Identification of candidate genes for use in molecular breeding - A case study with the Norway spruce defensin-like gene, Spi 1

In this study we have investigated whether the defensin-like gene spi 1, is olated from Norway spruce, contributes to quantitative disease resistance a nd is a suitable candidate for utilisation in Norway spruce breeding progra mmes. The following questions have been raised: (1) Can the putative defens e gene, spi 1, improve the defense towards microbial pathogens in a model p lant species, tobacco? (2) Is it possible to produce transgenic plants of N orway spruce that overexpress spi 1 and are less susceptible to the pathoge nic fungus Heterobasidion annosum? Compared to control plants, tobacco plan ts expressing spi 1 under an enhanced CaMV 35S promoter permitted less grow th of the bacterial pathogen Erwinia carotovora. Embryogenic cultures of No rway spruce were transformed with a similar construct. The general phenotyp e of regenerated transgenic plants was normal, although it was difficult to maintain certain sublines in culture owing to poor initial growth. Among t he transformed plants those with the highest content of SPI 1 displayed red uced fungal growth in the sapwood after inoculation with H. annosum. In con clusion, the spi 1 gene increases resistance in both homologous and heterol ogous systems.