Interaction between potato and the endophyte Burkholderia phytofirmans.

Bacterial endophytes have been de fi ned as „bacteria, which for all or part of their life cycle invade tissues of living plants and cause unapparent and asymptomatic infections entirely within plant tissues, but cause no symptoms of disease“ (WILSON 1995). Endophytes colonize a similar ecological niche as plant pathogens and may gain entry into plants by a number of mechanisms (reviewed by STURZ et al. 2000). Strain PsJN forms endophytic and epiphytic populations when co-cultured with potato (FROMMEL et al. 1991), tomato (PILLAY and NOWAK 1997), or grapevines (COMPANT et al. 2005). The bacterium not only stimulates plant growth (AIT BARKA et al. 2000, BENSALIM et al. 1998, FROMMEL et al. 1991, LIU et al. 1995, PILLAY and NOWAK 1997), it also induces developmental changes (FROMMEL et al. 1991), leading to better water manage-ment (LAZAROVITS and NOWAK 1997) and enhanced resistance to a low level of potato pathogens (RICHARDS 1997, STEWART 1997). Despite the fact that strain PsJN promotes plant growth of many different plant species, it has been repeatedly observed that plant performance greatly varies between different cultivars (CONN et al. 1997, PIL-LAY and NOWAK 1997, BENSALIM et al. 1998). N-acyl-L-homoserine lactones (AHLs) are produced by a range of Gram-negative bacteria and are used to regulate expression of various genes in a cell-density dependent man-ner. This phenomenon is known as quorum sensing (QS) and is frequently found in plant-associated bacteria including pathogens. The structures of AHLs vary in the chain length of their acyl chain and chain lengths of 4-16 carbon atoms (EBERL 1999). The principal aim of this study was to study the molecular interaction between the plant and microbial genotype as well as to study the effect of AHLs. Two, closely related, AHL-producing