Transport via xylem and accumulation of aflatoxin in seeds of groundnut plant

Aflatoxin contamination in groundnut seeds in the absence of any aflatoxigenic fungi leads to a hypothesis
that aflatoxins are present naturally in soil and is transferred to seeds through uptake by roots. A survey
was conducted on the natural occurrence of aflatoxins in agricultural soils, among nine main
groundnut-growing regions of Karnataka state, India. All 71 soil samples collected in this survey were
contaminated with aflatoxins esp. AFB1. An in vitro xylem sap experiment proved the ability of groundnut
plant roots to absorb AFB1, and transport to aerial plant parts via the xylem. Hydroponics experiment also
proved the uptake of AFB1 by the roots and their translocation to shoot. Uptake was affected by the initial
concentration of toxin and pH of the medium. Among the 14 varieties screened, GPBD4 and MLT.K.107
(III) recorded highest and least AFB1 uptake, respectively. The above results were validated using a greenhouse
experiment. Here, the aflatoxin absorbed by root gradually transferred to shoot that was later
found in seeds towards the end of experiment. Thus, the groundnut seeds can also get contaminated with
aflatoxin by direct uptake of aflatoxin through conducting tissue in addition to fungal infection. The present
study revealed the novel mode of aflatoxin contamination in groundnut seeds without fungal
infection.