Springer Science and Business Media LLC

Interveinal chlorosis and leaf margin wrinkling are widespread symptoms of Cannabis sativa. They are traditionally attributed to the so-called hemp streak virus (HSV), but its existence has not been demonstrated yet. To our knowledge, no molecular investigation has so far been performed in order to identify the causal agent of this symptomatology, we therefore decided to use traditional and molecular virology techniques to better characterize symptoms and pursue the etiological agent. No pathogenic virus was found by using targeted PCR reactions and by RNA sequencing, whereas we were able to detect the Cannabis cryptic virus (CanCV) with both techniques. We, therefore, developed an RT-qPCR assay based on a CanCV-specific TaqMan probe and applied it to a wide range of symptomatic and symptomless plants, using a two-step (for quantification), or a one-step (for fast detection) protocol. Both symptoms and the virus were only shown to be transmitted vertically and did not pass via mechanical inoculation or grafting, though we could not find any cause-effect correlation between them. In fact, the virus was found in all the tested hemp samples, and its abundance varied greatly between different accessions and individuals, independently from the presence and severity of symptoms. The suggestion that hemp streak is caused by a virus is therefore questioned. Some abiotic stresses seem to play a role in triggering the symptoms but this aspect needs further investigation. For breeding purposes, a selection of parental plants based on the absence of symptoms proved to be efficient in containment of the disease.

The dynamics of wheat spindle streak mosaic bymovirus in winter wheat were studied during two crop cycles in a field site with a history of high virus incidence. Individual plants of two susceptible cultivars were sampled from autumn to spring and the presence of virus antigen in roots and leaves was determined by ELISA. Virus incidence was higher in cv. Frankenmuth than in cv. Augusta. During year one, incidence of viral antigen in roots remained very low for four months after sowing, and did not reach maximum levels until the following spring. During year two, incidence of viral antigen in roots rose to maximum levels in autumn, only three months after sowing. These results strongly suggested that root infection occurred in spring as well as in autumn. In both cultivars and in both years, we detected the virus in roots one month prior to its detection in leaves, suggesting that virus moves slowly from roots into leaves. Maximum incidence of virus in leaves occurred in spring of both years, coinciding with the period of symptom development. Typical symptoms (yellow streaks, spindles, and mosaic) were observed in year two, whereas only mild mosaic was observed in year one. Virus antigen was detected in nonsymptomatic leaves from two months after sowing through crop senescence. Because antigen could be detected in roots throughout the crop cycle, and zoosporangia and cystosori of the fungal vector could be detected one and two months, respectively, after sowing, it is possible that wheat spindle streak mosaic bymovirus is acquired and/or spread by the vector during the majority of the crop cycle.

To better characterise at the molecular level the nature of plant responses to infection by Rhodococcus fascians PCR-based differential display patterns of Atropa belladonna leafy gall (LG) and non-infected plant tissues were compared. Six differentially expressed genes were identified and their altered expression was confirmed by RT-PCR. Three of them corresponded to up-regulated genes which encode proteins involved in plant defence. The three remaining cDNA fragments which correspond to down-regulated genes in LG, encoded proteins with similarity to a multicystatin, a miraculin and a methallothionein-like protein, respectively. Upon elimination of the bacteria from infected plant tissue, the expression of up-regulated genes was maintained, whereas expression of down-regulated genes resumed suggesting a potential role of these up-regulated genes in plant growth and development.

Over the past few decades, several biotic stresses caused severe economic losses in Peach orchards in Northwest Pakistan. To investigate some of the causal agents, we isolated fungi from fruits with brown to black colored small sunken lesions in several orchards of the Swat valley in northwest Pakistan. Morphological characterization coupled with ITS-based barcoding revealed C. spicifera to be associated with the peach fruit rot. The pathogenicity of C. spicifera was confirmed through Koch’s postulates. Among four growth media, C. spicifera showed rapid growth on acidified potato dextrose agar (APDA). Eco-friendly strategies for developing control measures of C. spicifera were also evaluated. In vitro analysis revealed that the mycelial growth of C. spicifera was inhibited by crude extracts from Casuarina equisetifolia, Capsicum annuum, Parthenium hysterophorus, Withania coagulans and Cannabis sativa. The extracts showed different degrees of inhibition; the most effective were methanol, ethyl acetate, chloroform and butanol extracts from C. annuum; ethanol extract of Withania coagulans and n- hexan extract of P. hysterophorus. Furthermore, we evaluated the antifungal activity of different concentration of essential oils (EO) using the disc diffusion method. EO obtained from Euclaptus citriodora, Mintha piperita, Cymbopogan citratum and Ocimum tenuiflorum effectively inhibited mycelial growth of C. spicifera at a concentration of 40-60ul/ml after seven days of incubation. Finally, we tested the antagonistic effect of Bacillus subtilis and Trichoderma harzianum against C. spicifera at 12 days after incubation. B. subtilis and T. harzianum inhibited growth of C. spicifera up to 95% and 80%, respectively. These findings provide information on devising alternatives to synthetic fungicide in the field to manage the newly identified C. spicifera from Peach fruits.

Blast, caused by Pyricularia oryzae, on wheat can negatively impact yield. This study investigated the effect of blast on seed germination and kernel weight of seeds obtained from the infected spikes of plants from the wheat cultivars BR-18 (moderately resistant) and BRS-Guamirim (susceptible). Spikes of each plant were inoculated at anthesis (0) as well as at 7, 14, and 21 days after anthesis (daa) with a conidial suspension of P. oryzae. Non-inoculated spikes served as the control treatment. Seed germination and the weight of 1000 seeds were determined. Based on regression analyses, blast severity was great both at anthesis and 7 daa causing great reductions on seed germination and weight of 1000 seeds. Blast severity in the spikes of plants from cultivar BR-18 was reduced by 38, 35, 45, and 41% at anthesis and at 7, 14, and 21 daa, respectively, in comparison to spikes from plants of cultivar BRS-Guamirim. Blast severity was lower on spikes from 14 to 21 daa in comparison to anthesis and caused less impact on seed germination and weight of 1000 seeds. In conclusion, the negative effect of blast on seed germination and weight of 1000 seeds was dependent on the level of basal resistance of each cultivar and the time when the spikes were infected by P. oryzae.

In 2010, symptoms of cobweb disease were observed on cultivated Pleurotus eryngii crops in Spain. Based on morphological and genetic analyses, the causal agent of cobweb was identified as Cladobotryum mycophilum. Pathogenicity tests on fruit bodies were performed using conidial suspensions of three C. mycophilum isolates. The causal agent was re-isolated in 80–85 % of the fruit bodies inoculated internally and 15–40 % of those fruit bodies inoculated on the cap surface. The results pointed to a certain resistance of the P. eryngii cap surface to the mycelium of C. mycophilum. Two cropping trials inoculated with C. mycophilum were set up to evaluate the pathogenicity of the causal agent of cobweb in two casings. At the end of the growth cycle, 50–60 % of the inoculated blocks cased with mineral soil, and 20–33 % of the inoculated blocks cased with black peat showed cobweb symptoms. This difference in the appearance of the disease and its aggressiveness may be partly explained by different electrical conductivity values of the casing materials used. In vitro sensitivity of the C. mycophilum isolates and P. eryngii strains against four fungicides (chlorothalonil, prochloraz-Mn, thiabendazole and thiophanate-methyl) was assessed in radial growth experiments on fungicide-amended media. The most effective fungicides for inhibiting the in vitro growth of C. mycophilum were prochloraz-Mn and chlorothalonil, while prochloraz-Mn was also the most selective fungicide between P. eryngii and C. mycophilum, and chlorothalonil was the most toxic fungicide against the P. eryngii mycelium.

In release trials with sterile males ofAdoxophyes orana in an apple orchard of 1.4 ha in 1971 and in an other orchard of 1.9 ha in 1973 and 1974 a marked decrease in the population ofA. orana was observed. Release of sterile males seemed to cause the effect. Immigration of moths, usually not more than a few hundreds, did not disturb the programme but would obviously prevent eradication and control at low level. Other tortricids increased in the absence of chemical control but less competition fromA. orana might also offer some explanation. The other tortricids were responsible for up to 9% damage among apples. Consequently the sterile male method specifically against one pest does not result in an important reduction in the number of sprays and a specific control method is not always the solution to pest problems in integrated control. Twee loslaatproeven met steriele mannetjes ter bestrijding van de vruchtbladrollerAdoxophyes orana worden beschreven. In de eerste, uitgevoerd in 1971 bij Overberg, werden 41000, met 25 krad gamma-stralen gesteriliseerde mannetjes bij de eerste vlucht, en 56000 tijdens de tweede vlucht losgelaten. In geen van de proeven werden de mannetjes van de wijfjes gescheiden. De sexe verhouding was circa 1∶1. Alle losgelaten motten waren gemerkt met Calco Red Oil D. Terugvangsten met vanglampen gaven een verhouding tussen losgelaten en wilde motten van 4∶1 in de eerste vlucht en 13∶1 in de tweede vlucht (Tabel 3). Tellingen van de aantallen larven, door het afzoeken van hele bomen, wezen op teruggang van het aantal rupsen (Tabel 4). De vangst aan wilde mannetjes in de vanglamp wijst op een duidelijke immigratie uit de omgeving (Tabel 3). Het aantal andere bladrollersoorten bleek sterk toe te nemen (Tabel 4). In de tweede proef, uitgevoerd in 1973 en 1974 bij Lienden, werden tijdens de eerste en tweede vlucht van 1973 resp. 17000 en 37000 mannetjes losgelaten en in 1974 resp. 55000 en 26000. De bestralingsdosis bedroeg 25 krad. De wijfjes werden in gelijke aantallen mee losgelaten. De motten waren gemerkt met ‘Rotor kleurstoffen’ en werden teruggevangen in feromoonvallen. De terugvangverhouding bedroeg in 1973 tijdens de eerste vlucht 9∶1 (Tabel 3). In 1974 was deze resp. 9∶1 en 21∶1. De larvetellingen (Tabel 4) wezen weer op sterke teruggang vanA. orana. Ook hier bleken andere soorten sterk in aantal toe te nemen (Tabel 5) zodat toch nog een vrij belangrijke bladrollerschade in de oogst ontstond. Hoewel de populatiedaling in beide proeven zeer duidelijk was, kan toch nog niet met zekerheid tot succes van de methode worden geconcludeerd omdat in de laatste jaren de betekenis vanA. orana in geïntegreerd bestreden percelen afnam. Een belangrijke moeilijkheid blijkt ook de statistische bewerking van de tellingen te zijn, daarA. orana zeer sterk pleksgewijs voorkomt. Het verdelingstype kon niet altijd worden vastgesteld maar leek soms op dat van een negatieve binomiaal met k-waarden keliner dan 1 (Tabel 6). Ook in deze proef werden aanwijzingen voor immigratie gevonden (Tabel 8). Deze is niet zo sterk dat het loslaatprogramma werd verstoord maar zou wel een uitvoerige campagne in de weg staan. Door het toenemend optreden van andere bladrollersoorten wordt het doel van de specifieke bestrijding vanA. orana verijdeld, daar toch nog chemische bestrijding noodzakelijk blijft. De specifieke bestrijdingsmethode hoeft dus niet altijd een oplossing van een plaagprobleem in de geïntegreerde bestrijding te geven.