Effects of hedging on maturation in radiata pine: western gall rust susceptibility

Resistance of Pinus radiata (radiata pine) to Endocronartium harknessii (western gall rust) was investigated in a clonally replicated study including several putative maturation states. Rooted cuttings from 4 heights of hedging of donor plants and from free-growing trees, together with seedlings serving as a juvenile control, were naturally infected by the fungus. Since earlier studies had shown that resistance to western gall rust was maturation related, it was hoped that incidence of the disease could be used to assess the effects of hedging height on maturation. In their 5th growing season, the 3 stocktypes could be characterized as follows; seedlings commonly had heavy infection, tree-origin stecklings had no infection and hedge-origin stecklings varied, with intermediate levels of infection. Trends of decreasing infection with increasing hedge height suggested that height of hedging may have affected maturation in at least some of the clones, but the relationship was not sufficiently strong or consistent so that infection levels could serve as a reliable index of maturation. Clonal variation was a significant component of total variation in disease susceptibility, emphasizing the potential value of selection in controlling western gall rust in plantation forestry.