Molecular identification of phytoplasmas in fasciated cacti and succulent species and associated hormonal perturbation

Abstract

Fasciation, a frequent phenomenon in Cactaceae, has been attributed to various causes. The present study reports on phytoplasma-induced fasciation in Euphorbia coerulescens (Euphorbiaceae), Orbea gigantea (Asclepiadaceae), Opuntia cylindrica (Cactaceae), and Senecio stapeliiformis (Asteraceae). DNA was extracted from symptomless and fasciated tissues and amplified by nested PCR using universal primers P1/P7 followed by R16F2n/R16R2 produced amplicons of 1.2 Kb. The nucleotide sequence analyses of the amplicons indicated that fasciated plants were infected by phytoplasma. Phylogenetic analysis placed the cacti fasciation phytoplasmas in 16SrII group. The hormonal content of symptomless and fasciated tissues including indole-3-acetic acid (IAA), kinetin (Kin), N⁶-benzyladenine (BA), abscisic acid (ABA), and gibberellic acid (GA₃) was quantified by high performance liquid chromatography (HPLC). The results indicated that fasciation in O. gigantea was correlated with the accumulation of Kin and IAA increasing five and two times, respectively, as compared to symptomless tissue. However, there was no consistent pattern of hormones in other fasciated species (E. coerulescens, O. cylindrica, and S. stapeliiformis), suggesting that different plant species might have different mechanism to develop fasciation associated with phytoplasma infection.

Keywords:

• cactus
• cristation
• fasciation
• phytoplasma