New mite-borne virus isolates from rakkyo,shallot and wild leek species

Flexuous viruses were transmitted from rakkyo (Allium chinense) and wild leek species (especiallyA. commutatum) to plants of crow garlic (A. vineale), by transfer of dry bulb mites. By electron microscope decoration tests using three antisera and by inoculations onto test plants, it was concluded that from each of the two natural host species at least two viruses were isolated. The viruses from wild leeks are both pathogenic onAllium spp. and may be of economic importance. Decoration tests on a virus mixture from shallot obtained earlier, revealed another new mite-borne virus in this species. The mite-borne viruses ofAllium spp. appear to be very common; they are largely diverse and their identification remains difficult.     

Use of carbendazim and carbendazim-resistant yeasts to create different yeast densities on wheat leaves for field studies on biological control

Phyllosphere yeasts may play an important role in suppressing necrotrophic pathogens. In a randomized block design, yeast densities on flag leaves and second leaves of field-grown wheat were left unchanged (D), or were lowered by sprayings with carbendazim (A), or were raised by sprayings with a mixture ofSporobolomyces roseus, Cryptococcus laurentii var.flavescens and nutrients (B), or with carbendazim, carbendazim-resistantS. roseus andC. laurentii var.flavescens and nutrients (C). The application of carbendazim to plots A and C would avoid a biased interference of carbendazim due to other effects than reducing the natural yeast population. Prolonged differences in yeast density would be reflected in differences in severity of diseases caused by carbendazim-insensitive necrotrophic pathogens.Both treatments B and C enhanced the yeast density about 10-fold at the beginning of leaf colonization, 2 to 3 weeks after leaf emergence. Untreated leaves (D), however, were rapidly leaves. Initially, the yeasts were suppressed by carbendazim (A). However, progressively the yeast population consisted of carbendazim-resistant strains which made the carbendazim sprayings ineffective. Therefore, the substantial differences in yeast density were of limited duration. The effect of the treatments on naturally occurringMycosphaerella graminicola (anam.Septoria tritici), Puccinia recondita f. sp.tritici and the total necrotic leaf area (D-value) is discussed.Samenvatting Fyllosfeergisten kunnen misschien een belangrijke rol spelen in de onderdrukking van necrotrofe pathogenen. In een blokkenproef werd de dichtheid van gisten op vlagbladeren en tweede bladeren niet beïvvloed (D) of verlaagd door bespuitingen met carbendazim (A), of verhoogd door bespuitingen met een mengsel van gisten (Sporobolomyces roseus enCryptococcus laurentii var.flavescens en voedingsstoffen (B), of met een mengsel van carbendazim, carbendazim-resistenteS. roseus enC. laurentii var.flavescens en voedingsstoffen (C). De grootste verschillen in dichtheden van de gistpopulaties werden verwacht tussen de behandelingen A en B of C. Door alle veldjes A en C met carbendazim te behandelen wordt een eenzijdig effect van carbendazim, berustend op andere eigenschappen dan de onderdrukking van de natuurlijke gistpopulatie, voorkomen. Langdurige verschillen in de populatiedichtheden van de gisten zouden weerspiegeld kunnen worden in verschillen in aantasting door carbendazimongevoelige necrotrofe pathogenen.Aan het begin van de bladkolonisatie door gisten, 2 tot 3 weken na het verschijnen van het blad, leidde zowel behandeling B als C tot, een 10-voudige verhoging van de gistdichtheid. De onbehandelde bladeren (D) werden echter spoedig door de van nature voorkomende gisten gekoloniseerd en het verschil tussen de onbehandelde en met gist bespoten bladeren werd snel kleiner. Aanvankelijk werden de gisten door carbendazim (A) onderdrukt. Geleidelijk bestond de gistpopulatie echter uit carbendazim-resistente stammen, zodat de carbendazim bespuitingen nauwelijks meer effect hadden. Hierdoor werden grote verschillen in gistdichtheden niet langdurig gerealiseerd. Het effect van de behandelingen op de natuurlijke infectie doorMycosphaerella graminicola (anam.Septoria tritici), Puccina recondita f. sp.tritici en op het totale dode bladoppervlak (D-waarde) wordt besproken.     

Control of Phytophthora cryptogea in the hydroponic forcing of witloof chicory with the rhamnolipid-based biosurfactant formulation PRO1

Rhamnolipids, extracellular metabolites of Pseudomonas aeruginosa with surfactant properties, proved to be very effective in controlling the spread of brown root rot disease caused by Phytophthora cryptogea in the hydroponic forcing system of witloof chicory ( Cichorium intybus var. foliosum ). The biosurfactant was applied as the product PRO1, a formulation of 25% rhamnolipids in oil. Both an in vitro screening and in vivo experiments in a mini-hydroponic system demonstrated the ability of PRO1 to control brown root rot. A 25  µ g mL⁻¹ rhamnolipids nutrient solution was enough to obtain good control of an artificial infection with a zoospore suspension of P. cryptogea . The biosurfactant PRO1 performed well in a semicommercial system under growers' conditions. A treatment of 25  µ g mL⁻¹ rhamnolipids (100  µ g mL⁻¹ PRO1) reduced the disease incidence significantly in two independent experiments. However, PRO1 was not effective when a mycelial suspension was used as inoculum. Rhamnolipids have good potential to limit the spread of P. cryptogea in the hydroponic forcing system of witloof chicory, and can be used as a preventive measure against brown root rot.     

The Role of the Bark Beetle, Hylastes ater (Coleoptera: Scolytidae), as a Sapstain Fungi Vector to Pinus radiata Seedlings: A Crisis for the New Zealand Forestry Industry?

The role of the bark beetle Hylastes ater in the re-establishment of Pinus radiata forest in New Zealand is discussed. H. ater was found to be a dominant factor in seedlings mortality in the first year following planting. However, seedling mortality is usually relatively low. In contrast, it was found the large numbers of seedlings were sub-lethally damaged by H. ater feeding attempts, particularly in high risk sites. High risk sites were identified as sites that were harvested during March and April (autumn) when the peak flight activity of H. ater occurred, and subsequently planted with P. radiata seedlings the following winter. H. ater was found to vector sapstain fungi to seedlings during feeding attempts, and a strong relationship between the severity of damage and presence of sapstain fungi was identified. The role of H. ater as a vector of these fungi and the potential implications to the New Zealand forest industry are discussed.     

不同时期使用农抗120控制花生网斑病侵染源的试验研究

用农抗120防治花生网斑病,不同使用方法效果不一。用常规喷洒叶面方法控制再侵染源,防效为21.4％,相当于多菌灵(29.4％);用农抗120和杀菌剂(抗枯灵或多菌灵等)混合,在花生播种时喷洒地面一次,控制初侵染源,防效为48.6％,用农抗120同杀菌剂混合,播种时喷洒地面,以控制初侵染源,7月上旬再喷洒叶面,控制再侵染源,效果最佳,防效高达70％以上。     

乾宁狼尾草和中序狼尾草的某些生物学特性初探与核型分析

从牧草种质资源鉴定利用角度,对中国产狼尾草属的两个新野生种农艺性状生长、栽植密度以及核型分析等方面,进行了比较研究。结果表明,乾宁狼尾草与中序狼尾草在自然状况下,结实率低,分别仅为41.2％和17.8％,但两者营无性繁殖的地下茎十分发达。生长分析的各项指标上,乾宁狼尾草最大叶面积指数13.1比中序狼尾草3.56大,平均净同化作用率前者小,后者大(36.2和54.1克平方米~(-2)周~(-1)),两者差异均极显著(P=0.01),平均相对生长率分别为0.56和0.52克~(-1)周~(-1),与其它各项均不显著。不同栽植密度,使得草种对光照条件、CO_2流通率以及单位植株营养面积表现出巨大差异,导致形成的生物量也不尽同。乾宁狼尾草与中序狼尾草分别以35cm和25cm行距栽植时,当年生物产量较高;从营养成分上,不单含高量的粗蛋白,营养期与开花期分别达21.45％、16.02％和21.05％、16.88％;赖氨酸含量也表现出同步优势。经染色体数目及核型分析,两种的体细胞染色体数均为36,属四倍体(X=9)。其核型彼此无差异。初步可认定两种,亲缘关系属同源染色体组。     

油松短枝嫁接技术的研究(Ⅱ)

继油松短枝嫁接技术的研究(Ⅰ),讨论了提高短枝嫁接苗萌芽率的各种技术措施。促使短枝嫁接苗萌芽是提高成苗率的关键技术。采取综合措施成苗率可高达92％,这一技术已在油松良种基地建设中应用。     

小果宜昌橙—柑桔属宜昌橙的新变种

本文对柑桔属宜昌橙(Citrus ichangensis Swingle)的一个新变种——小果宜昌橙进行了定名,并介绍了该变种的主要特征。 该变种形态类似宜昌橙,与宜昌橙的主要区别是子房心室少(5-7个),每个心室中胚珠少(3-4个),果实小。而宜昌橙子房心室7—10个,每个心室胚珠4-8个,果实较大。本变种为常绿乔木,树高3-5m,枝梢有刺,叶、花、果上均有油胞。果实长圆形,果皮紧、淡橙黄色,汁胞柔软,味酸苦,具有5—7个囊瓣。种子大、单胚,子叶白色。叶柄具翼,很宽大,大体上与叶片等长。主要分布于云南省的漾濞、巍山、保山、腾冲等县。     

热胁迫对辣椒花粉发育及其生活力的影晌

用光学和荧光显微镜及扫描电镜观察等方法，研究了热胁迫对辣椒花粉形成发育、生活力、萌发率及雌性系统的影响。发现辣椒不同耐热性品种在高温胁迫下，花粉、花药发育过程出现异常，花粉生活力、体外萌发率下降，花粉管生长延迟，正在生长的花粉管伸长停滞。这些影响感热性品种比耐热性品种表现更为明显。在雌性系统中未见明显影响。     

高寒牧区青稞南北向条播增产试验

在高寒牧区巴音布鲁克种种青稞，南北向条播比东西向条播能充分利用太阳光能，可提高种子产量１４．６％，南北向条播的适宜密度为３３０万株／ｈｍ＾２，种子产量最高。