Indian J. Plant ?hysiol., Vol. 2, No. 2, pp. 151-155 (ApriL-June, 1997)
SHORT COMMUNICATION
GROWTH AND YIELD RESPONSE OF DIFFERENT CROP SPECIES TO LOW
LIGHT AND HIGH TEMPERATURE-HUMIDITY STRESS
S. SINGH"
Central Agricultural Research Institute, Port Blair- 744101
Received on 26 Aug., 1996, Revised on 30 Nov., 1996
Different crop species showed differential growth and yield response to environmental stress. Low light stress (65% NL) alone caused marked increase in the stature and foliage growth of plant in all crop species tested. However, the same environmental condition reduced the bioproductivity and economic yield of maize, sorghum and green gram, but improved the same in groundnut and okra. Reduction in economic yield by low radiation was mainly due to low number of pods per plant and seeds per pod in green gram and low grains per sink in maize and sorghum. However, the improvement of economic yield in groundnut and okra was mainly attributed to greater seed size (1000 seed wt.). Different crop species, when subjected to low radiation with high temperature and humidity (65% NL/ 38°C) showed greater shoot elongation and leaf area expansion, but manifested lower economic as well as biological yield under the same conditions. Both the cereals (maize and sorghum) failed to form the grains under low light with high temperature and humidity stress, while same stress induced parthenocarpic fruits in okra. Groundnut and green gram, however, developed the seeds under same conditions. Irrespective of different crop species, vegetative growth showed greater stability than reproductive growth under diverse environmental stress.
Since the growth and productivity of any crop species are governed to a great extent by its surrounding enviromnents, hence any climatic changes especially the rise in temperature and humidity and fall in the solar radiation in the near future due to global warming would certainly influence the growth and productivity of several crop species in various agro-climatic zones (Sinha, 1992; Parry, 1992). Though different crop species of diverse origin (tropical and temperate) and photosynthetic pathways (C3 and C4) have differential ability to adapt themselves to the changing environments, the identification of crop species with greater gro\\1h and yield stability under altered climatic enviromnents will
be of great significance in order to stabilize and sustain the productivity of various crops in the near future. Keeping this in view, a pot experiment with different crop species was conducted to examine the effect of low light and high temperature-humidity stress on growth and productivity.
*Present Address: Division of Environmental Sciences,
Pure seeds of five different crop species of tropical origin and distinct photosynthetic pathway (C
3 and C4)
and nature of pollination (self and cross pillinated) namely maize, sorghum (C4 plant), and green gram, groundnut and okra (C3 plant) were sown in the cement pots pre-fertilized with full dose ofNPK. Fifteen day after seedling
Indian Agricultural Research Institute, New Delhi- 110012
S SfNGH
emergence, two unifom1 seedlings of each crop were left in each pot following thinning. Eight pots each of different crop species were arranged in three similar sets and different set was subjected to diverse climatic conditions i.e (i) control/normal condition (I 00% normal light/ 32°C), (ii) low light stress (65% NL/3T'C) and (iii) low light coupled with high temperature and humidity (65% NL/38°C) from seedling to maturity stage of the crops. Temperature, humidity and light intensity were measured thrice in a day (8.00 AM, 12.00 Noon and 2.00PM) regularly and mean value of the same is presented in the table. Low light stress alone was created by covering the crop chamber partially with polyethylene sheet (UV stabilized), while low light with high temperature and humidity was created by covering the crop chamber fully with same plastic sheet. Plants were sampled twice at flowering and maturity to record the growth and yield observations. The leaf area of cereal crops maize and sorghum was measured by multiplying the length x width x factor, while the leaf area of other crop species was measured by leaf disc method (Singh eta!., 1989). Dry weight of plants was taken following drying the plant materials in the hot air oven at 70°C for 3 days. Yield and yield components were recorded ai maturity.
Low radiation ( 65% NL/3 2 °C) caused marked increase in the vertical shoot growth (plant height) of all the crop species, while low radiation coupled with high temperature and humidity (65% NL/38°) accelerated shoot elongation in green gram, groundnut and okra and finally these crop plants recorded maximum shoot length under such adverse climatic conditions (Table I). The height of okra plant under low radiation with high temperature and humidity was around four times greater than that of control plants, while same environmental condition reduced the heig!J.t of sorghum but enhanced the stature of maize to a great extent. The increase in plant stature under such environmental stress was mainly attributed to greater elongation of internodes and leaf blade (Table I). The number of leaves per plant both in detem1inate and indeterminate crops remained almost unchanged under such environmental stress, however, the leaf area expansion was greater under such conditions, regardless to different crop species. Low light stress (65% NL)
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lowered the biological yield of maize, sorghum and green gram, but enhanced the same in groundnut and okra. However, low radiation coupled with high temperature and humidity manifested lower dry matter production in all the crop species tested. The specific leaf weight (SLW) of all the crop plants reduced drastically by low radiation and high thermal humid stress, while the leaf weight ratio (L WR) was enhanced to some extent by such envirorunental stress (Table I). The senescence ofleaves generally delayed by low radiation stress.
Low light stress (65% NL) caused marked reduction in the grain yield of maize, sorghum and green gram, while improved the productivity of groundnut and okra (Table II). Low radiation induced reduction of grain yield was mainly attributed to low number of pods per plant and seeds/pod in green gram and low grains per cob and ear head in maize and sorghum, respectively. However, the improvement of economic yield in groundnut under same low light stress was mainly because of greater seed size and weight ( 1000 seed weight) as the number of pods per plant reduced slightly by low light stress without affecting the number of seeds per pod. Harvest index was invariably lower under low light stress than under normal light condition. Low light stress when coupled with high temperature and humidity (65% NL/38°C) caused complete failure of grain setting in cross pollinated crops maize and sorghum , while the same enviromnental condition induced parthenocarpic fruits in okra. Groundnut and green gram, however, have been able to form and develop the seeds under same environmental stress (Table II). Failure of grain fo;mation in maize and sorghum under low radiation with high thermal-humid stress was mainly due to loss of pollen viability. It is clearly evident from the results that tropical legumes were more tolerant to heat and lo\\ radiation as compared to the tropical cereals in respect of grain/seed setting. Irrespective of different crop species, vegetative grov.th showed greater stability than reproductive growth under such environmental stress.
Moderate 10\v light stress (65°/., NL) caused greater reduction in economic yield than in bioloigcal yield of maize, sorghum and green gram, however, improved the economic yield slightly and biological yield markedly in groundnut and okra. Reduction in growth and yield of
ENVIRONMENTAL FACTORS AND CROP GROWftl
Table
I. Growth and growth parameters of different crop species as influenced by environmental stressCrop/ Plant No. of Leaf areal Specific Leafwt. Av. length Days to
treatment height leaves/ plant leafwt. ratio on internode flowering
em plant dm2 mg/cm2
Maize
TO 185 15 36.4 6.13 0.29 11.5 50
Tl 272 15 32.7 5.25 0.26 16.5 52
T2 259 15 32.1 5.1)6 0.29 15.7 50
COat 5% 21 NS 2.4 0.25 NS 1.3 NS
Sorghum
TO 193 10 2l.l 6.17 0.17 16.5 55
TJ 237 10 22.0 4.27 0.17
22.0 53
T2 180 10 23.6 4.62 0.33 15.0 65
COatS% 10 NS 0.85 0.85 0.05 2.5 5
Green gram
TO 65 27 8.3 5.87 0.21 4.2 36
T1 75 32 10.2 6.33 0.39 7.0 38
T2 127 26 10.5 3.87 0.28 8.0 38
COatS% 12 4 NS 1.5 0.06 2.5 NS
Groundnut
TO 37 145 27.6 7.12 0.43 1.7 35
Tl 69 120 31.2 5.66 0.40 3.5 35
T2 146 147 32.0 4.48 0.35 4.0 30
COatS% 21 12 2.3 1.6 0.05 L2 NS
Okra
TO 61 10 3.30 6.41 0.10 7.4 37
T1 100 11 6.4 5.44 0.12
10.5 37
T2 176 13 16.5 4.04 0.28 Jl.4 37
COatS% 18 NS 3.3 0.95 0.06 1.6 NS
TO Control/normal condition: Av. temp. 32°C, RH 60%, light intensity 74 Klux
T1 Low light stress: A v. temp. 32°C, RH 60%, light intensity 48 Klux
T2 Low light/high temp. and humidity: Av. temp. 38-40°C, RH 75%, light 48 Klux
different crop species under low radiation have been grov.1h phase. Generally, the C
4 plants have greater light reported by several workers (Nayak and Murty, 1980; saturation point than C, plants (Black, 1971; Hatchet a!. Sengupta and Jadhav, 1988; Singh, 1994). Low light 1971 ), but in the present investigation, it is clearly evident induced reduction of economic yield in these crops was from the results that green gram (C
3 plant) also require mainly due to impaired biological yield and harvest greater amount of light for proper growth and yield. index, which indicate the possibility of greater light However, the improvement of economic and biological requirement by these crops especially during ripening yield as well in groundnut and okra under moderate
lndianJ Plant Physiol., VoL 2, No.2, pp. 151-155 (ApriL-June, 1997)
S. SINGH
Table II. Impact of environmental stress on yield and yield components of different crop species
Crop/ No. of No. of 1000 seed/ Economic Straw Biological Harvest
treatment sinks/ seeds grains/ grain wt. yield yield yield index
plant sink g g/pot %
Maize
TO 240 137.0 65.5 164.0 229.5
28.5
Tl 98 185.6 37.4 160.0 197.4 17.0
T2 0 0 0 147.0 147.0 0
CDat5% NS 23 12.5 8.5 6.5 21.5 6.5
Sorghum
TO 1500 28.6 85.8 131.3 217.1 39.5
Tl 1170 25.2 59.0 134.8 193.8 30.5
T2 0 0 0 114.7 114.7 0
CDat5% NS 150 NS 11.0 G2 25.0 5.0
Green gram
TO 63 11 35.6 49.5 48.1 97.6 50.4
Tl 38 10 37.3 28.0 40.1 68.1 41.2
T2 32 6 44.5 17.5 37.5 55.0 31.7
CDat5% 5 3 5.6 7.5 5.0 16.0 7.5
Groundnut
TO 48 1.7 741.0 60.1 75.0 135.1 44.6
Tl 44 1.7 870.0 29.0 112.5 178.0 37.0
T2 21 1.8 778.0 29.5 83.6 112.5 26.5
CDat5% 8 NS 25 3.5 6.5 15.0 6.0
Okra
TO 4 43 60.1 18.6 19.7 38.3 48.0
T1 4 41 60.0 19.4 26.2 45.6 45.6
T2 8 0 0 0 62.7 62.7 0
CDat5% 2 12 NS NS 6.5 8.\l 6.5
lowlight stress may perhaps be due to greater net carbon assimilation under moderate reduction of solar radiation as most of the
c3
plants suffer from photorespiration under high light intensity (Zelitch, 1971; Black, 1971; Hatch, eta!., 1971 ). Slight improvement in grain yield of groundnut and okra under moderate low light stress mainly attributed to greater seed size (1000 seed wt.) and biological yield, despite reduction in harvest index clearly indicate t4e possibility of photorespiratory loss of assimilate in these crop species, when grown under highlight intensity. Irrespective of differernt crop species, reduction of harvest index under low light stress shows that partitioning of assimilates from source of sink is more vulnerable to low radiation as compared to photosynthetic production.
Marked depletion in economic and biological yield of green gram and groundnut and complete destruction of grain yield with substantial reduction in biological yield of maize. sorghum and okra under low radiation with high thermal-humid stress might be due to impaired
154
ENVIRONMENTAL FACTORS AND CROP GROWTH
photosynthetic activity and greater, respiratory loss of assimilates under the situation (Black, 1971; Zelitch,
1971 ). Complete failure of grain setting in cross pollinated crops like maize and sorghum and other self pollinated crop okra under low radiation with high temperature and humidity may perhaps be due to loss of pollen viability in these crops, where pollen grains were directly exposed to adverse environments. However, the crop plants where the pollen grains were not directly exposed to the environments as in the case of legumes (cleistogamy), have been able to form and develop the seeds following pollination. Thus failure of pollination and seed setting in maize and sorghum and successful pollination and fertilization in legumes under adverse climates clearly indicate the possibility of loss of pollen viability by direct exposure to adverse climatic conditions especially high temperature and humidity stress. Greater influence of adverse climatic conditions on reproductive growth than on vegetative growth regardless to different crop species reflects greater sensitivity of reproductive growth than vegetative growth to adverse climates as has been reported by Singh {1994). Induction of parthenocarpic fruits in okra under low radiation coupled with high temperature and humidity may perhaps be due to the development of ovary without pollination and fertilization.
IndianJ. PlantPhysiol., Vol. 2, No.2, pp. 151-155 (ApriL-June, 1997)
Author is grateful to the Director, CARl, Port Blair for providing necessary facilities and encouragement.
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