Identification and pathogenicity of Neophysopella species associated with Asian grapevine leaf rust in Brazil

Asian grapevine leaf rust (AGLR) causes severe crop losses in Brazilian viticulture, mainly in latitudes <25°S. The purpose of this study was to identify the pathogen(s) involved with AGLR in Brazil, based on phylogenetic and morphological analysis and pathogenicity tests. In total, 56 monouredinial isolates from six Brazilian states were identified using the internal transcribed spacer 2 and the large subunit rRNA gene D1/D2 regions. All 50 isolates from the south-central region were classified as Neophysopella tropicalis, and the other six isolates from the north-east region as Neophysopella meliosmae-myrianthae. This result provides evidence that two pathogen introductions from different sources may have occurred in the country. For both species, paraphyses were cylindrical, incurved, aseptate, and hyaline, while urediniospores were short-pedicellate, obovoid or obovoid-ellipsoid, with the wall colourless or pale yellowish, evenly echinulate. Representative isolates from both species caused typical AGLR symptoms on Vitis vinifera 'Merlot' and V. labrusca 'Niagara Rosada'. Overall, regardless of the Neophysopella species, isolates caused similar leaf disease severities. Higher disease severity was observed in Niagara Rosada (average of 40.3% of diseased leaf area) compared to Merlot (20.5%). This study reports, for the first time, the characterization of Neophysopella species associated with AGLR in Brazil.     

Formation of satellite uredinia as an important trait related to grapevine colonization by Phakopsora meliosmae-myrianthae

Phakopsora meliosmae-myrianthae, the causal agent of Asian grapevine leaf rust, significantly reduces the photosynthetic efficiency of grapevine leaves in green symptomless tissues surrounding lesions. This study took a close look at grapevine leaf colonization kinetics by P. meliosmae-myrianthae and compared it to P. pachyrhizi–soybean and Uromyces appendiculatus–bean colonization. It is already known from the literature that soybean rust, similar to grapevine rust, has a negative effect on leaf photosynthesis greater than would be expected based on visual lesions. However, in contrast to soybean and grapevine rusts, the effect of bean rust on leaf photosynthesis is proportional to the diseased leaf area. Colonization progress was monitored by fungal biomass assessed via histological staining and quantitative polymerase chain reaction (qPCR). Individual lesions of P. meliosmae-myrianthae on grapevine, P. pachyrhizi on soybean and U. appendiculatus on common bean leaves were evaluated every 3–4 days, and the number of uredinia was counted. Staining showed that mycelial colonization did not extend beyond the lesion border. The number of P. pachyrhizi and P. meliosmae-myrianthae uredinia within the lesions increased over time (on average 14-fold), whereas the number of U. appendiculatus uredinia remained the same. These findings were corroborated by qPCR, which revealed a greater increase in fungal biomass for Phakopsora spp. than for U. appendiculatus until 12 days post-inoculation. The high number of satellite uredinia within lesions might be directly related to the impact of this pathogen in photosynthetic efficiency on symptomless areas of diseased grapevine leaves. This study identified accelerated formation of satellite uredinia as an important feature of grapevine colonization by P. meliosmae-myrianthae.     

Aetiology of anthracnose on grapevine shoots in Brazil

Anthracnose is an important disease in vineyards in south and southeast Brazil, the main grape‐producing regions in the country. This study aimed to identify the causal agents of grapevine anthracnose in Brazil through multilocus phylogenetic analyses, morphological characterization and pathogenicity tests. Thirty‐nine Elsinoë ampelina and 13 Colletotrichum spp. isolates were obtained from leaves, stems and berries with anthracnose symptoms collected in 38 vineyards in southern and southeastern Brazil. For E. ampelina isolates, the internal transcribed spacer (ITS), histone H3 (HIS3) and elongation factor 1‐α (TEF) sequences were analysed. HIS3 was the most informative region with 55 polymorphic sites including deletions and substitutions of bases, enabling the grouping of isolates into five haplotypes. Colonies of E. ampelina showed slow growth, variable colouration and a wrinkled texture on potato dextrose agar. Conidia were cylindrical to oblong with rounded ends, hyaline, aseptate, (3.57–) 5.64 (?6.95) μm long and (2.03–) 2.65 (?3.40) μm wide. Seven species of Colletotrichum were identified: C. siamense, C. gloeosporioides, C. fructicola, C. viniferum, C. nymphaeae, C. truncatum and C. cliviae, with a wide variation in colony and conidium morphology. Only E. ampelina caused anthracnose symptoms on leaves, tendrils and stems of Vitis vinifera and V. labrusca. High disease severity and a negative correlation between disease severity and shoot dry weight were observed only when relative humidity was above 95%. In this study, only E. ampelina caused anthracnose symptoms on grapevine shoots in Brazil.     

First report of oospore formation in Plasmopara viticola,the causal agent of grapevine downy mildew,in highland regions of southern Brazil

This work evaluates the formation of oospores of Plasmopara viticola, the causal agent of grape downy mildew (DM), in highland regions in southern Brazil. Leaves of susceptible and resistant grape genotypes naturally infected with the pathogen were collected in the autumn of 2017, 2018, and 2019 from vineyards located in the highlands of Santa Catarina state. Leaf tissues were evaluated by light microscopy and scanning electron microscopy. Oospores of P. viticola were identified in both susceptible and resistant host genotypes. They were concentrated in the central regions of the DM lesions, close to the leaf veins, and exhibited a rounded shape, yellowish colour, thick wall, and a diameter ranging from 16.28 to 49.15 µm. The formation of oospores is strong evidence that sexual reproduction is occurring in P. viticola in the climatic conditions of the highlands of southern Brazil. Sexual reproduction contributes to the maximization of genetic diversity via meiosis. Populations with high genetic variability are more likely to break resistance mechanisms conferred by resistance genes and to develop resistance to fungicides applied for disease control. To our knowledge, this is the first scientific study to prove the formation of P. viticola oospores in Brazil. The results presented provide a solid basis for further studies on sexual recombination in P. viticola. Genetic improvement programmes for grapevines, disease management methods, and disease prediction models need to consider the sexual reproduction of this pathogen, otherwise their effectiveness may be compromised.     

Susceptibility of invasive taxa of European blackberry to rust disease caused by the uredinial stage of Phragmidium violaceum under field conditions in Australia

European blackberry ( Rubus fruticosus agg.) is an aggregate of closely related taxa, with at least 15 taxa naturalized in Australia. Biological control of this Weed of National Significance, using the nonindigenous rust fungus Phragmidium violaceum , is effective when the weather is conducive to multiple cycles of infection, but some blackberry taxa escape severe disease. Thirty-one taxa of naturalized R. fruticosus agg. from southeastern Australia were isolated, their DNA phenotype determined and clones of each taxon inoculated with P. violaceum isolate SA1. Disease development was monitored for at least four generations of uredinia on large potted plants under field conditions. Although variation in mean disease severity appeared continuous over the range of Rubus clones tested, counts of uredinia and telia enabled identification of eight resistant taxa. Fine scale variation in susceptibility to rust disease was observed when different clones of R. leucostachys with the same DNA phenotype were found to express either resistance or susceptibility to P. violaceum (SA1). There were significant differences among 23 Rubus taxa rated as susceptible to rust disease in the mean number of leaves emerging per latent period of uredinia (LELPU). Mean LELPU appeared to account for some of the variation in two measures of mean disease severity observed among susceptible Rubus clones, although the correlation was insignificant (0·10 <  P  > 0·05).     

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.     

Colletotrichum falcatum and Fusarium species induce symptoms of red rot in sugarcane in Brazil

Red rot is an important disease of sugarcane, reported from the main producing countries of the crop. The main causal agent is Colletotrichum falcatum, which induces reddish internal stalk rot, resulting in loss of quality and quantity of sugars. While the occurrence of this disease has been reported in plantations in Brazil, the aetiology of the disease is not yet fully understood. We isolated and identified the fungi associated with sugarcane plants showing symptoms of red rot. Thirty isolates were recovered and grouped by morphology within the genera Colletotrichum and Fusarium. Based on phylogenetic analyses of DNA sequences from ITS, ACT, SOD, GAPDH, and EF-1α, eight isolates were identified as C. falcatum (n = 6) and C. plurivorum (n = 2). Twenty-two isolates belonged to the Fusarium fujikuroi species complex and were identified as F. sacchari (n = 8), F. proliferatum (n = 3), and F. madaense (n = 11). Coinfection with C. falcatum and Fusarium species were frequently observed. C. falcatum and Fusarium strains induced reddening of internal tissues and stalk rot in sugarcane plants, symptoms of red rot, while Fusarium species also induced symptoms of pokkah boeng. C. plurivorum, whose sexual stage was observed on the surface of stems, did not induce stalk rot or leaf symptoms. The results obtained in this study clarify the aetiological agents of red rot of sugarcane in Brazil. The conditions that lead to the development of specific symptoms of red rot or pokkah boeng are under investigation.     

Dothistroma needle blight: an emerging epidemic caused by Dothistroma septosporum in Colombia

Plantation forestry in Colombia is based mainly on non‐native species of Pinus and Eucalyptus. Since 2008, a disease with symptoms similar to those of dothistroma needle blight (DNB) has been found affecting large areas planted to Pinus spp. The aim of this study was to identify the causal pathogen as well as to document the levels of disease incidence and severity. Isolates from each of three forestry zones, collected from different host species, were compared based on rDNA sequence of the ITS regions. These were conclusively identified as Dothistroma septosporum, one of two Dothistroma spp. known to cause DNB. Susceptibility was greatest on low elevation Pinus tecunumanii followed by Pinus kesiya and Pinus oocarpa. Pinus maximinoi and high elevation P. tecunumanii showed tolerance to D. septosporum. The disease incidence in the different zones varied significantly with the North zone being the most severely affected. This constitutes the first report of disease distribution and susceptibility of hosts, as well as the first consideration of the relative importance of D. septosporum in Colombia.     

台湾新发生重大外来入侵物种——虎纹非洲大蜗牛的检疫鉴定

虎纹非洲大蜗牛Achatina panthera (Férussac, 1832)是近年来台湾新发生的重大外来入侵物种, 对农林生产和人畜健康构成严重威胁, 目前中国大陆尚无分布?本文厘清了该蜗牛分类历史和系统学地位, 通过核对实物标本结合现有文献, 重新描述了虎纹非洲大蜗牛的形态特征, 并与近似种的主要形态鉴别特征进行了比对?首次测定该蜗牛的COⅠ基因序列, 并建立了分子比对鉴定方法?最后提出了相应的检疫风险管理措施, 可为有关部门应对虎纹非洲大蜗牛的入侵提供科学依据?     

Characterization and pathogenicity of Septoria gaurina associated with leaf blotch disease on Gaura parviflora in China

Gaura parviflora, a flowering plant of the family Onagraceae, is regarded as an invasive plant in China, but is subject to leaf blotch disease. Based on morphological features, we identified the causal agent to be Septoria gaurina. However, the phylogenetic position of S. gaurina remains unknown. Multilocus phylogenetic analysis using the internal transcribed spacer (ITS), β-tubulin (Tub2), actin (Act), calmodulin (Cal), translation elongation factor 1-α (EF), and 28S nrDNA (LSU) nucleotide sequences indicated that the isolates belonged to the Septoria genus. Pathogenicity tests demonstrated that the isolates produced symptoms on the leaves of G. parviflora. These symptoms included small, water-soaked, circular lesions formed on leaves inoculated with conidial droplets, and bigger, water-soaked lesions on leaves inoculated by conidial spraying. To our knowledge, this is the first report of S. gaurina as the causative agent of leaf blotch disease of G. parviflora in China.     

Identification and pathogenicity of Fusarium species associated with pokkah boeng of sugarcane in Brazil

Brazil is the world’s biggest producer of sugarcane (Saccharum spp. hybrids). Pokkah boeng is an important fungal disease in this crop caused by members of the Fusarium fujikuroi species complex (FFSC) and characterized by deformation of the aerial part of the plant and stem rot. While the occurrence of symptoms has been reported in plantations in Brazil, no official reports of the disease exist. In this study, species of the FFSC were identified that are associated with sugarcane plants with symptoms of pokkah boeng in Brazil. This was achieved using two-loci molecular phylogeny, sexual compatibility and analysis of morphological markers. The ability of strains to cause disease in plants of sugarcane, maize, sorghum and millet was also evaluated. The 39 isolates studied were identified as F. sacchari, F. proliferatum and another, still unknown, phylogenetic lineage that is sister to F. andiyazi. Crossing field isolates of F. sacchari and F. proliferatum with their respective tester strains produced fertile perithecia and viable ascospores. All three species induced symptoms of pokkah boeng on inoculated sugarcane plants and caused stem rot in maize, sorghum and millet. Symptoms on sugarcane are chlorosis and necrosis of leaves, punctured lesions, twisted leaves, reduction of the total leaf area, death of the top of the plant and stalk rot. The findings confirmed the aetiology of the disease in Brazil, generated basic knowledge for the development of strategies for diagnosis and monitoring of the disease and support breeding programmes for selecting resistant germplasm.     

Role of oospores as primary inoculum for epidemics of downy mildew caused by Peronospora arborescens in opium poppy crops in Spain

This study investigated the role of Peronospora arborescens oospores as primary inoculum for downy mildew of opium poppy and infection types that they may give rise to in Spain using an integrative experimental approach that combined pathogenicity tests in growth chambers and field microplots, together with molecular detection of P. arborescens infection by specific nested-PCR assays. The results demonstrated that oospores in infested soil or leaf debris were effective inoculum for ingress of the pathogen through underground plant tissues early in poppy seedling growth. This gave rise to systemic infections that reproduced the stunting, chlorotic syndrome frequently observed in affected plants in commercial fields. Additionally, infection of underground tissues of older plants by oospore inoculum could remain asymptomatic. Results also suggested that sporangia formed on infected plants are effective in producing secondary local infections that later may become systemic and either symptomatic or asymptomatic. Finally, and more importantly, those delayed symptomatic or asymptomatic systemic infections, as well as secondary local infections of capsules, can give rise to infected seeds. This research on the biology of P. arborescens on poppy plants and epidemiology of downy mildew may help to develop knowledge-based disease-management strategies of use in the protection of yields of opium poppy crops in Spain and elsewhere.     

Potential of a coevolved rust fungus for the management of Himalayan balsam in the British Isles: first field releases

In 2014, the rust fungus Puccinia komarovii var. glanduliferae, native to the foothills of the Himalayas from Kashmir to Western Nepal, became the first fungal agent to be released into Europe for the classical biological control of a non-native weed. The target, Impatiens glandulifera or Himalayan balsam, is a prolific invader of riparian habitats in Europe and North America. During the period 2015–2018, a strain of the rust from India was released at a total of 36 sites, in 17 counties in England and Wales. There was limited field infection in 2015 and inoculation experiments conducted under controlled conditions revealed significant variation in the susceptibility of plant populations to the rust, with some showing immunity. Subsequently, a second strain of the rust from Pakistan was released in 2017 and was found to infect a different cohort of Himalayan balsam populations. The rust mass production methodology, and field inoculation and monitoring protocol, are detailed, and plants were tested for susceptibility to both rust strains prior to field release. Levels of foliar infection at selected sites in 2017 and 2018 are presented, as well as seedling infection rates in the spring of 2019. The results show that the rust is able to overwinter and establish populations in stands of Himalayan balsam in England. The issues involved with measuring the impact of the biological control agent are discussed.     

Introduced weeds pollinated by introduced bees: Cause or effect?

In the present review we attempt to synthesize evidence for a causative relationship between the presence of non-native bee pollinators and the successful establishment and spread of introduced weed species. Using data drawn from the literature and from our own survey conducted in New Zealand, we show that introduced bees favor foraging on introduced plant species, and that in some cases they depend totally on these plants as sources of nectar and pollen. It is also apparent that the flowers of many introduced plants are visited, exclusively or predominantly, by introduced bees. Accepting that visitation does not necessarily imply pollination, and not all plants require pollination to reproduce, we review relationships between seed set of exotic weeds and visitation by introduced pollinators. Although few studies have been carried out, we show that those reported so far all point to increased seed set when introduced plants are visited by non-native bee species. There is clear evidence for a positive link between the spread of weeds and the presence of introduced bees. Nevertheless, ecologists have neglected this aspect of weed population biology and remarkably few studies have been conducted on the importance of pollinator availability in the management of weed species. We suggest several avenues along which future research can be conducted and highlight how the management of present and future weed species may be influenced by this research.     

Nitrogen metabolism disorder in watermelon leaf caused by fusaric acid

The effect of fusaric acid (FA) on the activity of leaf nitrogen (N) metabolism enzymes in watermelon seedlings supplied with different N forms was studied. The results showed that FA inhibited nitrogen uptake and caused decreased leaf amide and protein but increased the content of ammonium and amino acids. When treated with FA the activities of enzymes in the pathway for the synthesis of amino acid in leaves (GS, GOGAT, and GDH) were decreased by 15–23%, 13–40%, and 71–86%, respectively. The activity of asparagine synthetase was decreased by 34–57%. The proteinase activity was initially increased by 37–125% at 12 h after treatment of FA but then subsequently decreased. The activity of glutamate-pyruvate aminotransferase was increased by 280–400%, though the activity of glutamate-oxaloacetate aminotransferase was decreased by 30–63%. It was suggested that FA inhibited the uptake of ammonium in seedlings and suppressed the activities of amino acid and amide synthases, while stimulating proteinase activity.A new pathogenic mechanism of watermelon infection by Fusarium spp. was found as FA caused the complete disorder and collapse of the host plant's nitrogen metabolism. This work provides a new insight into the progression of watermelon wilting caused by Fusarium oxysporum f.sp. niveum.     

Aetiology of leaf spot of garlic and onion caused by Stemphylium vesicarium in Spain

Surveys between 1989 and 1993 in the major garlic production areas of Spain identified a new leaf spot disease, characterized by white and purple lesions followed by extensive necrosis. Isolation and pathogenicity tests with fungal isolates taken from these spots indicated that Stemphylium vesicarium was the causal agent. Pseudothecia of the teleomorph stage, Pleospora sp., were found on leaf debris from affected plants. Inoculation of garlic and onion plants with residues carrying mature pseudothecia, or with ascospore suspensions obtained from the pseudothecia, resulted in the development of white and purple leaf spots. Wetness periods longer than 24 h were required for symptom development under controlled conditions. Isolates of S. vesicarium from garlic, onion and asparagus caused disease in all three hosts. In garlic, cv. Blanco de Vallelado was most susceptible, while lines B4P17 and B6P1, and cvs Iberose and Golourose were less susceptible to the disease.     

广西澳洲坚果干花病病原菌鉴定

笔者于2022年4月在广西南亚热带农业科学研究所澳洲坚果种质资源圃内发现澳洲坚果干花病, 该病害危害花序, 造成花瓣变褐、花序轴干枯甚至整个花序干枯死亡。本研究根据柯赫氏法则鉴定病原菌, 并依据其形态学特征及TEF-TUB-ITS多基因联合建树明确病原种类, 结果显示其致病菌为亚洲新拟盘多毛孢Neopestalotiopsis asiatica与腐生新拟盘多毛孢N. saprophytica。这是亚洲新拟盘多毛孢与腐生新拟盘多毛孢造成澳洲坚果干花病的首次报道。     

The reliability of leaf bioassays for predicting disease resistance on fruit: a case study on grapevine resistance to downy and powdery mildew

This study was designed to assess the reliability of grapevine leaf bioassays for predicting disease resistance on fruit in the field. The efficacy of various grapevine quantitative trait loci (QTLs) for conferring resistance to downy and powdery mildew was evaluated in bioassays and in a 2‐year field experiment for downy mildew. The resistance genes studied were inherited from Muscadinia rotundifolia (Rpv1 and Run1) and from American Vitis species through cv. Regent (QTLRgP and QTLRgD). In bioassays, genotypes carrying Run1 blocked powdery mildew development at early stages. Genotypes combining Run1 with QTLRgP displayed no greater level of resistance. For downy mildew, genotypes carrying Rpv1 and/or QTLRgD were more resistant than the susceptible cv. Merlot, and showed a high level of leaf resistance in the field (<10% severity). Disease levels on bunches were much higher than those on leaves, with a high variability between Rpv1 genotypes (1–48%). A Bayesian decision theory framework predicted that an OIV‐452 threshold of 5 in leaf bioassays allowed accurate selection of grapevine genotypes (P = 0·83) with satisfactory disease severity on bunches. Therefore, this study validates that the use of early bioassays on leaves, as currently performed by grapevine breeders, ensures a satisfactory level of resistance to downy mildew of bunches in the field.     

Effect of Trichoderma viride pre-inoculation in pine species with different levels of susceptibility to Fusarium circinatum: physiological and hormonal responses

Pine pitch canker (PPC), caused by Fusarium circinatum, affects Pinus species worldwide. Although no effective solutions have yet been found to control it, there is a growing interest in using biological control agents (BCA) such as Trichoderma to avoid the application of chemical-based products. Using species with an increasing level of susceptibility to PPC (Pinus pinea, Pinus pinaster and Pinus radiata), this study aimed to evaluate the effect of Trichoderma viride pre-inoculation on disease development, assessing several physiological and hormonal parameters. A 2-week period elapsed between T. viride and F. circinatum inoculation. Sampling for each species was performed independently when at least 50% of the plants of one of the inoculated groups developed disease symptoms. Fusarium circinatum infection reduced water status and photosynthesis, but increased proline, abscisic acid and jasmonic acid concentrations in plants of P. radiata and P. pinaster with symptoms; while in P. pinea water relations were maintained and anthocyanin accumulation occurred in the presence of F. circinatum. In P. radiata, T. viride pre-inoculation accelerated disease progression, with some PPC-induced responses augmented (decreased water potential and photosynthesis; increased substomatal CO₂ concentration) and novel changes not found in seedlings inoculated exclusively with F. circinatum (increased electrolyte leakage and salicylic acid; decreased relative water content). This suggests that T. viride may be initially recognized as an invading organism, subverting the plant defence mechanisms for successful root colonization. If seedlings are not allowed to recover from this state, pathogen infection may thus be facilitated, highlighting the importance of application timing in BCA strategies.