Effects of temperature on Phytophthora porri in vitro and in planta

Cardinal temperatures for mycelial growth ofPhytophthora porri on corn-meal agar were <5 (minimum), 15–20 (optimum) and just above 25 °C (maximum). The number of infections after zoospore inoculation of young leaf plants was relatively low at supra-optimal temperatures, but was not affected by sub-optimal temperatures. Even at 0 °C plants were infected. The incubation periods needed for symptom formation were 36–57 d at 0 °C, 13–18 d at 5 °C, and 4–11 d at > 11 °C, and were fitted to temperature between 0 and 24 °C with a hyperbolical model (1/p=0.00812*T+0.0243). Oospore germination, reported for the first time forP. porri, was strongly reduced after 5 h at 45 °C, and totally absent after 5 h at 55 °C. Soil solarization for six weeks during an exceptionally warm period in May–June 1992 in The Netherlands raised the soil temperature at 5 cm depth for 17 h above 45 °C, but did not reduce the initial level of disease in August significantly

Genetical studies of resistance to Phytophthora porri in Allium porrum, using a new early screening method.

A new screening method was developed to evaluate resistance of leek (Allium porrum) to Phytophthora porri, based on inoculation by 24 h-immersion of leek plantlets in the 3–6 leaf stage in a suspension of ca. 100 zoospores.ml-1. The immersion test was used for identifying new sources of resistance and to determine the genetic basis of resistance. Within winter leek, five resistance classes were defined on the basis of average field scores of 21 plants. Clones from these plants were tested with the immersion technique. The average scores per resistance class in immersion and field tests were significantly correlated (P<0.01). The correlation of single-date field scores with the immersion test scores was better in the second half of the epidemic season. A selection experiment yielded a strong response to selection for resistance (53–97%) but no response to selection for susceptibility. This may indicate that resistance is due to few recessive genes in the studied winter leek. Crosses between landraces and winter leek were analyzed by means of F2 (selfed F1) and BC1, progenies. This analysis indicated the presence of few loci with dominant genes for resistance in accession CGN 873243, and additive polygenes in accession Pl 36835

A structured expert evaluation method for the evaluation of children's computer games

Inspection-based evaluation methods predicting usability problems can be applied for evaluating products without involving users. A new method (named SEEM), inspired by Norman’s theory-of-action model [18] and Malone’s concepts of fun [15], is described for predicting usability and fun problems in children’s computer games. This paper describes a study to assess SEEM’s quality. The results show that the experts in the study predicted about 76% of the problems found in a user test. The validity of SEEM is quite promising. Furthermore, the participating experts were able to apply the inspection-questions in an appropriate manner. Based on this first study ideas for improving the method are presented