract was added.Control treatmentsreceived 5 ml distilled water. There were three replications.The disheswere placed in an incubatorat 24"C in the dark. Seeds germination was recorded every 24 h foy 4 consecutivedays and was expressedin percentage.Seeds were consideredgerminated if 2 mm long radicle had emergedfrom the seedcoat.

In the bioassay,a germinationperiod of 4 dayswas used,though 90-95% of controls had germinatedafter 2 days.A differencein germinationpercentage after2 days is describedas a "germinationreduction". Where somerecovery had takenplace by day 4, this is referredto as "germinationdelay". Where the reduction persistedup to day 4, this is describedas "germinationinhibition" and was often permanent. Thus, germination reduction = germination delay + germination inhibition. Phytotoxicity of Vulpia species 187

I Differentialphytotoxicity I To determinedifferential phytotoxicity of Vulpia spp. and their plant I partstwo studieswere conducted.In the first study, aqueousextracts were made fromthe pure residuesof whole plants of V. bromoides and V. myuros. Treatments usedwere individual pure extracts and a mixture of equal proportions' Each treatmentwas replicated thrice and bioassaysfollowed the general methods describedabove.

In the secondstudy, plantsof the most widespreadspecies V. myuros (4) wereseparatedinto seeds,inflorescence (top 10 cm sectionofthe plant), shoot (withoutinflorescence), root and the whole plant (without roots).Ten grams dry weightof eachpart was used.Treatments were arrangedin a factcrial designwith threereplicates. Preparation of extractsand bioassaysfollowed the generalmethods describedabove.

Data were statistically analysed using MicroStat software. An arcsin transformationwas usedwhen the percentagesfell outsidethe 30'70% range.

RESULTS AND DISCUSSION

Differentiol Phytoloxicity between Vulpia species

Germination

All aqueousextracts caused significant reduction in seed germination (Figurel). Differencesin phytotoxicity between Vulpia specieswas evident in termsof germination de'layand inhibition. V. bromoide.tpossessed a stronger phytotoxicpotential than V. myuros. Aqueous extract from V. bromoides residues causeda 50% germination reduction relative to the control, of which 52ohwas attributedto the germinationdelay and 48Yoto inhibition. The V. myuros extract causeda 22Yo germination reduction, 9lYo of which was due to the delay in germination;the inhibition effect was not significant.There was also a difference inthe percentage delay in total germination, being 34Yofor V. bromoides and 20%o forV. myuros. Aqueous extract of the mixture was intermediatebetween the two species,close to V. myttros, but still significantly different from Y. bromoides. 188 An, Pratley and Haig

100 o E E i 5% t.s.d.

(\l3so * g60 s(6 F A40 Eru 820 E f o €o 234 Germinatingperiod (day)

FigureL Effectof aqueousextracts of Vulpiaresidues on wheat germination

Coleoptile height and root length

The residuesof both Vulpfa speciespossessed strong allelopathicpotential. V. bromoides residues inhibited the coleoptile and root growth by 63% and 7lo/o of control, whereasthe inhibition in V. myuros was 3loh and 57yo,respectively. The most severeinhibition was associatedwith V. bromoidesresidues, the least with V. myuros residues and the mixture was intermediate. These results are consistentwith the findings on germination,indicating that the residuesof both Vulpia speciespossess strong allelopathicpotential, but their relative phytotoxicity is different, with V. bromoides beins more phytotoxic than V. myuros (Figure 2).

The residues of the both Vulpia speciesused for this experiment were obtained from the plants grown under identical conditions. Therefore, the differential phytotoxicity shown by the two speciesshould reflect their genetic difference in producing phytotoxins.

The data show that not only the extracts of individual Vulpia species possessstrong allelopathicpotential but also that the mixture of theseextracts is phytotoxic. Since V. bromoides and V. myuros are the most common Vulpia species in southern Australia and often occur in mixed stands in the field; the strong phytotoxic potential of such a mixed stand can be as significant as individual species in causing germination reduction, inhibiting seedling emergence and adversely affecting the establishmentand productivity of subsequentcrop and pastureplants. Phytotoxicity of Vulpia species 189

rlR0

I s i60

4 940

!

0

V.myuros zs Mixture

Figure2. Relativephytotoxicity of decomposingresidues of different Vulpia specieson seedling elongationin wheat. Means identified by the same letter are rrot significantly different at the 5o/o level(Duncan's new multiple-rangetest)

Differentialphytotoxicity among plant parts

Germination

All plant parts significantly reducedseed germination to varying degrees (Tablel). Shootsdepressed the most, the seedsand inflorescenceleast, with remainingparts intermediate. Overall, the proportion of inhibition to germination f !, i reductionwas smallerthan that of delay, with seedsbeing the least,the shoot and wholeplant largest (Figure 3). The proportion of delay to total germination rate t, increasedwith the order of shoot, whole plant, inflorescence,root and seeds, indicatingthe decreasingtoxic levels.

Tablel. Phytotoxicityof different plant partsof V. myuros on wheat germination

Treatment Germination(%\

Days after sowing 2

Control 20 a 100 a 100 a 100 a Seeds 2 b 75 b 85 b 95 a Infloresce nce 0 b 80 b 90 b 95 a Shoot 0 b 25 d 65 75 b Root 0 b 55 80 bc 90 ab Wholeplant 0 b 40 cd 75 bc 80 b

*Datawithin a column followed by the sanreletters are not significantly diff'erent(Duncan's new nrultiple-rangetest, p< 0.05) 190 An, Pratley and Haig

s

€to 0

I

oil

8o 40

o 6'"

Inflorescence Whole plant

+ Figure 3. Effect of various plant parts of Vulpia on the germination reduction (germination delay germination inhibition) in wheat. Means identified by the sameletter are not significantly different at the 57o level (Duncan's new multiple-range test).

ri 80 5

N ;60

d oo 640

o (t')a 20

Inflorescence Whole plant

Figure 4. Relative phytotoxicity of decomposingresidues from plant parts of l'ulpia on seedling elongation in wheat. Means identified by the same letter are not significantly different at the 5% level (Duncan's new multiple-rangetest).

Seedlingelohgation

The phytotoxiceffects of plantparts on radicleand coleoptileelongation reflecteda similar patternto germination(Figure 4). Inhibition of root and coleoptilegrowth was more pronounced than that of germination.Coleoptile and radicle lengthswere inhibited up to 55o/oand 68%. respectivelyrelative to the control.Coleoptile elongation followed the order,seeds > inflorescence> whole Phytotoxicity of Vulpia species l9l plant> root> shoot.Inhibition of radicle elongationwas similar exceptthat there wereno significantdifferences among shoot, root and whole plant components. Differentialphytotoxicity among plant parts was evident, with the shoot having thegreatest inhibition effect and the seedsthe least.

It has been previously reported that individual parts of plants differ in phytotoxicity,with the aerial parts often being more toxic than the underground parts(5, 24). Most crop residues,such as corn, wheat, sorghum and oat, contain water-solublesubstances that inhibit the germinationand growth of other crops. Theaqueous extracts of their seedshad the leasteffect and the stem extractshad thegreatest inhibitory effect on wheat seedlings(6,7 , l6). A number of phenolic acids(ferulic, p-coumaric, syringic, vanillic, and p-hydroxybenzoic) were identifiedand quantitatively estimated in theseresidues. Differences among plant partsin phytotoxicity may be due to the distribution of secondarymetabolites, suchas phenolic compounds, vary'ing from one plant componentto another(2,9, I 8).

The data presentedherein indicate that the Iarge quantities of Vulpia residues,when left on the soil surface and carried over from one seasonto the next,may be a primary causeof failed establishmentof crop and pasturespecies inautumn. Management strategies aimed at minimising deleteriouseffects of Vulpia residuesshould include the avoidanceof carry over of large amountsof residues onthe soil surface from one seasonto the next.

ACKNOWLEDGEMENTS

Thefinancial support of the Grain Research& DevelopmentCorporation ofAustralia is gratefully acknowledged.

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