COMPETITIVE ABILITY OF SEXUAL HYBRIDS OF PHYTOPHTHORA CACTORUM SCHROETER
恶疫霉有性杂交后代的竞争能力研究*

Zoospores of hybrids (five single oospore cultures) derived from intraspecific outcross resistant to metalaxyl and chloroneb and their wild-type parents(AP14 and PK9) sensitive to the both chemicals were haed respectively at the ratio 1:1,1:9 and 1:49 and smeared on 10% V6 agar plates or inoculated on apple slices. After 4 ~5 day's incubation at 25 C, the mixtures were induced to produce zoospores. About 200 single-zoospore isolates were established from each mixed culture. All of the single zoospore isolates were inoculated on 10% V6 aged plates amended with metalaxyl 20 ug/ml or chloroneb 100 ug/ml to distinguish the offsprings of hybrids from those of wild-type parents. Results showed that the percentages of offsprings from hybrids and wild-type parents in 27 out of 30 combinations grown on V6 agar were not significantly different from their expectancy values(P=0.05), and the percentages of offsprings from hybrids and wild-type parents in all of 30 combinations grown on apple slices were fitted with their expectancy values. Further, the zoospores of hybrids and their wild-type parents were mixed at the ratio 1: 1 and inoculated on 10% V 6 agar or apple slices, and the offspring percentages from the both were tested in three successive sporulating cycles. When hybrid APK-9 or APK-24 was co-cultured with wild-type parent AP14 respectively, the percentages of offsprings from hybrids were 49.1% --54.2% at the sporulating cycle 1 and decreased tO 1.8%~6.2% at cycle 3. However, when the two hybrids co-cultured with another wild-hoe parent PK9, the percentage of offspring from hybrids increased from 44.4% ~54.2% at cycle 1 to 72.1%~75.0% at cycle 3. The results from our studies suggest that the hybrids derived from intraspecific outcross in Phytophthora cactorum have vigorous competition ability with wild-type parents in vitro and in vivo, and indicate that the sexual recombination of inter-isolates may play an important part in the genetic diversity of the species.