Isolation and pathogenicity of Phytophthora species from declining Rubus anglocandicans

Rubus anglocandicans is the most widespread and abundant blackberry species within the European blackberry (Rubus fruticosus) aggregate in Western Australia (WA). European blackberry is also one of the 32 Weeds of National Significance in Australia. A disease recorded as ‘blackberry decline’ was first observed in some blackberry sites in WA in 2006. A disease survey was conducted in the Manjimup‐Pemberton region along the Warren and Donnelly River catchments in WA between 2010 and 2012. Phytophthora amnicola, P. bilorbang, P. cryptogea, P. inundata, P. litoralis, P. multivora, P. taxon personii, P. thermophila and a P. thermophila × amnicola hybrid were recovered from declining and adjacent decline‐free sites, as well as from streams and rivers. Phytophthora cinnamomi was isolated from dying Banksia and Eucalyptus species from two non‐decline sites. Of these species, P. bilorbang and P. cryptogea were more pathogenic than the others in under‐bark inoculations using excised stems (primocanes), in planta primocane inoculations in blackberry growing wild in native forest stands, and in glasshouse pot trials. It was concluded that blackberry decline is a complex syndrome and Phytophthora species, in particular P. bilorbang and P. cryptogea, together with temporary inundation, are major biotic and abiotic factors contributing to blackberry decline.     

Effectiveness of fumigants and grafting against tomato brown root rot caused byColletotrichum coccodes

In an attempt to find effective control measures againstColletotrichum coccodes, an emerging pathogen causing root rot on tomato in northern Italy, four experimental trials were carried out during the years 2005 and 2006 in Piedmont and Liguria in order to evaluate the effectiveness of the combination of different rootstocks (Beaufort F1, He Man F1, Maxifort) with various fumigants. In the presence of medium to high disease incidence, the best results were obtained by combining the use of a resistant tomato rootstock with soil fumigation with dimethyl disulfide at 40 or 80 gm⁻² or metham sodium at 192 g m⁻². Chloropicrin, applied at 20 g m⁻², and the tested rootstocks alone, did not enable effective control of the pathogen. The need to monitor the appearance of new diseases and the resurgence of old ones is stressed.     

Characterization of accessions and species of Macadamia to stem infection by Phytophthora cinnamomi

Phytophthora cinnamomi is a major pathogen in most macadamia plantations worldwide. Due to stem lesions, stem cankers and leaf defoliation, it results in loss of productivity and tree death. This study examined accessions of the four Macadamia species and their hybrids, produced via rooted stem cuttings or germinated seeds, for susceptibility to stem canker and necrotic lesions caused by P. cinnamomi. Plants were wound‐inoculated with agar containing P. cinnamomi. The symptoms produced in inoculated plants were used to characterize host susceptibility variation within and among the population. Lesion length and severity of stem canker were recorded. The four species and hybrids differed significantly in stem canker severity (P < 0.001) and lesion length (P = 0.04). Macadamia integrifolia and M. tetraphylla hybrids were the most susceptible. Macadamia integrifolia had the greatest stem canker severity and the most extensive lesions above and below the site of inoculation. Restricted lesion sizes were observed in M. ternifolia and M.  jansenii. The effects of basal stem diameter and the method of propagation either from cuttings or from seed were not significant. The genetic variation in the reaction of macadamia accessions to stem infection by P. cinnamomi is discussed.     

Age‐related susceptibility of Eucalyptus species to Phytophthora boodjera

Phytophthora boodjera is a newly described pathogen causing damping off and mortality of Eucalyptus seedlings in Western Australian nurseries. This study evaluated the age‐related susceptibility of several taxa of mallee Eucalyptus to P. boodjera in sterilized washed river sand‐infestation pot trials. Phytophthora cinnamomi and P. arenaria were included for comparison. Seedlings of Eucalyptus taxa were inoculated at 0, 2, 4, 12 and 88 weeks with individual Phytophthora isolates. Pre‐emergent mortality in the presence of Phytophthora was almost 100%. Post‐emergent mortality was 50–100%, depending on isolate, compared to 0% for the control. Mortality was also high for inoculated 1 month‐old seedlings (46–68%) and root length of surviving seedlings was severely reduced. Death from root infection was not observed for seedlings inoculated at 12 and 88 weeks, but they developed root necrosis and reduced root dry weight compared to non‐inoculated controls. Phytophthora boodjera is a pre‐ and post‐emergent pathogen of mallee eucalypts. These eucalypts are susceptible to P. boodjera at all life stages tested, but the mortality rates declined with plant age. Similar results were obtained for P. cinnamomi and P. arenaria. The events leading to its recent appearance in the nurseries remain unknown and further investigations are underway to determine if this is an introduced or endemic pathogen. The approach used here to understand the impact of a Phytophthora species on multiple hosts at different seedling ages is novel and sets a benchmark for future work.     

Identification of a genetic lineage within Xanthomonas arboricola pv. juglandis as the causal agent of vertical oozing canker of Persian (English) walnut in France

A new bacterial disease of Persian (English) walnut (Juglans regia) has been observed in France. This disease, called vertical oozing canker (VOC), is characterized by vertical cankers on trunks and branches of affected walnut trees with oozing exudates. To determine the aetiology of the disease, a study was carried out in 79 walnut orchards and nurseries located in southeastern and southwestern France. Bacterial analysis from diseased samples yielded 36 strains identified as Xanthomonas arboricola and 32 strains identified as Brenneria nigrifluens on the basis of biochemical tests. The causal agent of VOC was identified as X. arboricola by pathogenicity tests on walnut. Fluorescent amplified fragment length polymorphism (F‐AFLP) was carried out on 36 strains of X. arboricola collected in this study, 24 strains of X. arboricola pv. juglandis isolated from walnut blight symptoms and one strain of X. arboricola pv. corylina included as an outgroup. Based on cluster analysis of F‐AFLP data, most X. arboricola strains responsible for main VOC outbreaks showed a high degree of similarity, forming a cluster clearly separate from strains of X. arboricola pv. juglandis isolated from walnut blight symptoms. It is suggested that VOC is caused by a distinct genetic lineage within the pathovar juglandis of X. arboricola that is also able to cause classical bacterial blight symptoms on walnut leaves and fruits.     

Evaluation of Trichoderma harzianum for controlling root rot caused by Phytophthora capsici in pepper plants

The ability of Trichoderma harzianum to control the rotting of pepper ( Capsicum annuum ) plant roots caused by Phytophthora capsici was studied. Interactions between the fungi were assessed in vitro on three culture media (V8c, Czapek and 2% water agar) and in vivo in plants grown in a substrate inoculated with P. capsici and T. harzianum . Studies on mutual antagonism in vitro showed that P. capsici was inhibited by T. harzianum ; however, the intensity of inhibition differed according to the medium used, being greatest on Czapek. Analysis of the fungal populations in the plant growth substrate showed that T. harzianum consistently reduced that of P. capsici over time. This reduction in the pathogen population was associated with a reduction in root rot of between 24 and 76%, although plant growth (dry weight) was still reduced by 21.2–24.7%, compared with the uninoculated control. In the absence of T. harzianum with the same pathogen inoculum levels, the reduction in dry weight was 59.8–68.6%, suggesting that T. harzianum reduced the damage.     

Zoospore chemotaxis of closely related legume‐root infecting Phytophthora species towards host isoflavones

Phytophthora niederhauserii, P. pisi, P. sojae and P. vignae are closely related species that are pathogenic to various legume plants. While P. sojae and P. vignae are reported to specifically infect soybean and cowpea, respectively, P. pisi is reported to attack pea and faba bean. Phytophthora niederhauserii is considered to have a broad host range. Zoospores of some Phytophthora species are chemotactically attracted to the isoflavones that are secreted by their host plants. The focus of the current study was to determine the chemotaxic behaviour of zoospores from closely related legume‐root infecting Phytophthora species and to investigate the correlation, if any, to host preference as determined by greenhouse pathogenicity tests. The results showed that P. sojae and P. vignae were attracted to the non‐soybean isoflavone prunetin as well as to the soybean isoflavones genistein and daidzein, which is in contrast with their host specificity on soybean and cowpea, respectively. On the other hand, P. pisi and P. niederhauserii were only attracted to prunetin, previously reported to be produced by pea, but not to the isoflavones associated with the non‐host soybean. The lack of responsiveness to genistein and daidzein in P. pisi may represent a recent adaptation to the host specialization towards pea. However, the affinity of P. niederhauserii to prunetin shows that this trait can also be present in taxa not specifically associated with legume hosts.     

云南主栽核桃品种对Alternaria alternata叶枯病的抗病性评价

为了解云南地区不同核桃品种对叶枯病的抗性,从而为核桃抗病品种选育和叶枯病的防治提供依据,试验采用田间调查和离体叶片接种法获得病斑面积和病情指数,采用聚类分析的方法对田间调查和离体接种的病斑面积进行聚类分析,并结合病害分级标准,综合评价云南主栽37个核桃品种对Alternaria alternata的抗病性。结果表明:‘大泡核桃1’叶片上未出现病斑,‘小圆果’病斑面积最小,为5.05 mm~2,而‘圆菠萝2’病斑面积最大,达到887.68 mm~2;采用Ward最小偏差平方和法和欧式距离进行聚类分析,其聚类效果与接种结果和田间调查结果的吻合度最好。通过田间调查和离体接种综合评价,将37个核桃品种分为13个抗病品种、15个中抗品种、7个中感品种和2个感病品种。     

核桃枝枯病小新壳梭孢巢式PCR检测方法的建立

近年来,小新壳梭孢Neofusicoccum parvum导致的核桃枝枯病屡有报道,该病防治困难,发病率高,是核桃的一种灾难性病害。为建立N.parvum的快速、灵敏的分子检测体系,根据N.parvum的几丁质合酶1基因(CHS1)及其前后100bp序列,分别设计了两对特异性引物CT-WK3-S/CT-WK3-A和CT-N-S/CT-N-A,建立了N.parvum的巢式PCR检测方法。结果表明,建立的体系可以从不同来源的5个N.parvum菌株中特异性地扩增出97bp的目的条带,灵敏度达30fg/μL,是常规PCR的10倍,而从其近缘种葡萄座腔菌属Botryosphaeriasp.的病原菌及其他供试菌株均未扩增出任何条带。以感染N.parvum的核桃组织总DNA为模板进行检测,可以在发病早期检测出N.parvum的存在。本研究建立的巢式PCR体系可以为核桃枝枯病的田间检测提供思路。     

Variation in susceptibility of lettuce cultivars to fusarium wilt caused by Fusarium oxysporum f.sp. lactucae

Lettuce cultivars adapted to Californian growing conditions were screened for resistance to fusarium wilt caused by Fusarium oxysporum f.sp. lactucae in order to determine if differences in susceptibility among currently grown cultivars might contribute to management of this disease. Based on a preliminary evaluation of 46 cultivars, eight that were among the most resistant of their horticultural type (iceberg, romaine or leaf) were selected for further testing. The relative susceptibility of these cultivars was assessed by: (i) root-dip inoculation, (ii) sowing seeds into infested potting mix and (iii) transplanting seedlings into an infested field. Evaluations of disease severity showed that both methods (i) and (ii) produced cultivar rankings that were significantly correlated with rankings from field trials [method (iii)]. Two romaine and two leaf cultivars were highly resistant to fusarium wilt (mean disease severity rating of ≤1·3 on a 1–4 scale) under all test conditions. Other romaine and leaf cultivars, however, were highly susceptible in root–dip tests, so there was no consistent association between cultivar type and susceptibility to fusarium wilt. Likewise, there was considerable variation in susceptibility to wilt among iceberg cultivars, but all were significantly more susceptible than the most resistant romaine and leaf cultivars.     

Fusarium rot of melon is caused by several Fusarium species

Fusarium rot of melon, caused by species of the genus Fusarium, has become an important postharvest disease for many Brazilian producers. Due to the delayed onset of symptoms, this disease is often only detected when fruits arrive at the importing country, thus generating economic loss for the exportation of the fruit. This study was developed with the aim of investigating which Fusarium species cause fruit rot in melon and to evaluate any differences in aggressiveness and development of symptoms. Species were identified through phylogenetic analysis of two loci and morphological markers. The 28 isolates obtained from diseased melon fruits of different commercial cultivars were identified as Fusarium falciforme (FSSC), F. sulawesiense, F. pernambucanum (FIESC), and F. kalimantanense (FOSC). Three isolates belong to a new phylogenetic lineage within the F. fujikuroi species complex (FFSC). All isolates were tested for pathogenicity, and first symptoms of rot in Canary melon were observed 2 days after inoculation. Isolates of F. falciforme and F. sulawesiense were shown to be more aggressive. Our results extend information on Fusarium species that cause fruit rot in melon and support the development of management strategies, as there is currently no efficient control for this disease. To our knowledge, this is the first report of the occurrence of species of the FSSC, FOSC, and FFSC from muskmelon fruits in Brazil.     

32份木薯种质对疫霉根腐病的抗性评价和农艺性状分析

通过田间自然发病和室内离体接种方法对32份木薯种质进行了棕榈疫霉根腐病抗病性评价,结果表明,供试的32份木薯种质中,高抗种质7份,抗病种质7份,中感种质8份,感病种质7份,高感种质3份。其中高抗种质为‘H360’、‘华南11号’、‘华南8号’、‘H588’、‘桂热3号’、‘H873’和‘H971’;抗病种质为:‘F556’、‘H502’、‘GR911’、‘C-4’、‘F10’、‘南植188’和‘H47’。对其中14份抗棕榈疫霉根腐病木薯种质的农艺性状进行了鉴定和评价,结果表明‘华南8号’、‘GR911’、‘F556’、‘C-4’、‘H360’可以进一步加以利用。     

Contrasting canopy and fibrous root damage on Swingle citrumelo caused by ‘Candidatus Liberibacter asiaticus’ and Phytophthora nicotianae

Huanglongbing (HLB), associated with the phloem‐limited bacterium ‘Candidatus Liberibacter asiaticus’ (Las), is devastating trees in citrus orchards of Florida. Additionally, Phytophthora nicotianae, omnipresent in citrus soils, causes root rot that reduces water and nutrient uptake by fibrous roots. To investigate fibrous root damage and replacement and canopy size in relation to infection of fibrous roots by Las and P. nicotianae, rootstock seedlings of Swingle citrumelo (Citrus paradisi × Poncirus trifoliata) were inoculated with Las or P. nicotianae in two greenhouse pot trials. Phytophthora nicotianae caused root damage within 5 weeks post‐inoculation, which led to greater reduction of canopy size than for Las‐infected seedlings by the end of the experiment. Las increased accumulation of fibrous root biomass at 5 weeks post‐root trimming (wpt) in the 2014 trial and at 11 wpt in the 2015 trial. New root length was not consistently increased by Las. Reduced total leaf area of symptomless Las‐infected seedlings compared to noninoculated controls might be due to the combined effect of altered carbohydrate allocation between shoots and roots and altered leaf morphology.     

Trichothecene production is detrimental to early root colonization by Fusarium culmorum and F. graminearum in fusarium crown and root rot of wheat

Fusarium culmorum (Fc) and F. graminearum (Fg) belong to the predominant causal agents of fusarium crown and root rot (FCR) in wheat. While many studies have been done to investigate crown rot, including stem base infection, root colonization and mycotoxin production associated with root rot is not well understood. In this study the impact of mycotoxins on the colonization of wheat roots and stem bases was analysed by using Fc and Fg isolates that varied in both quantity and types of trichothecenes they produce. Seedling inoculations in growth chambers with a high deoxynivalenol (DON)- and 3-acetyldeoxynivalenol (3ADON)-producing isolate led to more severe symptoms and 20-times greater colonization of the stem base, as measured by Fc DNA accumulation, than isolates that produced less DON/3ADON. In contrast to stem base colonization, in vitro inoculations of roots with a Tri5 deletion mutant deficient in Fg trichothecene production led to three-times higher colonization than the wildtype. Furthermore, an Fc isolate that produced low levels of zearalenone resulted in twice the level of colonization of a high DON/3ADON-producing isolate included in the study. When root inoculation with a low DON/3ADON-producing Fc isolate was supplemented with exogenous DON, DON production decreased by more than half per unit weight of Fc DNA, and root colonization doubled compared to the untreated control. Therefore, in contrast to its potential role as an aggressiveness factor in stem base infection, trichothecene production by Fc and Fg is detrimental to the early stages of wheat root colonization in FCR.     

Potential susceptibility of Australian native plant species to branch dieback and bole canker diseases caused by Phytophthora ramorum

Susceptibility to branch dieback caused by Phytophthora ramorum was tested using a detached branch assay for 66 Australian native plant species sourced from established gardens and arboreta in California. Six of these species were further tested for their susceptibility to bole cankers caused by P. ramorum using a sealed log assay. Isopogon formosus and Eucalyptus denticulata were identified as potentially highly susceptible Australian branch dieback hosts. Thirteen potentially tolerant Australian host species included Banksia attenuata, B. marginata, E. haemastoma, E. regnans, Pittosporum undulatum and Billardiera heterophylla. Eucalyptus regnans was identified as a potentially highly susceptible bole canker host, while E. diversicolor and E. viminalis were considered potentially tolerant species to bole cankers caused by P. ramorum. Phytophthora ramorum was able to infect all 66 species, as confirmed by reisolation. These results extend the known potential host range for P. ramorum, confirm it as a possible threat to Australian plant industries and ecosystems and highlight additional associated hosts that are important in the global horticultural trade, native forests and plantation forestry.     

Phytophthora pachypleura sp. nov., a new species causing root rot of Aucuba japonica and other ornamentals in the United Kingdom

Isolates of an unknown Phytophthora species from the ‘Phytophthora citricola complex’ have been found associated with mortality of Aucuba japonica in the UK. Based on morphological characteristics, growth–temperature relationships, sequences of five DNA regions and pathogenicity assays, the proposed novel species is described as Phytophthora pachypleura. Being homothallic with paragynous antheridia and semipapillate sporangia, P. pachypleura resembles other species in the ‘P. citricola complex’ but can be discriminated by its distinctively thick‐walled oospores with an oospore wall index of 0·71. In the phylogenetic analysis based on three nuclear (ITS, β‐tubulin, EF‐1α) and two mitochondrial (cox1, nadh1) DNA regions, P. pachypleura formed a distinct clade within the ‘P. citricola complex’ with P. citricola s. str., P. citricola E and P. acerina as its closest relatives. Phytophthora pachypleura is more aggressive to A. japonica than P. plurivora and P. multivora and has the potential to affect other ornamental species.     

Early survival of Quercus ilex subspecies from different populations after infections and co‐infections by multiple Phytophthora species

Forests in Europe are threatened by increased diversity of Phytophthora species, but effects on trees of simultaneous infections by Phytophthora and ecological consequences of their coexistence are unknown. This study explored variation in early survival of Quercus ilex to Phytophthora infections and assessed interactions between Phytophthora species when trees were co‐infected. Three Phytophthora species (P. cinnamomi, P. gonapodyides and P. quercina), seeds from 16 populations of Q. ilex (ballota and ilex subspecies) and two infection times were used as sources of variation in two experiments. The influence of Phytophthora species, Q. ilex subspecies and populations on plant germination and survival were analysed using generalized linear mixed models and survival analysis techniques. Germination rates were not influenced by Phytophthora spp. (P = 0.194) but by the subspecies and populations of Q. ilex (P < 0.001). In Phytophthora‐infested soils, Q. ilex subsp. ilex germinated at higher rates than Q. ilex subsp. ballota. Plant survival was strongly influenced by Phytophthora species (P < 0.001), not by the subspecies and populations of Q. ilex. Seedling mortality was reduced and delayed if a less virulent Phytophthora species infected plants prior to infection by a more virulent Phytophthora species. The results help to explain oak decline syndrome and the lack of natural and artificial regeneration of Q. ilex forests. Lack of interspecific variability of early survival to Phytophthora spp. discourages direct sowing for artificial reforestation programmes. Large, thick seeds, giving plants rapid growth, are advantageous traits when soils are infested with Phytophthora spp.     

Production of phytotoxic metabolites by five species of Botryosphaeriaceae causing decline on grapevines, with special interest in the species Neofusicoccum luteum and N. parvum

In recent years an increasing number of species of Botryosphaeriaceae have been associated with grapevine decline worldwide. Five species isolated from declining grapevines in Spain (Botryosphaeria dothidea, Diplodia seriata, Dothiorella viticola, Neofusicoccum luteum and N. parvum) were checked for toxin production in liquid cultures. Cultural conditions for all fungi were adjusted to obtain optimal production of phytotoxic culture filtrates, by growing the fungi in steady liquid cultures of Czapek–Dox broth for different time intervals. Phytotoxicity of D. seriata and N. parvum reached a maximum after 14 days while the remaining species showed the highest phytotoxicity levels after 21 days in culture. All fungi produced hydrophilic high-molecular weight compounds with phytotoxic properties. In addition, N. luteum and N. parvum produced lipophilic low-molecular weight phytotoxins, not detected consistently among the remaining species. This led to a more exhaustive study on the phytotoxicity of N. luteum and N. parvum. Culture filtrates and corresponding extracts of both species were consistently highly phytotoxic in different assays. The gas-chromatography analysis of the acetylated O-methyl glycosides of the phytotoxic exopolysaccharides produced by N. parvum showed these substances to be composed mainly of glucose, mannose and galactose. Results suggest that phytotoxic metabolites could be involved in the virulence of both species in planta.     

Crop damage and yield loss caused by two species of rodents in irrigated fields in northern Nigeria

We investigated the damage and yield loss caused by two rodent species, Arvicanthis niloticus and Mastomys (Praomys) natalensis, in cereal crops in fields near Kano, northern Nigeria from August, 1990 to April, 1992. Using the random cluster technique, we selected 100 clusters of 30 hills in each rice and wheat field, and assessed damage fortnightly, using the Cut Tiller Count method. In premature crops, damage increased from tillering stages to the dough stages. Differences in the percentages of damage (yield loss) in mature rice (4.8% in 1990 and 12.6% in 1991) and in wheat (30.0% in 1991 and 21.7% in 1992) were statistically significant between years. Severe yield losses in wheat, compared to low and moderate levels in rice (grown for the most part during the rains), were probably a result of greater consumption of the wheat, grown entirely by irrigation during the dry season when other rodent food sources were less abundant. Results of ANOVA showed significant effects of developmental stage of the crop, year of cultivation, and their interactions on the magnitude of crop damage.