International Journal of Horticulture 2015, Vol.5, No.12, 1
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RAPD (Williams et al., 1990). RAPD is easy and cheap,
with no need for DNA probes or sequence information
for primer design, very small amounts of DNA (10 ng
per reaction) are required, and the procedure is
automatable.
Various DNA-sequence polymorphisms have been
employed to examine genetic relationships among
Cucurbita pepo
accessions with high precision.
Allozyme polymorphisms revealed a primary division
within
C. pepo
into three subspecies (Decker 1985,
1988). The polymorphism of
Cucurbita pepo
for fruit
shape led to the proposal that this species having eight
edible-fruited groups of cultivars (Paris, 1986).
Accordingly, these are Acorn, Scallop, Crookneck,
Straightneck, Pumpkin, Vegetable Marrow, Cocozelle
and Zucchini. The first four cultivar-groups are in
C.
pepo
subsp. texana and the last four are in
C. pepo
subsp.
pepo
(Paris et al., 2003).
The germplasm pool of the genus
Cucurbita
is
characterized by abundant diversity (Diez et al., 2002).
The enormous morphological diversity of the cultivated
races of squash has resulted from variable climate and
geographical exposure in which its wild ancestors
evolved, coupled with selection pressure (Lira Saade,
and Montes Hernandez, 1994). Many sources of
exotic and unique germplasm have been discovered
and utilized over the years for squash improvement
(Paris and Brown, 2005). Traits such as yield, disease
resistance, fruit quality have been found and incorporated
into current germplasm and have resulted in large
improvements in the crop. During the past few
decades, enormous effort has been made toward
collecting, preserving, and understanding squash
germplasm. The most important centers of squash
germplasm include National Plant Germplasm System
(NPGS), USAand The World Vegetable Center (AVRDC),
Taiwan. Genetic stocks consisting of accessions identified
as source of resistance to major disease, insect pests,
as well as morphological, agronomic characteristics.
Cucurbita
is a New World genus of about 20 species;
they have been and remain important in diets of world
populations ranging from the tropics to warm, temperate
regions. Cultivation of the domesticated
Cucurbita
species has spread beyond their new world origin.
Three
Cucurbita
species,
C. pepo
,
C. moschata
,
C.
maxima
comprise the principal cultivated squash
and/or pumpkin crops. Both mature and immature fruit
are the most important edible plant parts, although for
some species; seeds, flowers, roots and even leaves are
consumed.
Cucurbita pepo
L. is believed to be the oldest
of the domesticated species. In addition,
Cucurbita pepo
L.
is the most diverse
Cucurbita
species, has slightly more
cold temperature tolerance than other related species
(Rubatzky and Yamaguchi, 1997).
Summer Squash (
Cucurbita pepo
L.) is the most
important
Cucurbita
species, have a mild flavor; eaten
raw or cooked and have a short storage life compared
to the strongly flavored winter squash. In contrast to
summer squash, the postharvest life of winter squashes
and pumpkins is much longer and the fruit are not
eaten raw. Roasted seeds of some species are a
favorite and highly nutritious food.
Fruit quality may include; color, size, firmness, S.S.C.,
and nutritional value which involve the content of
various phytochemicals and vitamins. Ascorbic acid
(vitamin C) is one of the most important nutritional
quality factors in many horticultural crops and has
many biological activities in the human body. More
than 90% of the vitamin C in human diets is supplied
by fruits and vegetables (Lee and Kader, 2000). The
content of vitamin C in fruits and vegetables can be
influenced by various factors such as genotypic
differences.
The objectives of current investigation were the
characterization and analysis of genetic diversity among
squash accessions. In addition, the genetic relationship
among those accessions and landraces of squash was
studied.
Materials and Methods
Plant material
A total of 14 [thirteen summer, spaghetti and acorn
squash (
Cucurbita pepo
L.) and one winter squash
(
Cucurbita moschata
L.)] germplasm collections were
analyzed in this study. Eight genotypes were obtained
from National Plant Germplasm System (NPGS), USA.
Three genotypes were supplied from commercial sources.
Three genotypes were obtained from local sources. Names,
source, origin and type of all genotypes are presented in
Table (1).
Morphological and chemical evaluation
A Field experiment was conducted at the Experimental
Research Farm, Faculty of Agriculture, Suez Canal
University, Ismailia, Egypt. The experiment was carried
