甘肃地方苜蓿农家品种脯氨酸积累能力与抗旱性的研究

本文依据“脯氨酸维持积累时间”和“脯氨酸维持积累量”指标评介了四个甘肃地方苜蓿农家品种的抗旱能力。结果表明:敦煌苜蓿的抗旱能力高于会宁、秦安、灵台苜蓿,其中会宁苜蓿居二,灵台苜蓿抗旱性最差。这一抗旱排序与叶片相对含水量及气孔指标所得到的结果相一致。证明了“脯氨酸维持积累时间”和“脯氨酸维持积累量”可以作为首蓿抗旱性的鉴定指标。     

Chromosome and plasmid-encoded N-acyl homoserine lactones produced by Agrobacterium vitis wildtype and mutants that differ in their interactions with grape and tobacco

Agrobacterium vitis causes crown gall disease on grapevines. It also induces a specific necrosis on grape roots and a hypersensitive response (HR) on tobacco that are regulated by a complex quorum-sensing regulatory system. Strain F2/5 produces at least six N-acyl-homoserine lactones (AHLs) that function as signal molecules in quorum-sensing. The AHLs differ in acyl side chain length (8–16 carbons) as determined by gas chromatography/mass spectrometry and electrospray ionization tandem mass spectrometry. Mutant derivatives of F2/5 differ in ability to cause necrosis and the HR and show variable AHL profiles as determined by a thin-layer chromatography/biosensor assay. All wildtype A. vitis strains revealed the presence of long-chain AHLs regardless of tumorigenicity or ability to cause the HR. Whereas genes encoding long-chain AHLs are predicted to reside on the F2/5 chromosome, the determinants for short-chain AHLs were shown to be located on conjugal plasmids.     

阿魏蘑、白灵菇及杏鲍菇亲缘关系的研究

利用PCR产物克隆测序测定了阿魏蘑、白灵菇与杏鲍菇rDNA内转录间隔区(ITS)的序列,并对所测序列进行分析.结果表明,阿魏蘑、白灵菇和杏鲍菇三者之间具有较近的亲缘关系,白灵菇与杏鲍菇具有非常近的亲缘关系,但阿魏蘑、白灵菇和杏鲍菇为3个不同的种.     

模糊隶属法对玉米苗期耐旱性的拟合分析

在略高于玉米萎蔫系数的干旱条件下,以出苗率和生物学产量耐旱系数之乘积为指标,测定了17个玉米自交系和10个杂交种的苗期抗旱性。并用模糊隶属法,以干旱胁迫下的胚芽鞘长度,出苗率,根重,生物学产量,脯氨酸含量,电导率和离体叶片保水力等指标对各品种耐旱性进行了拟合分析。结果表明,在略高于萎蔫系数的干旱条件下,以出苗率和生物学产量的耐旱系数之乘积为指标,可以准确鉴定玉米苗期的耐旱性,与耐旱性的综合评价拟合良好(相关系数r=0.914)。     

西北干旱灾害及其气候趋势研究

利用西北五省1950～2000年降水、温度和农作物旱灾面积资料,用降水的Z指标法,农作物受旱成灾率确定了西北干旱指标和旱灾等级,分析了西北旱灾特征及气候变化趋势。表明西北农业旱灾以70、90年代最严重,而且呈增加趋势,气温在升高,降水在减少。根据预测21世纪前十年西北干旱有所减轻。     

关中西部四灌区旱情规律分析

为给关中西部灌区水资源合理调控提供依据，在简述干旱及其分类的基础上，指出了关中西部各类干旱多源于气象干旱。对该区7个气象站的年降水进行分析表明，各气象站年降水量的变差系数均为0．25，偏态系数均为0．5。以兴平气象站作为代表站对不同历时的旱情进行了分析，结果显示11月到来年2月发生重旱和特旱的概率较大，在30％左右，特别是12月份，概率达54％，且以特旱为主；7、8月份以中旱和重旱为主；夏玉米播前发生特旱的概率较高，达27％，拔节孕穗和抽穗开花期以特旱为主，概率达33％；冬小麦的越冬和麦黄期以特旱为主，发生概率在30％左右。     

灰色灾变理论在宁南山区干旱气候预测中的应用

在分析宁南山区干旱气候特征及其对农业生产影响的基础上 ,借助灰色灾变理论分别建立了春旱、夏旱、秋旱、春夏连旱、夏秋连旱、全年旱等六种干旱类型的 GM( 1 ,1 )预测模型 ,并对 2 0 0 0～ 2 0 2 0年的干旱气候做出预测。经对 2 0 0 0年和 2 0 0 1年预测结果验证 ,吻合性良好。此外 ,提出了宁南山区抗旱防旱的综合农业措施。研究结果可对广大旱区抗旱减灾 ,促进农业生产发展提供科学指导。     

Effect of air temperature, rain and drought on hot water weed control

The influence of rain and drought before, and air temperature during, weed control with hot water was studied in laboratory experiments on the test weed Sinapis alba (white mustard). The plants were grown in a greenhouse and treated outdoors. There was no difference in weed control effect when S. alba plants at the four‐leaf stage were treated at the air temperatures 7°C and 18^°C. The effective energy dose for a 90% fresh weight reduction was 465 kJ m^?2 for both air temperatures. Weed control of S. alba at the four‐ to six‐leaf stage in rainfall above the rainwater run‐off level increased the required effective energy dose by 20% (i.e. 120 kJ m^?2) compared with dry plants. A short period of drought just before treatment on S. alba at the two‐ to four‐leaf stage increased the plant fresh weight reduction, which was 22% at low energy dose (190 kJ m^?2) and 44% at high energy dose (360 kJ m^?2). Hot water weed control should thus be carried out when the plants are drought stressed and avoided when the plants are wet. The air temperature seems to be of little importance in the range 7–18^°C.     

Predicting effective doses for the joint action of two fungicide applications

A function was derived to predict fungicide efficacy when more than one application of a single active ingredient is made to a crop, given parameters describing the dose–response curves of the component single-spray applications. In the function, a second application is considered to act on that proportion of the total pathogen population which was uncontrollable at the time of the first application (represented by the lower asymptote of the dose–response curve for the first treatment), plus any additional part of the population which survived the first application as a result of a finite dose being applied. Data to estimate the single-spray dose–response curve parameters and validate predictions of two-spray programme efficacy were obtained from separate subsets of treatments in four field experiments. A systemic fungicide spray was applied to wheat at a range of doses, at one or both of two times (t₁ and t₂), in all dose combinations. Observed values of the area under the disease progress curve (AUDPC) for septoria leaf blotch (Mycosphaerella graminicola) were used to construct response surfaces of dose at t₁ by dose at t₂ for each culm leaf layer. Parameters were estimated from single-spray and zero-dose treatment data only. The model predicted a high proportion (R² = 71–95%) of the variation in efficacy of the two-spray programmes. AUDPC isobols showed that the dose required at t₂ was inversely related to the dose at t₁, but the slope of the relationship varied with the relative timings of t₁ and t₂ in relation to culm leaf emergence. Isobols were curved, so the effective dose – the total dose required to achieve a given level of disease suppression – was lower when administered as two applications.     

Functional analysis of the 3′ end of avrBs3/pthA genes from two Xanthomonas species

The phytopathogens Xanthomonas oryzae pathovar (pv.) oryzae and Xanthomonas axonopodis pv. citri each contain several avrBs3/pthA family genes. Structural features of these genes important for avirulence and/or virulence functions include a central region of multiple direct repeats and three nuclear localization signals (NLSs) and an acidic activation domain (AAD) at the 3′ end. To identify other regions critical to function in the 3′ ends of these genes, we constructed several chimeras using apl1 and apl2 from X. axonopodis pv. citri and avrXa10 and avrXa7 from X. oryzae pv. oryzae and evaluated their functions by inoculation to citrus and rice. The apl1 and avrXa7 genes are major virulence determinants in citrus and rice, respectively, while the contributions of apl2 and avrXa10 to virulence are negligible or not measurable. Constructs that contained a 417 bp HincII-SphI fragment from the 3′ end of apl1 in combination with the repeats from avrXa7, avrXa10, and apl1 caused a canker phenotype on citrus. Interchange of the HincII-SphI fragment between avrXa7 and avrXa10 abolishes avrXa7 avirulence function and reduces its virulence but it does not affect avrXa10 avirulence function in rice. avrXa7 caused a hypersensitive response (HR) in citrus and replacement of it's 3′ end with that of apl1 resulted in loss of canker and induction of HR. Thus, the HincII-SphI fragment of the avrBs3/pthA gene family is important for avirulence and virulence functions in two different plant species, Oryza sativa and Citrus natsudaidai HAYATA.