Iron source and cytokinin mitigate the incidence of chlorosis and hyperhydration in vitro

Abstract

Two Vaccinium genotypes growing in vitro (V. pahalae, ohelo, and V. myrtillus, bilberry) were examined under variable iron (Fe) and growth regulator regimes in order to elucidate the cause(s) of abnormal tissue formation. Two Fe sources (200, 300, and 400 μM Fe from FeEDTA and 150, 200 and 250 μM Fe from a combination of 100 μM FeEDTA supplemented with FeEDDHA) were used in combination with 12.3 μM 2iP (N‐[3‐methyl‐2‐butenyl]‐1‐H‐purine‐6‐amine), 18.2 μM zeatin, or 11.4 μM zeatin riboside. No hyperhydration and only trace chlorosis occurred in 2iP treatments, but growth was substandard, as reflected by significantly lower fresh and dry mass yields from shoots harvested after eight weeks. Although zeatin or zeatin riboside treatments induced greater shoot proliferation, the incidence of hyperhydration and chlorotic foliage was severe, especially for ohelo, in all treatments with supplemental FeEDTA. In FeEDTA‐supplemented media, exogenous zeatin riboside accumulated in foliage by the end of a growth cycle, and was associated with hyperhydrated and chlorotic tissue quality, especially at high levels of Fe. Alternatively, the use of FeEDDHA to supplement media Fe levels resulted in no evidence of chlorosis, dramatically reduced incidence of hyperhydration, and less accumulation of zeatin riboside in foliage tissue.