Nematode ascaroside enhances resistance in a broad spectrum of plant–pathogen systems

Recognition of specific molecule signatures of microbes, including pathogens, induces innate immune responses in plants, as well as in animals. Analogously, a nematode pheromone, the ascaroside ascr#18, induces hallmark plant defences including activation of (a) mitogen‐activated protein kinases, (b) salicylic acid‐ and jasmonic acid‐mediated defence signalling pathways and (c) defence gene expression and provides protection to a broad spectrum of pathogens. Ascr#18 is a member of an evolutionarily conserved family of nematode signalling molecules and is the major ascaroside secreted by plant–parasitic nematodes. Here, we report the effects of ascr#18 on resistance in four of the major economically important crops: maize, rice, wheat and soybean to some of their associated pathogens. Treatment with low nanomolar to low micromolar concentrations of ascr#18 provided from partial to strong protection in seven of eight plant–pathogen systems tested with viruses, bacteria, fungi, oomycetes and nematodes. This research may have potential to improve agricultural sustainability by reducing use of potentially harmful agrochemicals and enhance food security worldwide.     

Influences of blackberry margins on population dynamics of Drosophila suzukii and grape infestation in adjacent vineyards

Understanding the dynamics of pest insect populations in relation to the presence of non‐crop habitats and infestation levels of adjacent crops is essential to develop sustainable pest management strategies. The invasive pest species Drosophila suzukii (Diptera: Drosophilidae) is able to utilize a broad range of host plants. In viticulture, scientific risk assessment for D. suzukii has only recently started and studies assessing the effects of field margins containing wild host plants on D. suzukii population dynamics and on infestation risks in adjacent vineyards are lacking. Thus, in a one‐year field study, the role of different field margins on fly abundance and crop infestation in adjacent vineyards of Vitis vinifera, variety “Pinot Noir,” were investigated. Different monitoring methods were conducted to assess fly distribution, sex ratio and grape infestation in 14 vineyards adjacent to field margins containing either blackberry (BB) Rubus spp. or non‐host (NH) plants. Our results show that blackberries strongly enhanced D. suzukii abundance within field margin vegetation all year long, whereas fly abundance in vineyards adjacent to BB margins was just enhanced in some seasonal periods. Moreover, the influence of BB margins was limited by distance. However, high fly numbers in BB field margins did result in zero egg infestation of “Pinot Noir” berries. These results may have important implications for winegrowers to make efficient management decisions: regardless of high abundance of adult D. suzukii, only grape berry monitoring can assess the actual infestation risk and the potential need to take management action.     

Soil tillage reduces arthropod biodiversity and has lag effects within organic and conventional crop rotations

Crop rotation systems in organic and conventional farming systems differ in crop types, management and duration. However, changes in arthropod communities over the entire rotation system are poorly understood, as many studies have surveyed only single years or have not covered the entire rotation period. Here, we describe changes in arthropods in two contrasting systems at a split organic‐conventional farm: an 8‐year organically managed rotation with five crops and a 5‐year conventionally managed rotation with three crops. Arthropods were classified into three functional groups, representing epigeal predators, foliar predators/parasitoids and herbivores/pollinators. Epigeal predators were particularly reduced by soil tillage which occurred annually in the conventional rotation, but was intermittent in the organic. Arthropods were most abundant on the conventional rotation, but most taxonomically diverse on the organic. In the conventional system, all functional groups showed a cyclical change in their taxonomic composition that closely matched the crop rotation sequence, whereas in the organic rotation, the cycle was less clear. Whilst the current year's crop type was the major determinant of arthropod community composition, there was a significant “lag effect” for many taxa from the preceding year's crop. Our results suggest that both the amounts of soil tillage (e.g., in no‐till systems) and crop rotation order have major impacts on arthropods in agroecosystems. Rotations with excessive soil tillage are likely to reduce the abundance of some groups of beneficial arthropods, especially epigeal predators.     

The effects of nitrogen and fungicide on cereal aphid population development and the consequences for the aphid-yield relationship in winter wheat

In a field trial, done over two seasons, nitrogen and fungicide inputs to winter wheat were varied to obtain a range of yields to study the effects on aphid population development and the aphid-yield loss relationship. In the first year, the maximum density of Metopolophium dirhodum and total aphid index were significantly higher in the plots receiving the largest amount of nitrogen but there were few other consistent effects on aphid population development. In the second year there were no significant effects of either nitrogen or fungicide on aphid population development. Mean yields were high in 1987 and 1988 (7.0 and 8.5 t/ha respectively) with less than a 2 t/ha range in either year. There were no significant effects of aphids on yield in the first year but in the second, aphids caused a significant reduction. Damage per aphid unit did not change with increase in yield. The use of this approach in determining pest-yield loss relationships is discussed.     

Transgenic Arabidopsis leaf tissue expressing a modified oryzacystatin shows resistance to the field slug Deroceras reticulatum (Müller)

Transgenic Arabidopsis thaliana has been developed which expresses the oryzacystatin mutant OCI86, which is an inhibitor of the major proteinase present in the digestive gland of the slug, Deroceras reticulatum. When fed on leaf tissue from plants expressing this inhibitor the growth of juvenile slugs was significantly reduced by 31% compared with those feeding on control leaf tissue. Furthermore, while surviving slugs did not individually consume less when feeding on leaf tissue expressing OCI86, the total amount of leaf tissue eaten was 50% less, due to reduced survival of slugs. The synthetic cysteine proteinase inhibitors E64 and leupeptin also significantly reduced slug weight gain (by at least 40%) and digestive gland cysteine proteinase activity when administered in an artificial diet, indicating that their antimetabolic effects are due to direct inhibition of gut proteolytic activity. These results suggest that transgenic crop plants expressing phytocystatins could be used to suppress the growth rates of slug populations in the field.     

Effects of Nutrient Limitation on Aboveground Carbon Dynamics during Tropical Dry Forest Regeneration in Yucatán,Mexico

Tree growth (as diameter increment), litterfall production, and litter biomass were studied in two secondary tropical dry forests of the Yucatán Peninsula under four treatments of nutrient addition. The studys objective was to assess how variations in the nutrient supply affect aboveground net primary production and carbon (C) accumulation on the floor of two forests in different stages of regeneration. The study included an area of young forest (10 years old) with phosphorus (P)-poor soils and an area of old forest (around 60 years old) where soil P was comparatively less limiting. Four replicate plots (12 × 12 m) at each forest were either left intact (controls) or fertilized with nitrogen (N), P, or N plus P during 3 consecutive years. After 3 years of fertilization, relaxation of the constraints on nutrient limitation resulted in increased trunk growth rates at both the young and old forests. This effect was more pronounced with the addition of P or N plus P (trunk growth doubled with respect to controls), whereas N addition increased tree growth by 60% in comparison to trees in plots without nutrient supplements. In both forests, there were no significant differences in litterfall production among treatments during the first 2 years after fertilization. In the 3rd year of nutrient addition, litterfall production was significantly higher in plots fertilized with N plus P compared to control plots at both forest sites; however, changes in litterfall were not accompanied by litter accumulation in the floor of the two forests. The results of this study support the hypothesis that there is nutrient limitation during tropical dry forest regeneration. They further show that it may be maintained in the long term during secondary succession.     

作物最高理论产量计算方法的应用——以合肥地区水稻为例

本文以合肥地区水稻为例,探讨了作物最高理论产量的计算方法,即首先根据“ＦＡＯ”农业生态带理论,计算出作物光温生产力指数,再根据当地的气候（主要是水分状况）对作物的光温生产力指数进行订正,从而求出作物的最高理论产量。     

The potential benefits from cultivar specific red clover -potato crop rotations

The aim of this study was to determine if endophytic bacteria could contribute to cultivar specific interactions between red clover (Trifolium pratense L.) and potatoes (Solanum tuberosum L.) in crop rotations. Endophytic bacteria were isolated from the roots of four red clover cultivars (AC Charlie, Altaswede, Marino and Tempus) grown in the field. Populations of bacteria from each cultivar were similar. The most abundant genus was Rhizobium, but species of Curtobacterium, Pseudomonas, and Xanthomonas were common to all cultivars. Plantlets of two potato cultivars, Russet Burbank and Shepody, were inoculated individually with the seven bacterial isolates most frequently recovered from each red clover cultivar, and grown in Magenta vessels for 6 wk. Significant differences were found for plant height, and wet weights of roots, shoots and their total. Potato cultivars differed for root wet weight only, while red clover cultivar, as a source of bacteria, had a significant effect on all traits except plant height. Differences among bacteria were significant for all traits except shoot wet weight. There was a significant interaction of potato cultivar by red clover cultivar. The potato cultivar Russet Burbank did best with bacteria from the red clover cultivar, Marino; and Shepody, with bacteria from Altaswede.     

Early phosphorus nutrition,mycorrhizae development,dry matter partitioning and yield of maize

We conducted a field experiment to test the hypothesis that improved phosphorus nutrition occurs in maize plants with rapid arbuscular (AM) mycorrhizae development at early developmental stages and that this also is reflected in dry matter allocation and final yield. A split-split plot design was used with previous crop (Zea mays L.-maize and Brassica napus L.-canola), tillage practices (no-tillage or conventional tillage) and P fertilization (5 levels) as factors chosen to modify mycorrhizae development at early developmental stages of maize. Previous cropping with canola resulted in decreased shoot-P concentration and shoot growth of maize at early stages. No-tillage resulted in higher shoot-P concentration but lower shoot weight than conventional tillage. Greater shoot-P uptake was related to a rapid intraradical development of mycorrhizae (previous crop of maize) or rapid connection to a mycorrhizal mycelium network (no-tillage treatments). Maize yield and harvest index were lower after cropping with canola. The yield for conventional tillage was higher than that for no-tillage but the harvest index was lower. The hypothesis was supported at early stages of maize growth by the effect of previous crop but not by results of tillage, because an unknown factor reduced growth in the no-tillage system. The hypothesis was supported at maturity by increased biomass allocation to grain relative to total shoot weight in treatments with greater shoot-P concentration at early stages.     

Reducing Meloidogyne incognita Injury to Cucumber in a Tomato-Cucumber Double-Cropping System

The effects of a root-knot nematode-resistant tomato cultivar and application of the nematicide ethoprop on root-knot nematode injury to cucumber were compared in a tomato-cucumber double-cropping system. A root-knot nematode-resistant tomato cultivar, Celebrity, and a susceptible cultivar, Heatwave, were grown in rotation with cucumber in 1995 and 1996. Celebrity suppressed populations of Meloidogyne incognita in the soil and resulted in a low root-gall rating on the subsequent cucumber crop. Nematode population densities were significantly lower at the termination of the cucumber crop in plots following Celebrity than in plots following Heatwave. Premium and marketable yields of cucumbers were higher in plots following Celebrity than in plots following Heatwave. Application of ethoprop through drip irrigation at 4.6 kg a.i./ha reduced root galling on the cucumber crop but had no effect on the nematode population density in the soil at crop termination. Ethoprop did not affect cucumber yield. These results indicate that planting a resistant tomato cultivar in a tomato-cucumber double-cropping system is more effective than applying ethoprop for managing M. incognita.