Soil metabolism of the herbicide napropamide in cereals, maize, sugar beet and vegetable field replacement crops

The metabolism of the herbicide napropamide has been studied in the field in the soil of replacement crops (cereals, corn, sugar beet, potato and several vegetables). Napropamide was soil applied in the autumn and the soil left fallow during the winter. Crops were sown in April of the following year and simulated the replacement crops that are grown in the event of failure of the first autumn-sown crop. Trials were made twice, i.e. during the 1987-1988 and 1988-1989 crop seasons. The soil metabolism of napropamide was also studied in a rose nursery. Napropamide was transformed by microbiological processes in the soil into the corresponding monoethylamide and acid. These compounds did not generally accumulate in the soil, and their individual concentrations did not exceed that of residual napropamide during the observed growing seasons. The kinetics, metabolic pathways and agricultural implications of the herbicide are briefly discussed.     

Tolerance ofsclerotinia sclerotiorum to glyceollin i,a soybean phytoalexin

Glyceollin I was fungistatic rather than fungicidal towardSclerotinia sclerotiorum. Within the mycelial mat apical cells were more vulnerable than mature cells.S. sclerotiorum removed large amounts of glyceollin from solution by a non-energy-requiring process. Contribution from Ministero dell’Università e della Ricerca Scientifica e Tecnologica.     

Preliminary studies on the insecticidal activity and wash-fastness of twelve pyrethroid treatments impregnated into bednetting assayed against mosquitoes

The insecticidal properties of twelve pyrethroid preparations impregnated into polyester netting were compared, before and after washing, with a view to assessing their suitability for treating bednets (mosquito nets) in the field. Bioassays were carried out by exposing the mosquitoes, Anopheles gambiae Giles sensu stricto andAedes aegypti L. to netting with two concentrations of insecticide, on washed and unwashed samples, for 30 s and 3 min at different times after impregnation. Mortality was recorded after 24 h. Permethrin applied at 97°C at pH 3.4 resulted in increased uptake by polyester fibres. The performance of most insecticides on unwashed netting had not declined appreciably 12 weeks after impregnation. However, all the insecticides were depleted by washing. The treatments with best insecticidal activity after washing were cypermethrin, lambda-cyhalothrin applied at ambient temperature and normal pH and permethrin applied in a hot acid solution.     

A computer-based system for the management of the rust disease of French prunes1

Rust (Tranzscheliu discolor) is the most important disease of French prunes in New South Wales (NSW), Australia. Infection by this fungus occurs only when leaves are wet. The length of time for which the leaves are wet and the temperature during such periods are major determinants of whether infection occurs and its likely severity. The use by prune growers of new rust management strategies depends on knowledge of infection events and therefore requires ready access to environmental data from orchards. To satisfy this need, microprocessor-based device called a Prune Rust Infection Predictor (PRIP) was developed. The instrument measures air temperature, rainfall, and the presence or absence of free water tree canopies. Measurements are taken at 5-min intervals during wet periods. The instrument calculates whether or not conditions have been suitable for rust infection and potential severity of infection. The system has been operated by advisory staff of NSW Agriculture Fisheries since the 1988/1989 growing season. Potential infection period and related environmental data are collected by personal computers via permanently installed telephone lines from PRIPs located within prune orchards. Prune growers are then advised by recorded telephone messages and given appropriate disease mangement advice. Cumulative potential infection period values are used to provide a prognosis of current-season rust epidemic severity. An expert system is also being developed to assist growers in making decisions on specific rust management options.     

Pectate lyases of Erwinia chrysanthemi: Pel E-like polypeptides and pelE homologous sequences in strains isolated from different plants

Pel E, one of the four major pectate lyases produced by Erwinia chrysanthemi (Echr) strain EC16, was purified to homogeneity and was found to have an apparent molecular weight of 47 500 and a pI of 10. Antibodies produced against this preparation inhibited Pel E activity, but did not affect Pel A, Pel B or Pel C activities. Immunotitration revealed that Pel E accounted for a major fraction of the total extracellular Pel activity ranging from 40–60% in culture and potato tuber tissue. Isoelectric focusing of the extracellular Pels produced by various Echr strains indicated that while the Pel profiles of strains isolated from various hosts were different, the profiles of strains isolated from the same host were very similar. A significant proportion (ranging from 39 to 74%) of the Pel activity of these strains was inhibited by the anti-Pel E antibodies. DNA hybridization under stringent conditions indicated the presence of pelE homologous sequences in the genomes of E. chrysanthemi strains. We conclude that a Pel E-like enzyme occurs in all E. chrysanthemi strains examined.     

Rhizobacteria with broad-spectrum antifungal activity*

Antifungal rhizobacteria were obtained from maize, barley and chicory using direct or indirect isolation procedures. Effective isolates were tested for broad-spectrum activity against a set of phytopathogenic fungi. Isolates with broad-spectrum activity were identified as Pseudomonas fluorescens, P. cepacia, Serratia liquefaciens, S. plymuthica and Bacillus sp. Broad-spectrum compounds produced by P. cepacia and Erwinia herbicola were characterized as pyrrolnitrin and herbicolin-like compounds respectively.     

一种由麦二叉蚜和麦长管蚜传播的小麦黄矮病毒株系的鉴定

 通过对采自我国内蒙古丰镇县13个春小麦病株标样进行4种蚜虫连续传毒比较,不同温度饲毒和接种试验,薄膜饲毒,2种蚜虫成若蚜传毒比较和血清学酶标试验等,明确我国内蒙古丰镇县小麦黄矮病毒株系为由麦二叉蚜和麦长管蚜有效传播的麦二叉蚜麦长管蚜株系(GAV)。对于这个株系,禾缢管蚜与玉米蚜是不能传播的。这种株系在我国冬麦区春麦区都有分布。     

Identity and pathogenicity of Rhizoctonia spp. associated with bare patch disease of cereals at a field site in Western Australia

Roots of seedlings of wheat and barley affected by bare patch disease at a field site in Western Australia were assessed for root damage and plated to isolate fungi. The patches were variable in shape and size and had the most severely affected plants in the centre. Of the 165 isolates ofRhizoctonia spp. obtained, 90% were multinucleate and 10% binucleate, the former being predominant in the plants at the centre of the patch. The relative frequency of binucleate isolates increased with proximity to the periphery. The increase in activity of avirulent binucleate isolates towards the periphery of the patch may be related to the sharp and abrupt edging of the patch. A variety of other species of fungi such asFusarium spp.,Mortierella spp.,Bipolaris sorokiniana, Pythium sp. andTrichoderma sp. were encountered within the patches. The multinucleate isolates belonging to anastomosis groups (Ag) 2–1, 2–2 and 8 (Thanatephorus cucumeris) were most pathogenic to wheat. The binucleate isolates of Ag C, D, E, and K (Ceratobasidium sp.) were less pathogenic. It is suggested that the bare patch disease is caused by a complex of root rot fungi composed of one or more anastomosis groups ofRhizoctonia spp. and other associated fungi.Samenvatting Van kiemplanten van tarwe en gerst, afkomstig van een met kale-plekkenziekte besmet perceel in West Australië werd de mate van wortelbeschadiging bepaald en werden schimmels uit de wortels geïsoleerd. De plekken waren verschillend van vorm en afmeting; de zwaarst aangetaste planten werden in het centrum ervan aangetroffen. Van de 165 verkregen isolaten vanRhizoctonia spp. was 90% meerkernig en 10% tweekernig. De meerkernige overheersten in de centra van de plekken. Relatief gezien nam het aantal tweekernige isolaten toe naarmate de herkomst dichter bij de periferie van de plekken was. De scherpe begrenzing van de ziekte aan de randen van de plekken zou in verband kunnen staan met het toenemen van de activiteit van de avirulente tweekernige isolaten in de nabijheid van de periferie van de plekken. Een aantal andere schimmels, zoalsFusarium spp.,Mortierella spp.,Bipolaris sorokiniana, Pythium sp. enTrichoderma sp. werd eveneens in de plekken aangetroffen. De meerkernige isolaten die tot de anastomosegroepen Ag 2–1, 2–2 en 8 (Thanatephorus cucumeris) behoren, waren voor tarwe het meest pathogeen. De tweekernige isolaten van de anastomosegroepen Ag C, D, E en K (Ceratobasidium sp.) waren minder pathogeen. Gesuggereerd wordt, dat de kale-plekkenziekte veroorzaakt wordt door een complex van verschillende wortelschimmels, die behoren tot een of meer anastomosegroepen vanR. solani en andere daarmee geassocieerde schimmels.     

The use of incidence counts for estimation of cereal aphid populations. 3. Population development and the incidencedensity relation

The relation between the population density of the cereal aphid,Sitobion avenae, and the proportion of wheat tillers infested is examined. Three of the six models considered require the assumption that the aphids' spatial configuration can be described by a single statistical distribution; as this is not true forS. avenae these models are unsuitable. When the other three models were applied to field sample data, only that of Nachman (1981) yielded a regression equation that remained constant throughout the development of the aphid population.Samenvatting Om in de praktijk gebruik te kunnen maken van incidentie (de fractie bezette halmen) voor het schatten van graanluispopulaties moet dezelfde relatie tussen dichtheid en incidentie tijdens het hele groeiseizoen gelden. Uit analyses van veldgegevens voor de graanluisSitobion avenae blijkt dat wel het geval te zijn, zodat bepalingen van incidentie kunnen worden gebruikt om de populatiedichtheid betrouwbaar te schatten.     

Potato plant response to seed tuber bacterization in the field in various rotations

The effects of a seed tuber treatment with antagonistic isolates of fluorescentPseudomonas spp. were investigated on potato plants from 1981 to 1984. The experimental plots were located in fields in short and long rotations of potato. The short rotations are characterized by serious yield reductions which are caused by unknown microbial factors. The reductions varied from 30% in 1982 to only 3% in 1983 in the 3-year rotations. A statistically significant increase in yield (four to five months after planting) of ware potatoes varying from 9 to 20% was obtained in these plots through tuber bacterization, but only in 1981. In 1982 and 1983 initially significant improvements in shoot or tuber weight of seed potatoes were no longer detectable at ware potato harvest at the end of the growing period. Seed tuber bacterization had no effect on tuber yield in long rotations. Initial colonization of basal root parts by 53×10⁴ colony forming units (cfu) of antibiotic-resistant mutants per gram of root (fresh) dropped significantly to 20×10⁴ cfu per gram after three months. The bacterization effect on tuber yield depended on the development of harmful microbial activity and of introduced antagonists during the growing period. Seed tuber bacterization is more promising for seed potatoes than for ware potatoes in short rotations, the latter being harvested two months later.Samenvatting De invloed van pootgoedbehandeling met antagonistische isolaten van fluorescerendePseudomonas-soorten op de aardappelteelt, werd onderzocht in de periode van 1981 tot en met 1984. De proefvelden maakten deel uit van zowel ruime als nauwe rotaties met aardappelen. Kenmerkend voor de nauwe rotatie is, dat de opbrengst aanzienllijk gereduceerd wordt als gevolg van de aanwezigheid van nog onbekende microbiële factoren. Deze opbrengstverlaging varieerde van 30% in 1982 tot slechts 3% in 1983 in de 3-jarige rotaties. Pootgoedbacterisatie had in deze proefvelden een significante toename van de eindopbrengst (vier tot vijf maanden na pootdatum) van consumptieaardappelen tot gevolg, die varieerde van 9 tot 20%, echter allen in 1981. In 1982 en 1983 werd het effect van bacterisatie ook in de loop van de groeiperiode onderzocht. Aanvankelijk significante toenames van zowel spruit-als knolgewicht waren aan het einde van het groeiseizoen niet meer aantoonbaar. Pootgoedbacteristie bleek geen effect te hebben op aardappel in ruimte rotaties. Aanvankelijk werden de basale wortelgedeelten gekoloniseerd door antibioticum-resistente mutanten met 53×10⁴ kolonievormende eenheden (kve) per gram wortel(vers); dit aantal liep (drie maanden na pootdatum) echter significant terug tot 20×10⁴ kve per gram. Het effect van bacterisatie op de eindopbrengst werd bepaald door de ontwikkeling van de schadelijke microbiële activiteit en de ontwikkeling van de geïntroduceerde antagonisten tijdens het groeiseizoen. Pootgoedbacterisatie in nauwe rotaties biedt meer mogelijkheden voor de teelt van pootaardappelen dan die van consumptieaardappelen, die geruime tijd later geoogst worden.