ARS | Publication request: RESISTANCE OF TULARE WALNUT (JUGLANS REGIA CV. TULARE) TO AFLATOXIGENESIS

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 26, 2002
Publication Date: February 15, 2003
Citation: MAHONEY, N.E., MOLYNEUX, R.J., MCGRANAHAN, G., MCKENNA, J., LESLIE, C.A. RESISTANCE OF TULARE WALNUT (JUGLANS REGIA CV. TULARE) TO AFLATOXIGENESIS. JOURNAL OF FOOD SCIENCE. v. 68. p. 619-622. 2003.

Interpretive Summary: Compounds harmful to humans can be introduced into food stuffs when molds grow on them. One of these aflatoxin, is strictly regulated and can affect the export market for California tree nuts (almonds, pistachios and walnuts) when present. The walnut variety "Tulare" has now been shown to be highly resistant to formation of aflatoxin when the fungus grows on the kernel of the nut. The source of the resistance has been shown to be located in the seed coat but not in the kernel from which the seed coat had been removed. It should be possible to breed new walnut varieties which contain this factor, enhancing the safety and marketability of walnuts for human consumption.

Technical Abstract: The ability of tree nuts to inhibit production of aflatoxins by Aspergillus flavus was investigated in vitro. Walnuts were much more resistant to aflatoxin formation than almonds or pistachios. The walnut cultivar 'Tulare' showed complete suppression of toxin production. Kernel without seed coat had no activity and the inhibitory factor(s) were shown to be specifically located in seed coat tissue. When seed coat was added back to 'Tulare' kernel media, aflatoxin was decreased to the detection limit or below. Aflatoxin production declined rapidly with seed coat maturity and was independent of growing location and rootstock. Breeding programs could increase resistance, enhancing marketability and safety of walnuts for human consumption.