Evidence that a Leaf-Disk Test Allows Assessment of Isolate-Specific Resistance in Brassica oleracea Crops Against Downy Mildew (Peronospora parasitica)

A rapid resistance/susceptibility test for Peronospora parasitica (downy mildew) was established by inoculating leaf-disks of four Brassica oleracea accessions. Several conditions were tested: disk disinfection or not, agar medium with or without nutrients and with 50 or 100 ppm of benzimidazole. Using disinfected disks placed on agar (no nutrient and benzimidazole at 50 or 100 ppm), the responses of leaf-disks to four isolates were similar to those obtained using the classical cotyledon test, whereas undesired contaminations occurred in all other conditions. The possible effect of the particular leaf used for obtaining the disks was also studied. In each incompatible interaction tested, disks were resistant whatever the leaf used. In compatible interactions, susceptible phenotypes were observed on disks derived from the six lowest leaves, but disks from upper leaves were resistant. The genetic basis of resistance in a F1 hybrid broccoli was assessed, by testing six isolates on an F2 population derived from this hybrid. The cotyledon test only allows inoculation of two isolates per seedling, whereas many isolates can be tested on each plant by using leaf-disks. The segregation of the resistance to each of the six isolates was analysed: two dominant genes (tightly linked) control resistance to all isolates (one to five isolates; the other to only one isolate).     

Effect of chitin on biological control activity of Bacillus spp. and Trichoderma harzianum against root rot disease in pepper (Capsicum annuum) plants

Two bacterial isolates and one strain of Trichoderma harzianum were tested alone and in combination with chitin for efficacy in control of root rot disease caused by Phytophthora capsici and Rhizoctonia solani in pepper plants under greenhouse conditions. These bacteria (Bacillus subtilis HS93 and B. licheniformis LS674) were isolated from repeatedly washed roots of pepper plants. In in vitro assays, HS93, LS674 and T. harzianum were antagonistic against P. capsici and R. solani and produced high levels of chitinase. Seed treatment and root drenching with bacterial suspensions of HS93 with 0.5% chitin was more effective against Phytophthora and Rhizoctonia root rot than addition of the organisms without chitin. LS674 and T. harzianum reduced Rhizoctonia but not Phytophthora root rot. In two greenhouse tests, seed treatment and root drenching with HS93 amended with chitin enhanced its biocontrol activity against P. capsici but not on R. solani. The effects of LS674 and T. harzianum against R. solani were significantly enhanced when they were used as suspensions with 0.5% chitin for root drenching, but this had no effect on P. capsici. In both greenhouse experiments, the use of 0.5% chitin alone for root drenching reduced Rhizoctonia root rot. Reduction of root rot disease was accompanied by increased yield. These results show that the antagonistic activity of HS93, LS674 and T. harzianum may be stimulated by chitin resulting in significant improvements in their effectiveness against pathogens.     

Current therapies in exotic animal oncology.

The majority of information on oncology therapies has been reported in humans, canine, and feline patients, and laboratory animals with experimentally induced tumors. A variety of treatments,including radiation therapy, chemotherapy, photodynamic therapy, and others have been used with exotic animals. There are many species of exotic pets, and anatomic differences, as well as husbandry and nutritional requirements, must be taken into account to provide optimal care. By providing a broad overview of therapies and considerations for treatment, this article is intended to provide the practitioner with an overview of approach and options when addressing oncology cases in exotic animals.     

Recognition of the Nor98 variant of scrapie in the Swedish sheep population.

Within the framework of the active surveillance for transmissible spongiform encephalopathies in sheep in Sweden, 4 cases of the atypical form of scrapie, Nor98, were identified during 2003. Nor98 is a recently recognized and poorly understood variant of scrapie, first described in Norway. The cases were positive by the rapid test (enzyme-linked immunosorbent assay). Immunohistochemical staining showed diffuse thin-granular staining of the cerebellar cortex. Western immunoblotting analysis of specimens of brain stem and cerebellum showed a light band of approximately 12 kDa. Typical scrapie was ruled out based on the confirmatory testing. The affected ewes were from 4 different flocks. They were between 7 and 9 years old. Two were of the ARQ/ARQ genotype, 1 ARR/ARQ, and 1 ARR/AHQ. Two ewes had shown ataxia, and the other 2 had no clinical signs. Whole-flock slaughter was applied, and testing of the flock mates did not reveal additional cases. Nor98 differs from typical scrapie in its epidemiology, frequency of genotypes of sheep affected, clinical signs, microscopic lesions, distribution of scrapie prion protein in the brain, and characteristics of the immunostaining and immunoblotting profiles.     

Identification and Characterisation of Bacteria Causing Soft-rot in Agave tequilana

Agave tequilana is the raw material for the production of the alcoholic beverage tequila. A bacterial disease has affected the A. tequilana crop in recent years. Previous reports based on colony and cell morphology, Gram stain and potato rot indicated that Erwinia sp. is the main pathogen. We isolated a several bacterial isolates capable of producing soft-rot symptoms in greenhouse pathogenicity assays. An extensive characterisation involving pathogenicity tests, fatty acid profile, metabolic and physiological properties, ribosomal DNA sequence and intergenic transcribed spacer amplification (ITS-PCR) and restriction banding pattern (ITS-RFLP) was made of each isolate. Three different species: Erwinia cacticida, Pantoea agglomerans and Pseudomonas sp. were identified. Fatty acid and metabolic profiles gave low similarity values of identification but 16S rDNA sequence, ITS-PCR and ITS-RFLP confirmed the identification of E. cacticida. In the phylogenetic tree, E. cacticida from blue agave was grouped neither with E. cacticida type strains nor with Erwinia carotovora. This is the first report that associates E. cacticida with A. tequilana soft-rot symptoms.     

Evaluation of Olive Cultivars for Resistance to Verticillium dahliae

Resistance of 23 important olive cultivars to Verticillium dahliae has been evaluated in four experiments under controlled conditions. Nine-month-old nursery olive plants were inoculated with a cotton non-defoliating (ND) (V4) or a cotton defoliating (D) (V117) isolate of V. dahliae. Resistance was evaluated by assessing symptom severity using a 0–4 rating scale and estimating the area under disease progress curves. The percentage of plants killed and of those which recovered from the disease were used as additional parameters for including a particular cultivar into a defined category. Most of the evaluated cultivars were susceptible, although at different levels, to both isolates of V. dahliae. All cultivars were more susceptible to the D pathotype than to the ND one. A group of 11 cultivars, including several important Spanish cultivars, were susceptible or extremely susceptible to both pathotypes of V. dahliae. A second group showed differences of resistance depending on the pathotype used. They were susceptible or extremely susceptible to the D pathotype but resistant or moderately susceptible to the ND one. Finally, 'Frantoio', 'Oblonga' and 'Empeltre' were moderately susceptible to the D isolate of V. dahliae and resistant to the ND one. The resistance of 'Empeltre' was evident by the plant ability to recover from infection with either isolates. 'Empeltre' is considered to be a valuable cultivar for inclusion in breeding programmes for resistance to Verticillium wilt.