Potentiation of soybean resistance against Phakopsora pachyrhizi infection using phosphite combined with free amino acids

Considering the importance of Asian soybean rust (ASR), caused by Phakopsora pachyrhizi, in the decrease in soybean yield, this study investigated the potential of using phosphite combined with l -α-free amino acids (referred to as induced resistance [IR] stimulus hereafter) to boost defence responses of soybean plants against P. pachyrhizi infection. Plants were sprayed with water (control), acibenzolar-S-methyl (ASM) or IR stimulus and noninoculated or inoculated with P. pachyrhizi. Urediniospore germination was not affected by the IR stimulus in vitro. Reduced ASR severity, lower malondialdehyde concentration and less colonization of leaf tissues by P. pachyrhizi (lower TEF-1α expression from 1 to 15 days after inoculation [dai]) occurred for IR stimulus-sprayed plants. The pattern of gene expression for IR stimulus-sprayed and infected plants was strikingly similar but sometimes more remarkable than that in ASM-sprayed and infected plants. Higher production of phenolics and lignin along with stronger up-regulation of PAL1.3 (5 and 10 dai), PAL2.2 (3 dai), PAL3.1 (1, 3 and 5 dai), ICS1 (5 dai), CHIA1 (1, 5 and 10 dai), CHI1B1 (5 dai), PR-1A (5 and 10 dai), NR1-2 (5 and 10 dai) and INR-2 (5 and 10 dai) for IR stimulus-sprayed plants increased their resistance against ASR. In addition, IR stimulus-sprayed and infected plants showed less impairment of the photosynthetic apparatus and maintained high concentrations of chlorophyll a + b and carotenoids. These findings highlight the potential of using this IR stimulus for developing a well-tuned and effective defensive strategy in soybean plants against P. pachyrhizi infection.     

Evaluation of soybean genotypes for resistance against the rust-causing fungus Phakopsora pachyrhizi in East Africa

Soybean rust, caused by the biotrophic fungus Phakopsora pachyrhizi, is the most important foliar disease of soybean (Glycine max) worldwide. Deployment of resistant soybean cultivars is the best option for managing this disease. Genes conferring resistance to P. pachyrhizi have been identified, but pathotypes of the rust fungus overcoming these resistance genes have also been found. To identify novel resistance genes, soybean genotypes from both local and international sources were screened at multiple locations in Tanzania and Uganda in 2016 and 2017. The results from this screening revealed that infection types, disease severities, and sporulation levels varied among the genotypes and locations. The majority of the genotypes had tan-coloured (TAN) lesions and developed moderate sporulation, implying susceptibility, while only seven of the 71 lines had reddish-brown (RB) lesions and showed low disease severities in all of the screening environments. We identified seven genotypes that were the most resistant to rust in the most locations over the two years. These genotypes will be useful for further studies and, ultimately, for rust management, as they show broad resistance to various pathotypes of the rust fungus.     

复合改性粘土对除草剂2,4-D的控制释放作用研究

采用无机/有机复合改性粘土作制剂载体,探讨了其对阴离子型除草剂2,4-D的控制释放作用,目的在于延长2,4-D的持效期,同时减轻其污染.利用无机和有机改性的结合优势,复合改性粘土具有更强的吸附性能,能够显著延缓2,4-D在水中和土壤中的释放.分析其水中释放动力学数据得出,2,4-D释放50%所需时间(t_(50))长达73.8 h,远大于有机改性粘土作载体时的1 h.土壤层释放实验表明,当2,4-D载药量在20～80 mg/g之间时,复合改性粘土均能保持良好的控制释放效果.     

Diversity and distribution of pathotypes of the soybean rust fungus Phakopsora pachyrhizi in East Africa

Phakopsora pachyrhizi is a biotrophic fungus that causes rust on soybean, leading to devastating yield losses. Development of resistant cultivars for deployment in different geographic regions requires a comprehensive understanding of the prevalent P. pachyrhizi pathotypes. To determine the pathotypes existing in four East African countries, 65 isolates were tested on 11 soybean host differentials. In addition, the virulence spectrum of isolates collected from the same region over multiple years was compared. The majority of the isolates (54%) belonged to pathotype 1000, which was found in all countries. The pathotypes with the most complex virulence spectrum, which comprised isolates from Kenya and Malawi, were virulent on four differentials. All pathotypes were virulent on soybean genotypes carrying the Rpp1 resistance gene to P. pachyrhizi, but they were avirulent on cultivars carrying the Rpp1b, Rpp2, or Rpp3 gene, as well as on cultivar No6-12-1 that carries Rpp2, Rpp4, and Rpp5. Two of the pathotypes were virulent on cultivar UG 5 that carries Rpp1 and Rpp3 and on Hyuuga that carries Rpp3 and Rpp5. The isolates collected from different countries differed in their virulence spectrum across the years. Shannon's index (H) and Simpson's index (S) of diversity indicated that the isolates from Malawi were more diverse (H = 1.55, S = 0.90) while those from Uganda had lower diversity (H = 0.78, S = 0.46 ). The Rpp genes that were found to provide resistance to all pathotypes of P. pachyrhizi can be employed for soybean breeding aimed at durable rust resistance.     

Quantifying the detrimental effect of airborne dust on herbicide efficacy

One side effect of human activity and global climatic change is more airborne dust. This not only has undesirable effects on human health and the environment, but may also adversely affect many agricultural processes, including herbicide efficacy. This is particularly relevant in parts of the world where dust storms are common and limited rainfall means dust persists on plants for protracted periods. Accordingly, a series of greenhouse dose–response pot experiments was carried out to quantify the effect of a dust concentration of 1,500 µg/m³ on the performance of paraquat, glyphosate, sulfosulfuron and 2,4-D+MCPA. Dust-treated and untreated seedlings of Hordeum spontaneum and Sinapis arvensis were sprayed with sulfosulfuron and 2,4-D+MCPA, respectively, while paraquat and glyphosate were applied to both weed species. The efficacy of glyphosate and paraquat decreased significantly in the presence of dust on both species. Similar results were observed for 2,4-D+MCPA on S. arvensis. In contrast, the efficacy of sulfosulfuron on H. spontaneum was not affected by dust. In the presence of dust, the doses of glyphosate, paraquat and 2,4-D+MCPA required for a 90% effect were enhanced by a factor of 1.9 to 2.6. The negative impact on glyphosate efficacy was more pronounced in S. arvensis than H. spontaneum, while it was similar for paraquat. Future studies should consider the amount, duration and composition of dust as well as its impact on other weeds and herbicides. Potential approaches to overcome the detrimental influence of dust on the performance of herbicides were also suggested for future studies.     

Herbicides used in combination can reduce the probability of herbicide resistance in finite weed populations

A simulation study was conducted to examine the effect of pattern of herbicide use on development of resistance to two herbicides with different modes of action in finite weed populations. The effects of the size of the treatment area (analogous to initial weed population), germination fraction and degree of self‐pollination in the weed were investigated. The results indicate that the probability of developing resistance to one or both herbicides decreases as the size of the area/initial population decreases. For treatment areas of 100 ha or less with an initial weed seedbank of 100 seeds m^?2 and initial frequencies of the resistance genes of 10^?6, development of resistance to both herbicides (double‐resistance) is uncommon within 50 years for all types of weeds if both herbicides are used in all years (used in combination). If herbicides are used in alternate years (rotated) double‐resistance almost always occurs in 100 ha areas but is uncommon in areas of 1 ha or less. The results suggest that adoption of practices that limit movement of weeds in conjunction with using herbicides in combination rather than in rotation can substantially delay development of herbicide resistance.     

A major variation in the virulence of the Asian soybean rust pathogen (Phakopsora pachyrhizi) in Bangladesh

Asian soybean rust (ASR) caused by Phakopsora pachyrhizi is a major threat to soybean production in Bangladesh. Understanding the yearly changes and the current status of pathogenic structures is essential for developing appropriate breeding strategies for obtaining ASR-resistant soybean lines. Thirty-four P. pachyrhizi samples were collected from ASR hotspot areas (Chandpur, Lakshmipur, Noakhali, Barisal and Bhola districts) of Bangladesh in 2018 and 2019 and evaluated for pathogenicity on 12 soybean differential lines. The tested samples showed similar and dissimilar pathogenicity patterns on the differentials, yielding 21 distinct pathotypes. The cluster analysis, principal coordinate analysis and principal component analysis of the disease phenotypes of 47 samples collected in 2016, 2018 and 2019 indicated a higher pathogenic diversity and virulence variation in the P. pachyrhizi samples of 2018 and 2019 compared to that of 2016. The pathogenicity profiles of the Bangladeshi P. pachyrhizi samples appeared distinct from those of Argentinian and Brazilian samples, but showed slight similarities with Japanese, Mexican and Paraguayan samples. Furthermore, none of the resistance genes for P. pachyrhizi (Rpp genes) was solely effective against all the tested samples from 2018 and 2019, while samples (BdRP-48, BdRP-56 and BdRP-58) virulent to all Rpp1–Rpp6 genes were detected. The Rpp-pyramided line No6–12–1, carrying Rpp2, Rpp4 and Rpp5, was capable of conferring robust resistance to these virulent samples. Altogether, these results indicate an increase in the virulence of the current ASR pathogen in Bangladesh, which can be resolved by pyramiding different resistance genes in soybean cultivars.     

Frequency and distribution of herbicide resistance in Raphanus raphanistrum populations randomly collected across the Western Australian wheatbelt

In 2003, a random survey was conducted across the Western Australian wheatbelt to establish the extent and frequency of herbicide resistance in Raphanus raphanistrum populations infesting crop fields. Five hundred cropping fields were visited, with 90 R. raphanistrum populations collected, representative of populations present in crop fields throughout the Western Australian wheatbelt. Collected populations were screened with four herbicides of various modes of action that are commonly used for the control of this weed. The majority of Western Australian R. raphanistrum populations were found to contain plants resistant to the acetolactate synthase (ALS)‐inhibiting herbicide chlorsulfuron (54%) and auxin analogue herbicide, 2,4‐D amine (60%). This survey also determined that over half (58%) of these populations were multiple resistant across at least two of the four herbicide modes of action used in the screening. Only 17% of R. raphanistrum populations have retained their initial status of susceptibility to all four herbicides. The distribution patterns of the herbicide‐resistant populations identified that there were higher frequencies of resistant and developing resistance populations occurring in the intensively cropped northern regions of the wheatbelt. These results clearly indicate that the reliance on herbicidal weed control in cropping systems based on reduced tillage and stubble retention will lead to higher frequencies of herbicide‐resistant weed populations. Therefore, within intensive crop production systems, there is a need to diversify weed management strategies and not rely entirely on too few herbicide control options.     

复合改性粘土对除草剂2,4-D的控制释放作用研究

采用无机/有机复合改性粘土作制剂载体,探讨了其对阴离子型除草剂2,4-D的控制释放作用,目的在于延长2,4-D的持效期,同时减轻其污染。利用无机和有机改性的结合优势,复合改性粘土具有更强的吸附性能,能够显著延缓2,4-D在水中和土壤中的释放。分析其水中释放动力学数据得出,2,4-D释放50%所需时间(t50)长达73.8 h,远大于有机改性粘土作载体时的1 h。土壤层释放实验表明,当2,4-D载药量在20~80 mg/g之间时,复合改性粘土均能保持良好的控制释放效果。     

The origin and genetic diversity of the causal agent of Asian soybean rust,Phakopsora pachyrhizi,in South America

A sequence‐based approach was used to investigate molecular genetic variations in Phakopsora pachyrhizi, an obligate biotrophic pathogen that causes Asian soybean rust. In Argentina, the samples came from uredinium‐bearing leaves taken from 11 soybean fields; in Brazil, the samples comprised urediniospores from leaves of 10 soybean genotypes that had been grown in three experimental stations during two growing seasons. PCR‐based cloning techniques were used to generate DNA sequences for two gene regions and alignments were supplemented with data from GenBank. A total of 575 sequences for the internal transcribed spacer region (18 ribotypes) and 160 partial sequences for a housekeeping gene encoding ADP‐ribosylation factor (10 haplotypes) were obtained. Ribotype accumulation curves predicted that about 20 bacterial clones would recover 5–6 ribotypes (c. 70–80% of the total molecular variation) per locality. The samples from the three experimental stations in Brazil displayed most (14 out of 16) ribotypes found worldwide; the lack of genetic structure and differentiation at a diverse geographic scale suggests that both local and distant sources provide airborne inoculum during disease establishment. Soybean genotypes with resistance genes for the Asian soybean rust did not decrease the molecular genetic variation of fungal populations.     

Soybean production in eastern and southern Africa and threat of yield loss due to soybean rust caused by Phakopsora pachyrhizi

Soybean is a major source of oil and proteins worldwide. The demand for soybean has increased in Africa, driven by the growing feed industry for poultry, aquaculture and home consumption in the form of processed milk, baked beans and for blending with maize and wheat flour. Soybean, in addition to being a major source of cooking oil, is also used in other industrial processes such as in the production of paints and candle wax. The demand for soybean in Africa so far outweighs the supply, hence the deficit is mainly covered through imports of soybean products such as soybean meal. The area under soybean production has increased in response to the growing demand, a trend that is expected to continue in the coming years. As the production area increases, diseases and insect pests, declining soil fertility and other abiotic factors pose a major challenge. Soybean rust disease, caused by the fungus Phakopsora pachyrhizi, presents one of the major threats to soybean production in Africa due to its rapid spread as a result of the ease by which its spores are dispersed by the wind. Disease control by introducing resistant soybean varieties has been difficult due to the presence of different populations of the fungus that vary in pathogenicity, virulence and genetic composition. Improved understanding of the dynamics of rust ecology, epidemiology and population genetics will enhance the effectiveness of targeted interventions that, in turn, will safeguard soybean productivity.     

Benchmark study on glyphosate-resistant cropping systems in the United States. Part 6: Timeliness of economic decision-making in implementing weed resistance management strategies

BACKGROUND: The introduction of glyphosate‐resistant (GR) crops in the late 1990s made weed control in maize, cotton and soybean simple. With the rapid adoption of GR crops, many growers began to rely solely on glyphosate for weed control. This eventually led to the evolution of GR weeds. Growers are often reluctant to adopt a weed resistance best management practice (BMP) because of the added cost of additional herbicides to weed control programs which would reduce short‐term revenue. This study was designed to evaluate when a grower that is risk neutral (profit maximizing) or risk averse should adopt a weed resistance BMP. RESULTS: Whether a grower is risk neutral or risk averse, the optimal decision would be to adopt a weed resistance BMP when the expected loss in revenue is greater than 30% and the probability of resistance evolution is 0.1 or greater. However, if the probability of developing resistance increases to 0.3, then the best decision would be to adopt a weed resistance BMP when the expected loss is 10% or greater. CONCLUSION: Given the scenarios analyzed, risk‐neutral or risk‐averse growers should implement a weed resistance BMP with confidence that they have made the right decision economically and avoided the risk of lost revenue from resistance. If the grower wants to continue to see the same level of return, adoption of BMP is required. Copyright © 2011 Society of Chemical Industry     

Adsorption,Desorption and Mobility of Four Commonly Used Pesticides in Malaysian Agricultural Soils

Working with Malaysian agricultural soils, high Freundlich adsorption distribution coefficients (K_ads(f)) were observed for paraquat (28·7 and 1419) and glyphosate (83·8 and 417) and lower values for 2,4-D (0·57 and 5·26) and lindane (2·65 and 14·1) in a sandy loam and a muck soil, respectively. Desorption of 2,4-D and lindane from the muck soil occurred. The adsorption of the pesticides was not affected by temperature (20°C/30°C), pH or addition of the pesticides as a mixture. Leaching of 2,4-D and lindane was evident under a high water influx (200 mm). Comparable results in the leaching of 2,4-D were observed between laboratory studies and a VARLEACH model prediction. © 1997 SCI.     

全球非选择性除草剂市场分析及预测(2020年)(上)

全球非选择性除草剂主要为草甘膦、草铵膦、百草枯、敌草快,2018年这些产品市场规模为83.2亿美元,它们的市场份额占非选择性除草剂总量95%。计上其它小宗的产品,全球非选择性除草剂市场达到85亿美元左右,这块占全球除草剂市场的32%,可见,非选择性的需求"扮演"着除草剂市场基石的作用。虽然非选择性除草剂市场整体稳定,可产品间表现不一。目前草甘膦市场需求增长疲态已经出现,未来不可能在像其刚出现时那样经历持续增长。草铵膦具有杀草谱广、低毒、内吸好、活性高和环境友好等特点,也是全球第二大转基因作物耐受除草剂,市场份额9.2亿美元,同时,百草枯受到全球广泛性禁用,市场萎缩严重,敌草快市场表现的不温不火。     

Weed control in conventional and herbicide tolerant winter oilseed rape (Brassica napus) grown in rotations with winter cereals in the UK

Two winter oilseed rape (Brassica napus) cultivars, tolerant to glyphosate and glufosinate, were compared with a conventional cultivar at three sites over 4 years, in 3‐year crop rotations in the UK. The winter oilseed rape was grown in Years 1 and 4, with winter cereals, which received uniform herbicide treatments, in the intervening years. The second winter oilseed rape treatments were applied to randomised sub‐plots of the original plots. Weed densities were recorded in autumn and spring and weed biomass was measured in summer. At most sites, there was only one application of glufosinate or glyphosate, whereas two products were often used on the conventional variety. The timing of glyphosate and glufosinate application was, on average, 34 days later than that of the conventional broad‐leaved weed control treatments. Overall weed control, across all sites and years, was not statistically different between the conventional, glyphosate and glufosinate treatments. However, glyphosate achieved higher control of individual weed species more frequently than the other treatments. Glufosinate and the conventional treatments were similar in performance. The treatments in Year 1 sometimes affected weed populations in the subsequent cereal crops and, in rare instances, those in the rape in Year 4. Carry‐over effects were small after most treatments. In general, weed survival was greater in the oilseed rape crops, irrespective of the treatment, than it was in the intervening cereal crops.     

Influence of weed management measures on glyphosate resistance and endophyte infection in naturalized Italian ryegrass (Lolium multiflorum)

Recently, glyphosate‐resistant Italian ryegrass (Lolium multiflorum Lam.) was found on rice paddy levees in a western region of Shizuoka Prefecture, Japan. Naturalized populations of Italian ryegrass are frequently infected with fungal Epichloë endophytes. Endophytes often confer benefits to their host grasses. This study investigated the influence of five weed management treatments on glyphosate resistance and endophyte infection in Italian ryegrass that was growing on paddy levees where glyphosate‐resistant individuals were dominant. The weed management treatments were: (i) mowing once before the grass flowered; (ii) mowing once during flowering; (iii) mowing twice during flowering; (iv) glyphosate application before flowering; and (v) no treatment. The seeds were collected from the treatment plots in 2013 and 2014. The seeds were examined for endophyte infection and the seedlings that had been grown from the seeds were tested for the frequency of glyphosate resistance. The seedlings that had been derived from the glyphosate treatment showed higher frequencies of glyphosate resistance than those seedlings that had been derived from all the other treatments. Endophytes were found in all populations of the seeds from the paddy levees, with higher infection rates in the seeds that had been derived from the glyphosate treatment and the twice‐mowed treatment. There was a significant relationship between the endophyte infection frequency in the seeds and glyphosate resistance in the seedlings that had been grown from the same populations. The results indicate that where glyphosate herbicides are frequently used, selection for glyphosate‐resistant Italian ryegrass occurs, and along with this, the frequency of endophyte infection also increases.     

Performance of dual and triple fungicide premixes for managing soybean rust across years and regions in Brazil: A meta-analysis

Soybean rust in Brazil is currently controlled with several commercial fungicide premixes composed of demethylation inhibitors (EPOXiconazole, CYPRoconazole, PROThioconazole, TEBUconazole), quinone-outside inhibitors (AZOXystrobin, TriFLoXystrobin, PYRAclostrobin, PICOxystrobin), and succinate demethylation inhibitors (BENZovindiflupyr, BIXaFen, FLUXapyroxad). Here, we summarize the performance of eight premixes evaluated in 177 cooperative trials conducted in 46 locations across 10 states from 2015 to 2020. All fungicide treatments were sprayed three times starting at R1/R2. Percentage control (, %), from back-transforming meta-analytic estimates of the log of the ratio, ranged from 56.2% (PICO + CYPR) to 76.8% (BIXF + TFLX + PROT). Estimates of mean yield difference (, kg/ha) between fungicide-treated and untreated plots were greatest for BIXF + TFLX + PROT (1,080) followed by PICO + BENZ (1,010), PYRA + EPOX + FLUX (981.5), AZOX + BENZ (910), TFLX + PROT (891), PICO +TEBU (682), TFLX + CYPR (646), and PICO + CYPR (600). Significant declines in both and in as little as 4 years were detected for AZOX + BENZ (35.3%; 550 kg/ha) and PICO + BENZ (15.5%; 359.8 kg/ha). Variance in was reduced by the inclusion of baseline severity as covariate. In trials where baseline disease was ≥70%, yield was 250 kg/ha greater compared to areas with low baseline disease. Disease control and yield response were generally greater in the south-east, where the frequency of profitable scenarios was 30% higher on average than in the north-west. Results of this meta-analysis are critical for supporting decisions during planning of fungicide programmes.     

Matching herbicide application rates with the environmental conditions and growth stages of nodding thistle (Carduus nutans) and hairy buttercup (Ranunculus sardous) in pastures

Glasshouse experiments were conducted to evaluate whether herbicide application rates could be reliably reduced without compromising the efficacy of the herbicide. The seedling, and vegetative and preflowering plants of nodding thistle ( Carduus nutans ) and hairy buttercup ( Ranunculus sardous ) were treated with different rates of glyphosate or a mixture of picloram and triclopyr. Half of the plants were well-watered at all times while the other half was moisture-stressed for 1 week before the herbicide treatments were applied. Hairy buttercup was more susceptible to glyphosate than nodding thistle, while both were equally susceptible to the picloram/triclopyr mixture. Moisture stress significantly reduced the efficacy of both herbicide treatments, regardless of the plant development stage or the herbicide rate applied.