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31.
The genetic and virulence variability of 112 isolates of Phaeoisariopsis griseola , collected from various locations in Central America, were studied using seven random amplified polymorphic DNA (RAPD) primers and 12 common-bean differential genotypes. Broad molecular diversity ( H  = 0·92) among isolates was found using RAPD markers. Fifty pathotypes were identified on 12 differential bean genotypes, 29 of which were represented by only one isolate. Only 18 pathotypes were found in two or more countries. Pathotype 63-63 was the most virulent and caused leaf spots on all 12 common-bean differential genotypes. Comparison of virulence phenotypes and RAPD profiles to known Andean P. griseola isolates confirmed that all isolates belonged to the Mesoamerican group. Pairwise comparison between individual RAPD loci showed that the majority were in gametic phase linkage disequilibrium, revealing that P. griseola maintains a genetic structure that is consistent with asexual reproduction. The molecular and virulence diversities of P. griseola isolates from Central America imply that using single resistance genes to manage angular leaf spot is inadequate and stacking resistance genes may be necessary to manage the disease effectively.  相似文献   
32.
Laboratory and greenhouse experiments were conducted to determine the effects of aqueous extract and the debris of Mile-a-Minute ( Mikania micrantha H.B.K.) on the germination and growth of four test species, viz. tomato ( Lycopersicon esculentum Mill.), Chinese cabbage ( Brassica chinensis L.), corn ( Zea mays L.) and long bean ( Vigna sesquipedalis L.). Germination percentage, radicle length and fresh weight of two crops, Chinese cabbage and tomato, decreased progressively when plants were exposed to increasing concentrations (12.5, 25, 37.5 and 50 g L−1) of aqueous extract of Mikania , but did not affect those of corn and long bean seedlings. The emergence of tomato and Chinese cabbage was greatly reduced when Mikania debris was incorporated into the soil, irrespective of the amount of debris and the decomposition period. In contrast, the emergence of corn and long bean seedlings was not affected. The application of fertilizer (NPK 15 : 15 : 15) enhanced the fresh weight of all seedlings tested as compared with those not supplied with the fertilizer. Four compounds were identified in the leaf extract of Mikania , viz. caffeic acid, p -hydroxybenzaldehyde, resorcinol and vanillic acid.  相似文献   
33.
甜玉米玉米螟的发生危害与防治措施   总被引:7,自引:2,他引:7  
研究了吉林省公主岭地区甜玉米上亚洲玉米螟Ostrinia furnacalis(Guene)的发生危害和防治措施。田间抗螟性人工接虫鉴定结果表明,甜玉米710A和普通玉米自交系丹340的食叶级别为9级,即高感玉米螟,而单交种邢抗5号和邢抗2号的食叶级别为5级,为中抗型。与普通感虫和中等抗虫性玉米品种相比,取食甜玉米的玉米螟幼虫存活率高3~7倍,发育速度更快,提前约4~8天(1~2个龄期),说明甜玉米比普通玉米感虫。甜玉米比普通玉米及早播比晚播田更吸引玉米螟产卵。田间小区试验表明,化学杀虫剂的防治效果比白僵菌和苏云金杆菌的好,以氯菊酯喷雾防治效果最好,虫孔减退率达90%;其次是杀螟灵颗粒剂、Bt喷雾和Bt颗粒剂;而白僵菌的防治效果较差,喷雾防治效果好于颗粒剂。大田防治效果与小区试验基本相同。同时还分析了氯菊酯防治甜玉米玉米螟的防治策略、防治时期、施用次数等。此外,对Bt制剂作为化学杀虫剂的取代品及与其它生物防治方法协调使用的优点与潜力进行了讨论。  相似文献   
34.
转 Bt基因抗虫棉对棉大卷叶螟抗性的研究   总被引:7,自引:0,他引:7  
:转Bt基因抗虫棉对棉铃虫有很好的抗性,对棉大卷叶螟(SyleptaderogataFabricius)的抗性未见报道。作者研究表明,棉大卷叶螟在棉田为聚集分布型,低龄幼虫有集中为害习性;抗虫棉对其有很好的抗性,平均虫株率为2.2%,较常规棉中棉所12降低96.6%;百株虫量为133.8头,较常规棉降低88.4%。  相似文献   
35.
玉米疯顶病种子传播研究   总被引:2,自引:0,他引:2  
连续3a对不同来源的玉米种子,利用显微镜镜检和试种观察植株发病显症的方法,检测其携带玉米疯顶病病菌状况。结果表明,病株病穗籽粒、病株健穗籽粒、病田健株籽粒都有较高的带菌率。因此,病菌随种子调运远距离传播是造成各地病害突发的主要原因。  相似文献   
36.
日光温室黄瓜栽培CO_2浓度的消长规律初探   总被引:7,自引:0,他引:7  
近 3a(年 )的研究结果表明 :日光温室内CO2 浓度有明显的季节变化和日变化。在整个生长期内因通风时间和通风量的不同 ,日光温室内的CO2 浓度 11月和 3月较高 ,5月较低。各时期日变化基本相同 ,但变化幅度因季节而异 ,上午随Pn的逐渐增大而下降 ,中午 12 :0 0~ 14 :0 0时降至最低 ,下午又随Pn的减小而缓慢回升。叶片的光合作用、呼吸作用和土壤呼吸是影响日光温室内CO2 浓度日变化的主要因素。有机肥施用量对室内土壤呼吸和日光温室CO2 浓度有较大影响 ,在有机肥充足的条件下 ,室内CO2 浓度基本满足黄瓜光合作用的需要 ,无须补施 ,如果在作物生长期间再定时随水向土壤中冲施有机肥 ,效果就更好  相似文献   
37.
Summary The performance of Parthenium hysterophorus , native to the tropical Americas and invasive to several countries, was evaluated for response to soil quality. Phenological (six stages) and quantitative growth variables [relative growth rates in height (Rh) and diameter (Rd)] were measured every fortnight. Based on harvest data, the variables, root:shoot (R:S) ratio, specific leaf area (SLA), relative growth rate in biomass (Rw), net assimilation rate (NAR) and dry matter allocation to plant components, were determined. High clay content in soils prolonged the rosette stage, enhanced Rh and Rd and hampered root growth, but promoted biomass allocation to shoots. The extreme degree of plant mortality was observed, with only 33.3% individuals surviving to reproduce in the soils with highest clay contents. This appears to be one of the most important findings that certainly has a major bearing on the range of adaptation of the weed. Seed mass declined whereas seed production increased in relatively coarser soils with the exception of nearly pure sand. In soils rich in clay, plants produced a smaller number of larger seeds. These data suggest that variation in fundamental functional traits would enable P. hysterophorus to adjust to a variety of habitat conditions.  相似文献   
38.
Infection processes of Pyrenophora semeniperda on seedling and adult wheat leaves and wheat ears were investigated. Almost 100% germination of conidia occurred on seedling leaves, compared with 20–30% on adult leaves. Appressoria formed over the anticlinal epidermal cell walls and haloes always accompanied infection. Sometimes papillae formed within the leaves as a resistance mechanism. Infection hyphae ramified through the intercellular spaces of the mesophyll resulting in cellular disruption. The infection processes on floral tissues were similar to those observed on leaves; however, no infection occurred on anther, stigmatic or stylar tissues. Infection of ovarian tissue occurred both with and without appressoria formation. Hyphae grew mainly in the epidermal layers and appeared unable to breach the integumental layer as no growth was observed in endosperm or embryo tissues. The optimum dew period temperature for conidial germination was 23·6°C, compared with 19·9°C for lesion development, 20·4°C for the production of infection structures on seedling leaves and 23·7°C for floret infection. Leaf disease development occurred in a logistic manner in response to dew period, with maximum infection observed after 21 h compared with > 48 h in seeds. An initial dark phase during the dew period was necessary for infection and temperature after the dew period had an effect, with significantly more numerous and larger lesions being formed at 15°C compared with 30°C. Seedling leaves were found to be more susceptible than older leaves, under both field and controlled environment conditions. Infection of wheat seeds following inoculation of ears, or after harvest burial of inoculated disease-free seeds, was demonstrated. In the latter, 3-week-old seedlings were slightly stunted, whereas older plants were unaffected. The apparent unimportance of this plant pathogen as a cause of leaf disease in relation to its poor adaptation to dew periods and dew period temperature is discussed, along with the importance of its seed borne characteristics.  相似文献   
39.
A simple procedure to evaluate relative resistance and tolerance of tomato cultivars to the begomoviruses causing tomato yellow leaf curl (TYLC) disease in Spain was developed. To estimate the resistance and tolerance levels of a cultivar, several formulae were developed based on the ratio of infected plants, virus titre (estimated by tissue–print hybridization) and symptom intensity. The formulae were applied to five commercial tomato cultivars (Amoretto, Birloque, Royesta, Tovigreen and Ulises) naturally infected by TYLC viruses. The analyses showed that Ulises, Birloque and Tovigreen exhibited a moderate resistance, and Ulises was also highly tolerant. There was a positive correlation between symptom intensity and virus titre in infected plants, suggesting that the hybridization technique could also be used as an early estimator of tolerance. Finally, molecular hybridization and nucleotide sequence analyses of the begomovirus intergenic region showed that the local TYLC virus population consisted of a single species, Tomato yellow leaf curl virus (TYLCV, formerly TYLCV-Israel), with low genetic variation (nucleotide identity between isolates higher than 97%).  相似文献   
40.
引起糖甜菜细菌性叶斑病的萎蔫短小杆菌新致病变种   总被引:3,自引:0,他引:3  
 1995年在内蒙古临河市新发现了糖甜菜细菌性叶斑病,从病斑所分离的10个细菌菌株经柯赫氏法则验证,均确系该病的病原菌。采用形态观察、表型特征和生理生化特性测定、数值分析、血清学反应、细胞化学成分分析、DNA G+C mol%和DNA-DNA同源性测定进行了鉴定,并与植物病原棒形细菌15个标准菌株进行了比较。该病原菌为革兰氏阳性细菌,不规则短杆状,有一根鞭毛、亚极生或侧生,结合其生理生化特性、细胞化学成分和DNA G+C mol%和DNA-DNA同源性测定结果,认为应属于短小杆菌属(Curtobacterium)的萎蔫短小杆菌(Cur. flaccumfaciens),数值分析也支持这一结论。此外,据血清学反应结果及其对短小杆菌属的其它植物寄主的致病情况,认为该病原菌应是萎蔫短小杆菌种下的一个新的致病变种,定名为Curtobacterium flaccumfaciens pv. beticola pv. nov. Chen et al.,2000(萎蔫短小杆菌糖甜菜致病变种)。  相似文献   
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