Abstract:

Objective: This study aims to clarify the effect of the different kinds of resin-stimulant pastes on resin production and growth of Pinus elliottii, and to screen out the resin-stimulant paste suitable for P. elliottii in Guangdong, so as to guide actual production and reduce the cost of resin tapping. Method: This study was conducted in the half-sib progeny test forest of P. elliottii in Hongling Seed Orchard, Taishan, Guangdong. Six treatments were set, and they were non-tapping (T0, for growth control), conventional tapping without any resin-stimulant paste treatment (T1, for experimental control), and tapping treated with different components of resin-stimulant pastes (T2-T5). The main components of the pastes were K₂SO₄, naphthalene acetic acid (NAA), benzoic acid (BA) and 2-chloroethylphosphonic acid (CEPA), respectively. In 2018, the trees were treated and harvested seven times, and in 2019, they were treated and harvested six times. Before the treatment, the basic value of resin yield was harvested without resin-stimulant pastes. The resin yield and growth trait were all measured per tree. Result: The result in 2018 showed that the effects of both family and resin-stimulant paste treatment were extremely significant (P < 0.01), however their interaction effects were not significant (P > 0.05). The first two collections showed that the resin stimulating effect was extremely significant, with the resin increase rate over 135%. However, resin stimulating effect decreased in the third collection. By the fourth time, only T5 treatment group had a stimulating effect, but it did not reach a significant level. From the fifth to seventh times, T2-T4 treatment group did not have a significant stimulating effect, but T5 treatment still maintained the resin increase rate of more than 19%. The total yield of resin for seven collections showed that T5 treatment group had the best resin stimulating effect, with a resin increase rate of 51.73%. The result in 2019 showed that the family effect was not significant in the first collection (P > 0.05), while the family effect in the other collections was extremely significant (P < 0.01). The background value of the resin yield in each treatment group showed no significant difference, and then the following six collections showed significant resin stimulating effect, with the resin increase rate ranging from 29% to 269%. The total of the resin yield for six collections showed that T5 treatment had the best resin stimulating effect, with a resin increase rate of 160.61%. The ranking of resin production of each family varied greatly in different years and different treatments, and among them family I2 and I7 were relatively stable. The result of the two-year growth showed that the family effect was significant, however there was no significant difference in the growth among the different treatment groups, and there was no significant difference in the one-year increment of tree height and diameter at 0.9 m height among different treatment groups. The resin production of different collections in the same year had an extremely significant correlation. The correlation coefficient ranged from 0.245 5 to 0.854 4. In the two years, the first harvest of resin production had the lowest correlation coefficient with the total production. The correlation analysis between the resin production and growth showed that there was a stable extremely significant and positive correlation between resin production and diameter at 0.9 m height, however the correlations between resin production and height growth showed no significant, significant, or extremely significant levels in different periods of time and with different treatments. A significant negative correlation was even detected between resin production and height in 2018. Conclusion: The resin-stimulants with different components have significantly different effects on the resin increasing of P. elliottii. The same resin-stimulant pastes have different resin increasing effects under different climatic conditions. This study shows that T5, with 20% sulfuric acid and 3% CEPA as the main components, has the best and most stable resin stimulating effect, and has no significant interaction with the family. Thus, T5 is suitable for popularization in P. elliottii forests. The resin yield of the same tree varies greatly at different harvests. When measuring resin yield traits, it should be avoided to only use the data of the first resin tapping. The resin production of different families also changes greatly in different harvests, different years, and different treatments. Among the 11 families tested, the resin productions of families I2 and I7 are relatively high and stable. The use of resin-stimulant pastes has no significant effect on the growth of tree height and diameter at 0.9 m height in a short period of time. There is a strong correlation between resin production and tree diameter. To a certain extent, tree diameter could be used as an indirect selective indicator of resin production. Although the correlation between resin production and tree height is weak, the resin-stimulant effect of P. elliottii with higher tree height is more significant when the T2, T3 and T4 resin-stimulant pastes are applied.

Key words: Pinus elliottii, resin production, resin-stimulant paste, growth, mixed model