苎麻疫霉有性生殖导致菌落形态和生长速率在无性后代持续变异的研究*

研究了苎麻疫霉（PhytophthoraboehmeriaeSawada）菌株JS-5自交S1代单卵孢株的菌落形态和生长速率在其单游动孢子无性系后代的遗传与变异。结果表明，亲本菌株JS-5的菌落形态和生长速率在连续4代单游动孢子无性系后代稳定遗传，而该菌株的自交S1代的约2／3单卵孢株的上述性状在其单拘无性后代中发生分离，且上述性状的分离在无性单孢后代中至少可连续保持3～4代。本研究结果提示，苎麻疫霉有性生殖导致上述性状的变异，除有性生殖过程中的基因重组外，有性生殖还诱导产生了一种新的机制参与上述性状遗传与变异的调控。本研究还观察到供试菌株及其后代所产生的游动孢子绝大多数细胞内只含有1个细胞核，表明上述机制与异核现象无关。有性生殖导致生物学性状在随后的无性后代中发生持续变异可能是苎麻疫霉生物学性状遗传多样性的重要机制之一。

CONTINUING VARIATION IN SUCCESSIVE ASEXUAL GENERATIONS OF PHYTOPHTHORA BOEHMERIAE FOLLOWING SEXUAL REPRODUCTION

The inheritance of colony morphology and growth face in successive zoospore generahons of Phytophthora boehmeriae Sawada following sexual reproduchonwas inveshgated in this paper. The wild-type isolate JS-5 of this species obtained from cotton boil rot hssue in Jiapsu was used as test material. Progeny were devided into parental type A, types B, C and D for those different from type A but with a dishnct uniform pattern, and type M for those with the overlaPPing appearance of tWo different types. The parental isolate JS-5 showed the same colony type as type A and displayed lithe variahon in growth rate in four successive zoospore generahons. However, cultures derived from selfed oosPOres in S. progeny of the same isolate consisted of type A, B, C, D and M, and the oospore cultures showed considerable valuation in growth rate. Of the eighteen selfed oospore cultures tested further,tWelve displayed more than one colony type and showed obvious variahon in growth rate in their zoospore progeny. From the tWelve cultures, tWo M type oospore cultures,JS-5-1 and JS-5 -23, were selected to study the inheritance and variation of the two characters in subsequent progeny of asexual lines of monospores further. The colony mor'Phohology and growth rate of isolate JS-5-1 showed obviously conhnuing vanahon in over three successive zoospore generations. Similar vallahon in zoospore progeny following selfing was observed in isolate JS-5-23. The above resultS suggested that except for causing gene recombination, the sexual reproduchon induced a new mechanism which may engaged in regulating and controlling the inheritance and variahon of the characters. Futhermore, it was observed that over 99% of the zoosPOres produced by isolate JS-5 and itS progeny contained only one nucleus in the cell, which indicated the above mechanism was not associated with heterokaryosis. Thephenomenon of conhnuing variahon in asexual generations induced by sexual reproduction may play an imper'tant role in genehc diversity of biological characters of P. boehmeriae.