Host selection and establishment of striped mealybug, Ferrisia virgata, on cotton cultivars

The striped mealybug, Ferrisia virgata (Hemiptera: Pseudococcidae), is a polyphagous and cosmopolitan species, which attacks a wide variety of crops, including cotton. Lately, it has been found infesting colored fiber cotton and emerging as an important pest in the Northeast of Brazil. Therefore, this study investigated the effects of colonization, establishment, plant distribution and dispersal of F. virgata on cotton cultivars. Preference experiments were set up in the laboratory and in the greenhouse, in which cultivars were offered simultaneously to nymphs or females and the number of insects on each cultivar was counted after 24 h, 48 h, 22 days and 60 days, respectively. Meanwhile, attack of different plant structures and dispersal were investigated under field conditions. Results showed that F. virgata is able to become established on colored cotton fiber cultivars (BRS Verde, BRS Rubi, and BRS Safira) as well as on white cotton cultivars (BRS 201 and CNPA 7H) without showing any preference among these cultivars. Females produce a large number of offspring to enhance nymph survival and host plant colonization, since the number of first instars successfully established after migration is low (<10%). In addition, its short range dispersal can easily occur from plant to plant. Therefore, strategies to manage F. virgata will be needed to facilitate colored cotton production, especially in organic farms infested by this mealybug species.     

Antibiosis of Eucalyptus plants on Podisus nigrispinus

The predator Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae) has been used as a natural enemy to control herbivorous insects in eucalyptus plantations. However, because of the short co-evolutionary history of the predator with this imported plant species, the defensive compounds of eucalyptus may have a negative effect on the predator. Therefore, the survival and development of P. nigrispinus were studied on eucalyptus (Eucalyptus urophylla; exotic host plant) and guava (Psidium guajava; native host plant). P. nigrispinus performance was indeed superior on guava plants than on eucalyptus. The number of fertile eggs and nymphal survival were 52.6% and 12.0% on guava compared with 20.0% and 1.3% on eucalyptus, respectively. Longevity of P. nigrispinus was 115 days on guava and 98 days on eucalyptus. This shows that the predator is not yet fully adapted to the exotic host plant. One possible reason is that the plant toxic compounds in eucalyptus act on this predator by antibiosis.     

Diversity of stem borer parasitoids and their associated wild host plants in South Africa and Mozambique

The diversity of lepidopterous stem borers, their parasitoids and their associated wild host plants was studied in South Africa between 2006 and 2009 and in Mozambique between 2005 and 2010. In South Africa, 20 species of parasitoids were recovered from 17 stem borer species collected on 16 wild host plant species. From Mozambique, 14 parasitoid species were recorded from 16 stem borer species collected on 14 wild host plant species. The highest diversity of parasitoids was recorded on stem borers that attacked the host plants Phragmites australis (7 spp.) and Panicum maximum (6 spp.), in South Africa and Mozambique, respectively. Bracon sp. (Hymenoptera: Braconidae) and Procerochasmias nigromaculatus (Hymenoptera: Ichneumonidae) were the most recorded parasitoid species in South Africa while Cotesia sesamiae (Hymenoptera: Braconidae) parasitized most stem borer species in Mozambique. The most common tachinid parasitoid recorded in this study was Sturmiopsis parasitica (Diptera: Tachinidae). Parasitism of stem borers during the off season was previously thought to occur mainly in natural habitats but this study shows that although natural habitats provided refuges for some parasitoid species, stem borer parasitism was generally low in wild host plants, irrespective of whether collections were done during the cropping or off-season. Parasitoid beta diversity did not depend on habitat or host plant species, but was determined by stem borer diversity.     

Clarifying the source of <Emphasis Type="Italic">Conicofrontia sesamoides</Emphasis> Hampson (Lepidoptera: Noctuidae) population in South African sugarcane using morphological identification and mitochondrial DNA analysis

Valid identification of a novel pest species and clarifying its origin are the primary steps in understanding population structure and development of biocontrol programs. In this study geographical populations of Conicofrontia sesamoides Hampson (Lepidoptera: Noctuidae) collected during surveys conducted in the years 2009, 2014 and 2015 were morphologically identified and their genetic diversity was analysed by using sequences of the mitochondrial cytochrome-c oxidase I (COI) gene in an attempt to examine host plant, or/and altitude associated differences among populations and determine the source of the newly recorded population of this species in the South African sugarcane. The C. sesamoides specimens in this study were collected from Miscanthus capensis (Nees) (Poaceae) and sugarcane (Saccharum officinarum L.) (Poaceae) in Eastern Cape and KwaZulu-Natal Provinces of South Africa. Analysis of Molecular Variance showed a moderate to highly significant genetic differentiation between C. sesamoides populations from different host plants (FST?=?0.115, p?=?0.14) and altitudinal range (FST?=?0.159, p?=?0.18). This result was however, contradictory to outcomes of phylogenetic analyses, haplotype networking and uncorrected sequence divergence (0.0–1.54%) which revealed no detectable genetic differentiation between populations from different host plants and altitudes. As it is difficult to measure FST accurately without a large data set, the very small sample used in the analysis might have resulted in inflation of the FST value in this study. After evaluation of the results, it was concluded that the sugarcane population of C. sesamoideshas originated from the population residing in wild host plants in the Eastern Cape and/or KwaZulu-Natal provinces of South Africa. Possible reasons for the host plant expansion and its implications to commercial sugarcane production in the country are discussed.     

Characterisation of a protein from Venturia inaequalis that induces necrosis in Malus carrying the Vm resistance gene

Apple scab (black spot) is caused by the fungus, Venturia inaequalis. Race 1 isolates of this fungus are avirulent on Malus hosts carrying the resistance gene V_m. Detached leaves from a V_m host (resistant, differential host 5) and ‘Royal Gala’ (susceptible, host 1) were inoculated with a conidial suspension of V. inaequalis. In the resistant reaction, a hypersensitive response (HR), characterised by necrosis and the accumulation of autofluorescent materials in epidermal and mesophyll cells, was observed at the site of fungal penetration. No HR was observed in the susceptible host. V. inaequalis grown in vitro produced an elicitor that induced necrosis, similar to the HR, when infiltrated into leaves of the resistant V_m host. No response, however, was observed in the susceptible host. The elicitor was proteinaceous and a fraction with elicitor activity was isolated using ultra-filtration, acetone precipitation and ion-exchange chromatography. The elicitor activity was resistant to boiling but it was abolished by digestion with proteinase K. The protein fraction contained three major proteins all with low isoelectric points (pI 3·0–4·5). The fraction also elicited necrosis in the differential host 4, but not in any of the other resistant hosts tested, including differential hosts 2, 3, and 6. Therefore, the fraction may contain elicitors with more than one host specificity.     

Mating type gene MAT1-2-1 is common among Japanese isolates of Verticillium dahliae

Mating type genes of Verticillium dahliae, a wilt pathogen affecting many plant species, were identified to examine sexual recombination between Japanese pathotypes. We amplified a DNA sequence encoding high mobility group (HMG) box from V. dahliae using PCR. A cloned genomic DNA fragment included a sequence homologous to MAT1-2-1 gene. Despite that sequence's presence in all V. dahliae isolates we used, MAT1-1-1 (an opposite mating type gene) was never amplified. We concluded that V. dahliae is potentially heterothallic. Furthermore, sexual bias practically obviates sexual recombination between Japanese pathotypes. This report describes, for the first time, a mating type gene of phytopathogenic Verticillium.     

Overexpression of StRbohA in Arabidopsis thaliana enhances defence responses against Verticillium dahliae

Plant NADPH oxidases are key regulators of plant–microbe interactions and reactive oxygen species (ROS) are essential to plant defences against pathogens. A significant part in the role played by ROS has been ascribed to plant respiratory burst oxidase homologs (RBOHs). In potato (Solanum tuberosum), where RBOHs were previously shown to be involved in wound-induced oxidative burst, we assessed their expression after inoculation with Verticillium dahliae Kleb. and showed that StRbohA was the only homolog to be differentially induced in potato in response to inoculation. In order to investigate the potential role of this gene in plant protection against wilt diseases, we used Agrobacterium-mediated transformation of Arabidopsis to assess the effects of its overexpression on plant responses to V. dahliae. After inoculation with this pathogen, the transformed Arabidopsis line overexpressing StRbohA showed lower disease severity (percent damaged leaf area and vascular discoloration) as compared to the wild type. It also had higher ROS production and more cell death caused by hydrogen peroxide (H₂O₂), compared to the wild type. Suberization of root cells was also more pronounced in the line overexpressing StRbohA, and supports a possible role for StRBOHA in plant resistance to V. dahliae. Together, these findings indicate that overexpressed StRbohA in Arabidopsis enhances the ROS-mediated defence mechanisms against V. dahliae and can be a potential tool to improve plant resistance to this and other soilborne pathogens that cause wilts in economically important crops.     

Variability of Cuban and International Populations of Alternaria solani from Different Hosts and Localities: AFLP Genetic Analysis

As causal agent of early blight disease in tomato and potato, Alternaria solani is an internationally important horticultural pathogen. Genetic variability was surveyed by amplified fragment length polymorphism analysis in a total of 112 isolates from potato and tomato, representing pathogen populations from different Cuban provinces together with isolates from the USA, Brazil, Turkey, Greece and China. Also included in the analysis were isolates from catenulated Alternaria spp. from Brazil, Canada, Greece and Russia, along with single isolates of Alternaria porri, Alternaria alternata and a Curvularia sp. UPGMA clustering revealed a differentiation between the isolates of A. solani and all other species with the exception of A. porri which could not be distinguished from A. solani. Among the isolates of A. solani, two distinct subclusters were formed, with high genetic significance revealed by bootstrapping, corresponding to a general subdivision based on the respective solanaceous host. The results are discussed with regard to potential host specificity of A. solani on tomato and potato, and in terms of the comparative contributions of regional and international genetic variability in populations of this ubiquitous plant pathogen.     

Morphometric and developmental consequences in Spodoptera litura due to feeding on three varieties of sweet potato plants (Ipomoea batata)

The tobacco caterpillar, Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae), is a polyphagous pest defoliating sweet potato, Ipomoea batata (Lam) (Convolvulaceae), throughout Asia. The study of morphometric parameters of S. litura as a result of feeding on three varieties (RNSP1, KIRAN and RNSP3) of host plant revealed that a greater number of egg masses were laid on the KIRAN variety than on the others. I. batata varieties showed statistically significant effects on length, breadth and weight of different larval instars. KIRAN-fed larvae molted to bigger-sized pupae. S. litura larvae reared on KIRAN variety had the highest feeding index as well as growth index. The low concentrations of phenols and carbohydrates coupled with elevated levels of proteins and amino acids were found in KIRAN as compared with RNSP1 and RNSP3. Collectively, the results of this study revealed that KIRAN cultivar was the most suitable food plant for the development of S. litura. Concurrently, it is suggested that this cultivar is therefore least suitable for sweet potato cultivation.     

Affordable and reliable plant sap-mediated template preparation for the detection of various phytopathogens by PCR assay

Plant pathogens like ‘Ca. Liberibacter’, phytoplasma, viruses and viroids cause diseases to almost all economically important plants. A simple and fast sap-mediated polymerase chain reaction (PCR) method for the detection of these pathogens infecting various plant hosts is described in the present study. Sap from selected plants was drawn aseptically on parafilm, from the mid-rib of young leaves. Depending on the type of host plant, sap was diluted to optimal concentration before PCR analysis. ‘Ca. Liberibacter’, Citrus tristeza virus (CTV) and Citrus exocortis viroid (CEVd) infecting citrus, and ‘Ca. Phytoplasma’ infecting pepper and sandal trees were tested by sap-mediated PCR. The reliability of this procedure was evaluated by comparing the findings with previously described protocols. The sap-mediated nucleic acid template preparation for PCR assay is devoid of laborious nucleic acid extraction and expensive chemicals. Hence the present method is rapid, economical and so can be employed for diagnosis of large number of plant samples.     

Alternaria host-selective toxins: determinant factors of plant disease

Seven diseases caused by pathotypes of Alternaria alternata, which produced host-selective toxins (HSTs), a diverse group of low-molecular-weight secondary metabolites, are known, and each HST has an essential role as a determinant of pathogenicity in all interactions between the plant host and A. alternata. Although these HST-producing pathotypes are morphologically indistinguishable, each has a distinct host range and can be distinguished by its specificity on the respective host plant, hence their designation as pathotypes of A. alternata. In 1933, Tanaka made the first discovery of a HST; fungus-free culture filtrates of A. kikuchiana (now called A. alternata Japanese pear pathotype) were toxic to susceptible cultivar Nijisseiki, but not to resistant cultivars. Over the 80 years since then, the structure of HST molecules, target sites and mode of actions of HSTs, and the molecular genetics of HST production regulating by supernumerary chromosomes encoding HST gene clusters have been studied extensively. We focus this review on studies of low-molecular-weight HSTs produced by A. alternata and give an overview of various types of HST studies.     

Mitochondrial DNA Variability in Fusarium Proliferatum (Gibberella Intermedia)

Restriction fragment length polymorphisms (RFLP) were used to assess genetic diversity of mitochondrial DNA (mtDNA) among 184 isolates of Fusarium proliferatum recovered from maize, asparagus, palms and reed. All strains were cross-fertile with standard mating type tester strains of Gibberella intermedia. Sixteen mitochondrial haplotypes were identified following digestion of DNAs with HaeIII, with seven, seven, five and six different haplotypes from maize, asparagus, palms and reed, respectively. Four haplotypes (I, III, IV and VII) were found on more than one host. Of these four, haplotype I was dominant on maize, representing 71% of the isolates. The banding patterns for haplotypes III and IV were >90% similar to the banding pattern of haplotype I. Haplotypes I, III and IV accounted for 87% of the isolates from maize, but were less common on the other hosts, accounting for 70%, 52% and 33% of the isolates from asparagus, palms and reed, respectively. Thirteen of the 16 haplotypes were recovered from only a single host plant species. When comparing the banding patterns and frequencies of these haplotypes, at least five were recovered at a higher frequency from one host relative to the others. Our results suggest that mtDNA RFLP analysis is a useful indicator of genetic divergence in Fusarium proliferatum.     

Phylotype and sequevar variability of Ralstonia solanacearum in Brazil,an ancient centre of diversity of the pathogen

The β‐proteobacterium Ralstonia solanacearum causes bacterial wilt of many plant species. Knowledge of phylotype and sequevar variability in populations of this microorganism is useful for implementing control measures, particularly host resistance. To this end, 301 isolates of R. solanacearum were collected from different geographic regions and hosts in Brazil. Their phylotype and sequevar characterization was used to determine the amount and distribution of phenetic and phylogenetic variability. Isolates were classified into phylotypes I (n = 48), clade 1; and phylotype II, clades 2–5. Phylotype II was divided into subclusters IIA (n = 112) and IIB (n = 141). Phylotype II was widely distributed, whereas phylotype I isolates were found in Central, Northern, and Northeastern regions of Brazil. There were 108 haplotypes identified among endoglucanase (egl) gene sequences from 301 isolates and 32 haplotypes among DNA repair (mutS) gene regions from 176 isolates. The egl and mutS sequence analyses identified eight known (1, 4, 7, 18, 27, 28, 41 and 50) and four new (54, 55, 56 and 57) sequevars. Phylotype IIB showed high diversity in sequevars and host range. Multiplex PCR, using primers specific to the Moko ecotype, characterized banana and long pepper isolates as sequevar 4 and 4/NPB, respectively. This constitutes the first report of the emergent ecotype IIB/4NPB in a new host, long pepper. The majority of sequevars were associated with geographic regions. This high variability of R. solanacearum in Brazil suggests use of host resistance to control bacterial wilt should be mainly focused by region.     

Dynamics of infection-related morphogenesis and pathogenesis in Colletotrichum orbiculare

Colletotrichum orbiculare (syn. C. lagenarium) is the causal agent of anthracnose disease on cucurbit plants. This fungus forms dome-shaped, melanized appressoria as a host invasion structure. Strain 104-T (MAFF240422) of C. orbiculare, which was originally isolated from a cucumber plant in 1951 by Dr. Yasumori, Kyoto University, has proven to be an excellent experimental model for the study of fungal pathogenesis and morphogenesis because of its stable pathogenicity and synchronous infection-related morphogenesis. This review considers the discoveries made during 60 years of study on C. orbiculare. In particular, we focus on advances made in the last two decades, which have provided a basis for the molecular analysis not only of fungal morphogenesis, but also of plant–microbe interactions, including plant immunity to adapted and nonadapted Colletotrichum fungi. This substantial body of innovative research was originated by the Phytopathological Society of Japan and represents a major contribution to the international research communities working on plant pathology, plant–microbe interactions, and fungal molecular genetics. This review deals with the past achievements and future prospects in the study of Colletotrichum biology, focusing on the molecular genetics of C. orbiculare with regard to four aspects: (1) metabolic and functional development of infection structures, (2) signaling pathways required for fungal pathogenesis, (3) pathogen-associated molecular patterns (PAMPs) and host basal resistance, and (4) establishment of host specificity.     

Incidence and pathogenicity of races and isolates of Verticillium dahliae in Crete, southern Greece

Classification of 32 Verticillium dahliae isolates originating from 19 plant species in eight different botanical families to races and determination of host range pathogenicity were carried out. The physiological races of isolates were identified using the two differential tomato cultivars ??Belladonna?? (susceptible to both races 1 and 2 of V. dahliae) and ??Ace 55VF?? (resistant to race 1, susceptible to race 2 of V. dahliae). Among these isolates, 14 were race 2 (43.8%), 12 race 1 (37.5%) and six nonpathogenic (18.7%) on tomato. The host range pathogenicity of isolates was determined using four differential hosts (eggplant, turnip, tomato (Ve ^? ) and sweet pepper). Among isolates, five were pathogenic to both eggplant and turnip (15.6%), 21 to eggplant, turnip and tomato (65.6%), five to eggplant, turnip, tomato and sweet pepper (15.6%) and one was pathogenic to eggplant, turnip and sweet pepper (3.2%). The pathogenicity of isolates on the aforementioned five hosts was investigated on the basis of external symptoms and by calculating the relative areas under disease progress curves (relative AUDPC). Results showed that eggplant was the most susceptible, followed by turnip and tomato cv. Belladonna, while sweet pepper and tomato cv. Ace 55VF were less susceptible to all the isolates used. The pathogenicity of isolates varied from highly to mildly virulent on eggplant and turnip while on Belladonna, Ace 55VF and sweet pepper it varied from highly virulent to nonpathogenic. Belladonna exhibited a similar level of susceptibility to races 1 and 2 of V. dahliae, but was more susceptible than Ace 55VF to race 2. Interestingly, the isolates originating from eggplant were clearly more virulent than those originating from tomato and black nightshade on all solanaceous plants tested.     

A yellows disease system with differing principal host plants for the obligatory pathogen and its vector

A stolbur‐type phytoplasma is the putative pathogen of grapevine yellows disease that causes economic damage to vineyards in most growing areas around the world. The pathogen is known to be transmitted to vines by two planthoppers, Hyalesthes obsoletus and Reptalus panzer; the latter is found in Europe but has not yet been observed in Israel. The establishment of a vector–pathogen–plant relationship requires that the pathogen and the vector meet on a shared host plant. This does not happen in the ecosystem examined here, where two different principal host plants for the obligate pathogen and its vector exist: the pathogen is established on vines, while its vector, H. obsoletus, develops on Vitex agnus‐castus. The present study verified that: (i) the vector cannot complete its life cycle on vines; (ii) V. agnus‐castus does not grow in the immediate vicinity of vines, and does not harbour the pathogen; and (iii) the pathogen is not vertically transmitted from mother to offspring. Moreover, in a thorough search of plants in vine growing areas, no other plants were found that host both the vector and the pathogen. However, it was found that the planthopper can acquire the phytoplasma from infected vines. Nonetheless, this does not prove the ability of the planthopper to further transmit the pathogen to vines and does not explain the presence of the vector on the non‐preferred vines. Thus, the enigma of the pathogen–vector–host triangle in this system remains unresolved.     

Phenotypic and pathogenic traits of two species of the Fusarium graminearum complex possessing either 15-ADON or NIV genotype

Fusarium head blight (FHB) in Brazil is caused mainly by two members of the Fusarium graminearum species complex, each possessing either a DON/15-ADON chemotype (F. graminearum sensu stricto, Fgss) or a NIV chemotype (F. meridionale, Fmer). In this work, we aimed to characterize and compare isolates belonging to each species, obtained either from wheat or barley, in relation to phenotypic traits (mycelial growth, sporulation and germination) and pathogenicity (in vitro glume infection and in vivo central floret inoculation) to two Brazilian wheat cultivars, Guamirim (moderate susceptible) and BRS 194 (susceptible). Results showed significantly higher growth rates, greater spore production and quicker germination for the Fgss isolates compared to the Fmer isolates, which were also more sensitivity to tebuconazole than the Fgss isolates. All isolates were capable of infecting glume tissues of both varieties, with an overall higher infection frequency for Fgss than Fmer isolates when inoculated in cv. Guamirim than in cv. BRS194, which showed similar infection frequency between the species. Accordingly, in the central-floret inoculation assay, Fgss isolates were also more aggressive than Fmer isolates towards cv. Guamirim, but not towards BRS194, based on the mean area under disease progress curves. It is hypothesized that phenotypic traits and host resistance may play a role in the selection of more aggressive populations under field conditions, thus partially explaining the dominance of Fgss populations associated with FHB of wheat in Brazil.