水稻粳型亲籼系的分子标记辅助育种

分子标记辅助聚合育种是累加有利基因的有效手段。培育粳型亲籼系是有效克服水稻籼粳亚种间杂种不育性，从而利用水稻亚种间杂种优势的重要途径之一。本研究利用以PCR为基础的分子标记进行辅助选择，对不同粳型亲籼系中不同分化度的特异亲和基因进行了聚合，并将4个抗白叶枯病基因和来源于IR24的两个恢复基因导入粳型亲籼系中。主要结果如下：1、以粳型亲籼系G2417-2-1和粳型广亲和系G2605为亲本构建分离群体，利用本研究筛选的与S-b，S-c,S-d三个F1花粉不育基因座位紧密连锁的PCR标记进行辅助选择。在F2共选择到特异亲籼聚合植株6株，它们分别是58号，93号，94号，115号，139号，200号；广亲和聚合植株4株，它们分别是11号，14号，121号，177号。2、对当选聚合系的亲籼性和亲粳性综合分析表明：各个特异亲籼聚合系的亲粳性之间及各个广亲和聚合系的亲籼性之间都有显著差异。特异亲籼聚合系的平均亲籼性和平均亲粳性与亲本G2417-2-1相比都没有显著差异。广亲和聚合系的平均亲籼性高于亲本G2605，平均亲粳性显著低于亲本G2605。这些聚合系的亲和性与其MAS基因型相一致。3、利用四类粳型亲籼系与携带有2个恢复基因和4个抗白叶枯病基因的品系构建回交群体，应用本研究筛选的以PCR为基础的分子标记进行辅助选择。在BC1F1共选择到2个恢复基因和4个抗白叶枯病基因全杂合的植株19个，其中以IC31为受体的5株，以IC32为受体的11株，以IC33为受体的2株，以IC34为受体的1株。4、当选的19个单株自交繁殖BC1F2，利用与目标基因紧密连锁的单一分子标记进行MAS。共选择到各类可供进一步利用的材料393株，其中携带有两个纯合恢复基因的植株158株，同时携带有两个纯合恢复基因和两个纯合显性抗白叶枯病基因的植株40株。5、从上述158个植株中选出两个显性抗性基因均纯合或者任意三个抗性基因均纯合的植株共45株，通过标记加密进一步验证其基因型。结果表明，在Rf3，Rf4，Xa4，Xa21，xa5和xa13等六个基因座位上均带有纯合基因型的植株有3株。本研究通过粳型亲籼系不同分化度的特异亲和基因的聚合获得了新粳型亲籼系；通过聚合恢复基因和抗白叶枯病基因到粳型亲籼系中，使粳型亲籼系不仅能解决亚种间杂种不育性，用于两系杂交稻育种，而且由于具有抗白叶枯病基因，可以改善其对白叶枯病的抗性；由于有恢复基因而具有恢复能力，从而可以实现籼粳亚种间的三系配套。     

水稻F1花粉不育基因的精细定位及其遗传分化研究

水稻籼粳亚种间杂种的不育性限制了亚种间的遗传交流和杂种优势利用。本研究通过发展位置特异性的微卫星标记将F1花粉不育基因S-6座位进行了精细定位；通过分析近等基因系中代换片段的遗传效应，鉴定出了F1花粉不育基因S-d座位，利用位置特异性的微卫星标记将S-d进行了定位；根据基因组的序列资料和利用较大的作图群体对S-6和S-d两个座位进行了物理作图；通过分子标记辅助选择培育了一批复等位基因近等基因系，对育性基因的遗传分化进行了研究。取得了如下主要结果：1、根据S-6座位初步定位的结果发展位置特异性的微卫星标记，将F1花粉不育基因座S-6进行了精细定位。结果表明多态性标记均与S-6座位紧密连锁，其中R830STS、PSM7、PSM8、PSM9、．PSM59和PSM60位于S-6座位一端，与S-6座位遗传距离分别为1．5cM、1．2cM、0．9cM、0．9cM、0．9cM和0．9cM，而PSM202、PSM206、PSM208、RMl3、R2213SSTS和RM413位于S-6座位的另一端，与S-6座位的遗传距离分别为0．9cM、2．1cM、3．8cM、4．1cM、4．4cM和5．3cM。2、根据S-6座位精细定位的结果，从IRGSP下载了S-6座位所在区域克隆的序列，将克隆的序列进行了拼接，同时将与S-6座位紧密连锁的分子标记与序列拼接图进行了电子整合。根据整合的结果发展位置特异性的微卫星标记和STS标记，利用500株的作图群体，最终将S-6座位界定在PSM8与PSM215之间182．2kb的范围，其中PSM214、T17、T18和T19与S-6座位完全连锁。3、通过对近等基因系E11-5中代换片段遗传效应的分析，在第1染色体的代换片段上鉴定出一个新的F1花粉不育基因座S-d。根据基因组的序列发展位置特异性的微卫星标记将S-d座位进行了定位。结果表明多态性标记均与S-d座位紧密连锁，其中PSM27、PSM24、．PSM26、PSM23、PSM31、PSM25、PSM37、PSM41、PSM42、PSM43、．PSM44、．PSMl2和PSMl3位于S-d座位的一端，与S-d座位的遗传距离分别为10．6cM、7．2cM、7．2cM、6．8cM、6．8cM、6．4cM、6．4cM、4．8cM、4．8cM、3．2cM、1．6cM、0．4cM和0．4cM，而RM84、RM86、RM323、RMl和RM283位于S-d座位的另一端，与S-d座位的遗传距离分别为3．8cM、4．6cM、6．7cM、7．5cM和8．7cM。4、根据S—d座位定位的结果，从IRGSP下载了S-d座位所在区域克隆的序列，将克隆的序列进行了拼接，同时将与S-d紧密连锁的分子标记与序列拼接图进行了电子整合。根据整合的结果发展位置特异性的微卫星标记和STS标记，利用2160株的作图群体，最终将S-d座位界定在67．8kb的范围内，其中PSM93和PSM74位于S-d座位的两侧且各与S-d仅有一个重组，而PSM95、PSM96、T1和T2与S-d座位完全连锁。RiceGAAS注释分析表明在此区段有17个ORF。，其中3个ORF可能与杂种不育性有关。BLAST分析表明此段序列籼粳之间的同源性较低，这也可能是杂种不育的一个原因。5、通过分子标记辅助选择，在F1花粉不育基因s-n、s-6、s-c和s-d座位各培育了一批复等位基因近等基因系，测交分析表明各不育基因座位上的不育基因不仅分化为相对的S^i和S^j，而且基因型类型相同的复等位基因的遗传分化也达到了显著差异的水平。携带有多个复等位基因的近等基因系的测交分析表明，复等位基因近等基因系的遗传效应为各基因座位遗传效应的累加，各基因的遗传效应相互独立，彼此间无相互作用。     

水稻S-c座位的PCR标记精细定位及分子标记辅助选择

以粳型品种台中65及其近等基因F1不育系TISL5为材料,利用STS和SSLP标记对水稻F1花粉不育基因座位S-c进行了精细定位,RG227STS和RM218分别位于S-c的两侧,与S-c的距离分别为0.3cM和4.3cM.通过对40个籼、粳和中间型品系标记基因型的鉴定,分析了分子标记基因型与S-c基因型之间的关系,建立了以PCR为基础的分子标记辅助选择体系.利     

水稻粳型亲籼系S-c座位基因型分析

S-c是控制水稻籼粳亚种间杂种F1花粉不育性的基因座位之一。在该座位,台中65的基因型为Sj/Sj,广陆矮4号的基因型为Si/Si。以台中65和广陆矮4号为遗传测验种,分别与4个粳型亲籼系配组,根据部分F2群体中植株花粉育性表型及与S-c紧密连锁分子标记基因型的偏态分离程度,测定了这4个粳型亲籼系在S-c座位的基因型,结果表明,G2416-3的基因型为Si-2/Si-2;G2605和G3004-4的基因型均为Si-1/Si-1;G2417-2-1的基因型为Sn/Sn。本文还对F1花粉不育性基因遗传分化的测定方法进行了讨论。     

籼粳杂种花粉不育基因的定位

以IR36（indica）和热研2号（japonica，广亲和品种）为亲本，构建了包含180个单株的F₂群体及包括110个标记的分子连锁图谱。利用该F₂群体，进行了水稻花粉不育数量性状基因座(quantitative trait locus, QTL)的检测和遗传效应分析，共检测到3个花粉不育QTL，分别位于第3、5、7染色体上，此外，共检测到9个由雄配子引起的偏分离QTL，其中7个与ga-14和ga-11位点的配子败育类型相同。与花粉形态鉴定相比，偏分离的数据对检测F₁杂种花粉败育基因更为敏感。在第5、6染色体上控制偏分离的2个QTL位点，其杂合基因型出现的频率偏高。在qHPS-5位点，粳型纯合子表现出比杂合子和籼型纯合子更低的育性水平。本研究获得的分子标记将有助于聚合尽可能多的中性亲和基因以解决亚种间F₁杂种的花粉不育性问题。     

水稻籼粳亚种间杂种不育性的研究进展

克服杂种不育性是利用籼粳亚种间杂种优势的关键。由此对水稻亚种间杂种不育性的原因、细胞学基础及两种主要基因遗传模式进行了总结,并详细综述了利用“亲和基因”克服籼粳杂种不育性的两种有代表性的学说-广亲和基因和特异亲和基因分子定位的最新研究进展,并提出了两“亲和基因”共同利用的初步设想:将聚合了Si等位基因的粳型亲籼系与聚合了不同广亲和基因(中性亲和基因的广亲和力强、亲和谱广泛的粳型品种进行杂交和回交,选育出聚合不同广亲和基因和Si等位基因的粳型亲籼系,再与籼稻品种杂交,真正实现直接利用籼粳亚种间杂种优势。     

栽培稻(Oryza sativa L.)亚种间F1花粉不育基因S-a的精细定位及克隆

水稻籼粳亚种间存在着强大的杂种优势,但杂种育性普遍偏低成为这一杂种优势利用的主要障碍.研究证明,花粉不育是导致杂种不育的主要原因之一.张桂权和卢永根等(1987-1994)鉴定了6个花粉不育基因座位(S-a,S-b,S-c,S-d,S-e和S-f).其中S-a基因座位已被庄楚雄等(1996)初步定位在水稻第一染色体着丝粒附近.本论文是在此基础上,利用美国Cornell大学、日本RGP构建的水稻高密度遗传图和日本构建的BAC/PAC物理图及其基因组测序资料,对S-a作进一步的精细定位,建立了包含该基因的TAC重叠群,并通过序列分析发现S-a候选基因,为分离鉴定S-a基因及研究该基因在水稻杂种不育中的分子作用机理打下了基础.本研究主要结果如下1. 构建了台中65(含S-aj) 及其近等基因系TILS4(E4,含S-ai )杂交的F2群体,观察了706株F2个体的花粉育性分离状况.其中可育株367株,半不育株339株,分离比为1∶1.2. 利用前人筛选的多态性标记R2159、R1928和本研究新获得的多态性标记GR2、GR1、AR1、D2.3M、D1.5S、F12M1,用706株F2群体对S-a进行了的精细定位.结果表明S-a与分子标记R2159、GR2、GR1、AR1、R1928、F12M1、D1.5S和D2.3M之间的遗传距离分别为2.07cM,1.21cM,0.65cM,0.42cM,0.42cM,0.45cM,0.14cM和0cM.与S-a紧密连锁的5个分子标记(<0.5cM)分布在S-a两侧,其中D2.3M为S-a的0cM标记.依据该区域物理距离对遗传距离的平均换算值200kb/cM,将基因定位在约30kb范围内.3. 构建了籼稻广陆矮4(含S-aj)、粳稻台中65(含S-aj)和S-ai近等基因系(E4)的基因组TAC文库,各文库分别包含12万、10万和11万平均大小为43kb的克隆,各文库覆盖率平均约达10倍水稻基因组大小.依据定位结果,用覆盖S-a的100kb范围内所设计的单/低拷贝片段为探针,筛选粳稻台中65、籼稻广陆矮4和不育近等基因系E4的TAC基因组文库,构建了基于TAC克隆的S-a座位的物理图.4. 根据基因序列分析,在与S-a座位完全连锁的标记D2.3M两旁30kb范围内发现了3个开放读码框,其中一个是具有bHLH结构域的转录因子,一个是N端有DENN结构C端有8WD40重复的转录因子,另一个是丝氨酸/苏氨酸型的蛋白激酶.本研究将其定为S-a的候选基因,分别进行基因序列及其表达的分析.5. 用特异引物进行RT-PCR,从台中65和E4小穗RNA中扩增出HLH转录因子的cDNA片段.测序分析表明该片段与预测的外显子结构一致.利用RT-PCR和Southern杂交证明该bHLH在E4和T65的幼穗部表达,但表达量很低.同时进行的RT-PCR也证明WD40重复的转录因子在E4的幼穗中表达.8WD40重复的转录因子和蛋白激酶基因的进一步测序和基因表达分析工作正在进行中.     

豫粳6号B与TR2604间杂种花粉不育基因的定位

阐明BT型杂交粳稻组合间育性差异的遗传基础有助于三系法杂交粳稻组合的选育。根据TR2604与豫粳6号A(B)、9201A(B)后代的花粉育性及小穗育性,明确了豫粳6号A(B)/TR2604 F₁不育由双亲间特异性不亲和造成。遗传分析表明豫粳6号A(B)与TR2604 F₁花粉不育受单基因S38(t)控制。以352株豫粳6号A/TR2604//TR2604、豫粳6号B/TR2604//豫粳6号B等群体中单株为定位群体,将S38(t)定位于第7染色体上标记RM18和RM234之间,与两标记遗传距离分别为0.43 cM和0.14 cM,两标记间物理距离为180 kb,相关结果为S38(t)图位克隆工作奠定了基础。     

豫粳6号保持系与恢复系TR2604间杂种花粉不育基因的定位

阐明BT型杂交粳稻组合间育性差异的遗传基础有助于三系法杂交粳稻组合的选育。根据TR2604与豫粳6号A(B)、9201A(B)后代的花粉育性及小穗育性,明确了豫粳6号A(B)/TR2604 F1不育由双亲间特异性不亲和造成。遗传分析表明豫粳6号A(B)与TR2604 F1花粉不育受单基因S38(t)控制。以352株豫粳6号A/TR2604//TR2604、豫粳6号B/TR2604//豫粳6号B等群体中单株为定位群体,将S38(t)定位于第7染色体上标记RM18和RM234之间,与两标记遗传距离分别为0.43 cM和0.14 cM,两标记间物理距离约为180 kb,相关结果为S38(t)图位克隆工作奠定了基础。     

9311与日本晴间一个杂种不育基因的鉴定与定位

以克服亚种间杂种不育来充分发掘亚种间杂种优势是提高水稻单产的一条有效途径。本研究,从一套以日本晴为背景,9311为供体的染色体片段代换系中鉴定出一个系T9424,其与日本晴配置的F₁植株小穗与花粉育性较双亲显著降低,双亲间存在不亲和。重测序结果表明T9424在第1、第4和第5染色体上导入9311片段。日本晴/T9424 F₂群体内单株基因型及育性鉴定结果表明,T9424与日本晴间杂种不育基因位于第5染色体上。利用F₂群体内790株单株将该杂种不育基因定位于第5染色体分子标记PSM8与A14之间110kb的物理区段内。对日本晴/T9424 F₁植株花粉与胚囊育性鉴定结果表明该杂种不育基因同时控制雌、雄配子败育,将该基因暂命名为S39(t)。相关结果有助于加深对水稻亚种间杂种不育现象的认识,为该基因克隆及其育种利用奠定基础。     

Location of a high-lysine gene and the DDT-resistance gene on barley chromosome 7

Summary The high-lysine gene in Risø mutant 1508 conditions an increased lysine content in the endosperm via a changed protein composition, a decreased seed size, and several other characters of the seed. The designation lys3a, lys3b, and lys3c, is proposed for the allelic high-lysine genes in three Risø mutants, nos 1508, 18, and 19. Linkage studies with translocations locate the lys3 locus in the centromere region of chromosome 7. A linkage study involving the loci lys3 and ddt (resistance to DDT) together with the marker loci fs (fragile stem), s (short rachilla hairs), and r (smooth awn) show that the order of the five loci on chromosome 7 from the long to the short chromosome arm is r, s, fs, lys3, ddt. The distance from locus r to locus ddt is about 100 centimorgans.     

Biological Activity and Quantification of Suspected Allelochemicals from Alfalfa Plant Parts

Autotoxicity restricts reseeding of alfalfa (Medicago sativa L.) after alfalfa until autotoxic chemical(s) breaks down or is dispersed into external environments. A series of aqueous extracts from leaves, stems, roots and seeds of alfalfa ‘Vernal’ were bioassayed against alfalfa seedlings of the same cultivar to determine their autotoxicity. The highest inhibition was found in the extracts from the leaves. Extracts at 40 g dry tissue l^?1 from alfalfa leaves were 15.4, 17.5 and 28.7 times more toxic to alfalfa root growth than were those from roots, stems and seeds, respectively. A high‐performance liquid chromatography (HPLC) analysis with nine standard compounds showed that the concentrations and compositions of allelopathic compounds depended on the plant parts. In leaf extracts that showed the most inhibitory effect on root growth, the highest amounts of allelochemicals were detected. Among nine phenolic compounds assayed for their phytotoxicity on root growth of alfalfa, coumarin, trans‐cinnamic acid and o‐coumaric acid at 10^?3 m were most inhibitory. The type and amount of causative allelochemicals found in alfalfa plant parts were highly correlated with the results of the bioassay, indicating that the autotoxic effects of alfalfa plant parts significantly differed.     

Simultaneous Determination of Four Phenolic Acids in Radix Salviae Miltiorrhizae Formula Granules by QAMS

[Objectives]This study aimed to establish a QAMS(quantitative analysis of multi-components by single-marker)method for simultaneous determination of four phenol...     

Changes in Seed Yield and Quality with Maturity in Onion (Allium cepa L., cv. 'Early Cream Gold')

Development of onion (Allium cepa L., cv. ‘Early Cream Gold’) seed under cool climate conditions in Tasmania, Australia occurred over a longer duration than previously reported, but similar patterns of change in yield components were recorded. In contrast to previous studies, umbel moisture content declined from 85 to 67 % over 57 days while seed moisture content decreased from 85 to 31 %. Seed yield continued to increase over the duration of crop development, with increasing seed weight compensating for seed loss resulting from capsule dehiscence in the later stages of maturation. Germination percentage was high and did not vary significantly from 53 to 77 days after full bloom (DAF), but mean germination time declined and uniformity of germination increased significantly over the same time period. The percentage abnormal seedlings declined with later harvest date, resulting in highest seed quality at 77 DAF. The results of this study suggest that the decision to harvest cool climate onion seed crops before capsule dehiscence will result in a loss of potential seed yield and quality.     

Pollen and pollination experiments. III. The viability of apple and pear pollen as affected by irradiation and storage

Summary Apple and pear pollen was irradiated with doses of 0, 50, 100, 250 and 500 krad (gamma rays) and stored at 4°C and 0–10% r.h. From the in-vitro germination percentages an average LD 50 dose of about 220 krad was estimated. For both irradiated and untreated pollen a close and corresponding lineair relationship existed between germination percentage and pollen tube growth.Irradiated pollen was much more sensitive to dry storage conditions than untreated pollen, resulting in less germination and more bursting. Apparently, irradiation caused the pollen cell membrane to lose its flexibility faster than normal. Rehydration of dry-stored, irradiated pollen in water-saturated air restored germination percentages up to their initial levels. The importance of this procedure in germination trials is stressed.     

Water Extraction Process of Chinese Herbal Compound Man Gan Ning

[Objectives]To optimize the water extraction process of Chinese Herbal Compound Man Gan Ning and establish a method for its extraction and content determination...     

Present status and future strategy in breeding faba beans (Vicia Faba L.) for resistance to biotic and abiotic stresses

Progress is being made, mainly by ICARDA but also elsewhere, in breeding for resistance to Botrytis, AScochyta, Uromyces, and Orobanche; and some lines have resistance to more than one pathogen. The strategy is to extend multiple resistance but also to seek new and durable forms of resistance. Internationally coordinated programs are needed to maintain the momentum of this work.Tolerance of abiotic stresses leads to types suited to dry or cold environments rather than broad adaptability, but in this cross-pollinated species, the more hybrid vigor expressed by a cultivar, the more it is likely to tolerate various stresses.     

Optimization of Extraction Technology and Determination of Content of Total Phenols of Leaves in Acanthopanax giraldii Harms

[Objectives] To determine the optimum extraction technology for total phenols of leaves in Acanthopanax giraldii Harms.[Methods]The single factor test and ortho...     

Cytoplasmic male sterility,resistance to gall mite and mildew,and season of leafing out in black currants

Summary Cytoplasmic male sterility (cms) is described in the F₁ hybrids Ribes × carrierei (R. glutinosum albidum × R. nigrum) and R. sanguineum × R. nigrum. In backcrosses to R. nigrum, progenies with R. glutinosum cytoplasm were either all male sterile, or segregated for full male fertility (F) and complete (S) and partial (I) male sterility. Ratios of F:I+S suggested that two linked genes controlled cms, F plants being dominant for one (Rf ₁) and recessive for the other (Rf ₂).Segregation for cms in relation to three linded genes, Ce (resistance to the gall mite, Cecidophyopsis ribes), Sph ₃(resistance to American gooseberry mildew, Sphaerotheca mors-uvae) and Lf ₁(one of two dominant additive genes controlling early season leafing out) indicated that Rf ₁and Rf ₂were in this linkage group. The gene order and approximate crossover values appeared to be: % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqef0uAJj3BZ9Mz0bYu% H52CGmvzYLMzaerbd9wDYLwzYbItLDharqqr1ngBPrgifHhDYfgasa% acOqpw0xe9v8qqaqFD0xXdHaVhbbf9v8qqaqFr0xc9pk0xbba9q8Wq% Ffea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qqQ8frFve9Fve9Ff0dme% aabaqaciGacaGaamqadaabaeaafaaakeaacaWGdbGaamyzamaamaaa% baGaaiiiaiaacccacaGGWaGaaiOlaiaacgdacaGG0aGaaiiiaiaacc% caaaGaaiiiaiaacccacaGGGaGaamOuaiaadAgaliaaigdakmaamaaa% baGaaiiiaiaacccacaGGGaGaaiiiaiaaccdacaGGUaGaaiOmaiaacs% dacaGGGaGaaiiiaiaacccacaGGGaGaaiiiaaaacaWGsbGaamOzaSGa% aGOmaOWaaWaaaeaacaGGGaGaaiiiaiaacccacaGGGaGaaiiiaiaacc% cacaGGGaGaaiiiaiaacccaaaGaamitaiaadAgaliaaigdakmaamaaa% baGaaiiiaiaacccacaGGGaGaaiiiaiaacccacaGGGaGaaiiiaiaacc% cacaGGGaGaaiiiaiaacccacaGGGaaaaiaadofacaWGWbGaamiAaSGa% aG4maaaa!6E4D!\[Ce\underline { 0.14 } Rf1\underline { 0.24 } Rf2\underline { } Lf1\underline { } Sph3\]. Crossover values of 0.36 for Ce-Lf ₁, and 0.15 for Lf ₁-Sph ₃were estimated from the relative mean differences in season of leafing out between seedlings dominant and recessive for Ce and Sph ₃.It is suggested that competitive disadvantage of lf ₁-carrying gametes and/or zygotes at low temperatures may be implicated in the almost invariable deficit of plants dominant for the closely linked mildew resistance allele Sph ₃. Poor performance of lf ₁- (and possibly lf ₂-) carrying gametes and young zygotes during periods of low temperature at flowering might also account for the liability of some late season cultivars and selections to premature fruit drop (running off).     

Screening techniques and sources of resistance to parasitic angiosperms

Parasitic angiosperms cause great losses in many important crops under different climatic conditions and soil types. The most widespread and important parasitic angiosperms belong to the genera Orobanche, Striga, and Cuscuta. The most important economical hosts belong to the Poaceae, Asteraceae, Solanaceae, Cucurbitaceae, and Fabaceae. Although some resistant cultivars have been identified in several crops, great gaps exist in our knowledge of the parasites and the genetic basis of the resistance, as well as the availability of in vitro screening techniques. Screening techniques are based on reactions of the host root or foliage. In vitro or greenhouse screening methods based on the reaction of root and/or foliar tissues are usually superior to field screenings and can be used with many species. To utilize them in plant breeding, it is necessary to demonstrate a strong correlation between in vitro and field data. The correlation should be calculated for every environment in which selection is practiced. Using biochemical analysis as a screening technique has had limited success. The reason seems to be the complex host-parasite interactions which lead to germination, rhizotropism, infection, and growth of the parasite. Germination results from chemicals produced by the host. Resistance is only available in a small group of crops. Resistance has been found in cultivated, primitive and wild forms, depending on the specific host-parasite system. An additional problem is the existence of pathotypes in the parasites. Inheritance of host resistance is usually polygenic and its transfer is slow and tedious. Molecular techniques have yet to be used to locate resistance to parasitic angiosperms. While intensifying the search for genes that control resistance to specific parasitic angiosperms, the best strategy to screen for resistance is to improve the already existing in vitro or greenhouse screening techniques.