Improving biological control by combining biocontrol agents each with several mechanisms of disease suppression

ABSTRACT Two biocontrol agents, a yeast (Pichia guilermondii) and a bacterium (Bacillus mycoides), were tested separately and together for suppression of Botrytis cinerea on strawberry leaves and plants. Scanning electron microscopy revealed significant inhibition of Botrytis cinerea conidial germination in the presence of Pichia guilermondii, whereas Bacillus mycoides caused breakage and destruction of conidia. When both biocontrol agents were applied in a mixture, conidial destruction was more severe. The modes of action of each of the biocontrol agents were elucidated and the relative quantitative contribution of each mechanism to suppression of Botrytis cinerea was estimated using multiple regression with dummy variables. The improvement in control efficacy achieved by introducing one or more mechanisms at a time was calculated. Pichia guilermondii competed with Botrytis cinerea for glucose, sucrose, adenine, histidine, and folic acid. Viability of the yeast cells played a crucial role in suppression of Botrytis cinerea and they secreted an inhibitory compound that had an acropetal effect and was not volatile. Bacillus mycoides did not compete for any of the sugars, amino acids, or vitamins examined at a level that would affect Botrytis cinerea development. Viable cells and the compounds secreted by them contributed similarly to Botrytis cinerea suppression. The bacteria secreted volatile and non-volatile inhibitory compounds and activated the defense systems of the host. The nonvolatile compounds had both acropetal and basipetal effects. Mixture of Pichia guilermondii and Bacillus mycoides resulted in additive activity compared with their separate application. The combined activity was due to the summation of biocontrol mechanisms of both agents. This work provides a theoretical explanation for our previous findings of reduced disease control variability with a mixture of Pichia guilermondii and Bacillus mycoides.     

The detection of an unidentified type of adenovirus in the stools of calves with weak calf syndrome by use of a commercial kit designed for the detection of human adenoviruses

An outbreak of polyarthritis in newborn calves in a large collective dairy herd was characterized by intra-articular blood-tinged synoviae, blood tainted faeces and massive subcorneal haemorrhages. Faecal samples from eight clinical newborn cases, 10 from unrelated dairy farms and 10 faecal samples from healthy calves were examined by the Rida Quick rotavirus/adenovirus-combi test . A specific adenovirus antigen precipitin-line was seen in the reaction in all the faecal samples from the diseased calves (n = 8), while all the others (n = 20) were negative. In addition, the same positive reaction was noted when one aqueous humor and two synovial samples were tested with this kit. Several other enteropathogens were found sporadically, but no conclusive significance could be attributed to their presence. Bovine viral diarrhoea and infectious bovine rhinothracheitis viruses as well as Chlamydia spp. and Mycoplasma spp. were not involved in this episode.     

Necrotizing stomatitis associated with Fusobacterium necrophorum in two goats

Necrotizing stomatitis associated with Fusobacterium necrophorum in two goats is described. Arcanobacterium pyrogenes was the dominant component of the microbial flora cultured under aerobic condition. Treatment with penicillin, at a dose of 50 000 IU/kg for 6 days was used successfully in the cure of the disease.     

Identification of<Emphasis Type="Italic">Trichoderma</Emphasis> biocontrol isolates to clades according to ap-PCR and ITS sequence analyses

A collection ofTrichoderma isolates, with different biocontrol capabilities, were identified by molecular methods. Arbitrarily-primed PCR (ap-PCR) using repeat motif primers was performed on DNA from aTrichoderma spp. collection of 76 isolates, and representative isolates were further characterized into three main clades by internal transcribed spacer (ITS) sequence analysis. Consequently, a reliable phylogenetic tree was constructed containing isolates belonging to theT. harzianum clade (comprisingT. aureoviride, T. inhamatum, andT. virens), theT. longibrachiatum andT. saturnisporum cluster, and that including the speciesT. asperellum, T. atroviride, T. koningii andT. viride. http://www.phytoparasitica.org posting July 14, 2004.     

Isolation of Neisseria cuniculi from a case of ovine pneumonia

Neisseria cuniculi was isolated in pure culture from the lungs of a 2-month-old pneumonic lamb. Mouse LD50, evaluated by intraperitoneal and pulmonary inoculation of the microorganism, was 2 X 10(7) colony-forming units in both cases. The role of the organism in pathogenesis of the disease could not be determined. This organism has not previously been reported in sheep.     

Integrated control of soilborne and bulbborne pathogens in Iris

Coating iris bulbs with a preparation ofTrichoderma harzianum was highly effective under greenhouse conditions in reducing incidence of diseases caused byRhizoctonia solani andSclerotium rolfsii. In field experiments with irises for bulb production, the incidence ofR. solani in plants and bulbs was effectively reduced (up to 93%), and the yield increased (by 35–41%), by applyingT. harzianum either as a bulb coating or broadcast application (biological treatment), treating soil with pentachloronitrobenzene (PCNB; quintozene) (chemical treatment), or solarizing the soil by mulching it with transparent polyethylene sheets (physical treatment) prior to planting. Combined treatments,i.e., chemical-biological or physicalbiological, were the most effective.T. harzianum bulb treatment and broadcast application in field plots increasedTrichoderma population density in the soil by 4–27 times.     

Keratoconjunctivitis and periorbital papillomatosis associated with heavy periorbital infestation by the tail louse Haematopinus quadripertusus in heifers

Heifers (Israeli-Holstein), aged 12-18 months, permanently maintained in open barns on an inadequate nutritional regime were found to be moderately to heavily infested by Haematopinus quadripertusus, the tail louse. The severely infested heifers showed keratoconjunctivitis and periorbital papillomatosis. Two treatments with an alpha-cypermethrin pour-on product 14 days apart controlled the lice, and were followed by alleviation of the inflammation and regression of the papillomas.     

Infectious bovine keratoconjunctivitis and lymphofollicular hyperplasia of the third eyelid in heifers

On a dairy cattle farm, infectious bovine keratoconjunctivitis was diagnosed in 29 (24%) calves and heifers aged from 2 weeks to 1 year old. The highest infection rate (18%) occurred in animals aged 3-6 months. The bacteriological examination of swabs from the affected animals yielded several species of bacteria: Moraxella bovis, Neisseria ovis, N. cuniculi, plasma coagulase-negative Staphylococcus spp., alpha-haemolytic Streptococcus spp., Arcanobacterium pyogenes and Escherichia coli. Moraxella bovis and N. ovis were the most common isolates. Hyperplasia of the lymphatic tissue of the third eyelid in the form of nodules 7-8 mm in diameter was diagnosed in two heifers aged 8 and 10 months.     

Rapid spread of a bacterial symbiont in an invasive whitefly is driven by fitness benefits and female bias

Maternally inherited bacterial symbionts of arthropods are common, yet symbiont invasions of host populations have rarely been observed. Here, we show that Rickettsia sp. nr. bellii swept into a population of an invasive agricultural pest, the sweet potato whitefly, Bemisia tabaci, in just 6 years. Compared with uninfected whiteflies, Rickettsia-infected whiteflies produced more offspring, had higher survival to adulthood, developed faster, and produced a higher proportion of daughters. The symbiont thus functions as both mutualist and reproductive manipulator. The observed increased performance and sex-ratio bias of infected whiteflies are sufficient to explain the spread of Rickettsia across the southwestern United States. Symbiont invasions such as this represent a sudden evolutionary shift for the host, with potentially large impacts on its ecology and invasiveness.     

Host immune system gene targeting by a viral miRNA

Virally encoded microRNAs (miRNAs) have recently been discovered in herpesviruses. However, their biological roles are mostly unknown. We developed an algorithm for the prediction of miRNA targets and applied it to human cytomegalovirus miRNAs, resulting in the identification of the major histocompatibility complex class I-related chain B (MICB) gene as a top candidate target of hcmv-miR-UL112. MICB is a stress-induced ligand of the natural killer (NK) cell activating receptor NKG2D and is critical for the NK cell killing of virus-infected cells and tumor cells. We show that hcmv-miR-UL112 specifically down-regulates MICB expression during viral infection, leading to decreased binding of NKG2D and reduced killing by NK cells. Our results reveal a miRNA-based immunoevasion mechanism that appears to be exploited by human cytomegalovirus.