Phenolic Compounds and Other Factors Controlling Rhizogenesis In Vitro in the Apple Rootstocks M.9 and M.26

Abstract

Summary A number of factors that affect the in vitro rooting of M.9 both during the shoot proliferation and the root-inducing phase of the micropropagation process have been examined. Work with the phenolic compound phloroglucinol (1, 3, 5 trihydroxybenzene) has shown that it can precondition shoots to root whilst shoots are multiplying on a cytokinin-based medium. Excision of single shoots and exposure to auxin and phloroglucinol (PG) also stimulated rooting compared to auxin-alone controls, although the size of the effect was not as great as that recorded during shoot multiplication. The easier-to-root M.26 was not affected by PG at either stage of the micropropagation process. Ageing of shoot cultures increased the capacity for auxin-induced rooting but shoot etiolation was without effect. A number of phenolic compounds at 10 -3 M, were assessed as IAA synergists during the root- initiation phase. Of the simple phenols only PG and hydroquinone had any effect on root number. Salicylic acid completely inhibited the root-inducing effect of IAA. The phenylpropanoids ferulic acid and umbelliferone significantly reduced rooting whilst chlorogenic acid increased root number. Phloridzin and its degradation products phloretin, phloretic acid and PG all increased root number compared to IAA controls.