26. Inheritance of low temperature tolerance at young seedling stage

Hiroko MORISHIMA

National Institute of Genetics, Mishima, 411 Japan

Cultivars of Japonica type are known to be less damaged by a low temperature treatment followed by exposure to high temperatures at the young seedling stage than Indica cultivars (Oka 1958). Strains of the common wild rice (Oryza rufipogon), except for some Chinese ones, are generally more susceptible to this treatment than cultivars.

A population of an upland cultivar (Ch55) collected in Yunnan, China was found to be highly polymorphic for various Indica-Japonica diagnostic characters including the above-mentioned low temperature tolerance (Morishima 1989). To examine the inheritance of these characters, five lines derived from different individuals of the original population were intercrossed, and six F2 populations were studied regarding low temperature tolerance using the method described by Oka (1958). Five to ten progeny seedlings with a 1.0 to 1.5 cm plumule length derived from each F2 plant were kept at 0°-1°C for 4 days and 30°C for the following 3 days. Degree of injury was scored individually into 4 classes, e.g., 0 (resistant) -1-2-3 (susceptible), and the average value was used as the index representing the F2 plant. The result showed that susceptible (S) X resistant (R) crosses segregated into resistant and susceptible plants giving 10R: 54S or 1R: 3S ratios, an S X S cross giving a IR: 15S ratio, and a R X R cross giving a 7R: 9S ratio (Table 1). These results suggest that complementary recessive genes are responsible for cold resistance. Three-locus genotypes of parental lines were tentatively assumed as shown in Table 1. By assuming that when at least two out of three loci carry recessive alleles in homozygous state then the carrier exhibits resistance, the segregation patterns observed in six F2 can be interpreted consistently.

The presently used method is sensitive to a slight fluctuation of experimental conditions, sometimes yielding inconsistent segregation patterns from the same F2 population. This might be partly because gene interactions are affected by environmental conditions. To confirm the genetic basis of this resistance, farther analysis is under way using F3 lines. Low temperature resistance in rice seedlings so far reported were controlled by a single dominant gene (Chuong and Omura 1982; Tajima et al. 1983; Kwak et al. 1984; Nagamine 1991). The low temperature resistance reported in this study seems to be controlled by a different genic system.

Table 1. Frequency distributions of index for low temperature resistance
observed in six F2 populations
==============================================================================
P1XP2                   Resistant<--Index(X10)-->Susceptible
Presumed
genotype       0  2  4  6  8 10 12 14 16 18 20 22 24 26 28 30   X2        P
==============================================================================
5-11x1-3   P1                                1           1
(aBCxAbc)  P2              1                                    4.41
           F2  2  7  4  1  2  3  2 10 24 24 72 14 16  8  8  7 (10:54) .050-.025
               ___________________ __________________________
                        21                    183

5-10x6-11  P1                                2        1  1
(AbCxaBc)  P2           2  1  1                                 0.74   .50-.25
           F2        1  3  1  3  1     2  5  4  3 10  8 12 22 (10:54)
                     _____________     ______________________
                           9                    66

5-10x5-13  P1                                1           1
(AbCxAbC)  P2  1                                                2.22   .25-.10
           F2 13  5  5  6  2  4  7  7 22 25 57  5  9  3  2  2 (1:3)
              _________________  ____________________________
                   35                           139

5-10x1-3   P1                             1              1
(AbCxAbc)  P2  1                                                0.04   .90-.75
           F2 18 15 15  5  8  5  4  6 27 34 60                (1:3)
              ________ _______________________
                 48             149

5-11x5-10  P1                          1     1
(aBCxAbC)  P2                                1                  2.19   .25-.10
           F2 10  5  4       15 10 17 24 41 69  8  6  6  2  2  (1:15)
              ________       ________________________________
                 19                          200

6-11x5-13  P1        1
(aBcxAbc)  P2  1                                                0.01    .90 <
           F2 14  4 17 11 14  4  4  4  1  3  1  1           1  (7:9)
              ________ ______________________________________
                35                    44

References

Chuong, P. V. and T. Omura, 1982. Studies on the chlorosis expressed under low temperature conditions in rice, Oryza sativa L. Bull. Inst. Trop. Agr., Kyushu Univ. 5: 1-58.

Kwak, T. S., B. S. Vergara, J. S. Nanda and W. R. Coffman, 1984. Inheritance of seedling cold tolerance in rice. SABRAO J. 16(2): 83-86.

Nagamine, T., 1991. Genic control of tolerance to chilling injury at seedling stage in rice, Oryza sativa L. Jpn. J. Breed. 41: 35-40.

Morishima, H., 1989. Intra-populational genetic diversity in landraces of rice. Proc. 6th Intern. Congr. SABRAO, Tokyo, p. 159-162.

Oka, H. I., 1958. Intervarietal variation and classification of cultivated rice. Ind. J. Genet. Plant Breed. 18: 79-89.

Tajima, K., A. Amemiya and N. Kabaki, 1983. Physiological study of growth inhibition in rice plant as affected by low temperature, II. Physiological mechanism and varietal difference of chilling injury in rice plant. Bull. Natl. Inst. Agr. Sci. D34: 69-111.