Studies of yield losses I. The self-limiting effect of injurious or competitive organisms on crop-yield

Summary Four hypothetical models illustrate how competition between pathogens diminishes the effect of individuals as numbers increase. As a result the relation between crop yield or growth and the initial population level is not linear. The effect on yield falls off as the initial population increases or when graphed the yield curve tends to become horizontal.Samenvatting Aan vier modellen wordt duidelijk gemaakt, hoe concurrentie tussen schadelijke organismen de invloed van het individu op de waardplant kan verminderen. Als gevolg daarvan zal de relatie tussen het aantal organismen en de oogstderving of de groei niet rechtlijning zijn. Het effect wordt relatief minder als het aantal schadelijke organismen stijgt. In een grafiek heeft de lijn de neiging om horizontaal te worden bij hogere aantallen organismen, bijvoorbeeld fig. 6 (oogst verticaal, schadelijke organismen horizontaal).For the mathematics the reader is referred to the appendix.     

Eop1 from a Rubus strain of Erwinia amylovora functions as a host-range limiting factor

Strains of Erwinia amylovora, the bacterium causing the disease fire blight of rosaceous plants, are separated into two groups based on host range: Spiraeoideae and Rubus strains. Spiraeoideae strains have wide host ranges, infecting plants in many rosaceous genera, including apple and pear. In the field, Rubus strains infect the genus Rubus exclusively, which includes raspberry and blackberry. Based on comparisons of limited sequence data from a Rubus and a Spiraeoideae strain, the gene eop1 was identified as unusually divergent, and it was selected as a possible host specificity factor. To test this, eop1 genes from a Rubus strain and a Spiraeoideae strain were cloned and mutated. Expression of the Rubus-strain eop1 reduced the virulence of E. amylovora in immature pear fruit and in apple shoots. Sequencing the orfA-eop1 regions of several strains of E. amylovora confirmed that forms of eop1 are conserved among strains with similar host ranges. This work provides evidence that eop1 from a Rubus-specific strain can function as a determinant of host specificity in E. amylovora.     

Limits of a simple model to predict yield losses in maize

In order to estimate yearly variations and accuracy of prediction of maize yield losses due to weeds, we used supplementary maize individuals that mimic weeds and reduce the experimental variability. Biomass decrease at various growth stages and grain yield losses of maize were interpreted through regression analyses in terms of density and biomass of supplementary individuals. Comparison of losses due to weeds and supplementary maize does not allow the calculation of equivalent weed-maize density or biomass at the same competitive effect. In most cases regression curves obtained in maize-maize experiments were different from one year to another. The use of results from several trials, previously published, on the effect of plant spacing on maize yield over a number of years also showed a large variation in predicted values, which confirmed the inaccuracy of an empirical predictive model using weed density and biomass. Limites d'un modèle simple de prédiction des pertes de rendement dans le maïs Afin d'évaluer les variations annuelles et l'incertitude liées à la prédiction des pertes de rendement dues aux mauvaises herbes chez le maäs, nous avons utilisé des pieds supplémentaires de maäs pour simuler les mauvaises herbes et réduire la variabilité expérimentale. Les pertes de biomasses à différents stades du développement et les pertes de rendement en grain ont été interprétées par des analyses de régression en fonction de eadensité et de la biomasse des plantes supplémentaires de maäs. La comparaison avec les pertes dues aux mauvaises herbes n'a pas permis d'aboutir à des fonctions de densité ou de biomasse équivalentes pour le même effet compétitif. Les régressions obtenues dans le système maäs-maäs ont été le plus souvent différentes d'une année à l'autre. L'utilisation des résultats de nombreux essais pluriannuels déjà publiés sur l'effet de la densité de semis sur le rendement du maäs a montréégalement une forte incertitude sur les valeurs prédites, ce qui confirme l'imprécision d'un modèle empirique de prédiction de la compétition fondé sur la densité et la biomasse des mauvaises herbes. Grenzen eines einfachen Modells zur Vorhersage von Ertragsverlusten beim Mais Zur Abschätzung der jährlichen Schwankungen und der Genauigkeit der Vorhersage von Ertragsverlusten beim Mais infolge Unkrautkonkurrenz wurden zusätzliche Maispflanzen eingesetzt, um die Wirkung von Unkräutern zu simulieren und die Versuchsgenauigkeit zu erhöhen. Die Abnahme der Biomasse in verschiedenen Entwicklungsstadien und die Ertragsverluste des Maises wurden anhand der Dichte und der Biomasse der zusätzlichen Maispflanzen regressionsanalytisch untersucht. Durch Vergleich der Verluste durch Unkräuter und zusätzliche Maispflanzen kann eine äquivalente Unkraut-Mais-Dichte oder -Biomasse für die gleiche Konkurrenzwirkung nicht gefunden werden. Von Jahr zu Jahr waren die Regressionskurven der Mais-Mais-Versuche meistens verschieden. Bei der Verarbeitung von früher veröffentlichten Ergebnissen aus verschiedenen Versuchen in einer Reihe von Jahren zur Wirkung der Pflanzdichte auf den Ertrag beim Mais zeigte sich ebenso eine groβe Variation der vorhergesagten Werte, wodurch die Ungenauigkeit eines empirischen Prognose-Modells auf der Grundlage von Unkrautdichte und -biomasse bestätigt wurde.     

Studies on the epidemiology and yield losses from rice black-streaked dwarf disease in a recent epidemic in Zhejiang province, China

The spread of rice black-streaked dwarf disease, which has emerged as a major problem on winter wheat and the two summer rice crops (early indica and late japonica ) grown in central and southern Zhejiang province, China, is documented from 1995 to 2007. The late japonica crop suffered the most: up to 64 640 ha were affected with estimated losses of c . 120 000 t grain per year. Peak adult numbers of the small brown planthopper vector, Laodelphax striatellus , coincided with the seedling stages of both rice crops and the proportion of the insect population carrying virus increased during 1998–2005. Seedlings with three to four leaves were the most susceptible, whereas plants inoculated after the end of tillering developed few or no symptoms. Disease levels were strongly correlated with numbers of viruliferous vectors. In sowing-date experiments with both rice crops, the earliest sowings had the most disease and suffered the greatest yield losses. With the last sowing date (25 days after the first), there were almost no losses. There were yield losses of 0·80% for every 1% increase in disease incidence in early indica rice and rather more (0·92%) in the late japonica crop. There were large differences in susceptibility between cultivars, indicating the possibility, within currently available germplasm, of using more resistant cultivars to help contain the disease. Changes in cropping practice and in recent winter weather conditions have probably contributed to the emergence of the virus as a major pathogen in eastern China.     

小麦纹枯病产量损失估计研究

研究了小麦纹枯病病情指数与产量损失率及千粒重的关系。结果表明,产量损失率随着病情指数的增加而增大;千粒重随着病情指数的增加呈下降趋势,并在此基础上组建了病情指数与产量损失率的关系模型,病情指数与千粒重的关系模型。     

Simulation modelling of yield losses caused by wheat stem rust

Stem rust, or black rust, of wheat, caused by Puccinia graminis f. sp. tritici, has recently re-emerged in several parts of the world, with epidemics occurring in eastern Africa, as well as northern and southern Europe. Damage mechanisms from disease dynamically affect the physiology of the crop as it grows and develops, and as the epidemic progresses, leading to yield losses in the stem rust-diseased wheat stand. Process-based agrophysiological models that include disease-induced damage mechanisms can help to better understand the physiological processes leading to yield losses, and to inform strategic decisions such as breeding strategies. Such models have not been developed for wheat stem rust so far. Two damage mechanisms for stem rust, light stealing and assimilate diversion, were incorporated in the agrophysiological simulation model WHEATPEST. The model, tested from experimental field data retrieved from the literature, provides a satisfactory representation of the system, although consistently underestimates relative yield losses by about 6.9%, resulting in relative yield losses between 17% and 56%. Analyses highlight the importance of the diversion of assimilates toward the pathogen in the magnitude of yield loss. Considering only the reduction of green leaf area would underestimate damage from stem rust by at least threefold. The analysis also shows the importance of the dynamic interplay between disease and crop growth, especially the dynamics of leaf area, on yield loss. Directions to consider additional damage mechanisms are proposed, and perspectives for future research, especially in relation to plant breeding strategies under climate change, are offered.     

The estimation of yield losses in wheat from severity of infection by Septoria species

Equations to assist the estimation of national losses from the results of disease surveys carried out at GS75 were derived from five fungicide trials and two inoculation experiments in the field. The equations indicate that the percentage loss in grain yield is equal to 5.412x_i^0.6, 1.011x_ior 0.551x_ii where x_i and x_ii are the percentage area infected on the flag and second leaves respectively.     

Studies on the breakdown of p-chlorophenyl methylcarbamate. II. In cultures of a soil Arthrobacter sp.

p-Chlorophenyl methylcarbamate (PCMC) underwent spontaneous hydrolysis in aqueous solution to p-chlorophenol with concomitant loss of ability to inhibit hydrolysis of the phenylcarbamate isopropyl phenylcarbamate (propham). A phenylcarbamate-degrading soil Arthrobacter sp. had no direct effect on PCMC itself but formed 4-chlorocatechol during the metabolism of p-chlorophenol.     

Weed competition in willow coppice crops: the cause and extent of yield losses

Growth in 2-year-old willow Salix spp., grown in the short-rotation coppice (SRC) system on agricultural land, was compared in 30 weeded and 30 unweeded plots in each of 2 years after cutting. Non-destructive assessment methods of both crop and weed biomass were used. Coppice growth in year I was greater in the weeded plots than in the unweeded plots. In year II, coppice growth was not different between plots so that, over the 2-year study period, the coppice yield reductions with weeds reflected the losses in year I only. There was considerable variation in the amount of weeds in the unweeded plots. The relationship between the volume of weeds present and the extent of the coppice yield reduction over 1 and 2 years after cutting are described by linear models. Soil moisture and nutrient content, when measured in mid-summer, were not different between plots in either year. In year I, mid-summer coppice height was greater in the weedy plots, while stem numbers in both years and canopy density in year II were lower in the weedy plots. These results indicate that tall weeds competing for light and space in the first year of growth, rather than moisture or nutrient stress, caused fewer (and taller) stems to grow from the coppice stools, leading to the observed reductions in biomass.     

Research priorities for rice pest management in tropical Asia: a simulation analysis of yield losses and management efficiencies

ABSTRACT A simulation study was conducted to assess the current and prospective efficiency of rice pest management and develop research priorities for lowland production situations in tropical Asia. Simulation modeling with the RICEPEST model provided the flexibility required to address varying production situations and diverse pest profiles (bacterial leaf blight, sheath blight, brown spot, leaf blast, neck blast, sheath rot, white heads, dead hearts, brown plant-hoppers, insect defoliators, and weeds). Operational definitions for management efficacy (injury reduction) and management efficiency (yield gain) were developed. This approach enabled the modeling of scenarios pertaining to different pest management strategies within the agroecological contexts of rice production and their associated pest injuries. Rice pests could be classified into two broad research priority-setting categories with respect to simulated yield losses and management efficiencies. One group, including weeds, sheath blight, and brown spot, consists of pests for which effective pest management tools need to be developed. The second group consists of leaf blast, neck blast, bacterial leaf blight, and brown plant-hoppers, for which the efficiency of current management methods is to be maintained. Simulated yield losses in future production situations indicated that a new type of rice plant with high-harvest index and high-biomass production ("New Plant Type") was more vulnerable to pests than hybrid rice. Simulations also indicated that the impact of deployment of host resistance (e.g., through genetic engineering) was much larger when targeted against sheath blight than when targeted against stem borers. Simulated yield losses for combinations of production situations and injury profiles that dominate current lowland rice production in tropical Asia ranged from 140 to 230 g m(-2). For these combinations, the simulated efficiency of current pest management methods, expressed in terms of relative yield gains, ranged from 0.38 to 0.74. Overall, the analyses indicated that 120 to 200 x 10(6) tons of grain yield are lost yearly to pests over the 87 x 10(6) ha of lowland rice in tropical Asia. This also amounts to the potential gain that future pest management strategies could achieve, if deployed.     

Plant‐parasitic nematodes of potential phytosanitary importance,their main hosts and reported yield losses

The potential phytosanitary importance of all named plant‐parasitic nematode species was determined by evaluating available information on species characteristics, association with economically‐important crop hosts, and ability to act as vectors of viruses or form disease complexes with other pathogens. Most named species of plant‐parasitic nematodes (PPN) are poorly known, recorded from a single location only, not associated with economically‐important crops, and not known to be associated with other plant disease organisms. However, 250 species from 43 genera fulfilled one or more of the criteria to be considered to present a phytosanitary risk. The genera and number of species (in parentheses) considered as posing phytosanitary risk included: Achlysiella (1), Anguina (8), Aphasmatylenchus (1), Aphelenchoides (12), Aphelenchus (1), Belonolaimus (2), Bitylenchus (3), Bursaphelenchus (4), Cactodera (3), Ditylenchus (8), Dolichodorus (1), Globodera (3), Helicotylenchus (7), Hemicriconemoides (3), Hemicycliophora (3), Heterodera (25), Hirschmanniella (5), Hoplolaimus (5), Ibipora (3), Longidorus (10), Macroposthonia (2), Meloidogyne (38), Merlinius (3), Nacobbus (1), Neodolichodorus (2), Paralongidorus (2), Paratrichodorus (11), Paratylenchus (3), Pratylenchus (24), Punctodera (3), Quinisulcius (3), Radopholus (5), Rotylenchulus (3), Rotylenchus (1), Scutellonema (5), Sphaeronema (1), Subanguina (3), Trichodorus (5), Tylenchorhynchus (8), Tylenchulus (2), Vittatidera (1), Xiphinema (15) and Zygotylenchus (1). For each of the 250 species main hosts and yield loss estimates are provided with an extensive bibliography. Of the 250 species, only 126 species from 33 genera are currently listed as regulated pests in one or more countries worldwide. Almost all of these 250 species were also associated with economically important crops and some also acted as vectors for viruses.     

中稻主要病虫为害损失和防治效益试验

通过中稻主要病虫害的防治试验,结果表明,在病虫害偏重发生年份,在病虫害基本控制的常规防治区稻谷单产达611.2 kg/667m2情况下,完全未打药防治区病虫为害损失稻谷245.4 kg/667m2,损失率40.15%.单种病虫不防治区,稻飞虱、纹枯病、稻纵卷叶螟、螟虫未防治的损失率分别为28.88%、27.49%、15.31%和7.33%.由此可见,在水稻生产中,加强病虫害监测,科学指导农民防治病虫害,是减少粮食损失,增加农民收入的有效途径.     

Modelling the economics of herbicide treatment in wheat and barley using data on prevented grain yield losses

Losses in grain yield prevented by controlling weeds were measured in 59 fields of (southern hemisphere) spring-sown wheat (Triticum aestivum L.) (cv, Otane) and 45 fields of spring-sown barley (Hordeum vulgare L.) (cv. Corniche) in five consecutive growing seasons from 1988/89 until 1992/93 in the Canterbury region of New Zealand. The losses were measured as the differences in yield between weeded and non-weeded plots located in randomly positioned pairs in the fields. In the first 2 years, the weeding was by push hoe in‘organically grown crops. For the last 3 years, the fields were under prophylactic herbicide regimens with nonweeded plots created by excluding commercial herbicide applications (made mostly in October for wheat and November for barley) with polyethylene sheets placed temporarily over the plots. For each season the distributions of yield losses were modelled using the normal distribution and probabilities of ‘breaking even’ on herbicide use derived by substituting cumulative probability density functions into a simple break-even model for herbicide use. The model assumed that herbicide application in the current crop has no flow-on economic effect for succeeding crops. The mean annual yield losses prevented by herbicide application were positively correlated with September and October rainfall for wheat and bailey respectively. As a consequence, the probabilities of breaking even on herbicide use increased with increasing spring rainfall. Using historical rainfall records, probabilities of breaking even were estimated for each of the 48 years from 1947 to 1994. Averaging over these years, the analysis revealed that at current grain prices prophylactic use of the commonly applied herbicides is likely to be uneconomic in 24% (95% confidence limits 6% and 50%) of fields of average-yielding Otane wheat and in 26% (95% confidence limits 1% and 91 %) of fields of average-yielding Corniche barley in Canterbury. It was concluded that there is potential for withholding herbicide treatments without jeopardizing profitability in these crops, particularly in seasons with low spring rainfall.     

Feeding behaviour as a limiting step in insecticide absorption for the wireworm Agriotes sp. (Coleoptera: Elateridae)

The fipronil control of wireworms field populations (larval Agriotes sp., Coleoptera: Elateridae) is difficult because of the low integumental penetration rates of this insecticide into the target larval body. The main way of insecticide absorption being associated with food, analysis of the larval feeding behaviour is of key importance for designing a strategy of dietary chemical control of those subterranean pests. In this purpose, a standard method for assessing the long-term survival of field specimens in the laboratory was developed together with experimental designs for investigating food searching and choosing by larvae. Larval biological performances under those laboratory conditions were checked monthly. Three criteria were taken into account for measures: the duration of individual survival, the gain in average body weight, and the moulting rhythm. Experimentation revealed that seed flour was highly desired by larvae and that larval feeding choice was affected over short distances only. This suggests the involvement of dietary preference rather than attractivity in the larval feeding behaviour. This implies that, at the operational step, insecticide had better be associated to food, either as a coating on the seeds, or inside preferred baits.     

Studies of Salvia reflexa Hornem.: II. Examination of specialized leaf surface structures

Scanning electron microscope examination ofadaxial leaf surfaces of Salria reflexa revealed specialized structures from which chemical release was apparently promoted by immersion in water. The significance of ihese slruciures and their contents is discussed in relation to the alletopathic activiiy of this species.     

Estimation of rice yield losses due to the African rice gall midge,Orseolia oryzivora Harris and Gagne

Abstract

The African rice gall midge, Orseolia oryzivora Harris and Gagne (Diptera: Cecidomyiidae), is an important pest of rice, Oryza sativa, in Burkina Faso as well as other countries in West and East Africa. In spite of its importance, little is known regarding the relationship between gall midge populations and grain yield losses. To determine yield losses the gall midge was reared in cages and adult midges were placed on caged plants of the rice variety ITA 123 at different population levels. The seven treatments consisted of different numbers of insects infested on the plants; 0 insect pairs (non‐infested check), and 1, 5, 10, 15, 20 or 25 midge pairs/cage. The loss in yield in relation to the non‐infested control was highly positively correlated (R² = 0.81) with the percentage of gall midge damaged tillers. The infestation by the insect on the plants resulted in the compensatory production of tillers which developed in response to the gall midge damage but the compensation was not sufficient to make up for the loss of yield due to the damaged tillers. Yield loss ranged from 0% in the control to 65.3% in the treatment with 25 pairs of adults. One per cent of tillers damaged resulted in 2% grain yield loss.     

Studies on the reinfection and yield of virus-tested and commercial stocks of rhubarb cv. Timperley Early

Ten commercial stocks of rhubarb cv. Timperley Early were found to be infected with turnip mosaic, arabis mosaic and to a lesser extent cherry leaf roll, strawberry latent ringspot and cucumber mosaic viruses. Significant yield differences were recorded between the stocks in forcing experiments, but these were not related to virus incidence. The performance of a mixture of these infected commercial stocks was compared with that of virus-tested stocks in canning, early green-pulled, and forcing experiments. A significant yield advantage was recorded in the first 2 years from the virus-tested stock harvested for canning, but not in the other two experiments. Of the five viruses isolated, turnip mosaic most frequently reinfected virus-tested stocks and there appeared to be a connection between reinfection of the healthy plants and subsequent reduction in their yield.     

Assessment of yield losses caused by chickpea chlorotic dwarf geminivirus in chickpea (Cicer arietinum) in India

Yield losses caused by chickpea chlorotic dwarf virus in chickpea were estimated by comparing uninfected and infected plants in the field at two locations in India. When infection was before flowering, yield losses of individual plants amounted to nearly 100% in the three cultivars studies. Plants that became infected during flowering had yield losses of 75–90%. Percentage of crop loss is likely to equal percentage of disease incidence, since plant densities in farmers' fields are probably too low to allow uninfected plants around infected ones to compensate the yield losses of infected plants.Submitted as Journal Article No. 1624 by ICRISAT.     

近10年农作物主要病虫害发生危害情况的统计和分析

2006-2015年,我国农作物病虫草鼠害总体处于严重发生状态,各类病虫害年发生面积在4.603 5亿~5.075 3亿hm2次,年均挽回粮食损失9 684.68万t,占全国粮食总产的17.35%;年均实际损失粮食1 965.49万t,占全国粮食总产的3.53%。五大粮食作物中每年通过防治挽回损失的比例,水稻、小麦、玉米、大豆和马铃薯分别占55.18%、21.29%、18.97%、1.88%和2.68%,实际造成损失的比例分别占33.67%、23.31%、35.13%、2.11%和5.79%。影响全国粮食生产最为重要的10种(类)病虫害依次为稻飞虱、水稻纹枯病、稻纵卷叶螟、玉米螟、小麦蚜虫、二化螟、稻瘟病、小麦纹枯病、小麦赤霉病、小麦白粉病;某一个病虫暴发危害时最高可实际造成200万t以上的粮食损失,总损失可达2 200万t,占某类粮食总产的12%左右,对国家粮食安全影响巨大。最具暴发和流行危害特点的种类主要有稻飞虱、稻纵卷叶螟、稻瘟病、小麦条锈病、小麦赤霉病和黏虫等6种。本文运用大量翔实的历史数据统计分析了近10年来水稻、小麦、玉米三大粮食作物病虫害的危害损失和暴发危害情况。