Weed management challenges in small-holder potato systems in Bhutan

Over the past four decades potato has emerged as the most important cash crop for Bhutanese mountain farmers. Farmers' feedback and field observations were used to describe weed populations, weed management and weed-production environment-yield interactions in small-holder potato production systems. Weed species across a range of locations in order of declining importance are: Persicaria runcinata , Galium aparine , Fagopyrum dibotrys , Digitaria ciliaris , Commelina maculata , Galinsoga parviflora and Persicaria nepalensis. The same species were common in the traditional buckwheat and maize production systems as well as the more recently established potato production systems. Limited associations between soil properties, management practices, weed species abundance and potato yield were observed. Species emerging as potential problem weeds, especially P. runcinata and F. dibotrys , are little known outside the Himalayan region. The increase in P. runcinata , reported by 42% of the respondents, was attributed to the use of metribuzin, cutting of rhizomes by plough or spade, high inputs of fertiliser and continuous cultivation of potato by 61%, 17%, 9%, 9% and 4% of respondents respectively. Metribuzin application reduced growth of P. runcinata but could not fully control it. Metribuzin is an effective and affordable weed management tool for small-holder potato farmers, but perennial weed species need further research, combining mechanical and chemical methods with cropping strategies.     

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.     

Two independent gene loci controlling non-brittle pedicels in buckwheat

The shattering habit in buckwheat occurs because of brittle or weak pedicels. Brittle pedicels are observed in wild buckwheat but not in cultivated buckwheat. Using 2 self-compatible lines, 01AMU2 with brittle pedicels and Kyukei SC2 (KSC2) with non-brittle pedicels, produced by an interspecific cross between Fagopyrum esculentum cv Botansoba (non-brittle) andF. homotropicum (brittle), we investigated the inheritance of brittle pedicels. F₁ plants derived from crosses between Botansoba × 01AMU2 and Botansoba × KSC2 had brittle pedicels. The F₂ population derived from the cross between Botansoba × 01AMU2 showed segregation of brittle and non-brittle pedicels that fit the expected 3:1 ratio, suggesting that non-brittle pedicel in Botansoba is controlled by a single recessive gene (sht1). Another F₂ population, derived from the cross between Botansoba × KSC2, showed segregation of brittle and non-brittle pedicels that fit an expected ratio of 9:7,suggesting that non-brittle pedicel in KSC2is controlled by a different single recessive gene (sht2). Thus, brittle pedicel is achieved by 2 complementary genes Sht1 and Sht2. The sht1 locus is linked to the S locus with a recombination frequency of5.46±1.18 (%). We investigated whether common buckwheat has the allele sht2by crossing 6 common buckwheat lines withKSC2. An analysis of the preliminary data showed that some of the F₁ had brittle pedicels and others had non-brittle pedicels, suggesting that some common buckwheat lines possess both the allelesSht2 and sht2. This revised version was published online in July 2006 with corrections to the Cover Date.     

Studies on the Influence of Photoperiod and Temperature on Floral Traits in Buckwheat (Fagopyrum esculentum Moench) under Controlled Stress Conditions

Floral traits of three Japanese and one European buckwheat varieties were studied in a phytotron under three photoperiods (short-day 10/14 h, long-day 14/10 h, extreme long-day 18/6 h) and two thermoperiods (25/20, and 15 °C constant temperature). The Japanese varieties showed a strong delay in flowering under prolonged day length, whereas one European variety reacted almost day-neutral. Also affected by the photoperiod were the number of flower clusters as well as their sizes. A constant low temperature of 15 °C led to a strong delay in flowering under short- and long-day in all the varieties tested. In particular, the Japanese varieties were sensitive to temperature, developing more flower clusters under high temperature. Furthermore the experiments revealed complex genotype/pliotopenod/thermoperiod interactions. The study, conducted to investigate the causes of low seed-set observed in buckwheat, offered some suggestions for new breeding strategies. Insensitive genotypes, showing less sensitivity to photoperiod as well as to thermoperiod, should be included in further buckwheat improvement.     

普通荞麦愈伤组织诱导及其分化的正交设计试验研究

用正交设计法研究不同激素处理及不同外植体对普通荞麦愈伤组织诱导及分化过程中的影响。结果表明，在本实验设计中，2，4-D是诱导普通养麦愈伤组织的主要因素；诱导愈伤组织的最佳培养基为MS＋2．0mg／L 2，4-D＋1．5mg,／L 6-BA；愈伤组织分化的主要因素是6-BA；愈伤组织分化的最佳培养基为MS＋2．5mg／L 6-BA＋1．0mg／LKT。     

Seed protein variation for identification of common buckwheat (Fagopyrum esculentum Moench) cultivars

Summary Total seed proteins of 24 common buckwheat cultivars and cultivated populations within a molecular weight range of 30 to 54 kDa were analysed by SDS-PAGE. Single seed analysis of six cultivars identified a total of 18 alternative protein bands with different mobilities. Differences of individual protein band frequencies extracted from single seeds among six buckwheat cultivars varied distinctively, indicating high intravarietal polymorphism. The relation between frequencies of protein bands revealed by single seed analysis and their appearance on the bulk seed analyses was demonstrated. Regarding to band mobility rate and relative band intensity among 24 bulk samples analysed, 14 had distinctive electrophoregrams while the other 10 were ranged into four distinct groups. Analysis of endosperm and cotyledon proteins showed that proteins stored in these main seed parts are tissue specific. The observed electrophoretic polymorphism related to proteins stored in the cotyledons while there was no apparent variability with endosperm proteins.     

Richards Plant Growth Model

In this paper, the Richards function in the form y(t) = A(I +be^−kt)^1/(1-m) was used to precisely analyze plant growth. The first, second and third derivative formulae of the above function were given. A new parameter, G₁₂= f(m) was derived, enabling the calculation of the coordinates of critical points which mark the principal growth phases. The coefficients of Richards model describing the dry matter accumulation in buckwheat plants were numerically calculated. The growth curve, growth rate curve and the growth acceleration curve were also drawn, A high usefulness of approximation of the growth process of buckwheat plants by means of Richards function was confirmed statistically.     

Breaking Strength of Pedicel as an Index of Grain-Shattering Habit in Autotetraploid and Diploid Buckwheat (Fagopyrum esculentum Moench.) Cultivars

Abstract

The grain-shattering habit was compared among diploid and autotetraploid cultivars of common buckwheat (Fagopyrum esculentum Moench.). In the first experiment, one diploid and one autotetraploid cultivar were grown in the field, and the number of grains shed naturally by wind or rain, and the number of grains detached by threshing the plants (by dropping from 1 m height onto a concrete floor, five times) were measured to evaluate grain shattering. The number of the naturally shed grains in the field was higher in the diploid than in the autotetraploid cultivar, although the number of grains detached by threshing was not different between the two cultivars. In another set of experiments, breaking bending strength and breaking tensile strength of pedicels were measured as indices of grain-shattering habit to examine the difference in shattering among two autotetraploid and four diploid cultivars (two summer types and two autumn types). They were grown in summer and autumn seasons to examine the environmental effect on grain shattering. Both breaking strengths were about two times higher in the autotetraploid cultivars than in the diploid cultivars. The breaking strength was well correlated with the diameter of pedicels. The values of grain-shattering resistance traits obtained in the autumn cropping season were higher than those obtained in the summer cropping season.     

荞麦属(Fagopyrum Mill)植物资源的RAPD研究

以10个随机引物对荞麦属(Fagopyrum)11个种(含大粒组7个种,小粒组4个种)共50份栽培及野生荞麦资源进行RAPD研究.初步建立了养麦属不同物种的RAPD指纹图谱.系统聚类分析表明,荞麦属大粒组和小粒组组间以及不同荞麦种间在DNA水平上差异极大.在大粒组中苦荞DNA与其他种之间有较大的差异.大野荞和毛野荞分别与甜荞和苦荞在RAPD水平上较近缘,支持它们分别是甜荞和苦荞祖先种的假说.     

温度对荞麦芽菜、叶片及籽粒芦丁含量的影响

在智能人工气候箱条件下,分析研究了生长在3种培养温度下的4个荞麦品种芽菜的芦丁含量以及开花结实期温度处理对荞麦叶片和种子芦丁含量的影响.结果表明,随着培养温度的提高,荞麦芽菜的芦丁含量呈降低趋势;而开花结实期较高的温度则增加叶片和籽粒的芦丁含量.