Molecular Diversity of Agriculturally Important Aspergillus Species

Although Aspergillus species are not usually considered as serious plant pathogens, Aspergilli are frequently encountered in plant products. The most important consequence of their presence is mycotoxin contamination. The main mycotoxins produced by Aspergilli are the aflatoxins, ochratoxin A and patulin, which are produced by a variety of Aspergillus species in different plant commodities. Phylogenetic analysis of sequences of the ribosomal RNA gene cluster is useful for clarifying taxonomic relationships among toxigenic Aspergilli causing pre- and postharvest contamination of agricultural products. Molecular data has enabled us to clarify the taxonomy of black Aspergilli, A. flavus and its relatives, and sections Circumdati and Clavati, which include ochratoxin and patulin-producing species. Phylogenetically unrelated species were found to produce the same mycotoxins, indicating that mycotoxin-producing abilities of the isolates have been lost (or gained) several times during the evolution of the genus. The data also indicate that biosynthetic gene-based probes are necessary for molecular detection of these mycotoxin-producing organisms. The organisation of the biosynthetic genes of patulin and ochratoxins is unknown, although experiments are in progress in several laboratories to clarify the genetic background of biosynthesis of these mycotoxins. Identification of biosynthetic genes responsible for mycotoxin production is essential for clarifying the evolution of mycotoxin biosynthesis in Aspergilli, and to develop specific gene probes for the detection of mycotoxin-producing Aspergilli in agricultural products.     

Mapping of QTL lengthening the latent period of Puccinia striiformis in winter wheat at the tillering growth stage

The winter wheat lines Luke and AQ24788-83 are respectively susceptible and slow-rusting at tillering stage to yellow (stripe) rust, caused by Puccinia striiformis f. sp. tritici (Pst). A mapping population consisting of 206 recombinant inbred lines was developed from the cross Luke?×?AQ24788-83. These lines were evaluated at the tillering stage in the field trials for infection type (IT) and disease incidence (DI) and in greenhouse trials for IT and latent period (LP). A significant negative correlation was found between LP and DI. A genetic map with 473 marker loci was constructed and used for identifying QTL associated with LP and IT. Two QTL, QYr.cau-1BS and QYr.cau-5AS, were mapped on 1BS and 5AS respectively, explaining collectively up to 46.4 % of LP phenotypic variance. QYr.cau-5AS was clearly distinct, in terms of mapping position, from all six yellow rust resistance genes/QTL previously reported on 5A. QYr.cau-1BS could not be spatially differentiated from three (i.e. YrAlp, Yr15, and YrH52) of the six genes/QTL known on 1BS and centromere-vicinity regions, but was determined to be different from these three genes based on phenotype. The two QTL identified here, therefore, are likely to be novel to the currently known Pst resistance genes/QTL. A minor QTL on 3AL was detected to be associated with both IT and LP. Expression of quantitative resistance at early wheat growth stages and usefulness of the QTL are discussed for the wheat-Pst system.     

Expression profiling of rice genes in early defense responses to blast and bacterial blight pathogens using cDNA microarray

In order to understand the defense machinery in the model cereal crop rice, we performed a large-scale analysis of rice gene expression in response to rice blast Magnaporthe grisea (M. grisea) or Magnaporthe oryzae and bacterial blight Xanthomonas oryzae pv. oryzae (Xoo) during the early incompatible and compatible interactions. Using a gene chip containing 10 254 rice cDNAs representing 9240 unique genes, we identified 794 and 612 genes differentially expressed in the incompatible and compatible rice–M. grisea interactions, respectively, with 274 genes co-regulated during both interactions. In the rice–Xoo pathosystem, 454 and 498 differentially expressed genes were identified in the incompatible and compatible interactions, respectively, including 237 co-regulated genes in the both interactions. By clustering differentially regulated genes from all these interactions, we identified 29 co-regulated genes in the all four interactions, and 86 and 74 co-regulated genes in the two incompatible and two compatible interactions, respectively. These differentially expressed genes could be classified into three categories, including M. grisea- and Xoo-regulated, M. grisea-specific, and Xoo-specific. The expression patterns of representative defense-related genes were further confirmed by RT-PCR. The large-scale expression data from our microarray analysis indicated the existence of distinctive as well as shared defense pathways between the rice–M. grisea and rice–Xoo interactions.     

Characterization of tolerance to Fusarium oxysporum f.sp., cubense infection in banana using suppression subtractive hybridization and gene expression analysis

Identification of defense response genes in the host is one of the most essential steps in understanding disease resistance mechanisms in plants. In this study, suppression subtractive hybridization (SSH) library was constructed to study the genes involved in response to fusarium wilt disease in banana. Here cDNAs from a tolerant genotype Musa acuminata spp. burmannicoides ‘Calcutta-4’ infected by Fusarium oxysporum f.sp., cubense were used as tester and cDNAs from uninfected ‘Calcutta-4’ as driver population. After hybridization and cloning, EST library of 83 non-redundant clones were obtained. Based on sequence analysis and homology search in NCBI database the clones were assigned to different functional categories. The expression pattern of selected eight defense related genes namely peroxidase, glutaredoxin, polyphenol oxidase, glutamate synthase, S-adenosyl methionine synthetase, 14-3-3, heat shock protein, mannose binding lectin were analyzed through real-time PCR in contrasting genotypes. It was observed that the expression of these genes during initial progression of disease was found to be higher in tolerant genotype ‘Calcutta-4’ than in susceptible genotype ‘Kadali’.     

Influence of rice development on the function of bacterial blight resistance genes

Disease resistance genes most commonly used in breeding programs are single, dominant genes with relative effectiveness that is sometimes influenced by plant developmental stage. Knowing the developmental stages at which a resistance gene is functional is important for disease management. In rice, resistance at the seedling stage is crucial, because wounding during transplanting increases the potential for bacterial blight disease, and not all bacterial blight resistance genes are effective at the seedling stage. Effectiveness of the bacterial blight resistance genes Xa4, xa5, and Xa7, all in a common genetic background, was evaluated at different developmental stages by measuring lesion length and bacterial numbers after inoculation with the bacterial pathogen, Xanthomonas oryzae pv. oryzae. The Xa4 and xa5 genes controlled disease at all growth stages. In contrast, Xa7 was not fully functional in very young seedlings, but was completely effective by 21 days after sowing (das). The effects of plant developmental stage on interactions of the Xa7 gene with X. oryzae pv. oryzae strains carrying different mutant avrXa7 alleles were also tested. If a partial or fully functional avrXa7 allele was present, Xa7 resistance was effective at all growth stages tested after the transplant stage (>21 das).     

Mycotoxin Production and Molecular Variability of European and American Isolates of Fusarium Culmorum

The main causative agents of Fusarium head blight are Fusarium graminearum and Fusarium culmorum. We examined the mycotoxin-producing abilities and molecular variability of 37 Fusarium culmorum isolates collected from the Pan-Northern Hemisphere, together with isolates representing related species. Mycotoxin-producing abilities of the isolates were tested by thin layer chromatography and by PCR using primer pairs specific for the Tri7 and Tri13 genes. Thirty isolates belonged to chemotype I (producing deoxynivalenol and 3-acetyl-deoxynivalenol), while seven represented chemotype II (producing nivalenol and/or fusarenone X). The presence of a functional Tri7 gene correlated well with nivalenol production. Isolates belonging to chemotype I were in general more pathogenic in in vitro tests than those belonging to chemotype II. Phylogenetic analysis of the random amplified polymorphic DNA profiles (RAPD) of the isolates enabled the isolates to be clustered into different groups. Most isolates from Hungary exhibited identical RAPD profiles. A similar clustering was found on the tree based on restriction analysis of the intergenic spacer region data. Sequence analysis of a putative reductase gene fragment of the isolates was also carried out. A correlation was detected between the geographic origin of the isolates and their position on the cladogram produced based on sequence data. The presence of mating type gene homologues was also tested with primer pairs specific for MAT1-1 and MAT1-2. The isolates carried either MAT1-1 or MAT1-2 homologues. No correlation was observed between clustering of the isolates based on RAPD, restriction analysis of the intergenic spacer region or sequence data and the distribution of MAT idiomorphs. Similarly, no correlation was detected between mycotoxin-producing abilities or aggressiveness and molecular characteristics of the isolates. Statistical analysis of RAPD data and lack of strict correlation between trees based on different data sets supported the view that Fusarium culmorum has a recombining population structure. The presence of mating type gene homologues in the isolates indicates that the recombining population structure is caused by ongoing or past meiotic exchanges.     

拮抗真菌HTC的鉴定及其对辣椒疫病的生物防治潜力

为明确拮抗真菌HTC对辣椒疫霉Phytophthora capsici的拮抗机制,采用平板对峙、形态学鉴定和18S rDNA序列比对分析等方法对菌株HTC进行了鉴定,并研究其发酵液与抗生物质粗提液对辣椒疫霉不同发育阶段的影响。经鉴定,菌株HTC为金色毛壳菌Chaetomium aureum。在平皿对峙试验中,菌株HTC的红色分泌物能抑制辣椒疫霉菌丝的生长,抑制率为59.1%,后期HTC菌丝可缠绕并降解辣椒疫霉菌丝。发酵液与抗生物质粗提液对辣椒疫霉不同发育阶段均有抑制作用,发酵液对辣椒疫霉菌丝生长的抑制率高达97.58%,对辣椒疫病的防治效果均高于70%。浇灌发酵液后,可提高辣椒苗的苯丙氨酸解氨酶、过氧化物酶、多酚氧化酶的活性,并明显促进辣椒苗生长,鲜重和干重增加32.27%和18.09%。研究表明,金色毛壳菌菌株HTC是一株具有开发潜力的生防菌株。     

Tolerence of Wheat and Barley at Different Stages of Growth to 2, 4-D Sprays

Abstract

The tolerance of wheat and barley to 2, 4-D sprayed at six stages of growth, ranging from the 3-leaf stage up to the ripe grain stage, was studied. Five concentrations ranging from 500 to 8000 ppm (a.e.) of 2, 4-D were tested.

All the concentrations sprayed at the 3-leaf stage were phytotoxic to wheat and barley, whereas at the 5-leaf, jointing, and booting-to-heading stages, only 4000 and 8000 ppm were phytotoxic and caused lodging in the two crops. Reductions in plant height were significant at all concentrations used in the case of barley, and at 1000 ppm and above in the case of wheat.

The 8000 ppm treatment, applied at the jointing and anthesis stages, caused significant reductions in the grain yield of wheat; in the case of barley, significant reductions in the grain yield were observed at concentrations ranging from 2000 to 8000 ppm, sprayed at the 3-leaf, booting-to-heading, arid anthesis stages. At the 5-leaf stage, the 1000 ppm treatment gave a highly significant increase of 18.7% in the grain yield over the unweeded check. Significant reductions in the 1000-kernel weight and test weight of the two crops were observed only at the higher concentrations used.

The protein percentages of wheat and barley seeds were significantly increased as a result of the application of 2, 4-D at 2000 to 8000 ppm, sprayed at the 3-leaf, jointing, booting-to-heading, and anthesis stages of growth. However, significant reductions in the protein yield of the two crops were observed at these treatments. No significant effects were observed on the straw yield and germination percentages of wheat and barley as a result of 2, 4-D applications at the various stages of growth.     

绿盲蝽对冬枣不同生长期的为害

为了解绿盲蝽对其重要果树寄主冬枣的为害特点,通过对各生长期叶、蕾、花、幼果等易受害部位接虫试验,研究绿盲蝽对冬枣的为害规律及其对冬枣坐果的影响。结果显示,不同生长期各部位的被害率和刺点数均随着接虫数的增加而增大。嫩叶期最幼嫩的部位顶芽和第1片叶被害率均为100%,第4、5片叶的被害率均为0;相同接虫密度下,花的刺点数显著高于蕾和幼果;花蕾并存时,花的刺点数显著高于蕾,而被害率无显著差异。花期受害后,坐果数显著降低,其中接1、2、3、4、5头绿盲蝽坐果数分别降低了49.49%、59.60%、84.85%、94.95%、94.87%。研究表明,绿盲蝽对冬枣的为害有明显趋嫩和趋花性,花期受害后对产量的影响最大,应加强对花、幼果期绿盲蝽种群的控制。     

Predicting potato tuber yield loss due to early blight severity in the Midwestern United States

Although early blight is among the most damaging foliar diseases of potato, the information available on the disease-yield relationship is scarce. Twenty-three field trials were conducted from 2003 to 2016 across North Dakota and Minnesota potato growing regions to study the relationships among disease severity estimated from tuber initiation (TI) to early bulking (growth stage III to IV) and late bulking/tuber maturation (growth stage IV to V) and yield. The strength of the association and the functional relationships between crop and disease variables were assessed based on estimates of the Fisher’s Z transformation of Pearson correlation r, the intercept (β₀) and slope(β₁) for each trial, which were combined and analyzed using meta-analytic models. At TI to early bulking stage, random-effect model estimated a slope of 0.20 mt/ha/%^?1 for an expected yield (intercept) of 61.88 mt/ha. Each unit increase in percent severity at this growth stage would result in a 32 percentage point (pp) yield reduction. During late bulking/tuber maturation crop growth stage, the random-coefficients β₀ and β₁ were 65.89 mt/ha and 0.13 mt/ha/%^?1, respectively. In relative terms, yield would be reduced by 19 pp. for each unitary percentage increase in early blight severity. Based on these meta-analysis results, growers are able to predict potential yield loss for each percentage increase of early blight severity at two growth stages, which can be useful for crop-loss assessments.     

Morphological and molecular identification and PCR amplification to determine the toxigenic potential of Fusarium spp. isolated from maize ears in southern Poland

The average amount of precipitation in spring and summer 2010 and 2011 coupled with relatively high temperatures caused massive Fusarium spp. infection of maize and yield losses in southern Poland. In order to examine the cause of this disease outbreak, Fusarium spp. were isolated and fungal strains were identified based on morphological characters and species-specific PCR assays. A total of 200 maize samples were processed, resulting in the obtention of 71 strains, which belonged to five Fusarium species, F. poae being the predominant one (74.56%). Other isolates were identified as F. graminearum, F. oxysporum, F. verticillioides and F. proliferatum. PCR-based detection of mycotoxin-synthesis-pathway genes was also used to determine the potential of the analyzed strains to produce trichothecenes (DON and NIV) and fumonisins (FUM). Only 14 isolates revealed the potential to produce DON (11 strains) and FUM (3 strains). HPLC analyses of grain samples revealed the presence of DON only – other mycotoxins were not detected. Moreover, 57.1% of potentially mycotoxin-producing isolates indicated the toxicity in a biological test.     

Genetic Markers for the Analysis of Variability and for Production of Specific Diagnostic Sequences in Fumonisin-Producing Strains of Fusarium Verticillioides

Fusarium verticillioides(Gibberella moniliformis, Gibberella fujikuroi mating population A) is the main source of fumonisins, a group of toxins which contaminates commodities, causing chronic and acute diseases in humans and animals. Fumonisins are produced during colonisation and infection of host plants even when disease symptoms are not recognisable. Early detection and control of F. verticillioides is crucial to prevent fumonisins from entering the food chain. DNA-based strategies have been used to search for markers to develop sensitive, robust and specific diagnostic assays, mainly based on PCR. The different approaches used, based either on DNA markers unrelated to fumonisin production or on information about the genes involved in fumonisin production, are described and discussed. The ability of these methods to discriminate between the two populations occurring within F. verticillioides, fumonisin-producing and fumonisin non-producing strains, is also addressed.     

橡胶树白粉菌侵染过程转录组学分析

为明确橡胶树白粉菌Erysiphe quercicola参与致病过程相关基因的表达情况，基于RNA-Seq测序技术对橡胶树白粉菌侵染过程进行转录调控研究，通过对病原菌孢子（0 h）及3个侵染时期（接种1、3和30 d）的转录组进行比较，筛选差异表达基因并对其进行功能注释分析，同时对不同侵染阶段的基因表达趋势进行聚类分析。结果表明，相比于病原菌孢子，3个侵染时期（接种后1、3和30 d）分别有198、458和27个差异表达基因。基因功能富集分析发现氧化还原酶相关基因在侵染1 d阶段显著富集，可能参与病原菌侵染前期对活性氧的防御。基因表达趋势聚类分析显示不同侵染阶段的基因共分为51种表达类型，其中编码候选效应蛋白基因集中分布在侵染1 d后上调表达的6个类型当中。表明橡胶树白粉菌侵染过程相关基因具有明显的功能倾向性和表达趋势特征。     

Within-plant distribution of an invasive mealybug,Phenacoccus solenopsis,and associated losses in cotton

The cotton mealybug Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae), an invasive pest species, has appeared on a large scale on cotton in India since 2006. Its distribution within the plant, and associated yield losses in cotton, were studied over 2 years. Distribution of P. solenopsis was observed within the cotton plant from vegetative to boll formation stage. In the vegetative and square formation stages, the highest mealybug population was recorded on the upper portion of the stem, followed by the middle leaves of the plant. In the boll formation stage, there was no significant difference in distribution of the insect among plant parts. Losses in cotton due to the mealybug varied between 14.9% at Grade 1 and 53.6% at Grade 4, on a 0 to 4 severity index, with a mean reduction of 35% and 32%, during 2008 and 2009, respectively. There was a significant relationship between severity of infestation and decrease in seed cotton yield. The information generated from this study will help in the early detection of mealybug infestation and estimation of yield losses corresponding to the severity grade of the damage.