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Cold resistance evaluation
Wilting degrees of 126 accessions were equal to or lower than that of
cheek Dongfanghong 3 (wilting degree 3). Among them, the CRI of about
86 accessions were equal to or higher than that of cheek Dongfanghong
3 (CRI=1), such as Jinfeng 1, Ji 82-4255, Shi 83-5307 and Tang
85-5032 etc. Twenty-seven accessions have advanced comprehensive
agronomic characteristics, such as Tang 84-6054, Jimai 17, and
Luoting 1840 etc. The CRI of about 59 accessions (wilting degree
equal to or lower than cheeks) were equal to or higher than that of
both Dongfanghong 3 and Taishan 1, such as Tang 85-5032, Shi 81-5090,
Heng 87-6105, Heng 86-5001, Tang 85-6148, Jizi 88-4295, Hebei 1 and
Jizixixuan 3 etc.
There are 16 genotypes with both resistance to cold and drought and
tolerance to salinity, such as Shi 86-8107, Jimai 22, Bao 436 and Shi
86-5031 etc. (Table 2).
The correlations of abiotic stress and other agronomic
characteristics: No any correlation was found between drought
resistance and other characters (Table 3).
That increasing hydraulic resistance in the seminal root can improve
harvest index was first proposed by Passioura (1972). Works
subsequently have shown that this can best be achieved by decreasing
the diameter of the main xylem vessel in the seminal roots (Richards
and Passioura 1981a, b). Richards (1985)
reported that in all environments lines with small xylem
vessels yielded more than lines with larger vessels, and the field
advantage was greatest in the driest environments. Higher yields of
the determinate tillering cereals over conventional type in dry
environments have been found by Donald (1979), Islam and Sedgley
(1981) and Richards (1983). Lupton (1987) reported if drought occurs
before flowering, the lines with floppy leaves may be drought
resistant, and if drought occurs after flowering the lines with erect
leaves may be drought resistant.
No any correlation existed between salinity tolerance and other
characters. Jones (1981) reported that salinity resistance
conditioned by osmoregulation is often recognized by the "succulent"
appearance of the plant. Blum (1988) stated seeds germination in
saline media is often used as a singular criterion for salinity
resistance or in combination with other criteria. The rate of
surviving plants associated with salinity tolerance in salt stress
conditions (Dewey 1962). In all the reports we know there is no
correlation between drought resistance and salinity tolerance.
There is a significantly negative correlation between wilting degree
and plant height in coldness condition. It means that the higher the
plant is, the lower the wilting degree of the plant is, or the more
cold resistant the plant is. Also there is significantly positive
correlation between wilting degree and spikelets per spike,
net-spikelets per spike and 1000-grain weight. No any correlation was
found between cold resistance and other characters (Table
3). Blum (1988) reported that both tissue-water content and plant
erectness were highly and negatively correlated with field winter
survival index. Dexter et al. (1932) reported that the rate of
leakage of electrolytes from plant tissues after a freezing stress
was indicated as a potential criterion for freezing tolerance (Quamme
1982). Leakage is considered to be proportional to the rate of damage
in living cells. The rate of accumulation of sugar in the hardened
tissues was often correlated (Rajki 1972) with survival after
freezing. Gusta et al. (1983) found that a moderate correlation
between osmotic potential and winter survival in wheat. Whether
osmotic adjustment is evaluated by chemical or psychrometric method
it can evidently be evaluated only in a limited number of samples out
of the whole population. So, we consider the best selection criteria
is the rate of winter survival in the field or CRI mentioned
above.
Acknowledgments
The authors are grateful to Mr. Hu Fushun, Mr. Qiao Shiyuan, Ms. Lu
Li and Mr. Zhang Xianying for the help in resistance evaluation.
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