iSUMMARYThisstudyexploredtheuptake,accumulationandtranslocationofphosphorus(P)incerealsin supportof more sustainable management of this critical and finite nutrient. A pot experiment evaluated two low phytate (lpa 1-1 and lpa M955) and two normal phytate (Harrington and Sanette)cultivarsofspringbarleywithtotalseedPconcentrationsof3.4mgg-1,6.1mgg-1,4.3 mg g-1 and 4.4 mg g-1 respectively and their growth response under Soil P Index 1 with and without added P. The lpa lines yielded as well as normal phytate barley and even better under P-limiting conditions. The lpa barley cultivars lpa1-1 and lpa M955 had 17% and 15% less total plant P uptake on average compared to Harrington and 22% and 20% less compared toSanetterespectivelyatharvesting.Amongallfourcultivars,lpa1-1hadthelowestseedtotal P concentration by 23%, 30% and 14% compared to lpa M955, Harrington and Sanette respectively due to lower P translocation to the grain, both with and without added nutrient P. Both lpa 1-1 and lpa M955 however,had significantly lower seed phytic acid concentration ranging between 50% -90% lower than Harrington and Sanette but the mineral elements content was unaffected by the reduction in seed phyticacid. CultivarresponseundervaryingsoilPenvironments(Index1,2and3)withandwithout added nutrient P was investigated. Soil P Index 1 had the highest response to added nutrient P resulting in 42%, 47%, 37% and 26% increase in total plant P uptake in lpa 1-1, lpaM955, Harrington and Sanette respectively. An average of all four cultivars showed P addition increased total plant P uptake by 38% (Index 1), 15% (Index 2) and 11% (Index 3) while totalplant dry weight increased by 22%, 9% and 3% under soil P Index 1, 2 and 3 respectively. All four cultivars showed no significant total plant dry weight increase at soil P Indices 2 and 3 as aresult of added nutrient P confirming current fertilizer recommendation systems. A higher soil P environment (Index 3) resulted in an unnecessary increase in total plant P uptake, seed total P concentration as well as seed phytic acid concentration in allcultivars despite no significantincreaseintotalplantdryweight.Bothlpa1-1andlpaM955translocatedanaverage of 10% less plant P to the seed than Harrington and Sanette under soil P Index 1 and 2. lpa 1-1hadthelowesttotalplantPuptakeamongallfourcultivarsundervaryingsoilPenvironments ranging between 9% -28% lower than lpa M955, 13% -25% lower than Harrington and 7% -28% lower than Sanette. Despite this, all four cultivars had no significant differences in total plant dry weightand consequent grain yield confirming that lpa 1-1 utilizes less P to achieve similar plant yield to normal phytate barely (Harrington andSanette. A mutagenized lpa 1-1 population of 3119 lines was screened for further reductions in seed total P concentration compared to lpa 1-1 and the parent Harrington. The M3 population hadseedtotalPconcentrationsrangingfrom1.7to4.7mgg-1with>90%beinglowerthan3.7 mg g-1. Selection of 220 reduced seed total P concentration lines produced an M4 population with <3.4 mg g-1seed total P concentration. Three M4 lines with 30% seed total P concentration reduction compared to lpa 1-1 were screened in a pot experiment under soil P Index 1 both with and without added nutrient P. Like lpa 1-1, they performed and yielded the equally as well as Harrington but with lower total plant P uptake, however, they showed even furtherreductionsinseedtotalPconcentration(3.0–3.4mgg-1)andconsequentlylowerphytic acid (0.15 –0.18 mg/100g). This suggests that thelow phytate trait is heritable and that it is possibletofurtherreduceseedtotalPconcentrationandsubsequenttotalplantPuptakewithout affecting theyield.The gene that most likely mutated in lpa 1-1 resulting in reduced seed total P concentrationisasulfatetransportergene,HvST.UsingtheCRISPR/Cas9geneeditingtoolto specifically target HvST in Golden Promise barley, 11 potential mutants were identified in the T0 generation. Grains from six T0 lines were phenotyped and all showed 40% lower seed total PconcentrationcomparedtoGoldenPromise.ThisconfirmedthatHvSTisthegeneresponsible for the low seed total Pconcentration. Wheat homologues of HvST were also identified using BLAST (basic local alignment search tool) and 13 wheat TILLING lines having variation in this sequence were selected. Genotyping of their progeny identified variations in target alleles corresponding to the HvST gene. Phenotypingis needed to detect whether these wheat lines display a low phytate trait.There ispotential for breeding the low phytate trait into high yielding commercial cereals to develop low P cultivars without a yield penalty. The findings suggest that inorganic P fertilizers can be used more efficiently thereby reducing water pollution and improving human and animal nutrit