Evidence for induced systemic protection to fusiform rust in loblolly pineby plant growth-promoting rhizobacteria

Trials conducted in 1997 and 1998 tested eight strains of plans growth-prom oting rhizobacteria (PGPR) for their capacity to induce systemic protection in loblolly pine to the causal agent of fusiform rust. Pine seeds were tre ated with bacteria at time of sowing, and seedlings were artificially inocu lated with basidiospores of Cronartium quercuum f. sp. fusiforme 1 month In ter. Six months after basidiospore inoculation, seedlings were evaluated fo r the fusoid swelling or galls characteristic of rust infection. Compared w ith seedlings from seed not treated with bacteria, two bacterial isolates, Bacillus pumilus (SE34) and Serratia marcescens (90-166), significantly (P = 0.05) reduced the number of galls in 1997 and 1998. Combined data from 19 97 and 1998 resulted in two additional isolates, B. pumilus (INR7) and B. p umilus (SE52), significantly (P = 0.05) reducing the number of galls. Avera ged over both years, 31% of control seedlings were infected with fusiform r ust, while those seedlings treated with bacterial strains SE34, 90-166, INR 7, and SE52 had 13, 14, 15, and 16% infection, respectively. These four PGP R strains ap pear to have induced systemic resistance to fusiform rust in l oblolly pine, resulting in less infection over nontreated control seedlings .