One hundred variants ofChrysanthemum. morifoHum cv. 'Parliament', selected on a single plant basis for early flowenng at low temperature, were tested on a clonal basis. These variants originated from irradiated or non-irradiated microcalli subjected to a one-step greenhouse selection procedure, or, a two-step selection procedure (preselection in vitro at 6 °C followed by selection in the greenhouse). Clones originating from irradiated calli flowered significantly earlier than the controls. Most of the low-temperature tolerant (LTT) mutants were found among plants obtained by the one-step selection procedure. Variants originating from slowly regenerating calli yielded more LTT mutants as compared to those of fast(er) regenerating caUi. We therefore conclude that, irradiation and subsequent selection of plants from slowly regenerating calli considerably increases the efficiency of selecting LTT mutants. The expected advantage of a preselection in vitro at low-temperature could not be confirmed.
The effect of in vitro cold treatment (-1-6 °C, 90 days) on selection of low-temperature tolerant (LTT) mutants was investigated using X-irradiated (15 Gy and 20 Gy) and non-irradiated cell suspensions of Chrysanthemum morifoHum cv. 'Parliament'. Low temperature reduced significantly the number of regenerating calli, especially in the irradiated cultures. After the end of the cold stress 684, 197 and 54 plants were obtained from the 0 Gy, 15 Gy and 20 Gy treated cultures, respectively. Testing these plants in the greenhouse (-1-12 °C, winter low-Hght) most of the early flowering variants were selected from the 15 Gy population.Selection at the cell level is based on the hypothesis that mitosis of low-temperature tolerant (LTT) mutants is less inhibited by suboptimal temperature than that of non-mutated 'normal' cells. Solid (non-chimeric) LTT mutants in Chrysanthemum have been regenerated either with (PREIL et al. 1988) or without in vitro cold treatment (BROERTJES and LOCK 1985). The efficiency of both procedures was compared by using in vitro cultures of the same origin in simultaneously running experiments. A previous paper reported on the regeneration of plants from X-irradiated suspension cultures at 24 °C and on screening for early flowering in the greenhouse at suboptimal temperature and light conditions (HUITEMA et al. 1989). In the second part of the series of experiments described here, the effect of an in vitro cold treatment on LTT-mutant selection was investigated. Plants regenerated after the cold stress were tested for low-temperature tolerance using the same procedure outlined in part one.
Material and MethodsProcedures of suspension culture and mutation induction by X-irradiation in Chrysanthemum cv. 'Parliament' were described by HuiTEMA et al. (1989). After irradiation plated cell aggregates (< 2 mm) were cultured at 6 °C and 16 h daily illumination (10;uE m"^ sec'S Philips TLD 25) for 90 days and then transferred to 24 °C temperature conditions. Most of the microcalli (40 Petri dishes per X-irradiation variant of 0 Gy, 15 Gy and 20 Gy) turned brown and died during low temperature treatment. The surviving green calli were placed on fresh MS medium (MURASHIGE and SKOOG 1962) supplemented with 2.0 mg/1 indole-3-acetic acid (IAA) and 0.2 mg/1 6-benzylaminopurine (BA). Regenerating shoots were rooted on MS medium of 1/3 concentration containing 2 mg/1 IAA. After rooting, the plants were grown in the greenhouse in a peatperhte substrate (2:1, v/v) for one month at 23 °C. They were planted in beds on November 4th 1985 as described by HuiTEMA et al. (1989). The temperature was kept at 17 °C for two weeks and then lowered to 12 °C. All plants were topped at the same as. Copyr,ght Clearance Center Code Statement: 0179-9541/91/0702-0131$02.50/0
In order to improve mutant selection procedures. 5000 plantlets were regenerated in three different har.-ests (flush A, B and G) from X-irradiated (15 and 20 Gy) and non-irradiated cell suspensions of Chrysanthemum morifohum cv. 'Parliament', .\fter screening under suboptimal energv conditions (12 °G greenhouse temperature, winter low-light), a total of 95 early flowering plants were selected. These plants flowered at least as earK' as a lowtemperature tolerant (ETT) mutant E,, used as a reference. The percentage of earl\' flowering variants was highest among plants obtained from calli, Xirradiated with 15 Gy and regenerating relatively late (flush B). It appeared that the applied selection method (c.q, harvest) had a large impact on the number of early plants obtained.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.