Oospores of Phytophthora infestans produced in vitro and in planta, from a cross between US-17 and US-8 genotypes, were exposed to a variety of environments and their survival was assessed. Additionally, the pathogenic characteristics of some resultant progeny isolates were assessed. Viability of oospores as measured by plasmolysis declined slightly over a period of 18 months whether they were stored in water at 4°C, in soil at 18°C, or in soil under natural field conditions. In comparison, viability as measured by germination was lower overall but appeared to increase after storage in soil. Oospores produced in planta were buried in the field in the fall of 1998, and were capable of infecting both tomato and potato leaflets when recovered in May 1999. Single oospore progeny (n = 53) from the in vitro cross were analyzed individually for genetic and pathogenicity characteristics. All 53 progeny tested for restriction fragment length polymorphisms with probe RG57 were hybrids. All but one progeny produced sporulating lesions on detached potato or tomato leaflets in growth chamber tests, but most lesions were smaller and developed more slowly than those produced by either parental isolate. In a further test of pathogenicity, under field conditions, none of a subset of 10 A2 progeny was capable of initiating a detectable epidemic in small plots of either potatoes or tomatoes.

In recent years, late blight, caused by Phytophthora infestans (Mont) De Bary, has increased in severity in many parts of the world, and this has been associated with migrations which have introduced new, arguably more aggressive, populations of the pathogen. In Taiwan, late blight has been endemic on outdoor tomato crops grown in the highlands since the early 1900s, but recent epidemics have been more damaging. To ascertain the present status of the Taiwanese population of P infestans, 139 isolates of the pathogen collected and maintained by the Asian Vegetable Research and Development Center (AVRDC) were characterized using mating type, metalaxyl sensitivity, allozyme genotype, mitochondrial haplotype and RFLP fingerprinting. Up to 1997, all isolates were found to belong to the old clonal lineage of P infestans (US-1 and variants), but in isolates from 1998 a new genotype appeared, and by 2000 this had apparently completely displaced the old population. This new genotype was an A1 mating type and has the dilocus allozyme genotype 100/100/111, 100/100 for the loci coding for glucose-6-phosphate isomerase and peptidase, respectively. These characters, together with RG57 fingerprinting, indicated that these isolates belonged to the US-11 clonal lineage, a minority (11%) being a previously unreported variant of US-11. Whereas metalaxyl-resistant isolates were not detected in the old population, 96% of the new genotypes proved resistant, with the remainder being intermediate in sensitivity. It may be inferred from this sudden, marked change in the characteristics of the Taiwanese P infestans that a new population of the pathogen was introduced around 1997-98 and that this may well have already been metalaxyl-resistant when it arrived, although a role for in situ selection cannot be excluded.

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Differential display with three time points revealed that thiram altered expression of numerous genes in the biocontrol fungus Fusarium oxysporum CS-20. Of the 101 bands purified from the differential display gel, 86 were successfully cloned, and 64 sequenced. Based on nucleic acid sequences, homology to known products was found using BLASTn for 26 sequences and homology to hypothetical proteins was found for six sequences, also from Gibberella zeae. One band (BM1 24-1) showed homology to an ABC transporter from three different fungi. Because of its association with detoxification functions, the ABC transporter was selected for further study.

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