Informative ISSR Markers Help Identify Genetically Distinct Accessions of Oryza rufipogon in Yield Improvement

Inter simple sequence repeat(ISSR) polymorphism was used to determine genetic diversity and phylogenetic relationships in 90 genotypes of wild and cultivated species of Oryza from different geographical regions of the world. In all the 17 primers used in ISSR-PCR, a total of 11 464 bands were amplified at 253 band positions/loci. The primer UBC-809 amplified the maximum bands(1 059) at 21 band positions. UBC-810 and UBC-835 amplified the minimum of 391 bands each at 7 and 14 band positions, respectively. The mean polymorphism information content ranged from 0.44 to 0.84 and resolving power ranged from 8.69 to 23.53. Un-weighted pair group method with arithmetic mean dendrogram and population structure based on the 17 primers separated all genotypes into 4 major clusters with a genetic similarity of 53%–100%. The first two clusters consisted of 30 O. rufipogon accessions each. In the third cluster, O. nivara and O. longistaminata grouped as one sub-cluster and all other O. nivara accessions and cultivars grouped as another sub-cluster. The fourth cluster had only five O. rufipogon accessions which can be a source of new genes. Four sub-populations were identified within O. rufipogon and two sub-populations within O. nivara at K = 7. A subset of six primers with high resolving power values were the most informative and grouped all genotypes almost similarly as the 17 primers did. Use of these six highly informative primers in ISSR-PCR is a cost effective and robust method for assessing genetic diversity in large germplasm collections of wild rice species.     

High Temperature Modifies Resistance Performances of Rice Varieties to Brown Planthopper,Nilaparvata lugens(Stl)

To investigate the effect of temperature on the resistance characteristics of rice varieties with different resistance genes to brown planthopper(BPH),Nilaparvata lugens(Stl),the resistances of IR26(Bph1)and IR36(bph2)to BPH population in Hangzhou,China were monitored in greenhouse during September in 2007 and 2008 by using the standard seedling screening techniques(SSST)developed by the International Rice Research Institute(IRRI).Furthermore,the changes in resistance of IR26 and IR36 to BPH,soluble sugar and oxalic acid contents in 25-day-old rice plants of susceptible variety TN1 and resistant varieties IR26 and IR36 were detected at five temperatures(22℃,25℃,28℃,31℃ and 34℃).IR26 completely lost resistance both in greenhouse and at the five tested temperatures.IR36 still had moderate resistance at natural temperature,but its resistance decreased gradually when the temperature increased from 25℃ to 34℃,and fully lost its resistance at 31℃ and 34℃.The highest durable resistance of IR26 and IR36 were recorded at 25℃.The soluble sugar content in plants of the three tested rice varieties increased with temperature increase,and the oxalic acid content increased with the temperature increase at first,maximized at 25℃,and then declined.Two-way ANOVA indicated significant effects of temperature and rice variety on contents of soluble sugar and oxalic acid in rice plants.     

Genome-wide markers for seed yield and disease resistance in perennial ryegrass

The market success of perennial ryegrass(Lolium perenne L.) cultivars depends on sufficient seed production, as they are propagated by seed. However, breeding for high quality forage production reduces seed yield, and breaking the negative correlation would help to overcome the problem. The foliar disease crown rust is another factor affecting reproductive capacity and thereby seed yield. We evaluated seed yield-related traits and resistance to crown rust in a collection of commercial cultivars and ecotypes of perennial ryegrass and identified genome-wide markers associated with the traits. The study revealed high variation between the ecotype and cultivar groups as well as between years. A genome-wide association study identified 17 DNA single-nucleotide polymorphisms(SNPs) of which eight were associated with crown rust and nine with flag-leaf length. The SNP markers were located within or near predicted genes functioning in defense against pathogens. The identified genes are strong candidates for a further in-depth functional study to continue unravel determination of leaf architecture and crown rust resistance in perennial ryegrass.     

Tolerance evaluation of rice varieties to the brown plan-thopper,Nilaparvata lugens feeding

The brown planthopper, Nilaparvata lugens (Stal) (BPH) is one of the most important insect pests of rice in China and other east-southern Asian countries. Utilization of rice resistance varieties is one of the most e-conomic and effective ways for controlling N. lugens . The resistance of rice varieties declined due to the change of BPH biotype. The current resistance screening methods based on biotic reaction also may eliminate numerous rice varieties with high-yielding and/ or good grain quality which were not resistant to BPH but had strong tolerance to BPH.     

Marker-Assisted Pyramiding of Genes Conferring Resistance Against Bacterial Blight and Blast Diseases into Indian Rice Variety MTU1010

Two major bacterial blight(BB) resistance genes(Xa21 and xa13) and a major gene for blast resistance(Pi54) were introgressed into an Indian rice variety MTU1010 through marker-assisted backcross breeding. Improved Samba Mahsuri(possessing Xa21 and xa13) and NLR145(possessing Pi54) were used as donor parents. Marker-assisted backcrossing was continued till BC2 generation wherein PCR based functional markers specific for the resistance genes were used for foreground selection and a set of parental polymorphic microsatellite markers were used for background selection at each stage of backcrossing. Selected BC2F1 plants from both crosses, having the highest recoveries of MTU1010 genome(90% and 92%, respectively), were intercrossed to obtain intercross F1(ICF1) plants, which were then selfed to generate 880 ICF2 plants possessing different combinations of the BB and blast resistance genes. Among the ICF2 plants, seven triple homozygous plants(xa13xa13Xa21Xa21Pi54Pi54) with recurrent parent genome recovery ranging from 82% to 92% were identified. All the seven ICF2 plants showed high resistance against the bacterial blight disease with a lesion lengths of only 0.53–2.28 cm, 1%–5% disease leaf areas and disease scoring values of ‘1' or ‘3'. The seven ICF2 plants were selfed to generate ICF3, which were then screened for blast resistance, and all were observed to be highly resistant to the diseases. Several ICF3 lines possessing high level of resistance against BB and blast, coupled with yield, grain quality and plant type on par with MTU1010 were identified and advanced for further selection and evaluation.     

Genome-wide association study identifies novel loci and candidate genes for drought stress tolerance in rapeseed

Rapeseed(Brassica napus)is one of the most important oil crops worldwide;however,drought seriously curtails its growth and productivity.Identifying drought-tolerant germplasm is an efficient strategy for addressing water shortages.Here,we phenotyped a panel of 264 B.napus accessions at full-bloom stage using water loss ratio(WLR)as drought-tolerant index.It identified 8 low-WLR and 6 high-WLR accessions,regarded as droughttolerant and drought-sensitive,respectively.Comparing with drought-sensitive accessions at the seedling stage,drought-tolerant accessions had shown better performance in maintaining fresh and dry weights,and performed the higher expression of drought-induced marker genes under drought stress.Subsequently,a total of 139 SNPs(single nucleotide polymorphisms)were identified associated with the WLR using a genome-wide association study(GWAS)among 264 B.napus accessions,with the largest number SNPs at chromosome A10,and 13 SNPs significantly were associated with the WLR(-log₁₀(p-value)>6).Furthermore,4 putative candidate genes(BnaC09.RPS6,BnaC09.MATE,BnaA10.PPD5 and BnaC09.Histone)were screened involving in drought tolerance in B.napus.Together,our results highlight the WLR's importance in drought tolerance and establish the foundation for improving WLR-associated drought tolerance in rapeseed.     

Distribution of Magnaporthe grisea Population and Virulence of Predominant Race in Jiangsu Province,China

Three hundred and forty-two mono-conidial isolates were obtained from rice blast specimens collected from five typical areas in Jiangsu Province during 2000-2002. The isolates could be classified into seven groups, thirty races when assessed with seven Chinese differential rice cultivars. The race ZG1 was predominant one of Magnaporthe grisea with a frequency of 65.00% in 2000, 56.90% in 2001 and 60.38% in 2002; the races ZB and ZC groups were also important in Jiangsu Province. By inoculating 130 ZG1 race isolates on thirteen Japanese cultivars with known resistance genes, forty-two pathotypes were found. Among them, 30.77% of ZG1 race isolates had virulence to rice cultivars Shin 2(Pita-ks, Pi-sh), K1(Pi-ta), Pi 4(Pi-ta2, Pi-sh), being the predominant pathotype, indicating the resistances of cultivars Shin 2 (Pita-ks, Pi-sh), K1(Pi-ta), Pi 4(Pi-ta2, Pi-sh) had lost the resistance in Jiangsu Province. Rice cultivar K3(Pi-kh) was highly resistant to Magnaporthe grisea with 100% resistance frequency, and resistant to the two single isolates, 2003-184(ZC5) and 2003-14-1(ZG1), however, it was infected by a mixture of the two isolates. It was suggested that the change in virulence stemmed from the interaction of different pathotype isolates was one of the reasons that made variety lose its resistance.     

Rapid generation advance(RGA) in chickpea to produce up to seven generations per year and enable speed breeding

This study was aimed at developing a protocol for increasing the number of generation cycles per year in chickpea(Cicer arietinum L.).Six accessions,two each from early(JG 11 and JG 14),medium(ICCV 10 and JG 16),and late(CDC-Frontier and C 235)maturity groups,were used.The experiment was conducted for two years under glasshouse conditions.The photoperiod was extended to induce early flowering and immature seeds were germinated to further reduce generation cycle time.Compared to control,artificial light caused a reduction in flowering time by respectively 8–19,7–16,and 11–27 days in early-,medium-,and late-maturing accessions.The earliest stage of immature seed able to germinate was 20–23 days after anthesis in accessions of different maturity groups.The time period between germination and the earliest stage of immature seed suitable for germination was considered one generation cycle and spanned respectively 43–60,44–64,and 52–79 days in early-,medium-,and late-maturing accessions.However,the late-maturing accession CDCFrontier could not be advanced further after three generation cycles owing to the strong influence of photoperiod and temperature.The mean total number of generations produced per year were respectively 7,6.2,and 6 in early-,medium-,and late-maturing accessions.These results have encouraging implications for breeding programs:rapid progression toward homozygosity,development of mapping populations,and reduction in time,space and resources in cultivar development(speed breeding).     

Interspecifc hybrid plants obtained from cultivars （AA） crossed with wild Oryza species （CC）

Wild dee O.officinalis(CNW 258, CNW 259) and O. eichingeri (CNW 260, CNW 261) have CC genome and high resistance to brown planthopper (BPH) and whitebacked planthopper (WBPH). To transfer the resistant gene(s) of the wild rice into Asian cultivated rice, the interspecific crosses between O. sativa L. (AA) and O. officinafis and O.eiclungeri (CC) was made in present study.     

Antixenosis and Tolerance of Rice Genotypes Against Brown Planthopper

Nine genotypes were evaluated under greenhouse conditions for antixenosis and tolerance against brown planthopper(BPH, Nilaparvata lugens St?l). In antixenosis studies, proportion of insects settled on a test genotype in relation to the susceptible control TN1 was recorded, with significantly lower proportion of nymphs(55.22%–59.18%), adult males(60.33%–60.75%), and adult females(80.56%–79.26%) settled on RP2068-18-3-5 and Ptb33 in relation to those on TN1. Based on number of feeding sites, the test genotypes were ranked in order from the highest to the lowest as RP2068-18-3-5, Ptb33, MR1523, Rathu Heenati, Sinnasivappu, ARC10550, MO1, INRC3021 and TN1. The order was exactly reverse in terms of fecundity expressed as number of eggs laid per female. In tolerance studies, days to wilt, functional plant loss index and plant dry weight loss to BPH dry weight produced were recorded. RP2068-18-3-5, Rathu Heenati and Ptb33 performed better than the other test genotypes. These results helped in relative quantification of BPH resistance levels in the genotypes. RP2068-18-3-5, a new effective source of BPH resistance, can be used in resistance breeding after tagging of resistant genes/QTLs linked to different parameters of antixenosis and tolerance with selectable molecular markers.     

Characterization of Myanmar Paw San Hmwe Accessions Using Functional Genetic Markers

Paw San Hmwe(PSM) rice has been cultivated in many areas of Myanmar for a long time. Strong aroma,good taste and its elongation during cooking are the key characteristics of PSM rice. Thirty-one PSM accessions were genotypically characterized,and their physical grain and cooking quality traits were studied. We used specific gene markers associated with aroma,apparent amylose content(AAC) and alkali spreading value to determine the alleles carried by different PSM accessions. The results revealed that six PSM accessions(PSM10,PSM12,PSM13,PSM21,PSM22 and PSM30) had a 3-bp insertion in Os2 AP gene. Gel consistency(GC) allele was predominant among the PSM accessions for gelatinization temperature(GT),however,the phenotype observed was between low and intermediate GT because of the combination of the GC allele with the presence of low GT allele at heterozygous state from the other loci of the SSIIa gene. Intermediate to high AAC was observed among the PSM accessions corresponding to the haplotype identified for the single nucleotide polymorphism G/T and the(CT)n repeat in the Wx gene. The characterization and grouping data of PSM accessions posted benefits to Myanmar seed banks,and our results will help in maintaining the integrity of PSM rice variety.     

lsozyme analysis on progenes of somatic hybrids of Oryza sativa L.and O.officinalis

Some wild species of Oryza possess agronomically useful traits such as disease/insect resis tance and salt tolerance. However, the use of wild Oryza species for rice improvement has been hampered by the sexual incompatibility or sterility of hybrids obtained by conventional methods. We have used protoplast fusion as a method to incorporate useful trait of wild O ryza species into cultivated rice and obtained somatic hybrid plants between O.satlva and O.officinalis and their progenies. Isozyme analysis is a method to confirm somatic hybrids and to determine the nuclear constitution of somatic hybrids. The esterase and peroxidase isozyme analysis in progenies of somatic hybrids were herein reported. Two breeding lines PF52 and PF79 were F_2 lines developed form somatic hybrids of O.sativa L.cv. 02428 and O.officinalis accesion. O.sativa L.cv. 02428 and O.officinalis were used as control. Fresh leaves from plants growing in greenhouse were homogenized with extraction     

Identification and Genetic Analysis of Gall Midge Resistance in Rice Germplasm 91-1A2

Resistance to rice gall midge in rice germplasm 91-1A2 was identified and genetically analyzed. F1s of rice population were derived from 91-1A2 which crossed with rice materials Jinggui, TN1, W1263 (Gm1), IET2911 (Gm2), BG404-1 (gm3), OB677 (Gm4), ARC5984 (Gm5) and Duokang 1 (Gm6) as a male parent. The resistance of all parental lines and F1, BC1F1 and F2 populations to rice gall midge was identified. The results showed that 91-1A2 and all F1s were resistant to Chinese rice gall midge biotype IV. The segregation ratio of resistant plants to susceptible ones in BC1F1 and F2 were accorded with 1:3 and 9:7 rules by χ2 test, suggesting that the resistance of 91-1A2 to Chinese rice gall midge biotype IV was controlled by two dominant genes which were new resistance genes, non-allelic to the known rice gall midge resistance genes.     

Osa-mi R439 Negatively Regulates Rice Immunity Against Magnaporthe oryzae

Osa-miR439 is a rice-specific microRNA family. Here we showed that Osa-miR439 acted as anegative regulator in rice immunity against blast fungus Magnaporthe oryzae. Osa-miR439 differentiallyresponded to M. oryzae between susceptible and resistant rice accessions. The accumulation ofOsa-miR439 was constitutively more in the susceptible accession than in the resistant one. Transgeniclines overexpressing Osa-miR439a (OX439a) showed higher susceptibility associating with lower inductionof defense-related genes and less hydrogen peroxide (H2O2) accumulation at the infection sites than thecontrol plants. In contrast, transgenic lines expressing a target mimic of Osa-miR439 (MIM439) displayedcompromised susceptibility associating with increased H2O2 accumulation. Furthermore, we found thatthe expression of three predicted target genes was decreased in OX439a but increased in MIM439 incomparison to control plants, and this expression was differential in susceptible and resistant accessionsupon M. oryzae infection, indicating that Osa-miR439a may regulate rice blast resistance via these genes.Our results unveiled the role of Osa-miR439a in rice blast resistance and provided the potentiality toimprove the blast resistance via miRNA.     

QTL mapping of qSCN3-1 for resistance to soybean cyst nematode in soybean line Zhongpin 03-5373

Soybean cyst nematode(SCN,Heterodera glycines Ichinohe)is one of the most economically destructive pathogens.The soybean line Zhongpin03-5373(ZP),which combines resistance genes from several donors,is highly resistant to SCN race 3(SCN3).In our previous study,two QTL(rhg1 and GmSNAP11)were identified in a population of recombinant inbred lines derived from a cross between ZP and the susceptible parent Zhonghuang 13.The two QTL explained around one-third of the resistance,suggesting the presence of further QTL contributing to SCN resistance.In the present study,we used an improved version of the geneticmap comprising the previously applied 1062 molecular markers and 47 newly developed InDel(insertion-deletion)markers.The improved map revealed a novel locus contributing to SCN3 resistance:qSCN3-1,flanked by InDelmarker InDel1-7 and SNPmarker Map-0047,explained 4.55%of the phenotypic variance for resistance to SCN3 and was not involved in digenic epistatic interaction with rhg1 and GmSNAP11.Haplotypes of Map-0047_CAPS(a CAPS marker developed for Map-0047)and InDel1-7 were significantly associated with SCN3 resistance in a panel of 209 resistant and susceptible accessions.Using further allele-combination analysis for three functional markers representing three cloned resistance genes(rhg1,Rhg4,andGmSNAP11)and twomarkers flanking qSCN3-1,we found that adding the resistance allele of qSCN3-1 greatly increased soybean resistance to SCN,even in diverse genetic backgrounds.The qSCN3-1 locus will be useful for marker-assisted polygene pyramid breeding and should be targeted for the future identification of candidate genes.     

Effect of Nitrogen on Water Content, Sap Flow, and Tolerance of Rice Plants to Brown Planthopper, Nilaparvata lugens

Water content (WC) and sap flow from leaf sheath of rice plants with varying nitrogen levels at different growth stages, and fluctuations in relative water content (RWC) of rice plants being damaged by brown planthoppcr (BPH), Nilaparvata lugens were determined in the laboratory, and the tolerance of rice plants to BPH at different nitrogen regimes was evaluated in the greenhouse at International Rice Research Institute (IRRI), the Philippines. The results indicated that both WC and RWC were increased significantly, as the amount of sap flow from rice plants was reduced statistically, with the increase of nitrogen content in rice plants. RWC in rice plants applied with high nitrogen fertilizer decreased drastically by the injury of BPH nymphs, while the reduced survival duration of rice plants with the increase of nitrogen content was recorded. These may be considered to be one of the important factors in increasing the susceptibility to BPH damage on rice plants applied with nitrogen fertilizer.     

Breeding of R8012,a Rice Restorer Line Resistant to Blast and Bacterial Blight Through Marker-Assisted Selection

Genetic improvement is one of the most effective strategies to prevent rice from blast and bacterial blight(BB) diseases,the two most prevalent diseases jeopardizing rice production.Rice hybrids with dural resistance to blast and BB are needed for sustainable production of food.An incomplete diallele design resulted in 25 crosses between five blast and five BB resistant germplasm accessions.Only one pair of parents,DH146 × TM487,showed polymorphism for all the markers to identify one blast resistance gene Pi25 and three BB resistance genes,Xa21,xa13 and xa5,thus it was used in the marker-assisted selection(MAS).F2 individuals of DH146 × TM487 were genotyped using flanking markers of RM3330 and sequence tagged site(STS) marker SA7 for Pi25.The resistant F2 plants with Pi25 were used for pyramiding BB resistance genes Xa21,xa13 and xa5 identified by the markers pTA248,RM264 and RM153,respectively in subsequent generations.Finally,after selection for agronomic traits and restoration ability among 12 pyramided lines,we acquired an elite restorer line,R8012 including all four target genes(Pi25+Xa21+xa13+xa5).Hybrid Zhong 9A/R8012 derived from the selected line showed stronger resistance to blast and BB,and higher grain yield than the commercial checks uniformally in experimental plots,2007 state-wide yield trial and 2008 nation-wide yield trial.This study provides a paradigmatic example to show that MAS is a practically feasible tool in effectively pyramiding multiple resistance genes.The resultant restoring line and its hybrid would play an important role in securing rice production in China.     

玉米抗病性遗传改良

In this paper the main diseases of corn were elaborated on: Corn northern leaf blight,Corn southern leaf blight,Corn head smut,Corn smut,Corn stem rot(Corn stalk rot),Curvularia leaf spot of Corn,Gray leaf spot of Corn,Corn rust disease.Dwarf mosaic disease of Corn,Corn ear rot and their pathogens and prevalence.It indicted the genetic characteristics of resistance and research progress,the collection and screening of resistant resourses,the breeding and improvement methods of resistant varieties.     

Clubroot resistance introgression in interspecific hybrids between Raphanus sativus and Brassica napus

Clubroot is a prevailing soil-borne disease affecting rapeseed production worldwide.However,few clubroot resistant rapeseed accessions were available for breeding.Identification and introgression of new clubroot resistant genes from closely related species by distant hybridization is an effective strategy.In the present study,9 radish(Raphanus sativus L.,2n=18,RR)lines resistant to Plasmodiophora brassicae pathotype 4 were used as donors to transfer clubroot resistance into a susceptible rapeseed(Brassica napus L.,2n=38,AACC)line by distant hybridization combined with embryo rescue.Nine intergeneric crosses were made but only 1(411×93039)produced F1 plants both from embryo rescue and natural seed-setting.Authenticity of triploid F1 hybrids(2n=28,ACR)were verified by flower color,cytological observation and molecular marker analysis,and 2 genuine F1 hybrids were identified.After chromosome doubling,these synthetic allohexaploid plants(2n=56,AACCRR)became partially fertile(pollen viability rate=35%)and were backcrossed with rapeseed parent to generate a BC1 population(2n=47,AACCR).Totally 178 BC1 plants were obtained,of which the majority(96.1%)were resistant to clubroot.These backcrossing progenies could be used for the breeding of new rapeseed varieties resistant to clubroot.