In this study, natural cycling of BoHV-1 infection was investigated in two groups of dairy cattle containing 2120 head. Group
1 comprised 127 animals and they were monitored for BoHV-1 infection virologically and serologically in six consecutive sampling
periods. It consisted of naive heifers between 6 and 8 months of age, while in group 2, age, sex and the BoHV-1 serostatus
of the animals were disregarded. The animals in group 1 were found to have seroconverted at the second sampling. Results of
the serological study showed slight antibody response after natural BoHV-1 infection in the herd and neutralizing titres fell
below protective levels in the 6–8 months after the peak. During the 2-year study period, one recurrence was detected after
primary infection. Virus isolation studies revealed a cytopathic effect indicative of BoHV-1 in two nasal swabs taken during
the fifth sampling period from animals with mild upper respiratory tract symptoms. As the study was carried out under natural
conditions, it is not known whether the viruses isolated were from recurrences or re-infections. Data from cross-neutralization
tests with herd isolates showed higher antibody response than those with the reference virus. The dynamics of BoHV-1 in both
groups were found to be statistically similar. 相似文献
Summary Components of partial resistance, infection frequency and latency period, were determined in 71 winter and spring wheat genotypes in the seedling stage, after infection with three races of leaf rust (Felix 3B, Clement B and Betuwe 85C) at three different day/night temperature regimes (24/18°C, 18/12°C and 12/6°C). The genotypes were split into two groups and two separate experiments were carried out. Five genotypes, SVP 84039, Akabozu, Banco, BH 1146 and Orso, conferred a low infection frequency and a long latency period and Westphal 12A a long latency period, indicating a relatively high level of partial resistance. The correlation coefficient between infection frequency and latency period was low. Race-specificity was not found. There was a significant temperature effect on the latency period. In the second experiment the temperature x genotype interaction was significant. Temperature-response functions of transformed data demonstrated that the latency periods of four relatively resistant genotypes, Westphal 12A, Banco, BH 1146 and Orso and of Sarno and Mirela were most sensitive to temperature. The range between the genotypes with the longest and the shortest latency period was highest at 12°C. Therefore, low temperature regimes are preferred to distinguish differences in level of partial resistance. 相似文献
Several resistance sources and resistance mechanisms to aflatoxin formation and corn earworm (Helicoverpazea Boddie) damage to maize (Zeamays L.) have been identified. Based on this knowledge, experiments were initiated toward achievement of the following objectives: (1) to confirm earlier determinations on resistance traits of germplasm sources and to identify quantitative trait loci (QTL) associated with each of the traits, and (2) upon estimation of the degree of QTL effects on each trait, to generate a maize population, with chemical and physical resistance to Aspergillus spp. and ear-feeding insects, for inbred development. A 2-year field experiment to evaluate selected genotypes inoculated with A. flavus and infested with corn earworm revealed that significant variation exists among the genotypes for aflatoxin contamination and corn earworm damage. The protection of maize ears against aflatoxin contamination was primarily dependent on resistance to fungal infection and ear-feeding insects, and excellent husk coverage and tightness. A major QTL (p1) identified on chromosome 1S had effects of 54.0, 42.1, and 28.3% on the phenotypic variability for concentrations of silk maysin, 3′-methoxymaysin+apimaysin, and chlorogenic acid, respectively. Markers/QTLs for husk phenotypic traits and total aflatoxin concentrations have been determined, but more detailed mapping of these chromosomic regions will be necessary to locate precise markers/QTLs for husk traits and aflatoxin production. Realizing the complexity of the Aspergillus–aflatoxin-maize system and the factors affecting aflatoxin contamination, we are directing our program toward marker-assisted breeding to enhance or improve general genetic resistance to ear-feeding insects and invasion by Aspergillus spp. 相似文献
Crown rust caused by Puccinia coronata Cda. f. sp. avenae Eriks., is a major fungal disease of cultivated oats (Avena sativa L.) in Tunisia. Six landrace oats (MtK2, JT5, BJ35, GT1, ZN3 and JT0) locally collected and previously screened for their relative oat crown rust resistance were used in this experiment. These
accessions were evaluated during a two cropping season in field plots under heavy natural oat crown rust infection. Assessment
criteria to crown rust reactions were AUDPC, latent period, uredinia size and number of uredinia per cm2 of infected leaf area. Principal components analysis showed that the variables were grouped in two components. These two
principal components explained 83.56% of the total variance. The projection of the point-cloud representing the populations
on the plan formed by the principal components ‘Fact 1’ (63.83%), in abscissa, and ‘Fact 2’ (19.73%) in ordinate, permitted
to distribute the accessions in several groups. Three landrace oats (MtK2, JT5, and JT0) showed the lowest value of all the components used. These landrace oats might be good sources of effective and durable resistance
to crown rust. 相似文献
Sclerotinia sclerotiorum (Lib.) de Bary is a major limiting factor for sunflower (Helianthus annuus) production. This study was conducted to (1) evaluate a large number of current sunflower lines for their reaction to Sclerotinia, and (2) determine the optimum allocation of resources for their selection. A set of 85 inbred lines was screened under artificial leaf infection in three environments. The test revealed ample variation for all resistance traits in the current germplasm. A line selected from NDBLOS, an oilseed sunflower germplasm poo, and its derivatives were most resistant to Sclerotinia. Lines derived from interspecific crosses with the wild species Helianthus tuberosus and Helianthus argophyllus also showed satisfactory Sclerotinia resistance. The evaluation of five plants per plot in two replications and four environments appears to be a reasonable allocation of resources in order to optimize the selection response. 相似文献
In the years 2002–2005, special trials concerning the level of infection of pea varieties by downy mildew were performed in Poland. In these trials, the large number of varieties were tested in many locations (environments), separately on reach and light soils. Obtained trial data are unique because of the large scale of the performed investigations and also for the fact that all the observations were made by the same observer. In a paper, two methods of statistical analysis of such (ordered) data are compared.
Several models have been proposed for the statistical interpretation of ordinal data. One of the most popular is the cumulative-type fixed logistic model. In the present work, using two field pea data sets, we considered whether adding random effects to the simple logistic model can improve inference. It was investigated whether there is any difference between the decisions concerning varieties resulting from the simple logistic model and the proposed mixed logistic model. The two models were also compared in terms of goodness of fit. According to two applied goodness-of-fit statistics, the mixed model performed better in all the cases. Statistical analysis (what is important for practical agriculture) enabled identification of the most resistant and the most susceptible variety from the analyzed set of cultivars. 相似文献