In vitro studies on endogenous levels of phenolics in different explants of cashew (Anacardium occidentale L.) var. BPP-6

Endogenous levels of phenols, OD-phenols, and tannins were studied in the explants viz. young leaf (YL), mature leaf (ML), shoot bud (SB) and sub-apical meristem (SAM) of 16 year-old field grown cashew (Anacardium occidentale L.) var. BPP-6. The explants were cultured on MS (Murashige and Skoog) medium supplemented with or without antioxidants. The highest phenol content (11.75 mg g-1 fw) of intact shoot bud was reduced to 1.01 mg g-1 fw (89%) by 6 DAI (day after inoculation) when it was cultured on medium and to 44% when supplemented with antioxidants. But the SAM tissue maintained high initial level of phenols in vitro unaltered upto 18 DAI and reduced abruptly by ten-fold at 24 DAI. The OD-phenols of SAM were progressively reduced to 50% till 12 DAI and maintained a plateau thereafter upto 24 DAI. The intact ML tissue recorded highest concentration of tannins (253.17 mg g-1 FW). The tannin level of all the explants was reduced (94-86%) when cultured on MS basal medium. Although, the initial level of phenols of all explants, except SB, enhanced when cultured on 3/4 strength MS medium, the levels were declined overtime. However, the YL and ML tissues contained low levels of OD-phenols and tannins at 24 DAI. The 3/4 strength MS medium when supplemented with antioxidants could reduce the five-fold high concentration of phenols of intact SB tissue to four-fold low concentration at 6 DAI. The tannin content of all the explants was found reduced (97-81%) when strength of MS medium was supplemented with antioxidants, which could have caused a steady fall in phenol content of SAM, ML and SB. Further, a substantial reduction of OD-phenols (50%) was also recorded by all the explants. The MS medium supplemented with" antioxidants progressively reduced tannin content to 92-88% in YL and effectively in all other explants. The SAM tissue however consistently maintained low levels of tannin in vitro. The 3/4 strength MS medium supplemented with antioxidants since reduced the accumulation of phenolics, it could be assessed as a suitable medium for in vitro culture of SAM, ML and SB explants. However, it is noteworthy that low phenolics in explant is only a fraction factor of physiological and hormonal melee of the explants that decide the callusing regeneration ability.