麦棉套作复合根系群体对棉花根系生长的影响

【目的】探索麦棉套作两熟中棉花根系对逆境适应的生理机制，为采取合理调控措施、解决麦棉两熟双高产栽培中棉花弱苗晚发问题提供依据。【方法】在麦棉套作模式下，采用池栽和盆栽相结合的试验方法，设置麦棉自然根系套作(根系和肥水均可相互通过)、纱网隔根套作(肥水可相互通过，根系不能相互通过)和塑膜隔根套作(根系和肥水均不能相互通过)3种麦棉复合根系群体，研究套作小麦对棉花根系活力、内源保护酶活性及膜脂过氧化作用的影响。【结果】在麦棉共处期，麦棉自然套作复合根系中小麦根系对肥水的激烈竞争，导致棉花根系干物质累积量和根冠比均显著低于隔根处理。而小麦根系强烈的生理活动，使套作棉花根系处理相对隔根处理处于一种逆境胁迫状态，其根系活力增强，超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)等内源保护酶活性明显提高。同时，根系细胞膜脂过氧化程度也相应增大。到小麦收获后，种间竞争解除，麦棉自然根系处理棉花根系生长的环境条件得以改善，根系膜脂过氧化程度降低，但由于前期影响还未能完成消除，其根重仍明显低于隔根处理。【结论】套作棉花通过提高根系内源保护酶活性来适应小麦对其造成的营养逆境胁迫。     

共生固氮在农牧业上的作用及影响因素研究进展

共生固N是生物固N的主体部分,具有固N效率高、应用范围广等特点。叙述了主要豆科作物年固N量及固N量占豆科作物本身所吸收N的比例,阐述了豆科作物在与非豆科作物间套轮作中固定N素的转移及对非豆科作物的影响,并介绍了影响豆科作物-根瘤菌共生体共生固N效率的主要因素。开展豆科作物-根瘤菌共生体系方面的研究对农业可持续发展具有重要意义。     

Size, symbiotic effectiveness and genetic diversity of field pea rhizobia (Rhizobium leguminosarum bv. viciae) populations in South Australian soils

Field pea (Pisum sativum L.) is widely grown in South Australia (SA), often without inoculation with commercial rhizobia. To establish if symbiotic factors are limiting the growth of field pea we examined the size, symbiotic effectiveness and diversity of populations of field pea rhizobia (Rhizobium leguminosarum bv. viciae) that have become naturalised in South Australian soils and nodulate many pea crops. Most probable number plant infection tests on 33 soils showed that R. l. bv. viciae populations ranged from undetectable (six soils) to 32×10³ rhizobia g⁻¹ of dry soil. Twenty-four of the 33 soils contained more than 100 rhizobia g⁻¹ soil. Three of the six soils in which no R. l. bv. viciae were detected had not grown a host legume (field pea, faba bean, vetch or lentil). For soils that had grown a host legume, there was no correlation between the size of R. l. bv. viciae populations and either the time since a host legume had been grown or any measured soil factor (pH, inorganic N and organic C). In glasshouse experiments, inoculation of the field pea cultivar Parafield with the commercial Rhizobium strain SU303 resulted in a highly effective symbiosis. The SU303 treatment produced as much shoot dry weight as the mineral N treatment and more than 2.9 times the shoot dry weight of the uninoculated treatment. Twenty-two of the 33 naturalised populations of rhizobia (applied to pea plants as soil suspensions) produced prompt and abundant nodulation. These symbioses were generally effective at N₂ fixation, with shoot dry weight ranging from 98% (soil 21) down to 61% (soil 30) of the SU303 treatment, the least effective population of rhizobia still producing nearly double the growth of the uninoculated treatment. Low shoot dry weights resulting from most of the remaining soil treatments were associated with delayed or erratic nodulation caused by low numbers of rhizobia. Random amplified polymorphic DNA (RAPD) polymerase chain reaction (PCR) fingerprinting of 70 rhizobial isolates recovered from five of the 33 soils (14 isolates from each soil) showed that naturalised populations were composed of multiple (5-9) strain types. There was little evidence of strain dominance, with a single strain type occupying more than 30% of trap host nodules in only two of the five populations. Cluster analysis of RAPD PCR banding patterns showed that strain types in naturalised populations were not closely related to the current commercial inoculant strain for field pea (SU303, ≥75% dissimilarity), six previous field pea inoculant strains (≥55% dissimilarity) or a former commercial inoculant strain for faba bean (WSM1274, ≥66% dissimilarity). Two of the most closely related strain types (≤15% dissimilarity) were found at widely separate locations in SA and may have potential as commercial inoculant strains. Given the size and diversity of the naturalised pea rhizobia populations in SA soils and their relative effectiveness, it is unlikely that inoculation with a commercial strain of rhizobia will improve N₂ fixation in field pea crops, unless the number of rhizobia in the soil is very low or absent (e.g. where a legume host has not been previously grown and for three soils from western Eyre Peninsula). The general effectiveness of the pea rhizobia populations also indicates that reduced N₂ fixation is unlikely to be the major cause of the declining field pea yields observed in recent times.     

套播小麦高产栽培主要农艺措施优化方案研究

为了解决小麦早播与晚稻成熟期偏迟的矛盾 ,1998～ 1999年度选择了基本苗、氮肥用量与共生期 3个对套播小麦生育影响较大的农艺因子 ,采用 3 11A近似饱和最优设计进行试验 ,结果表明 ,氮肥量与共生期对套播小麦产量影响极大 ,是生产中应重点控制的因子 ;产量 5 2 5 0kg/hm2 的最佳措施为基本苗 183～ 2 3 7万株 /hm2 、纯氮 2 44.5～ 2 62 .5kg/hm2 、共生期 8.5～ 10 .5d ;上述结果反映了旱冬年特点 ,与上年度 (烂冬年 )比较 ,基本苗较接近 ,适宜氮肥用量偏高 10 %左右 ,共生期偏长约 3～ 4d。     

海带及其共附微生物的生物活性研究进展

综述了海带的活性物质及其共附生微生物的生物活性研究进展。     

大豆共生固氮能力对土壤无机氮浓度的响应与调控

通过对国内外大豆共生固氮总量及占大豆一生需氮量的比例,以及大豆共生固氮能力对土壤无机氮浓度的响应的综述,提出了如何提高大豆共生固氮能力的途径。明确了协调土壤环境氮浓度和大豆根瘤固氮之间的关系,是充分发挥大豆共生固氮潜力和提高产量的关键所在。     

柠条锦鸡儿根瘤菌及其共生固氮基因多样性

为研究西北干旱地区豆科植物柠条锦鸡儿(Caragana korshinskii)根瘤菌的系统发育地位及共生基因多样性,对从甘肃省分离得到的菌株进行16SrRNA PCR-RFLP和序列分析,构建系统发育树,确定其分类地位,并通过分析共生基因nodA和nifH,确定种群共生类型。结果表明:从柠条根瘤内分离到64株菌,共有7个PCR-RFLP 16SrRNA基因型,主要归属于Ensifer(占分离总数43.8%)、Mesorhizobium(31.2%)、Rhizobium(25%),其中,Ensifer为主要类群,约占34.4%。共生基因nodA和nifH与Ensifer和Mesorhizobium模式菌株同源性较高,与16SrRNA基因确定的根瘤菌分类地位相比,发现部分共生基因与16S rRNA基因确定的分类地位不同,揭示了共生基因横向转移现象的发生。     

黑曲霉拮抗菌Xenorhabdus bovienii445筛选、鉴定及发酵优化

【目的】从现有共生细菌资源中筛选对黑曲霉具有高拮抗作用的菌株,为寻求安全高效的生物保鲜材料提供更多选择。【方法】采用平板对峙法和琼脂扩散法,分别对现有昆虫病原线虫共生菌进行初筛和复筛,对筛选出的高效拮抗共生细菌进行生理生化以及16S rRNA 序列进化分析鉴定,通过单因素试验和响应面分析法优化菌株培养条件,利用损伤接种法在红地球葡萄上验证对黑曲霉防治效果。【结果】分离筛选共获得20株拮抗共生菌,复筛得到1株抑菌效果显著的共生细菌(445),经生理生化及分子生物学分析为伯氏致病杆菌Xenorhabdus bovienii,GeneBank ID:OK560680,与菌株Xenorhabdus bovienii strain Xb139 (MG995576.1)聚于同一分支,相似性达99.79%。获得445菌株抑菌活性的最优培养条件为接种量3.06 %、pH 7.0、装液量100.15 mL/250 mL,抑菌圈直径为(29.67±0.28) mm,抑菌效价为10.59 cm/mL,比优化前提高39.16%。Xenorhabdus bovienii 445发酵液对黑曲霉具有较好防治效果,3 d后防效为63.50%。【结论】筛选得到1株高效拮抗黑曲霉的昆虫病原线虫共生细菌,其发酵液对黑曲霉有良好的抑制效果,具有较好的生防潜能。     

Symbiotic relationships and root nodule ultrastructure of the pasture legume Biserrula pelecinus L.—a new legume in agriculture

Biserrula pelecinus is a pasture legume species new to Australian agriculture. The potential N benefit from B. pelecinus pastures in agricultural systems may not be realised if its symbiotic interactions with Mesorhizobium spp. are not well understood. This study evaluated the symbiotic interactions of four strains of Biserrula root-nodule bacteria (WSM1271, WSM1283, WSM1284, WSM1497) with four genotypes of B. pelecinus (cv. Casbah, 93GRC4, 93ITA33, IFBI1) and with a range of related legumes, including species known to be nodulated by strains of Mesorhizobium loti and other Mesorhizobium spp. Structures of root nodules were studied using light and electron microscopy enabling the ultrastructure of effective and ineffective nodules to be compared. B. pelecinus always formed typical indeterminate, finger-like nodules. The number of bacteroids inside symbiosomes varied between host×strain combinations, however, nodules formed by ineffective associations had well developed peribacteroid membranes and abundant bacteroids. Considerable variation was found in N₂-fixing effectiveness of strains isolated from B. pelecinus on the four B. pelecinus genotypes. Strains WSM1271, WSM1284 and WSM1497 nodulated Astragalus membranaceus, only strains WSM1284 and WSM1497 nodulated Astragalus adsurgens. Strain WSM1284 also nodulated Dorycnium rectum, Dorycnium hirsutum, Glycyrrhiza uralensis, Leucaena leucocephala, Lotus edulis, Lotus glaber, Lotus maroccanus, Lotus ornithopodioides, Lotus pedunculatus, Lotus peregrinus, Lotus subbiflorus and Ornithopus sativus. The four strains from B. pelecinus did not nodulate Amorpha fruticosa, Astragalus sinicus, Cicer arietinum, Hedysarum spinosissimum, Lotus parviflorus, Macroptilium atropurpureum or Trifolium lupinaster. M. loti strain SU343 nodulated all four genotypes of B. pelecinus. However, M. loti strain CC829 only nodulated B. pelecinus genotypes 93ITA33 and IFBI1 and the nodules were ineffective. The root nodule isolates from H. spinosissimum (E13 and H4) nodulated B. pelecinus cv. Casbah whereas the commercial inoculant strain for Cicer (CC1192) could not nodulate any genotype of B. pelecinus. These results indicate that strains WSM1271, WSM1283 and WSM1497 isolated originally from B. pelecinus have a specific host range while strain WSM1284 is promiscuous in its capacity to nodulate with a broad range of related species. As B. pelecinus can be nodulated by Mesorhizobium spp. from other agricultural legumes, particularly Lotus, there is an opportunity to utilise this trait in cultivar development.     

Host-rhizobia interaction for effective inoculation: evaluation of the potential use of the ureide assay to monitor the symbiotic performance of tepary bean (Phaseolus acutifolius A. Gray)

Domesticated and wild-type tepary beans (Phaseolus acutifolius A. Gray) were grown with or without inoculation with rhizobia in pots under bacteriologically controlled conditions in a temperature-controlled glasshouse. Seeds were inoculated with a mixture of seven strains isolated from nodules collected from domesticated field-grown tepary bean in Arizona, USA, or with a commercial inoculant strain for Phaseolus vulgaris (CC511). Different degrees of plant reliance upon N₂ fixation for growth were generated by supplying the inoculated plants throughout growth with nutrients containing a range of concentrations of ¹⁵N-labeled NO₃ (0, 1, 2, 5 or 10 mM). An uninoculated treatment that received 10 mM ¹⁵N-labeled NO₃ was included to provide data for plants solely dependent upon NO₃ for growth. Six weeks after sowing, shoots were harvested for dry matter determination and subsequent ¹⁵N analysis, root-bleeding xylem sap was collected, and nodulation assessed. With regard to shoot biomass production, domesticated lines were more responsive to inoculation, but less responsive to applied N than wild types. All inoculated plants were nodulated, but the field isolates from tepary bean were more effective in N₂ fixation than strain CC511. It was concluded that tepary bean requires a specific inoculant to benefit from fixation of atmospheric N₂. Xylem sap samples were analysed for ureides (allantoin and allantoic acid), amino acid content (α-amino-N), and NO₃ concentration. The amount of ureide-N present in xylem sap was expressed as a percentage of total solute N, described as the relative abundance of ureide-N (RUN), for each N treatment and was compared to the proportion of plant N derived from N₂ fixation (%Ndfa) calculated using a ¹⁵N dilution technique. The RUN values ranged from 8% for saps collected from uninoculated plants provided with 10 mM NO₃ in the nutrient solution (%Ndfa=0) to 86-91% for nodulated plants grown in the absence of externally supplied NO₃ (%Ndfa=100). These data indicated that ureides were the principal product of N₂ fixation exported from the nodules to the shoot in xylem sap. Since RUN values were closely related to %Ndfa, it was proposed that N-solute analysis of xylem sap could provide a valuable analytical tool to monitor the symbiotic performance of tepary bean.