Exploring Allelochemical Compositions in The Roots of Two Varieties of Anacardium occidentale (Cashew)

Abstract

Allelochemicals are chemicals released by plants that affect other plants and pests. The chemicals are provided by different parts of the plant or released through the natural decomposition of the associated plants. Anacardium occidentale has been reported to exhibit allelopathy. The bark and inner parts of the roots of the two varieties (red and yellow) of Anacardium occidental (Linn) were qualitatively and quantitatively analysed for the presence of allelochemicals. The samples were also subjected to Gas Chromatography-Mass Spectrometry (GC/MS) analysis. The qualitative results showed that flavonoids, tannins, and phenols were present in both the bark and inner parts of the roots, whereas alkaloids, saponins, and terpenoids were present only in the bark of the roots. The quantitative results showed that while the root bark of the red variety had the highest saponin content, that of the yellow variety had the highest phenol content. The GC/MS results for both samples showed the presence of different compounds, and one of the compound peaks observed in the inner root was not identified; 9,12– octadecadienoic acid (fatty acid) was the compound with the highest composition identified in the yellow variety.  Similar compounds were identified in the root bark of the red and yellow varieties, which include 3-Tridecyl phenol with molecular formula C19H32O and molecular weight 276, which occurred at a retention time range of 41.703–41.712 min and had the lowest percentage compositions of 2.816 and 4.732% in red and yellow varieties, respectively. The compounds with the highest percentage compositions of 32.389 and 41.944% in red and yellow, respectively, were identified as (Z)-3-(Heptadec-10-en-1-yl) phenol (molecular formula C23H38O with molecular weight 330), occurring within the retention time range of 48.246 – 48.263 min. Other compounds with higher percentage compositions were identified in the samples, including (Z)-3-(pentadec-8-en-1-yl) phenol and 3-((4Z,7Z)-Heptadeca-4,7-dien-1-yl) phenol. However, 1,2,4,-Benzenetriol (molecular formula C6H6O with molecular weight 252) was only identified in the red variety, with a percentage composition of 8.883%, which occurred at a retention time of  22.040 min. The compounds identified in the bark were mostly phenols, whereas those in the inner roots were more fatty acids.