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Results and Discussion
Monthly mean minimum and maximum temperatures along with
ranges during the study period are shown in Table
1. The average temperatures were well above the optimum
temperatures for vegetative and reproductive growth, as
shown by accelerated developmental phases of the tetraploid
and hexaploid genotypes. For example, Mexicali, Anza, and
Yecora Roja, commercial day-length insensitive wheat
cultivars in California, reached the flowering stage 51
days, 51 days, and 41 days after seeding, respectively. All
tetraploid and hexaploid genotypes flowered and produced
seed.
Numbers of dead and live plants and the survival rate for
each Aegilops species are presented in Table
2. The chi2 test for equality of survival
rates was highly significant (chi2 = 27.552, P
< 0.001), indicating large differences among the species
for heat resistance during early stages of growth. However,
when Ae. squarrosa and Ae. speltoides ssp.
ligustica accessions were excluded from the
chi2 analysis, the chi2 value was
insignificant (chi2 = 6.394, 0.10 < P <
0.25), which indicates similarity of survival rates of the
remaining Aegilops species. The survival rates of
Ae. squarrosa and Ae. speltoides ssp.
ligustica were the same, but higher than those of
other groups (Table 2).
The responses of different species to heat stress in the
latter stages of growth were quite different. None of the
plants belonging to Ae. squarrosa, Ae.
speltoides ssp. speltoides, or Ae.
sharonensis which survived heat stress during early
stages of growth produced heads. This could be due to their
vernalization requirements, or to their susceptivility to
heat during reproductive stages. Of 20 Ae. speltoides
ssp. ligustica plants and of 49 Ae. bicornis
plants that survived only 8 and 1 plants, respectively,
produced heads, but none set seeds. In contrast, all plants
from two accessions of Ae. longissima, G1414 and
G1415, and six accessions of Ae. searsii, G1416,
G1417, G1418, G1419, G3069, and G3528, produced seed-bearing
heads, indicating their resistance to heat during both
vegetative and reproductive stages. The mean number of days
from seeding to flowering and the mean of some yield-related
traits for these promising accessions are presented in
Table 3. Considerable variation
was observed for different traits among these heat-resistant
accessions.
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