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Recovery from drought-induced desiccation at the vegetative growth stage in direct-seeded rainfed rice
105
Field Crops Research, 10 (1985) 105--112 Elsevier Science Publishers B.V., Amsterdam - - P r i n t e d in The Netherlands
RECOVERY FROM DROUGHT-INDUCED DESICCATION AT THE VEGETATIVE GROWTH STAGE IN DIRECT-SEEDED RAINFED RICE
J.A. MALABUYOC, E.L. ARAGON and S.K. DE DATTA
The International Rice Research Institute, P.O. Box 933, Manila (Philippines) (Accepted 10 September 1984)
ABSTRACT
Malabuyoc, J.A., Aragon, E.L. and De Datta, S.K., 1985. Recovery from drought-induced desiccation at the vegetative growth stage in direct-seeded rainfed rice. Field Crops Res., 10: 105--112. Prolonged soil moisture stress causes desiccation o f leaf and other plant parts of most cultivated annual crops. The ability to recover from desiccation during vegetative growth is important to the productive capacity o f rice. A study conducted in the 1981 and 1982 dry seasons showed that after 36 days o f imposed drought, soil moisture tension (SMT) at 20-cm depth reached 10 bars in Maahas clay soil (Andaqueptic Haplaquolls). A t that SMT, drought-susceptible rice lines were desiccated and drought-tolerant varieties averaged 50% dead leaves. Seven days after sprinkler-irrigation to relieve soil moisture stress, the desiccated rice lines did not show recovery hut stand recovery in those with partial leaf drying was up to 100%. A significant relationship between drought tolerance, as indicated by degree o f desiccation, and percentage recovery was observed. Results suggest that farmers in rainfed areas should grow drought-tolerant modern rice lines with good recovery ability. During dry spells, the visual degree o f desiccation at the vegetative growth stage permits the farmer to estimate potential plant recovery upon relief o f soil moisture stress.
INTRODUCTION
Available soil moisture often determines rainfed rice production. Thirty days without rain, as in Cuenca, Batangas, Philippines, in the 1974 wet season (IRRI, 1975), can cause crop failure. Prolonged dry spells stop plant growth, and cause desication and, ultimately, tissue death (Kramer, 1969). Plants differ considerably in the ability to tolerate desiccation (Begg and Turner, 1976). Blum (1982) cited reports on varying leaf water potential maintenance among varieties or strains of different crop species under moisture stress. O'Toole and Moya (1978) reported differences in leaf water potential up to 6 bars at dawn and 14 bars at midday between droughttolerant and susceptible rice cultivars, after 31 days of imposed soil moisture stress.
0378-4290/85/$03.30
© 1985 Elsevier Science Publishers B.V.
106
Recovery ability after drought stress is an important determinant of grain yield (Chang et al., 1974; De Datta et al., 1975). Drought recovery ability can be more important than drought tolerance (Sarkar and De Datta, 1975). An earlier attempt to relate drought tolerance and recovery in rice was made in pot experiments using Mimosa pudica L. as the indicator plant (IRRI, 1971). When the soil had dried to 13% moisture, when mimosa plants no longer responded to mechanical stimuli, all plants were rewatered. Mimosa plants recovered fully. Rice varietal reaction ranged from full recovery to death. Chang et al. (1972) concluded from results of that study that drought tolerance and drought recovery ability are unrelated. Our field study sought to determine the relationship between tolerance to severe drought at vegetative stage and drought recovery ability when soil moisture becomes available. The study was conducted at IRRI in the 1981 and 1982 dry seasons on a Maahas clay soil (Andaqueptic Haplaquolls). MATERIALS AND METHODS
We used four rice lines with different reactions to soil moisture stress: (1) Salumpikit, a drought-tolerant tall Philippine traditional variety; (2) IR442-2-58, a moderately tolerant semidwarf breeding line; (3) IR20, a drought-susceptible lowland semidwarf variety; and (4) IRAT 9, an intermediate-statured drought-susceptible accession from the Ivory Coast. These varieties and line were checks in the IRRI field drought screening test (Malabuyoc et al., 1980). Plots of each check variety and line planted with every 46 drought screening entries and each of the 4240 and 3507 entries, in 1981 and 1982, respectively, represented individual units of observation. Rice seeds were hand-drilled on dry granular soil in January 1981 and 1982, then sprinkler-irrigated twice weekly until 30 days after rice emergence. Ammonium sulfate at 60 kg N/ha was applied in equal splits 10 and 20 days after germination. TABLE I S t a n d a r d E v a l u a t i o n S y s t e m for R i c e ( I R R I , 1 9 8 0 ) Scale
Drought tolerance
R e c o v e r y ability
0 1
N o visible e f f e c t Slight leaf tip d r y i n g
5
25 - - 50% leaves fully d r i e d
9
All p l a n t s a p p a r e n t l y d e a d
--9 0 - - 1 0 0 % plant recovered 4 0 - - 60% p l a n t s recovered 0 - - 19% p l a n t s
recovered
107
Soil was allowed to dry naturally. Soil moisture status at 20-cm depth was monitored using the gravimetric and tensiometric methods. Drought tolerance at vegetative stage was scored as leaf drying percent at 10 bars soil moisture tension (SMT). After scoring, the field was sprinkler-irrigated twice and drought recovery ability was recorded 7 days after the first irrigation. Drought tolerance and recovery ability was judged by the Standard Evaluation System for Rice (IRRI, 1980) (Table I). The desorption curve o f disturbed soil at 20-cm soil depth (Fig. 1) was determined using 5- and 15-bar pressure plate extractors. Simple linear correlation analyses between drought tolerance and recovery for each o f the four rice lines and all drought test entries were done. Soil moisture content (% by wt) 80
70
60
50
40
x,.__
30-
20-
1oi-
o
l 2
I I I I 4 6 8 10 Soil moisture tension (bors)
I 12
14
Fig. 1. Desorption curve for Maahas clay soil (Andaqueptic Haplaquolls) in a field drought
screening site (IRRI, 1979 dry season). RESULTS AND DISCUSSION
Buildup o f soil moisture stress SMT increase from 0 to 1 bar was gradual and was reached 21 days after imposed drought in 1981 and 24 days after imposed drought in 1982. In-
Character
IRAT 9 (Susceptible variety) D e s i c c a t i o n score Recovery score IR20 (Susceptible variety) Desiccation score Recovery score I R 4 4 2 - 2 - 5 8 ( T o l e r a n t line) D e s i c c a t i o n score Re c o v e r y s core Salumpikit (Tolerant variety) D e s i c c a t i o n score Recovery score
Variety/Line
0 0
0 0
0 2
5
0 4
6
0 9
7
8
9
97
99
103
96
0 4
0 5
0 0
0 0
0 30
0 11
0 0
4 45
0 46
0 2
28 14
4 24
0 20
49 3
10 9
1 63
10 0
39 3
0 18
3 1
45 1
41 4
8 44
2 0
1 0
58 2
61 33
1 0
0 0
3 0
27 4
98
94
88
101
n
4
n
3
1982
1981 12
Score frequency distribution
0 0
0 0
0 13
0 25
1
0 2
0 1
0 2
8 72
0 0 1 57
0 0
0 0
23
1 0
0 0
0 0
31 0
4
0 2
51 10
7 10
0 53
5
1 2
1 0
6 0
46 0
6
1 1
1 0
40 1
40 31
7
0 0
0 0
44 0
34 1
8
1 1
0 0
3 0
65 96
9
F r e q u e n c y d i s t r i b u t i o n o f d e s i c c a t i o n a n d r e c o v e r y scores o f t w o d r o u g h t s u s c e p t i b l e rice varieties, a d r o u g h t t o l e r a n t line, and a d r o u g h t t o l e r a n t variety ( I R R I , 1981 a n d 1 9 8 2 d r y seasons)
T A B L E II
b~ 00
109
crease from 1 to 10 bars was rapid, 15 days in 1981 and 21 days in 1982 (Fig. 2). Slower SMT buildup in 1982 was caused b y a March t y p h o o n which dropped 22 mm of rain at the experimental site.
Soilmoisturetension(bars) 10
0
o 1981
10
J
20 50 40 Soil moisturestressdays
~
•
50
60
Fig. 2. Buildup of soil moisture tension relative to days from start of soil moisture stress (IRRI, 1981 and 1982 dry seasons).
Rice response to 10 bars S M T Of the 96 plots planted to IRAT 9 in 1981, plants in 27 plots were desiccated and two-thirds or more of the leaves in 69 other plots had dried at 10 bars SMT (Table II). In 1982, 65 of 101 I R A T 9 plots had all apparently dead plants. In both years, more than two-thirds of leaves in all IR20 plots were desiccated at 10 bars SMT. Moderately drought-tolerant IR442-2-58 had from one-half to two-thirds desiccated leaves and tolerant Salumpikit had about 50% dead leaves. Sullivan (1971) suggested 50% kill point as an indication of drought tolerance. Our results confirmed those of earlier drought studies with the four rices (IRRI, 1974; Yoshida et al., 1974; Malabuyoc et al., 1980). Drought recovery ability Seven days after soil moisture stress was relieved, the four rice lines exhibited varying degrees of recovery. In 1981, IRAT 9 had some plots with up to 40% recovery. However, one-third of the plots had less than 20% recovery. In 1982, I R A T 9 died in most plots (Table II). Four-fifths o f IR20 plots had 40 -- 70% stand recovery in 1981, but only two-thirds had similar recovery in 1982.
110
In 1982, when it took longer to reach 10 bars SMT, drought recovery was less for IRAT 9 and IR20. Duration of water stress was related to crop yield by Begg and Turner (1976) and O'Toole and Moya (1981). Our results suggest that poor recovery from severe soil moisture stress could be a major cause of reduced grain yield. IR442-2-58 and Salumpikit had similar 70 to 100% drought recovery (Table II), but Salumpikit scored better than IR442-2-58. On average, IR442-2-58 and other semi-dwarfs had excellent drought recovery capability, while traditional upland genotypes (of which Salumpikit is one), had poor recovery (De Datta et al., 1975). The higher drought tolerance allowed Salumpikit to have an equally excellent recovery stand.
Relationship between drought tolerance and recovery ability There was significant correlation between drought tolerance and recovery scores for each rice tested each year (Figs. 3 and 4), and the relationship between drought and recovery scores of all drought test entries was likewise significant. Recovery score 9 IRAT9
8 7
+o.785x
J
r= ( n =96)
6
/ t
IR20 ,~,s ~ = 14- Q594X ,- s r = 0.42 "----s " (n=105)
5 4 -E41 I
I
I
I
I
l
Other rices o1+o.748x
IR442-2-58 y =l + 0 . 7 5 0 X r = 0.49~K'~J A
~, ~ " ""
i1 5
7
~"
Solurnpi'kit ~ = 0.44 * ~ (n = 9 7 )
I
I
I
I
I
4
5
6
7
8
9
I
I
I
I
I
I
3
4
5
6
7
8
9
Drought score
Fig. 3. Relationship between drought tolerance in rice and recovery ability as measured by visual scoring using the 1980 Standard Evaluation System for Rice (IRRI, 1981 dry season).
111
The relatively low but significant r-values were because recovery varied more than drought scores (Figs. 3 and 4), a result of different soil drying rates in the field (Supapoj et al., 1982). Plants located in faster soil drying field spots were exposed to longer stress periods. Their recovery was less even if the drought score was similar. Recovery score 9 IRAT9
/
8
~ : ~+o 389x
7
r = 026 *~ - - ~ - ~ ~ (n = 101 )
6
IR20 -----._.____ , , , , , ~ , " ~ " ~ " = 5+0.590X " " r : 0.22* m (n:88)
5 4 5
I
_ -
I
I
Salumpikit }= O+ 0.697X r = 054-** (n:97) ~ j ~ I
,,¢
1
I
t
Other rices ~= -17+1.029X
/ /
,/ IR442-2-58
j~,)=o+o.464x /
41 I 3
I
I 4
I 5
r = 0.24* (n:94) I I I 6 7 8
i
-..41 I 3 Drought score
I 4
I 5
I 6
I 7
I 8
9
F i g . 4 . Relationship between drought tolerance in rice and recovery ability as measured by visual scoring using the 1980 Standard Evaluation System for Rice (IRRI, 1982 dry season).
CONCLUSIONS
Results from this study justify the use of visual scoring in field screening rice for drought tolerance and recovery ability. Thousands of rice lines can be evaluated at one time using visual scoring, which is impossible with the tissue water status measurements screening technique (Kramer, 1969; Sullivan, 1971). O'Toole and Moya (1978) reported a positive relationship between visual scoring based on leaf drying and maintainance of high leaf water potential. The positive relationship between drought tolerance and recovery ability
112
means that the degree of desiccation during a dry spell would help rice farmers predict stand potential when rains resume. Results further suggest the importance of growing drought-tolerant modern rices with good recovery ability to minimize hazards of total crop failure in rainfed rice.
REFERENCES Begg, J.E. and Turner, N.C., 1976. Crop water deficits. Adv. Agron., 28: 101--217. Blum, A., 1982. Evidence for genetic variability in drought resistance and its implications in plant breeding. In: Drought Resistance in Crops with Emphasis on Rice. International Rice Research Institute, Los Ba~os, Philippines, pp. 53--68. Chang, T.T., Loresto, G.C. and Tagumpay, O., 1972. Agronomic and growth characteristics of upland and lowland rice varieties. In: Rice Breeding. International Rice Research Institute, Los Ba~os, Philippines, pp. 645--661. Chang, T.T., Loresto, G.C. and Tagumpay, O., 1974. Screening rice germplasm for drough~ resistance. SABRAO J. 6: 9--16. De Datta, S.K., Chang, T.T. and Yoshida, S., 1975. Drought tolerance in upland rice. In: Major Research in Upland Rice. International Rice Research Institute, Los Ba~os, Philippines, pp. 101--116. I R R I (International Rice Research Institute), 1971. Annual Report for 1970. Los Ba~os, Philippines, 265 pp. IRRI (International Rice Research Institute), 1974. Annual Report for 1973. Los Bafios, Philippines, 264 pp. I R R I (International Rice Research Institute), 1975. Annual Report for 1974. Los Ba~os, Philippines, 384 pp. IRRI (International Rice Research Institute), 1980. Standard Evaluation System for Rice. Second edn. Los Ba~os, Philippines, 44 pp. Kramer, P.J., 1969. Plant and Soil Water Relationships: A Modern Synthesis. Tata McGraw-Hill Publ. Co. New Delhi, 482 pp. Malabuyoc, J.A., Aragon, E.L. and De Datta, S.K., 1980. A Field Screening Technique for Evaluating Rices for Drought Tolerance. Paper presented at the l l t h Annual Meeting of Crop Science Society of the Philippines, 27--29 April 1980, Baybay, Leyte, Philippines. O'Toole, J.C. and Moya, T.B., 1978. Genotypic variation in maintainance of leaf water potential in rice. Crop. Sci., 18: 873--876. O'Toole, J.C. and Moya, T.B., 1981. Water deficits and yield in upland rice. Field Crops Res., 4: 247--259. Sarkar, J.P. and De Datta, S.K., 1975. Drought Tolerance in Rice: Screening Technique and Selection Criteria. I R R I Saturday seminar, 18 August 1975, Los Ba~os, Philippines. Sullivan, S.Y., 1971. Techniques for measuring plant drought stress. In: K.L. Larson and J.D. Eastin (Editors), Drought Injury and Resistance in Crops. Crop Sci. Soc. Am., Madison, WI 53711, pp. 1--18. Supapoj, N., Boonwite, C., O~roole, J.C., De Datta, S.K. and Jackson, B2., 1982. Using check varieties to adjust visual scores for non-uniform soil drying in drought resistance field screening. Int. Rice Res. Newsl., 7(4): 12. Yoshida, S., Shioya, M., De Los Reyes, E., Coronel, V. and Parao, F.T., 1974. Physiological Basis and Technique for Screening for Drought Resistance. I R R I Saturday Seminar. 16 March 1974, Los Bathos, Philippines.
Field Crops Research, 10 (1985) 105--112 Elsevier Science Publishers B.V., Amsterdam - - P r i n t e d in The Netherlands
RECOVERY FROM DROUGHT-INDUCED DESICCATION AT THE VEGETATIVE GROWTH STAGE IN DIRECT-SEEDED RAINFED RICE
J.A. MALABUYOC, E.L. ARAGON and S.K. DE DATTA
The International Rice Research Institute, P.O. Box 933, Manila (Philippines) (Accepted 10 September 1984)
ABSTRACT
Malabuyoc, J.A., Aragon, E.L. and De Datta, S.K., 1985. Recovery from drought-induced desiccation at the vegetative growth stage in direct-seeded rainfed rice. Field Crops Res., 10: 105--112. Prolonged soil moisture stress causes desiccation o f leaf and other plant parts of most cultivated annual crops. The ability to recover from desiccation during vegetative growth is important to the productive capacity o f rice. A study conducted in the 1981 and 1982 dry seasons showed that after 36 days o f imposed drought, soil moisture tension (SMT) at 20-cm depth reached 10 bars in Maahas clay soil (Andaqueptic Haplaquolls). A t that SMT, drought-susceptible rice lines were desiccated and drought-tolerant varieties averaged 50% dead leaves. Seven days after sprinkler-irrigation to relieve soil moisture stress, the desiccated rice lines did not show recovery hut stand recovery in those with partial leaf drying was up to 100%. A significant relationship between drought tolerance, as indicated by degree o f desiccation, and percentage recovery was observed. Results suggest that farmers in rainfed areas should grow drought-tolerant modern rice lines with good recovery ability. During dry spells, the visual degree o f desiccation at the vegetative growth stage permits the farmer to estimate potential plant recovery upon relief o f soil moisture stress.
INTRODUCTION
Available soil moisture often determines rainfed rice production. Thirty days without rain, as in Cuenca, Batangas, Philippines, in the 1974 wet season (IRRI, 1975), can cause crop failure. Prolonged dry spells stop plant growth, and cause desication and, ultimately, tissue death (Kramer, 1969). Plants differ considerably in the ability to tolerate desiccation (Begg and Turner, 1976). Blum (1982) cited reports on varying leaf water potential maintenance among varieties or strains of different crop species under moisture stress. O'Toole and Moya (1978) reported differences in leaf water potential up to 6 bars at dawn and 14 bars at midday between droughttolerant and susceptible rice cultivars, after 31 days of imposed soil moisture stress.
0378-4290/85/$03.30
© 1985 Elsevier Science Publishers B.V.
106
Recovery ability after drought stress is an important determinant of grain yield (Chang et al., 1974; De Datta et al., 1975). Drought recovery ability can be more important than drought tolerance (Sarkar and De Datta, 1975). An earlier attempt to relate drought tolerance and recovery in rice was made in pot experiments using Mimosa pudica L. as the indicator plant (IRRI, 1971). When the soil had dried to 13% moisture, when mimosa plants no longer responded to mechanical stimuli, all plants were rewatered. Mimosa plants recovered fully. Rice varietal reaction ranged from full recovery to death. Chang et al. (1972) concluded from results of that study that drought tolerance and drought recovery ability are unrelated. Our field study sought to determine the relationship between tolerance to severe drought at vegetative stage and drought recovery ability when soil moisture becomes available. The study was conducted at IRRI in the 1981 and 1982 dry seasons on a Maahas clay soil (Andaqueptic Haplaquolls). MATERIALS AND METHODS
We used four rice lines with different reactions to soil moisture stress: (1) Salumpikit, a drought-tolerant tall Philippine traditional variety; (2) IR442-2-58, a moderately tolerant semidwarf breeding line; (3) IR20, a drought-susceptible lowland semidwarf variety; and (4) IRAT 9, an intermediate-statured drought-susceptible accession from the Ivory Coast. These varieties and line were checks in the IRRI field drought screening test (Malabuyoc et al., 1980). Plots of each check variety and line planted with every 46 drought screening entries and each of the 4240 and 3507 entries, in 1981 and 1982, respectively, represented individual units of observation. Rice seeds were hand-drilled on dry granular soil in January 1981 and 1982, then sprinkler-irrigated twice weekly until 30 days after rice emergence. Ammonium sulfate at 60 kg N/ha was applied in equal splits 10 and 20 days after germination. TABLE I S t a n d a r d E v a l u a t i o n S y s t e m for R i c e ( I R R I , 1 9 8 0 ) Scale
Drought tolerance
R e c o v e r y ability
0 1
N o visible e f f e c t Slight leaf tip d r y i n g
5
25 - - 50% leaves fully d r i e d
9
All p l a n t s a p p a r e n t l y d e a d
--9 0 - - 1 0 0 % plant recovered 4 0 - - 60% p l a n t s recovered 0 - - 19% p l a n t s
recovered
107
Soil was allowed to dry naturally. Soil moisture status at 20-cm depth was monitored using the gravimetric and tensiometric methods. Drought tolerance at vegetative stage was scored as leaf drying percent at 10 bars soil moisture tension (SMT). After scoring, the field was sprinkler-irrigated twice and drought recovery ability was recorded 7 days after the first irrigation. Drought tolerance and recovery ability was judged by the Standard Evaluation System for Rice (IRRI, 1980) (Table I). The desorption curve o f disturbed soil at 20-cm soil depth (Fig. 1) was determined using 5- and 15-bar pressure plate extractors. Simple linear correlation analyses between drought tolerance and recovery for each o f the four rice lines and all drought test entries were done. Soil moisture content (% by wt) 80
70
60
50
40
x,.__
30-
20-
1oi-
o
l 2
I I I I 4 6 8 10 Soil moisture tension (bors)
I 12
14
Fig. 1. Desorption curve for Maahas clay soil (Andaqueptic Haplaquolls) in a field drought
screening site (IRRI, 1979 dry season). RESULTS AND DISCUSSION
Buildup o f soil moisture stress SMT increase from 0 to 1 bar was gradual and was reached 21 days after imposed drought in 1981 and 24 days after imposed drought in 1982. In-
Character
IRAT 9 (Susceptible variety) D e s i c c a t i o n score Recovery score IR20 (Susceptible variety) Desiccation score Recovery score I R 4 4 2 - 2 - 5 8 ( T o l e r a n t line) D e s i c c a t i o n score Re c o v e r y s core Salumpikit (Tolerant variety) D e s i c c a t i o n score Recovery score
Variety/Line
0 0
0 0
0 2
5
0 4
6
0 9
7
8
9
97
99
103
96
0 4
0 5
0 0
0 0
0 30
0 11
0 0
4 45
0 46
0 2
28 14
4 24
0 20
49 3
10 9
1 63
10 0
39 3
0 18
3 1
45 1
41 4
8 44
2 0
1 0
58 2
61 33
1 0
0 0
3 0
27 4
98
94
88
101
n
4
n
3
1982
1981 12
Score frequency distribution
0 0
0 0
0 13
0 25
1
0 2
0 1
0 2
8 72
0 0 1 57
0 0
0 0
23
1 0
0 0
0 0
31 0
4
0 2
51 10
7 10
0 53
5
1 2
1 0
6 0
46 0
6
1 1
1 0
40 1
40 31
7
0 0
0 0
44 0
34 1
8
1 1
0 0
3 0
65 96
9
F r e q u e n c y d i s t r i b u t i o n o f d e s i c c a t i o n a n d r e c o v e r y scores o f t w o d r o u g h t s u s c e p t i b l e rice varieties, a d r o u g h t t o l e r a n t line, and a d r o u g h t t o l e r a n t variety ( I R R I , 1981 a n d 1 9 8 2 d r y seasons)
T A B L E II
b~ 00
109
crease from 1 to 10 bars was rapid, 15 days in 1981 and 21 days in 1982 (Fig. 2). Slower SMT buildup in 1982 was caused b y a March t y p h o o n which dropped 22 mm of rain at the experimental site.
Soilmoisturetension(bars) 10
0
o 1981
10
J
20 50 40 Soil moisturestressdays
~
•
50
60
Fig. 2. Buildup of soil moisture tension relative to days from start of soil moisture stress (IRRI, 1981 and 1982 dry seasons).
Rice response to 10 bars S M T Of the 96 plots planted to IRAT 9 in 1981, plants in 27 plots were desiccated and two-thirds or more of the leaves in 69 other plots had dried at 10 bars SMT (Table II). In 1982, 65 of 101 I R A T 9 plots had all apparently dead plants. In both years, more than two-thirds of leaves in all IR20 plots were desiccated at 10 bars SMT. Moderately drought-tolerant IR442-2-58 had from one-half to two-thirds desiccated leaves and tolerant Salumpikit had about 50% dead leaves. Sullivan (1971) suggested 50% kill point as an indication of drought tolerance. Our results confirmed those of earlier drought studies with the four rices (IRRI, 1974; Yoshida et al., 1974; Malabuyoc et al., 1980). Drought recovery ability Seven days after soil moisture stress was relieved, the four rice lines exhibited varying degrees of recovery. In 1981, IRAT 9 had some plots with up to 40% recovery. However, one-third of the plots had less than 20% recovery. In 1982, I R A T 9 died in most plots (Table II). Four-fifths o f IR20 plots had 40 -- 70% stand recovery in 1981, but only two-thirds had similar recovery in 1982.
110
In 1982, when it took longer to reach 10 bars SMT, drought recovery was less for IRAT 9 and IR20. Duration of water stress was related to crop yield by Begg and Turner (1976) and O'Toole and Moya (1981). Our results suggest that poor recovery from severe soil moisture stress could be a major cause of reduced grain yield. IR442-2-58 and Salumpikit had similar 70 to 100% drought recovery (Table II), but Salumpikit scored better than IR442-2-58. On average, IR442-2-58 and other semi-dwarfs had excellent drought recovery capability, while traditional upland genotypes (of which Salumpikit is one), had poor recovery (De Datta et al., 1975). The higher drought tolerance allowed Salumpikit to have an equally excellent recovery stand.
Relationship between drought tolerance and recovery ability There was significant correlation between drought tolerance and recovery scores for each rice tested each year (Figs. 3 and 4), and the relationship between drought and recovery scores of all drought test entries was likewise significant. Recovery score 9 IRAT9
8 7
+o.785x
J
r= ( n =96)
6
/ t
IR20 ,~,s ~ = 14- Q594X ,- s r = 0.42 "----s " (n=105)
5 4 -E41 I
I
I
I
I
l
Other rices o1+o.748x
IR442-2-58 y =l + 0 . 7 5 0 X r = 0.49~K'~J A
~, ~ " ""
i1 5
7
~"
Solurnpi'kit ~ = 0.44 * ~ (n = 9 7 )
I
I
I
I
I
4
5
6
7
8
9
I
I
I
I
I
I
3
4
5
6
7
8
9
Drought score
Fig. 3. Relationship between drought tolerance in rice and recovery ability as measured by visual scoring using the 1980 Standard Evaluation System for Rice (IRRI, 1981 dry season).
111
The relatively low but significant r-values were because recovery varied more than drought scores (Figs. 3 and 4), a result of different soil drying rates in the field (Supapoj et al., 1982). Plants located in faster soil drying field spots were exposed to longer stress periods. Their recovery was less even if the drought score was similar. Recovery score 9 IRAT9
/
8
~ : ~+o 389x
7
r = 026 *~ - - ~ - ~ ~ (n = 101 )
6
IR20 -----._.____ , , , , , ~ , " ~ " ~ " = 5+0.590X " " r : 0.22* m (n:88)
5 4 5
I
_ -
I
I
Salumpikit }= O+ 0.697X r = 054-** (n:97) ~ j ~ I
,,¢
1
I
t
Other rices ~= -17+1.029X
/ /
,/ IR442-2-58
j~,)=o+o.464x /
41 I 3
I
I 4
I 5
r = 0.24* (n:94) I I I 6 7 8
i
-..41 I 3 Drought score
I 4
I 5
I 6
I 7
I 8
9
F i g . 4 . Relationship between drought tolerance in rice and recovery ability as measured by visual scoring using the 1980 Standard Evaluation System for Rice (IRRI, 1982 dry season).
CONCLUSIONS
Results from this study justify the use of visual scoring in field screening rice for drought tolerance and recovery ability. Thousands of rice lines can be evaluated at one time using visual scoring, which is impossible with the tissue water status measurements screening technique (Kramer, 1969; Sullivan, 1971). O'Toole and Moya (1978) reported a positive relationship between visual scoring based on leaf drying and maintainance of high leaf water potential. The positive relationship between drought tolerance and recovery ability
112
means that the degree of desiccation during a dry spell would help rice farmers predict stand potential when rains resume. Results further suggest the importance of growing drought-tolerant modern rices with good recovery ability to minimize hazards of total crop failure in rainfed rice.
REFERENCES Begg, J.E. and Turner, N.C., 1976. Crop water deficits. Adv. Agron., 28: 101--217. Blum, A., 1982. Evidence for genetic variability in drought resistance and its implications in plant breeding. In: Drought Resistance in Crops with Emphasis on Rice. International Rice Research Institute, Los Ba~os, Philippines, pp. 53--68. Chang, T.T., Loresto, G.C. and Tagumpay, O., 1972. Agronomic and growth characteristics of upland and lowland rice varieties. In: Rice Breeding. International Rice Research Institute, Los Ba~os, Philippines, pp. 645--661. Chang, T.T., Loresto, G.C. and Tagumpay, O., 1974. Screening rice germplasm for drough~ resistance. SABRAO J. 6: 9--16. De Datta, S.K., Chang, T.T. and Yoshida, S., 1975. Drought tolerance in upland rice. In: Major Research in Upland Rice. International Rice Research Institute, Los Ba~os, Philippines, pp. 101--116. I R R I (International Rice Research Institute), 1971. Annual Report for 1970. Los Ba~os, Philippines, 265 pp. IRRI (International Rice Research Institute), 1974. Annual Report for 1973. Los Bafios, Philippines, 264 pp. I R R I (International Rice Research Institute), 1975. Annual Report for 1974. Los Ba~os, Philippines, 384 pp. IRRI (International Rice Research Institute), 1980. Standard Evaluation System for Rice. Second edn. Los Ba~os, Philippines, 44 pp. Kramer, P.J., 1969. Plant and Soil Water Relationships: A Modern Synthesis. Tata McGraw-Hill Publ. Co. New Delhi, 482 pp. Malabuyoc, J.A., Aragon, E.L. and De Datta, S.K., 1980. A Field Screening Technique for Evaluating Rices for Drought Tolerance. Paper presented at the l l t h Annual Meeting of Crop Science Society of the Philippines, 27--29 April 1980, Baybay, Leyte, Philippines. O'Toole, J.C. and Moya, T.B., 1978. Genotypic variation in maintainance of leaf water potential in rice. Crop. Sci., 18: 873--876. O'Toole, J.C. and Moya, T.B., 1981. Water deficits and yield in upland rice. Field Crops Res., 4: 247--259. Sarkar, J.P. and De Datta, S.K., 1975. Drought Tolerance in Rice: Screening Technique and Selection Criteria. I R R I Saturday seminar, 18 August 1975, Los Ba~os, Philippines. Sullivan, S.Y., 1971. Techniques for measuring plant drought stress. In: K.L. Larson and J.D. Eastin (Editors), Drought Injury and Resistance in Crops. Crop Sci. Soc. Am., Madison, WI 53711, pp. 1--18. Supapoj, N., Boonwite, C., O~roole, J.C., De Datta, S.K. and Jackson, B2., 1982. Using check varieties to adjust visual scores for non-uniform soil drying in drought resistance field screening. Int. Rice Res. Newsl., 7(4): 12. Yoshida, S., Shioya, M., De Los Reyes, E., Coronel, V. and Parao, F.T., 1974. Physiological Basis and Technique for Screening for Drought Resistance. I R R I Saturday Seminar. 16 March 1974, Los Bathos, Philippines.