** Shares of GrainCorp GNC.AX fall as much as 19.3% to A$5.81, hitting lowest level since Nov 29, 2021

** Agribusiness firm expects FY26 underlying NPAT between A$20 million ($13.88 million) and A$50 million, down from A$87 million reported in FY25

** Flags pressure on grain export margins

** Stock top loser on the benchmark index .AXJO, which is down 0.5%

** GNC down 14.2% YTD

($1 = 1.4413 Australian dollars)

(Reporting by Jasmeen Ara Shaikh in Bengaluru)

((Jasmeenaraislam.Shaikh@thomsonreuters.com;))