Effects of serial subculture in vitro on the endogenous levels of indole-3-acetic acid and abscisic acid and rootability in microcuttings of ?Jonathan? apple

Abstract

Proliferating axillary shoots of the difficult-to-root apple cultivar `Jonathan' acquired an enhanced ability to form adventitious roots with increasing number of subcultures in vitro . The transition between the difficult-to-root and the easy-to-root condition occurred at the fourth subculture .Endogenous levels of free IAA and ABA in shoot tissues were analysed by gas chromatography/mass spectrometry/single ion monitoring (GC/MS/SIM) using negative ion chemical ionisation . Tissues from the mother plants grown in the glasshouse contained more IAA and ABA than those from tissue-culture material . After establishment in vitro there was no variation in the IAA content throughout the subcultures but a decrease in ABA content was observed after the fourth transfer . The IAA/ABA ratio increased from 0 .2 in difficult-to-root shoots from the initial culture up to 0 .7 in easy-to-root shoots from the long-term subculture. 1 . IntroductionThe propagation of apples from cuttings is difficult because most apple cultivars and rootstocks do not readily form roots under conventional nursery conditions [23] . However, the rooting ability of apple cuttings can be improved by `conditioning' the mother plants using treatments such as heavy pruning and blanching [11], application of growth retardants [6,9] or exposure to low light intensity [7] . Success in the striking of cuttings is determined as much by the management of the stock plants prior to severance as by the conditions under which root formation occurred [18] . Most of the research done on root formation is concerned with cuttings after excision from the stock plants .Recent reviews on adventitious root formation [10,13] have drawn attention to the importance of the physiological state of the mother plants at time of collection of the cuttings . Investigations on the hormonal balance in stock and the results are conflicting . In Dahlia [3] and in Rhododendron [24] the capacity of cuttings to form adventitious roots is not correlated with the endogenous level of IAA in the mother plants . In stock plant of Bougainvillea, Hibiscus [5] and Vitis [2], however, enhanced root formation of cuttings is associated with high IAA content . Similarly very little is known about the occurrence of ABA in mother plants . In Rhododendron the rooting ability of cuttings is positively correlated with a high ABA content in stock plants [24] but high ABA levels are found to be inhibitory in Sequoia sempervirens [8] .Difficult-and easy-to-root microcuttings of the same apple cultivar can be produced in vitro by repeated subculture under specific conditions [19] .

Micropropagation of mature British wild cherry

“…Another possibility is that environmental conditions prior to culture initiation, possibly resulting in altered growth regulator concentrations, gave rise to this contrast. Although correlations between ratios of indoleacetic acid and abscisic acid, and shoot production with time, have not been investigated with wild cherry, Noiton et al (1992) have demonstrated a correlation between this ratio and increasing rootability of apple shoots with subculturing.…”

Progress in tissue culture, genetic transformation and applications of biotechnology to trees: an overview

“…Several limitations such as low shoot proliferation in forest trees, excessive phenolic exudation (Linington 1991), basal callusing (Marks and Simpson 1994), vitrification (Monsalede et al 1995), and shoot tip necrosis (Bargchi and Alderson 1996) are pronounced in tree tissue culture. Further, difficulty in rooting (Noiton et al 1992;Harada and Murai 1996) has also had a negative effect on micropropagation of woody forest tree species in vitro. In this section we have attempted to describe the trend of research activities during the last decade.…”

Effects of in vitro subculture on the physiological characteristics of adventitious root formation in microshoots of Castanea mollissima cv. ‘yanshanhong’

“…Fuji, Starkrimson) and cultivar 'Jonathan' (Malus× domestica Borkh. ), proliferating axillary shoots acquired an enhanced rooting ability with increasing the number of subcultures in vitro (Chang et al 1991;Noiton et al 1992). Precocious walnut (Juglans regia L.) shoots have a high rooting rate by induction in vitro after they have been subcultured for 4 years (Pei et al 2002).…”