Growth in vitro cultures of strawberry (Fragaria × ananassa Duch.) depending on different photoperiods.

Abstract

The influence of three photoperiods: a) 16/8 (d/n) control, b) 4/2 (d/n) (4 cycles per 24 h), and c) 22/2 (d/n) on the growth of in vitro cultures of strawberry (Fragaria x ananassa Duch.) cultivars ‘Senga Sengana’ and ‘Elsanta’ was investigated. The application of 22/2 (d/n) photoperiod was not advantageous as it did not increase culture efficiency, stimulated the growth of callus at the explant base and caused chlorosis of leaves. Photoperiod 4/2 (d/n) significantly enhanced shoot proliferation of ‘Senga Sengana’ cultures when compared to control 16/8 (d/n). The reaction of ‘Elsanta’ cultures was not so distinct. As the change of photoperiod from 16/8 (d/n) to 4/2 (d/n) needs neither special instrumentation nor creates any additional costs it could be recommended in strawberry micropropagation, especially in the case of cultivar ‘Senga Sengana’. Wojciech Litwinczuk, Agnieszka Zubel 82 INTRODUCTION The method of micropropagation of strawberry was elaborated about thirty years ago by Boxus (1974) and numerous studies regarding that technique have been published so far. However, the articles describing the reaction of strawberry in vitro cultures on different photoperiods were not found. The application of shortened light/dark cycles was proved to be beneficial in micropropagation of some woody plants species (Morini et al. 1991, 1992, Zimmerman and Scorza 1994, Litwinczuk 2000). It is well known that many strawberry cultivars are sensitive to photoperiod. The purpose of this study was to examine the reaction of strawberry in vitro cultures on different light/dark cycles. MATERIAL AND METHODS The experiment was carried out on in vitro cultures of two strawberry cultivars (Fragaria×ananassa Duch.) ‘Senga Sengana’ and ‘Elsanta’. The influence of three photoperiods: a) 16/8 (d/n) 16 hours of day and 8 hours of night (control), b) 4/2 (d/n) (4 cycles per 24 h), and c) 22/2 (d/n) was investigated through three subsequent 4-week long subcultures. Cultures were grown under fluorescent light (Fluora, OSRAM) at 51.6 μmol m s PPFD in glass jars closed with plastic transparent cup. The basic medium recommended by Boxus (1999) supplemented with 6-benzylaminopurine (BA, 0.5 mg dm), gibberellic acid (GA3, 0.1 mg dm ), indole-3-butyric acid (IBA, 0.1 mg dm), glucose (40.0 g dm) and Bacto-Difco agar (6.4 g dm) was applied. Additionally, an other medium was used in the third subculture also. It was prepared by replacing glucose with mannitol (40.44 g dm). A small glass vessel containing 12 cm of medium with mannitol was placed inside a glass jar filled with 60 cm of the basic medium. Each combination (photoperiod) was represented by 10 jars in first subculture and 6 jars in second and third ones. The replication was one jar containing 7 cultures grown on basic medium (and additionally 2 cultures on mannitol medium in the third subculture). Thus, each combination was represented by at least 42 cultures grown on basic medium in each subculture and 12 cultures for mannitol medium. The following data were collected at the end of each subculture: number of shoots (rosettes), number of stolons, fresh weight of shoots, fresh weight of callus, number of rooted cultures, length of the longest petiole, length of the biggest terminal leaflet, width of the biggest terminal leaflet, and then subjected to ANOVA and LSD mean separation test at α=0.05 significance level using Statgraphics 4.2 computer software. Percent data (number of rooted cultures) were transformed using arcsin of square root for analysis of variance. Original means are presented in Tables 1 and 2. Micropropagation of strawberry under three photoperiods 83 RESULTS The investigated photoperiods influenced growth of strawberry clones in vitro on media supplemented with glucose. The application of 22/2 (d/n) photoperiod was not advantageous as it did not improve shoot proliferation of both ‘Elsanta’ and ‘Senga Sengana’ in vitro cultures, whereas stimulated the growth of callus at the explant base and caused chlorosis of leaves when compared to control [16/4 (d/n)] (Tables 1 and 2). Photoperiod 4/2 (d/n) significantly enhanced shoot proliferation of ‘Senga Sengana’ cultures (Table 1). However, in principle such reaction of ‘Elsanta’ cultures was not distinct as the significantly better proliferation of shoots under 4/2 (d/n) photoperiod was only recorded in the third passage (Table 2). The leaf blades of both clones grown under 4/2 (d/n) cycle were significantly reduced (Tables 1 and 2). On the other hand, the leaf petioles of ‘Elsanta’ were visibly elongated under mentioned photoperiod (Table 2). In general, other studied traits of in vitro cultures of both clones remained unchanged under examined photoperiods (Tables 1 and 2). The growth of cultures on the medium supplemented with mannitol was poor and was not influenced by studied photoperiods (Table 3). DISCUSSION The fact that many strawberry cultivars are sensitive to photoperiod and plants develop stolons under short night conditions is well known. However, none of studied photoperiods stimulated stoloning in vitro although all of them belong to ‘short night’ regime. Possible other factors which exist in vitro suppressed such process. Nevertheless, improved shoots proliferation was achieved while shortened photoperiod 4/2 (d/n) was used, especially in the case of ‘Senga Sengana’. The same effect for in vitro cultures of peach, plum, and sour cherry was reported by Morini et al. (1991, 1992), as well as Zimmerman and Scorza (1994). However, they did not find the reason of such phenomenon. It is also not possible in the present study. In comparison to other examined photoperiods, the 4/2 (d/n) cycle should improve photosynthesis through more stable level of CO2 and its better utilisation by cultures in vitro. However, the fresh weight of cultures grown on mannitol medium (which was contingent only on CO2 level in the jar) under 16/4 (d/n) and 4/2 (d/n) cycles remained similar or was even smaller in the last case (Table 3). Too small sample size (only 12 cultures) do not permit to state whether the differences were significant or not. The dry weight of cultures was not determined as well. Thus it is impossible to find out whether better shoot proliferation was caused by improved photosynthesis of cultures. On the other hand, examined photoperiods differed in the march of temperature on the shelves (Figure 1 and Table 4). Wojciech Litwinczuk, Agnieszka Zubel 84 Table 1. Effect of studied photoperiods on the growth of strawberry ‘Senga Sengana’ in vitro cultures on medium supplemented with glucose

Abstract from the paper’s OpenAlex record; open copy licensed cc-by-nc-nd. Read at the source ↗

The text the model read, with the source record’s inline markup (italics, sub- and superscripts) rendered and its character entities decoded; quote offsets refer to the raw text.