Foliar resistance to late blight in potato clones evaluated in national trials in 1997

Changes in the oomycetePhytophthora infestans in the United States and other parts of the world pose a significant threat to potato production. A continual evaluation of potato clones for resistance to late blight is necessary to identify clones with resistance and to monitor the stability of resistance in light of the emergence of new and more aggressive strains of this pathogen. Twentytwo potato clones (10 cultivars and 12 selections) were evaluated in 1997 for late blight resistance at seven U.S. locations. Seven late blight differentials (R₁R₂R₃R₄, R₁R₂R₄, R₁R₃R₄ R₃, R₈ R₁₀, and R_multi) were also included in the test at five of these locations. The US-8 strain of P.infestans was present at all locations. Percent infected foliage was recorded at approximately weekly intervals following the onset of disease. Area under the disease progress curve (AUDPC) was calculated. The nonparametric stability statistics mean absolute rank differences (S _i ⁽¹⁾ ) and variances of the ranks (S _i ⁽²⁾ ) were used to analyze phenotypic stability. Although neither of these statistics was significant for individual clones, both of these statistics were significant when summed over clones, indicating the importance of genotype × environment interactions on the rankings of these clones across locations. The most late blight-resistant and susceptible clones were the most stable; clones in the intermediate ranges were most subject to rank changes due to genotype × environment interactions. The most late blight-resistant clones were AWN86514-2, B0692-4, B0718-3, and B0767-2. The most susceptible clones were B0811-13, B1004-8, Nor-Donna, and Krantz. AUDPC was very low for the late blight differentials R₈ and R_multi, moderately low for R₁₀ and very high for the remaining differentials. This study is important in characterizing the reaction of potato clones to new strains of P.infestans.     

Restriction of potato and tomato late blight development by sub‐phytotoxic concentrations of boron

Boron is a microelement required for normal growth and development of plants but its positive effect is restricted to a narrow range of concentrations. The gradual increase in use of recycled water, which contains high concentrations of boron for irrigation, has already raised the level of boron in soils and plants in southern Israel. This research was conducted to examine the direct effects of sub‐phytotoxic boron concentrations on potato late blight epidemics and to explore the mode of action of boron against Phytophthora infestans. When boron was applied alone to field grown potato plants it did not affect the epidemic. However, together with a reduced rate of the fungicide Melody Duo (propineb + iprovalicarb), boron improved late blight suppression compared to plants treated with the fungicide alone. The ED₅₀ of boron against P. infestans (256·4 mg L^?1) was about 6400 times higher than the ED₅₀ value of the fungicide chlorothalonil (0·04 mg L^?1), indicating that boron does not have a direct fungicidal activity that would explain the level of protection seen in the field. In greenhouse experiments conducted with potted tomato plants, boron decreased late blight severity in both treated leaves and distant leaves not treated with boron. The results suggest that boron is active locally but also may induce systemic acquired resistance against P. infestans.     

Effect of dietary boron on immune function in growing beef steers*

Thirty‐six Angus and Angus × Simmental cross steers (initial BW 269.5 ± 22.3 kg) were used to determine the effects of dietary boron (B) on performance and immune function. Steers were fed on one of the three dietary treatments: (i) control (no supplemental B; 7.2 mg B/kg DM), (ii) 5 mg supplemental B/kg DM and (iii) 50 mg supplemental B/kg DM, from sodium borate for 78 days. Supplementation of dietary B had no effect on body weight (BW) gain, feed intake or gain:feed during the study. Jugular blood samples were collected prior to feeding on days 28, 63 and 77 for plasma‐B analysis. Supplementation of dietary B increased (p < 0.001) plasma B‐concentration in a dose‐responsive manner. Furthermore, plasma B‐concentration was correlated (p < 0.001; R² = 0. 95) to daily B‐intake (mg B/day). Jugular blood was also collected, from an equal number of steers from each treatment, on day 42 or 44 for determination of in vitro production of interferon‐γ and tumour necrosis factor‐α from isolated monocytes and assessment of lymphocyte proliferation. Dietary B did not affect T‐ or B‐lymphocyte proliferation or in vitro cytokine production from monocytes. On day 49 of the study, the humoral immune response was assessed by i.m. injection of a 25% pig red blood cell (PRBC) solution for determination of anti‐PRBC IgG and IgM titre responses. Boron‐supplemented steers had greater (p = 0.035) anti‐PRBC IgG titres than controls on day 7 but not on day 14 or 21 post‐injection. Anti‐PRBC IgM titres did not differ throughout the sampling period. Results from this study indicate that supplemental B had minimal effects on immune function and did not affect performance of growing steers.     

Abdominal fluid from a dog

A 2-year-old intact female mixed-breed dog with a 1-month history of lethargy and anorexia was evaluated for abdominal distension and an abdominal mass. The dog's last heat cycle, her third, was 1 month prior to presentation, and no reproductive cycle abnormalities were noted at any time. Hematologic and serum biochemical abnormalities were consistent with hemorrhage and inflammation. Ultrasonographic examination confirmed a large midabdominal mass and a moderate amount of abdominal fluid. Cytologically, the fluid showed evidence of pyogranulomatous inflammation, hemorrhage, and mesothelial reactivity, as well as ciliated columnar cells and free cilia that were interpreted as likely of oviductal origin. The mass was removed surgically, and the histopathologic interpretation was oviductal hamartoma with marked stroma formation and acute hemorrhage. To the authors' knowledge, this is the first reported case of oviductal hamartoma in any species and the first reported case detailing the finding of ciliated columnar epithelial cells in the abdominal fluid of a dog. Ciliated columnar epithelial cells in abdominal fluid should be considered indicative of a likely underlying oviductal lesion.     

The Population Structure of Phytophthora infestans from the Toluca Valley of Central Mexico Suggests Genetic Differentiation Between Populations from Cultivated Potato and Wild Solanum spp

ABSTRACT The population structure of Phytophthora infestans in the Toluca Valley of central Mexico was assessed using 170 isolates collected from cultivated potatoes and the native wild Solanum spp., S. demissum and S. xendinense. All isolates were analyzed for mitochondrial DNA (mtDNA) haplotype and amplified fragment length polymorphism (AFLP) multi-locus fingerprint genotype. Isolate samples were monomorphic for mtDNA haplotype because all isolates tested were of the Ia haplotype. A total of 158 multilocus AFLP genotypes were identified among the 170 P. infestans isolates included in this study. P. infestans populations sampled in the Toluca Valley in 1997 were highly variable and almost every single isolate represented a unique genotype based on the analysis of 165 AFLP marker loci. Populations of P. infestans collected from the commercial potato-growing region in the valley, the subsistence potato production area along the slopes of the Nevado de Toluca, and the native Solanum spp. on the forested slopes of the volcano showed a high degree of genetic diversity. The number of polymorphic loci varied from 20.0 to 62.4% for isolates collected from the field station and wild Solanum spp. On average, 81.8% (135) of the AFLP loci were polymorphic. Hetero-zygosity varied between 7.7 and 19.4%. Significant differentiation was found at the population level between strains originating from cultivated potatoes and wild Solanum spp. (P = 0.001 to 0.022). Private alleles were observed in individual isolates collected from all three populations, with numbers of unique dominant alleles varying from 9 to 16 for isolates collected from commercial potato crops and native Solanum spp., respectively. Four AFLP markers were exclusively found present in isolates collected from S. demissum. Indirect estimation of gene flow between populations indicated restricted gene flow between both P. infestans populations from cultivated potatoes and wild Solanum hosts. There was no evidence found for the presence of substructuring at the subpopulation (field) level. We hypothesize that population differentiation and genetic isolation of P. infestans in the Toluca Valley is driven by host-specific factors (i.e., R-genes) widely distributed in wild Solanum spp. and random genetic drift.     

Sulfatide synthesis: inhibition by experimental allergic encephalomyelitis serum

The rate of (35)S incorporation into cerebroside sulfate in cultures of embryo mouse spinal cord shows a rapid acceleration at the time of myelin formation. Exposure of cultures to dilute serum from rabbits with experimental allergic encephalomyelitis results in almost complete inhibition of sulfatide synthesis. Within 24 hours after replacement of inhibiting medium with normal medium there is an increase in sulfatide synthesis followed by myelination.     

Stability of resistance to Phytophthora infestans in potato: an international evaluation

Ten institutions in nine countries joined together to test the stability of resistance of 14 potato genotypes to the oomycete pathogen Phytophthora infestans in three separate trials. Seven of the genotypes were tested in one trial involving seven locations, and all 14 were tested in two subsequent trials, each involving eight locations. Stability of resistance was tested with nonparametric tests and with an additive main effects and multiplicative interaction (AMMI) model. Overall, resistance to P. infestans was robust; resistant genotypes were consistently resistant in all locations and trials. The nonparametric analysis indicated that specific genotypes were basically stable across sites for resistance. In trial 3, the Z statistic for overall stability was significant at 0·05%, indicating a significant level of interaction across the trial, but there were no significant interactions for specific genotypes in this trial. The genotype by environment (G × E) effect of the AMMI model was highly significant in both trials, but the mean square of G × E was less than 10% of the genotype effect in each trial. The first two principal components (PCA1 and PCA2) of the AMMI analyses together explained 75 and 80% of the interaction effects in trials 2 and 3, respectively. Based on both nonparametric and AMMI analyses, Ecuador and Argentina were locations of relatively high interaction effects for both trials 2 and 3, although in Ecuador this interaction was not associated with any particular potato genotype. Other locations also had high interaction effects, but these occurred in only one trial. The genotypes Chata Blanca and, to a lesser extent, Torridon were relatively unstable in trials 2 and 3, but in the case of Torridon, resistant, this did not represent a significant loss of resistance.