A PLANT-GROWTH PROMOTING RHIZOBACTERIUM AND TEMPERATURE EFFECTS ON PERFORMANCE OF 18 CLONES OF POTATO

A survey of genotypic responses to beneficial bacterium (Pseudomonas s p, strain PsJN) was conducted in vitro and ex vitro, under two tempera ture conditions, using eighteen clones of potato of different heat str ess tolerance: temperate adapted cultivars Kennebec and Russet Burbank ; heat tolerant DTO-2, DTO-28, DTO-33, LT-1, LT-2, LT-5, LT-6, LT-7, L T-8, LT-9, Y84-02, NDD277-2, Desiree, and Maine-47; and heat sensitive abscissic acid (ABA)-deficient mutants 11401-01 and 9120-05. Nodal ex plants taken from 6-week-old bacterized and non-bacterized control pla ntlets were cultured in vitro on a hormone-free potato nodal cutting m edium, and placed at either 20/15 C or 33/25 C day/night temperature, 12h photoperiod and 250 mu E m(-2) s(-1) mixture of fluorescent and in candescent Light, for six weeks. The tuberization.response was studied ex vitro after two weeks acclimation of 2-week old plantlets at 33/25 C. The acclimated plantlets were transplanted to 3L plastic nursery p ots containing peat-based Pro-Mix growing medium and placed in growth chambers at either 20/15 or 33/25 C day/night temperature, 12 h photop eriod, 475 mu E m(-2) s(-1) light and approximate to 80% RH, for 12 we eks. Compared to the non-bacterized controls, bacterization significan tly increased stem length of 12, shoot biomass of 9, and root biomass of 2 clones at 20/15C; and stem length of 14, shoot biomass of 15, and root biomass of 13 clones at 33/25C. High temperature increased lengt h of internodes and had either no effect or slightly decreased node nu mber. Temperature increase had the most dramatic effect on root develo pment. An average shoot to root ratio decreased from 3.7 at 20/15 C to 1.7 at 33/25 C for non-bacterized plantlets and, respectively, from 4 .3 to 1.5 for bacterized. The beneficial effect of bacterization on ro ot biomass was the most pronounced in LT-1 and Maine-47 at 20/15 C and LT-8, Maine 47, DTO-2, Kennebec, NDD277-2 and 11401-01 at 33/25C. The temperature elevation did not significantly affect root biomass of LT -6, DTO-28 and Desiree. Temperature stress caused severe reduction in tuber number and tuber fresh weight. ABA-deficient mutants did not pro duce any tubers and LT-8, LT-9, Y84-027 and DTO-28 tuberized very poor ly at 33/25C. DTO-33, Desiree; LT-1 and Kennebec gave the highest numb er of tubers per pot and Kennebec, LT-1, Desiree and LT-7 the highest yields at this temperature. There was no significant effect of bacteri zation on tuberization at 20/15 C but at 33/25 C bacterization signifi cantly enhanced tuber number and weight in LT-7 and reduced tuber weig ht in DTO-2. Although there was no clear link between the in vitro res ponse of particular clones to bacterization and their heat stress tole rance, improvement of ex vitro performance of heat tolerant LT-7 indic ates that rhizosphere bacteria may play a role in clonal adaptation of potato to heat stress.