Intra-specific competition in maize: Early established hierarchies differ in plant growth and biomass partitioning to the ear around silking

Early interferences among plants within a maize stand determine the establishment of extreme plant types (i.e. dominant and dominated individuals). The development of these hierarchies takes place well before [from the seventh leaf stage (V₇) onwards] the start of the critical period for kernel set (i.e. a 30-day period centered in silking). Kernel number per plant (KNP) is significantly related to plant growth rate around silking (PGR_S) and biomass partitioning to the ear during this period. Previous evidence has demonstrated that at high stand densities, extreme plant types may exhibit similar PGR_S values but set different KNP. We tested the hypothesis that early established plant hierarchies differ in biomass allocation to the ears during the period around silking. Two hybrids of contrasting tolerance to crowding (DK752 and DK765 as the tolerant and the intolerant hybrid, respectively) were cropped at different interplant competition intensities (6, 12, 12 pl m⁻² thinned to 6 pl m⁻² at V₉ and 6 pl m⁻² shading from V₉ onwards) during 2003/2004 and 2004/2005 in Argentina. For all treatments, the coefficient of variation (CV) of plant biomass increased from V₃ (ca. 1.2%) to V_9-10 (ca. 22%). From V₇ onwards, plant growth rate of dominant individuals was higher (P < 0.05) than that of the dominated plants. Hence, dominant plants exhibited higher (P < 0.05) PGR_S (ca. 4.5 g pl day⁻¹) than dominated individuals (ca. 3.7 g pl day⁻¹). As PGR_S declined in response to increased plant population density (ca. 5.1 and 2.8 for 6 and 12 pl m⁻², respectively), biomass partitioning to the ear was reduced (ca. 0.44 and 0.33 for 6 and 12 pl m⁻², respectively). For all treatments, however, dominant plants exhibited a greater biomass partitioning to the ear (ca. 0.41) than the dominated individuals (ca. 0.36). Consequently, the former were the individuals with the highest ear growth rate (ca. 1.9 and 1.4 g per ear per day for the dominant and dominated plant, respectively) and KNP (ca. 623 and 490 kernels per plant for the dominant and dominated plant, respectively) of the stand. We identified three traits on DK765 related to the low tolerance to high-density stress of this genotype: (i) a higher plant-to-plant variability (CV ca. 26% and 19%, for DK765 and DK752, respectively), (ii) a lower biomass partitioning to the ear around silking (ca. 0.26 and 0.39 for DK765 and DK752, respectively), and (iii) a higher response rate of KNP to ear growth rate around silking (ca. 370–738 and 360–414 kernels per g, for DK765 and DK752, respectively). Hence, as stand density was increased, KNP of DK765 was sharply reduced, especially in the dominated individuals of the stand.     

国外玉米耐密性研究进展

文章从玉米耐密性的遗传改良、影响因素以及高密度的不利影响等方面,对国外玉米耐密性的研究进展进行了综述,指出现代玉米杂交种的产量提高主要归功于耐密性的增强;耐密性是一个复杂的生理性状,受很多因素的影响;高产性和稳产性的统一是现代优良杂交种的必备条件。     

甜高粱酿酒酵母耐受性分析

[目的]分析4株甜高粱酿酒酵母菌的耐受性.[方法]研究了4株发酵工程实验室保存的甜高粱酵母菌和1株商业酵母菌对乙醇、蔗糖、酸、碱、渗透压的耐受性,通过观察在这4种因素下菌落的生长情况,对其耐受性进行分析.[结果]试验表明,4株甜高粱酵母菌均表现出不同的耐受性,在不同的胁迫环境下均表现出较强的抗胁迫能力.[结论]研究可为利用甜高粱秸秆进行乙醇发酵的菌种选择提供参考依据.     

鸡致病性大肠杆菌耐药性的研究进展

大肠杆菌是一种常见致病菌,近年来,大肠杆菌的耐药株不断增多,特别是多重耐药株的大量出现,使其治疗变得十分困难。本文对鸡致病性大肠杆菌耐药现状以及产生耐药性机制的研究作以综述,以期为进一步研究鸡大肠杆菌病的综合防治提供依据。     

茶树根内生细菌的分离及其茶多酚耐受性的初步研究

本实验研究了茶树根内生细菌的分离方法及对茶多酚的耐受性,并对内生细菌进行了初步的鉴定。结果表明,分离茶树内生细菌时采用75%的酒精2min和2%次氯酸钠20min表面消毒处理,消毒彻底;含茶多酚的细菌营养平板可作为茶树根内生细菌的选择性分离平板。茶树内生细菌对茶多酚的耐受浓度,最高不高于0.5g/L;经鉴定主要为芽孢杆菌属(Bacillus sp.)。     

硒在大蒜体内的生物富集及其抗氧化作用

大蒜对硒具有强的生物富集作用，并能将吸收的无机硒的７８．２４％转化为有机硒。经ＳｅｐｈａｄｅｘＧ－１５０柱层析，聚丙烯酰胺凝胶电泳，ＳＤＳ－聚丙烯酰胺凝胶电泳，首次从富硒大蒜中分离到一种分子量为３００００Ｄ的含硒蛋白，进一步研究其抗氧化作用，发现该蛋白能提高谷胱甘肽过氧化物酶、超氧化物歧化酶、过氧化氢酶活性，降低过氧化物酶活性。ＥＰＲ表明，Ｎａ２ＳｅＯ３处理组大蒜体内活性氧相对含量比对照低３１．９１％。     

粪肠球菌益生特性的体外评价

通过体外法研究粪肠球菌的生长特点、耐酸性、耐胆盐性和抑菌性等，以评价其益生效果。结果表明：①粪肠球菌在培养2 h后进入对数期，8 h到达稳定期；② 经pH 2、3、4的人工胃液处理3 h后，粪肠球菌极显著降低至2.71×10⁵、1.03×10⁷和5.65×10⁷CFU/mL（P<0.01）；③粪肠球菌经含质量分数为0.2%和0.3%的胆盐溶液处理3 h后，极显著降低至1.46×10⁶和1.37×10⁶ CFU/mL（P<0.01）；④粪肠球菌对大肠杆菌O₁和O₇₈均在混合培养至10 h时表现极显著的抑制作用（P<0.01）。可见，粪肠球菌生长繁殖速度快，能耐受胃肠道环境，对大肠杆菌O₁ 和O₇₈有一定的抑制作用，适合作为微生态制剂的生产菌种。     

黄淮海区玉米品种耐荫性综合评价及指标筛选

以 35个玉米品种为材料，花期利用遮光度为 50%遮阳网人工模拟寡照环境，测量雌雄间隔期、株高、穗位高、雄穗分枝数、雄穗长度、产量等 14个性状，运用相关性分析、主成分分析、聚类分析、回归分析等多元统计分析方法对玉米品种进行耐荫性评价，筛选出玉米品种耐荫性评价关键指标，根据鉴定指标对玉米品种进行耐荫性划分。利用主成分分析和逐步回归优化出产量、行粒数、雌雄间隔期、穗粗 4个耐荫性评价指标，以产量、行粒数、雌雄间隔期、穗粗 4个性状平均隶属函数值进行聚类分析，将 35个玉米品种分成耐荫性强、耐荫性弱两大类型。通过分析建立玉米品种花期耐荫性评价体系，产量、行粒数、雌雄间隔期、穗粗作为玉米品种花期耐荫性鉴定指标。     

Tolerance and safety evaluation of sodium sulfate:A subchronic study in laying hens

Sodium sulfate (Na₂SO₄) is a readily available chlorine-free source of sodium, which could be used to reduce sodium chloride to maintain the ratio between chlorine and sodium in poultry diets. Dietary supplementation with excessive levels of Na₂SO₄ might be detrimental to bird''s health and performance. A subchronic study was carried out to investigate the potential adverse effects of an accidental oversupply of Na₂SO₄ in the diets of laying hens. Four hundred and fifty 21-week-old Hy-Line White layers were randomly assigned to 5 treatments with 6 replicates. The birds were fed diets supplemented with 0 (control), 0.3%, 0.6%, 1.5%, and 3.0% Na₂SO₄ for 8 weeks. Laying performance, egg quality parameters, clinical blood parameters, histopathology, intestinal barrier functions, and intestinal microflora composition were measured. No clinical signs of intoxication or mortality were observed during the experimental period. The results of this study showed that the optimal levels of Na₂SO₄ (0.3% to 0.6%) significantly improved the laying rates, average daily egg mass, and eggshell quality of hens compared to the control (P < 0.05). However, 3.0% Na₂SO₄ produced negative effects on laying performance, eggshell quality, blood biochemistry, and particularly on liver and kidney pathology, and intestinal morphology and barrier functions compared with the controls. Although minor changes were observed in clinical blood parameters of hens receiving 1.5% Na₂SO₄, these were not considered to be of toxicological significance due to the absence of any organ pathological changes in hens. In conclusion, our results indicated that a Na₂SO₄ concentration of 1.5% was non-deleterious to laying hens after a daily administration for 56 d, namely that dietary supplementation of up to 5 times the maximum recommended dose is safely tolerated by laying hens.