Agriculture Reference
In-Depth Information
flooding if appropriate tolerant rootstocks are used. Grafting of eggplants
was started in the 1950s, followed by grafting of cucumbers and tomatoes
in the 1960s and 1970s (Edelstein, 2004). Romero et al.
(1997) reported
that melons grafted onto hybrid squash rootstocks were more salt toler-
ant than the nongrafted melons. However, tolerance to salt by rootstocks
varies greatly among species, such that rootstocks from
Cucurbita
spp.
are more tolerant of salt than rootstocks from
Lagenaria siceraria
(Mat-
subara, 1989). Grafted plants were also more able to tolerate low soil tem-
peratures.
Solanum lycopersicum
x
S. habrochaites
rootstocks provide tol-
erance of low soil temperatures (10 °C to 13 °C) for their grafted tomato
scions, while eggplants grafted can be grafted on wild brinjal (
S. integri-
folium)
as rootstocks to overcome low temperature (18 °C to 21 °C). Most
of the vegetables are unable to tolerate excessive soil moisture. Tomatoes
in particular are considered to be one of the vegetable crops most sensi-
tive to excess water. Until now, genetic variability for tolerance of excess
soil moisture is limited or inadequate to prevent losses. Many accessions
of eggplant are highly tolerant of flooding (Midmore et al.,
1997), thus,
can be grafted to improve the flood tolerance of tomato using eggplant
rootstocks which were identified with good grafting compatibility with
tomato and high tolerance to excess soil moisture. In addition to protec-
tion against flooding, some eggplant genotypes are drought tolerant and
eggplant rootstocks can therefore provide protection against limited soil
moisture stress.
8.4.2 DEVELOPMENT OF STRESS TOLERANT VARIETIES
8.4.2.1. HEAT AND COLD TOLERANT GENOTYPES
Till today,
s
everal heat tolerance genotypes have been developed in veg-
etables particularly in tomato
.
AVRDC, Taiwan has made significant con-
tributions to the development of heat-tolerant tomato and Chinese cabbage
lines (
Brassica rapa
subsp.
pekinensis
and
chinenesis
) adapted to hot and
humid climate. The key to achieving high yields with heat tolerant culti-
vars is the broadening of their genetic base through crosses between heat
tolerant tropical lines and disease resistant temperate or winter varieties
(Opena and Lo, 1981). The heat tolerant tomato lines were developed us-
ing heat tolerant breeding lines and landraces from the Philippines (e.g.,
