水稻对白叶枯病的成株抗性

有些水稻品种对白叶枯病(Xanthomonas campestris pv.oryzae)的侵染表现出成株期抗性,其植株在苗期感病,随着植株成长由感病转为抗病。13个有成株抗性的品种中,有些能抗供试的4个菲律宾小种,而另一些只对1或2个小种有成株抗性。菌系与品种间互作较强,表明有些水稻品种对白叶枯病的成株抗性似乎属“小种专化”。抗性转变的情况多种多样,有些品种从苗期到孕穗期逐渐由感病转为抗病,另一些品种从感病转向抗病的界限非常明显。不同品种对同一菌系的转抗叶位不同,同一品种对不同菌株的转抗叶位也不一样。具有 Xa-6基因的品种的成株抗性仍表现稳定。高温对感病品种和成株抗性品种在转抗以前的感病阶段的病情发展有促进作用。具有 xa-5基因的 IR1545-339在高温下仍然有其鉴别抗性反应,对其有致病力的小种4的病情类似TNI。     

水稻纹枯病拮抗细菌的种群分布及其生物多样性研究

 通过对从菲律宾Laguna省水稻植株上分离获得的700个细菌菌株进行离体与生物测定发现:在水稻生态系统中,存在着大量格兰氏阴性、非致病性、对纹枯病有拮抗作用的细菌。用Biolog微板的方法鉴定了195个细菌菌株的种类。在147个格兰氏阴性菌株中有14个属39个种,在48个格兰氏阳性菌株中有8个属13个种。在195个被测菌株中最为常见的种是Stenotrophomonas maltophilia,Pseudomonas aeruginosa和Pseudomonas pudita,并且上述3个种内具有拮抗性能较强菌株的比例相当高。因此,这3个种的细菌对水稻病害的生物防治很有潜力。用PCR的方法分析上述3个细菌种部分菌株的生物多样性,结果表明:同一属不同种菌株之间的DNA带谱有一定的交叉;不同属之间的DNA带谱的差异明显大于种之间的差异。     

Rice varietal difference in sheath blight development and its association with yield loss at different levels of N fertilization

Variety and nitrogen (N) fertilizer input are the two main factors that influence the development of sheath blight (ShB) caused by Rhizoctonia solani in intensive and high-input rice (Oryza sativa L.) production systems. This study was conducted to determine the varietal difference in ShB development and its association with yield loss across N rates. Two indica inbred and two indica/indica F₁ hybrid varieties were grown under 0 and 90 kg N ha⁻¹ in 2003 wet season (WS) and under 0, 75, 145, and 215 kg N ha⁻¹ in 2004 dry season (DS). Inoculation was done in 3.2 m² in each experiment unit to achieve uniform disease development. Disease intensity was quantified by measuring relative lesion height (RLH) and ShB index (ShBI) of inoculated 10 hills at flowering and 14 days after flowering. Plant traits, grain yield, temperature, and relative humidity inside the canopy were also measured. Consistent and significant varietal differences in ShB intensity were observed across N rates in both WS and DS. Among the four varieties, IR72 and IR75217H had higher RLH and ShBI than PSBRc52 and IR68284H at all N rates. Sheath blight index at 14 days after flowering had the closest correlation with yield loss from ShB. Varieties with taller stature, fewer tillers, and lower leaf N concentration such as IR68284H generally had lower RLH and ShBI, and consequently lower yield loss from the disease. Disease intensity and yield loss from ShB increased with increasing N rates, but the magnitude of yield loss varied among varieties. This suggests that fertilizer N should be managed more precisely and differently for varieties with different plant type in order to reduce the disease development and maximize grain yield in the irrigated rice systems.     

利用抗病基因多样性持续控制水稻病害

 利用抗病基因多样性持续控制水稻病害,已经成为近年来国内外的研究热点之一。由于该技术可大幅度减少农药的施用量,具有明显的增产增收效果,并为实现农业的可持续发展提供了一个崭新的思路,因此得到了国内外科学家和广大农民的普遍认可。作者对这一领域的研究现状、存在的问题及今后的发展前景作一评述。     

Characterization of some biological control agents from rice seeds in China and in the Philippines

It is well known that rice seed contains large amount of seedborne bacterial pathogens. However, little is known about antagonistic bacteria of the rice seed.     

稻种病原菌Acidovorax avenae subsp. avenae的特征化研究

 从中国浙江省嘉兴市的稻种上分离出一种细菌,经细菌学、 鉴别培养基、致病性、Biolog及脂肪酸分析测定,表明该细菌属于Acidovorax avenae subsp. avenae。 该细菌在水稻苗期产生褐色条斑,与浙江省60年代报道的细菌性褐条病相似,但在细菌学特征上完全不同。A. avenae subsp. avenae既可从褐变稻谷上,也可从健康种子上分离到。用10⁸和10¹⁰个/mL细菌接种稻谷, 种子的发芽及活力明显受到影响。此细菌的种传发病率为0.2%～5.0%,表明种子是传播此种细菌病害的重要侵染源。     

Colonisation of the respiratory tract of lambs by strains of Mycoplasma ovipneumoniae

The age and time of year when colonisation of the nasal cavity of lambs by Mycoplasma ovipneumoniae occurs; the persistence of the organism, and its prevalence in the lungs at slaughter were examined in 2 flocks of sheep in New Zealand. No colonisation had occurred at the time of weaning at 6–7 weeks, but M. ovipneumoniae was recovered from most lambs on at least one occasion before they were slaughtered when about 8 months old. In most cases, colonisation of the nasal cavity by M. ovipneumoniae was a transient phenomenon. At slaughter M. ovipneumoniae was recovered from the lungs of 89% of the lambs of one flock and 80% of the other flock.

Bacterial restriction endonuclease DNA analysis (BRENDA) of 34 nasal isolates from one flock showed that it was possible to identify 7 “groups” each with markedly different BRENDA patterns. Lambs initially colonised by one strain, often lost that strain, and if recolonisation occurred it was with a different strain.

M. ovipneumoniae was recovered at slaughter from the lungs of most lambs, both normal and pneumonic. The isolates from one flock were examined by BRENDA, and approximately 90% of them gave similar or identical patterns. The predominant strain isolated from the lungs had been recovered from the nasal cavity of many of the lambs about 3 weeks earlier. This suggests that the nasal and lung isolates do not represent independent populations. However, nasal strains may differ in their ability to colonise the lungs.     

Effect of a Soil Amendment on the Survival of Ralstonia solanacearum in Different Soils

ABSTRACT The effect of a soil amendment (SA) composed of urea (200 kg of N per ha) and CaO (5,000 kg/ha) on the survival of Ralstonia solanacearum in four Philippine soils was investigated in a series of laboratory experiments. Within 3 weeks after application, the SA either caused an initial decrease, a final decline, or no change in the pathogen population, depending on the particular soil type. An initial decrease occurred in a soil with a basic pH and resulted in a significantly (P < 0.001) lower pathogen population immediately and at 1 week after amending the soil. This decrease was probably due to the high pH in the soil during urea hydrolysis. A final decline in the R. solanacearum population after 3 weeks occurred in two soils in which nitrite accumulated after 1 week. In these soils, no decline in bacterial levels occurred when nitrite formation was inhibited by 2-chloro-6-trichloromethylpyridine. In the soil with low pH, no nitrite accumulated and the R. solanacearum population did not decline. The suppressive effects of pH and nitrite on R. solanacearum growth were confirmed by in vitro experiments. Ammonium reduced the growth of R. solanacearum, but was not suppressive. Interactions of pH with ammonium and nitrite also occurred, whereby ammonium reduced growth of R. solanacearum only at pH 9 and nitrite was suppressive only at pH 5. Nitrate had no effect on R. solanacearum growth in vitro.     

温室条件下拮抗细菌Bacillus subtilis B5423-R对水稻纹枯病水平扩展和垂直扩展的抑制

BacillussubtilisB5 42 3对水稻纹枯病的抑制作用主要是通过其产生的拮抗素。在温室条件下 ,于水稻分蘖盛期接种纹枯病菌Rhizoctoniasolani,并采用 2d喷 1次、不同次数对单株喷雾B5 42 3 -R(B5 42 3的标记菌株 ,是利福平抗性的突变体 )的方法进行试验 (对纹枯病水平扩展的抑制 ) ;类似地 ,采用 2d喷 1次、不同次数对小区内所有稻株喷雾B5 42 3 -R的方法进行试验 (对纹枯病垂直扩展的抑制 )。结果表明 1～ 2次喷雾未能显著地降低蚊枯病病丛率和相对病斑高度 ,而连续 3次喷雾使B5 42 3 -R在稻株的群体数量于纹枯病侵染的早期即最初的 6～ 7d内维持在 1× 1 0 6cfu/g以上 ,显著地降低了病丛率和相对病斑高度。