Micropropagation, a technique used to rapidly increase available stock of new cultivars, can be used for propagation of apple rootstocks (Webster and Jones, 1989). Micropropagation is also useful for production of stock plants with improved rooting ability (Quamme and Hogue, 1994; Webster and Jones, 1991). For apple, micropropagation is inefficient in the proliferation stage (Aklan et al., 1997; Dobránszki and Teixeira da Silva, 2010; Isutsa et al., 1998; Pua et al., 1983; Webster and Jones, 1989). Efficiency of proliferation requires a rapid increase in the number of new shoots that elongate sufficiently to transfer to the rooting stage. For some woody plant taxa or genotypes, in vitro shoot growth is stunted with poor axillary branching and shoot tips that fail to elongate (Geng et al., 2012; Moreira da Silva and Debergh, 1997; Naik et al., 1999; Tao and Sugiura, 1992; Webster and Jones, 1989).
Some otherwise promising rootstocks have limited commercial use because propagation is difficult (Nelson, 1976; Quamme and Hogue, 1994). For example, poor shoot proliferation and insufficient shoot elongation occur with ‘Ottawa 3’ (Ott.3), ‘Malling 9’ (M.9), ‘Malling 26’ (M.26), ‘Budagovsky 9’ (B.9), and ‘P 2’ (Aklan et al., 1997; Lane and McDougald, 1982; Pua et al., 1983; Webster and Jones, 1991). New rootstocks in the Geneva series such as G.41 have been selected for reduced suckering and lack of burr knots, but with the undesirable consequence of being difficult to propagate (Robinson et al., 2011). Previous research on micropropagation of the Geneva series focused on rooting and establishment of viable explants (Isutsa et al., 1998), but methods to enhance shoot proliferation are necessary to decrease the time for rapid propagation of newly released cultivars.
Axillary shoot proliferation and elongation can be enhanced by altering the spectral light quality of in vitro plantlets (Chee and Pool, 1989; Economou and Read, 1987). Compared with white light, blue light increases in vitro shoot number in Amelanchier (Behrouz and Lineberger, 1981) and plum (Baraldi et al., 1988), but decreases shoot number and shoot length in Spiraea and apple (Norton et al., 1988a, 1988b). Red light increases the length of axillary shoots in apple (Muleo and Morini, 2006, 2008), plum (Muleo and Thomas, 1997), Azorina vidalii (Moreira da Silva and Debergh, 1997), and Vaccinium corymbosum (Noė et al., 1998), but not in grape (Chee and Pool, 1989). The inconsistent responses may be the result of variation in physiology among taxa or in conditions among experiments (Baraldi et al., 1988; Economou and Read, 1987; Norton et al., 1988a). At low intensity, blue light has little effect on shoot growth of tobacco, but at higher intensity, it enhances shoot growth compared with red or yellow light (Seibert et al., 1975). At low intensity, red light produces the greatest proliferation rate, but under higher intensity, red light does not differ from white or blue light in its effect on shoot proliferation (Baraldi et al., 1988). Altering light quality can be an efficient method for improving shoot proliferation, because it does not increase the duration of the propagation cycle, unlike prolonged subculturing (Webster and Jones, 1991).
Few studies have measured variation in response to light quality among apple rootstock cultivars. In MM.106 apple, culturing under red or blue light reduces in vitro shoot number compared with white or green light, but red light increases shoot length (Muleo and Morini, 2006). In contrast, shoot number and shoot length of the M.9 apple are increased by red light relative to blue, yellow, green, white, or far-red light (Muleo and Morini, 2008).
GA3, added to proliferation media in combination with cytokinin and auxin, improves shoot proliferation in apple (Pua et al., 1983), but responses may vary with explant condition (Elliot, 1972). Light quality can affect phytohormone balance in developing shoots, with red and blue light altering endogenous auxin and gibberellins (Baraldi et al., 1995). We hypothesized that light quality may alter responses of apple rootstocks to exogenous GA3.
The purpose of this study was to test the effect of blue and red light on in vitro shoot growth of three apple rootstocks, B.9, G.30, and G.41, which vary in their ease of propagation. Additionally, we tested the effect of blue and red light in combination with GA3 on in vitro shoot growth of G.30.
Aklan, K., Çentiner, S., Aka-Kacar, Y. & Yalcin-Mendi, Y. 1997 In-vitro multiplication of clonal apple rootstocks M-9, M-26 and MM106 by meristem culture Acta Hort. 441 325 327
Baraldi, R., Luna, V., Bottini, R., Bertazza, G. & Bogino, J. 1995 The effect of light quality on Prunus cerasus II. Changes in hormone levels in plants grown under different light conditions Photochem. Photobiol. 62 800 830
Baraldi, R., Ross, F. & Lercari, B. 1988 In vitro shoot development of Prunus GF655-2: Interaction between light and benzyladenine Physiol. Plant. 74 440 443
Behrouz, M. & Lineberger, R.D. 1981 Influence of light quality on in vitro shoot multiplication of Amelanchier laevis HortScience 16 406 (abstr)
Chee, R. & Pool, R.M. 1989 Morphogenic responses to propagule trimming, spectral irradiance, and photoperiod of grapevine shoots recultured in vitro J. Amer. Soc. Hort. Sci. 114 350 354
Druart, P. 2003 Micropropagation of apples (Malus sp.), p. 433–463. In: Jain, S.M. and K. Ishii (eds.). Micropropagation of woody trees and fruits. Kluwer Academic Publishers, Boston, MA
Geng, F., Moran, R.E. & Zhang, D. 2012 Chilling duration affected the microshoot elongation of G.30 apple rootstock HortScience 47 98 (abstr.)
Grant, N.J. & Hammatt, N. 1999 Increased shoot and root production during micropropagation of cherry and apple rootstocks: Effect of subculture frequency Tree Physiol. 19 899 903
Kim, S., Hahn, E., Heo, J. & Paek, K. 2004 Effects of LEDs on net photosynthetic rate, growth and leaf stomata of chrysanthemum plantlets in vitro Sci. Hort. 101 143 151
Lane, W.D. & McDougald, J.M. 1982 Shoot tissue culture of apple: Comparative response of five cultivars to cytokinin and auxin Can. J. Plant Sci. 62 689 694
Moreira da Silva, M.H. & Debergh, P.C. 1997 The effect of light quality on the morphogenesis of in vitro culture of Azorina vidalii Plant Cell Tiss. Org. Cult. 51 187 193
Muleo, R. & Morini, S. 2003 Effects of light quality on micro-propagation of woody species. Kluwer Academic Publishers, Boston, MA. p. 3–35.
Muleo, R. & Morini, S. 2006 Light quality regulates shoot cluster growth and development of MM.106 apple genotype in in vitro culture Sci. Hort. 108 364 370
Muleo, R. & Morini, S. 2008 Physiological dissection of blue and red light regulation of apical dominance and branching in M.9 apple rootstock growing in vitro J. Plant Physiol. 165 1838 1846
Muleo, R. & Thomas, B. 1997 Effect of light quality on shoot proliferation of Prunus cerasifera are the result of differential effects on bud induction and apical dominance J. Hort. Sci. 72 483 491
Naik, S., Pattnaik, S. & Chand, P.K. 1999 In vitro propagation of pomegranate (Punica granatum L. cv. Ganesh) through axillary shoot proliferation from nodal segments of mature tree Sci. Hort. 79 175 183
Noė, N., Eccher, T., Del Signore, E. & Montoldi, A. 1998 Growth and proliferation in vitro of Vaccinium corymbosum under different irradiance and radiation spectral composition Biol. Plant. 41 161 167
Norton, C.R., Norton, M.E. & Herrington, T. 1988a Light quality and the control of shoot length in woody ornamental plants grown in vitro Acta Hort. 227 453 456
Norton, C.R., Norton, M.E., Herrington, T. & Phillips, D. 1988b Light quality and light pipe in the micropropagation of woody ornamental plants Acta Hort. 226 413 416
Quamme, H.A. & Hogue, E.J. 1994 Improved rooting of Ottawa 3 apple rootstock by soft wood cuttings using micropropagated plants as a cutting source Fruit Var. J. 48 170 173
Robinson, T.L., Hoying, S.A. & Fazio, G. 2011 Performance of Geneva rootstocks in on-farm trials in New York State Acta Hort. 903 249 255
Seibert, M., Wetherbee, P.J. & Job, D.D. 1975 The effects of light intensity and spectral quality on growth and shoot initiation in tobacco callus Plant Physiol. 56 130 139
Sun, Q.R., Sun, H.Y., Bell, R.L., Li, G., Tao, J.H. & Li, Q. 2014 Optimisation of the media for in vitro shoot proliferation and root induction in three new cold-hardy and dwarfing or semi-dwarfing clonal apple rootstocks J. Hort. Sci. Biotechnol. 89 381 388
Webster, C.A. & Jones, O.P. 1989 Micropropagation of apple rootstock M.9: Effect of sustained subculture on apparent rejuvenization in vitro J. Hort. Sci. 64 421 428