Effect of rotation of cowpea (Vigna unguiculata) with fonio (Digitaria exilis) and millet (Pennisetum glaucum) on Macrophomina phaseolina densities and cowpea yield

Macrophomina phaseolina, the causal agent of charcoal rot, causes great damage to cowpea in the Sahel. One of the few options to manage the disease is by cropping nonhosts that may reduce the soil inoculum below a damage threshold level. To test this, fonio (Digitaria exilis) and millet (Pennisetum glaucum) were cropped continuously for 3 years in plots with a natural infestation of 24-53 microsclerotia g(-1) soil at the onset of the experiment. Next, a susceptible cowpea variety was grown to quantify disease incidence and severity on these soils. Fonio and millet both reduced microsclerotial densities in soils from the first year onwards. Reductions under fonio (81% after the 2(nd) year; 86% after the 3(rd) year) were significantly stronger than under millet (56 and 66% for the 2(nd) and 3(rd) year respectively). Fonio was not infected by M. phaseolina, while the root systems of millet had low densities of microsclerotia. Cowpea yielded significantly more hay and pods after 3 years of fonio than of millet. Cowpea yields and disease incidence (dead plants) could be explained well by pre-planting microsclerotial densities. We conclude that rotation of cowpea with a gramineous crop may lead to a relatively fast decline of inoculum density. In the case of a high inoculum density, fonio can be grown for three years to reduce M. phaseolina densities in soi

The potential of biological soil disinfestation to manage Fusarium foot and root rot in Asparagus

In a field experiment on an abandoned asparagus field we studied the effect of Biological Soil Disinfestation (BSD) on survival of buried inoculum samples of three test pathogens (Fusarium redolens f.sp. asparagi (FRA), Rhizoctonia tuliparum (RT) and Verticillium dahliae (VD)) and on the Fusarium infestation level. The BSD treatments involved incorporation of grass into moist soil and covering the soil with airtight plastic. The amount of grass incorporated was varied (42, 62 or 102 tons of grass/ha) as well as the depth of incorporation (40 or 80 cm). It was found that BSD greatly reduced all three pathogens in buried soil samples and that incorporation of 62 or 102 tons of grass per ha to 80 cm soil depth resulted in a significant decrease in soil infestation in the upper 40 cm; in the deeper layer the decrease was lower. Asparagus plants grown from seed in the field for one year showed a strong decrease in Fusarium root rot severity with all BSD treatments. The results clearly show the potential of BSD to decrease soil infestation levels of Fusarium pathogens and to contribute to an enhanced life span of replanted asparagus crop

Assessing risks and benefits of floral supplements in conservation biological control

The use of flowering field margins is often proposed as a method to support biological control in agro-ecosystems. In addition to beneficial insects, many herbivores depend on floral food as well. The indiscriminate use of flowering species in field margins can therefore lead to higher pest numbers. Based on results from field observations and laboratory experiments we assessed risks as well as benefits associated with the provision of nectar plants in field margins, using Brussels sprouts as a model system. Results show that Brussels sprouts bordered by nectar plants suitable for the cabbage white Pieris rapae L., suffered higher infestation levels by this herbivore. In contrast, nectar plants providing accessible nectar for the diamondback moth Plutella xylostella L., did not raise densities of P. xylostella larvae in the Brassica crop. Margins with Anethum graveolens L., selected on the basis of its suitability as nectar plant for parasitoids, significantly increased the number of adult Diadegma semiclausum Hellen in the crop. This didn't translate into enhanced parasitism rates, as parasitism of P. xylostella by D. semiclausum exceeded 65 % in all treatments, irrespective of the plants in the field margin. Our findings emphasize the importance of taking a multitrophic approach when choosing flowering field margin plants for biocontrol or other ecosystem service

The sustainability of cotton : consequences for man and environment

This project aimed to summarise literature that compares conventional, IPM, and organic cotton production systems in terms of environmental impact; to select indicators which can be used to compare the environmental impact of conventional, IPM, and organic cotton production systems and to start a discussion on the social aspects relevant for trade in sustainable cotton

Decline of carpophores of mycorrhizal fungi in stands of Pinus sylvestris

The carpophores of mycorrhizal fungi have declined drastically during this century in the Netherlands and in other European countries. In contrast, saprophytic and pathogenic fungi did not show a significant change. In this thesis, the possible causes of the decline of mycorrhizal mycoflora have been examined. The hypothesis was put forward that the functioning of mycorrhiza was hampered, either through a decrease of tree vitality or by changes in soil chemistry, both resulting from air pollution. Pinus sylvestris was chosen as study object, because in the Netherlands (1) its vitality has decreased considerably, (2) mycorrhizal mycoflora of coniferous tree species decreased more strongly than that of deciduous species, (3) it is the only native conifer which possesses ectomycorrhizas and (4) plantations of P. sylvestris of the same age and on the same soil type can be found throughout the country.In a pot experiment, mycorrhizas of Paxillus involutus appeared to be sensitive to SO 2 fumigation alone, or in combination with NH 3 pollution, in contrast to mycorrhizas of Laccaria proxima . Photosynthesis, measured on P. involutus -inoculated seedlings, was inhibited by SO 2 fumigation. However, effects on plant growth were negligible (Chapter 2).Nitrate and ammonium salts in a pot experiment had a significant negative effect on the mycorrhizas ( Paxillus involutus and Suillus bovinus ), and a significant positive effect on plant growth. Ammonium treatments affected the seedlings more positively and the mycorrhizas more negatively than nitrate. The N content of seedling needles fertilized with ammonium was higher than those treated with nitrate. It was suggested that a high N uptake by the plant decreased the carbohydrate availability for the mycorrhizal fungi (Chapter 3).Ammonium and nitrate fertilization at rates of 0, 30 and 60 kg N ha -1yr -1in two young stands of P. sylvestris during three years had a similar, significantly negative effect on the number and total dry weight of carpophores and on the number of fruiting species. However, the number of carpophores of Laccaria proxima increased due to the fertilization treatments in one stand. Mycorrhizal frequency and number of mycorrhizas were not affected (Chapter 4).Field observations revealed that the mycorrhizal mycoflora of young stands of P. sylvestris included species which have become rare during this century in the Netherlands (Chapter 5). Especially in first rotation young stands on drift sands many of these species were found, several of them in large numbers. This seems to be related to the fact that first rotation stands have become rare in the Netherlands. There was a considerable difference in the mycorrhizal mycoflora of first rotation young stands compared to that of second rotation young stands and of old stands. However, a literature survey showed that the fungal species which appeared to occur specifically in the first rotation young stands were also common in humus-rich and mature stands in Poland, Finland and Russia. Possible explanations for this difference are discussed.In 50 to 80-year-old stands of P. sylvestris , the number of mycorrhizal fruiting species as well as the number and total dry weight of their carpophores had highly negative correlations with the NH 3 deposition and ambient NO x concentration, and to a lesser extent with ambient SO 2 concentration (Chapter 6). The mycorrhizal mycoflora showed insignificant positive correlations with tree vitality, expressed as the needle occupation of the trees. The mycorrhizal mycoflora was very poor in most old plots.Young stands had a much richer mycoflora than old stands. Over the three years of field observations, more species (factor 3) and more carpophores (factor 13) were found in the young plots.The mycorrhizal mycoflora in 5 to 10-year-old stands was negatively influenced by infection of trees by Lophodermium seditiosum. High positive correlations were found with ambient NO x concentrations and could be partially ascribed to infection by L.seditiosum, which occurred in the less polluted areas.The mycorrhizal frequency exceeded 95% in all but one of the old plots and in all young plots, indicating that the decrease of carpophores preceedes that of mycorrhizas.The following conclusions were drawn:(1) No decline of carpophores of mycorrhizal fungi could be detected in young stands of P.sylvestris, this in contrast to the situation in old stands.(2) The carpophores of mycorrhizal fungi in young stands are negatively affected by (artificial) nitrogen fertilization. The mycorrhizas of seedlings can be negatively affected by nitrogen fertilization and by SO 2 fumigation.(3) The nitrogen effect on the mycorrhizas is likely to be a result of decreased supply of carbohydrates by the plant, caused by the increased uptake of nitrogen compounds.(4) The effects of nitrogen deposition and SO 2 pollution on P.sylvestris and mycorrhiza depend on the fungal species involved.(5) The age of forest soils determines to a great extent the mycoflora. The ageing of Dutch forests contributes to the decrease of mycorrhizal mycoflora. It is not clear to what extent air pollution influences the succession of mycorrhizal fungi.(6) Nitrogen pollution is the major factor explaining the decrease of mycorrhizal mycoflora. The absence of effects of nitrogen pollution in young plots is explained by the high nitrogen losses due to clear-cutting and soil ploughing, decreased interception of air pollutants by smaller trees and the higher need for external nitrogen of young trees.(7) Carpophores of mycorrhizal fungi are more sensitive to nitrogen pollution than mycorrhizas.(8) It is proposed that the decline in mycorrhizal mycoflora during stand development might not occur if air pollution, particularly nitrogen pollution, is drastically diminished, and if the excess nitrogen in the ecosystem is removed

Hygienization aspects of composting

• Compost use in agriculture always brings about the risk of introducing plant and human pathogens. • The backbone of the hygienization process consists of temperature, moisture content and chemical compounds formed during composting and activity of antagonists. • Compost produced by proper composting, i.e. a process that produces high temperatures during asufficiently long thermophilic phase can be applied safely. • Farmers should invest in good relationships with compost producers

Morphology of Verticillium dahliae and V. tricorpus on semi-selective media used for the detection of V. dahliae in soil

The morphology of two soil-borne Verticillium species, V. dahliae and V. tricorpus, was studied on two semi-selective agar media, in the absence and presence of soil. Morphology of the fungi differed considerably between the media, with respect to presence and shape of microsclerotia, dark hyphae (i.e. short melanised hyphae attached to the microsclerotia) and dark mycelium (i.e. melanised mycelium throughout the colony). On modified soil extract agar (MSEA), a pectate based agar, V. dahliae always had globose to elongate microsclerotia, without dark hyphae or dark mycelium, whereas V. tricorpus always had dark hyphae or dark mycelium, and micro sclerotia.. whenever present, were globose to irregular in shape. On ethanol agar (EA), V. dahliae had large microsclerotia and abundant dark hyphae, whereas V. tricorpus did not form microsclerotia, but always abundant dark mycelium. For the first time we observed the formation of dark hyphae by V. dahliae to a great extent. in the presence of soil, most characteristics were less pronounced, and V. dahliae microsclerotia were smaller, but V. tricorpus produced large microsclerotia, even when they were absent in pure culture. Morphological characteristics suitable for discrimination between the two species on MSEA plates in the presence of soil were selected and tested with fresh isolates from agricultural fields. The two fungi could be distinguished using qualitative characteristics and microsclerotial size. Molecular analysis and morphology on potato dextrose agar confirmed all identifications made on soil dilution plates

Effecten van verse organische stof

Organische stof is essentieel voor de chemische, fysische en biologische bodemkwaliteit in de akkerbouw. Een goed bodembeheer dient o.a. gericht te zijn op het handhaven en/of verbeteren van het gehalte en de kwaliteit van de organische stof in de bodem en op het handhaven en/of verbeteren van de verschillende bodemfuncties. Een handvat voor het beheer van organische stof is de organische stofbalans, die gericht is op een voldoende aanvoer van effectieve (=stabiele) organische stof. De balans houdt echter geen rekening met de effecten van verse organische stof op de bodemkwaliteit. Daarom heeft Productschap Akkerbouw aan PPO en NMI/BLGG AgroXpertus gevraagd in een bureaustudie de effecten van verse organische stof op de bodemkwaliteit in beeld te brengen. Daarbij ging het met name om de biologische bodemkwaliteit, zoals bodemgezondheid en ziektewerendheid

Characterization of Armillaria isolates from tea (Camellia sinensis) in Kenya

Armillaria is a primary root rot pathogen of tea (Camellia sinensis) in Kenya. The main species presently described in this country are A. mellea and A. heimii. A survey covering fourteen districts of Kenya was carried out and forty-seven isolates of Armillaria collected. Cultural morphology, rhizomorph characteristics, somatic incompatibility and features of basidiomata were used to characterize the isolates, together with molecular analysis based on randomly amplified polymorphic DNA (RAPD), inter-simple sequence repeat (ISSR), restriction fragment length polymorphism (RFLP) of the internal transcribed spacer (ITS) and the intergenic spacer (IGS) regions and sequence of the IGS region. It can be concluded that two Armillaria species were present and they were different from A. mellea. The first group was morphologically similar to A. heimii but this was contradicted by the molecular data, suggesting that A. heimii could be a complex of several species. The second group was different from the first and morphological and molecular data strongly suggest that it could be a new Armillaria species