Number Of Primary Infections Research Articles

Partial resistance of lettuce to downy mildew (Bremia lactucae). 4. Resistance after natural, semi-artificial and artificial infestation and examples of mutual interference of resistance levels

Field experiments were carried out in 1980 to investigate the relationship between components of resistance and disease level after inoculation (INOC), after infestation by spreader plants (SPREAD-PLANT) and after natural infestation (NAT-INFEST) of 10 partially resistant or susceptible genotypes. Besides, two latin square field experiments were performed in 1981 with four genotypes, in one experiment with small (30 cm) distances between the plots (SMALL-LAT) and in the other with distances of 10 m (BIG-LAT). Very significant differences occurred between plant genotypes for components of resistance and for disease level. Per experiment there was usually a (very) significant correlation between components of resistance such as latent period (LP), number of primary infections (PI) and number of infected leaves (IL) and between these components and disease level (DL).

Factors affecting the acquisition of resistance against Schistosoma mansoni in the mouse. The effect of varying the route and the number of primary infections, and the correlation between the size of the primary infection and the degree of resistance that is acquired.

Mice given primary infections of Schistosoma mansoni by percutaneous or subcutaneous routes were found to acquire a higher degree of resistance against homologous challenge after 7--8 weeks than mice infected intraperitoneally. Mice infected by the intraperitoneal route tended to have smaller worm burdens than those infected with the same number of cercariae by the other two routes and this may, in part, have contributed to the relative lack of efficacy of intraperitoneal infections in inducing resistance to re-infection. The same degree of resistance was acquired after primary percutaneous infection irrespective of whether it was administered in 3 equivalent weekly doses, or the same total number of cercariae was administered as a single infection. The same degree of resistance was also observed when a percutaneous challenge was administered on the same or a different skin site to that which received the percutaneous primary infection. The degree of resistance to re-infection acquired after a percutaneous primary infection correlated well with the size of the primary worm burden and the number of eggs in the intestine and liver, but did not correlate with the number of eggs in the lungs.