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A SUGI CLONE HIGHLY PALATABLE TO HARES:
SCREENING FOR BIOAC_IIVE CHEMICA S
HIROFUMI ttlRAKAWA, TADAKAZU NAKAStIIMA, YOSttlOKI HAYASHI,
SEIJI OHARA, and TSUTOMU KUWAHATA
Forestry and Forest Products Resealch Institute
PO Box 16, Tsukuba-Norin, Ibaraki 305, Japan
INTRODUCTION
Herbivores often selectively feed on some plant individuals over other conspecifics. Such differences in palatability
are usually chemically determined. Although typically confounded with environmental factors (Rousi et al. 1989, 1991,
1993), genetic control of the differences in palatability observed among geographic origins (Matsuura and Maeda 1981;
Radwan et al. 1982; Hansson et al. 1986; Rousi et al. 1989, 1991), among families (Rousi et al. 1989, 1991), and among
clones (Radwan 1972, Hara 1973, Dimock et al. 1976, Kuwahata and Tanbara 1983) is obvious.
Although mammalian herbivores can cause severe damage to trees, it is usually difficult to control such animals,
because of economical, aesthetic, and ethical reasons. Breeding for resistance is one of the possible solutions to this problem.
Therefore, efforts have been made to find the chemical agents responsible for the variation in palatability among trees.
Atetsu 4 (A4), an elite sugi clone, Cryptomeria japonica, which originated in Atetsu, Okayama, Japan, is extremely
palatable to hares. Its high palatability was first observed at a test planting site of 32 sugi clones, where A4 was highly
damaged by hares just 1 year after planting. Later, an unusually high mortality rate was found in A4 at another test site of 37
clones 5 years after planting, and damage by hares were considered to be the main cause of the mortality (Kuwahata and
Tanbara 1983).
This paper reconfirms the high palatability of A4 to hares, analyzes some of the chemical properties of the three sugi
clones, and tests the palatability of crude chemical extracts and separated fractions using filter paper trials.
MATERIALS AND METHODS
Plant Materials and Hares
The palatable sugi clone, A4, and two other unpalatable sugi clones, Uda 36 (U36) and Niimi 4 (N4), were used. The
clones were transplanted to the nursery of the Forestry and Forest Products Research Institute in Ibaraki, and leaves were
collected from trees at each feeding trial and, when stocked for use in chemical analysis, frozen at -43°C. Captive hares,
Lepus brachyurus, kept in pens at the institute, were used for palatability tests. The hares were outdoors and maintained on
commercial food pellets. They were either born in captivity or captured in the wild soon after birth.
Palatability Test
Feeding trials were conducted using two hares in separate 3.6 x 3.6 m pens. Fresh leaves or extracted residues of the
clones were put on shallow mesh trays (24 x 32 x 1cm) and offered to the hares. Consumption was monitored by measuring
the weight of the remnants over several days. Corrections were made for changes in leaf weight due to dehydration by
measuring controls.
Mattson, W.J., Niemel_i, P., and Rousi, M., eds. 1996. Dynamics of forest herbivory: quest for pattern and principle.
USDA For. Serv. Gen. Tech. Rep. NC-183, N.C. For. Exp. Sta., St. Paul, MN 55108.
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