Evidence of a partial reproductive barrier between wild and cultivated pearl millets (Pennisetum glaucum)

Summary The occurrence of seed malformation in association with reduced thousand grain weight and germination ability has been observed in crosses between cultivated female plants and wild male plants. A survey of 16 cultivated accessions (P. glaucum subsp. glaucum) and 11 wild accessions (P. glaucum subsp. monodii) ranging over the whole species diversity showed this postzygotic incompatibility was general, but its intensity varied greatly with the cultivated female accession used and very little with the wild male parent origin. About 15% of the 123 cultivated x wild crosses observed gave normal seeds. Seed malformation has never been observed in crosses between cultivated accessions and appeared independent of genetic distances between the parents. The reciprocal crosses between wild female plants and cultivated male plants gave normal-looking seeds with good germination but consistently reduced thousand grain weight. Both seed malformation and seed small size are an expression of a genetic imbalance. These slight reproductive barriers seem to have been built during the domestication process.Abbreviation ICRISAT International Crop Research Institute for the Semi-Arid Tropics     

Temperature effects on seed germination and expression of seed dormancy in wheat

Because preharvest sprouting decreases quantity and quality of wheat grain, researchers need effective protocols to assess response to preharvest sprouting conditions. The aim of this study was to determine which temperature gives the greatest difference in seed germination and expression of seed dormancy in 10 spring wheat genotypes. The genotypes were grown in the field near Swift Current, Saskatchewan in 2000 in a randomized complete block with four replicates. Seed samples were harvested at approximately 25% moisture content (wet weight basis) and dried to 12% moisture content with minimal after-ripening. Germination was under controlled environment at temperatures of 10, 15, 20 and 30 °C in darkness. A weighted germination index (WGI) was calculated. The analysis of WGI, for each temperature, showed highly significant (p ≤ 0.01) genotype effects on germination. Most genotypes decreased in WGI (increased dormancy) as temperature was increased from 10 to 30 °C. The greatest differences in seed germination tended to be at 15 °C and 20 °C. The level of seed dormancy depended on the genotype and germination temperature. This revised version was published online in August 2006 with corrections to the Cover Date.     

Recurrent Mass Selection for Reduced Seed Dormancy in Cuphea lanceolata and Cuphea laminuligera

Seed dormancy is a domestication barrier in certain Cuphea species. Between and within species variation has been observed for seed dormancy in agronomically promising Cuphea species, e.g., C. laminuligera Koehne and C lanceolata Ait. In tins note, we report on progress made in reducing seed dormancy through recurrent mass selection in the C. lanceolata population LN43 and LN78. The germination percentages of unselected LA12 and LN43 populations increased from 0.0 % to greater than 95.0 % following an after-ripening period of 20 weeks. We observed no germination percentage differences between unselected and selected LN43 populations following two cycles of selection. In contrast, there were highly significant differences between the unselected and selected populations of LA12 following two cycles of selection. The germination percentages of cycle zero (C₀) and cycle two (C₂) populations after-ripened 10 weeks were 10.7 and 92.7 %, respectively. After one cycle of selection in the C. Lanceolata population LN78, the germination percentage of seed after-ripened 10 weeks had increased from 1.3 % for the C_o population to 28.7 % for the C₀ population. In summary, mass selection greatly reduced seed dormancy in LA12 and LN78, but had no effect in LN43.     

Genetic analysis and linkage study of seed weight in lentil

Summary The genetics of seed weight was studied in crosses between the cultivated lentil L. culinaris and the wild species L. orientalis and L. ervoides. Seed weight was found to be under polygenic control with additive and dominant gene action and with partial dominance of low seed weight alleles. High heretability estimates were obtained in the analysed crosses. Nuclear-cytoplasmic interaction was found to affect seed weight in crosses involving accession No.138 of L. orientalis. Factors affecting seed weight were linked to morphological and DNA markers distributed over several linkage groups. High seed weight in segregating generations were usually associated with alleles of marker loci originated from the cultivated parent. Factors enhancing seed weight were detected in accession No.138 of L. orientalis, indicating the potential of wild genetic resources for seed weight improvement in lentil.     

滇重楼种子休眠机理研究

探讨滇重楼种子休眠机理,为打破种子休眠促进滇重楼实生育苗提供理论基础。采用重量法、胚率测定、ELISA等方法对种子吸水特性、萌发抑制物及种胚休眠与发育的内源机理进行了研究。结果表明,滇重楼种子休眠属于形态学-生理学休眠类型。滇重楼种胚发育不完全、种子中存在萌发抑制物质是种子休眠的主要原因。种子不存在吸水障碍,与休眠无关。内源激素ABA和GA3在滇重楼种子休眠与萌发过程中起着重要作用,ABA是引起休眠的关键因素,ABA含量的降低是滇重楼种胚发育的始动因子,GA3有助于种子的生理后熟。萌发抑制物的存在可能抑制了种胚发育,而与生理学后熟过程无关。在自然条件下,滇重楼生境中较长的低温时期可能是滇重楼种子具有较长时间休眠的外界原因。     

Genetic variation for seed dormancy in Cuphea laminuligera and Cuphea lanceolata

Summary Various Cuphea species are adapted to temperate climates and characterized by caprylic, capric, and lauric acid-rich seed oils. These fatty acids are solely commercially available from palm kernel and coconut oils; thus, there is considerable interest in Cuphea as an alternative source of these fatty acids. Cuphea is a genus of undomesticated species characterized by seed dormancy and seed shedding. Our goal is to eliminate these domestication barriers in a few species with agronomic potential. Our objective was to survey existing Cuphea laminuligera and C. lanceolata germplasm for genetic variation for seed dormancy (germination percentage after a certain seed storage period). Recurrent half-sib family selection was practiced in various open-pollinated and synthetic populations. Half-sib family seed were evaluated for germination percentages at 26° C after various seed storage periods. There was significant genetic variation among families in every population. Additive genetic variance, half-sib family-mean heritability, and expected selection response magnitudes depended on the length of the seed storage period within a given population. Estimates of these parameters were significantly greater for longer seed storage periods within a population. Heritability estimates ranged from 0.00 to 0.79. Expected half-sib family selection responses ranged from 0.0 to 23.9%. Our study demonstrated there is substantial genetic variation for seed dormancy in C. laminuligera and C. lanceolata.     

The genetic relations between length of time to germination and seed dormancy in lisianthus (Eustoma grandiflorum)

Summary The inheritance of speed of germination and its genetic relations with seed dormancy was investigated in lisianthus (Eustoma grandiflorum). The study was based on data from parental, F1, BC1F1 and F2 generations of a cross between a normally germinating genotype (P1) and a chill-requiring genotype (P2). The mean post-chilling germination speed of P2 was considerably lower than that of P1. Germination speed was found to be under nuclear embryonic control. Analysis of generation means for prechilled seeds revealed an additive gene action with complete dominance of the alleles conferring higher germination speed, since the means of the F1 and the BC1 (P1) were indentical to that of P1. Such dominance was not found for unchilled seeds, in which the mean germination speed of the F1 and the BC1 (P1) was lower than that of P1. It was hypothesized that slow germination speed was induced by pleiotropic effects of seed dormancy alleles. Seed prechilling seemed to eliminate these effects in progeny heterozygous for dormancy alleles, but not in progeny homozygous for dormancy alleles.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, No 1292-E, 1993 series.     

Variation in response to infection with Erysiphe graminis hordei and Puccinia hordei in some wild barley populations in a centre of diversity

Summary The Near East Fertile Crescent extending from Iran to Israel is the centre of origin of cultivated barley and a region of great genetic diversity in wild barley, Hordeum spontaneum C. Koch (syn. H. vulgare ssp. spontaneum (C. Koch Thell)). Wild barley accessions collected from different parts of this region were evaluated for their reactions to infection with three isolates of Erysiphe graminis hordei and two of Puccinia hordei. One culture of each pathogen was isolated in Israel and the others, either in Japan or the United States. Out of a total of 330 wild barley accessions collected from 14 sites in Iran, Turkey and Syria, only 18.8% were resistant to the Israeli culture, and 14.8% were resistant to a composite of the Japanese and American cultures of E. graminis hordei. Out of 105 accessions collected from six sites in Iran and Turkey, none was found to be resistant to the Israeli culture and 34.3% were resistant to the American culture of P. hordei. Considerable variation was observed both within and among sites for reactions to infection with different cultures of each of the two pathogens. The results of this study were compared with those of an earlier study involving wild barley accessions from Israel to illustrate the relative importance of different subregions in the Near East Fertile Crescent as sources of new genes for resistance to E. graminis hordei and P. hordei. Implications of these studies for in situ conservation of genetic diversity in wild barley are discussed.     

Variation in developmental patterns of wild barley (Hordeum spontaneum L.) and cultivated barley (H. vulgare L.)

Summary Six wild barley (Hordeum spontaneum) accessions, from a diverse range of habitats, and two spring-cultivated barleys, were examined for variation in durations of development phases. The durations of the leaf initiation and spikelet initiation phases were longer and spikelet growth phases shorter, in wild than in cultivated barley. Across all wild and cultivated barleys the rate and duration of spikelet initiation were negatively correlated, but neither was related to the number of spikelets per spike. The number of spikelets was positively correlated with the number of leaves and the ratio of the number of spikelets to the number of leaves declined with increasing time to anthesis, indicating that each successive leaf was associated with a diminishing increase in the number of spikelets. The duration of culm elongation and final culm length were shorter in accessions of cultivated barley compared with wild barley. This paper also discusses the feasibility for increasing the number of spikelets per spike through breeding for genetic changes in lengths of pre-anthesis phases of development.Abbreviations ANOVA Analysis of variance - HV Hordeum vulgare - CE Culm elongation - DR Double ridge - HS Hordeum spontaneu - ° Cd Degree days     

Relationship between sprouting in wheat and embryo response to endogenous inhibition

Summary Seed dormancy in wheat (Triticum aestivum L. em Thell) is important for minimizing pre-harvest sprouting. To facilitate breeding cultivars that tolerate pre-harvest sprouting conditions, we assessed mode and magnitude of variation of seed dormancy among genotypes and investigated involvement of endogenous water-soluble inhibitor(s) in seed germination. Embryo bio-assays established that water-soluble inhibitor was ubiquitous among the wheat cultivars studied and did not diminish in quantity during after-ripening. Germination response of embryos was decreased by endogenous inhibitor, but the effect markedly declined as embryos aged at room temperature. Variation in dormancy among cultivars was primarily caused by differential response of their embryos to endogenous inhibitor. Gibberellic acid counteracted the initial inhibitory effect of endogenous inhibitor on germination but not the subsequent inhibitory effect on seedling growth. We concluded that pre-harvest sprouting resistance involves multiple factors, particularly embryo receptivity to endogenous inhibitor, and that variation in inhibitor quantity is not solely responsible for genotypic differences in susceptibility to pre-harvest sprouting. The possibility of additional approaches to breeding for pre-harvest sprouting resistance is indicated.Contribution no. 81-389-j, Department of Agronomy, Kansas State University, Manhattan, KS 66506, U.S.A.     

Genotypic variation in polyphenol content of barley grain

The polyphenol content in pearl barley, which is highly correlated to a browning reaction after heat treatment, was investigated using 1,347 cultivated barley varieties (H. vulgare) and two wild accessions (H. vulgare subsp. spontaneum) collected from different areas of the world. The polyphenol content in the cultivated barley shows a wide variation ranging from 0.19 to 0.75 mg/g with a nearly normal frequency distribution. The polyphenol content in the hulless varieties from Japan and Korea was low. On the other hand, the polyphenol content in wild barley was about two times higher than the average value recorded in cultivated barley. Based on HPLC analysis, five lowest-polyphenol content local varieties do not represent proanthocyanidin-free mutants. This revised version was published online in August 2006 with corrections to the Cover Date.     

木芙蓉种子萌发特性研究

对木芙蓉种子进行机械破损、不同药剂浸种等处理，结果表明：砂纸摩擦、丙酮浸种均可促进木芙蓉种子的萌发，以砂纸摩擦5min结合丙酮浸泡3h处理获得的效果最佳；木芙蓉种子对赤霉素不敏感；一年陈种子在发芽率上明显高于新种子。初步得出：种皮障碍是木芙蓉种子萌发的主要限制因素之一；木芙蓉种于需要后熟。     

The genetics of hard seed coat in the genus Lens

Summary Seeds of the cultivated lentil are capable of germinating shortly after maturation. The seed dormancy of wild lentil species is due to a hard seed coat. In crosses between the cultivated species L. culinaris and its wild progenitor L. orientalis the hard seed coat of the wild species was controlled by a single recessive gene in homozygous condition. In a cross between the wild species L. ervoides and L. culinaris the hard seed coat of L. ervoides was controlled by a single dominant gene. The significance of the genetics of seed coat hardness in the domestication of lentil is briefly discussed.     

花生种子休眠解除过程中相关基因的表达分析

种子休眠性是花生重要的农艺性状,外源乙烯利能诱导花生种子休眠的解除,为了阐明乙烯利作用下花生种子休眠解除的分子机制,设置吸胀的休眠种子为对照,100 mg L–1乙烯利处理吸胀休眠种子后不同时间的样品(AE1、AE2、AE3)进行转录组分析,比较了花生种子休眠解除过程中ABA、GA、ETH、auxin相关基因的表达。结果表明,15个与GA、40个与ABA、60个与ETH、56个与auxin相关的unigenes在花生种子休眠解除过程中表现显著差异表达。荧光定量PCR结果显示,ABA合成关键基因Ah NCED2和代谢关键基因Ah CYP707A1在种子休眠解除过程中均受外源乙烯利诱导,表达差异显著;在休眠和无休眠种子吸胀萌发过程中,Ah NCED2和Ah CYP707A1的表达趋势不同,Ah NCED2对于种子休眠的维持发挥积极作用,而Ah CYP707A1对于种子休眠解除发挥积极作用。     

Genetic diversity and population structure of wild and cultivated barley from West Asia and North Africa

Population structure and relationships within and among 185 accessions of wild (Hordeum vulgare ssp. spontaneum) and cultivated barley (H. v. ssp. vulgare) from five countries in the West Asia and North Africa (WANA) region were studied using 36 simple sequence repeat (SSR) markers. The accessions were divided into subspecies/origin (S/O)‐groups and marker results were analysed in relation to genetic diversity and genetic structure. Wild barley from WANA was found to be highly diverse. The landraces from different countries of the Near East showed genetic diversity that was nearly as high as the wild barley from the same country. Further analyses showed that wild barley from Palestine/Israel represented the group with the highest diversity and the most complex structure. However, this group was distantly related to the cultivated barley in WANA, while the wild barley from the rest of the WANA region was closely related to the cultivated WANA barley. The high diversity and the close relationship to the wild barley make the WANA landraces an interesting genetic resource for both conservation and exploitation.     

Inheritance and geographical distribution of phenol reaction-less varieties of barley

Summary The reaction of spikes and grains of barley to phenol was investigated using 8,849 cultivated and 349 wild accessions collected from the world. The pericarp and hull of the grain were stained dark brown by a 1% phenol solution and the reaction of awn was sharpest. Phenol reaction was controlled by a dominant gene, named Phr (phenol reaction) which was located on chromosome 2. All the wild strains of various Hordeum species showed a positive reaction to phenol indicating it was the prototype of the trait. Only 51 accessions of cultivated barley showed negative reaction to phenol. They were distributed along the so-called Silk-road and the type of variety was limited suggesting that it was a rather new mutation which occurred in the Middle East. Synteny of the chromosome region involving the phenol reaction gene in some gramineous plants was discussed.     

Random amplified polymorphic DNA (RAPD) variation in Fagopyrum tataricum Gaertn. accessions from China and the Himalayan region

The diversity among 52 landraces and cultivars of tartary buckwheat (Fagopyrum tataricum Gaertn.) and one accession of its wild ancestor, F. tataricum ssp. potanini Batalin, from diverse geographic origins was examined using random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) markers. Eighteen primers produced a total of 240 fragments, of which 153 (63.75%) were monomorphic and 87 (36.25%) polymorphic bands. UPGMA-based pairwise Jaccard’s coefficient of similarity was used to deduce the relationships among 53 genetically diverse accessions. The similarity between cultivated tartary buckwheat accessions ranged from 0.61 to 1.00. Four distinct clusters were formed which corresponded well with the geographic distribution of the tartary buckwheat. Nepalese accessions showed maximum diversity followed by Chinese accessions. Tartary buckwheat accessions from the Himalayan region of northwestern India revealed a narrow gene pool. The wild buckwheat accession did not group with any of the three cultivated tartary buckwheat groups, and formed its own single-entry group. Genetic similarity (0.59) of Chinese buckwheat accessions with the wild ancestor reaffirmed that cultivated tartary buckwheat originated in the Yunnan province of northwestern China. Consistent with some earlier reports, our study demonstrated the usefulness of the RAPD technique for the characterization of plant genetic resources and assessment of diversity between species. This revised version was published online in August 2006 with corrections to the Cover Date.     

密花香薷种子形态及萌发特性研究

以密花香薷种子为试验材料,对种子的形态、种子质量、萌发特性进行了观测。结果表明:密花香薷的种子为近卵圆形,灰褐色,长2.123～2.705 mm,宽1.414～1.806 mm,千粒重2.808 g,生活力67.50%,净度88.23%,含水率13.18%。种子的种皮薄,不是造成种子发芽率低的原因;随着贮藏时间的延长,种子的发芽率逐渐提高,种子存在后熟现象;黑暗有利于种子的萌发;赤霉素和硝酸钾对打破种子休眠的最适浓度分别为7%和800 mg/L。     

The domestication and improvement of cowpeas (Vigna unguiculata (L.) Walp.)

Summary Physiological and morphological characteristics of the two wild and three domesticated subspecies of cowpeas are compared. The wild accessions are alike in having small, hard seeds borne in dehiscent pods, but differ in other characteristics. We suggest that the wild subsp. dekindtiana, from the seasonally-arid tropics, is more likely to have been the progenitor of modern cowpeas than the other wild subspecies (subsp. mensensis), but that subsp. dekindtiana was first cultivated in the humid tropics where its pods are slow to dehisce. Domestication has been associated with changes in the structure of pod valves and seed coats which reduce pod dehiscence and seed hardness. Pods and seeds have increased in size, mainly by increases in the rate of dry weight accumulation, and their increase has been only partly paralleled by increase in the area of subtending leaves. There has been no increase in the maximum photosynthetic rate of leaves, but the duration of their photosynthetic activity has increased. Domesticates are less sensitive than are wild plants to some environmental controls, such as in the response of germination to temperature, but in their flowering responses to daylength both wild and cultivated forms retain sensitivity under conditions where this is of adaptive value.     

Ribosomal DNA spacer-length polymorphisms in three samples of wild and cultivated barleys and their relevance to the origin of cultivated barley

This study was conducted to provide additional data for evaluating two important issues surrounding the origin of cultivated barley: (i) the level of genetic diversity of the two‐rowed wild barley from Tibet, and (ii) the distribution of rDNA allele 104 in wild and cultivated barleys in the Occidental region. A total of 198 accessions consisting of three distinct samples were used: 82 entries of two‐rowed wild barley from Tibet, 57 accessions of two‐rowed wild barley from 8 countries with a broad range of representation of two‐rowed wild barley in the world, and 59 landrace accessions from four countries representing a part of the barley‐growing areas in the Middle East. These were assayed for rDNA spacer‐length variants (slvs). In all, 27 rDNA space length pheno types were detected, from which 10 slvs were identified as alleles at the two rDNA loci. The two‐rowed wild barley samples from Tibet had the lowest level of genetic variation as evaluated by rDNA polymorphism. Together with results of previous studies, the two wild forms (two‐rowed and six‐rowed) from Tibet could not account for the large genetic diversity observed in the cultivated barley of this region, suggesting that Tibet is unlikely a centre of origin for cultivated barley. In samples from the Occidental region, allele 104 of Rm2 was very rare in wild barley, but occurred at the highest frequency in cultivated barley, while the reverse is the case for allele 107, which is consistent with previous results. The implications of such a contrasting distribution of these rDNA alleles between wild and cultivated barleys in the origin and evolution of cultivated barley were discussed.