| With widespread use of herbicide,weed resistance has become a matter of concern.American sloughgrass(Beckmannia syzigachne Steud.)is one of the most troublesome weeds.American sloughgrass is a troublesome annual gramineous weed which affects the yield of wheat and oil plants in China.The overreliance on acetyl-coenzyme A carboxylase(ACCase)inhibiting herbicides has resulted in resistance evolution in this weed.Previous study done by our team confirmed that plastidic ACCase amino acid substitutions was one of reasons conferred high level resistance to fenoxaprop-P-ethyl in several American sloughgrass populations collected from Anhui,Jiangsu,Shangdong provence.Five amino acid substitutions had been identified,and they were Ile1781 Leu,Trp2027Cys,Ile2041 Asn,Asp2078Gly and Gly2096 Ala.The objective of the present study was to clarify the fitness cost associated with specific ACCase amino acid substitution in American sloughgrass,predict resistant weed evolution in the field,and then provide a theoretical basis for the comprehensive management of resistant weeds.Based on the previous study,the fitness cost associated with five specific ACCase amino acid substitutions was cleared,and the main results were as follows:1.Mother plants heterozygous(M/W)for one specific mutant were identified using CAPS/dCAPS makers from original resistant populations,and then homozygous mutant(M/M)genotype palnts and wide genotype(W/W)plants were segregated from progeny plants.Homozygous mutant(M/M)genotype palnts 1781M/M,2027M/M,2041M/M,2078M/M,2096M/M shared a similar genetic background with corresponding wide genotype(W/W)plants 1781W/W,2027W/W,2041W/W,2078W/W,2096W/W.2.The whole-plant bioassay was used to screen sensitivity of derived wide genotype plants,and the results showed that 1781W/W,2027W/W,2041W/W,2078W/W genotype plants were all susceptible to fenoxaprop-P-ethyl,clodinafop-propargyl,fluazifop-P-butyl,haloxyfop-P-methyl,sethoxydim,clethodim,pinoxaden,respectively.2096W/W genotype plants developed high level resistance to fenoxaprop-P-ethyl with resistance factor(Rf)63.5 and low resistance to clodinafop-propargyl and pinoxaden.3.The whole-plant bioassay was used to identify the resistance background of derived mutant genotype plants,and results showed that 1781M/M genotype plants evolved high level resistance(Rf>10)to all herbicides used in this test.2027M/M,2041M/M genotype plants evolved high level resistance to fenoxaprop-P-ethyl,clodinafop-propargyl,fluazifop-P-butyl,haloxyfop-P-methyl,pinoxaden,low level resistance(2<Rf<5)to sethoxydim,clethodim.2078M/M genotype plants evolved high level resistance to fenoxaprop-P-ethyl,clodinafop-propargyl,fluazifop-P-butyl,haloxyfop-P-methyl,pinoxaden and moderat resistance to sethoxydim,clethodim(5<Rf<10).2096M/M genotype plants evoled high level resistance to fenoxaprop-P-ethyl,clodinafop-propargyl,fluazifop-P-butyl,haloxyfop-P-methyl and moderate resistance to sethoxydim,clethodim,pinoxaden.4.Pariwise comparisons of the germination functions of the different genotype seeds(M/M and W/W)under optional germination conditons showed that: fresh 2041M/M genotype seeds had an acceleration in seeds germination(0.8 day earlier in the times to reach 50% germination(t G50))than 2041W/W genotype seeds,and two genotypes seeds had a similar germination function after stored 4 months later.Other mutant genotype seeds had no significant difference in germination fuction compared with corresponding wide genotype seeds.5.Pariwise comparisons of the germination functions of the different genotype seeds(M/M and W/W)under stress germination conditons showed that: a)Over the p H ranging 4 to 10,germination of all genotype seeds was all >92.5%.b)Germination of 1781M/M genotype seeds increased significantly(increased 16.4%,14.8%,39.3%,65.9% at-0.2,-0.3,-0.4,-0.5MPa,respectively)as osmotic potential <-0.1 MPa compared with 1781W/W genotype seeds.c)Germination of 1781M/M genotype seeds increased 2.8%,36.3% compared with responding wide genotype seeds at 80 mM,160 mM NaCl,respectively.d)2027M/M,2041M/M,2078M/M,2096M/M genotype caused no significant effects.6.Accelerated ageing(40°C,100% relative humidity)experiment showed that: a)2078M/M genotype seeds had a significant acceleration in seeds ageing(1.71 day earlier in the incubation times causing 50% reduction in viability(P50)).b)Germination of 2027M/M genotype seeds was 18.75% after 16 d incubation,while germination of 2027W/W genotype seeds was 2.5%.c)A higher b-parameter was observed in 2096M/M genotype seeds(b=4.45)than 2096W/W(b=2.58),but the germination of 2096M/M genotype seeds was always higher than wide genotype seeds over all the incubation time.d)1781M/M,2041M/M genotype caused no significant difference in accelerated ageing function.7.Pariwise comparisons of the plant vegetative growth traits of the different genotype plants(M/M and W/W)showed that: a)1781M/M genotype plants exhibited significant higher RGR(increasing 10.5% in classic growth analysis and 7.34% in combined growth analysis)and NAR values(7.34~31.7%)than 1781W/W wide genotype plants.b)2078M/M genotype plants showed lower RGR and NAR values(8.53~15.4%).2027M/M,2041M/M nor 2096M/M genotype plants showed no difference in comparison with corresponding wide genotype plants in growth traits.8.Competition experiment with wheat in pot showed that: a)2027M/M genotype plants produced less seeds than 2027W/W genotype plants,and the highest can be reduced by 66.6%.b)Seed production and above dry biomass of 2078M/M plants reduced by up to 41.3% and 39.7% than 2078W/W palnts,respectively.c)1781M/M genotype plants showed a decreasing seed production(12.2~14.9%),but an increasing dry biomass(10.9~18.1%)than 1781W/W genotype plants at low level of competition pressure.9.Competition experiment in field indicated that: a)Seed production of 2027M/M genotype plants decreased 20% than wide genotype plants.b)2078M/M plants showed lower(20~30%)seed production,above dry biomass and plant height than 2078W/W genotype plants.c)2041M/M genotype plants only showed a reduction in biomass(12.5%)but not in other traits.10.Low tempreture and drought stress experiment showed that only in 2078M/M genotype seedlings,SOD and CAT activity were lower(10%)than wide genotype seedlings under low tempreture condition,and CAT activity deceased about 9% under drought stress.Herbicied resistance and fitness cost endowed by specific plastidic ACCase mutatioin were confirmed in American sloughgrass.Homozygous mutant alleles Ile1781 Leu,Trp2027Cys,Ile2041 Asn,Asp2078Gly or Gly2096 Ala could confer broad resistance to ACCase inhibiting herbicides.Paticular ACCase mutant usually has pleiotropic effects on weed life cycle.Homozygous Asp2078 Gly mutantion could result in significant finess cost,and this may adversely affect the spread of this mutant allele.Homozygous Trp2027 Cys mutantion caused a slight fitness cost,and this may have less impact on the spread of this resistance gene.Fitness advantage result from homozygous Ile1781 Leu may provide favorable conditions for the spread of Ile1781 Leu alleles.Ile2041 Asn or Gly2096 Ala mutant alleles only altered fitness slightly(but significantly). |
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