Germination and radicle growth in unprimed and primed seeds of sweet sorghum as affected by reduced water potential in NaCl at different temperatures

The effects of reduced water potential ( ) in NaCl and pre-osmopriming in PEG, on seed germinationand early radicle growth at different temperatures were assessed in the laboratory for sweet sorghum[Sorghum bicolor (L.) Moench] cv. Roce. Five salt solutions (with a of 0-control, -0.22, -0.42, -0.82 or-1.23MPa) and four temperatures of 10, 15, 25 or 35 oC were used for germination tests. Daily and finalgermination, seed moisture at 4 and 24 h of imbibition and radicle length 2 days after initial germinationwere recorded. Sorghum seeds seem to be more tolerant to reduced at optimum temperature. Indeed,at 25 oC, downto-0.82MPa seed germinationwas not affected. The increase in incubation temperature to35 oC determined a greater seedwater content and a faster germination than at 25 oC at all s, despite thelower final germination percentage. With the lowering of temperature to 15 oC, germination percentagesignificantly declined with the decrease of and at -0.82MPa it reduced to less than 50%. At 10 oCseeds failed to germinate at <-0.22MPa due to combined depressive effects of reduced and lowtemperature. Seed priming enhanced germination and shortened the delay in germination time due tothe increase in saline stress, at suboptimal temperatures only. This effect could be explained by the fasterwater absorption occurring in primed seeds as compared to those unprimed, at these temperatures,regardless of salt concentration of the solution.Root growth was more sensitive than germination to salt stress. Indeed, the increase in NaCl concentrationadversely affected root elongation at all temperatures. The beneficial effects of PEG-osmoprimingwere evident on root growth at all temperatures except the optimal one.From a practical point of view, when early sowings of sweet sorghum are requested, the use of primedseeds is suggested, as PEG-osmopriming is helpful in overcoming the negative effect imposed by reducedwater potential upon seed germination under suboptimal thermal conditions. When salinewater is availablefor irrigation at sowing, it may be useful to sow when optimal or nearly optimal temperature maybe encountered in the soil in order to avoid the combined stress of temperature and salinity.