BYDV PREDICTOR: a simulation model to predict aphid arrival, epidemics of Barley yellow dwarf virus and yield losses in wheat crops in a Mediterranean-type environment

BYDV PREDICTOR, a simulation model, was developed to forecast aphid outbreaks and Barley yellow dwarf virus (BYDV) epidemics in wheat crops in the grainbelt region of southwest Australia, which has a Mediterranean-type climate. The model used daily rainfall and mean temperature to predict aphid ( Rhopalosiphum padi ) buildup in each locality before the commencement of the cereal-growing season in late autumn, and to forecast the timing of aphid immigration into crops. The introduction of BYDV by aphid immigrants, aphid buildup within the crop, spread of BYDV, and yield losses were predicted for different sowing dates. The model simulations were validated with 10 years' field data from five different sites in the grainbelt, representing a wide range of scenarios. When first aphid arrival dates ranging from 1 June to 2 September were compared with predictions, 65% of the variation between sites and years was explained. Progress curves for the predicted percentage of plants infected with the serotype BYDV-PAV closely resembled the starting point and shape of those recorded in 14 out of 18 scenarios. Sensitivity analysis confirmed that the combination of a high proportion of immigrants vectoring BYDV, early sowing of crops and early start to aphid arrival relative to sowing date led to the most BYDV spread and greatest yield loss. The model was incorporated into a decision support system used by farmers in targeting sprays against aphids to prevent virus spread in autumn and winter. BYDV PREDICTOR could serve as a template for modelling similar virus/aphid vector pathosystems in other regions of the world, especially those with Mediterranean-type climates.     

蛋白质激发子Hrip1对小麦黄矮病的诱抗作用

小麦黄矮病是由大麦黄矮病毒（barley yellow dwarf virus,BYDV）引起的一种小麦病毒病,其传播介体是小麦蚜虫,在小麦生产中造成巨大的经济损失。近年来,植物诱导抗性作为一种新兴的植物病虫害防治措施引起了广泛的关注。蛋白质激发子Hrip1可以激活多种植物的免疫防御反应诱导植物产生广谱抗性。本研究评价了Hrip1对小麦黄矮病的诱抗效果。用30 μg/mL的Hrip1溶液进行小麦浸种和幼苗喷雾,随后接种BYDV,接种后第14 d,Hrip1对小麦黄矮病控制效果在50%以上,接种后第21 d控制效果仍在30%以上。实时荧光定量PCR检测结果显示,在Hrip1处理的小麦幼苗体内,BYDV外壳蛋白mRNA的数量显著低于对照组;EPG结果显示,在Hrip1处理的小麦幼苗上,麦二叉蚜寻找叶片刺吸位点和韧皮部取食位点的时间增加。以上结果表明：Hrip1能够有效地抑制BYDV在小麦体内的增殖;影响传毒媒介麦二叉蚜的取食行为,抑制其传毒能力。此外,Hrip1处理小麦能有效缓解BYDV引起的叶片黄化和植株矮化的症状。因此,Hrip1可以作为生物诱导剂综合控制小麦黄矮病。     

大麦黄矮病毒GPV与GAV株系间异源装配现象的初步研究

 以我国麦区的大麦黄矮病毒GPV、GAV株系为材料,利用它们的蚜传特异性,将由禾谷缢管蚜传播的GPV和由麦长管蚜传播的GAV混合侵染到岸黑燕麦上,并进行继代传毒。混合侵染后代蚜传表现型的变化初步表明存在异源装配现象,且表现型混合发生的比例较高。用DAS-ELISA和RT-PCR法对混合侵染后代进行了测定,进一步证明了异源包装现象的存在。部分基因的核苷酸序列分析初步显示所测定的混合侵染后代中没有发生基因重组。     

Occurrence of barley yellow dwarf virus in pastures of western France

As pasture grasses are preponderant in the agriculture of western France, their role as reservoirs of barley yellow dwarf virus (BYDV) and its aphid vectors has been studied from 1984 to 1986. Aphids were observed on most crops of five pasture grass species (brome grass, cocksfoot, tall fescue, Italian and perennial ryegrass) but in very low numbers. Rhopalosiphum padi was the most numerous species. The incidence of BYDV was high, with levels of infection ranging from 6 to 80% depending on the species of pasture grasses. Fescue pastures were highly infected with BYDV, whereas the virus was not detected in cocksfoot pastures. PAV-, RPV-, MAV-like isolates of BYDV were detected in pasture grasses, but RPV- and MAV-like isolates were only detected from ryegrass and brome grass, respectively. The role of these grasses as source of viruliferous aphids infecting cereals is discussed.     

兼抗麦长管蚜和大麦黄矮病毒的小麦种质田间鉴定筛选

为鉴定筛选兼抗麦长管蚜和大麦黄矮病毒(Barley yellow dwarf virus, BYDV)的小麦种质,采用自然感蚜/感病系数法,对36个外引和远缘杂交选育的小麦种质材料进行了2年的田间鉴定,并分析了感虫性与感病性的相关关系。结果表明,2年中均兼抗麦长管蚜和BYDV的种质仅有KOKIPPCAS、KOK、Amigo-3和PI137739共4个材料,占总鉴定材料的11.11%;对二者均敏感的有98-10-35q-9、186Tm39、Tam200e12-14a、Tam200(27)7、小偃22、西农1376和小偃6号共7个材料,占19.44%。其它材料仅抗虫或仅抗病,或仅在一年中表现抗病或抗虫,如材料98-10-30和98-10-35a8抗麦长管蚜,但对BYDV敏感;材料Tam200(13)G和PIG23(2)C感蚜,但对BYDV有抑制作用。BYDV发生普遍率(发病株率)和严重度(病情指数)与有蚜株率显著相关,严重度还与感蚜指数显著相关,但感病植株的病级均值与有蚜株率无显著相关性。表明自然界长期的进化和选择使许多抗病虫基因得以保存下来,但较多抗性基因只在抗病或抗虫的某一方面表现有效,需给予更多关注。     

Aphid Abundance on Cereals in Autumn Predicts Yield Losses Caused by Barley yellow dwarf virus

ABSTRACT Barley yellow dwarf virus (BYDV) damage to winter cereals and population dynamics of the aphid Rhopalosiphum padi during fall were monitored in fields during 10 years at various locations in the northern half of France. Logistic regression was used to examine whether a simple risk probability algorithm based only on the autumnal population dynamics of R. padi can accurately predict yield losses caused by BYDV and, therefore, the need for insecticide treatment. Results showed that the area under the curve of the percentage of plants infested by R. padi during autumn was highly significantly related to BYDV yield losses. Then, a cost/benefit analysis was performed to estimate the optimal decision threshold resulting in the lowest annual average costs of BYDV damage and control. A "model use" strategy allowed a reduction in the annual average costs of BYDV disease and control of up to 36% when compared with a "prophylactic spraying" strategy. The optimal decision threshold was highly sensitive to variation in disease prevalence. This property was used to propose an easy way to adapt the model to any production situation through the determination of the most accurate decision threshold.     

Transmission of barley yellow dwarf virus by cereal aphids collected from different habitats on cereal farms

Cereal aphids were collected from cereal crops, from Poa annua within cereal fields, from Lolium perenne pastures and from wild grasses in hedge bottoms and around farm buildings. The frequency of barley yellow dwarf virus (BYDV) transmission was assessed by aphid transmission tests. There were differences in transmission rates between aphid species, between host species and between years. The transmission rates of Rhopalosiphum padi from the different host species were broadly similar whereas for Sitobion avenae, P. annua within cereal fields was significantly better than the other host species. Wild grasses other than P. annua were relatively poor sources of virus. A large percentage of aphids frequently transmitted more than one strain, suggesting that host plants are often infected with more than one BYDV strain.     

宁夏地区春小麦黄矮病流行趋势预测的初步研究

通过23年(1970—1993)的研究,初步明确了东南方冬麦区黄矮病情、春麦区拔节初期麦二叉蚜量和东南方冬麦区麦蚜迁出迟早等是影响宁夏春麦区黄矮病流行的关键因素,黄矮病历年流行程度与春小麦生长期间的主要气象因子相关不密切。针对麦蚜远距离迁飞所致春麦黄矮病,首次提出了以2个预测式为基础的黄矮病流行趋势预测办法,并据此进行了多次成功的预报。     

The role of Poa annua in the epidemiology of barley yellow dwarf virus in autumn-sown cereals

Studies of cereal aphids and barley yellow dwarf virus (BYDV) from 1989 to 1992 revealed that Poa annua is an abundant weed of commercial winter barley crops during the summer months. P. annua was frequently infected with BYDV, and there were usually similarities with the BYDV infection of the surrounding barley crop. These P. annua weeds were often infested by cereal aphids both in July (pre-harvest) and in September (in cereal stubble fields). Poa -infested cereal stubbles may be major local sources of viruliferous aphids, increasing the risk of BYDV in nearby winter cereals. P. annua plays an important role in the epidemiology of S. avenae -transmitted BYDV.     

青海省小麦种质资源对大麦黄矮病毒的抗性鉴定

为明确青海省不同小麦种质资源对大麦黄矮病毒(Barley yellow dwarf virus,BYDV)的抗性差异,于2014—2015年采用堆测法人工接种鉴定了178份种质资源的抗病性。结果显示,不同小麦种质资源对黄矮病的抗性存在较大差异,甘A100、川766、陕1059、兰麦-2的病情指数依次为14.83、23.60、23.99和24.66,表现出较好的抗病性;病情指数在50.00以上的高感品种有69份,包括尕老汉、白板麦、兴热密穗等,其中白板麦病情指数高达72.35,高于感病对照阿勃;其余种质资源病情指数在25.00~50.00之间,表现为感病;甘A101、甘A99、藏515、藏519、木汉麦、群科大白麦、拉胎板麦、小红麦-2和朗县折达25初期表现感病,后期恢复健康,有一定的耐病性;抗病性不同的种质资源感染BYDV后,对小麦产量的影响差异很大,抗病对照中4产量损失8.96%,耐病品种产量损失在13.64%~19.74%之间,高病品种尕老汉产量损失达41.91%,表明小麦种质资源中抗BYDV的品种极少。     

The Effects of Cultural Measures on Cereal Pests and Their Role in Integrated Pest Management

The influences of cultural control measures on invertebrate pests and their natural enemies in cereals (wheat, barley and oats) are described and discussed, with emphasis on the major pests in north-west Europe. Possibilities for additive and synergistic combinations of cultural measures are identified, together with opportunities for integrating cultural measures with chemical and biological control where appropriate. Recent studies confirm the central role of cultural control measures in integrated pest management and integrated production of cereal crops. However, cultural measures often have opposing effects on different pests as well as diseases and weeds, so that appropriate measures must be selected on the basis of an assessment of the risks from key pests, diseases and weeds. Crop rotation is not an important means of controlling cereal pests, but its use is recommended for control of cereal diseases and weeds, as well as pests of crops grown in rotation with cereals. Diversification of crops and non-crop habitats in predominantly cereal growing areas is thought to increase numbers of certain parasitoids and polyphagous predators of cereal pests. The presence of weeds or an intercrop in a field together with cereals may reduce the severity of aphid and slug damage to cereals. Trap cropping has not yet been adequately tested in wheat, barley or oats. Cover crops reduce damage by wheat bulb fly in a following wheat crop, but increase the risk of slug damage. Resistance to a wide range of cereal aphid species has been identified in wheat and barley, but in Europe, more emphasis is placed on selecting cultivars with resistance to cereal diseases rather than pest resistance. Resistance in wheat to wheat bulb fly and wheat blossom midge is recorded, and resistance to slug damage has been reported in some laboratory studies. Early sowing of winter cereals results in more damage by certain dipterous pests and increased numbers of the aphid vectors of barley yellow dwarf virus (BYDV), but early sowing results in less damage by wheat bulb fly and slugs in autumn/winter and by late infestations of aphids in summer. Avoidance of ploughing results in reduced incidence of wheat bulb fly, yellow cereal fly and aphids, but increased numbers of slugs, wheat blossom midge and bibionid larvae. Avoidance of ploughing can result in greater numbers of certain polyphagous predators, particularly in the first weeks following crop establishment. The presence of straw residues results in increased slug populations, but reduced incidence of yellow cereal fly and wheat blossom midge. Preparation of fine, firm seedbeds discourages attack by slugs and wheat bulb fly on cereals. Drilling at slightly greater depth in rough cloddy seedbeds helps to protect wheat seeds from slug damage. Nitrogen fertiliser applied in spring can help cereal plants compensate for losses by wheat bulb fly or slugs. However, nitrogen applications tend to result in increased summer infestations of aphids.     

棉蚜在不同棉花品种上的取食行为及相对取食量的研究

应用电动穿刺记录技术(EPG)对棉蚜在不同棉花品种上的取食行为进行了测定,结果记录到棉蚜的6种取食行为基本波型。棉花的多毛、红叶性状及抗、感水平对棉蚜的取食都有显著的影响。与CK非洲E40相比,多毛可以显著降低棉蚜的取食周期E2,并可显著延长第1非取食周期和增加蚜虫口针的刺探频率。棉蚜在多毛品种上的取食周期占总时间的6.0％,仅为CK品种的1/2。棉蚜在红叶棉上取食周期E2占总时间的百分率(10％)要显著低于黄叶棉品种(15％)(P<0.01)。而棉蚜在抗、感品种间的取食周期E2及取食前期波型C的周期差异也达到了极显著水平(P<0.01)。用同位素液闪技术测定了棉蚜在抗、感品种上的相对取食量,结果显示棉蚜在抗蚜品种上相对取食量也明显低于感蚜品种,并且随着取食周期的增长,抗、感品种之间比值差异更大。     

Yield Effects of Barley yellow dwarf virus in Soft Red Winter Wheat

ABSTRACT Three cultivars of soft red winter wheat were evaluated to determine the relationship between the incidence and time of infection by Barley yellow dwarf virus (BYDV) and yield. Wheat was planted in 1995, 1996, and 1997 in a split-plot design with six replicates at sites in Indiana and Illinois. Yield plots were infested with different amounts of viruliferous aphids, and the incidence of BYDV in each plot was measured. In a 2-year study in Illinois with cv. Clark and the PAV-IL isolate of BYDV, yields were assessed following aphid infestation in fall, early spring, and late spring. Early spring infections resulted in larger yield reductions than late spring infections in both years and larger than fall infections in one year. Regression analyses to relate incidence of infection and yield with data from fall and early spring infections provided R(2) values of 0.89 and 0.51 for the 1996 to 1997 and 1997 to 1998 seasons, respectively. An additional study at the same site in the 1996 to 1997 season compared the yield responses of cvs. Clark, Y88-3e, and PT8935b. Increases in the incidence of BYDV correlated with decreases in yield, with R(2) values of 0.80, 0.78, and 0.90 for the three cultivars, respectively. Estimated yield losses in both studies and all cultivars ranged from 27 to 45 kg/ha or 0.34 to 0.55% for each percent increase in virus infection. In a third study over a 2-year period in Indiana with the same three wheat genot ypes and a second BYDV isolate (PAV-P), BYDV treatments resulted in significant reductions in yield, but yield loss and the incidence of BYDV were not linearly correlated. Given the differences in yield reductions caused by the two BYDV isolates, PAV-P may be an attenuated strain of BYDV and may cross-protect plants from naturally occurring strains of the virus.     

Global crop production and the efficacy of crop protection - current situation and future trends

Actual and potential crop losses of eight major food and cash crops have been estimated by evaluating data from literature and field experiments. Total losses were calculated from yield reductions due to pathogens, animal pests and weeds on a regional, continental and global level. Since 1965, worldwide production of most crops has increased considerably. Simultaneously, crop losses in wheat, potatoes, barley and rice increased by 4 to 10 percent, in maize, soybean, cotton and coffee losses remained unchanged or slightly decreased. The efficacy of crop protection practices was calculated as the percentage of potential losses prevented by control. The efficacy is highest in cotton (55 percent), it reaches only 34 to 38 percent in the food crops rice, wheat and maize. The variability among cropping areas is high: In Western Europe, 61 percent of potential crop losses is prevented, in North America and Oceania 44, in all other regions 38 percent. Due to the small share of Western Europe in worldwide production of 8 percent, the efficacy of actual crop protection worldwide is only 40 percent.In view of population growth and rising food demand crop production has to be increased substantially. As potential loss rates often increase with attainable yields high productivity largely depends on effective crop protection management. Scenarios for the production of food crops by the year 2025 in developed and in developing countries are given. Recent and future developments in crop protection can contribute to establish sustainability in agriculture and to preserve natural resources. However, although effective control methods have been developed for most biotic yield constraints, the use of crop protection products is regulated by economic considerations rather than by food demand.     

Occurrence of barley yellow dwarf virus in cereals and grasses of the low-rainfall wheatbelt of South Australia

South Australia is in the dry temperate zone where most cereal crops are grown in an area of low rainfall, with a crop-free season from December to April. The incidence of barley yellow dwarf virus (BYDV) was assessed by ELISA from 1989 to 1991 in wheat crops and irrigated pastures of South Australia. The incidence of BYDV was low in most wheat crops of the low-rainfall area in 1989 and 1990 (less than 1% of plants infected), but moderate levels of infection (1–10%) were observed in some early-sown crops. BYDV infection was more widespread in the high-rainfall area (south east of South Australia). A high incidence of BYDV was observed in the irrigated pastures of the three areas surveyed (4–86%). Of the five previously described strains, the Rhopalosiphum padi/Sitobion avenae strain (PAV) was the most common in wheat samples (> 90%). PAV and the R. padi-specific strain (RPV) were found in pasture grasses, alone or in mixed infection. Virus incidence was greater in Festuca spp. (56%) and Lolium perenne (30%) than in other species (2-–9%).     

A comparative study of the Barley yellow dwarf virus species PAV and PAS: distribution,accumulation and host resistance

This study investigated the distribution and characteristics of the Barley yellow dwarf virus (BYDV) species BYDV‐PAS, which was recently separated from BYDV‐PAV, the most commonly studied BYDV species. Throughout 3 years of experimental monitoring of BYDV incidence, PAS was the most frequently occurring species infecting cereals and grasses in the Czech Republic. Furthermore, Rhopalosiphum maidis and Metopolophium dirhodum were recorded as BYDV‐PAS vectors, even though M. dirhodum does not usually transmit BYDV‐PAV. In field experiments with barley and wheat, where virus accumulation, symptoms and effect on the yield were tested, BYDV‐PAV was more severe than PAS. Infection with the BYDV‐PAV isolate resulted in greater expression of symptoms and also in a greater reduction in plant height and grain weight per spike than BYDV‐PAS. In a sensitive cultivar of barley (Graciosa), the amount of viral RNA of BYDV‐PAV was also significantly higher than that of BYDV‐PAS. In a tolerant line (Wbon‐123), however, no such differences were found. In conclusion, although BYDV‐PAS seems to be dominant in the Czech Republic, BYDV‐PAV has the potential to cause more significant crop losses in barley and wheat.     

Cucumber mosaic virus infection of chickpea stands: temporal and spatial patterns of spread and yield‐limiting potential

Patterns of spread and yield losses were examined when migrant aphid vectors transmitted Cucumber mosaic virus (CMV) within chickpea (Cicer arietinum) plots. When numbers of chickpea plant infection foci were varied to provide initial infection incidences of 0·3–2%, rate of virus spread and its final incidence increased in proportion to initial virus incidence and pathogen progress curves reflected a polycyclic pattern of spread. Chickpea seed yields decreased by 44–45% when CMV incidence reached 61–74% at final assessment in plots with simulated 1–2% initial incidence. In chickpea plots with or without introduced lupin plant infection foci, cumulative spatial data for diseased plants were assessed using spatial analysis by distance indices (sadie ). When CMV spread within a plot, infection was concentrated in large patch clusters and was consistent with comprehensive localized spread around primary infection foci. When introduced infection foci were absent, there was more diffuse spread with many isolated clusters. In individual plants that developed CMV symptoms at different growth stages, shoot and pod dry weight were reduced by 60–65% and 77–79% (early infection) and 44 and 66% (late infection), respectively. Seed yield losses were 78–80% (early) and 65–67% (late), and reduction in 50‐seed weight was 20–25% regardless of time of infection, so seed number was reduced more by early than late infection. Infection also reduced seed quality as, in addition to smaller seed size, seed coats were discoloured and malformed: the proportions of malformed seeds were 9–11% (early), 3–6% (late) and 0·5% (healthy).     

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.     

Optimizing aphid biocontrol with the predator Aphidoletes aphidimyza,based on biology and ecology

Aphidoletes aphidimyza is one of the most important predators used in the augmentative biological control of aphids, key pests of many crops worldwide. Adult females are very efficient in locating aphid infestations over a relatively long range, up to 45 m, and deposit eggs near or within aphid colonies. The predatory larvae are aphid generalists preying on several agriculturally important aphid species. The successful use of this biocontrol agent in agricultural systems depends on several biotic and abiotic factors. Among biotic factors, aphid species, plant structure, interspecific competition and intraguild predation may significantly impact the predator´s population dynamics. Key abiotic conditions include day lengths (above a critical threshold to prevent diapause), availability of mating sites in the crop, temperature (above 15 °C to enable egg laying), air relative humidity (above 70%) and availability of pupation sites. Although several successes have been reported in open field crops with naturally occurring or released populations, commercial releases are primarily used in protected crops. Optimized emergence boxes combining provisioning of food sources for the adults, integration with the technological advances that occurred in the greenhouse environment lately, insights into the nutritional ecology in open field crops and exploration of the genetic variability are proposed as future directions to improve adoption and efficacy of A. aphidimyza in crop protection. © 2018 Society of Chemical Industry     

Leaf scald (Xanthomonas albilineans) incidence and its effect on yield in seven sugarcane cultivars in Guadeloupe

Seven 5—month-old sugarcane cultivars difTering in resistance to leaf scald disease were inoculated by the decapitation technique with Xanthomonas albilineans. The effects of disease progress and incidence on yields were studied for the plant (first harvest) and two ratoon crops (second and third harvest). The percentage of diseased stalks and disease severity at first harvest 5 months after inoculation were 0·7 and 0·4, respectively, for the most resistant cultivar and 71·0% and 63·3, respectively, for the most susceptible cultivar. They decreased in all cultivars in both ratoon crops, but were still important in one cultivar (B69379). Significant ( P = 0·05) yield reductions of 12% and 21% occurred in two of the seven cultivars (B69566 and B69379, respectively). The number of symptomatic sugarcane stalks in the first ratoon crop (second harvest) was lower than the number of stalks colonized by the pathogen. Symptoms and yield losses of cultivars R570 and B69566 varied with the crop. Yield losses occurred in cultivar R570 only in the plant crop when this cultivar displayed numerous symptoms. Cultivar B69566 appeared to recover from the disease to a certain extent from the plant to the second ratoon crop (third harvest), as did the resistant cultivars in the first ratoon crop. In contrast, severe leaf scald symptoms were observed in the case of cultivar B69379 regardless of the crop, and significant yield losses occurred in the two ratoon crops. These results support the recommendation that cultivar B69379 should not be replanted in Guadeloupe.