Bemisia tabaci (Hemiptera: Aleyrodidae) biotype B colonisation and leaf morphology relationships in upland cotton cultivars

Cultivars of upland cotton, Gossypium hirsutum L., are widely grown throughout the world for fibre production. They are also good reproductive hosts for Bemisia tabaci (Gennadius) biotype B. We studied the relationships between cotton leaf morphology and whitefly population densities in eight United States Deltapine and six Australian cotton cultivars and breeding lines at Holtville, California, in 1996. Results showed that okra-leaf cultivars and lines were colonised with fewer whitefly adults, eggs and nymphs compared to normal-leaf cultivars. The distance from underleaf surfaces of cotton leaves to the centres of nearest minor vascular bundles was negatively correlated with whitefly adult, egg and nymphal densities on leaves for all genotypes with the exception of the Australian breeding line 89013–114. Our results suggest that okra-leaf and distance from underleaf surfaces to the centre of nearest minor vascular bundles of cotton leaves are genetic traits that have potential for breeding whitefly-resistant upland cotton cultivars.     

Light interception and radiation use efficiency of okra and normal leaf cotton isolines

Okra-leaf cotton (Gossypium hirsutum L.) types have been reputed to produce equal or higher amounts of lint yield than normal-leaf types, while intercepting less or similar amounts of radiation. In this field study, okra- and normal-leaf cotton isolines were compared for their efficiency to produce dry matter utilizing intercepted radiation. At three weeks after first flower, the two leaf-shape isolines produced similar amounts of dry matter, with the okra-leaf type partitioning a larger fraction to fruiting organs. However, at the end of the season no differences in lint yield, yield components and fiber-quality properties were recorded between the two isolines. Fractional light interception throughout the period of the study was greater for the normal-leaf type compared to the okra-leaf type. The okra-leaf isoline utilized intercepted radiation more efficiently to produce dry matter. Values of radiation use efficiency were estimated at 1.897 and 2.636 g MJ⁻¹ of intercepted photosynthetically active radiation for the normal- and okra-leaf types, respectively. Growth chamber studies revealed similar single leaf carbon exchange rates, therefore radiation use efficiency differences between the leaf shape isolines could be attributed to light interception characteristics.     

供氮水平对番茄苗期Q型烟粉虱成虫种群动态的影响

烟粉虱(Bemisia tabaci)是重要的农业害虫。在栽培管理中,为了减少化学农药的施用,对该害虫采取生态防控措施日益得到重视。以Q型烟粉虱为研究对象,根据温室大棚内9次烟粉虱成虫种群数量调查和番茄苗期5项农艺指标测量,结合主成分分析、线性逐步回归分析及Pearson相关性分析,从"氮素-番茄-Q型烟粉虱"互作角度开展生态防控措施研究,旨在探明番茄苗期的烟粉虱成虫种群发生数量与氮素水平关系。结果表明:3个氮水平(高氮1134 mg·L^-1,标准氮945 mg·L^-1,低氮756 mg·L^-1)下的5个番茄指标(株高、茎粗、叶面积、叶绿素相对含量、叶片全氮含量)最大值基本呈现高氮>标准氮>低氮的规律;调查的9次烟粉虱虫口数量在最大峰值时的高低排序为高氮>标准氮>低氮。主成分分析表明,3种氮素水平下叶绿素相对含量是影响烟粉虱成虫虫口数量的主要因子。线性回归与相关性分析表明,3种氮素水平下的叶片全氮含量、叶绿素相对含量与虫口种群数量相关性较高。氮营养是影响植物和烟粉虱的关键因素之一,高氮水平下番茄长势较好,Q型烟粉虱虫口数量居多;作物叶片全氮含量和叶绿素相对含量可作为检测Q型烟粉虱种群发生消长的生态防控指标。     

Arsenophonus GroEL Interacts with CLCuV and Is Localized in Midgut and Salivary Gland of Whitefly B. tabaci

Cotton leaf curl virus (CLCuV) (Gemininiviridae: Begomovirus) is the causative agent of leaf curl disease in cotton plants (Gossypium hirsutum). CLCuV is exclusively transmitted by the whitefly species B. tabaci (Gennadius) (Hemiptera: Alerodidae). B. tabaci contains several biotypes which harbor dissimilar bacterial endo-symbiotic community. It is reported that these bacterial endosymbionts produce a 63 kDa chaperon GroEL protein which binds to geminivirus particles and protects them from rapid degradation in gut and haemolymph. In biotype B, GroEL protein of Hamiltonella has been shown to interact with Tomato yellow leaf curl virus (TYLCV). The present study was initiated to find out whether endosymbionts of B. tabaci are similarly involved in CLCuV transmission in Sriganganagar (Rajasthan), an area endemic with cotton leaf curl disease. Biotype and endosymbiont diversity of B. tabaci were identified using MtCO1 and 16S rDNA genes respectively. Analysis of our results indicated that the collected B. tabaci population belong to AsiaII genetic group and harbor the primary endosymbiont Portiera and the secondary endosymbiont Arsenophonus. The GroEL proteins of Portiera and Arsenophonus were purified and in-vitro interaction studies were carried out using pull down and co-immunoprecipitation assays. In-vivo interaction was confirmed using yeast two hybrid system. In both in-vitro and in-vivo studies, the GroEL protein of Arsenophonus was found to be interacting with the CLCuV coat protein. Further, we also localized the presence of Arsenophonus in the salivary glands and the midgut of B. tabaci besides the already reported bacteriocytes. These results suggest the involvement of Arsenophonus in the transmission of CLCuV in AsiaII genetic group of B. tabaci.     

Intergeneric transfer and functional expression of the tomato disease resistance gene Pto.

Plant disease resistance loci have been used successfully in breeding programs to transfer traits from resistant germplasm to susceptible plant cultivars. The molecular cloning of plant disease resistance genes now permits the transfer of such traits across species boundaries by genetic transformation of recipient hosts. The tomato disease resistance gene Pto confers resistance to strains of the bacterial pathogen Pseudomonas syringae pv tomato expressing the avirulence gene avrPto. Transformation of Nicotiana benthamiana with Pto results in specific resistance to P. s. pv tabaci strains carrying avrPto. The resistant phenotype is manifested by a strong inhibition of bacterial growth and the ability to exhibit a hypersensitive response. Resistance cosegregates with the Pto gene in transgene selfings and testcrosses. Our results demonstrate the conservation of disease resistance functions across genus boundaries and suggest that the utility of host-specific resistance genes can be extended by intergeneric transfer.     

Characterization of resistance, evaluation of the attractiveness of plant odors, and effect of leaf color on different onion cultivars to onion thrips (Thysanoptera: Thripidae)

Onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), is a worldwide pest of onion, Allium cepa L. In field studies on onion resistance conducted in 2007 and 2008 using 49 cultivars, 11 showed low leaf damage by T. tabaci. In laboratory studies, the 11 cultivars, along with two susceptible checks and four additional cultivars, were evaluated to characterize resistance to T. tabaci and to determine if color and/or light reflectance were associated with resistance to T tabaci. No-choice tests were performed with adults and the numbers of eggs and larvae were counted on each cultivar after three and 10 d, respectively. In choice tests in which all cultivars were planted together in a circle in a single pot, 100 adults were released and the number of adults on each plant was evaluated 24 h later. The behavioral response of walking T. tabaci adults to plant odors was studied in a glass Y-tube olfactometer. The reflectance spectrum of leaves was measured using a UV-VIS spectrophotometer. Results indicate that resistant cultivars showed an intermediate-high antibiotic effect to T. tabaci and all of them showed a very strong antixenotic effect. There were no significant preferences in the response of walking T. tabaci adults to plant odors. The two susceptible cultivars had the highest values of leaf reflectance for the first (275-375 nm) and second (310-410 nm) theoretical photopigment-system of T. tabaci, and these values were significantly different from most resistant cultivars. These results suggest a strong response of T. tabaci to onion cultivars with higher reflectance in the ultraviolet range (270-400 nm). Overall, these results appear promising in helping to identify categories of resistance to T. tabaci in onions that can be used in breeding programs.     

Resistance to silverleaf whitefly, Bemisia argentifolii (Hem., Aleyrodidae), in Gossypium thurberi, a wild cotton species

Abstract  Gossypium thurberi Todaro is a wild cotton species native to Mexico and parts of the southwestern USA. Four years of field studies in California's Imperial Valley revealed consistent very high levels of resistance in G. thurberi against silverleaf whitefly, Bemisia argentifolii Bellows and Perring, an important pest of cotton in many regions of the world. Naturally developing field infestations in plots of G. thurberi were significantly lower than in plots of the commercial cotton cultivars DP 5415, Siokra L23, and Stoneville 474. Gossypium thurberi has two morphological traits that, in past research, have been associated with lower levels of whitefly susceptibility: smooth- and okra-leaf; however, the levels of resistance observed in G. thurberi were significantly greater than in the cotton cultivar DP 5415, which is a smooth-leaf cotton, and Siokra L23 which, like G. thurberi , has both smooth- and okra-leaf traits. Therefore, the high level of resistance in G. thurberi seems to be due to factors above and beyond smooth- and okra-leaf. Siokra L23, which is among the least whitefly-susceptible cotton cultivars, developed whitefly populations over 30 times those on G. thurberi in all 3 years that Siokra L23 was tested. The difference in whitefly population development between G. thurberi and the other two cotton cultivars was even more striking, up to a 475-fold difference. In contrast to the clear results on naturally developing field infestations, experiments comparing nymphal survival among G. thurberi and commercial cotton cultivars did not detect antibiosis, and both choice and no-choice oviposition experiments did not detect antixenosis. Thus, the mechanisms of resistance in G. thurberi remain unknown.     

A new silverleaf-inducing biotype Ms of Bemisia tabaci (Hemiptera: Aleyrodidae) indigenous to the islands of the south-west Indian Ocean

Following the first detection of tomato yellow leaf curl virus (TYLCV) from Reunion (700 km east of Madagascar) in 1997 and the upsurge of Bemisia tabaci (Gennadius) on vegetable crops, two genetic types of B. tabaci were distinguished using RAPD-PCR and cytochrome oxidase I (COI) gene sequence comparisons. One type was assigned to biotype B and the other was genetically dissimilar to the populations described elsewhere and was named Ms, after the Mascarenes Archipelago. This new genetic type forms a distinct group that is sister to two other groups, one to which the B biotype is a member and one to which the Q biotype belongs. The Ms biotype is thought to be indigenous to the region as it was also detected in Mauritius, the Seychelles and Madagascar. Both B and Ms populations of B. tabaci induced silverleaf symptoms on Cucurbita sp., and were able to acquire and transmit TYLCV. Taken together these results indicate that the Ms genetic type should be considered a new biotype of B. tabaci.     

Electroantennogram responses of male Sphinx perelegans hawkmoths to floral and ‘green-leaf volatiles’

The effects of sublethal dosages of the chloronicotinyl insecticide imidacloprid on different strains of the tobacco whitefly, Bemisia tabaci Gennadius (Homoptera: Aleyrodidae), have been studied after leaf dip and systemic application. All bioassays were performed with the insecticide susceptible strain, SUD-S, and two Spanish biotypes, ALM-2 and LMPA-2, both resistant to conventional insecticides and with a lower susceptibility towards imidacloprid. Honeydew, excreted by all strains feeding on treated and untreated cotton leaf discs was quantified by photometric analysis of its carbohydrate content. EC50-values for the depression of honeydew excretion in female adults after systemic application of imidacloprid were calculated at 0.037 ppm, 0.027 ppm and 0.048 ppm for strains SUD-S, ALM-2 and LMPA-2, respectively, indicating no significant differences between strains in feeding behaviour throughout an 48 h testing period. Depending on the strain these EC50-values were 150- to 850-times lower than LC50-values calculated for mortality in the same bioassay. Starvation tests revealed mean survival times of >48 h for female adults placed on agar without leaf discs, indicating that sublethal dosages of imidacloprid which caused antifeedant responses, were probably not covered in common 48 h systemic bioassays, used to monitor resistance to imidacloprid. Effects of sublethal dosages on honeydew excretion after leaf dip application seem to be minor. In choice situations with systemically treated and untreated leaf discs in a single container, female adults of B. tabaci showed a clear preference for the untreated leaf discs. However, when using leaf discs treated by painting the surface with imidacloprid in the same bioassay, feeding activities on treated and untreated leaf discs were not significantly different. The results of the present study demonstrate the antifeedant properties of imidacloprid on B. tabaci, which might play an essential role after soil application or seed treatment under field conditions.     

An intervarietal genetic linkage map of Indian bread wheat (Triticum aestivum L.) and QTL maps for some metric traits

Bread wheat (Triticum aestivum L.) exhibits very narrow genetic diversity and hence there is high relatedness among cultivated varieties. However, a population generated from an intervarietal cross, with the parents differing in a large number of traits, could lead to the generation of QTL maps which will be useful in practice. In this report a genetic linkage map of wheat is constructed using a cross between two Indian bread wheat varieties: Sonalika and Kalyansona. The linkage map consisted of 236 markers and spanned a distance of 3639 cM, with 1211.2 cM for the A genome, 1669.2 cM for the B genome, 192.4 cM for the D genome and 566.2 cM for unassigned groups. Linkage analysis defined 37 linkage groups of which 24 were assigned to 17 chromosomes. The genetic map was used to identify QTLs by composite internal mapping (CIM) for three metric traits, viz. culm length (CL), flag leaf length (FLL) and flag leaf breadth (FLB). Of 25 QTLs identified in this study, 15 have not been reported previously. Multitrait CIM (MCIM) analysis was carried out for traits that were significantly correlated such as FLB-FLL and CL-FLB-FLL. Detection of a large number of QTLs for the three traits analysed suggests that in parent cultivars that are not too diverse, the differences at genetic level detected as polymorphisms may be mostly associated with QTLs for the observed differences.     

Variation in tomato host response to Bemisia tabaci (Hemiptera: Aleyrodidae) in relation to acyl sugar content and presence of the nematode and potato aphid resistance gene Mi

Two commercial cultivars of tomato, Alta and Peto 95, the accession line number LA716 of Lycopersicon pennellii and lines 94GH-006 and 94GH-033 (backcrosses between Peto 95 and LA716), with different leaf acyl sugar contents were screened for resistance to Bemisia argentifolii Bellows & Perring (corresponding to the Spanish B-biotype of Bemisia tabaci (Gennadius)), in greenhouse- and field-no-choice experiments. There was no oviposition on LA716 (with the highest acyl sugar content) while the greatest fecundity and fertility values were observed on the cultivar Alta (no acyl sugar content). However, no clear relationship was found between the low acyl sugar content in the other tomato cultivars tested and whitefly reproduction. Thus, resistance to B. tabaci did not appear to correlate with acyl sugar content below a threshold level of 37.8 microg cm-2 leaf. In a greenhouse choice-assay, B. tabaci exhibited reduced host preference and reproduction on the commercial tomato cultivars Motelle, VFN8 and Ronita all of which carry the Mi gene resistance to Meloidogyne nematodes and the aphid Macrosiphum euphorbiae (Thomas), than on the Mi-lacking cultivars Moneymaker, Rio Fuego and Roma. When data of Mi-bearing plants were pooled, the mean values for daily infestation and pupal production of B. tabaci were significantly lower than those of Mi-lacking plants. This reflected a level of antixenosis- and antibiosis-based resistance in commercial tomato and indicated that Mi, or another closely linked gene, might be implicated in a partial resistance which was not associated either with the presence of glandular trichomes or their exudates. These findings support the general hypothesis for the existence of similarities among the resistance mechanisms to whiteflies, aphids and nematodes in commercial tomato plants.     

Genetic linkage map construction and QTL identification of juvenile growth traits in Torreya grandis

Mei, Prunus mume Sieb. et Zucc., is an ornamental plant popular in East Asia and, as an important member of genus Prunus, has played a pivotal role in systematic studies of the Rosaceae. However, the genetic architecture of botanical traits in this species remains elusive. This paper represents the first genome-wide mapping study of quantitative trait loci (QTLs) that affect stem growth and form, leaf morphology and leaf anatomy in an intraspecific cross derived from two different mei cultivars. Genetic mapping based on a high-density linkage map constricted from 120 SSRs and 1,484 SNPs led to the detection of multiple QTLs for each trait, some of which exert pleiotropic effects on correlative traits. Each QTL explains 3-12% of the phenotypic variance. Several leaf size traits were found to share common QTLs, whereas growth-related traits and plant form traits might be controlled by a different set of QTLs. Our findings provide unique insights into the genetic control of tree growth and architecture in mei and help to develop an efficient breeding program for selecting superior mei cultivars.     

Seed priming with boron improves growth and yield of fine grain aromatic rice

Boron (B) is amongst the important micronutrients required for rice from start till physiological maturity. This study was conducted to explore the role of boron application in seedling emergence, leaf appearance and elongation, chlorophyll content, water relations and yield related traits of fine rice. Boron was applied as seed priming. For priming seeds of fine rice cultivars Super Basmati and Shaheen Basmati were soaked in 0.001 and 0.01?% aerated B solutions (w/v); while untreated dry seeds and water soaked (hydropriming) seeds were taken as control. Substantial improvement in seedling emergence was noted by seed priming in 0.001 and 0.01?% solutions. Rate of leaf emergence and elongation and tiller appearance were also improved in seedlings raised from seeds primed in 0.001?% B solution in the tested cultivars. Likewise, leaf chlorophyll contents were significantly improved by B especially with 0.001?% concentration; as was the case for water relations of rice cultivars. At final harvest, all yield contributing parameters were improved by B priming. Increase in yield was due to decrease in panicle sterility by B treatments. A linear increase in leaf and grain B contents was observed with increase in concentration of B priming solution. Overall, B application at very low rate substantially improved seedling emergence, leaf appearance and elongation, tillering, chlorophyll, water relations and yield related traits resulting in better yield and grain B contents. In this regard, seed priming offers an effective and pragmatic way of B application.     

钙肥对B型烟粉虱发育、存活及取食为害的影响

以清水为对照,研究了施用钙肥后一品红植株对B型烟粉虱发育、存活和取食为害的影响.结果表明:在温度(26±1)℃、相对湿度60％～80％条件下,钙肥处理的一品红植株上的B型烟粉虱在发育历期上与对照存在显著差异,卵期明显缩短,各龄若虫期延长,从卵到成虫的发育时间为20.18 d,而对照为18.72 d;但钙肥处理对B型烟粉虱各虫态的存活率无显著影响.B型烟粉虱的取食为害诱导了一品红叶片叶绿素荧光参数的变化,显著降低了叶片的光合作用能力,其中光化学效率(Fv/Fm)、光化学淬灭系数(qp)、光能利用效率(α)、最大光合速率(rETRmax)以及对光的耐受能力(Ik)显著降低,而非光化学淬灭系数(NPQ)显著增加.钙肥处理一品红受害叶片的光抑制参数(β)、rETRmax和Ik水平与对照相当.通过指甲油印迹法观察叶片下表皮细胞的形态结构发现,钙肥能有效增强叶片对B型烟粉虱为害损失的补偿.     

烟粉虱在我国的发生为害现状及其非化学控制对策(英文)

烟粉虱 (BemisiatabaciGennadius )是热带、亚热带和温带地区主要害虫之一。烟粉虱早在 40年代在我国就已有记载 ,现广泛分布于我国的 2 2个省市。过去烟粉虱在我国为害并不严重 ,近年来在广东和北京等地已成为蔬菜和园艺作物生产的严重障碍。除直接为害外 ,烟粉虱可传播番茄和南瓜曲叶病等5种难于防治的病毒病。到目前为止 ,已报到 1 8种寄生性天敌、1 7种捕食性天敌及 1种虫生真菌。本文简要慨述烟粉虱在我国的发生为害与传毒现状 ,并结合我国的具体情况提出非化学控制烟粉虱的对策。     

水稻轮回选择群体XTBG-HP1表型遗传多样性分析

该研究基于4个陆稻群体及172个水稻品种或杂交组合,构建了水稻多亲本隐性核不育轮回选择群体XTBG-HP1,并经过4次轮回重组,采用16个表型性状对其进行了遗传多样性分析。结果表明:(1)该群体14个数量性状符合正态分布,各表型均存在极端性状个体。(2)数量性状变异系数范围为0.08～0.41,均值为0.20; Shannon-Wiener多样性指数范围为0.72～1.92,均值为1.50。(3)群体在株型与产量构成因子性状方面有显著的相关性,对株型的选择可以实现产量性状的改良。(4)剑叶长、每穗粒总数、千粒重、穗长、粒长、一次枝梗数、有效穗数、剑叶宽、二次枝梗数、抽穗期10个性状可作为群体综合评价指标。(5)剑叶长、二次枝梗数、每穗粒总数3个表型性状具有较高的遗传变异、丰富的遗传多样性及与综合得分F值相关系数较高。综合以上结果发现,后期群体进行基因挖掘、品种改良以及优良育种材料的选育可以基于剑叶长、二次枝梗数及每穗粒总数3个表型性状,同时要充分利用群体株型与产量构成因子性状间的显著相关性。此外,该研究群体中极端单性状或综合得分F值较高的个体,可进一步用于品种选育。     

Prevalence of Wolbachia supergroups A and B in Bemisia tabaci (Hemiptera: Aleyrodidae) and some of its natural enemies

Wolbachia, a bacterial symbiont, is maternally transmitted in arthropods and nematodes. We report a systematic survey of Wolbachia taxonomy in the sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), and in some of its natural enemies. For the first time, Wolbachia infections in B. tabaci are correlated with various whitefly genetic groups, host plants, and natural enemies as well as with geographical regions. Polymerase chain reaction using 16S rDNA and fisZ genes revealed two Wolbachia supergroups, A and B, exist as single or double infections in B. tabaci as well as in some of its aphelinid parasitoids and predatory beetles. Approximately 89% of B. tabaci sampled were infected by Wolbachia, among which 34% were infected by A, 51% were infected by B, and 5% were infected by both A and B supergroups. These infection frequencies differed among B. tabaci genetic groups and locations. The invasive B. tabaci genetic group from the Middle East Asia Minor 1 (also referred as B biotype) and Mediterranean (also referred as Q biotype) was more likely to harbor A than B, whereas native genetic groups in AsiaI and AsiaII were more likely to harbor B than A. Although 60% of aphelinid parasitoids and 72% of coccinellid beetles also were infected by Wolbachia, they were more likely to host B than A. Furthermore, for the first time we report Wolbachia in B biotype from specimens collected outside of China. Construction of a phylogenetic tree clearly indicated that the Wolbachia sequences from different genetic groups of B. tabaci were not only similar to each other but also to sequences from beetles and parasitoids, which may provide evidence of coevolution and horizontal transmission of Wolbachia populations.     

Upregulation of temperature susceptibility in Bemisia tabaci upon acquisition of Tomato yellow leaf curl virus (TYLCV)

Acquisition of plant viruses has various effects on physiological mechanisms in vector insects. Bemisia tabaci is the only known vector of Tomato yellow leaf curl virus (TYLCV), which is a serious virus affecting tomato cultivars. In this study, the lifespan of Q1 biotype was compared between non-viruliferous (NV) and TYLCV-viruliferous (V) whiteflies. Total lifespan from egg to adult death of NV whiteflies was 62.54days but 10.64days shorter in V whiteflies. We investigated the temperature susceptibility of B. tabaci by comparing mortalities as well as heat shock protein (hsp) mRNA levels between NV and V whiteflies. For this, NV and V whiteflies were exposed for either 1 or 3h at 4, 25, and 35°C. The mortality of V whiteflies was higher than NV ones following exposure at either 4 or 35°C, but there was no significant difference at 25°C. Analysis of the expression level of heat shock protein (hsp) genes using quantitative real-time PCR showed that both cold and heat shock treatments stimulated higher expression of hsps (hsp40, hsp70, and hsp90) at various rates in V whiteflies than NV ones, but there was no difference at 25°C. All together, our results show that TYLCV acquisition accelerated the developmental rate and increased susceptibility to thermal stress in B. tabaci. Therefore, this modification may result in reduced vector longevity due to increased metabolic energy utilization. Our results provide insights into the complex interaction between vector fitness and thermal stress in relation to the acquisition and transmission of plant viruses.     

环境和遗传对烟草叶片结构的影响

叶片性状很大程度上反映了植物的功能及其对环境的适应。叶片性状的变异受环境及遗传特性的影响,但是很多研究未能很好区分出它们的相对影响。本研究通过将同一烟草品种种植于不同地点来认识环境对烟草叶片性状的影响;将不同的烟草品种种植于同一环境来了解遗传差异对烟草叶片性状的影响。研究发现,叶脉密度和叶片厚度受环境的影响较大,气孔密度和长度受环境的影响较小。气孔密度和叶片厚度受遗传的影响较大,叶脉密度和气孔长度受遗传的影响较小。在生长温度高的地方,烟草叶脉密度越大。研究结果对于认识植物对环境的适应性具有重要意义。     

辣椒碱对烟粉虱的生物活性及生长发育和生殖力的影响

在实验室条件下研究了辣椒碱对烟粉虱的生物活性及生长发育和生殖力的影响.结果表明:辣椒碱对烟粉虱各虫态均有杀虫活性,且随辣椒碱浓度的增大活性增强;辣椒碱浸叶法/浸虫法处理对烟粉虱成虫、卵和若虫的毒力(LC50分别为3525.79、1603.29和1526.27mg·L-1))均高于内吸法处理(LC50分别为5360.04、2359.19和5897.43 mg.L-1),两种处理方法下辣椒碱对烟粉虱卵的毒力均明显高于对成虫的毒力;2000和4000 mg·L-1浓度辣椒碱对烟粉虱成虫具有明显的拒食作用,烟粉虱在该两种浓度辣椒碱处理过的棉花叶上取食24 h的蜜露分泌量均显著低于取食非处理棉花叶后的蜜露分泌量;辣椒碱各试验浓度对烟粉虱成虫均表现出较强的产卵忌避作用,当辣椒碱处理浓度达4000 mg·L-1时,对烟粉虱的选择性产卵忌避率和非选择性产卵忌避率分别高达94.2％和83.0％.500、1000和2000 mg·L-1辣椒碱浸渍处理对烟粉虱存活卵和若虫的发育历期、成虫羽化率均没有影响,但辣椒碱4000mg·L-1处理明显延长烟粉虱若虫发育历期、降低成虫羽化率.不同浓度辣椒碱处理均明显抑制烟粉虱生殖力,且这种抑制作用随辣椒碱浓度的增大而增强.