74 RESEARCH REPORTS PNL Volume 12 1980
Wende, E.
Federal Research Centre for Hort. Plant Breeding, Ahrensburg, West Germany
A breeding program is underway to develop varieties of peas which are
specially suited to freeze-drying. Parental lines for crosses were chosen
from among 55 wrinkled varieties surveyed. Some of the special criteria
considered in the selection were: color of the fresh, immature pea; absence
of seedcoat splitting; quality of peas after freeze-drying; and the rehydration
properties (i.e. maintenance of shape of the green peas). Examination of
these quality characteristics was begun in F3 families derived from 3900 single
F2~single plants, originating, in turn, from 78 crosses.
R.H.S. color charts were used to evaluate the color intensity and vari-
ation in samples of fresh, deep-frozen, freeze-dried, and rehydrated green
peas. Progenies with light green color were rejected (group yellow-green
145 A-D). Samples from advanced generations were also studied to determine
the influence of the seedcoat and cotyledons on the color of green peas.
From this the following conclusions were drawn: 1) Color of the seedcoat,
which can vary from white to dark green, is of importance because the cotyledons
themselves are always green (with the exception of the off-color "blonds").
2) The thickness of the seedcoat increases the color of cotyledons when the
seedcoats are green and diminishes it when the seedcoats are white and thick.
3) Seedcoat and cotyledon color affect the maintenance of color, which normally
brightens during the freeze-drying process, and also influence the recovery
of shape of freeze-dried peas after rehydration.
Rehydration in boiling water was strongly influenced by the shrinking
of either the cotyledons and/or the seedcoat. The term "quality of green
peas" after freeze-drying reflects a capacity to rehydrate and this is based
on two essential charactistics: 1) rapid swelling of the cotyledons and 2)
good permeability of the seedcoat. Selection against seedcoat splitting
ordinarily is a desirable goal when breeding garden peas for canning or freezing,
but non-split seedcoats do not rehydrate rapidly and thus are undesirable from
the standpoint of breeding for adaptability to freeze-drying. Because of the
highly significant correlation between seedcoat splitting after freeze-drying
and rehydration capacity, it may be necessary to select lines which show seed-
coat splitting to some extent (i.e. clefts from 3 to 1 mm); if not, the seedcoat
must be perforated mechanically.
The structure of the seedcoat of fresh, frozen, and freeze-dried peas
was examined microscopically. The thickness of palisade tissue (macro- and
osteosclereids) was not affected even after preservation and only the parenchyma,
which also determines the thickness of the seedcoat, was influenced by deep-
freezing and freeze-drying. The greater destruction of parenchyma may result
in less seedcoat splitting.
The selection criteria described appear to be heritable characters in
view of the selection results achieved. Genetical analyses have just begun.