Histological Studies of Ditylenchus africanus Within Peanut Pods.
Ditylenchus africanus entered the immature pegs and pods of peanut (Arachis hypogaea cv. Sellie) at the peg-connection and subsequently invaded the parenchymatous regions of the hull exocarp and endocarp, and eventually the seed testa. The nematode caused malformations of the cells of infected tissues, cell wall breakage, and cell collapse. The damage appeared to be due to enzymatic activity. In some testae the entire parenchyma region, which aids in protection of the seed, was destroyed. In immature pods, the nematodes moved across the fibrous region of the mesocarp into the hull endocarp. In mature pods, however, the fibrous mesocarp of the hull was lignified and apparently was a barrier to penetration of the inner pod tissues. In late-harvested pods, increased numbers of eggs and anhydrobiotes were found in the hull tissues, and eggs in the seed testa, suggesting the onset of winter survival mechanisms of the nematode.
Population Dynamics of Ditylenchus destructor on Peanut.
The population development of Ditylenchus destructor in the roots, pegs, hulls, and seeds of eight peanut (Arachis hypogaea) genotypes was studied in the greenhouse. Although all genotypes tested were good hosts for D. destructor, differences in host suitability were observed. Invasion of the plant parts by Ditylenchus destructor proceeded more slowly in genotypes with long growth periods. During the second half of the growth period of these genotypes, D. destructor populations emigrated from the hulls and seeds into the soil but reinfected the pods after a few weeks. The genotypes with the longest growth periods supported the highest number of nematodes when each genotype was harvested at its usual harvest time. The long-season genotypes supported low numbers of nematodes when harvested before crop maturity.
Genotypic diversity in field isolates of Babesia bovis from cattle with babesiosis after vaccination.
OBJECTIVE
To determine whether particular genotypes of Babesia bovis were common to field isolates obtained from cattle properties in Queensland where the B bovis vaccine had apparently failed.


DESIGN
A comparative study of polymerase chain reaction genotypes in different populations of B bovis.


PROCEDURE
Two polymerase chain reaction assays were applied to analyse DNA extracts of B bovis vaccine (K, T and Dixie strains) and 27 field isolates from 24 properties where disease outbreaks had occurred despite the use of the vaccine. To evaluate the stability of the genotypes identified, 11 of the field isolates were inoculated into experimental cattle that had either been previously vaccinated with T strain or not vaccinated.


RESULTS
No particular genotype of B bovis was responsible for the problems observed in previously vaccinated herds. None of the isolates had genotypes identical to the vaccine strains used. No geographic trends among the genotypes were observed. Isolates that originated from the same property also had different genotypes. Blood passage of the 11 field isolates in either previously vaccinated or nonvaccinated cattle did not alter the original genotype.


CONCLUSION
No particular genotypes identified by the Bv80 and BvVA1 polymerase chain reaction assays could be associated with vaccine failures.