Restriction fragment length polymorphisms (RFLPs) have been used to detect chloroplast (cp) and mitochondrial (mt) DNA variation among 18 apple cultivars and three rootstocks. The distribution of RFLP patterns allowed the assignment of these genotypes into three groups of cytoplasmic relatedness. Our results also demonstrate maternal inheritance of cp- and mtDNAs in apple. Thus, the organelle DNA assay provides a convenient and reliable method to assess cytoplasmic diversity within the apple germ-plasm collection and to trace the maternal lineages involved in the evolution of apple.

IntroductionIn Japan, sugar beets (Beta vulgaris L.) are only cultivated in the Hokkaido region, where a transplanting technique is commonly employed. This technique entails seeding sugar beets in paper pot nurseries for about 45 days of cultivation in a greenhouse, and then transplanting the seedlings in the field. Commercial fungicide-pelleted seeds are typically used to protect sugar beets from seedling diseases. In the Hokkaido region, Pythium spp., Rhizoctonia solani and Aphanomyces cochlioides are the main causal pathogens at the seedling stage of sugar beet 11 . Infection by Pythium spp. primarily causes pre-emergence damping-off, while R. solani causes the pre-emergence death of seedlings and damages newly emerged seedlings. On the other hand, A. cochlioides causes little or no preemergence damping-off, but causes extensive post-emergence damping-off that could result in the destruction of entire fields, especially in warm and wet soil 13 . Fungicidepelleted seeds can stably control pre-emergence damping-off, but not post-emergence damping-off, and so the latter type of damping-off caused by A. cochlioides is the main cause of sugar beet seedling loss. Furthermore, after seedlings are transplanted in the field, A. cochlioides can also cause root rot (i.e., Aphanomyces root rot) from late June to the end of the growing season 28,29 . The pathogen is widely distributed throughout sugar beet production areas, persistent for long periods in the soil, and not easily controlled by chemicals and cultivation practices. As a result, Aphanomyces root rot is a chronic problem that could become particularly severe in certain fields or during years when warm and moist conditions prevail. Therefore, new control measures for both post-emergence Biocontrol of Sugar Beet Seedling and Taproot Diseases Caused by Aphanomyces cochlioides by Pythium oligandrum AbstractBiocontrol activities in the oospore suspensions of 17 isolates of Pythium oligandrum (PO) were examined for their effect against post-emergence seedling diseases. The seeds of sugar beet that had been commercially chemical-pelleted to prevent pre-emergence damping-off were sown in Aphanomyces cochlioides-infested soil on trays. PO isolate MMR2 proved most effective in controlling post-emergence damping-off, at a level equivalent to that of applying fungicides. Oospore suspensions stored for 188 days or 379 days at 4℃ were as effective against A. cochlioides post-emergence damping-off as chemical control. Treating soil with PO oospores by mixing suspensions into the surface of soil in paper pot nurseries or by drenching seedlings 32 days before transplanting could control Aphanomyces root rot in the field without additional applications. The control effect conferred by PO suspensions was also demonstrated in vitro. A polymerase chain reaction (PCR) assay used to detect PO indicated that this oomycete could colonize the rhizosphere of sugar beet plants cultivated in the field when applied before transplanting. These results suggest that PO has the potential to c...

The means of enhancing the growth of seedlings of apples, Malus pumila Mill. var. domestica Schneid. (cv. McIntosh, American Summer Pearmain, Jonathan, Golden Delicious, Starking Delicious, Fuji, Mutsu and Red Gold) and Malus sieboldii Rehd., through inoculation of arbuscular mycorrhizal (AM) fungus [Glomus etunicatum (GE) and Gigaspora margarita (GM)] were investigated. Eight weeks after inoculation, AM fungus infection occurred in all combinations of apple cultivars and fungus species. The rate of AM fungus-infected portions in a whole root system were: 31.7% in 'Golden Delicious', 50.5% in 'Jonathan' in GE-inoculated plants, and 24.0% for Mains sieboldii Rehd., and 50.7% in 'Starking Delicious' in GM-inoculated ones. Plant height and dry weights of top and roots were greater in all GE-infected seedlings than in noninoculated ones. The GM-infected seedlings made larger height and weight increments than did the noninoculated ones in all seedlings except those of 'Golden Delicious' and Moans sieboldii Rehd.. In 'McIntosh' seedlings, plant growth enhancement through symbiosis clearly appeared associated with both fungi. With both fungal species, P concentrations in the top or roots were higher in infected plants than in noninoculated plants; the effect appeared more noticeably in roots than in top. Consequently, it was confirmed that GE and GM infections and their plant growth enhancement through symbiosis occurred with the seedling stage in several apple cultivars.

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