恶疫霉有性杂交后代的竞争能力研究*

５株杂交个体（携带对甲霜灵和地茂散的抗性标记）的游动孢子分别与其野生型亲本ＡＰ １４和ＰＫ９（对甲霜灵和地茂散均敏感）按１：１、１：９和１：４９比例混合涂布在１０％Ｖ６培养基平板上或接种在苹果片上生长４～５ｄ，并诱导产生孢子囊和释放游动孢子，经单孢分离建立单孢无性系，在含甲霜灵或地茂散的培养基上检测杂交个体的单孢后代所占的百分率。结果是，在Ｖ６培养基平板上混合生长的３０个组合中，仅３个组合杂交个体的单孢后代在其单孢无性系群体中所占的比例显著低于野生型亲本，其余组合均符合其各自的期望值；在苹果片上混合接种的３０个组合，杂交个体与野生型亲本的单孢后代所占比例均符合其各自的期望值。进一步测定２个杂交个体（ＡＰＫ－９和ＡＰＫ－２４）分别与其野生型亲本以１：１的比例混合后在Ｖ６培养基平板上和苹果片上连续３个产孢循环过程中两者比例的变化，结果是，在杂交个体与野生型亲本ＡＰ１４的组合中，杂交个体的后代所占的百分率由第一个产孢循环的４９．１％～５４．２％至第三个产孢循环下降为１．８％～６．２％：而在与另一野生型亲本ＰＫ９的组合中，杂交个体的后代所占的百分率从第一个产孢循环的４４．４％～５４．２％至第３个产孢循环上升为７２．１

COMPETITIVE ABILITY OF SEXUAL HYBRIDS OF PHYTOPHTHORA CACTORUM SCHROETER

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.