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Annals of Botany 83 : 515–519, 1999
Article No. anbo.1999.0849, available online at http:\\www.idealibrary.com on

Epicuticular Wax Columns in Cultivated Brassica Species and in their Close Wild
Relatives

C. G O! M E Z -C A M P O*, M. E. T O R T O S A*, I. T E W A RI† and J. P. T E W A RI†
* Depto. de BiologıTa Vegetal, Uni ersidad PoliteT cnica de Madrid, 28040—Madrid, Spain, and † Dept. of

Agricultural, Food and Nutritional Science, Uni ersity of Alberta, Edmonton, T6G 2P5 Canada

Received : 5 October 1998 Returned for revision : 10 November 1998 Accepted : 22 January 1999

Three different types of epicuticular wax columns were found in Brassica species with a chromosome number (n) l
9 : long columns (LC), short columns (SC) and netted columns (NC). LC were found in B. incana and B. rupestris.
SC were found in B. illosa, B. macrocarpa, B. cretica, B. hilarionis and also in B. montana. B. insularis columns
were intermediate. NC waxes were found in B. oleracea and its close allies B. alboglabra and B. bourgeaui. Samples
of B. rapa (n l 10) and B. nigra (n l 8) examined did not show any wax columns but their amphidiploids with B.
oleracea (B. napus and B. carinata, respectively) seemed to inherit the NC type of wax present in B. oleracea.

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Key words : Brassica, waxes, wax columns, leaf surface.

INTRODUCTION Universidad Polite! cnica de Madrid (Go! mez-Campo, 1990).
The accessions used are listed in Table 1 with their respective
Cultivated Brassica species include three diploids (B. rapa L. chromosome numbers (n), their accession number, species
with a chromosome number (n) l 10, B. oleracea L. with name and authority and seed source or origin.
n l 9 and B. nigra (L.) Koch with n l 8) as well as three
amphidiploids which combine these three genomes in every Seedlings were grown in 25 cm clay pots in a glasshouse.
possible way (B. napus L. with n l 10j9, B. juncea with n They were watered by dripping water directly onto the soil
l 10j8, and B. carinata with n l 9j8). While B. rapa and to avoid any damage to the epidermal wax structure
B. nigra show no apparent close relatives, B. oleracea has a which might occur if sprinklers were used. Brassica wax
few wild related species growing in coastal habitats around development is affected by environmental conditions (Reed
the Mediterranean. Much work has been done to elucidate and Tukey, 1982 ; Shepherd et al., 1995). However, in this
the phylogenetic relationships among these species. How- study all plants were grown under the same conditions and,
ever, we are not aware of any comparative studies on the therefore, different wax types reflect genetic differences
structure of their epicuticular wax. In some Brassica species, among the various species examined.
the epicuticular wax is organized in three layers, i.e. a
continuous sheet, flat crystals and upright crystals (Conn Leaves from the sixth to eighth nodes were removed from
and Tewari, 1989 b). Only the upright crystal layer was young plants, taking care not to touch the laminas. Leaves
studied in the present investigation. were then transferred into 20 cm Petri dishes on moist filter
paper with ten drops of 2 % osmium tetroxide solution in
Epicuticular waxes on the surfaces of higher plants are water and left overnight in a fume hood. The next day, small
normally associated with conservation of water (Martin and pieces of leaves were mounted on metal stubs and allowed
Juniper, 1970). In addition, they confer other unique to air dry. Both leaf surfaces were mounted. After being
properties to plant surfaces and may also play other coated with platinum they were examined and photographed
important roles (Tewari and Skoropad, 1976 ; Bodnaryk, in a Hitachi-2500 scanning electron microscope.
1992 ; Knowles, Knowles and Tewari, 1996). By providing a
water-repellent surface, wax limits the deposition of water- RESULTS
borne spores of pathogens. In Brassica, it has been shown
that this is the major mechanism by which the glaucous B. In taxa which presented upright epicuticular wax crystals,
napus is less susceptible to Alternaria brassicae (Berk.) Sacc. three general types of wax columns were found to exist.
than the non-glaucous B. rapa (Tewari and Skoropad, 1976 ;
Conn and Tewari, 1989 a). Ecologically, waxy plants are First, there were long needle-like columns (LC) of approx.
mostly associated with dry habitats. In Brassica, wax is very 7 µm (meanps.d. l 6n86p1n2, measured in 20 properly
often present in coastal species. oriented columns). This type of wax was dominant in B.
incana and B. rupestris (Fig. 1 A). In B. incana they were
MATERIALS AND METHODS accompanied by abundant epidermal trichomes, while these
were very sparse in B. rupestris.
Plant material was mostly obtained from the seed bank of
crucifers kept in the Escuela T. S. de Ingenieros Agro! nomos, Next, there were short thick columns (SC) of approx.
3 µm (meanps.d. l 3n2p0n6, measured in 20 properly
0305-7364\99\050515j05 $30.00\0 oriented columns). These were dominant in Brassica illosa

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