小麦-大赖草易位系的RFLP分析

利用辐射、花药培养及杀配子基因效应已创制出一系列小麦 -大赖草易位系。为在其中找出可能的纯合易位系、明确易位所涉及的相关染色体以及易位断裂点的确切位置 ,利用了已被定位于小麦 7个部分同源群染色体长、短两臂上的 67个探针进行了RFLP分析 ,结果鉴定出 3个纯合的易位系 :T1BL·7Lr#1S、T4BS·4BL - 7Lr#1S和T6AL·7Lr#1S。其中 ,易位系T1BL·7Lr #1S和T6AL·7Lr #1S中染色体 7Lr #1的断裂点位于标记MWG80 8和标记ABG476.1之间 ,而 1B和 6A染色体上的断裂点都在着丝粒附近。易位系T4BS·4BL - 7Lr#1S中染色体 7L #1的断裂点位于标记BCD349和标记CDO5 95之间 ,4B染色体断裂点则位于标记CDO5 4 1和标记PSR1 64之间的长臂上。

花生对根结线虫病抗性温室快速鉴定方法

为了通过对花生抗线虫鉴定方法的比较，确定更加快速有效的抗性鉴定技术，作者于2002～2003年在佐治亚大学的Tifton试验站进行了温室盆栽试验。结果表明：侵然期幼虫(2000-4000条／株)与虫卵(8000—16000粒／株)均可以用于花生抗线性鉴定的温室接种，但与使用虫卵接种相比，以侵染期幼虫作为接种体需要多花3～5d的时间收集幼虫；接种后14d，可以依据0～5级的虫瘿分级标准将供试的4份花生种质区分开来；接种后6～10周依据卵块数量或每克根中的虫卵数可以进一步确认花生的抗性水平。虫瘿级数、虫瘿数量、卵块数量及每克根中的卵量之间存在着极显著(P<0．01)的正相关关系。根据研究结果提出了温室中花生抗线虫鉴定的程序方法：以8000粒卵／株为适宜接种量，接种后14d依据0-5级的虫瘿分级标准进行初筛，对初筛入选的材料再在接种后6周根据卵块数量或卵量验证其抗性。

Differences in Soil Microbial Biomass and Activity for Six Agroecosystems with a Management Disturbance Gradient

Different management practices in six agroecosystems located near Goldsboro, NC, USA were conducted including a successional field (SU), a plantation woodlot (WO), an integrated cropping system with animals (IN), an organic farming system (OR), and two cash-grain cropping systems employing either tillage (CT) or no-tillage (NT) to examine if and how microbial biomass and activity differ in response to alterations in disturbance intensity from six land management strategies. Results showed that soil microbial biomass and activity differed, with microbial activity in intermediately disturbed ecosystems (NT, OR, IN) being significantly higher (P ＜ 0.01) than systems with either high or low disturbance intensities. There was also a significant and a highly significant ecosystem effect from the treatments on microbial biomass C (MBC) (P ＜ 0.05) and on microbial activity (respiration) (P ＜ 0.01), respectively. Multiple comparisons of mean respiration rates distinctly separated the six ecosystem types into three groups: CT ＜ NT, SU and WO ＜ OR and IN.Thus, for detecting microbial response to disturbance changes these results indicated that the active component of the soil microbial community was a better indicator than total biomass.

Virulence of Xanthomonas oryzae pv. oryzae on Rice Near-Isogenic Lines with Single Resistance Gene and Pyramiding Lines in China

Ninety one isolates of Xanthomonas oryzae pv. oryzae were collected from different rice- growing regions in China and determined for their virulence on 24 rice near-isogenic lines containing single resistance gene and 2-4 genes: IRBB1 (Xa1), IRBB2 (Xa2), IRBB3 (Xa3), IRBB4 (Xa4), IRBB5 (xa5), IRBB7 (Xa7), IRBB8 (xa8), IRBB10 (Xa10), IRBB11 (Xa11), IRBB13 (xa13), IRBB14 (Xa14), IRBB21 (Xa21), IR24 (Xa18), IRBB50 (Xa4 + xa5), IRBB51 (Xa4 + xa13), IRBB52 (Xa4 + Xa21), IRBB53 (xa5 + xa13), IRBB54 (xa5 + Xa21), IRBB55 (xa13 + Xa21), IRBB56 (Xa4 + xa5 + xa13), IRBB57 (Xa4 + xa5 + Xa21), IRBB58 (Xa4 + xa13 + Xa21), IRBB59 (xa5 + xa13 + Xa21) and IRBB60 (Xa4 + xa5 + xa13 + Xa21). The results showed that most isolates were less virulent on lines with more than one genes pyramided than those with single resistance gene. The isolates tested were more virulent on IR24 and IRBB10, less virulent on IRBB5, IRBB7 and IRBB21. Based on interactions between isolates and rice near-isogenic lines, 7 cultivars with single gene (IRBB5, IRBB4, IRBB3, IRBB14, IRBB2, IRBB1 and IR24) were chosen as the differentials, and the tested isolates were classified into 7 virulence groups. The reaction patterns of the 7 groups in order were: RRRRRRR, RRRRRRS, RRRRRSS, RR/SRRSSS, RRRSSSS, RRSSSSS, RSSSSSS. The virulence frequencies were 7.69, 6.59, 14.29, 12.09, 14.29, 28.57 and 16.48% respectively. The elementary system for races identification has been established in China based on the results. It will be possible to compare with races in other countries, and the results will facilitate the development of rice resistance breeding to bacterial blight in China.

Phosphate-solubilizing microbes in rhizosphere soils of 19 weeds in southeastern China

Low phosphorus (P) availability is one of the most important factors limiting plant growth in red soils across southeastern China. Many non\|symbiotic microorganisms in rhizosphere can enhance P solubility, but little is known about the magnitude of their phosphorus\|solubilizing ability (PSA) and the difference in phosphorus\|solubilizing microorganisms (PSM) among plant species. The number of phosphorus\|solubilizing microorganisms and their PSA in rhizosphere soils of 19 weed species in a citrus orchard on red soil at Changshan, Zhejiang, China, were investigated. Inorganic P (powdered phosphate rock, PR) and organic P (lecithin, OP) were respectively used as the sole P\|source to examine the PSA of isolated microbes. The PS actinomycetes community varied greatly among the different weed rhizospheres while the PS fungus community showed to be most stable to the weed rhizosphere. The highest number of PR\|PS and OP\|PS bacteria was found in rhizosphere soil of \%Mollugo pentaphyll\%, and the highest number of PR\|PS and OP\|PS actinomycetes was found in rhizosphere soil of \%Polygonum lapathifolium\%. The highest number of PR\|PS fungi was found in \%Erigeron annuus\% and \%Mollugo pentaphyll\% rhizosphere soil, and the highest number of OP\|PS fungi was found in rhizosphere soil of \%Mazus stachydifolius\%. \%Mazus stachydifolius\% showed the strongest PR\|PS ability (6340.75μg) while \%Eragrostis pilosa\% showed the strongest OP\|PS ability (1301.84μg). The PR\|PS ability and OP\|PS ability of \%Mollugo pentaphyll\% was 4432.87μg and 1122.05μg respectively. A significant correlation between the number of PR\|PSM and OP\|PSM was found. Significant correlation was only found between the PR\|PS fungi number and its PSA( r =0.75, P <0.05) and between the number of OP\|PS fungi and its PSA( r =0.87, P <0.01}). It indicated that plant species had significant influence on components of the non\|symbiotic PSM community and their activity in its rhizosphere soil. Fungi play a leading role in phosphorus solubilization in weed rhizopshere. It suggested that weed conservation could benefit soil microbe development in agroecosystems, especially in the initial stage of agroecosystem development because there is less organic carbon in bare soil. The results suggested that weed conservation could increase PSA of PSM.

Seed Health Status of Sweet Corn (Zea mays L. saccharata Sturt) from Five Areas in China and Effect on Field Seedling Emergence

The health status of 18 sweet corn (Zea mays L. saccharata Sturt) hybrids classified to two types, collected from five areas in China, was examined by PDA method, and factors influencing seed health and relationships between seed health and field seedling emergence were studied. Seventeen fungal genera were isolated and Fusarium was the most frequently isolated. There were significant differences both in incidence of Fusarium and in percentage of infected seeds among 18 hybrids. Research also showed that significant and consistent differences both in seed-borne fungal taxa and in percentage of infected seeds existed between two types of sweet corn. Sugar enhanced corn is more slightly infected than super sweet corn both in fungal taxa (13 and 16, respectively) and in percentage of infected seeds (62.0 and 79.2%, respectively). There were also significant differences both in seed-borne fungal taxa and in percentage of infected seeds among five areas. Seeds from South China were most severely infected, for there were 14 fungal genera detected and the percentage of infected seeds was highly 99.1% while those from Northwest China were slightly infected, for there were 10 fungal genera detected and the percentage of infected seeds was only 14.3%. Further research showed that there were significant negative correlations both between incidence of Fusarium and percentage of field seedling emergence and between percentage of infected seeds and percentage of field seedling emergence. Percentage of field seedling emergence could be estimated by regression equations built by regression analysis.

Advances in Localization and Molecular Markers of Wheat Leaf Rust Resistance Genes

Genetic resistance is the most economical method of reducing yield losses caused by wheat leaf rust. To identify the leaf rust resistance genes in commonly used parental germplasm and released cultivars become very important for utilizing the genetic resistance to wheat leaf rust fully. Up to date, about 90 leaf rust resistance genes have been found, of which 51 genes have been located and mapped to special chromosomes, and 56 genes have been designated officially according to the standards set forth in the Catalogue of Gene Symbols for wheat. Twenty-four wheat leaf rust resistance genes have been developed for their molecular markers. It is very important to isolate, characterize, and map leaf rust resistance genes due to the resistance losses of the genes caused by the pathogen continuously.

Leucine zipper like structure in rice WRKY89 enhances its affinity for binding with W box elements

WRKY proteins are transcriptional regulators involved in plant responses to biotic and abiotic stresses, metabolisms, and developmental processes. In the present study, we isolated a WRKY cDNA, OsWRKY89 from a rice cDNA library. The deduced polypeptide contains 263 amino acid residues with a potential leucine zipper structure in its N-terminus, sharing low identity with other known WRKY members. OsWRKY89 and three deletion derivatives from its N-terminal were expressed in high levels in Escherichia coli as a C-terminally six-histidine-tagged fusion protein, and purified by employing one-step affinity chromatography on a Ni-NTA column. The recombinant OsWRKY89 protein was found to bind specially to sequences harboring W box cis elements by using electrophoretic mobility shift assays. This binding activity was decreased significantly by deletion of the leucine zipper-like structure in the N-terminal of Os- WRKY89. Using a yeast two-hybrid assay system, we found that the leucine zipper motif of OsWRKY89 was involved in the protein-protein interaction. Further deletion to remove partial WRKY domain abolished completely the interaction between the expressed protein and the W boxes, indicating that the WRKY domain is essential to the DNA-binding. These data strongly suggest that the leucine zipper-like motif of OsWRKY89 plays a significant role in the protein-protein and DNA-protein interactions.

Improving biocontrol activity of Pseudomonas fluorescens through chromosomal inte-gration of 2,4-diacetylphloro-glucinol biosynthesis genes

Antibiotic 2,4-diacetylphloroglucinol (2,4- DAPG) produced by Pseudomonas fluorescens CPF-10 and 2P24 is a principal factor enabling bacteria to suppress plant diseases caused by soilborne pathogens. In this study, a 2,4-DAPG biosynthesis locus phlACBDE cloned from strain CPF-10 was assembled into a mini-Tn5 transposon and in- troduced into the chromosome of P. fluorescens P32 (2,4- DAPG?), CPF-10 and 2P24 to construct the 2,4-DAPG over- producing derivatives P32-38, CPF10-9 and 2P24-48, respec- tively. All the transgenic strains showed an enhanced anti- biosis capacity against plant microbial pathogens in vitro and two strains, P32-38 and CPF10-9, provided significantly bet- ter protection against wheat take-all disease caused by Gae- umannomyces graminis var. tritici and tomato bacterial wilt caused by Ralstonia solanacearum in greenhouse. Compared to their parental strains, the 2,4-DAPG overproducing de- rivatives colonized to the same extent on the wheat tips in the autoclaved soil, but developed larger populations in natural soil. These results indicated that production of antibiotics 2,4- DAPG by biological control pseudomonads can contribute not only to their disease suppression capacities but also to the ecological competence in the resident microflora. Our re- search also suggests that it is a realistic approach to improve biocontrol capacity of P. fluorescens through the genetic modification of its antibiotic 2,4-DAPG production.