A viewpoint to apply water pricing to the Asian humid tropics

The OECD has introduced a water pricing mechanism and listed eight categories gleaned from experience in OECD countries. However, in the Asian humid tropics, it is too early to apply water pricing because there is seldom a concept of water right, or practical organization of water management. In almost all irrigation projects in Japan, area charge has been applied, and collected fees have recovered entire operation and maintenance costs. Although effective volumetric charge is employed in several regions in Japan, most farmers pay area-based annual charges at several times of the year via Land Improvement Districts. In the Asian humid tropics, it is important to facilitate the establishment of sound management organizations of irrigation water before introducing a strict water pricing mechanism to levy the charge.     

Weed control with selected herbicides in acetolactate synthase-resistant sorghum

The recent development of grain sorghum hybrids with resistance to acetolactate synthase (ALS)-inhibiting herbicides has allowed for the use of several post-emergence applied (POST) ALS-inhibitors to control weeds in the crop. Field experiments were conducted at four sites in Kansas in 2008 to evaluate the efficacy of nicosulfuron and nicosulfuron + rimsulfuron applied alone or in combination with dicamba, metsulfuron methyl, and atrazine. All POST treatments slightly injured sorghum 2 weeks after treatment (WAT) at Garden City and Hesston, whereas at Hays and Manhattan, only treatments that included dicamba caused injury. Nicosulfuron + rimsulfuron applied alone provided 41, 83, 74, and 93% control of grasses 4 WAT at Garden City, Hays, Hesston, and Manhattan, respectively. However, to obtain the highest level broadleaf weed control, nicosulfuron or nicosulfuron + rimsulfuron need to be applied with other broadleaf herbicides. POST treatment of nicosulfuron + metsulfuron methyl + dicamba + atrazine provided 90% or greater control of all broadleaf weeds at sorghum flowering. Sorghum grain yield was greater following all herbicide treatments compared with the weedy check. The POST treatment that provided the highest yield at Garden City was nicosulfuron + rimsulfuron + atrazine, whereas in Hesston and Manhattan, nicosulfuron + metsulfuron methyl + dicamba + atrazine provided the highest yields. This research showed that many grasses can be effectively controlled with POST applications of nicosulfuron or nicosulfuron + rimsulfuron in ALS-resistant sorghum. The research also indicated that broadleaf weed control is greater when nicosulfuron or nicosulfuron + rimsulfuron are applied with other broadleaf-control herbicides such as dicamba, metsulfuron methyl, and atrazine.     

Dry-matter yields and crude protein and rumen-degradable protein concentrations of three Arachis pintoi ecotypes at different stages of regrowth in the humid tropics

Well‐established stands of three ecotypes of Arachis pintoi (CIAT 17434, 18744 and 18748) were harvested from replicated plots (three blocks, each containing three plots for each ecotype) during the two dominant seasons (dry and wet) of the low altitude, humid tropics of Costa Rica. Each plot was further divided into six subplots so that, within each season, samples corresponding to 4, 6, 8, 10, 12 or 14 weeks of regrowth could be collected. For each harvest, dry matter (DM) yield of the leaf, stem and whole plant, and the leaf:stem ratio, were recorded. Samples of the whole plant were analysed for crude protein (CP), rumen‐degradable (RDP) and rumen‐undegradable protein (RUP) concentrations. DM yield of the leaf, stem and whole plant increased with advancing period of regrowth but the effects of period of regrowth varied somewhat among ecotypes and across seasons. Generally, DM yield was greater during the wet than during the dry season. The greatest difference between ecotypes for stem and total DM yields was evident during the dry season. In general, DM contents were low in the whole plant, leaf and stem samples (<220 g kg^?1) and increased with increasing period of regrowth. Increases in leaf:stem ratio were most dramatic during the dry season with greater periods of regrowth, although the ratio was fairly constant during the wet season. Whole‐plant CP concentration was relatively high after short periods of regrowth (up to 279 g kg^?1 DM) but declined with longer periods of regrowth; the relative decline was much greater during the dry season. The RDP concentration was relatively constant during the wet season (mean 115 g kg^?1 DM), but declined with longer periods of regrowth during the dry season (range 194–111 g kg^?1 DM). In general, the concentrations of RDP, on a CP basis, were greater during the dry season and ranged from 590 to 700 g kg^?1 CP. Season, ecotype and period of regrowth all exerted an effect on RUP concentrations.     

Growth and yield of perennial cassava in the subhumid subtropics

Growth and tuber yield of perennial cassava crops of up to 4 years' duration were compared with those of annual crops in a subhumid subtropical environment where low winter temperature limits crop growth to 8–9 months per year.Resumption of growth by perennial cassava was rapid; sprouting occurred at many nodes in spring, and its canopy intercepted more solar radiation than did young annual crops. However, total biomass production during a season was generally slightly less than that of annual crops.After four seasons of cropping, four annual crops combined produced 49.4 t ha⁻¹ of tuber dry weight. Corresponding yields for two 2-year crops, one annual plus one 3-year crop, and one 4-year crop, were 44.7, 40.3 and 38.1 t ha⁻¹, respectively. The higher productivity of the annual crops was partly related to irrigation applied in the first three seasons to the annual crops. In the fourth season when no irrigation was applied to any crop, the annual increments of tuber weight in 2- and 4-year crops were similar to the tuer yield of the annual crop. It was concluded that productivity of a 2-year crop is 90–100%, and that of 3- and 4-year crops is 80–90%, that of annual cassava.     

Persistence of seeds of some grass species in cultivated soil

Freshly collected ripe caryopses of twenty-five indigenous grasses were mixed with the top 7–5 cm of sterilized soil confined in cylinders sunk in the ground and cultivated three times yearly. There was a flush of seedlings of most species shortly after sowing, but species differed in the persistence of viable seeds. About one third, including Bromus sterilis, B. hordeaceus, Lolium perenne ssp. perenne, Arrhenatherum elatius and Alopecurus pratensis , produced few seedlings after the initial flush. Others such as Deschampsia cespitosa, Holcus lanatus and Poa trivialis , recognized as forming persistent seed banks in grassland soils, produced appreciable numbers of seedlings in the second year after sowing. Most persistent were species that occur as arable weeds ( Avena fatua, Poa annua ) or in wetlands ( Glyceria plicata, G. maxima, Alopecurus geniculatus ). Emergence from the seed bank generally followed soil disturbance but some species ( Aira praecox, Avena fatua, A. sterilis ssp. ludoviciana, Danthonia decumbens ) exhibited consistent seasonal patterns which may be associated with cyclic changes in germination requirements of the buried seeds.     

Response of selected soilborne fungi and bacteria to herbicides utilized in potato crop management systems in Maine

The response of nine soilborne fungi associated with potato production:Rhizoctonia solani, Fusarium solani ‘Coerculeum,’F. roseum ‘Sambucinum,’F. avenaceum, Helminthosporium solani, Verticillium alboatrum, Alternaria solani, Trihcoderma viride, andLaetisaria arvalis; and five soilborne bacteriaAzotobacter chroococcum, Bacillus subtilis, Erwinia carotovora subsp. carotovora,Pseudomonas aeruqinosa andPseudomonas fluorescens to the herbicides linuron, metribuzin, dinoseb, paraquat, EPTC, and dalapon were determined by growth on amended media. None of the herbicides increased radial growth of the fungi, and only dinoseb significantly (P = 0.05) reduced radial growth of all fungi at concentrations less than 64 ppm. EPTC, dalapon, linuron, paraquat, and dinoseb severely inhibited bacterial survival (91, 82, 44%, respectively) when evaluated on trypticase soy and cimmons citrate agar media amended with herbicides at concentrations of 1, 10, and 100 ppm. Dinoseb, when applied to field soil in pots, significantly reduced total microorganism populations in the top 5 cm of soil. Results suggest that soil applications of herbicides can selectively inhibit soil microflora with possible effects on disease incidence and severity, and may also be a factor in determining effectiveness of biolgical control agents.     

Assessment of some major yield-limiting factors on maize production in a humid temperate environment

Despite the availability of modern hybrids and better agronomic practices, there existed large gaps between attainable yield of maize (Zea mays L.) grown with recommended practices and producers’ harvest yields in the humid temperate regions of eastern Canada. A field experiment was conducted for 3 years in Ottawa, Canada, to determine the most important management yield-limiting factor(s) on rainfed maize grain production. A package of recommended practices (RP) was composed with the recommended levels of nitrogen (N), phosphorus (P), potassium (K), micronutrients, chemical weed control, and plant population density (PPD). Each factor was modified from the RP, making a total of 11 treatments. Under the low occurrence of diseases or insects, weed infestation was the most important yield-limiting factor, which reduced grain yield by 27–38%. While lack of preplant N application (100 kg ha⁻¹) reduced yield by 10–22%, there was no yield increment with additional sidedressing N (50 kg N ha⁻¹). Grain yield was reduced by 8–13% with low PPD (60,000 plants ha⁻¹) in all years, whereas increasing PPD to 90,000 plants ha⁻¹ did not improve yield, compared with the RP. Withhold P application did not affect yield in all years, but yield was reduced by up to 13% in the absence of K, and by 10% and 12% without Zn or Mn, respectively, in 1 year. Our results indicated that lack of weed control (i.e. herbicide use) was the major yield-limiting factor followed by fertilizer N and PPD. The responses of grain yield to K, Zn, and Mn were site and/or year specific. Our study provided experimental data and an insight understanding of yield gap between genotype's yield potential achievable with recommended practices and yields with producers’ practices.     

The nutritive value of some selected Tanzanian plant food sources

The chemical composition of different varieties of field beans (Vicia faba L.), cowpeas (Vigna unguiculata), groundnuts (Voandzeia subterranea), and sorghum (Sorghum vulgare) were determined. Nutrients analysed in these materials included amino acids, starch, sugar, fibre, minerals and antinutritional factors. All the materials were further tested in balance trials with rats; true protein digestibility (TD), biological value (BV), net protein utilization (NPU) and digestible energy (DE) were evaluated. Based on the chemical analyses as well as on the biological data, the nutritive value of plant materials between species as well as between varieties within species differed considerably. Therefore, more quality evaluation studies along with plant breeding programmes are needed to select the most promising varieties from the nutritional point of view.     

Tillage methods for the cropping of sorghum in legume fodder banks in the subhumid zone of Nigeria

Various methods of growing sorghum in stylo fodder banks were studied, with the intention of optimizing grain and fodder yields. Methods included ridging vs. flat seedbed preparation, transplanting vs. seeding, and suppressing or encouraging the growth of the forage legume during food crop growth. Planting on ridges gave 60% higher grain yields than planting on the flat. Yields were also 67% higher compared to direct seeding when sorghum was transplanted. On average, transplanting sorghum on ridges in fodder banks produced 1487 and 5230 kg/ha of grain and fodder, respectively, as compared to the corresponding yields of 1037 and 4946 kg/ha when planted outside the fodder bank. The use of herbicide reduced the legume content by 50% in the total fodder from a fodder bank and thus its nutritive value. As the cropping techniques tested do not deviate substantially from the existing traditional practices, no special cultivation methods are required to crop a land sown with stylo. This could facilitate adoption of short crop-legume ley rotations in the subhumid zone.     

The place of herbicides in the potato crop

Summary Cultivation of potato fields after planting is shown to be primarily for weed control and only of limited benefit to the crop itself. Yields have often been reduced by an excessive number of postplanting cultivations. The conventional management system using frequent post-planting cultivations has the disadvantage of increasing the spread of potato virus X, encouraging the formation of stable soil clods in the ridges by the passage of implements, and increasing susceptibility of the crop to frost after emergence. Moreover, the need for inter-row cultivation imposes a limitation on the spatial arrangement of plants in the field. The potato is highly susceptible to weed competition, but comparatively indifferent to the degree of post-planting cultivation. If herbicides are to replace cultivation as a method of weed control they must be effective and leave no toxic residue in the tubers. Suitable herbicides, many of them mixtures, have been found and specific local recommendations have been made. No single herbicide or mixture of herbicides is likely to be successful under the wide range of growing conditions and weed problems met in practice. The implications of replacing cultivation with herbicides are being widely investigated but so far no alternative to the system of plant arrangement in standard use has shown an outstanding advantage.

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Zusammenfassung Wichtigste Aufgabe der Bodenbearbeitung nach dem Auspflanzen ist die Bek?mpfung der Unkr?uter; sie ist für die Kartoffel von geringem direktem Nutzen. Obwohl die Ertr?ge in Versuchen oft durch übertriebene Bodenbearbeitung vermindert wurden. bleibt der weitverbreitete Glaube bestehen, dass Kartoffeln nicht ohne h?ufige und gründliche Bodenbearbeitung erfolgreich angebaut werden k?nnen. Bodenbearbeitung nach dem Auspflanzen bewirkt vorübergehend eine Bek?mpfung des Unkrauts, hat aber den Nachteil, die weitere Keimung von Unkraut zu f?rdern, das Kartoffelvirus X auszubreiten und z?he Erdklumpen zu bilden, die bei der mechanisierten Ernte st?rend wirken; ferner dürfte unter gewissen Umst?nden der gelockerte Boden weniger W?rme abgeben, was die M?glichheit von Sch?den durch Ausstrahlungsfroste am Blattwerk erh?ht. Ein weiterer Nachteil aller Formen mechanischer Reihenbearbeitung liegt in der Beschr?nkung, die sie der r?umlichen Anordnung der Pflanzen im Feld auferlegt. Die Kartoffel ertr?gt die Konkurrenz des Unkrautes nicht gut. Wenn Herbizide die mechanische Bodenbearbeitung als Unkrautbek?mpfungsmethode ersetzet sollen, müssen sie wirksam sein und keine sch?dlichen Rückst?nde in den Knollen hinterlassen. Herbizide variieren in ihren Wirkungen auf die Kartoffel, und in kleinerem Ausmass reagieren auch die Kartoffelsorten unterschiedlich. Verschiedene Herbizide sind nun zur Anwendung vor dem Auflaufen der Pflanzen empfohlen worden, n?mlich Paraquat, Dinoseb, Linuron, Monolinuron und Prometryn. Nach dem Auflaufen werden die Pflanzen leichter durch Herbizide gesch?digt, und obwohl 2,4-D und MCPA in begrenztem Umfang angewendet wurden, wird keines dieser Mittel sehr empfohlen. Behandlung mit Dalapon oder TCA vor dem Auspflanzen wird ebenfalls praktiziert, wenn das Grundstück mit Quecken (Agropyron repens) stark verunkrautet ist. Die h?ufig gebrauchten Herbizide im Kartoffelbau sind in dertabelle zusammengestellt. Offizielle Empfehlungen für die Anwendung von Herbiziden vor den Auspflanzen und vor dem Auflaufen basieren auf lokalen Bedingungen,und weder ein allgemein zuverl?ssig wirksames, einzelnes Herbizid, noch eine Mischung von Herbiziden hat Aussicht, bei der Vielfalt der Wachstumsbedingungen und der Unkrautprobleme in der Praxis erfolgreich zu sein. Wenn die Zahl der Bearbeitungsg?nge durch das Kartoffelfeld nach dem Auspflanzen durch die Anwendung von Herbiziden vermindert werden kann, werden sich zwei unmittelbare Vorteile ergeben. Erstens wird die Ausbreitung des Kartoffelvirus X eingeschr?nkt und zweitens wird die Erdklumpenbildung fast ganz verhütet. Wenn die Erdklumpenbildung verhütet werden k?nnte, würde dies die vollmechanisierte Ernte auf schwereren B?den sehr erleichtern. Die jetzt gebr?uchlichen Reihenabst?nde k?nnten radikal ge?ndert werden, wenn die mechanische Bodenbearbeitung nach dem Auspflanzen sich erübrigen würde, doch hat sich aus den untersuchten, alternierenden Versuchsverfahren noch kein anhaltender Vorteil ergeben.

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Résumé Nous avons montré que la fonction première de l'ameublissement du sol après la plantation était de détruire les mauvaises herbes; cet ameublissement a peu d'avantage direct pour la récolte. Bien que les expériences ont montré qu'un travail excessif du sol réduit souvent les rendements, l'opinion est largement répandue selon laquelle les pommes de terre ne peuvent donner un plein rendement sans de fréquents et complets ameublissements du sol. Le travail du sol après plantation réalise une destruction temporaire des mauvaises herbes mais il apporte aussi les désavantages de favoriser la germination de nouvelles mauvaises herbes, de propager le virus X de la pomme de terre et de former des mottes de terre dures qui contrarient la récolte mécanique; en outre, un sol dérangé peut, sous certaines circonstances, rayonner moins de chaleur durent les gelées par rayonnement accroissant ainsi les chances de dommages du froid au feuillage. Un inconvénient supplémentaire de toutes les formes de travail du sol entre les lignes est qu'il limite les dispositions spatiales des plantes dans le champ. La pomme de terre est très susceptible à la compétition des mauvaises herbes. Si les herbicides doivent, en tant que méthode de destruction des plantes nuisibles remplacer le travail du sol, ils doivent être efficaces et ne laisser aucun résidu nuisible dans les tubercules. Les herbicides ont des effets variables sur la pomme de terre, et, à un degré moindre, les variétés diffèrent dans leur réaction. Actuellement plusieurs herbicides ont été recommandés pour l'utilisation avant la levée, notamment les paraquat, dinoseb, linuron, monolinuron et prométryne. Apès la levée, la culture est plus facilement endommagée par les herbicides et, bien que le 2,4-D et le MCPA aient été utilisés dans une mesure limitée, aucun n'est largement recommandé. Le traitement avant la plantation avec le dalapon ou le TCA est également pratiqué là où le chiendent (Agropyron repens) infeste le sol. Dans letableau figurent les herbicides communément utilisés dans la culture de la pomme de terre. Les recommendations officielles pour l'utilisation d'herbicides avant la plantation et avant la levée sont basées sur les conditions locales et aucun herbicide simple ou mélange d'herbicides ne peut être universellement utilisé avec pleine efficacité et en toute sécurité dans les nombreuses conditions de croissance et pour tous les problèmes de mauvaises herbes rencontrés dans le pratique. Deux avantages immédiats résulteront de la réduction de la circulation dans le champ après plantation grace à l'utilisation des herbicides: d'abord l'extension du virus X peut être réduite et, ensuite, la formation de mottes de terre est presque totalement empêchée. Si l'absence de mottes pouvait être assurée, l'arrachage complètement mécanique dans les sols lourds serait grandement facilité. Les espacements entre les lignes en usage présentement pourraient être radicalement changés si le travail du sol après la plantation n'était pas plus longtemps requis, mais les divers espacements qui ont été expérimentés n'ont pas encore révélé de valeur certaine.

     

Effect of domestic processing and cooking on selected antinutrient contents of some green leafy vegetables

Three vegetables, 5 roots and tubers, 23 fruits and 3 stored products collected and consumed by tribals of Andhra Pradesh, India were analyzed for total carotenoids (TC) and Beta carotene (BC) contents using High Performance Liquid Chromatography (HPLC). The vitamin A activity expressed as retinol equivalents (RE) was calculated based on the in vivo conversion factor given by WHO. The results of the study indicated that the vegetables, roots and tubers analyzed showed negligible vitamin A activity with TC and BC content ranging from 0.01 to 0.61 and 0.14 to 0.23 mg%, respectively. Among the fruits, Canthium parviflorum contained very high TC (9.51 mg%) and BC (6.10 mg%) contents, and the edible orange color fresh rind portion analyzed had the highest (6.8 mg%) BC content. Other fruits contained negligible content of TC (0.0015 to 1.32 mg%) and BC (0.004 to 0.49 mg%). The edible pulp portion of the fruit (Diosphros melanoxylon contained no BC but the rind portion analyzed fresh and dried had BC) 0.79 and 2.17 mg%, respectively. Tribals were found to have distinct attitudes and beliefs towards food they use or avoid in certain physiological conditions.     

The effect of photoperiod on flowering and TPS production in the warm tropics

Summary Three similar field experiments with five cultivars were carried out to evaluate the effect of a 5-hour extension of the natural daylength and a 3-hour night break on flowering and TPS production in the warm tropics. Shoot length, number of inflorescence positions per plant and number of flowers per inflorescence varied considerably between the experiments. In each experiment, the supplementary photoperiods delayed cessation of shoot growth and thereby increased the orders of branching and the number of inflorescence positions per plant. The photoperiod treatments significantly increased the number of flowers at the last produced inflorescence positions, but not at other ones. Pollen production and quality, berry set, seed set and 100-seed weight were not affected by the photoperiod treatments. TPS production was characterized by variability in flowering and low and variable seed production per flower.     

大豆田除草剂混用技术及药害

为了指导大豆田杂草防除技术,介绍了大豆田杂草发生的主要种类与特点,除草剂混用品种的选择,除草剂药害的分类,除草剂药害调查分级与除草剂混用性能比较等,以及大豆田杂草防除技术和施用除草剂混剂不当造成的药害.     

Techniques for using sprouts for potato production in the tropics

A series of experiments were conducted in Vietnam to develop a system whereby detached sprouts from physiologically old green sprouted seed tubers could be used to grow potatoes. Three node segments from the mid or basal portion of the detached sprout produced the greatest percentage of shoots and roots. Growth was best in a medium of equal parts of sub-soil, pig manure and brick kiln ash. Sprout cuttings produced plantlets ready for transplanting in 14–20 days with mean daily temperatures of 22 to 24°C. When transplanted in mid-November, yields from sprout cuttings in field experiments were 10 to 18 t/ha which were 33% lower than from healthy seed tubers but more than the national average yield using degenerated seed tubers. Tubers produced by plants grown from sprout stored well and gave good yields when replanted the following year. Requests for reprints to International Potato Center, Box 933, Manila, Philippines.     

Rapid multiplication of potatoes in the warm tropics: rooting and establishment of cuttings

Summary To expand potato production in developing countries using cuttings as a source of good quality planting material, requires simple low cost methods to root and establish them. Experiments at a warm tropical site in the Philippines, to determine appropriate methods, showed that simple media ranging from fine sand to clay subsoil mixed with rice hulls enabled rooting which was not improved by hormones. Nitrogen rich media, such as volcanic soil or compost with additional P, were best for developing cuttings into strong transplants but there were no major differences in root and shoot development from cuttings differing in size and age. Tuberizations was favored by increasing the number of nodes buried in the media. Low solar radiation of 7 MJ/m²/day enabled high cutting survival up to root initiation, after which higher radiation supported larger root and shoot production.     

Persistence of chlorpyrifos residues in potatoes and the effect of processing

Summary Chlorpyrifos was sprayed on the ridges and foliage of potato plants at 0.4, 0.5 and 0.6 kg a.i./ha 21 days after planting (single spray) and repeated 21 days after the first spray (double spray) to control cutworms (Agrotis sp.). In unprocessed (i.e. not washed, boiled or peeled) potatoes, the residues persisted above the permitted level of 0.10 ppm on several sampling dates. Residues decreased with the time interval between spraying and sampling. Processing potatoes (i.e. washing, boiling followed by peeling) removed the toxicant to a considerable extent. Storing potatoes from chlorpyrifos-treated plots in country stores for 30 days after normal harvest reduced residues to below the detectable level irrespective of the application rate.

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Zusammenfassung Feldversuche mit sieben Behandlungen in vier Wiederholungen mit randomisierter Blockanlage wurden w?hrend des Herbstes 1979–80 und 1980–81 in der zentralen Kartoffelforschungsstation in Jalandhar (Punjab, Indien) durchgeführt, um die Rückst?nde des Insektizids Chlorpyrifos in Kartoffelknollen zu bestimmen. Chlorpyrifos wird eine Wirkung gegen Erdraupen (‘cutworms’),Agrotis sp., zugeschrieben. Es wurde auf Reihen und Kraut mit 0,4, 0,5 und 0,6 kg aktiver Substanz pro Hektar, einmal 21 Tage nach dem Pflanzen (Einfachspritzung) und dann 21 Tage sp?ter (Doppelspritzung) ausgebracht. Die Rückst?nde in den Kartoffelknollen wurden anhand der kolorimetrischen Methode von Getz & Watt (1964) bestimmt. In unverarbeiteten Kartoffeln (d.h. nicht gewaschen, gekocht oder gesch?lt) verblieben Rückst?nde oberhalb der erlaubten Grenze von 0,10 ppm bei zahlreichen Terminen der Probenahme. Die Mengen nahmen mit der Zeit zwischen Spritzen und Probenahme ab. Kartoffelverarbeitung (d.h. Waschen, Kochen mit anschliessendem Sch?len) hatte starke Reduzierung des Giftstoffes zur Folge. 30-t?gige Lagerung in l?ndlichen Lagern nach normaler Ernte reduzierte die Rückst?nde unter die Erfassungsgrenze, in beiden Jahren und bei allen Dosierungen. Die detaillierten Daten für die Rückst?nde werden in den Tabellen 1 und 2 gezeigt.

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Résumé Des essais de plein champ comprenant 7 traitements à 4 répétitions dans un dispositif à blocs randomisés ont été réalisés sur la Station de recherche de la pomme de terre à Jalandhar (Punjab) en Inde au cours des automnes 1979–80 et 1980–81, afin de déterminer les teneurs en résidus de l'insecticide chlorpyrifos dans les tubercules de pommes de terre. Le chlorpyrifos est un produit efficace contre les larves d'Agrotis sp. Il fut appliqué sur buttes et sur feuillage à la dose de 0,4, 0,5 et 0,6 kg de matière active à l'hectare, 21 jours après la plantation (une seule application), ou encore 21 jours après (en double application) puis les résidus dans les tubercules furent déterminés par la méthode colorimétrique de Getz et Watt (1964). Dans les tubercules non transformés (c'est-à-dire sans lavage, sans cuisson ou pelage) les teneurs en résidus étaient au dessus du seuil de tolérance de 0,10 ppm dans plusieurs échantillons. Les pommes de terre transformées (après lavage, cuisson et pelage) avaient beaucoup moins de résidus. La conservation dans les batiments de stockage de pays, pendant 30 jours après une récolte normale, a permis de réduire les teneurs en dessous du seuil décelable au cours des 2 années, quelle que soit la dose testée. Les teneurs en résidus sont détaillées dans les tableaux 1 et 2.

     

Developing rice cultivars for high-fertility upland systems in the Asian tropics

Traditionally, upland rice is grown in Asia in low-input, subsistence systems. More productive upland systems, using more fertilizer and improved varieties, are emerging in China and Philippines, and could contribute to productivity increases in rainfed environments in other countries. Here, we evaluate, on-station and on-farm, the yield under upland management of improved indica upland cultivars selected for yield under high-fertility conditions. These cultivars are compared with traditional and improved tropical japonica upland varieties, and with elite indica high-yielding varieties (HYV) developed for irrigated lowland production, to characterize the features of varieties that produce high yields in favorable upland environments. Forty-four improved and traditional varieties and experimental lines were evaluated in irrigated lowland, non-stressed upland, moderately stressed upland, severely water-stressed upland, and low-fertility upland environments in southern Luzon, Philippines. Correlations between yields in non-stress and mild-stress environments were low but positive. Some cultivars, like IR55423-01, were among the highest yielding under both conditions, indicating that high yield and moderate water-stress tolerance can be combined. Upland-selected indica varieties yielded 3.56 t ha⁻¹ in favorable upland environments on-station in southern Luzon, outperforming improved tropical japonica and irrigated varieties by 23 and 69%, respectively. They were also the highest-yielding class in infertile, acid soils. The improved upland indica cultivars are about 110 cm tall under favorable upland conditions and maintain a harvest index of nearly 0.4, or about one-third higher than other cultivar types. The best upland-adapted rice varieties produced average yields on-farm of 3.3 and 4.1 t ha⁻¹ in southern Luzon and Yunnan, respectively, outyielding traditional checks by 30–50% with moderate N application. Screening under both high-fertility, non-stress conditions and moderate reproductive-stage stress appears to be needed to develop cultivars combining high-yield potential with drought tolerance. Upland-adapted indica cultivars offer a new approach to increasing productivity and reducing risk in Asian rainfed rice systems.     

Persistence of an oilseed rape transgene in the environment

Transgenic bromoxynil (BX)-resistant spring oilseed rape (Brassica napus L.) was grown commercially in Canada only for two crop seasons – 2000 and 2001. We investigated the persistence of suspected BX-resistant oilseed rape volunteers in a 64-ha wheat field in Saskatchewan, Canada in 2007, 7 years after the BX-resistant cultivar BX Armor was grown. A small oilseed rape volunteer population, estimated at less than 100 plants, was observed in three main areas or patches in the field. These patches were located in low-lying areas that were too wet to plant or spray with herbicides in 2007. Viable seed was collected from 35 mature volunteers and F₁ progeny screened with BX at 280 g ai/ha in the greenhouse. Progeny of all of the volunteers were visually rated as BX-resistant; the presence of the Oxy 235 transgene in leaf tissue of progeny of all volunteers was confirmed by PCR analysis. This study has documented the longest persistence of oilseed rape volunteers in Canada. Volunteers were not observed in 2008 or 2009, because of drought conditions in spring of both years. Results support the findings from previous studies that persistence of volunteer oilseed rape populations in western Canada is generally ephemeral or transitory in the absence of seed bank immigration. However, this study shows that oilseed rape transgenes can persist in the environment for a number of years even after all cultivars with the conferred trait are removed from the market.     

Genetic analysis of resistance to green leafhopper Nephotettix virescens (Distant) in some selected rice varieties

The genetics of resistance to green leafhopper, Nephotettix virescens (Distant), in 15 cultivars of rice, Oryza sativa L., was studied. Results showed that cvs Katia Bagder 13–20, Laki 659, Lasane, Asmaita, and Choron Bawla possess two dominant genes for resistance. Single dominant genes convey resistance in cvs Hashikalmi, Tendeng, Rhissa, Ghaiya, ARC 10313, Chiknal, Garia, Bagdar and Chota Digha. Allele tests revealed that one of the two dominant genes of Choron Bawla is allelic to Glh-2. The single dominant gene in Chiknal and one of the two genes of Laki 659 are allelic to Glh-3. The second of the two genes of Katia Bagder 13–20, Laki 659 and Lasane are allelic to Glh-5. The two dominant genes of Asmaita and the single dominant genes of Hashikalmi, Ghaiya, ARC 10313 and Garia are non-allelic to and independent of Glh-1, Glh-2, Glh-3, glh-4 and Glh-5. The allelic relationships of these genes are not known and should be investigated.