Survival Of Inoculum Research Articles

Pathogenicity of Fusarium Species on Different Plant Parts of Spring Wheat Under Controlled Conditions.

Most of the Fusarium species responsible for Fusarium head blight of wheat in Saskatchewan, Canada, have also been isolated from discolored subcrown internodes/crowns of wheat. It was therefore of interest to compare the susceptibility of heads and ground/underground tissue of wheat to isolates of Fusarium species from different sources. Controlled-environment pathogenicity tests were conducted on heads, seeds, and seedlings of spring wheat. Overall, F. culmorum and F. graminearum were the most pathogenic species, although the former was more pathogenic than the latter. F. equiseti and F. poae were the least pathogenic species, whereas F. avenaceum had intermediate pathogenicity in the head and seed tests, but low pathogenicity in the seedling test. There was a similar pathogenicity among isolates of each Fusarium species from different sources to heads and ground/underground plant parts, indicating a lack of adaptation of these isolates. Our observations suggest that Fusarium inoculum on or in infected seed or plant debris might infect plants at or below soil level, which could then become a source of inoculum for infection of heads in the following season(s). Survival of fungal inoculum in underground plant parts might be important during dry conditions.

The use of molecular diagnostics to investigate the epidemiology of potato diseases

In recent years, quantitative molecular diagnostic assays based on real-time PCR have been developed for many pests and pathogens of potato. In addition, simple sequence repeat markers have been developed and used to track isolates of Phytophthora infestans. These diagnostic assays are now being used as tools to study unresolved questions in the epidemiology of potato diseases including late blight, powdery scab and black dot. Examples of various investigations designed to examine the relative contribution of seed and soil-borne inoculum in causing black dot and powdery scab on progeny tubers, the effect of environmental factors on the incidence and severity of powdery scab and the survival of asexual and sexual inoculum of P. infestans in soil are described. Consideration is given to the development of appropriate diagnostic assays, their use in conjunction with relevant and robust sampling techniques, and the interpretation of results to inform disease risk assessment and control strategies through industry collaboration.

Perspectives and vision for strain selection in bioaugmentation

Notwithstanding the phenomenally large and ever-increasing resource of pollutant-degrading microbial isolates in laboratories around the globe, inoculum survival remains the 'Achilles' heel' for bioaugmentation of contaminated land. Considerable effort has been invested into inoculum strain selection to facilitate pollutant biodegradation, ranging from the isolation of 'superbugs,' which are microorganisms highly resilient to environmental stresses, harboring catabolically superior pollutant-degrading enzymes, to the other extreme in 'priming', where pollutant degradation is carried out through the addition of soil enriched with an undefined consortium of pollutant-degrading microorganisms.

Survival of inocula and native AM fungi species associated with shrubs in a degraded Mediterranean ecosystem

Reconstitution of the potential of soil mycorrhizal inoculum is a key step in revegetation programs for semiarid environments. We tested the effectiveness of inoculation with native arbuscular mycorrhizal (AM) fungi or with an allochthonous AM fungus, Glomus claroideum, with respect to the growth of four shrub species, the release of mycorrhizal propagules in soil, within and outside the canopy, and the improvement of soil structural stability. Two years after outplanting, the mixture of native endophytes was more effective than, for Olea europaea subsp. sylvestris, Retama sphaerocarpa and Rhamnus lycioides, or equally as effective as, for Pistacia lentiscus, the non-native AM fungus Glomus claroideum, with respect to increasing shoot biomass and foliar NPK contents. The increases in glomalin concentration and structural stability produced by inoculation treatments in the rhizosphere soil of the all shrub species, except R. lycioides, ranged from about 55 to 173% and 13 to 21%, respectively. The mixture of native AM fungi produced the highest levels of mycorrhizal propagules in soil from the center of the canopy of P. lentiscus and R. lycioides, while plants of O. europaea and R. sphaerocarpa inoculated with G. claroideum had more mycorrhizal propagules than did those inoculated with the mixture of native fungi. The number of mycorrhizal propagules in soil outside the canopy of the four shrub species was 5–35 times higher in inoculation treatments than in soil of the non-inoculated plants.

Climate change and plant diseases in Ontario

Current models predict that expected climate change in Ontario will significantly affect the occurrence of plant diseases in agriculture and forestry in the coming years. Direct, multiple effects on the epidemiology of plant diseases are expected, including the survival of primary inoculum, the rate of disease progress during a growing season, and the duration of epidemics. These effects will positively or negatively influence individual pathogens and the diseases they cause. Changes in the spectra of diseases are also anticipated. Abiotic diseases associated with environmental extremes are expected to increase, and interactions between biotic and abiotic diseases might represent the most important effects of climate change on plant diseases. The management of plant diseases will also be affected. In agriculture, plant breeding programs are expected to adapt many crops to increased duration of growing seasons and, concurrently, to develop drought and stress tolerance. There will be opportunities for new crops and cultivars to be introduced, but effective systems must be in place to detect new pathogens and prevent them from entering with these new crops. Because of the long-lived nature of trees, forests are slow to adapt, and the impact of climate change will have to be considered in forest management plans. Adaptations in agriculture and forestry have been occurring in Ontario for over 100 years, but these may need to occur at an accelerated rate because of rapid changes in climate. It is critical that the infrastructure of agricultural and forestry research remains strong to ensure successful transition and adaptation.

Establishing the fungus <i>Beauveria bassiana</i> in pasture for clover root weevil (<i>Sitona lepidus</i>) control

The fungus Beauveria bassiana is a virulent pathogen of the clover root weevil a major introduced pest of clover in New Zealand Trials to investigate establishment of fungal inoculum in pasture were conducted in the Waikato region of New Zealand Granular formulations of conidia based on biopolymer technology successfully allowed the established of fungus in pasture However it did not support survival of inoculum into the second year Conidia on rice and conidial emulsions resulted in more successful establishment These results have implications for development of a biopesticide for clover root weevil based on B bassiana

Lime pelleting inoculated serradella ( Ornithopus spp.) increases nodulation and yield

Lime pelleting of the inoculated seed is recommended for most pasture legume species to improve survival of the rhizobia on the seed and to counter deleterious effects of soil or fertiliser acidity on rhizobial numbers. Except for New South Wales, lime pelleting is specifically not recommended for serradella ( Ornithopus spp.). Our objectives were to evaluate effects of lime pelleting on bradyrhizobial numbers on seed, and nodulation and growth of the serradella plants. Three experiments are reported at two acid-soil sites in northern New South Wales involving four cultivars of yellow serradella ( Ornithopus compressus) and Bradyrhizobium sp. ( Lupinus) strains WSM471 (current inoculant strain) and WU425 and WSM480. Lime pelleting increased bradyrhizobial numbers on seed, 24 h after inoculation, by an average of 90%. Similarly, lime pelleting increased nodulation and shoot dry matter of the inoculated plants by an average of 57 and 28%, respectively. The three strains were similar in effects on plant growth. Relative values for shoot dry weight, averaged over sites, were 100 for WSM471 and 98 for both WU425 and WSM480. Our results confirmed previous research that lime pelleting inoculated serradella seed was not deleterious to survival of the bradyrhizobial inoculum, and showed that it could result in enhanced symbiotic activity of the inoculum in some instances. We recommend lime pelleting of serradella and that WSM471 remain the inoculant strain.

Effect of previous crops on crown rot and yield of durum and bread wheat in northern NSW

The effect of previous crops (oilseed, legume, and cereal) on the incidence and severity of crown rot (Fusarium pseudograminearum, Fp) and yield of wheat was investigated in 3 field studies in northern New South Wales. The experiments were designed to compare the effectiveness of the Brassica break crops canola (Brassica napus L.) and mustard (B. juncea L.) with chickpea (Cicer arietinum L.) on reduction of Fp in subsequent wheat crops. Responses to previous broadleaf and cereal crops were investigated in Fp-tolerant bread wheat (Triticum aestivum L.) and Fp-susceptible durum wheat [Triticum turgidum L. ssp. durum (Dest.)]. In all experiments, broadleaf break crops increased the yield of Fp-susceptible durum wheat compared with durum after cereals (by 0.24–0.89 t/ha). The same response was observed for the Fp-tolerant wheat at 2 of the 3 sites (0.71 and 0.78 t/ha), with a lower yield (0.13 t/ha) after break crops than after cereals at one site during a drought. The yield of the Fp-susceptible durum wheat was generally higher after brassicas than after chickpea (yield advantage 0.27–0.58�t/ha), whereas there was no such difference in the tolerant wheat variety. In most cases, these yield responses to the previous crops were closely related to the severity of Fp infection. Overall yield of susceptible durum wheat was reduced by 1% for each 1% increase in Fp severity at harvest. Residual water and nitrogen (N) did not explain responses to previous crops, although common root rot (Bipolaris sorokiniana) may have contributed to some of the responses at the sites. There was little evidence that the lower disease and higher yield following brassicas compared with chickpea was related to suppression of Fp by biofumigation. More plausible explanations are that residual cereal residues decomposed more rapidly under dense Brassica canopies thus reducing Fp inoculum, that Fp severity was increased following chickpea due to higher soil N status, or that brassicas resulted in soil/residue biology that was less conducive to Fp inoculum survival. Evidence for the latter was provided by consistently higher levels of Trichoderma spp. isolated from wheat following brassicas compared with chickpea or cereals. Irrespective of the mechanisms involved, the results demonstrate that Brassica oilseeds provide an effective break crop for crown rot in northern NSW. Furthermore, brassicas may provide an excellent alternative rotation crop to chickpea for high value durum wheat due to an apparent capacity to more effectively reduce the severity of crown rot infection in subsequent crops.

SURVIVAL OF A SALMONELLA TYPHIMURIUM POULTRY MARKER STRAIN ADDED AS A DRY INOCULUM TO ZINC AND SODIUM ORGANIC ACID AMENDED FEEDS

ABSTRACTThe effects of different organic acid compounds on the survival of a dry inoculum of Salmonella typhimurium marker strain added to poultry feed were determined. Organic acids were added as 1% Zn or Na salts (w/w) to poultry feeds and stored at room temperature for 9 days. Reduction of S. typhimurium populations from 0 to day 9 was not substantially different between poultry layer ration nonamended feed (96.76%) and Zn acetate (99.72%) or Zn propionate (99.60%) amended feed. However, over 90% reduction of S. typhimurium populations occurred in Zn acetate and Zn propionate amended feed by day 3 while poultry layer ration populations reached 90% reduction by day 5. S. typhimurium populations after 9 days were nearly 40% more reduced in Na propionate amended feed than Na acetate amended feed. The results of this study indicated 1% Zn compounds may have potential to reduce survival of S. typhimurium in a poultry diet during the early stages of storage.

Inoculation of Mature Pedunculate Oaks ( Quercus robur ) with the Root Rot Fungus Collybia fusipes : Relationships with Tree Vigour and Soil Factors

The severity of natural infections induced by the root rot fungus Collybia fusipes depends on soil factors. Severely infected trees usually show reduced vigour, as evidenced by poor growth. However, it is not known whether reduced vigour could be a cause of the severe infection. The objective was to clarify the relationships between soil factors, tree vigour and susceptibility of Quercus robur to C. fusipes by artificially inoculating mature trees. Two experiments compared oak trees of different ages and dominance class and oak trees growing on different type of soils. The inoculum survival and the infection success were poor in both experiments when waterlogging was severe. Inoculum survival was better in soil with increasing sand/clay ratio, carbon/nitrogen ratio and decreasing pH and calcium, magnesium and phosphorus availability. The relationships between oak vigour and success of infection or surface area of lesions were inconsistent, with a slightly higher infection success on co-dominant/suppressed oaks in one experiment and a higher surface area of successful infection on dominant oaks in the second.

Detection, Survival, and Sources of Inoculum for Bacterial Diseases of Leafy Crucifers in Oklahoma.

Xanthomonas campestris pv. campestris, X. campestris pv. armoraciae, and Pseudomonas syringae pv. maculicola are bacterial pathogens that cause leaf spot diseases on leafy crucifers in Oklahoma. Polymerase chain reaction (PCR) amplification of the cfl gene from the gene cluster encoding the phytotoxin coronatine was used to identify coronatine-producing strains of P. syringae, and the expected 0.65-kb PCR product was detected in 19 strains of P. syringae pv. maculicola originating from diseased crucifers in Oklahoma. A simple, rapid PCR method based on primers from the cfl gene was developed to detect coronatine-producing strains of P. syringae in planta. Pathogenicity tests confirmed the cfl-positive strains to be P. syringae pv. maculicola. To monitor the survival of X. campestris pv. armoraciae and P. syringae pv. maculicola in the field, turnip and collards were inoculated with rifampicin-resistant strains and were buried beneath the soil or left on the soil surface. Both pathogens were recovered from turnip and collard debris up to 2 months following burial, but neither pathogen was recovered from soil after the debris had decomposed. However, both pathogens were recovered from plant debris left on the soil surface for up to 5 months. Four production fields were surveyed for sources of inoculum of the bacterial pathogens from October 1999 to May 2000. X. campestris pv. campestris was isolated from the weed shepherd's purse (Capsella bursa-pastoris) in all fields, and from volunteer turnip and kale in three fields. X. campestris pv. campestris and P. syringae pv. maculicola were isolated from surface debris and regrowth from crop stubble left in one field after harvest in the fall. X. campestris pv. campestris was detected in 6 of 51 lots of crucifer seed assayed. X. campestris pv. armoraciae and P. syringae pv. maculicola were not recovered from weeds, volunteer plants, or seed lots.

Survival in the soil of the ectomycorrhizal fungus Laccaria bicolor and the effects of a mycorrhiza helper Pseudomonas fluorescens

In disinfected forest nursery soils, inoculating Douglas fir ( Pseudotsuga menziesii) seedlings with the ectomycorrhizal fungal strain Laccaria bicolor S238N significantly increases tree growth after outplantating. However, the success of the inoculation depends on survival of the fungal inoculum in the soil during the pre-symbiotic life of the fungus. We followed the survival of L. bicolor S238N in autoclaved nursery soil in the glasshouse, and under gnotobiotic conditions in autoclaved or γ-irradiated nursery soil. We also studied the effect of the mycorrhiza helper bacterium Pseudomonas fluorescens BBc6R8, which promotes the Douglas fir- L. bicolor S238N symbiosis, on fungal viability. In the glasshouse, fungal viability was assessed by trapping with Douglas fir seedlings. We showed that the fungus retained its viability in a pre-symbiotic state in the soil at least for 23 weeks, which is much longer than that reported in the literature for other ectomycorrhizal fungi. The bacterium did not significantly modify the survival of the fungus. In the gnotobiotic experiments, ergosterol, a specific fungal membrane component, was used to quantify fungal biomass. Fungal behaviour differed with the disinfection technique used, which modified the chemical characteristics of the initial soil. There was no fungal growth in the autoclaved soil but there was a rapid increase of fungal biomass in the irradiated soil. The effect of the bacterium on fungal biomass also varied with a significant stimulation in the autoclaved soil vs. a significant inhibition in the irradiated soil. Our results show that the beneficial effect of the bacterium on the fungus depends on the condition of the fungus, i.e. the greatest benefit occurs when the fungus is growing under unfavourable conditions.

Oversummer Survival of Inoculum for Colletotrichum Crown Rot in Buried Strawberry Crown Tissue.

The oversummer survival of Colletotrichum gloeosporioides in strawberry crown tissue under field conditions was investigated in 1998 and 1999. Strawberry crowns infected naturally with C. gloeosporioides were placed inside cloth bags containing field soil, buried in the field at 5 or 13 cm, then recovered over 6 months of each year. The recovered crowns were plated onto a Colletotrichum spp. semiselective medium and speciated by colony, spore morphology, and molecular markers with species-specific DNA primers. Pathogenicity of selected isolates was confirmed by greenhouse bioassays on strawberry. Of the 428 isolates of Colletotrichum spp. recovered from buried crowns, 96% were C. gloeosporioides and 4% Colletotrichum acutatum. Following an initial increase in the detection of the fungus, survival of C. gloeosporioides was stable for 2 to 3 weeks, then declined. No Colletotrichum spp. were detected after burial for 56 days in 1998 and 98 days in 1999. Because the time between crop seasons is typically more than 170 days, these data support the hypothesis that inoculum of C. gloeosporioides does not survive in buried plant debris between seasons in Florida and, therefore, oversummering crop debris does not contribute inoculum for epidemics of Colletotrichum crown rot in Florida.

Seed transmission of maize downy mildew (Peronosclerospora sorghi) in Nigeria

In an area of Nigeria where downy mildew of maize is present, histological assessment of maize seed revealed the presence of mycelium and oospores of Peronosclerospora sorghi in the kernels. Seed transmission of downy mildew of maize was demonstrated when grain purchased at local markets gave mean seedling infection rates of 12·3% (untreated seeds) and 10·0% (in metalaxyl‐treated seeds) within 7 days of emergence, after storage in a desiccator for 30 days. When untreated seeds taken from nubbin ears of systemically infected plants from four states in southern Nigeria were planted at 9 days (17–22% moisture content) and 27 days (9–22% moisture content) after harvest, 20·0% infected seedlings resulted in both trials. Seeds from Borno state in northern Nigeria had 26·6% systemic seedling infection after 9 months of storage at 11% moisture content. When seeds harvested from maize plants inoculated with P. sorghi through silks were examined histologically, hyphae of P. sorghi were observed mostly in the scutellum of the embryo. Transmission of disease to seedlings was observed when the silk‐inoculated seeds (9% moisture content) were planted in pots in a greenhouse; however, no disease transmission was observed when such seeds were planted in the field. The epidemiological significance of seed transmission is discussed with particular reference to survival of inoculum and development of epidemics. Also noteworthy is the overall significance of seed transmission in Nigeria, where the major source of seed is that saved by farmers from their grain crop, occasionally supplemented by seed bought from the local market.

Winter Survival and Source of Primary Inoculum of Powdery Mildew of Dogwood in Tennessee.

A 3-year study (1996-1998) on the epidemiology of dogwood powdery mildew showed that Microsphaera pulchra is the primary powdery mildew pathogen of dogwoods (Cornus spp.) in mid-Tennessee, and the occurrence of Phyllactinia guttata is insignificant. Cleistothecia harvested from leaf debris in spring contained viable asci and ascospores and produced powdery mildew infection on disease-free plants. Ascospores that were morphologically similar to those of M. pulchra were trapped on sticky slides in the vicinity of dogwoods throughout spring. Previously infected plants that did not harbor cleistothecia failed to develop signs of infection under growth-chamber and greenhouse conditions conducive to powdery mildew infections. Results from these studies indicate that cleistothecia on leaf debris rather than mycelia on dormant buds constitute the main winter survival structure and primary sources of spring inoculum in mid-Tennessee.

Disease incidence and severity on beans in alleys between Leucaena hedgerows in Kenya.

The effects of inter-row spacing of Leucaena leucocephala in an alley cropping system on the incidence and severity of diseases on intercropped beans (Phaseolus vulgaris L.) and their yield were examined over two years (1993 and 1994) at Chepkoilel Campus in Kenya. Each experiment consisted of three randomized blocks with treatments of three alley widths (2 m,4 m and 8 m) and a treeless control with two intra-row spacings of Leucaena (0.5 m and 1.0 m). Hedgerows were coppiced at 1.0 m height and pruned subsequently at two-to-three months intervals. No fertilizer was applied but Leucaena loppings were incorporated as green leaf manure. Incidence of angular leaf spot (Phaeoisariopsis griseola) and anthracnose (Colletotrichum lindemuthianum) on beans were assessed at three growth stages in each season, using the Centro International de Agricultura Tropical (CIAT) scales. Microclimate was monitored in treatments, in 1994. Angular leaf spot and anthracnose decreased with increasing alley width and were more severe in bean rows adjacent to hedgerows. Light availability and diurnal temperaturereaching the bean canopy increased with alley width but relative humidity and leaf wetness duration decreased. Proximity to hedgerows also had markedly reduced light levels, lower temperatures and higher relative humidity. Higher incidence and severity of angular leaf spot and anthracnose on beans in alleys than on beans in treeless plots were examined in relation to microclimate, inoculum survival and dispersal. The pattern of the diseases was best explained by microclimate changes induced by Leucaena hedgerows, especially effects of humidity.

Field studies on the biofumigation of take-all by Brassica break crops

Biofumigation refers to the suppression of soil-borne pathogens and pests by biocidal compounds released by Brassica crops when glucosinolates (GSL) in their residues decay in soil. We conducted field studies at 2 sites to investigate the hypothesis that biofumigation by Brassica break crops would reduce inoculum of the take-all fungus Gaeumannomyces graminis var. tritici (Ggt) to lower levels than non-Brassica break crops, and thereby reduce Ggt infection and associated yield loss in subsequent wheat crops. High and uniform levels of Ggt were established at the sites in the first year of the experiments by sowing wheat with sterilised ryegrass seed infested with Ggt. Ggt inoculum declined more rapidly under Brassica crops than under linola and this reduction coincided with the period of root decay and reduced root glucosinolate concentrations around crop maturity. There was no consistent difference in inoculum reduction between canola (Brassica napus) and Indian mustard (Brassica juncea), nor between cultivars with high and low root GSL within each species. Despite significant inoculum reduction attributable to biofumigation, there were no differences in the expression of disease and associated impacts on the yield of subsequent wheat crops across the sites. Seasonal conditions, in particular the distribution of rainfall in both the summer–autumn fallow following the break crops and during the subsequent wheat crop, influenced inoculum survival and subsequent disease development. In wet summers, inoculum declined to low levels following all break crops and no extra benefit from biofumigation was evident. In dry summers the lower inoculum levels following brassicas persisted until the following wheat crops were sown but subsequent development of the disease was influenced more by seasonal conditions than by initial inoculum levels. Significant extra benefits of biofumigation were observed in one experiment where wheat was sown within the break crops to simulate grass weed hosts of Ggt. Under these circumstances there was greater reduction in Ggt inoculum under canola than linseed and an associated decrease in disease development. For host-dependent pathogens such as Ggt, we hypothesise that the benefits of biofumigation to subsequent wheat crops will therefore be restricted to specific circumstances in which inoculum is preserved during and after the break crops (i.e. dry conditions, grass hosts present) and where conditions in the following wheat crop lead to significant disease development (early sowing, wet autumn and spring, dry periods during grain filling).

Models of Early Spring Survival of Wheat Leaf Rust in the Central Great Plains.

Severe leaf rust epidemics, which result in economic yield reductions in the Great Plains wheat-producing region of the United States, are usually initiated by Puccinia recondita f. sp. tritici inoculum that has survived in the local field from the previous wheat crop until early spring. Models were developed for an epidemic year beginning at physiological maturity of one wheat crop to maturity of the following wheat crop. Meteorological variables for periods prior to final tiller development of the wheat crop during 1980 to 1992 at several sites in the central Great Plains winter-wheat-production area were used to model inoculum survival from one wheat crop until early spring of the next crop. Stepwise multiple regression was used to identify weather variables that explained the most variation in inoculum survival at the final tiller development wheat growth stage. Inoculum survival was recorded on a 0 to 9 scale with 0 indicating no survival and 9 indicating inoculum on all wheat plants in the field. Independent variables used in development of models were daily deviations from the 10-year average of maximum and minimum temperature, fungal temperature equivalence function, cumulative fungal temperature function, precipitation, cumulative precipitation, and snow cover averaged for 10-day periods prior to dates inoculum forecasts were desired. Models were constructed to forecast inoculum survival from data collected prior to fall wheat planting, the beginning of winter dormancy of the wheat, and the final tiller development wheat growth stage. Of the observed occurrences of leaf rust overwintering, 70% were forecast by models constructed using weather data prior to wheat planting decision time. Overwintering could be forecast by models constructed with data prior to the wheat entering winter dormancy 80% of the time. Models constructed with data collected prior to final tiller development in the spring forecast overwintering of leaf rust inoculum 95% of the time. Results from these models will be used to develop forecasts of leaf rust epidemics and resulting yield reductions.

Plant Pathogens and Plant Diseases

This book, written by a team of Australian plant pathologists, is design to give students and researchers a background in the principles of plant pathology and of managing plant diseases. The book is divided into five sections. The first deals with the agents that cause disease and includes fungi, bacteria, phytoplasmas, viruses, viroids, nematodes, parasitic plants and abiotic agents. There is also a useful and up-to-date chapter on serological and molecular techniques to detect and identify plant pathogens. Part two deals with the survival and dispersal of plant pathogens, including airborne and soilborne inoculum, and the role played by vectors. Part three covers infection processes, epidemiology and crop-loss assessment and this is something of a mixed bag, as it includes chapters on plant defence, disease prediction, and biocontrol of weeds using plant pathogens. Quantitative concepts of epidemiology feature in the introduction to part four, which concerns disease management. This may not appeal to the purist or disease modellers but does have the virtue for students of introducing disease growth curves in the context of strategies for control. The remainder of this section covers all aspects of disease management including quarantine and sanitation, chemical, cultural, genetic and biological approaches to disease control. The final part gives specific examples of different types of plant diseases and their control, based on the different types of pathogens, as well as a chapter on disease in natural communities and another on postharvest pathology. Inevitably the book has an Australian emphasis in the examples chosen, but the principles developed are universal and it should prove very useful for a variety of plant pathology courses. The editors have done well to compile such a range of information from different authors in a uniform style. The book is strong on the biology of the different pathogens, and particularly on practical aspects of disease management, which occupy approximately one third of the 550 pages. It is well illustrated with tables, keys and diagrams, although the production standards are not as high as in some other recent texts where glossy paper and even colour photos are included. It is easy to read and accessible for students, and with the very wide range of topics covered deserves to be considered as a core text for both introductory and intermediate level plant pathology courses. At the price of $A49 it is good value.

Survival and Extinction of Xanthomonas campestris pv. campestris in Soil

Carry-over of inoculum of X.c. pv. campestris in the soil from one cropping season to the next was studied in field experiments over three years. These studies were supported by laboratory and greenhouse experiments on quantitative assessment of bacteria by bioassay using the Most Probable Number technique, and on recovery rates of bacteria from the soil. The mean recovery rate from artificially infested soil was 58%. Extinction of X.c. pv. campestris in soil infested with infected plant debris proceeded exponentially and extinction rates depended on temperature, as did the decomposition of plant debris. In replicated field plots, over three years, infection foci of black rot disease were established. At harvest time, all plants were chopped and resulting plant debris was rotovated into the soil. The resulting soil infestation was sampled and showed clear infestation foci reflecting the original infection foci of the crop. These infestation foci decreased with time and disappeared after the winter. Follow-up crops remained virtually uninfected. The results show that in The Netherlands good crop and soil management impedes survival of inoculum from one year to the next, so that cabbage can be grown continuously. Polyetic carry-over of inoculum by debris in the soil can be avoided in The Netherlands.