Overproduction of the rhizobial adhesin RapA1 increases competitiveness for nodulation

Competition for nodulation is a complex problem where bacterial adhesins, which are required for root colonization, may play a role. However, the possible influence of adhesins on competitiveness was scarcely studied. In this work, the Rhizobium leguminosarum bv trifolii adhesion protein RapA1 was overproduced from a pHC60-derived plasmid and expressed in R200 strain. When an overproducing strain and a control-carrying empty vector were co-inoculated on clover plants, a positive effect of RapA1 on competition for nodule occupation was observed. Therefore, optimization of RapA1 expression may be considered for improvement of rhizobial competitiveness.     

Legumes as nitrogen suppliers of grassland on fen soil: Leguminosen als stickstofflieferanten für niedermoorgrünland

A 6-year trial was laid out with varied PK fertilization on fen soil and analysed for the capability of undersown clover species to fix atmospheric nitrogen. No mineral nitrogen was applied. On an average of the six test years, the share of white clover in the total crop yield of the sward was 17% after sowing once and that of red clover or Swedish clover was 19% after sowing twice. The annual mean shares of these two clover variants in the total yield varied only slightly over the test period. White clover showed typical seasonal dynamics in the test years, with yield portions increasing from spring to late summer. Undersown red and Swedish clovers reached the highest yield percentages in their 2nd and 3rd growths. The variants grown without PK fertilizer and clover yielded 45 dt DM ha^???1. With PK fertilizer dry matter yields increased to 57 and 68 dt ha^???1, respectively. With supplemental white clover or red/Swedish clover sown into the sward, substantial amounts of symbiotic nitrogen were accumulated in the harvestable plant matter, giving a total dry matter yield of 76 dt ha^???1. Clover yield shares up to 30% resulted in increasing DM yields which, however, declined again with even larger shares of clover. As to the ingredients of grasses, herbs and clover, the differences were mostly significant. On an average of the six test years, nitrogen fixation was 58.4?kg ha^???1 for white clover and 46.6?kg ha^???1 for red/Swedish clover.     

Positional effect of gene insertion on genetic stability of a clover yellow vein virus-based expression vector

The stability of the inserted genes in the viral expression vector varied depending on the sequence introduced and the position of insertion. Infectious cDNA to Clover yellow vein virus (pClYVV) was modified to insert a foreign gene at two independent sites: one, along with a polylinker, between the NIb and CP genes (pClYVV/CP/W) and the other between P1 and HC-Pro (pClYVV-Pst/CP). The green fluorescent protein (GFP) gene was inserted into either pClYVV/CP/W or pClYVV-Pst/CP. GFP gene was stably maintained and expressed in both vectors following serial passages in plants. Progeny viruses from both constructs accumulated in similar amounts and at rates of 70%–80% of that of the wild-type virus. On the other hand, progeny viruses carrying the human interferon- (hIFN) gene cloned in pClYVV-Pst/CP were genetically unstable owing to frequent deletions of the cloned gene during passage through plants. In contrast, the hIFN sequence cloned in pClYVV/CP/W was stably maintained in viruses after several passages in broad bean plants, and the progeny virus accumulated at the rate of about 50%–100% of that of the wild-type virus. The nucleotide sequence analyses indicated that the genetic instability of the inserted sequence results from homologous recombination of viral vector and inserted DNA sequences; it is not due to the inserted sequence alone.     

不同硫酸处理对白三叶种子发芽的影响

用49％硫酸和98％硫酸分别浸泡3min、5min、10min、15min、30min处理白三叶种子,研究不同处理对种子发芽的影响。通过比较不同处理时间内两者发芽率和发芽势得出：用49％的硫酸处理在5min时,白三叶的发芽水平最优。     

灰巴蜗牛在三叶草田的空间格局及理论抽样数

应用聚集度指标检验、线性回归方程检验方法研究探讨了灰巴蜗牛在三叶草田垂直方向和水平方向的空间格局。结果表明,灰巴蜗牛在垂直方向和水平方向的空间格局均为聚集分布,这种聚集是由灰巴蜗牛本身行为和不同生境决定的。并应用Iwao的m＊-m回归式计算在允许误差范围内的理论抽样数。     

优质粗饲料对奶牛生产性能的影响

为了探讨优质粗饲料对奶牛生产性能的影响,八一农大动科院,１９８９年在８５４农场用小叶章干草与玉米秸和大豆荚皮合用饲喂奶牛作对比试验;８５１１农场１９９３年用蜡熟期玉米青贮与乳熟期玉米青贮饲喂奶牛对作比试验．８５４农场１９９４年用小叶章干草,青贮和玉米秸青贮和大豆秸,青贮和稻草三种不同粗饲料组成饲喂奶牛作对比试验。     

Root parasite induced nitrogen transfer between plants is density dependent

Recent studies point to the importance of soil borne parasites as agents of vegetation change via their negative effect on host plants. Here we show that these soil organisms can influence vegetation characteristics by increasing the transfer of the plant growth-limiting nutrient nitrogen (N) from their host, a N-fixing legume, to neighbouring grass species, thereby benefiting the growth of the neighbour. Furthermore, the amount of N transferred from the legume to the neighbour, and its consequent effect on the neighbours growth, was dependant on the density of root infestation. This mechanism of N transfer from legumes to neighbouring plant species is likely to be an important agent of vegetation change.     

三叶草属牧草育种研究进展

进入20世纪80年代后,随着我国南方草地畜牧业的兴起,三叶草在人工草地建设中的作用越来越被重视。选育适宜不同地区种植的三叶草新品种工作开始起步。本文简要总结了国内外三叶草属牧草育种的概况,以期对今后三叶草属牧草的育种改良研究提供借鉴作用。     

西部地区生态足迹与苜蓿草产业发展战略研究

阐明了西部地区农业生态足迹及该区生态足迹承载力下降的原因 ,并提出该区发展苜蓿人工草地 ,改善农业生态环境 ,提高农业生态足迹承载力 ,实现农业可持续发展的对策。     

Genetic analysis of lethal tip necrosis induced by <Emphasis Type="Italic">Clover yellow vein virus</Emphasis> infection in pea

Clover yellow vein virus (ClYVV) elicits lethal tip necrosis in the pea line PI 118501. Pea line PI 118501 develops necrotic lesions and veinal necrosis on inoculated leaves, followed by systemic necrosis, leading to plant death. To understand the genetic basis of this lethal tip necrosis, we crossed lines PI 226564 and PI 250438, which develop mosaic symptoms in response to ClYVV inoculation. In reciprocal crosses of PI 118501 with PI 226564, all F₁ plants had mosaic symptoms with slight stem necrosis and early yellowing of upper leaves. Essentially the same symptom was manifested in PI 118501 × PI 250438 F₁ plants. In F₂ populations from the cross between PI 118501 and PI 226564, the observed ratios of necrosis, mosaic with slight stem necrosis, and mosaic fit the expected 1 : 2 : 1 ratio. These results indicate that a single incompletely dominant gene confers the induction of necrosis in PI 118501. This locus in pea, conferring necrosis induction to ClYVV infection, was designated Cyn1 (Clover yellow vein virus-induced necrosis). A linkage analysis using 100 recombinant inbred lines derived from a cross of PI 118501 and PI 226564 demonstrated that Cyn1 was located 7.5 cM from the SSR marker AD174 on linkage group III.