Erwinia amylovora populations resistant to oxolinic acid in Israel: prevalence, persistence and fitness

Oxolinic acid (OA) has been the only bactericide used against fire blight in pear and quince orchards in Israel since 1998. OA-resistant Erwinia amylovora strains (Ea-OA^R) were detected in several orchards in two restricted areas in the northern Galilee region during 1999–2001. In the following years, resistant strains could not be detected in some of these locations. Documenting the fate of Ea-OA^R strains in commercial orchards at eight sites in northern Israel during 2000/03 revealed that the resistant population appeared irrespective of the number of sprays applied and the severity of the disease. The persistence of the Ea-OA^R populations varied from site to site, ranging from 4 to 20 months; these differences could be attributed to the fire blight management activities of growers. Comparative studies on the fitness of Ea-OA^R and E. amylovora strains sensitive to OA (Ea-OA^S) were conducted in vitro and in planta using two strains of each group. In four of the six comparisons, disease incidence on detached blossoms inoculated with Ea-OA^S was significantly higher than that on blossoms inoculated with Ea-OA^R. In two experiments conducted on 8-year-old pear trees grown under netting, the colonization of Ea-OA^S in blossoms, annual shoots and perennial spurs was significantly higher than that of the Ea-OA^R. In two experiments conducted on 2-year-old trees grown under netting in an experimental station, the incidence of shoots exhibiting fire blight symptoms and the rate of symptom progress within the branches were significantly higher in trees inoculated with Ea-OA^S than in those inoculated with Ea-OA^R. The results of this study suggest that OA-resistant E. amylovora strains have lower fitness than wild-type strains. These findings may have implications for fire blight management.     

鸭梨、黄金梨果实结构与耐贮性的关系

以耐贮性强的鸭梨和不耐贮的黄金梨为试材,分别研究了果实组织结构的差异,结果表明:鸭梨果实表面角质层厚,且深入表皮细胞间隙,表皮细胞较厚,排列紧密,表皮下有4～5层含有大量被染成紫红色的单宁类物质;黄金梨角质层薄,表皮细胞少,不连续,甚至没有表皮细胞,表皮下细胞含单宁物质较少,有的几乎没有。此外,鸭梨近果皮果肉中石细胞多、石细胞团大;黄金梨近果皮果肉中石细胞少、石细胞团小。     

梨组织中苹果褪绿叶斑病毒的原位RT-PCR检测

 为了建立梨树苹果褪绿叶斑病毒原位RT-PCR检测技术, 用已知带有苹果褪绿叶斑病毒的库尔勒香梨和无病毒实生苗叶片为材料, 利用D IG标记, 研究了香梨病毒的叶片石蜡切片IS-RT-PCR检测技术。包括AMV逆转录酶、dNTPs、RNasin及互补引物浓度对cDNA合成的影响, 退火温度、Taq DNA聚合酶、Mg²⁺ 、引物浓度及循环次数对原位PCR效果的影响。结果表明: RNasin的用量大于0.2 U·μL^-1时,信号强度随着RNasin量的加大而增强; 只有当dNTPs浓度达1.0 mmol·L^-1时才能生成一定量的cDNA;AMV浓度在0.3～0.5 U·μL^-1均可进行正常的逆转录, 而且在该范围内产物的量随AMV浓度提高而增多; 引物浓度达到0.9μmol·L^-1以上时才能进行有效的逆转录, 并且生成的cDNA的量随引物浓度增大而增加。原位扩增ACLSV的cDNA适合退火温度为56℃。循环20～30次可出现较强的蓝色信号, 引物浓度在0.8～1.2μmol·L^-1时显色较好; Taq酶浓度为20 U·mL^-1以上, 均显示较深的蓝色; Mg^{2 +}浓度为1.5mmol·L^-1就可满足原位PCR所需。获得了苹果褪绿叶斑病毒的原位PCR优化检测体系, 利用建立的优化程序对香梨样品进行了检测验证, 取得了很好效果。     

不同果袋对黄金梨果实套袋效果试验

选用7种不同类型的果袋,在西北高原地区栽培条件下对黄金梨果实进行套袋试验.结果表明:套袋可显著改善黄金梨果实外观品质,提高果实商品质量.套袋黄金梨果实硬度较对照提高4.47%～17.91%,平均单果重、可溶性固形物含量分别较对照降低0.73%～8.45%和1.99%～7.81%.综合比较认为,在7种供试果袋中,以爱农小蜡袋 双层纸袋效果最好.     

南果梨和苹果梨适宜采收期果实生理生化指标初探

针对鞍山海城地区的南果梨和沈阳苏家屯地区的苹果梨初果期和盛果期适宜采收期的生理生化指标进行了详细调查，结果表明：南果梨在海城地区初果期和盛果期最适采收期分别在9月20日、9月15日左右，一级果主要生理指标是：种子变黑指数分别是96．7、95．2，可溶性固形物是16．6％、16．1％，果实自然落果率分别是1．89％、1．26％。苹果梨在苏家屯地区初果期和盛果期最适采收期均在9月30日左右，一级果主要生理指标是：种子变黑指数分别是95．7、96．1，可溶性固形物分别是13．1％、13．4％，果实自然落果率分别是1．98％、2．38％。     

Comparison of S-RNase,RNase T1, T2, and A effects on growth inhibition and RNA degradation of in vitro-cultured pear pollen

To obtain the basic information on fruit set regulation, effects of several RNases including S-RNase on pollen tube growth and RNA degradation in the tube were studied in the pear. Purified S-RNase from the Japanese pear ‘Kosui’ (S₄S₅) predominantly inhibited the growth of ‘Kosui’ pollen tubes (self) in vitro at 0.28 unit μL⁻¹, but it inhibited ‘Chojuro’ (S₂S₃) pollen (cross) only slightly. The same unit of RNase T₁ (EC 3.1.27.3) clearly inhibited the pollen tube growth, but the action was significantly weaker than that of the S-RNase against the self-pollen. Inhibitory effect of RNase T₂ (EC 3.1.27.1) and RNase A (EC 3.1.27.5) was only slight. The proteins other than the S-RNase extracted from pear style did not have any inhibitory action, though they possessed RNase activity 3.8 times higher than S-RNase. Thus, RNases tested here could not substitute for the S-RNase in specific inhibition against the self-pollen tube growth. Total RNA degradation by each RNase occurred in the pollen tubes as following order; S-RNase (self) ≥T₁ > T₂ ≥ A > S-RNase (cross). Degradation degree of 28S and 18S rRNA was as follows; S-RNase (self) > A > T₁ > T₂ > S-RNase (cross). The degradation of 5.8S and 5S rRNA was; S-RNase (self) > S-RNase (cross) > A > T₂ > T_1. The degree of rRNA degradation was, thus, not always in parallel with the degree of pollen growth inhibition. The S-RNase may degrade not only rRNA but also mRNA essential for pollen tube growth, and may be specifically adapted to inhibit the growth of self-pollen tubes. Therefore, controlling S-RNase amount in the style will produce self-thinning cultivars efficiently, which are unnecessary not only for hand-pollination but fruit-thinning practices in the pear. Practically, cultivar with weak self-incompatibility and small amount of S-RNase, such as ‘Okusankichi’, may be an expecting candidate for breeding self-thinning cultivars.     

Ultrastructural study on scab resistance expressed in epidermal pectin layers of pear leaves

Proliferation and collapse of subcuticular hyphae of Venturia nashicola race 1 were studied ultrastructurally, after inoculation of susceptible Japanese pear cv. Kousui, resistant Japanese pear cv. Kinchaku, resistant Asian pear strain Mamenashi 12 and nonhost European pear cv. Flemish Beauty leaves, to understand the nature of the resistance mechanism. After cuticle penetration by the pathogen, the hyphae were observed at lower frequency in epidermal pectin layers and middle lamellae of leaves of the three resistant plants than in those of susceptible ones. This result suggested that fungal growth was suppressed in the incompatible interaction between pear and V. nashicola race 1. In the pectin layers of all inoculated plants, some hyphae had modifications such as breaks in the plasmalemma with plasmolysis, necrotic cytoplasm and degraded cell walls. More hyphae had collapsed in the leaves of the three resistant plants than in those of the susceptible cv. Kousui. In collapsed hyphae, the polymerized cell walls broke into numerous fibrous and amorphous pieces, showing that the scab resistance might be associated with cell wall-degrading enzymes from pear plants.     

鸭梨果实石细胞分化特性研究

以鸭梨为试材,利用透射电镜显微技术和组织化学技术对梨果实石细胞分化及次生壁形成过程进行研究。结果表明,石细胞分化始于开花第7天,原生质体收缩于细胞一侧,随后胞内出现颗粒状凝聚物,次生壁逐渐增厚,之后胞质继续收缩消失,早期形成的石细胞多以群体形式同时出现。石细胞次生壁形成是逐步进行的,即先形成纤维素或半纤维素网架结构,再进行木质化填充。透射电镜下石细胞分化过程中依次呈现出细胞核染色质凝聚、细胞核变形、核膜界限不清晰的现象;胞内出现同心层次的自噬泡,形成大量囊泡;细胞核消失,内质网断裂并大量增生,质膜向内突起形成泡状结构;次生壁增厚,胞内细胞器仅有线粒体和内质网,最终细胞质收缩消失。     

多年生香豌豆的形态特征及经济性状研究

多年生香豌豆是黄河水利委员会天水水土保持试验站引进的国外优良牧草品种。试验针对多年生香豌豆的形态特征、经济性状及其生长状况进行了试验研究，发现多年生香豌豆无论是作为牧草还是水土保持物种都具有极高的经济价值和生态价值，适于黄土高原及其与青藏高原结合部的气候条件下生长，对于解决上述地区牧草品种单一，植被退化及农村饲料短缺等实际问题，改善西北地区生态环境，促进农业产业结构调整，实现区域生态经济可持续发展等都具有重要的意义。     

赤霉酸涂布剂在绿宝石梨上的应用效果研究

试验证明,应用赤霉酸涂布剂涂抹果柄,可以有效地减少绿宝石梨裂果率(较对照减少裂果25.38%),增大果个、提高产量(较对照增长14.15%),明显提高经济效益,并使可溶性固形物的含量增加2.55%,果心减小3.48%.用3%赤霉酸脂膏于花后10d涂抹果柄基部长度1.5cm,对减轻绿宝石梨裂果的作用和提高果实其他性状效果最好.