cursorial birds,when they were already adept cursors with a posterior centre of mass.
The cond proposal,that some theropods were derived from currently unknown,¯ighted ancestors,has been suggested19.As noted above,Caudipteryx's locomotory adaptations are consistent with it having been derived from¯ighted ancestors.However,there is no substantive evidence to support¯ighted ancestors for any other theropods.Nevertheless,this possibility cannot be dismisd. In the light of problems associated with theories(1)and(2), perhaps the third,that Caudipteryx was a condarily¯ightless, post-Archaeopteryx,cursorial bird,derves clor scrutiny than it has received so far.We®nd it a striking coincidence that the only unambiguously feathered theropod was also the only known ther-opod likely to have utilized locomotory mechanisms identical to tho of cursorial birds.M Methods
Hindlimb and trunk length data
We recorded data on hindlimb element(femur,tibia or tibiotarsus,metatarsal III or tarsometatarsus)and trunk lengths in mature,extant and extinct cursorial(or at least ground-living)birds(from eight orders and24genera,including tinamou,cassowary, ostrich,galliforms,roadrunners,bustards,moa and elephantbird)and38genera of theropod and ornithopod dinosaurs(e Supplementary Information).Data
were collected from avian and dinosaur specimens in muum collections or obtained from published data and/or scale reconstructions.Individuals were included only if the hindlimb skeleton was adequately known and the trunk was suf®ciently known that the describers were able con®dently to reconstruct the specimen.
The morphometric data collected from each individual included maximum femoral length,maximum tibia(or tibiotarsus)length(excluding the cnemial crest)maximum metatarsus(or tarsometatarsus)length and trunk length.We de®ned trunk length as the distance from the®rst dorsal vertebrae and/or head of the®rst dorsal rib to the posterior rim of the acetabulum.
Juvenile birds have,for a given trunk length,longer hindlimbs than their adult counterparts20;the same has been hypothesized for tyrannosaurids21and allosaurids22. Similarly,Bambiraptor feinbergi,a juvenile dromaeosaurid theropod,has a hindlimb/ trunk length ratio of2.0(ref.23)that is comparable to that en in cursorial birds,but we exclude it from our analys becau of its obviously early stage of development. Additionally,Sinornithoides youngi was excluded from this study.The specimen also exhibits a bird-like hindlimb/trunk length ratio,is very small and possd a cartilaginous sternum24.The obrvations indicate that this specimen,originally described as`nearing maturity',may have been more immature than its describers suppod.To avoid confoundi
ng ontogenetic variables,the largest individual for each genus(for which we had data)was ud in the analysis and data from known immature extant individuals were omitted as were extinct specimens who maturity has in doubt.
The developmental maturity of Caudipteryx(NGMC97±4±A and NGMC97±9±A)is indicated by the well ossi®ed sterna,sternal ribs,wrist bones and ankle bones14.Similar ossi®cation is prent in two more recently discovered,equivalently sized specimens, Caudipteryx dongi(IVPP V12344)25and Caudipteryx(uncatalogued IVPP specimen) (Z.Zhou,personal communication),but the former specimen also posss ossi®ed uncinate process.As the skeletal elements ossify late in development,there is little doubt that the individuals were mature.
Centre of mass calculations贪的成语
Lateral and dorsal pro®les of Deinonychus were compiled from reconstructions in ref.19. Lateral and dorsal pro®les of Caudipteryx were reconstructed from NGMC97±4±A and NGMC97±9±A.The axial body pro®les were mathematically combined to create a solid three-dimensional model from which body volume and the location of centre of mass were calculated(e ref.18for details).The lung was conrvatively assumed to have been spherical with a volume equal to10%of body volume and posit
ioned at the anterior portion of the trunk.The density of the lung(0.4kg m-1)was estimated using the ratio of mass-speci®c lung volume to mass-speci®c lung parenchyma volume in a large Nile crocodile26. Received8February;accepted24May2000.
1.Pennycuick,C.J.in The Origin of Birds and the Evolution of Flight(ed.Padian,K.)83±98(California
Academy of Sciences,San Francisco,1986).
2.Norberg,U.B.Vertebrate Flight1±291(Springer,Berlin,1990).
3.Roberts,T.J.&Humphreys,H.A.Hind limb forces during acceleration in wild turkeys.Amer.Zool.
39,65A(1999).
4.Alexander,R.M.Mechanics of posture and gait of some large dinosaurs.Zool.J.Linn.Soc.83,1±25
(1985).
5.Alexander,R.M.Dynamics of Dinosaurs and other Extinct Giants(Columbia Univ.Press,New York,
1989).
6.Gatesy,S.M.Caudofemoral musculature and the evolution of theropod locomotion.Paleobiology16,
170±186(1990).
7.Gatesy,S.M.&Biewener,A.A.Bipedal locomotion:effects of speed,size and limb posture in birds and
humans.J.Zool.Lond.224,129±147(1991).
8.Gatesy,S.M.Hind limb scaling in birds and theropods:implications for terrestrial locomotion.J.
Morphol.209,83±86(1991).9.Gatesy,S.M.Guinea fowl function.I:Cineradiographic analysis and speed effects.J.Morphol.240,
115±125(1999).
10.Gatesy,S.M.Guinea fowl limb function.II:Electromyographic analysis and motor pattern evolution.
J.Morphol.240,127±142(1999).
11.Carrano,M.T.Locomotion in non-avian dinosaurs:integrating data from hindlimb kinematics,in
vivo strains,and bone morphology.Paleobiology24,450±469(1998).
12.Gatesy,S.M.,Middleton,K.M.,Jenkins,F.A.Jr&Shubin,N.H.Three-dimensional prervation of
foot movements in Triassic theropod dinosaurs.Nature399,141±144(1999).
13.Galton,P.M.The posture of hadrosaurian dinosaurs.J.Paleontol.44,464±473(1970).
14.Ji,Q.,Currie,P.J.,Norell,M.A.&Ji,S.Two feathered dinosaurs from northeastern China.Nature393,
753±761(1998).
15.Sereno,P.C.The evolution of dinosaurs.Science284,2137±2147(1999).
16.Farlow,J.O.,Gatesy,S.M.,Holtz,T.R.,Hutchinson,J.R.&Robinson,J.M.Theropod locomotion.
Am.Zool.(in the press).
17.Feduccia,A.The Origin and Evolution of Birds2nd edn(Yale Univ.Press,New Haven,1999).
琵音
18.Henderson,D.M.Estimating the mass and centers of mass of extinct animals by3-D mathematical
slicing.Paleobiology25,88±106(1999).
19.Paul,G.S.Predatory Dinosaurs of the World(Simon and Schuster,New York,1985).
20.Manion,B.L.The Effects of Size and Growth on the Hindlimb Locomotion in the Chicken.Thesis,Univ.
Illinois at Chicago(1984).
21.Rusll,D.A.Tyrannosaurs from the Late Cretaceous of Canada.National Muum of Canada,
National Muum of Natural Sciences Publications in Paleontology1,1±34(1970).
22.Foster,J.R.&Chure,D.J.Hindlimb proportion allometry in juvenile and adult Allosaurus
(Dinosauria,Theropoda).J.Vert.Paleontol.19(suppl.To3),45A(1999).
23. al.Remarkable new birdlike dinosaur(Theropoda:Maniraptora)from the upper
Cretaceous of Montana.U.Kansas Paleontol.Contrib.13,1±14(2000).
24.Rusll,D.A.&Dong,Z.A nearly complete skeleton of a new troodontid dinosaur from the Early
押解的故事Cretaceous of the Ordos Basin,Inner Mongolia,People's Republic of China.Can.J.Earth Sci.30, 2163±2173(1993).
25.Zhou,Z.&Wang,X.A new species of Caudipteryx from the Yixian Formation of Liaoning,northeast
China.Vertebrata PalAsiatica38,111±127(2000).
26.Perry,S.1990.Gas exchange strategy in the Nile crocodile:a morphometric study.J.Comp.Physiol.B
159,761±769(1990).
Supplementary information is available on Nature's World-Wide Web site
()or as paper copy from the London editorial of®ce of Nature. Acknowledgements
We thank S.Gatesy,J.Gauthier,N.Geist,F.Hertel,T.Holtz,S.Hunter,J.Hutchinson, L.Martin,M.Norell,S.Olson,T.Roberts,C.Schaff,Z.Zhou,the National Geographic Society and the Carnegie Muum for data,access to specimens,helpful discussions and/ or reviews of early versions of this manuscript.This work was supported by NSF grants to J.O.F.and J.A.R.and W.J.H.
Correspondence and requests for materials should be addresd to T.D.J.
(e-mail:tdjones@sfasu.edu). ................................................................. Genetic diversity and
dia control in rice
Youyong Zhu*,Hairu Chen*,Jinghua Fan*,Yunyue Wang*,Yan Li*, Jianbing Chen*,JinXiang Fan²,Shisheng Yang³,Lingping Hu§,
Hei Leung k,Tom W.Mew k,Paul S.Teng k,Zonghua Wang k
&Christopher C.Mundt k¶
*The Phytopathology Laboratory of Yunnan Province,Yunnan Agricultural University,Kunming,Yunnan650201,China
²Honghe Prefecture Plant Protection Station of Yunnan Province,
Kaiyuan661400,China
³Jianshui County Plant Protection Station of Yunnan Province,Jianshui654300, China
§Shiping County Plant Protection Station of Yunnan Province,Shiping662200, China
k Division of Entomology and Plant Pathology,International Rice Rearch Institute,MCPO Box3127,1271Makati City,The Philippines
¶Department of Botany and Plant Pathology,2082Cordley Hall,
Oregon State University,Corvallis,Oregon97331-2902,USA .............................................................................................................................................. Crop heterogeneity is a possible solution to the vulnerability of monocultured crops to dia1±3.Both theory4and obrvation2,3 indicate that genetic heterogeneity provides greater dia sup-pression when ud over large areas,though experimental data are lacking.Here we report a unique cooperation among farmers,
rearchers and extension personnel in Yunnan Province, ChinaÐgenetically diversi®ed rice crops were planted in all the rice®elds in®ve townships in1998and ten townships in1999. Control plots of monocultured crops allowed us to calculate the effect of diversity on the verity of rice blast,the major dia of rice5.Dia-susceptible rice varieties planted in mixtures with resistant varieties had89%greater yield and blast was94%less vere than when they were grown in monoculture.The
experi-ment was so successful that fungicidal sprays were no longer applied by the end of the two-year programme.Our results support the view that intraspeci®c crop diversi®cation provides an ecological approach to dia control that can be highly effective over a large area and contribute to the sustainability of crop production.
Many ecological process are strongly in¯uenced by spatial scale6±9,causing a major dilemma for experimental biologists,as large-scale®eld experiments are often prohibitively expensive.For example,there have been increasing calls for ecological approaches to counter the negative environmental impacts of modern agricul-tural systems10,11.One such approach,the u of within-®eld crop genetic diversity,has been shown to reduce dia verity in experimental plots and has been ud commercially in some cas1±4.However,experimental procedure and the nature of patho-gen dispersal can cau substantial underestimation of the impact of incread diversity on dia in small-scale experimental plots2±4. On the other hand,obrvations at larger spatial scale are few4,and do not allow for unambiguous determination of causal relation-ships between diversity and dia occurrence.
Our experimental system was blast dia in rice(Oryzae sativa). Rice is the staple crop for about half of the population of the world12. The fungus that caus blast dia,Magnaporthe gria,spre
ads through multiple cycles of axual conidiospore production during the cropping ason,causing necrotic spots on leaves and necrosis of ia interacts on a gene-for-gene basis13,14with its host and has a very varied pathogenesis15.It exists as a mixture of pathogenic races,that is,genetic variants that attack host genotypes with different resistance genes.Thus,host resistance genes often remain effective for only a few years in agricultural production before succumbing to new pathogenic races16,17.
Our experimental site(Yunnan Province,China)favours the development of rice blast epidemics becau of its cool,wet climate. Farmers commonly make multiple foliar fungicide applications to control blast.Glutinous or`sticky'rice varieties are ud for confections and other speciality dishes and have higher market value than other rice types,but have lower yields and are highly susceptible to blast.Non-glutinous,hybrid rice varieties are less susceptible to rice blast and are attacked by a different spectrum ia races.Before1998,98%of rice®elds in the study area were sown with monocultures of the hybrid rice varieties Shanyuo22and Shanyuo63.The desirable glutinous varieties were planted in small amounts becau of their low yields and vulnerability to blast in this environment.We conducted large-scale tests,made possible through the cooperation of thousands of rice farmers,to determine how the occurrence of rice blast is affected by within-®eld varietal diversi®
cation using mixtures of commonly grown glutinous and hybrid rice varieties.Our approach was bad on an obrved farmer practice of dispersing single rows of glutinous rice between groups of four rows of hybrid rice at a rate suf®cient to meet local demand for glutinous rice(Fig.1).
In the®rst year of the experiment,four different mixtures of varieties(Fig.2)were planted in a812-ha area consisting of all rice ®elds in®ve townships of Shiping County,Yunnan Province. Becau of the excellent blast control provided by the variety mixtures,only one foliar fungicide spray was applied.Mixtures were compared to monoculture control plots at15survey sites. Unlike standard experiment station®elds,control plots of mono-cultures were small relative to the total area of mixtures planted by farmers in the surrounding area,reducing the potential impact of spore dispersal from the more heavily infected monocultures to the mixture plots2±4.The study was expanded to3,342ha of rice®elds in 1999.This area consisted of all rice®elds in10townships that spanned Jianshui and Shiping Counties,with®ve participating townships and15survey sites per county.Procedures were the same as in1998,except that no foliar fungicide applications were made.In addition,some farmers cho to plant mixtures in a ratio of1glutinous:6hybrid rows,rather than1:4.
Diversi®cation had a substantial impact on rice blast verity (Fig.2).In1998,panicle blast verity on
the glutinous varieties averaged20%in monocultures,but was reduced to1%when disperd within the mixed populations(Fig.2a).Panicle blast verity on the hybrid varieties averaged1.2%in monoculture and was reduced to varying degrees in mixed plots,though only the larger differences were statistically signi®cant(Fig.2b).Results from 1999were very similar to the1998ason for panicle blast verity on the susceptible varieties(Fig.2a),showing that the effect of diversi®cation was very robust among mixtures and between asons and counties.In contrast,effects of crop diversi®cation on blast verity of the hybrid varieties were larger in1999than in 1998.Panicle blast verity on the varieties averaged2.3%in
Glutinous monoculture
15 cm20 cm
Hybrid monoculture
15 cm 30 cm
Mixture
15 cm15 cm30 cm
------------------- 2.4 m
--------------------
o o o o o o o o o o o o o o
o o o o o o o o o o o o o o
o o o o o o o o o o o o o o
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o o o o o o o o o o o o o o
o o o o o o o o o o o o o o
o o o o o o o o o o o o o o
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o o o o o o o o o o o o o o
o o o o o o o o o o o o o o
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o o o o o o o o o o o o o o
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o o o o o o o o o o o o o o
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x x x x x x x x x x x
x x x x x x x x x x x
x x x x x x x x x x x
x x x x x x x x x x x
x x x x x x x x x x x
x x x x x x x x x x x
x x x x x x x x x x x
x
x x o x x x x o x x x x o x
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x x o x x x x o x x x x o x隆昌公寓
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x x x x x x x x x x
Figure1Planting arrangements in rice variety mixture and monoculture survey plots in 1999and patterned after tho ud by farmers in Yunnan Province.Each symbol reprents a hill of susceptible(O)or resistant(X)rice.Distances between hills within rows were15cm for glutinous monocultures,30cm for hybrid monocultures and30cm for mixtures.Spacings and arrangements were the same in1998,except that the distance between rows of glutinous rice in monoculture was13cm.
monoculture and was reduced to 1.0%in mixed populations (Fig.2b),despite the fact that hybrids were planted at the same density in both mixture and monoculture survey plots.
Several mechanisms may reduce dia verity in genetically diver plant populations 2,4,18.Incread distance between plant
genotypes,which dilutes inoculum of a given pathogenic race as it is disperd between compatible host varieties,has been consid-ered the most important mechanism contributing to dia reduc-tion in variety mixtures 2.Such dilution effects almost certainly had a role in reducing blast dia on the susceptible,glutinous varieties
510152025303540% P a n i c l e b l a s t s e v e r i t y
应接不暇的反义词
% P a n i c l e b l a s t s e v e r i t y
Huangkenuo Shanyou 63Huangkenuo Shanyou 22Zinuo Shanyou 63Zinuo Shanyou 22
Shanyou 63Huangkenuo Shanyou 22Huangkenuo Shanyou 63Zinuo Shanyou 22Zinuo
a
b
Figure 2Panicle blast verity (mean percentage of panicle branches that were necrotic due to infection by Magnaporthe gria )of rice varieties planted in monocultures and mixtures.a ,The susceptible,glutinous varieties Huangkenuo and Zinuo.b ,The resistant,hybrid varieties Shanyuo22and Shanyuo63.S98,Shiping County,1998;S99,Shiping County,1999;J99,Jianshui County,1999;open bar,blast verity for a variety grown in monoculture control plots;black bar,blast verity of the same variety when grown in
mixed culture plots in the same ®elds.Error bars are ;n ,number of plot means that contribute to individual bars for each of the four combinations of susceptible and resistant variety.All differences between pairs of monoculture and mixture bars are signi®cant at P ,0.01bad on a one-tailed t -test,unless indicated by 0.05(signi®cant at P ,0.05),0.10(signi®cant at P ,0.10)or n.s.(not signi®cant at P =0.10).
Table 1Grain yields and monetary value for rice varieties
Grain
(Mg per ha)
Crop value (US$per ha)Variety or mixture Hills m -2*,²
Shiping/98Shiping/99Jianshui/99Shiping/98Shiping/
Huangkenuo 38.1 3.6960.02 4.0760.07 5.1260.05129114241794Shanyuo6314.88.1460.078.4160.129.7160.07170917652039Mixture
18.58.7260.059.5360.1110.5360.12191221662341Huangkenuo 3.70.59(173) 1.19(300)0.92(186)205415323Shanyuo6314.88.13(100)8.34(99)9.61(99)1707
1751
2018
...................................................................................................................................................................................................................................................................................................................................................................
Huangkenuo 38.1 3.7960.03 4.1560.07 5.0860.10132814521778Shanyuo2214.87.9760.118.1260.069.0860.20167317051907Mixture
18.58.4060.128.7760.0910.0060.16183819412231Huangkenuo 3.70.53(151)0.71(177)0.94(191)184249330Shanyuo2214.87.88(99)8.06(99)9.05(
Zinuo
38.1 3.6260.04 3.9760.02 4.9060.09126813901716Shanyuo6314.88.2860.138.4060.089.6360.17173917652022Mixture 18.58.9060.229.2360.0310.4660.18193720562315Zinuo
3.70.48(146)0.84(217)0.84(177)170294296Shanyuo631
4.88.42(102)8.39(100)9.62(
Zinuo
38.1 3.4960.02 3.8260.03 4.8960.11122013371711Shanyuo2214.87.8460.068.1460.039.1460.05164617101919Mixture 18.58.2760.058.8660.079.9960.03180719652227Zinuo
3.70.51(160)0.75(203)0.92(193)178264321Shanyuo22
14.8
7.76(99)
8.10(99)
9.08(99)
1629
1701
1906
...................................................................................................................................................................................................................................................................................................................................................................The rice varieties were grown as monocultures or mixed in Shiping and Jianshui counties in 1998and 1999.Crop values bad on market prices of 0.21US$per kg for hybrid varieties and 0.35US$per kg for glutinous varieties.Italicized values of hills m -2,grain yield,and crop value are for the individual varieties within mixtures.Bold values in parenthes are per-hill yields of varieties in mixture expresd as a percentage of per-hill yield of the same variety in monoculture.*See also Fig.1.
²In 1998,density of glutinous varieties in monoculture was 40.4hill m -2.
in this study.In addition,canopy microclimate data collected at one survey site in1999indicate that hei
ght differences between the taller glutinous and shorter hybrid varieties resulted in temperature, humidity and light conditions that were less conducive for blast on glutinous varieties in the mixtures than in the monocultures. Dia reductions on hybrid varieties in the mixtures are more dif®cult to explain.Dilution and microenvironmental modi®ca-tions are unlikely mechanisms,as the hybrids were planted at the same density in mixtures and monocultures(Fig.1).The taller glutinous varieties may physically have blocked spore dispersal and/ or altered wind patterns compared with the hybrid monocultures. In addition,induced resistance may have some contribution to dia suppression in the hybrids.Induced resistance occurs when inoculation with avirulent pathogen race(s)induces a plant defence respon that is effective against pathogen races that would nor-mally be virulent on that host genotype.This has made signi®cant contributions to dia reductions in variety mixtures of other small grain crops19,20.
In1999,we determined the genetic composition of the pathogen populations derived from inter-planting and monoculture®elds using polymera chain reaction(PCR)®ngerprinting21of pathogen isolates.Preliminary results indicate that®elds with mixtures supported diver pathogen populations with no single dominant strain.In contrast,pathogen populations from monoculture®elds were dominated by one or a few strains.The more diver pathogen population from the mixed stands ma
y have contributed to greater induced resistance from incompatible interactions.In the longer term,this incread pathogen diversity may also slow adaptation of the pathogen to resistance genes functioning within a given mixture. Clarifying the mechanisms by which host diversity in¯uenced dia in our study will be helpful in extending the results to other agro-ecosystems.The mechanistic studies are currently underway. Grain production per hill of glutinous varieties in mixtures averaged89%greater than that in monoculture(Table1).As a result,glutinous rice in mixtures produced18.2%of monoculture yield,on average,though it was planted at rates of only9.2and9.7% that of monoculture in1998and1999,respectively(e also Fig.1). Reduced dia verity certainly had a role in this yield respon, though other factors(for example,improved light interception) may also have had an in¯uence.Despite the incread overall plant density in mixtures(e Fig.1,bottom),grain yields per hectare of the hybrids in mixture were nearly equal to the corresponding monocultures.Thus,mixed populations produced more total grain per hectare than their corresponding monocultures in all cas (Table1).Land equivalent ratios22,which estimate the ecological ef®ciency of mixed populations,indicate that an average of1.18ha of monoculture crop land would need to be planted to provide the same amounts of hybrid and glutinous rice as were produced in1ha of a mixture(Table2).After accounting for the differing market values of the two rice types,the gross value per hectare of the mixtures was14%greater than hybrid monocultures and40% greater than glutinous monocultures(Table1).
Though dia reductions are theoretically maximized in random mixtures of plants23,row mixtures provided the most practical approach in our speci®c application.As rice is hand-harvested in Yunnan Province,farmers can easily parate the hybrid and glutinous grains,which are ud for different purpos. However,many other approaches can be ud to attain within-®eld genetic diversity of crops3,24.For example,wheat(Triticum aestivum) mixtures are grown in the Paci®c Northwest of the USA under highly mechanized conditions4.In this ca,varieties are chon to be similar in height,maturity and market quality,planted as random mixtures,and harvested and marketed as bulk populations3. Commercial-scale u of crop diversity has provided obrva-tional support for the dia-suppressive effects of crop diversity in a limited number of cas4,25,26,most notably the control of barley (Hordeum vulgare)powdery mildew(caud by Erysiphe graminis) in the former East Germany26.However,the varietal diversi®cation program in Yunnan Province provided an unusual opportunity to determine causal relationships between crop diversity and dia, as replicated monoculture controls were available for comparison within a substantial expan of mixed culture.The impact of crop diversi®cation on blast verity in this study was greater than that reported from small-scale experimental plots with this dia3, although we do not have proof that this difference is due only to the spatial scale.By the cond year of the project,no foliar fungicides were needed for blast control in the diversi®ed area,though this may not be possible in all asons.T
he Yunnan diversi®cation program has resulted in great interest by farmers,and the practice has expanded to more than40,000ha in2000.
The`Green Revolution'has provided remarkable increas in crop productivity over the past four decades27.However,this agricultural transformation has also resulted in problems,including loss of crop genetic diversity11.The current world population of over six billion does not allow us to return to agricultural production practices of the past.Rather,we need to maintain the bene®ts of modern agriculture while addressing its drawbacks.In this regard,it is signi®cant that the diversi®cation program described here is being conducted in a cropping system with grain yields approaching 10Mg ha-1,among the highest in the world.The value of diversity for dia control is well established experimentally and diversity is increasingly being ud against wind-disperd pathogens of small grain cereals4.Recent experimental results indicate other applica-tions of diversity,for example,against soil-borne pathogens and for tree crops4.The effect of varietal diversi®cation will vary among dias and agro-ecosystems4.Further,one can not expect all variety mixtures to provide functional diversity to a given plant pathogen population24,28,nor can one predict the time for which they may remain effective.Indeed,we have identi®ed variety combinations that provide little or no blast control in Yunnan Province.Nonetheless,our results demo
nstrate that a simple,eco-logical approach to dia control can be ud effectively at large spatial scale to attain environmentally sound dia control.M
Methods
Study sites
In1998,townships participating in the diversi®cation experiment were Baxing,Baoxiu, Songchun,Maohe and Xincheng of Shiping County.The townships are contiguous,and all rice®elds in the®ve townships were involved in the diversi®cation program.In1999, the study area consisted of all rice®elds in ten contiguous townships:Chenguang,Dongba, Mianding,Nanzhuang and Xizhuang in Jianshui County;and Baxing,Baoxiu,Songchun, Maohe and Yafanzi in Shiping County.
Dia asssments
To monitor dia,survey plots were established at15sites per county,three in each of the ®ve townships participating in the diversi®cation program(15sites in1998,30sites in 1999).Seedlings were transplanted into the®eld in April or May in hills of4±5plants for glutinous varieties and1plant pe
r hill for the hybrid varieties,which produce a greater number of tillers per plant.All plots were managed by farmers and treated in the same manner as the surrounding mixed variety plantings,including fungicide application.In each of the survey sites,a®eld was divided into three plots.One plot was planted with the mixture grown most commonly by local farmers,and the remaining two plots were monocultures of the glutinous and hybrid variety included in that mixture.For mixtures, the same row spacing of hybrid rice was ud as in monoculture,but one row of glutinous rice was added between each group of four rows of hybrid rice,in an`addition'approach (Fig.1).Each of the four mixtures was evaluated for dia verity in3±5of the15survey
Table2Land equivalent ratios for rice yield produced in variety mixtures
County and year
Mixture Shiping
1998Shiping
1999
Jianshui
1999
............................................................................................................................................................................. Huangkenuo/Shanyuo63 1.16 1.28 1.17 Huangkenuo/Shanyuo22 1.13 1.16 1.18 Zinuo/Shanyuo63 1.15 1.21 1.17 Zinuo/Shayuo22 1.14 1.19 1.18 ............................................................................................................................................................................. Land equivalent=(yield ha-1of variety A in mixture/yield ha-1of variety A in monoculture)+(yield ha-1of variety B in mixture/yield ha-1of variety B in monoculture).
sites in each county,depending on the popularity of a given mixture with farmers.Plots ranged from100to450m2each,depending on®eld size.
Survey plots were assd in late August for the verity of blast symptoms,expresd as the percentage of panicle branches that were necrotic due to the effects ia.Dia was assd at®ve sampling points in each plot,distributed in a uniform pattern.Twenty hills resulting from the transplanting process were evaluated at each sampling point,with each hill containing about10panicles per hill,to give a total of approximately1,000 panicles evaluated per plot.Each sampled panicle was visually examined by experienced personnel to estimate the percentage of bra
nches that were necrotic due to infection by M. gria.Each panicle was given a rating29from0to5,where0is no dia;1is less than5% of panicle branches necrotic;2is5±30%necrotic;3is30±50%necrotic;4is greater than 50%necrotic;and5is100%necrotic.Dia verity was summarized within each plot as { n131 n232 n333 n434 n535 =S n0¼n5}3100,where n0 (5i)
the number of culms in each of the respective dia categories.Thus,a dia verity of 0%would indicate no dia and100%would indicate that100%of panicle branches were necrotic.
Yield evaluation
Plots were hand-harvested,threshed and weighed to determine grain yield.Individual varieties were evaluated parately in mixtures.Land equivalent ratios22were calculated as (yield ha-1of variety A in mixture/yield ha-1of variety A in monoculture)+(yield ha-1of variety B in mixture/yield ha-1of variety B in monoculture).
Statistical analys
Each survey plot was considered to be an experimental unit,and analys were bad on mean di
a verities and grain yield for each plot.Statistical analys were conducted parately by year and county owing to differences in dia level.One-tailed t-tests were ud to determine if blast verity for each of the two varieties in each of the four mixtures differed signi®cantly from its corresponding monoculture control.
Received18April;accepted30June2000.
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Acknowledgements
This work was supported by the Asian Development Bank,the Yunnan Province Government,The Ministry of Science and Technology of China,the International Rice Rearch Institute(IRRI),and a scienti®c agreement between IRRI and Oregon State University.We thank the personnel of the provincial and county Plant Protection Stations and participating farmers for their contributions to this project,and M.Hoffer for computer assistance and graphics.
Correspondence and requests for materials should be addresd to C.C.M.
(e-mail:st.edu). ................................................................. Fear memories require protein synthesis in the amygdala for reconsolidation after retrieval
Karim Nader,Glenn E.Schafe&Joph E.Le Doux
W.M.Keck Foundation Laboratory of Neurobiology,Center for Neural Science, New York University,New York,New York10003,USA .............................................................................................................................................. `New'memories are initially labile and nsitive to disruption before being consolidated into stable long-term memories1±5. Much evidence indicates that this consolidation involves the synthesis of new proteins in neurons6±9.The lateral and basal nuclei of the amygdala(LBA)are believed to be a site of memory storage in fear learning10.Infusion of the protein synthesis inhibitor anisomycin into the LBA shortly after training prevents
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C
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Figure1Schematic reprentation of the amygdala at four different rostral±caudal planes.The numbers reprent the posterior coordinate from bregma.Injector placements in the LBA are reprented by the®lled symbols;black®lled squares reprent ASCF group placements,grey®lled triangles reprent the low-do anisomycin,and black®lled circles reprent high-do group.L,lateral nucleus;B,basal nucleus;C,central nucleus.The placements for subquent experiments all demonstrate similar distributions as in this experiment and therefore are not shown.
