Family and Clonal Variation in Susceptibility of Pinus Radiata to Agrobacterium Tumefaciens in Relation to in Vitro Shoot Growth Rate

This work was carried out to examine the hypothesis that differences mAgrobacterium tumefaciens susceptibility observed among Pinus radiata D.Don clones and families after stem inoculation in vitro can be attributed to differences in growth rate at the time of inoculation. Agrobacterium tumefaciens strain 542 was used to inoculate in vitro shoots of 90 clones divided among 14 full-sib P. radiata families. The significant influence of host genotype at the clone and family levels on susceptibility of P. radiata to A. tumefaciens was confirmed, and further evidence was found that growth rate at time of inoculation is important. Significant correlations between growth rate at time of inoculation and gall frequency illustrated the tendency for families (r=0.72, p<0.01) and clones (r=0.58, p=0.01) with rapidly growing shoots to be more susceptible to the bacterium. Analysis of covariance, however, showed that genotype influenced susceptibility over and above its effect on growth rate, pointing to a genotypic component of resistance that is independent of growth rate.