Japanese Journal of Breeding

Plant regeneration from the protoplasts of the two species of the genus lilium (L. speciorubel var. Sweet memory, L. elegance var. Benisugata) was examined. The protoplasts of the lilies were isolated from the shoot primordia which had been obtained by the rotary culture of the shoot apex (Fig. 1a). High regenerable protoplasts were constantly obtained by the over-night enzymatic treatment (Table 2). Many starch granules were released from broken protoplasts at the enzymatic treatment (Fig. Ib). And they had a bad effect upon protoplasts electric-fusion (Fig. Ih). The problem could be successfully removed during droping the petri dishes with a slight gradient and taking the supernatant of a drop of the protoplasts suspension (Fig. 1c).

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This study was conducted to obtain estimates of genetic parameters on ripening time of fruits and fruit weight, using a Japanese pear seedling population of sixteen families and their parental cultivars. High correlations (r = 0.759^**) were observed between ripening time and fruit weight among families(Fig.1). In the case that the average of the ripening time of fruits of seedlings in a family was early, the average of fruit weight was low, and the reverse case as for the ripening time, the average of fruit weight was relatively high (Fig.1). High correlations (r = 0.793^**) were also observed between mid-parent of ripening time and the family mean of fruit weight (Fig.2). In the case that the ripening time of fruits of parents was early, the average of fruit weight of offsprings was low comparing with that of the offsprings of late-ripening parents (Fig.2). Significant correlations were observed also with in families, and in most of families early-ripening seedlings tended to bear a small fyuit (Fig.3, Table 2). Heritabilites of ripening time and fruit weight were estimated to be about 0.9∼1 and 0.6∼0. 7, respectively (Table 3). Both phenotypic and genetic correlation coefficients were estimated to be about 0.8 (Table 3). Breeding method of early-ripening Japanese pear cultivars and the use of indirect selection for fruit weight through ripening time were discussed.

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A new Japanese pear cultivar named 'Gold Nijisseiki', registered as Peer Norin 15, was developed by the Institute of Radiation Breeding, National Institute of Agrobiological Resources in 1991. Black spot disease caused by the Japanese pear pathotype of Alternaria alternata (Fr.) Keissler is the most important and serious disease of Japanese pear (Pyrus pyrlfolia Nakai var. culta Nakai). 'Nijisseiki' which is one of the most widely grown cultivars of Japanese pear is known to be susceptible to the disease. Susceptibility to black spot is controlled by a single dominant gene, and the majority of susceptible cultivars are heterozygous at this locus. 'Nijisseiki' was exposed to chronic irradiation (30 × 10^-2Gy∼4×l0^-2Gy/day) in the Gamma Field, and six resistant mutant branches were selected from trees by both natural infection, and selection after applying a phytotoxin solution (AK-toxin I). The induced mutants exhibited intermediate resistance to black spot disease, either by the inoculation test using a spore suspension or the phytotoxin method. However, black spot symptoms seldom developed under field condition.

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