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Results and discussion
The investigated traits were generally affected by both nucleus
source and cytoplasm type. The performance of alloplasmic lines of
cv. Chinese Spring and the euplasmic parent (Table
1) reflects the effect of drought and cold stress on the
agronomic characteristics investigated in the study. Alloplasmic
lines with cytoplasm from Aegilops speltoides and Ae.
crassa (6x) had significantly greater yield than the
corresponding euplasmic parent. These higher yields were associated
with a greater cold tolerance and a slightly better resistance to
yellow rust under field conditions. The alloplasmic lines with
cytoplasm of Ae. squarrosa, Ae. uniaristata and Ae
umbellulata exhibited the best tolerance to frost but were
susceptible to yellow rust. Higher grain protein was recorded in
ovata and triuncialis-derived alloplasmic lines but
this was associated with significantly lower kernel weight caused by
moisture stress. On the other hand, the (squarrosa)-CS
line presented a high protein content without a reduction in kernel
weight. These results point to the possibility of improving spring
wheat for certain traits such as frost tolerance, disease resistance
and drought tolerance using cytoplasm from alien species.
Jones Fife (JF) is a winter wheat cultivar that proved better adapted
than Chinese Spring to the relatively cold winter of the testing
environment. All alloplasmic lines of this cultivar were unaffected
by frost (Table 2). Disease infestation was
heavy with a susceptible reaction type on most entries with the
exception of lines with cytoplasm from T. dicoccoides
and Ae. uniaristata. These were also the highest yielding
entries with the first line being significantly better than the
euplasmic line (2611 kg/ha vs 1889 kg/ha). This alloplasmic line also
was the tallest entry in the group, suggesting that taller types may
have an advantage in drought stress-prone areas. Despite the
differences in protein content observed among this group of entries,
no alloplasmic line was better than the euplasmic parent. This
contrasts with other results showing a large increase in protein
content due to incorporation into wheat of nuclear genes from certain
genotypes of T. dicoccoides (Tahir 1983). Although
protein content may be affected by the cytoplasm to some extent, the
trait is primarily controlled by nuclear genes.
Significant differences were observed among the alloplasmic lines of
cv. Zargoon for grain yield and kernel weight. Zargoon (ZR) is an
improved cultivar which explains its relatively high yield under the
testing conditions (Table 3). Only the
alloplasmic (crassa 4x)-ZR line showed a comparable yield
(2667 kg/ha) to that of Zargoon. However, five of the 6 alloplasmic
lines were more tolerant to frost than Zargoon itself, suggesting a
cytoplasmic effect on cold tolerance in wheat. The
sharonensis cytoplasm was associated with less cold tolerance
and an extremely low kernel weight in the alloplasrnic lines of cv.
Chinese Spring and cv. Jones Fife. Kinoshita and Kihara (1983)
reported the pleiotropic effects of ovata cytoplasm for many
kinds of economically important characters. Similarly, in an analysis
of yield components in four wheat lines with the cytoplasm of
Aegilops ovata, Khok and Semerov (1990) found that
(ovata) - Mironovskaya 808 gave the highest yield of 9.36
t/ha, whereas (ovata) - Pavlovka gave the lowest yield (3.97
t/ha) as compared to 5.43 t/ha of euplasmic cv. Mironovskaya 808. The
performance of nucleo-cytoplasmic hybrids (alloplasmic lines) depends
on nucleo- cytoplasmic interaction, environments and degree of seed
set fertility.
The results of this study showed that agronomic traits of wheat grown
under moisture and cold stress are primarily controlled by nuclear
genes and in some cases by the cytoplasm type as well. This is the
case of grain yield, frost tolerance, disease resistance and to some
extent kernel weight and protein content. Furthermore, different
cytoplasms may be advantageous depending on the donor of the nuclear
genes. The dicoccoides cytoplasm was best in combination with
cv. Jones Fife whereas speltoides cytoplasm conferred better
performance under stress when combined with nuclear genes from cv.
Chinese Spring. The crassa cytoplasm seems to have favourable
effect on agronomic traits on all the three nucleus donor varieties
under stress conditions. These studies indicate a great possibility
of advantageous exploitation in breeding program of nucleo-cytplasmic
hybrids by broadening the genetic base of alloplasmic lines by a
large number of genotypes.
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