EFFECTS OF HEDGING ON MATURATION IN RADIATA PINE - WESTERN GALL RUST SUSCEPTIBILITY

Resistance of Pinus radiata (radiata pine) to Endocronartium harknessi i (western gall rust) was investigated in a clonally replicated study including several putative maturation states. Rooted cuttings from 4 h eights of hedging of donor plants and from free-growing trees, togethe r with seedlings serving as a juvenile control, were naturally infecte d by the fungus. Since earlier studies had shown that resistance to we stern 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 cha racterized as follows; seedlings commonly had heavy infection, tree-or igin stecklings had no infection and hedge-origin stecklings varied, w ith intermediate levels of infection. Trends of decreasing infection w ith increasing hedge height suggested that height of hedging may have affected maturation in at least some of the clones, but the relationsh ip 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, em phasizing the potential value of selection in controlling western gall rust in plantation forestry.