Electrical conductivity and resin flow in Pinus radiata seedlings.  G. Minko.  April 1979.  15 pp. (unpubl.)

SUMMARY

Pinus radiata seedlings can vary widely in quality. A quick and reliable test to determine the quality of seedling stock in the nursery and at the end of the storage period prior to planting is therefore needed. This study tested the relationships between quality of seedlings, electrical conductivity, and observed resin flow rate.

Quality of seedlings was found to be closely associated with the relative electrical conductivity between two points on the plant stem and to resin flow rate between these two points. To estimate resin flow of nursery stock for field planting a relationship was established between relative conductivity and resin flow rate.

It was found that comparisons of seedling quality based on their relative electrical conductivity are valid within a given seedling crop. However in making such comparisons it was necessary to have constant temperatures and seedlings free of surface moisture, a condition which is difficult to achieve in winter in seedling beds or in seedling storage. Because of the difficulties of the procedure the method was found impractical for day-to-day nursery practice.

In contrast measurement of resin flow grades provided a practical means (although destructive of the sample) for determining seedling quality at the end of conventional storage. It was found that groups are seedlings with an average estimated resin flow grade (determined from the amount of resin exuded from a cut surface) above 2.5 were of high quality (good survival and growth following planting out). Groups of seedlings with an average resin flow grade between 2.5 and 1.7 were acceptable, particularly under favourable field conditions; and groups of seedlings with an average resin flow below 1.7 should be rejected. Seedlings tested had been stored at field temperatures in standard cardboard containers. The results may not be applicable to seedlings which have been healed-in or watered following a period of storage.

Also published:

Minko, G. (1979)  Electrical conductivity and resin flow in relation to seedling quality in Pinus radiata.  For. Comm. Vic., For. Tech. Pap. 27: 3-9.