Optimal disinfection times for seeds of Mediterranean orchids propagated on nutrient media

Abstract

A time-consuming yet mandatory step during in vitro sexual propagation of orchids is the treatment of seeds with a disinfecting solution that also serves to scarify the seeds. If the seeds are not properly disinfected, microorganisms grow within the culture vessel, thus reducing the efficacy of the process and burdening the operation with unnecessary materials and labour. On the other hand, a long period of disinfection may damage the seed. The literature is inconclusive with respect to the proper combination of solution strength and duration of the treatment, especially with respect to Mediterranean orchids. The objective of this research is to determine optimal disinfection/scarification times for two species with thin and thick seed coats, respectively. Seeds of Anacamptis laxiflora (Lam.) and Himantoglossum robertianum (Loisel.) were treated in 1% NaClO solution for 5, 15, 25, 35 and 45 minutes and sown in modified organic Malmgren medium. Logistic regression models were fitted to the results. Due to the small number of observations per treatment, regression models of infection rates on treatment duration had no more predictive ability than the mean infection rate. On the other hand, regression models of germination rates on treatment duration proved statistically significant or nearly so. Treatment of only a few minutes in 1% NaClO seems to be optimal for seeds with relatively permeable seed coats such as those of A. laxiflora (Lam.). Conversely, treatment of 45 minutes in 1% NaClO may be inadequate for seeds with relatively impermeable seed coats such as those of H. robertianum (Loisel.).

Optimal scarification times for seeds of two Mediterranean orchids

“…In light of these results and those of our earlier study (Katsalirou et al 2017), the advice of Malmgren and Nyström (2018) to soak terrestrial orchid seeds in 0.3-1% NaClO solution for 5-45 minutes is only a general recommendation. We found that a few minutes more or less can make the difference between a successful and an unsuccessful sowing.…”

“…Seeds with thin testa imbibe solution fast. Katsalirou et al (2017) demonstrate that seeds of A. laxiflora can only be kept for a few minutes in 1% NaClO solution before their viability is reduced. However, too short a treatment may cause the operator to rush, increasing the possibility of error.…”

“…On the contrary, Rasmussen (1995) suggests a stronger NaClO solution (5%) and much longer treatment times, up to several hours. Further details of the scant literature are provided by Katsalirou et al (2017). The corollary is that, if mass Mediterranean orchid propagation is ever attempted for commercial or conservation purposes, optimal scarification times must be empirically determined for each species.…”

“…The objective was to determine treatment times that minimize infection of culture vessels and maximize OPTIMAL SCARIFICATION TIMES FOR SEEDS OF TWO MEDITERRANEAN ORCHIDS E I R I N I KAT S A L I ROU 1 , A RG Y R IO S G E R A K I S 2, * , and X E NOPHON HA L DAS 3 seed germination without unduly delaying the in vitro procedure. The first results were reported in Katsalirou et al (2017). Due to the small number of replications per treatment (n = 8), the predictive ability of regression models of percentage infection on treatment duration was no better than the mean percentage infection.…”

Optimization of in vitro asymbiotic seed germination protocol for Serapias vomeracea

“…In surface sterilization experiments of many in vitro germination studies, disinfectants such as ethyl alcohol (EtOH), sodium hypochlorite (NaOCl), calcium hypochlorite (CaOCl), hydrogen peroxide (H 2 O 2 ), silver nitrate (AgNO 3 ) and mercuric chloride (HgCl 2 ) have been commonly used (8). However, less toxic chemical compounds should be used in the surface sterilization treatment of orchid seeds since they have thin seed coats which make the embryo particularly vulnerable to toxic chemicals such as disinfectants (9). In this context, in addition to disinfectant selection, treatment duration is also important.…”