28. Genetics of leaf rolling under vegetative stage drought stress

B. N. SINGH and D. J. MACKILL

International Rice Research Institute, P.O. Box 933, Manila, Philippines

Leaf rolling is one of the drought avoidance mechanisms to prevent water deficits during drought stress (O'Toole and Change 1978). Loresto et al. (1976), Loresto and Chang (1981) and Chang and Loresto (1986) have suggested leaf rolling as a criterion for scoring drought tolerance in tall and semidwarf rice cultivars. Varietal difference in leaf rolling and unrolling have been observed and it is correlated with internal water status of the leaf tissue. lt is also related with the stomatal closure and decreases transpiration from rice leaves (O'Toole et al. 1979). Degree of leaf rolling during water stress shows diurnal variation and is maximum at 1300 hr.,; (O'Toole 1982). Leaf rolling is induced by the loss of turgor and poor osmotic adjustment (Hsiao et al. 1984). Delayed leaf rolling in an indication of turoor maintenance and a component of dehydration avoidance (Blum 1989).

Genetics of leaf rolling was studied in crosses of five drought resistant and two susceptible parents differing in their leaf rolling behavior during 1989 dry season (February to April) at IRRI in upland condition. The resistant parents were Salumpikit, MGL2, ITA 186, IR33353-64-1-2-1, and IR26702-155-2-3 and the susceptible parents were IR29725-22-3-3-3 and JR29692-65-2-3 (Table 1).Parents, F2 and F3 lines from 10 crosses were grown in Randomized Complete 

Table 1. Description of lines used for genetic study.
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Designation    Parentage          Origin         Plant Type
________________________________________________________________
Salumpikit     Land race          Philippines    Tall
IR33353-64-1-2-1 IR52/IR36//IR52  IRRI           Intermediate
MGL 2          Land race          India          Tall
ITA 186        Moroberekan/       IITA, Nigeria  Tall
               Juma 1/TOX7-3-2-3-2//
               SE 363G
IR26702-155-2-3 FR13A/IR48//IR42  IRRI           Semidwarf
IR29692-65-2-3  IR1794-32-3-1-1-3// IRRI         Intermediate
                IR9129-209-2-2-2-1
IR29725-22-3-3-3 IR19661-131-1-2/ IRRI           Semidwarf
                 IR9129-209-2-2-2-1
IR20(check)
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Block Design in four replications. Twenty F3 lines were randomized in each replication and a total of 80 F3 lines were undertaken for testing. Ten gram seeds of each line were dry seeded in 2.5 m long rows spaced 30 cm apart. Seeding was done in upland granular Maahas clay soil on February 2 and 3, 1989. Salumpikit and IR20 were put together as checks after each replication to compare the replication differences. Sprinkler irrigation was used after seeding at every 4 days until 30 days after seedling emergence and then the irrigation was stopped. Soil moisture status was monitored using tensiometers and gravimetric method. Rainless period occurred in April and leaf rolling was observed as first symptom of moisture stress. IR20 (check) and IR29725-22-3-3-3 first showed the rolling around 0.1 to 0. 2 MPa soil moisture tension (SMT) followed by IR29692-65-2-3 between 0.2 to 0.5 MPa. Among the resistant lines IR26702-155-2-3, ITA186 and MGL2 rolled between 0.5 to 1.0 MPa, IR33353-64-1-2-1 after 1.0 MPa SMT and Salumpikit did not show any symptoms even 5 days after 1.0 MPa SMT of drought stress. Rolling and unrolling did not change between 0900 to 1600 hrs. in dry season as stress beyond 1.0 MPa increased. Observations were recorded when susceptible parent showed rolled leaf in different replications and in different crosses.

In analyzing the F2 segregation pattern, out of 10 crosses, 3 showed goodness of fit for 3 rolled and 1 nonrolled (Table 2). All the F3 segregation of over 70

Table 2. Reaction of F2 population and F3 families for leaf 
         rolling unrolling
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                   F2 Segregation    Reaction of F3 Families
Parent/Cross       ________________   __________________________
              Rolled Unrolled P(3:1) Rolled Segre  Unrolled P(1:2:1)
                                             gating
________________________________________________________________
IR33353/IR29692    415  199  <0.01       20       32   23  0.40
IR33353/IR29725    771  280  0.23        19       37   19  0.99
IR26702/IR29692    605  251  <0.01       17       35   18  0.99
IR26702/29725      899  294  0.80        20       35   24  0.49
ITA186/IR29692     621  212  0.79        19       38   16  0.82
ITA186/IR29725     777  215  0.02        18       42   17  0.72
IR29692/Salumpikit 246  147  <0.01       16       31   17  0.95
IR29725/Salumpikit 319  161  <0.01       18       35   16  0.94
IR29692/MGL 2      688  282  <0.01       20       39   19  0.99
IR29725/MGL 2      393  282  <0.01       15       37   24  0.34
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lines in each cross showed a ratio of 1 homozygous resistant: 2 segregating and 1 homozygous susceptible with probability level of 0.34 to 0.99. The segregating F3 lines in 71 percent cases segregated in 3 rolled and 1 unrolled types (Table 3). Replication differences were observed in different F2 populations of the crosses, which might be due to micro-plot soil moisture variation. Some other possible reasons for sgregation distortion in F2 could be due to sterility on F1 plants, in

Table 3.Frequency distribution of percent unrolled plants in 
        segregating F3 families of different crosses
________________________________________________________________
Percent       Number of Segregating Liens in Different Crosses
Rolled  __________________________________________________ 
Plants IR33353/ IR33353 IR26702/ IR26702/ ITA186/ ITA186/ 
(Range)IR29692  IR29725 IR29692  IR29725  IR29692 IR29725 
________________________________________________________________
10-15       0        0       0        0        6       1 
16-20       4        1       2        4        5       1  
21-25       6        5      10       11       11      15 
26-30       5        4      12       12        8      10 
31-35       1       14       8        2        5      10   
36-40       1        5       1        3        2       2 
41-45       0        2       2        1        0       3 
46-50       2        2       0        0        1       0 
51-55       2        2       0        1        0       0 
56-60       2        1       0        1        0       0 
61-65       3        0       0        0        0       0 
66-70       1        1       0        0        0       0 
71-75       4        0       0        0        0       0 
76-80       1        0       0        0        0       0 
81-85       0        0       0        0        0       0 
________________________________________________________________
Total segre-
gating lines 32     37      35       35       38      42      

________________________________________________________________
Percent       Number of Segregating Liens in Different Crosses
Rolled  __________________________________________________ 
Plan                                                  Total 
(Range)           IR29692 IR29692/ IR29692  IR29725   Lines
               Salumpikit Salumpikit NGL2    MGL2
________________________________________________________________
10-15                0        3        2       0       13 
16-20                0        6        2       0       25  
21-25               10        4       13       2       87  
26-30               11        5       13       4       84  
31-35                5        6        5       7       63  
36-40                3        3        4       6       30  
41-45                1        4        0       3       16  
46-50                0        2        0       2        9  
51-55                1        1        0       0        7  
56-60                0        1        0       2        7  
61-65                0        0        0       3        6  
66-70                0        0        0       4        6  
71-75                0        0        0       1        5  
76-80                0        0        0       2        3  
81-85                0        0        0       1        1  
________________________________________________________________
Total segre-
gating lines        31       35       39      37      362
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crosses with MGL2, ITA186 and Salunipikit with susceptible parents; smaller F2 population in crosses with Salumpikit due to poor germination and occurrance of 3 to 10 percent resistant plants in two susceptible parents.

A new gene symbol of Ir is being proposed for leaf unrolling under water deficits.

References

Blum, A., 1988. Drought resistance. In Plant Breeding for Stress Environments. p. 43-77.

Chang, T. T. and G. C. Loresto, 1986. Screening techniques for drought resistance in rice. p. 108-129. In Approaches for incorporating drought and salinity resistance in crop plants. Ed. V. L. Chopra and R. S. Paroda. Oxford IBH, New Delhi.

Hsiao, T. C., J. C. O'Toole, E. B. Yambao and N. C. Turner, 1984. Influence of osmotic adjustment on leaf rolling and tissue death in rice. Plant Physiol. 75: 328.

Loresto, G. C., T. T. Chang and 0. Tagumpay, 1976. Field evaluation and breeding for drought resistance. Phil. Jour. Sci. 1: 36-39.

_____ and T. T. Chang, 1981. Decimal scoring systems for drought reaction and recovery ability in rice screening nurseries. Inter. Rice Res. Newsletter 6(2): 9-10.

O'Toole, J. C., 1982. Adaptation of rice to drought prone environments. p. 195-213. In Drought resistance in crops with emphasis on rice. International Rice Research Institute, P.O. Box 933, Manila, Philippines.

____ and T. T. Chang, 1978. Drought and rice improvement in perspective. IRRI Research Paper Series, No. 14. International Rice Research Institute.

____ and R. T. Cruz, 1979. Response of leaf water potential, stomatal resistance, and leaf rolling to water stress. Plant Physiol. 64: 628.

____, _____ and T. N. Singh, 1979. Leaf rolling and transpiration. Plant Sci. Lett. 16: 111-114.