Ability of five strains of Trichoderma pseudokoningii (antagonists) to suppress radial growth of Fusarium verticillioides (Sacc.) Nirenberg (= Fusarium moniliforme Sheldon) was examined in vitro These were T. pseudokoningii strai n1 (IMI 380933), strain 2 (IMI 380937), strain 3 (IMI 3809 39), strain 4 (IMI 380940) a nd strain 5 (IMI 380941). Each strain was paired with pathogen by inoculating at opposite ends of 9 cm petri plates using three pairing methods. Gradings were assigned to varied growth inhibition of pathogen by antagonists and analysed using GLM procedure (SAS). Growth suppression of F. verticillioides by all strains of T. pseudokoningii was significantly different (R2 = 0.98, p = 0.05) from control in all pairing methods. It differed significantly (p > 0.0003) among the strains in all pairing methods. Growth suppression also differed significantly among (p>0.0001) and within (p > 0.018) pairing methods. Growth suppression was best when antagonists were inoculated before pathogen. Suppression mechanisms include mycoparasitism and competition for space and nutrients. T. pseudokoningii strains 3 and 4 had the best (p = 0.05) growth suppression of F. verticillioides and could be used as biocontrol agents for endophytic F. verticillioides in maize plant. This experiment was conducted in the search for resedent microorganisms that might be capable of checking F. verticillioides within maize plant by competitive exclusion in subsequent experiment.
In the recent years earlier appearance of late blight on potato crops and the increase of infection pressure of Phytophthora infestans has been observed due to the changes in its population. The occurrence of P. infestans on potato plants at early plant growth stages points to the possibility of existence of other infection sources such as infected seed tubers or volunteer plants and their increasing role in the disease epidemiology. These changes have led to late blight epidemics developing earlier and more severely than previously and changes in the occurrence and development of first symptoms of P. infestans infection on potato plants. In the years 1997–2006, field studies were conducted at the Plant Breeding and Acclimatization Institute of Bonin with the emphasis on comparison of time of the occurrence and incidence level of late blight of potato. The criteria for pathogen infection pressure assessment were assumed to be the percentage of haulm destruction at the end of growing season and area under the disease progress curve (AUDPC), the late blight development rate defining the increase of destruction of above ground plant parts in unit time and also tuber yield and its healthiness. The observations carried out at Bonin revealed that both time of occurrence and severity of late blight differed and were dependent upon meteorological conditions and upon the year. Late blight occurred the earliest at Bonin in 2001 (42 days after planting). The time of occurrence of late blight depends upon rainfall in May and June. A very high infection rate of the pathogen was observed, particularly in 2006 (0.517) and in 2004 (0.400) despite late time of late blight appearance in the season. In these years AUDPC on the unprotected cultivar was 0.071 and 0.508, respectively. The 10 years of observations conducted at Bonin revealed that the yield and occurrence of tuber late blight depended mostly upon meteorological conditions in particular years.
The article presents the research into hygienizing process of chicken manure using calcium peroxide (CaO2) as an environmentally friendly biological deactivation agent. The influence of the addition of CaO2 to chicken manure on the bioavailability of phosphorus was also analyzed. The process of biological deactivation using CaO2, CaO and Ca(OH)2 agents was analyzed applying the disk diffusion method. To optimize the effect of the hygienizing parameters, (CaO2 concentration, pH, temperature and time) on the reduction of Enterobacteriaceae count the Taguchi method was applied. The content of bioavailable phosphorus was measured with the Egner-Riehm method and determined with spectrophotometry. The reduction in bacterial count followed an increase in the concentration of CaO2 in a sample. The optimal experimental conditions (CaO2=10.5 wt.%, pH=9.5, T=40°C, t=180 h) enabled a significant decrease in the Enterobacteriaceae count, from 107 cfu/g to 102 cfu/g. Analysis of the samples with Egner-Riehm method showed that the phosphorus content decreased with the addition of biocide CaO2: from 26.6 mg/l (for 3.5 wt.%) to 3.5 mg/l (for 10.5 wt.%). These values were slightly higher than the content of phosphorus deactivated with Ca(OH)2 i.e., from 11.25 mg/l (for 3.5 wt.%) to 4.49 mg/l (for 10.5 wt.%). The application of CaO2 for hygienizing chicken manure enables effective reduction of Enterobacteriaceae count to an acceptable level (below 1000 cfu/g). In comparison with the traditional techniques of hygienization, the application of CaO2 has a positive effect on the recovery of bioavailable phosphorus.
Three plant extracts viz. bulbs of Allium sativum L. (Liliaceae), seeds of Annona squamosa L. (Annonaceae) and leaves of Vitex negundo L. (Verbenaceae) were evaluated against cowpea wilt pathogen, Fusarium oxysporum f. sp. ciceris by mycelial dry weight method under laboratory condtions. The mean mycelium dry weights of F. oxysporum of methanol and benzene extracts of A. sativum obtained from 125 g of crused dry plant material (bulbs) were 0.0113 and 0.0174 mg, respectively. This was followed by methanol and petroleum ether extracts of A. squamosa (0.2396 and 0.2381 mg). They effectively controlled mycelial growth of cowpea wilt pathogen, however V. negundo extracts did not cause any significant mycelium growth inhibition when compared to other plant extracts tested. Among the three plant extracts, methanol extracts of A. sativum bulbs could possibly be used for controlling F. oxysporum.
Hass avocado cultivation in Colombia has grown rapidly in area in recent years. It is being planted in marginal areas, which leads to low yields, and in many cases is related to diseases. Ecological niche modeling (ENM) can offer a view of the potential geographic and environmental distribution of diseases, and thus identify areas with suitable or unsuitable conditions for their development. The aim of the study was to assess current and potential distribution of the major diseases on Hass avocado in Colombia. Areas planted with Hass avocado in Antioquia, Colombia were sampled for diseases including the following pathogens: Phytophthora cinnamomi, Verticillium sp., Lasiodiplodia theobromae, Phytophthora palmivora, Colletotrichum gloeosporioides sensu lato, Pestalotia sp., and Capnodium sp., and one disorder hypoxia-anoxia. These pathogens were selected based on their relevance (incidence-severity) and capacity to cause damage in different tissues of avocado plants. Severity and incidence of each disease were related to environmental information from vegetation indices and topographic variables using maximum entropy modeling approaches (MaxEnt). Models were calibrated only across areas sampled, and then transferred more broadly to areas currently planted, and to potential zones for planting. Combinations of best performance and low omission rates were the basis for model selection. Results show that Hass avocado has been planted in areas highly conducive for many pathogens, particularly for Phytophthora cinnamomi and hypoxia-anoxia disorder. Ecological niche modeling approaches offer an alternative toolset for planning and making assessments that can be incorporated into disease management plans.
Duck viral hepatitis (DVH) is an acute and fatal disease of young ducklings characterized by rapid transmission and damages. The most important agent of DVH is duck hepatitis virus 1 (DHV-1). The effective control of DVH was achieved by active immunization of 1-day-old duck- lings with an attenuated DHV-1 virus vaccine. However, the attenuated virus might reverse to virulence. In this study, a DHV-1 strain, Du/CH/LBJ/090809, was identified and its genomic se- quences were determined. The genome of Du/CH/LBJ/090809 is composed of 7,692 nt excluding poly A and the virus was clustered into genotype A by comparing with other referenced DHV-1 strains. Du/CH/LBJ/090809 could lead to 30% mortality of 10-day-old specific pathogen free (SPF) ducklings. The virus was passaged serially in SPF chicken embryonated eggs and three vi- ruses, passage 16 (P16), P29 and P40, were selected for genomic analysis. P29 and P40 were used to evaluate the attenuation in duckling by inoculating the virus to 10-day-old SPF ducklings. Re- sults of vaccination-challenge assay showed that the inactivated virus P40 could evoke protection against the pathogenic parent virus. Nucleotide and amino acid sequences of the genomes of Du/ CH/LBJ/090809, P16, P29 and P40 were compared. Changes both in nucleotides and amino acids, which might be contributed to the decreasing in virulence by chicken embryo-passaging of DHV- 1, were observed. We speculated that these changes might be important in the adaption and at- tenuation of the virulent virus. Additionally, strains obtained in this study will provide potential candidate in the development of vaccines against DHV-1.