Root Disease Incidence Research Articles

EFFECTS OF FARMING SYSTEM ON ROOT-ZONE FUNGAL POPULATIONS IN WHEAT

Effects of farming system on the composition of the root-zone microbiota and on the occurrence of root and stem-base diseases in winter wheat cv. Rywalka were analysed. The wheat was grown in organic, integrated and conventional systems of production and in monoculture over three years. Using classical methods, saprotrophic and pathogenic microorganisms, mainly fungi, were isolated from the root zone and identified on the basis of morphology and, where possible, designated as potential pathogens or antagonists. In roots, rhizoplane, and rhizosphere and non-rhizosphere soil the total frequencies of dominants (with frequency >5%) was 80.7- 98.7% and subdominants (with frequency 1–5%) was 0.5-14.5% and were similar in all production systems. Potential major soil-borne pathogens included Fusarium + Haematonectria. Potential pathogen antagonists included Chaetomium, Clonostachys, Gliomastix, Sarocladium and Trichoderma species. The low ratio of fungal pathogens : antagonists (Fusarium + Haematonectria : Clonostachys + Trichoderma spp.) in soil associated with lowest incidence of root and stem-base diseases, lower occurrence of Fusarium and Rhizoctonia in root and stem-base region and highest yield of grain in a conventional system for production of wheat cv. Rywalka confirms the cultivar’s suitability for high-input conventional farming. Benefits of microbiological approaches in the study of suitability of cultivar to a particular farming system is demonstrated.

Predicting Cereal Root Disease in Western Australia Using Soil DNA and Environmental Parameters.

Root diseases have long been prevalent in Australian grain-growing regions, and most management decisions to reduce the risk of yield loss need to be implemented before the crop is sown. The levels of pathogens that cause the major root diseases can be measured using DNA-based services such as PreDicta B. Although these pathogens are often studied individually, in the field they often occur as mixed populations and their combined effect on crop production is likely to vary across diverse cropping environments. A 3-year survey was conducted covering most cropping regions in Western Australia, utilizing PreDicta B to determine soilborne pathogen levels and visual assessments to score root health and incidence of individual crop root diseases caused by the major root pathogens, including Rhizoctonia solani (anastomosis group [AG]-8), Gaeumannomyces graminis var. tritici (take-all), Fusarium pseudograminearum, and Pratylenchus spp. (root-lesion nematodes) on wheat roots for 115, 50, and 94 fields during 2010, 2011, and 2012, respectively. A predictive model was developed for root health utilizing autumn and summer rainfall and soil temperature parameters. The model showed that pathogen DNA explained 16, 5, and 2% of the variation in root health whereas environmental parameters explained 22, 11, and 1% of the variation in 2010, 2011, and 2012, respectively. Results showed that R. solani AG-8 soil pathogen DNA, environmental soil temperature, and rainfall parameters explained most of the variation in the root health. This research shows that interactions between environment and pathogen levels before seeding can be utilized in predictive models to improve assessment of risk from root diseases to assist growers to plan more profitable cropping programs.

Cropping systems with maize and oilseed rape for energy production may reduce the risk of stem base diseases in wheat

Cropping systems with crops cultivated in short cycles on the same land provoke phytosanitary problems which may force more chemical inputs. However, the potential effects of cropping systems with emphasis on energy crops, i.e. maize and oilseed rape on the incidence and severity of stem base and root diseases of wheat have not been investigated thoroughly. We therefore analyzed the effects of varied percentages of maize and oilseed rape on stem base and root pathogens of winter wheat grown in four different cropping systems and rotations in two locations in Central and Northeastern Germany for three years. Our results demonstrate that short and intensive crop rotations with wheat combined with crops for bioenergy production do not necessarily enhance the risk by soil and straw borne diseases. Moreover, a suitable combination of wheat, oilseed rape and maize with adapted cropping methods (late sowing after maize, ploughing) can significantly mitigate the threat of stem base diseases in wheat. While disease incidence of sharp eyespot was always <5%, cropping systems had significant effects on the incidence and severity of eyespot, fusarium foot rot and take-all (in Northeastern Germany). Incidence of fusarium foot rot and take-all was significantly reduced by 70% and incidence of eyespot nearly to 0%, when wheat was planted after maize in a system with late sowing and ploughing, compared to wheat after oilseed rape with reduced tillage and early sowing. Further, these cropping systems with maize showed a low level of fusarium head blight. DON levels in grains were always low. The present study demonstrates that current shifts in crop rotations to a higher prevalence of maize due to novel market developments do not necessarily enhance the phytosanitary risks in the main crop wheat, if a suitable system of agronomic measures is applied, enabling highly productive and sustainable energy crop production systems.

Efficacy of various fungicides and indigenous biocontrol agents against red root rot disease of tea plants

An experiment was conducted to study the effectiveness of contact, systemic and botanical fungicides, and indigenous biocontrol agents in controlling red root rot disease of tea plants. In general, all tested bioagents, the combination of Pseudomonas fluorescens and Trichoderma atroviride reduced red root disease incidence recorded in two consecutive field experiments. Among the fourteen treatments tested, soil drenching of systemic fungicides was superior but similar to the combination between P. fluorescens and T. atroviride. In contrast, the maximum green leaf yield and plant growth was achieved when soil application of biocontrol agents was carried out. However, the performance of these biocontrol agents under various combinations was on par with systemic fungicides, but superior to botanical fungicides. Correspondingly, the physiological and biochemical parameters were also greatly increased in plants in several treatments when compared to untreated control. The disease increased from 31.5 % to 40.0 % in untreated control plots and those plants were unhealthy in terms of leaf yellowing, stunted growth with heavy flowering, drying of branches and sudden death of bushes. The tea quality parameters were significantly improved in treated plants including total liquor colour, thearubigins, theaflavins, highly polymerized substance and caffeine contents.

Impact of Continuous &lt;i&gt;Cucumis sativus&lt;/i&gt; L. Cropping on the Incidence of Root Diseases and Bacterial Community Structure

To investigate the change of cucumber root disease incidence and bacterial community shift in monocultrue soil, we established 4 treatments of greenhouse-pot cucumber, each representing various monoculture times, and monitored the bacterial variation in rhizosphere/bulk soil and root disease index. Results showed that culturable bacteria numbers gradually decreased as monoculture continued, a significant (P&lt;0.05) difference was observed in rhizosphere samples of the fourth cropping (FC) and the third cropping (TC) soil in contrast to that of non-continuous cropping (NC). The Eco-Physiological diversity index also declined with consecutive cucumber cropping. Analysis by denaturing gradient gel electrophoresis (DGGE) showed that a few dominant bacterial species, including Pseudomonas sp. (95% similarity), Bacteriovorax sp. (93% similarity) and 2 uncultured soil bacteria, declined in population, while Sphingomonas sp. (100% similarity) and one uncultured bacterium increased. For all samples analyzed using DGGE or culture dependent approach, the bacterial population shift was more sensitive in the rhizosphere than in bulk soils, less bacterial diversity and higher root disease incidences were both detected in continuous monocultured soils.

Relationship of site and stand characteristics to Armillaria root disease incidence on ponderosa pine in the Black Hills, South Dakota

Summary Ponderosa pine (Pinus ponderosa) in the Black Hills National Forest, SD, USA, was surveyed for Armillaria root disease (ARD). The root pathogen Armillaria ostoyae occurred on ponderosa pine seedlings, saplings, pole-size trees and large-diameter trees. The mean incidence of aboveground disease symptoms by stem count was low (0.2%), but in certain areas, the incidence was higher, affecting the regeneration success and tree longevity. Symptomatic ponderosa pine were in areas characterized by having higher elevation, greater annual precipitation, more seedlings, bigger large-diameter trees and greater odds of past harvesting activity than in areas without root disease. Stump density was positively spatially correlated with root disease incidence. No particular soil type was related to disease occurrence; though, in areas with symptomatic trees, soil available water holding capacity (AWC) was greater and soil permeability was less where root disease was present. Spatial analysis confirmed the relationships found in linear correlations, with soil AWC and stump density positively and soil permeability negatively correlated with per cent infected stems ha−1 and basal area infected.

Assessment of armillaria root disease infection in stands in south-central British Columbia with varying levels of overstory retention, with and without pushover logging

This trial, conducted near Nakusp, British Columbia, compares pushover logging (combination tree felling and root removal technique using large machines to push trees out of the ground) with handfalling logging (no root removal) for effects on the incidence of armillaria root disease in postharvest regeneration. Pushover logging did not reduce levels of root disease, expressed as percentage tree mortality, over handfalling harvesting on this site. High variability of measured disease levels within some treatments and few replicates lowered the power of the trial. However, in addition to being statistically insignificant, the mean differences between the two main treatments were small and biologically uninteresting, and the response was inconsistent in direction. The trial also included three mature timber retention levels as treatments, and there seemed to be a trend of declining root disease with increased retention of stems. This phenomenon should be further investigated as current literature is not clear on the response of armillaria to partial harvesting. There was a strong suggestion of a difference between susceptibility of natural and planted seedlings to armillaria root disease, with natural regeneration being less susceptible. Thuja plicata Donn ex D. Don was less affected by armillaria root disease than other species in this trial, whether it was planted or naturally regenerated.

Effect of host and inoculum patterns on take-all disease of wheat incidence, severity and disease gradient

The importance of the spatial aspect of epidemics has been recognized from the outset of plant disease epidemiology. The objective of this study was to determine if the host spatial structure influenced the spatio-temporal development of take-all disease of wheat, depending on the inoculum spatial structure. Three sowing patterns of wheat (broadcast sowing, line sowing and sowing in hills) and three patterns of inoculum (uniform, aggregated and natural infestation) were tested in a field experiment, repeated over 2 years. Disease (severity, root disease incidence, plant disease incidence and, when applicable, line and hill incidences) was assessed seven times during the course of each season and the spatial pattern was characterized with incidence-incidence relationships. In the naturally infested plots, disease levels at all measurement scales were significantly higher in plots sown in hills, compared to plots sown in line, which were in turn significantly more diseased than plots with broadcast sowing. Disease aggregation within roots and plants was stronger in line and hill sowing than in broadcast sowing. Analysis of the disease gradient in the artificially infested plots showed that the disease intensified (local increase of disease level) more than it extensified (spatial spread of the disease), the effect of the introduced inoculum was reduced by 95% at a distance of 15 cm away from the point of infestation. Yield was not significantly affected by sowing pattern or artificial infestation.

EFFECT OF VARIOUS TREATMENTS ON REDUCTION OF LEUCOSPERMUM 'HIGH GOLD' MORTALITY CAUSED BY ROOT DISEASES

One of the major problems of Proteaceae cultivation in Madeira Island is the high incidence of root diseases caused mainly by Rosellinia necatrix and Armillaria mellea and secondarily by Fusarium solani and Rhizoctonia solani, which lead to the death of plants older than 2 years. The compactness of the soils as well as its richness in organic matter and in other nutrients, together with the climatic conditions of the island (moderate temperatures and a high relative humidity), facilitate the development of root diseases. The aim of this experiment was to study the effect of various treatments in the reduction of mortality of 5-year-old Leucospermum 'High Gold' plants. The treatments consisted of the application to the roots of 1 L of the following solutions: iron sulphate (30 g/L) plus wettable sulphur (10 g/L) (T2 and T6), copper sulphate (25% copper) (20 g/L) with foliar application of Alga-E (15% of algae extracts) (1.5 ml/L) (T3 and T7), commercial bleach (30 ml/L) (T4 and T8), and Talosint (50% cubiet) (10 ml/L) (T5 and T9); the solutions were applied every 3 months (T2 to T5) or every 6 months (T6 to T9). After one year there were no significant differences between treatments, with a plant mortality of 4.8 to 14.3%. After two years, the lowest mortality was obtained with the application of commercial bleach every 6 months (T8) (28.6%); the other treatments gave higher mortality values but with no significant differences between them, except for treatment T5. Treatment T5 was the worst with 66.7% mortality which was statistically different from T4, T8 and T9. None of the treatments were effective in the reduction of the annual plant mortality; treatment T8 gave more consistent results in the two years of trialling period, with 9.5 and 21% for the first and second year, respectively.

Incidence of root and hypocotyl diseases in lupin crops in Western Australia between 1986 and 2005

Three separate surveys were carried out in commercial lupin crops in the major lupin growing region of Western Australia in 1986, 1990, and 2004–05. In total, 333 sites were sampled and plants assessed for the incidence and cause of root and hypocotyl rots. Measurements were made of plant density and sowing depth at all sites. In all surveys, root rot was more common than hypocotyl rot. Root rot occurred in more than 95% of sites in each survey; however, a greater proportion of sites had high levels of root rot in early surveys. The incidence of root rot within sites decreased from an average of 34.9% in 1986 to 10.2% in 2004–05. Hypocotyl rot incidence varied among surveys, incidence of infected paddocks, and within-paddock incidence was greatest in the 1990 survey. Hypocotyl rot incidence was lowest in the 2004–05 survey. Rhizoctonia solani and Pleiochaeta setosa were commonly isolated from root lesions and R. solani was the predominant pathogen isolated from hypocotyl lesions. Analysis of the R. solani isolates by pectic zymogram showed that the ZG3 strain was most regularly isolated from roots and hypocotyls. This series of surveys indicates that the incidence of root rots in commercial lupin paddocks in Western Australia has decreased dramatically over the past 20 years; however, root rot still occurs in most paddocks regardless of soil type, location, crop rotation, and management systems.

Effects of oleoresins and monoterpenes on in vitro growth of fungi associated with pine decline in the Southern United States

SummaryAs a means of exploring pine resistance to root disease and declines, the effects of host plant secondary metabolites on the growth of root colonizing fungi associated with three diseases/declines of southern pines – loblolly pine decline, littleleaf disease and annosum root rot were tested. The associated fungi –Leptographium huntii, L. serpens, L. terebrantis, L. procerum, Heterobasidion annosum and Phytophthora cinnamomi– were grown in saturated atmospheres or in direct contact with, pure monoterpenes and crude oleoresin collected from the four southern pines (Pinus taeda, P. eschinata, P. palustris and P. elliotti) for 7 day. Fungal growth was measured at 3, 5 and 7 day. Root‐infecting fungi differed significantly in sensitivity to crude oleoresin and pure monoterpenes. All fungi tested were inhibited, to some extent, by the resins tested. H. annosum and P. cinnamomi were strongly inhibited by all the monoterpenes tested. The ophiostomatoid fungi were significantly less affected by the compounds tested. L. huntii and L. serpens were less inhibited by monoterpenes than either L. terebrantis or L. procerum. These fungal growth studies show that the kind and amount of secondary metabolite produced by the host plant have a profound effect on tree pathogens. Alterations of tree physiology may have implications for defenses against tree pathogens as well as to the ecology and management of forest ecosystems. Difference in incidence of root disease observed in the field may be explained by the ability of the fungus to tolerate these host defense mechanisms.

Preplant Fungicide Dips of Strawberry Transplants to Control Anthracnose Caused by Colletotrichum acutatum in California

Bare-root daughter plants of strawberry (Fragaria ×ananassa) were inoculated with Colletotrichum acutatum, the cause of crown rot, root rot, and fruit rot of strawberry in California. Plants were subsequently dipped in fungicide solutions or washed with running tap water immediately before planting in Summer and Fall 2002 and Fall 2004. Fungicide treatments reduced plant dieback by up to 92% in fruit production fields. Plants treated with azoxystrobin, the premixtures of boscalid + pyraclostrobin and cyprodinil + fludioxonil had 50% to 92% reduction in disease incidence, increased canopy size by more than 100%, and produced significantly higher marketable yields in all planting dates than the inoculated plants that were not treated with the fungicides. Chlorothalonil and captan also significantly reduced disease incidence but did not consistently increase marketable yield compared with the untreated, inoculated control. The effects of propiconazole and trifloxystrobin were inconsistent in reducing disease incidence. Water wash did not reduce root and crown disease incidence but significantly increased marketable yields by 13% over the untreated, inoculated controls in one of two plantings. No pretransplant treatments provided protection against fruit and foliar infection; thus, in-season fungicide applications would be necessary for disease control in commercial production fields if environmental conditions favored disease development.

Preplant Fungicide Dips of Strawberry Transplants to Control Anthracnose Caused by Colletotrichum acutatum in California

Bare-root daughter plants of strawberry (Fragaria ×ananassa) were inoculated with Colletotrichum acutatum, the cause of crown rot, root rot, and fruit rot of strawberry in California. Plants were subsequently dipped in fungicide solutions or washed with running tap water immediately before planting in Summer and Fall 2002 and Fall 2004. Fungicide treatments reduced plant dieback by up to 92% in fruit production fields. Plants treated with azoxystrobin, the premixtures of boscalid + pyraclostrobin and cyprodinil + fludioxonil had 50% to 92% reduction in disease incidence, increased canopy size by more than 100%, and produced significantly higher marketable yields in all planting dates than the inoculated plants that were not treated with the fungicides. Chlorothalonil and captan also significantly reduced disease incidence but did not consistently increase marketable yield compared with the untreated, inoculated control. The effects of propiconazole and trifloxystrobin were inconsistent in reducing disease incidence. Water wash did not reduce root and crown disease incidence but significantly increased marketable yields by 13% over the untreated, inoculated controls in one of two plantings. No pretransplant treatments provided protection against fruit and foliar infection; thus, in-season fungicide applications would be necessary for disease control in commercial production fields if environmental conditions favored disease development.

Quantification of within‐season focal spread of wheat take‐all in relation to pathogen genotype and host spatial distribution

Within season gradient of wheat take‐all was measured in field experiments according to line or random sowing host spatial distribution, and two Gaeumannomyces graminis var. tritici (Ggt) isolates (G1i and G2i), representative of the G1 and G2 genotype groups in terms of aggressiveness. Root disease incidence and severity were assessed at six dates from early March to late June on plants located at regular distances from the inoculum sources. Simple models relating disease intensity at different levels of hierarchy fitted observed data well, and indicated a strong disease aggregation both within and among plants. Disease severity on source plants placed nearby the inoculum source increased over time, ranging from 5 to 46% at the first assessment, and from 55 to 98% at the last assessment, being in general larger for G2i than G1i. In line‐sown plots, disease progressed steadily along the line but did not extend beyond 20 cm, seldom reaching the neighbour line. Disease rarely reached 25 cm in the direct‐seeded crop stands. These results indicate that Ggt intensifies but does not spread to a large extent during a cropping season. Distance from the source, pathogen genotype and assessment date had a significant effect on disease severity according to mixed model analyses, disease spread being larger for G2i than G1i. However, no significant effect of host spatial distribution could be detected. Yield loss within 20 cm of the source plant ranged between 20 and 40%, and was not significantly affected by pathogen genotype or host spatial distribution.

Observations on root disease of Container whitebark pine seedlings treated with biological controls

I observed that whitebark pine ( Pinus albicaulis Engelm. [Pinaceae]) germinants treated with biological controls, one commercially available ( Trichoderma harzianum strain T-22), and the other being studied for potential efficacy ( Fusarium oxysporum isolate Q12), experienced less seedling mortality caused by root disease than did a non-treated control. Seedlings treated with the biological controls and non-symptomatic seedlings in the control treatment had similar morphology. The simple use of biological controls may be useful to nursery managers looking to reduce incidence of root disease in their container crops. Dumroese RK, 2008. Observations on root disease of container whitebark pine seedlings treated with biological controls. Native Plants Journal 9(2):92–97.

Spatio-temporal Development of Pea Root Rot Disease through Secondary Infections during a Crop Cycle

Spatio-temporal development of pea root rot was experimentally characterized. Experiments performed under controlled conditions with trap plants located at varying distances from a diseased source plant indicated that disease spread from a diseased plant to a healthy one was generally below 15 cm. A field experiment was conducted to measure disease spread gradients and the rate of secondary infection at two planting densities, 70 and 140 plants/m2. Relationships between plant and root disease incidences, and between root disease incidence and root disease severity indicated a strong disease intensification both within and between diseased plants. Measurement of disease gradients indicated that disease did not spread farther than 10 cm from the diseased source plant, i.e. one and two plants away along a row at low and high planting densities respectively. Disease did not spread to neighbouring rows, located 15 cm away. Rates of secondary infection over 14-day periods ranged between zero (no disease increase) and 0.35 plant/plant/day, and was in general larger in high-density plots than in low-density plots. Implications of the results for disease management are discussed.

양파 연작지의 분홍색뿌리썩음병 방제를 위한 담수처리 효과

양파 연작지 토양의 담수기간에 따른 분홍색뿌리썩음병의 방제효과, 양파의 생육 및 수량을 조사한 결과 토양병원균의 밀도변화는 담수기간이 길수록 균밀도의 감소효과가 뚜렷하여 처리 후 90일에는 무담수에 비해 <TEX>$1/2{\sim}1/3$</TEX> 수준으로 감소하였지만 양파 재배후 균밀도는 담수직후 보다는 전반적으로 증가하는 경향을 보였다. 양파 육묘상 담수처리에 의한 분홍색뿌리썩음병의 방제효과는 담수 60일 이상 처리에서 <TEX>$93.5{\sim}99.2%$</TEX>였고, 뿌리이병율도 무담수에 비해 <TEX>$1/11{\sim}1/18$</TEX> 수준으로 크게 감소하였다. 양파 재배포장에서의 발병율 또한 담수 60일 이상 처리에서 5% 미만으로 크게 감소하였다. 양파의 구중과 상품수량은 무담수에 비해 담수처리에서 증가되었으며, 담수기간이 길어질수록 대구의 비율이 늘어나는 경향을 보였다. 이와 같이 양파 분홍색뿌리썩음병이 심하게 발생하고 있는 연작지에 양파를 정식하기 전에 담수처리를 할 경우, 적어도 2년간, 60일 이상 담수처리를 하였을 때 효과적으로 분홍색뿌리썩음병균의 밀도와 병발생을 경감시킬 수 있으며, 정상적인 양파 육묘 및 생육에 의한 구비대로 수량 증수효과가 클 것으로 판단된다. Pink root disease of onion, a known worldwide constraint upon onion production, significantly reduces crop levels in the main Korea cultivation area. In order to examine the effect of flooding on incidence of pink root disease caused by Pyrenochaeta terrestris and on onion growth and on populations of soil fungi, field experiments were conducted during two seasons, 2003/04 and 2004/05 at Onion Research Institute. Populations of soil fungi from fields were assayed on selective media. Flooding treatment was effective in reducing populations of P. terrestris, Pythium spp., and Rhizoctonia sp. in soil; fungal populations in soils flooded for 90 days were reduced to 1/2 to 1/3 of those in non-flooded soils. In nursery bed, protective activities of soils flooded for over 60 days were 93.5 to 99.2% and their pink root incidences were less than 5%, which were 1/11 to 1/18 of that in control. Increased yield of onion bulbs was associated with control of soil borne pathogenic fungi by flooding treatments. As flooding period was prolonged, bulb grade showed the tendency to increase. Soil flooding for over 60 days resulted in effective disease control, facilitated accurate planning of plant population in the field, extension of the growing-season and consequently higher yields of better quality.

Black Stain Root Disease Studies on Ponderosa Pine - Parameters and Disturbance Treatments Affecting Infection and Mortality

Black stain root disease of ponderosa pine (Pinus ponderosa Doug. Ex Laws.), caused by Leptographium wageneri var. ponderosum (Harrington &amp; Cobb) Harrington &amp; Cobb, is increasing on many eastside Sierra Nevada pine stands in northeastern California. The disease is spread from tree to tree via root contacts and grafts but overland spread of the disease is most likely due to woody root feeding bark beetle (Coleoptera:Scolytidae) vectors. Soil and site relations along with disturbance are factors in the etiology of the disease (Harrington and Cobb 1988). Thinning and prescribed burning are important silvicultural tools in maintaining forest health in eastside pine stands. Because soil compaction is a concern in many sites, skid trails are treated by subsoiling equipment to alleviate compaction where this might be an issue. However, little is known of the effects of these silvicultural treatments on incidence of black stain root disease on sites with high disease risk. Because the woody root feeding insects that vector the disease respond to disturbance (Otrosina – Ferrell 1995), understanding consequences of different disturbances resulting from silvicultural treatments is essential for devising management plans to mitigate disease impact This paper summarizes preliminary results from two long-term studies initiated in 1996 and 2000 to address these issues.

Infiltration, soil moisture, root rot and nematode populations after 12 years of different tillage, residue and crop rotation managements

Tropical and subtropical highlands of the world have been densely populated and intensively cropped. Agricultural sustainability problems resulting from soil erosion and fertility decline have arisen throughout this agro-ecological zone. We assessed practices that would sustain higher and stable yields for wheat ( Triticum aestivum L.) and maize ( Zea mays L.) in this region. A long-term experiment (randomized complete block) was started in 1991 under rainfed conditions in the volcanic highlands of central Mexico (2240 m a.s.l.;19.31°N, 98.50°W; Phaeozem). Our objective was to determine infiltration, soil moisture content, root diseases and nematode populations at the end of 12 years of 16 management treatments from a factorial arrangement of: (1) four rotations (monocropping and rotation of maize and wheat), (2) two tillage (conventional tillage [CT] and zero tillage [ZT]) and (3) two crop residue management practices (residue retention and removal). Water infiltration and soil moisture levels were greater under ZT when residue was left in the field then when residue was removed. Higher infiltration rates and favourable moisture dynamics supported up to 30% yield increase. A significantly higher incidence of root rot was found in monoculture of maize under ZT than CT. Residue retention significantly increased maize root rot incidence compared to residue removal. Rotation of maize and wheat decreased the incidence of maize root rot up to 30%. In general, the incidence of root disease was lower in wheat (up to 3 on a scale of 7) than in maize (up to 3.93 on a scale of 4) for all treatment. In maize, both non-parasitic and parasitic nematodes increased under ZT; however, in wheat no effect of tillage was seen. Incidence of root rot and parasitic nematode populations were not correlated with yield. Although root diseases may have affected crop performance, they affected yield less than other critical plant growth factors such as infiltration and water availability. Both environmental conditions and microflora played a key role in the biology and expression of soil pathogens. In the semi-arid and rainfed subtropical highlands of central Mexico, positive effects were observed with zero tillage, crop rotations and crop residue retention, compared with common farming practices.

Introduced earthworms in agricultural and reclaimed land: their ecology and influences on soil properties, plant production and other soil biota

Accidental and deliberate introductions of earthworms into agricultural and reclaimed land are natural experiments that provide opportunities to understand the attributes of successful invaders and their impacts on local biota and ecosystem processes. We consider various case studies (e.g., earthworm invasions in agricultural soils in Australia and Brazil) and deliberate introductions of earthworms into reclaimed mine sites, landfills and cutaway peat in the U.K. and Ireland. Invasions of exotic earthworms, such as European Lumbricidae in Australia, have been geographically extensive, but remain very patchy at regional and field scales. Their impacts on soil properties, plant production and other biota are therefore also likely to be patchy. Various methods have been developed to deliberately inoculate exotic earthworms into disturbed lands, with varying degrees of success. The factors controlling success are, in general, poorly understood. A broad range of impacts of invasive earthworms on soil properties (e.g., soil structure, nutrient availability, burial of surface materials, incidence of root diseases) and plant yield and quality have been reported. Less is known of the impacts of invasive earthworms on other soil fauna, but they are likely to occur due to alterations in food availability and habitat structure. Influences on other biota are likely to extend to aboveground communities as well as those belowground. Introductions of earthworms to disturbed lands can yield substantial benefits in agricultural productivity and amelioration of soil degradation. However, the potential impact of the promotion or control of such introductions on non-target biota and ecosystem processes in pristine ecosystems nearby should be considered.