Investigation on diversity and population succession dynamics of endophytic bacteria from seeds of maize (Zea mays L., Nongda108) at different growth stages

Plant seeds are carriers of both beneficial bacteria and pathogens. Using the 16S rRNA gene clone library technique, we conducted a preliminary study on the community diversity and population succession dynamics of endophytic bacteria in seeds of reciprocal cross hybrid maize at different seed developmental stages. In both hybrid lines (108A and 108B), more types of endophytic bacteria were found at the proembryo-forming stage than in the other two stages, including 29 and 23 bacterial operational taxonomic units (OTUs), respectively. Undibacterium (39.20 and 30.00 % in 108A and 108B, respectively) was the first dominant bacterium to appear. At the milky stage, fewer types of endophytic bacteria in 108A and 108B appeared, including 18 and 16 OTUs, respectively, and the abundance of the dominant genus Burkholderia in the two seed samples reached 73.38 and 80.43 %, respectively. Limnobacter appeared as the second and third endophytic dominant bacterium in 108A (4.55 %) and 108B (5.07 %), respectively, in both seed samples. At the dough stage, the abundance of the first dominant bacterium, Burkholderia, in 108A and 108B was 78.26 and 84.80 %, respectively. Pantoea appeared as the second endophytic dominant bacterium in the both seeds (9.42 and 4.80 % in 108A and 108B, respectively). This is the first study on endophytic bacteria present during several crucial stages of the dynamic grain growth process of plant seeds conducted using culture-independent methods.     

Development of two isogenic sweet corn hybrids differing for glycinebetaine content

A hybrid of sweet corn, Zea mays L. (`1720'; Rogers Brothers Seed Co.), was found to be comprised of glycinebetaine-positive and glycinebetaine-deficient individuals in a 1:1 mixture. This phenomenon was traced to segregation for a single, nuclear, dominant gene determining leaf glycinebetaine content within the female inbred parent of this hybrid. Selection for homozygous recessive (glycinebetaine-deficient) and homozygous dominant (glycinebetaine-positive) genotypes of the female inbred parent enabled production of two isogenic versions of hybrid `1720' differing with respect to a single copy of the dominant allele, by mating these female parent selections with the common homozygous recessive (glycinebetaine-deficient) male parent. These two isogenic hybrids are shown to differ by a factor of 300- to 400-fold in glycinebetaine titer of young expanding leaves of salinized plants, but exhibit no striking differences in the levels of free amino acids or the level of N-methylnicotinic acid (nicotinic acid betaine; trigonelline). The only significant difference between the two hybrids in terms of amino acid composition was found to be in the level of alanine under nonsalinized conditions. The betaine-deficient hybrid exhibited a 14% lower alanine level than the betaine-positive hybrid. Betaine deficiency was not associated with altered stress-induced accumulation of amino acids such as proline, serine, and asparagine plus aspartate, attesting to the high specificity of the genetic difference between these isogenic hybrids with respect to betaine accumulation. This germplasm offers unique opportunities to test whether a single dominant allele determining stress-induced betaine accumulation capacity influences stress resistance in maize.     

Fine mapping and candidate gene prediction of a major QTL for kernel number per ear in maize

Kernel number per ear (KNE) is a maize yield component and an important breeding target for improving grain yield. As a complex quantitative trait, KNE has been assumed to be controlled by a set of quantitative trait loci (QTLs) with minor effects. Identification and genetic evaluation of these QTLs are prerequisites for improving KNE with a molecular breeding approach. In this study, we developed the chromosome segment introgression line SL19-41, which exhibited 95.60% recovery of the Ye478 background and showed a higher KNE and grain yield. The plant architecture and flowering time of SL19-41 were not significantly different from those of Ye478. We employed introgression line (IL)-derived mapping populations and identified a major QTL, KNE4, which is partially dominant. KNE4 was validated in a backcross population and a set of sub-introgression lines and was delimited to a 440-kb genomic region in Bin4.07. An allele included in the introgression fragment had a synergistic effect, noticeably increasing KNE and showing the potential to improve KNE in Ye478. Subsequently, the association between sequence polymorphism in the QTL interval and KNE variation revealed a putative candidate gene that encoded a long-chain acyl-CoA synthetase responsible. This result provides an available locus for the molecular improvement of KNE and for the isolation of functional genes underlying this QTL.     

重离子辐射诱导玉米突变体I478的特性研究

通过田间试验,对玉米自交系掖478和经重离子辐射掖478干种子所获得的突变体1478的主要农艺性状和配合力进行了比较分析,结果表明：（1）1478植株形态发生明显改变,主要表现出株高、穗位高显著增加,气生根颜色发生改变;（2）1478的果穗性状总体变好,果穗长度、行粒数、穗粒数、穗粒重等性状极显著优于自交系掖478,但其果穗穗行数显著少于自交系掖478;（3）1478的主要生育时期如抽雄期、开花期、成熟期显著迟于自交系掖478;（4）自交系掖478配制组合的穗行数、穗粗、出籽率的平均值大于突变体1478配制组合的相应性状的平均值,突变体1478配制组合的单穗重、穗长、行粒数、百粒重、秃顶长度大于自交系掖478配制组合的相应性状的平均值。突变体1478一般配合力好,组合1478×N172单穗重量极显著高于临奥1号,单穗重量比临奥1号增加9．6％,可继续对该组合进行鉴定。     

Birth of two second generation hybrid macaques

A male infant was born to a hybrid female monkey (Macaca mulatta × M. nemestrina) on 24 May 1973. On 4 July 1973, a second hybrid female macaque (M. nemestrina × M. nigra) also produced a viable female infant. These were the twenty-seventh and twenty-eighth hybrid births in our program, but the first second generation births.     

优异杂交水稻亲本灌浆期种子内生细菌多样性研究

通过传统微生物培养方法,对处于灌浆期的杂交水稻亲本"深08S"、"和620S"及"16A007"种子内生细菌群落结构多样性进行研究。实验表明,处于灌浆期的杂交水稻亲本种子仍然存在内生细菌群落结构的多样性。"深08S"种子内生细菌含6个OTU,第一优势菌属为Pantoea,丰度为52.04%,第二和第三优势菌属分别为Pseudomonas和Rhizobium;"和620S"种子内生细菌含10个OTU,第一优势菌属为Pantoea,丰度为69.02%,第二优势菌属为Pseudomonas,并列第三优势菌属为Rhizobium和Sphingomonas;"16A007"种子内生细菌含11个OTU,第一优势菌属为Pseudomonas,丰度为45.12%,第二优势菌属和第三优势菌属分别为Pantoea和Sphingomonas。由研究结果可见,具有遗传相关性的水稻种子"深08S"和"和620S"内生细菌的第一和第二优势菌属相同,同时,三种水稻亲本种子优势菌属都有Pantoea和Pseudomonas,表明水稻种子基因型对其内生细菌结构多样性具有一定的影响。     

A Dominant Gene for Male Sterility in Salvia miltiorrhiza Bunge

A natural male sterile mutant of Salvia miltiorrhiza (Labiatae, Sh-B) was found during field survey in 2002. Our objective was to analyze its genetic mechanism for producing F1 hybrid seeds and to develop a molecular marker linked to male sterile gene for selection of a hybrid parent line. The segregation ratios of male sterile plants to fertile plants in the progenies of both testcross and backcross were 1:1 in continuous experiments conducted in 2006–2009. The male sterile Sh-B was heterozygous (Msms). The male sterile plants could capture most pollen (2 granule/cm²·24 h) with row ratio (female : male 2 : 1) within 45-cm distance and harvest the largest amount of 6495 g hybrid seeds per hectare. We also developed DNA markers linked to the male sterile gene in a segregating population using bulked segregant analysis (BSA) and amplified fragment length polymorphism (AFLP) techniques. The segregating population was subjected to BSA-AFLP with 128 primer combinations. One out of fourteen AFLP markers (E11/M4208) was identified as tightly linked to the dominant male sterile gene with a recombination frequency of 6.85% and at a distance of 6.89 cM. This marker could be converted to PCR-based assay for large-scale selection of fertile plants in MAS (marker-assisted selection) at the seedling stage. Blastn analysis indicated that the male sterile gene sequence showed higher identity with nucleotides in Arabidopsis chromosome 1–5, and was more likely to encode S-adenosylmethionine-dependent methyltransferase, in which DNA methylation regulated the development of plant gametogenesis.     

Fine Mapping and Candidate Gene Prediction of a Pleiotropic Quantitative Trait Locus for Yield-Related Trait in Zea mays

The yield of maize grain is a highly complex quantitative trait that is controlled by multiple quantitative trait loci (QTLs) with small effects, and is frequently influenced by multiple genetic and environmental factors. Thus, it is challenging to clone a QTL for grain yield in the maize genome. Previously, we identified a major QTL, qKNPR6, for kernel number per row (KNPR) across multiple environments, and developed two nearly isogenic lines, SL57-6 and Ye478, which differ only in the allelic constitution at the short segment harboring the QTL. Recently, qKNPR6 was re-evaluated in segregating populations derived from SL57-6×Ye478, and was narrowed down to a 2.8 cM interval, which explained 56.3% of the phenotypic variance of KNPR in 201 F_2∶3 families. The QTL simultaneously affected ear length, kernel weight and grain yield. Furthermore, a large F₂ population with more than 12,800 plants, 191 recombinant chromosomes and 10 overlapping recombinant lines placed qKNPR6 into a 0.91 cM interval corresponding to 198Kb of the B73 reference genome. In this region, six genes with expressed sequence tag (EST) evidence were annotated. The expression pattern and DNA diversity of the six genes were assayed in Ye478 and SL57-6. The possible candidate gene and the pathway involved in inflorescence development were discussed.     

Inheritance of Cry1Ac resistance and associated biological traits in the cotton bollworm, Helicoverpa armigera (Lepidoptera: Noctuidae)

The analysis of reciprocal genetic crosses between resistant Helicoverpa armigera strain (BH-R) (227.9-fold) with susceptible Vadodara (VA-S) strain showed dominance (h) of 0.65-0.89 and degree of dominance (D) of 0.299-0.782 suggesting Cry1Ac resistance as a semi-dominant trait. The D and h values of F₁ hybrids of female resistant parent were higher than female susceptible parent, showing maternally enhanced dominance of Cry1Ac resistance. The progeny of F₂ crosses, backcrosses of F₁ hybrid with resistant BH-R parent did not differ significantly in respect of mortality response with resistant parent except for backcross with female BH-R and male of F₁ (BH-R × VA-S) cross, suggesting dominant inheritance of Cry1Ac resistance. Evaluation of some biological attributes showed that larval and pupal periods of progenies of reciprocal F₁ crosses, backcrosses and F₂ crosses were either at par with resistant parent or lower than susceptible parent on treated diet (0.01 μg/g). The susceptible strain performed better in terms of pupation and adult formation than the resistant strain on untreated diet. In many backcrosses and F₂ crosses, Cry1Ac resistance favored emergence of more females than males on untreated diet. The normal larval period and the body weight (normal larval growth) were the dominant traits associated with susceptible strain as contrast to longer larval period and the lower body weight (slow growth) associated with resistance trait. Further, inheritance of larval period in F₂ and backcross progeny suggested existence of a major resistant gene or a set of tightly linked loci associated with Cry1Ac sensitivity.     

利用RAPD分子标记对番茄杂交种纯度的鉴定研究

应用RAPD(RandomlyamplifiedpolymorphicDNA)分子标记对番茄京丹1号和毛粉802的F1代杂交种纯度进行鉴定的实验研究。该项研究使用了10个碱基的单随机引物和10个碱基的双随机引物进行扩增。在60个单引物扩增反应中获得7个京丹1号父本特有的核酸标记片段。但在14个双随机引物对京丹1号和毛粉802杂交组合的扩增反应中获得了7个京丹1号F1代杂交种特有的核酸标记片段和5个毛粉802父本特有的标记带。实验结果显示,双引物的扩增反应对鉴定双亲亲缘关系极近的杂交种纯度较单引物扩增反应更有效。其中,京丹1号的14个标记片段在北京蔬菜研究中心,种子纯度检测室又进行了重复扩增实验。实验结果为87%的RAPD标记可以在使用不同的PCR仪和不同来源的Taq酶的实验条件下得到。RAPD分子标记技术对鉴定双亲亲缘关系极近的杂交种纯度是真实可靠的。     

Genetic assessment of the effects of self-fertilization in a Lilium L. hybrids using molecular cytogenetic methods (FISH and ISSR)

Self-fertilization (also termed selfing) is a mode of reproduction that occurs in hermaphrodites and has evolved several times in various plant and animal species. A transition from outbreeding to selfing in hermaphroditic flowers is typically associated with changes in flower morphology and functionality. This study aimed to identify genetic effects of selfing in the F2 progeny of F1 hybrid developed by crossing Lilium lancifolium with the Asiatic Lilium hybrid ‘Dreamland.’ Fluorescence in situ hybridization (FISH) and inter-simple sequence repeats (ISSR) techniques were used to detect genetic variations in plants produced by selfing. The FISH results showed that F1 hybrid were similar to the female parent (L. lancifolium) regarding the 45S loci, but F2 individuals showed variation in the number and location of the respective loci. In F2 progeny, F2-2, F2-3, F2-4, F2-5, and F2-8 hybrids expressed two strong and one weak 5S signal on chromosome 3, whereas F2-7 and F2-9 individuals expressed one strong and two weak signals. Only two strong 5S signals were detected in an F2-1 plant. The ISSR results showed a maximum similarity value of 0.6269 between the female parent and the F2-2 hybrid. Regarding similarity to the male parent, a maximum value of 0.6119 was found in the F2-1 and F2-2 hybrids. The highest genetic distance from L. lancifolium and the Asiatic Lilium hybrid ‘Dreamland’ was observed in the F2-4 progeny (0.6352 and 0.7547, respectively). Phylogenetic relationships showed that the F2 progeny were closer to the male parent than to the female parent. Self-fertilization showed effects on variation among the F2 progeny, and effects on the genome were confirmed using FISH and ISSR analyses.     

Male sterility systems in wheat and opportunities for hybrid wheat development

The common wheat (Triticum aestivum L.) is a poly(hexa)ploid, derived from an amphi-diploidization process involving the donor species—Triticum urartu, Aegilops speltoides, Triticum turgidum, and Aegilops tauschii. The genetic diversity of the autogamous wheat is narrow, which is a major reason for lesser rate of yield gain in wheat, in contrast to rice and maize. It is desirable to encourage hybrid breeding, i.e., combining different lines into genetically divergent heterotic pools. Thus, hybrid plants are a unique combination of desired alleles produced by crossing between genetically different parental lines. Hybrid seed production in a crop requires male-sterile female parents along with a reliable outcrossing system. The male-sterile female parent prevents pollen shedding and self-fertilization, maintaining the purity of hybrid seeds. An outcrossing system enhances hybrid seed production. This article emphasizes the biological relevance of crossbreeding and self-pollination in wheat, and reviews different male sterility systems which could be utilized for the development of hybrid wheat. Several biotechnological approaches and their practical utility in generating cross-compatible male-sterile female parent lines have been discussed.     

玉米转录因子WRKY76克隆及抗纹枯病表达模式分析

玉米纹枯病是影响玉米产量和品质的重要病害之一。转录因子WRKY家族部分成员能够调控水杨酸和茉莉酸甲酯信号传递方式来激发防卫反应基因的表达。在NCBI上检索玉米中WRKY家族成员及拟南芥中抗病相关的WRKY家族成员,利用CLUSTAL X和MEGA5.05构建系统进化树,发现转录因子WRKY76可能参与玉米抗纹枯病的调控途径。该研究以玉米抗纹枯病材料R15和感病材料Ye478为对象,在玉米拔节期接种立枯丝核菌AG1-IA,首先分别于接菌前(对照)和接菌后1、2、4、6、12、24 h取叶鞘;然后分别进行水杨酸和茉莉酸甲酯胁迫处理,分别于处理前(对照)和处理后1、2、4、6、12 h取叶鞘,提取RNA,实时荧光定量PCR分析WRKY76转录因子基因在玉米叶鞘组织中不同胁迫条件下的差异表达。结果表明:在立枯丝核菌AG1-IA胁迫下,WRKY76转录因子基因在胁迫后1 h表达量达最大值,抗病材料R15的相对表达量高于感病材料Ye478且差异显著(P≤0.05);经水杨酸(Salicylic Acid,SA)处理,WRKY76在抗感材料中表达趋势相似,在感病材料掖478中,WRKY76被诱导而显著地上调表达,在抗病材料中,相对表达量峰值出现在胁迫后4 h,且相对表达量低于感病材料掖478。经茉莉酸甲酯(Methyl jasmine,Me JA)处理,WRKY76基因在感病材料中呈现下调表达趋势。WRKY76基因在1 h表达量为对照的0.6倍,其他调查时间点基本都在0.1~0.3之间。在抗病材料R15中,WRKY76基因表达呈现上升趋势,变化趋势不明显。这表明WRKY76转录因子基因能够被病原物、SA、Me JA诱导表达,可能参与植物抗纹枯病调控途径。     

Patterns of genomic variation in Chinese maize inbred lines and implications for genetic improvement

Key message

Genetic relationships among Chinese maize germplasms reveal historical trends in heterotic patterns from Chinese breeding programs and identify line Dan340 as a potential genome donor for elite inbred line Zheng58.

Abstract

The characterization of the genetic relationships, heterotic patterns and breeding history of lines in maize breeding programs allows breeders to efficiently use maize germplasm for line improvement over time. In this study, 269 temperate inbred lines, most of which have been widely used in Chinese maize breeding programs since the 1970s, were genotyped using the Illumina MaizeSNP50 BeadChip, which contains 56,110 single-nucleotide polymorphisms. The STRUCTURE analysis, cluster analysis and principal coordinate analysis results consistently revealed seven groups, of which five were consistent with known heterotic groups within the Chinese maize germplasm—Domestic Reid, Lancaster, Zi330, Tang SPT and Tem-tropic I (also known as “P”). These genetic relationships also allowed us to determine the historical trends in heterotic patterns during the three decades from 1970 to 2000, represented by Mo17 from Lancaster, HuangZaoSi (HZS) from Tang SPT, Ye478 from Domestic Reid and P178 from Tem-tropic I heterotic groups. Mo17-related commercial hybrids were widely used in the 1970s and 1980s, followed by the release of HZS- and Ye478-related commercial hybrids in the 1980s and 1990s, and the introduction of Tem-tropic I group in the 1990s and 2000s. Additionally, we identified inbred line Dan340 as a potential genome donor for Zheng58, which is the female parent of the most widely grown commercial hybrid ZhengDan958 in China. We also reconstructed the recombination events of elite line HZS and its 14 derived lines. These findings provide useful information to direct future maize breeding efforts.

     

Review of the Chinese species of the genus Varma Distant (Hemiptera,Fulgoromorpha, Tropiduchidae), with description of two new species

Two new species of Varma Distant, 1906, V. falcata Chang & Chen, sp. n. (China: Guizhou) and V. lobata Chang & Chen, sp. n. (China: Guizhou) are described and illustrated. The female genitalia of four speices including two known species are described and illustrated for the first time. The diagnostic characters of this genus are redefined. A checklist to the species of Varma in China is given. The Keys on male and female genitalia to the Chinese species of Varma are provided.     

Genetic architecture of male fertility restoration of <Emphasis Type="Italic">Triticum timopheevii</Emphasis> cytoplasm and fine-mapping of the major restorer locus <Emphasis Type="Italic">Rf3</Emphasis> on chromosome 1B

Key message

Restoration of fertility in the cytoplasmic male sterility-inducing Triticum timopheevii cytoplasm can be achieved with the major restorer locus Rf3 located on chromosome 1B, but is also dependent on modifier loci.

Abstract

Hybrid breeding relies on a hybrid mechanism enabling a cost-efficient hybrid seed production. In wheat and triticale, cytoplasmic male sterility based on the T. timopheevii cytoplasm is commonly used, and the aim of this study was to dissect the genetic architecture underlying fertility restoration. Our study was based on two segregating F₂ triticale populations with 313 and 188 individuals that share a common female parent and have two different lines with high fertility restoration ability as male parents. The plants were cloned to enable replicated assessments of their phenotype and fertility restoration was evaluated based on seed set or staining for pollen fertility. The traits showed high heritabilities but their distributions differed between the two populations. In one population, a quarter of the lines were sterile, conforming to a 3:1 segregation ratio. QTL mapping identified two and three QTL in these populations, with the major QTL being detected on chromosome 1B. This QTL was collinear in both populations and likely corresponds to Rf3. We found that Rf3 explained approximately 30 and 50% of the genotypic variance, has a dominant mode of inheritance, and that the female parent lacks this locus, probably due to a 1B.1R translocation. Taken together, Rf3 is a major restorer locus that enables fertility restoration of the T. timopheevii cytoplasm, but additional modifier loci are needed for full restoration of male fertility. Consequently, Rf3 holds great potential for hybrid wheat and triticale breeding, but other loci must also be considered, either through marker-assisted or phenotypic selection.

     

A hybrid of the invasive plant Sphagneticola trilobata has similar competitive ability but different response to nitrogen deposition compared to parent

Hybridization between introduced and related native species has been suggested to be a key driving force of evolutionary processes in invasions that may be accelerated by increasing nitrogen (N) deposition. We carried out two experiments to compare the competitive ability of a newly-reported putative hybrid (Sphagneticola calendulacea × Sphagneticola trilobata) to that of its invasive paternal parent and investigate its response to different N additions. Growth of the hybrid increased by 39.62 ± 15.69 % when grown with the native parent but showed no significant changes when grown with the invasive parent. Growth of invasive S. trilobata showed no significant changes when grown with the other two taxa. The hybrid and invasive parent inhibited the growth of the native parent by 33.27 ± 15.26 % and 78.56 ± 3.13 %, respectively. Low level N addition (50 kg N ha^?1) enhanced the growth of both the hybrid and native parent, whereas medium and high levels of N additions (150, 300 kg N ha^?1) had no effects on hybrid growth but decreased native parent growth. However, all N treatments had no significant effects on the growth of the invasive parent. Our results suggest that the hybrid is an equal competitor to its invasive parent and is more susceptible to N deposition. Therefore, this hybrid could be a threat to native diversity but may decline more than the invasive parent under high N conditions.     

An improved embryo-rescue protocol for hybrid progeny from seedless Vitis vinifera grapes × wild Chinese Vitis species

A highly efficient technique of embryo rescue is critical when using stenospermocarpic Vitis vinifera cultivars (female parents) to breed novel, disease-resistant, seedless grape cultivars by hybridizing with wild Chinese Vitis species (male parents) having many disease-resistance alleles. The effects of various factors on the improvement of embryo formation, germination, and plantlet development for seven hybrid combinations were studied. The results indicated that Beichun and Shuangyou were the best male parents. The best sampling time for ovule inoculation differed among the female parents. When hybrid ovules were cultured on a double-phase medium with five different solid medium types, percent embryo formation was highest (11.3–28.3%) on a modified MM3 medium. Percentages of embryo germination (15.4–55.4%) and plantlet development (11.15–44.6%) were all highest when embryos were cultured on Woody Plant Medium?+?5.7 μM indole-3-acetic acid?+?4.4 μM 6-benzylaminopurine?+?1.4 μM gibberellic acid?+?2% sucrose?+?0.05% casein hydrolysate?+?0.3% activated charcoal?+?0.7% agar. In the absence of other amino acids, the addition of proline significantly increased embryo formation (36.1%), embryo germination (64.6%), and plantlet development (90.5%). A highly efficient protocol has been developed for hybrid embryo rescue from seedless V. vinifera grapes?×?wild Chinese Vitis species that results in a significant improvement in breeding efficiency for new disease-resistant seedless grapes.     

Hybridization studies of Haemonchus contortus (rudolphi, 1803) and H. placei (place, 1893) (Nematoda: Trichostrongylidae)

Hybridization experiments between Haemonchus contortus from sheep and H. placei from cattle indicate that the H. placei vulvar morph type and the inability of the eggs to hatch and develop at 11°C were inherited as dominant traits in the hybrids. The size of the third stage larvae was similar to H. placei in hybrids from the mating of male H. placei × female H. contortus while larvae from the reciprocal mating were intermediate in size. Hybrids produced by the mating of thiabendazole resistant female H. contortus × non-resistant male H. placei were also resistant. The F₁ males of the mating between male H. contortus and female H. placei were sterile. Male sterility did not occur in the reciprocal cross until the F₂ generation. Female hybrids from these generations had a low level of fertility when backcrossed to males of either parent species. Cytological studies of the hybrid males indicated that sterility was due to several kinds of meiotic disturbance and that spermatogenesis stopped during metaphase I. The chromosomes in eggs of unfertilized females did not undergo meiosis and polar body formation; instead they increased in number by a process of endomitosis. Unfertilized eggs in the faeces were characterized by uneven cytoplasmic division and abnormal shape. It is proposed that hybrid sterility can lead to the local eradication of one species of Haemonchus by the other. Furthermore, the outcome of which species is eradicated can be influenced by such variables as initial population sizes, climate, and the local ratio of sheep to cattle.     

超级杂交稻两优培九及其亲本的光氧化特性

通过比较超级杂交稻两优培九和其亲本的光能利用与活性氧代谢的差异,为培育耐光氧化的杂交稻提供选亲配组的生理依据．使用TPS-光合仪和FMS2荧光仪(Hansateeh,UK)分别测定了人工光氧化处理后水稻叶片的光合速率与叶绿素荧光,同时测定了叶绿素、蛋白质和丙二醛的含量。以及超氧化物歧化酶和过氧化物酶的活性．结果表明,两优培九的光合速率低于母本2．4％,高于父本23％;光氧化处理8d后,与母本相比。两优培九的叶绿素、蛋白质、原初光化学效率、超氧化物歧化酶和过氧化物酶分别高于母本33％、15％、30％、32％和100％;光化学猝灭系数和丙二醛分别低于母本9％和50％。与父本相比,则差异不大．超级杂交稻两优培九在光氧化条件下光能利用率较高,在耐光氧化特性上具有超亲的光合生理特性．