PLANT PHYSIOLOGY

A section of Plant Physiology was established in June 1960 and subsequently the section was upgraded to a full fledged division in 1972 during fourth five year plan. The main emphasis on the research of the division is to identify physiologically elite donors/varieties for specific stress situations and assess the characters associated with such varieties so as to suggest appropriate morpho-physiological parameters for field selection of desirable plant types to specific ecological conditions.

Production physiology

Studies on transplanted rice

The dry matter production after flowering directly contributes to grain yield under optimum conditions in dry season. However, during wet season due to climatic constraints like low light and high night temperatures, the contribution of reserve carbohydrates becomes substantial for grain filling and yield.

The sink components like spikelet and grain number/m2 were associated with dry matter production at reproductive (r=0.56**) and ripening (r=0.79**) stages, respectively.

Yield was linearly related with panicle number/m2 (350-400 panicles/m2) but this relation fails at higher population density.

For growth of each spikelet the optimum source is 2.5 cm2 leaf area and 14 mg of stem weight at flowering stage, especially for early varieties like Ratna or Pallavi.

Major constraints for productivity in wet season are low grain number/panicle in early, high spikelet sterility in medium, and low panicle number in late duration varieties.

Besides efficient grain filling, proportion of high density grain is also a desirable trait. High density grain varieties are characterized by higher rate of translocation of photosynthates to panicle, higher phosphorylase and nitrate reductase activity in shoot, greater mobilization of nitrogen and rapid accumulation of starch in the developing grain.

High density grains

Proportion of high density grain decreased at higher nitrogen level, at lower light intensities and under curtailed photosynthetic surface. No negative relationship between the proportion of high density grain and spikelet number was noticed, indicting the possibility of combining these two traits for enhanced grain yield.

Studies on photosynthesis

Leaf thickness (SLW), leaf vein frequency, stomatal conductance, leaf nitrogen percentage and leaf protein showed high association with photosynthetic rate while leaf area and yield had a tendency for negative association.

Varieties with high photosynthetic rate concomitantly recorded high respiration including photo-respiration, exception cv. Ratna.

Maximum translocation of 14C assimilates to panicle was evident at 2 weeks after flowering. Assimilates produced during milk stage contributed 75% of total carbohydrates in grain. Varieties with high Pn were not necessarily efficient in translocation.

Cultivars with low photo-respiration

Cultivars, B 76, Adt 27, Tkm 6, IR 8 , Ratna, Pankaj, Vijaya were identified to possess the character of low photo-respiration.

Solar energy utilization

The proportion of solar energy utilization (Eu%) for economic and biological yield varied 2-3-fold among traditional and high yielding varieties. The Eu% for biological yield was associated with LAI and for economic yield with harvest index. The Eu% could be increased with high nitrogen application and high planting density.

Physiology of hybrid rice

Studies on the physiology of hybrid rice revealed that IR 19058-107-1 was efficient in several physiological traits including yield under low light followed by IR 54 and IR 58 which were photosynthetically efficient among 26 restorer examined. In late duration group, Savitri (Ponmani) and Mahsuri were superior and recently developed restorer Vajram was highly potential. Among maintainers, IR 33955-8-1-1 and IR 5475B possessed desirable productive traits. Hybrids developed from IR 54752A cms source were generally more productive among which 52A/Vajram, a medium duration hybrid was highly potential especially under low light.

Stress physiology

Drought

Tolerance to drought, in general , is associated with (i) higher germination in polyethylene glycol, (ii) less starch disintegration in root and low destruction of chlorophyll, (iii) tillering in quick succession before onset of drought, (iv) fast recovery on re-watering, (v) more root length (> 25 cm), (vi) higher leaf moisture content, greater accumulation of sugars in stem predominantly in the non-reducing form, and (vii) more proline during and at recovery phase.

Investigations on drought tolerance led to the identification of many varieties tolerant to drought at tillering and flowering. Among high-yielding varieties Rasi, C 22, CR 113-84-2, CR 143-2-, TNAU 6464, Taichung Native 1 x T 65 and Annada (MW 10) were promising with an yield potential of 2.0 to 2.5 t/ha with a drought index of more than 50%.

Characters like high germination in polyethylene glycol, coleoptile growth in D-mannitol (10 atm), chlorophyll stability to heat, recovery vigour on re-watering, high leaf water content, deep and ramified root system, high stem sugars and protein nitrogen in plants and high proline content during drought and recovery phases are associated with drought tolerance. Cultivar Lalnakanda 41 was identified as the best drought tolerant variety and crosses made with Bala were promising.

Salinity

Studies on tolerance to salinity led to the identification of the critical stages of saline injury. These are young seedling stage (3 leaf stage - after endosperm reserves are over) and flowering stage. The 50% reduction in yield was at 0.2% NaCl concentration in susceptible varieties, while similar reduction was at 0.4% NaCl in tolerant varieties.

Salt tolerant varieties absorbed less salts without showing any injury symptoms. Under salinity, amount of Na increased while K decreased in plants resulting in low K/Na ratio. In tolerant varieties, high K/Na ratio was maintained. The studies also revealed that sodium salts were more injurious than K or Ca, while chlorides and bicarbonates were more toxic than sulphates when given at iso-osmotic concentration. The donors identified for salt tolerance are Kalarata, Getu, Damodar, Dasal and SR 26B. Among high-yielding varieties Taichung Native 1, IR 8, Taichung Native 1 x T.65 and Leelavlati were found to be promising with this trait.

Low light stress

Lower incidence of solar radiation coupled with fluctuating light intensity due to overcast sky during wet season is one of the major constraints for rice production in eastern India. Varietal variation to low light stress was apparent. To assess the effects of these adverse factors on different rice cultivars, intensive investigations were carried out under simulated conditions of low light with varying level of solar radiation. A 50% reduction in normal light is sufficient to screen varieties for low light tolerance. The critical periods of low light injury were found to be reproductive and ripening stages of growth during which time spikelet and grain number are determined.

Mechanism of adaptability to low light

Influence of low light on the plant is characterized by increase in chlorophyll b resulting in reduction of chlorophyll a/b ratio, maintenance of higher photosynthetic activity and absorption of optimum nitrogen content and retarded senescence with lower respiration and higher carbohydrate translocation from shoot to the developing grains.

High specific leaf weight at flowering under normal light condition is significantly associated with biomass or grain yield at harvest under low light, suggesting its usefulness as a preliminary selection criteria for low light adapted variety. Further, a critical value of leaf area ratio 80 cm2/g found to be ideal ceiling under light stress situations to assure an yield of 2 t/ha or more.

Since leaf area ratio (LAR) and yield were negatively associated (r = - 0.59**) under low light, this phenomenon could be exploited for identifying varieties tolerant to light stress.

Waterlogging

Tolerance to waterlogging, in general, is associated with 1) fast early tiller development, 2) liberation of more oxygen from the root, 3) moderate pectin-methyl-esterase activity in the culm with optimum air space and less susceptibility to lodging , 4) greater chlorophyll especially chlorophyll `b' and higher photosynthetic rate of the top leaves above water level and 5) more grain number/ panicle, less spikelet sterility and higher harvest index.

Elite varieties for different water depths were identified. For shallow submergence (0-30 cm), T 1237, Mtu 16, Manoharsali, NC 1281 (traditionals) IR 5, CR 70-91, Taichung Native 1 x T 65, CRM 10-4622, (high-yielding varieties) were promising, while for intermediate depth (0-50 cm), Intan, Suresh (CN 540), IET 5638, IET 6206, C 4045, Hatipanjari, CRRI germplasm accession No. 2386 (Intass) and 1020 (T 535), CR 383-10 and Panidhan were the best. Flowering stage was found to be critical for flood and submergence injury. Characters like leaf sheath and stem elongation and oxygen liberation capacity of roots were associated with tolerance to waterlogging. High N and P fertilization in the seed bed favoured tolerance and foliar spray of GA + IAA at 10 ppm helped in seedling elongation and enhanced grain yield.

Submergence

Crop submergence at any growth stage limits rice productivity in eastern India. Considering the large dimension of the problem, efforts were made to develop the strategies to withstand the adverse effects of submergence to enhance productivity.

Mechanism of submergence tolerance

Tolerance to submergence, in general, is associated with 1) elongation of leaf sheath, culm and leaf or combination of these factors, 2) higher oxygen liberation by roots, 4) higher amylase and acid phosphatase activity of stem, 5) greater pre-submergence stored carbohydrate ,and 6) high specific leaf weight and maintenance of greater chlorophyll content during submergence.

Donnors for submergence tolerance

Extensive evaluation of germplasm accessions resulted in the identification of donors for submergence tolerance. These are: Fukoku ,T 1808, Hatipanjari, CR 383-10, Sarubhujini, T 300,B 24-92, T 535.

Basic studies on physiological aspects

Mineral nutrition

The deficiency of N and P affected crop growth drastically compared to other nutrients. The optimum N and P concentrations in water culture was 55 and 10 ppm in the wet season and 80 and 27 ppm in dry season. Varietal difference in tillering was due to high nitrogen uptake and sugar concentration in the tillering zone. Ethyl ammonium phosphate was an effective phosphorus source even under unfavourable pH of the growth medium. P32 tracer studies indicated higher uptake and utilization of phosphorus in surface placement, in combination with fertilizer nitrogen and under flooded condition. Field experiments under FAO/IAEA programme using N15 and P32 fertilizers indicated sub-surface placement of nitrogen, enhanced nitrogen uptake by 10% and utilization of both nitrogen and phosphorus fertilizers could further be enhanced by mixing both prior to application. Ammoniacal nitrogen fertilizer was more beneficial for basal dressing while for top dressing NH4 and NO3 fertilizers were equally effective. The response to combined nitrogen and phosphorus fertilizer, nitric phos increased with the increase in solubility of phosphates in the fertilizer.

Nutrio-physiological studies have indicated that the shy tillering varieties, Ptb 10 and Chianung 242, showed lower N and P concentrations than the high tillering types Chinsurah Boro II and Taichung Native 1. The lack of response to nitrogen in wet season was associated with low light and high temperature leading to high leaf weight ratio (LWR) at flowering of more than 25% which was found to be the threshold value for N response.

Senescence in rice

The senescence of rice leaves in general may not be a simple function of chronological leaf age during grain filling period. During post flowering, leaf senescence increased and a gradual accumulation of ethylene in leaf impaired the functional activity. In general, the japonica x indica hybrids exhibit slower senescence than the derivatives from De-geo-Woo-gen dwarfing gene source.

Varieties showing delayed panicle senescence also showed efficient mobilization of assimilates from shoot to panicle indicating the importance of differed panicle senescence for potential grain filling.

Photoperiodism

Rice is a short-day plant and treatment of 30-day-old seedlings with 8 hours short-day for 20 days was optimum. The critical photoperiod for rice seemed to be less than 12.5 hr as there was no flowering beyond this period. In wild species response was evident in O. officinalis than in O. perennis. Tetraploids were more sensitive to short days than diploids. Foliar spray of NAA at 10 ppm after flower initiation hastened flowering even under non inductive photoperiods indicating that after flower initiation the emergence of panicle is mostly under hormonal control.

Dormancy and germination

Seed dormancy is a desirable character, especially with early types grown during the monsoon season. The optimum temperature for germination varied from 26-37oC and germination failed below 15oC and above 47oC. The period for 80% germination extended from 3 days at 35oC to 11 days at 18oC. Even in early varieties there is a period of dormancy which was more in the wet season crop than in the dry season crop. Cool temperature during ripening phase appeared to induce dormancy. Many early types with moderate to high dormancy were identified e.g. Adt 19, adt 413, W 371, N 136, Mtu 17, IR 9, IR 5 etc. Dormancy can be broken by (i) heat treatment at 42oC for 8 days, (ii) soaking seeds in nitric acid pH 1.5 or 6.3 ml/l of water for 12-24 hr, and (iii) soaking in 0.5% thiourea solution for 2 hr. Seed viability can be maintained up to 10 years by keeping the seeds in desiccators with calcium chloride.

Foliar spray or soaking of panicles in 10% NaCl solution 20 days after flowering reduced moisture content and prevented sprouting. Even paraquat spray (0.1%) at 20-25 DAF reduced moisture content of seed from 25 to 16% without any adverse effect on subsequent germination.

Sterility

In 2500 entries of Genetic stock, the sterility per cent varied from 16-74%. Cultivars with low sterility are Pallavi, Taichung Native 1, x T 65, Shakti, Mahsuri (high-yielding), B 76, Bam 12, Ptb 18, Ptb 21 and H 4. Sterility, mostly a post-fertilization phenomenon, was high in wet than in dry season. Low light during flowering to 10 days after flowering especially on the day of anthesis was critical. High sterile cultures were characterized by low panicle Pn in spite of high leaf Pn, poor translocation, greater accumulation of soluble and amino nitrogen, low levels of proline, IAA and cytokinins in spikelets. Foliar spray of kinetin or exogenous feeding of proline to the panicle reduced sterility and increased panicle weight.

Development of an easy method for chloropyll estimation

A less complicated convenient procedure to extract chlorophyll from rice leaves was standardized. Incubating fresh leaf tissues (100 mg/25 ml) in acetone at 4oC in dark for 27 hours gave better result than the traditional grinding and centrifuging procedures or by using any other solvents.

Physiological studies on scented/long slender quality rice

Productivity of long slender rice either scented or non-scented is low in eastern India. The plant characters associated with such lower production were identified.

Crop Modeling

System Analysis and Simulation Modeling work started in the year 1986 under a collaborative programme known as SARP.

Crop growth model for water deficit situations

A simulation model was developed for economy in use of irrigation water under water deficit situations. Normal crop growth is a function of radiation use efficiency and cumulative PAR, but under defined stress situation, the model switches over to calculate crop growth rate through transpiration efficiency and rate of transpiration. The leaf senescence index was introduced to give a feedback for re-mobilization of carbohydrate and subsequent partitioning. Water balance on three layer soil profile was incorporated to precisely monitor soil-plant interaction and water uptake.

The model can advise the timing and amount of water needed for irrigation depending on the demand by the plant.

Crop growth modeling for low light stress situations

The macros model L1D. CSM was taken as the base model. Various physiological process oriented functions as appropriate to wet season of eastern India, were incorporated to simulate dynamics of crop growth more realistically. The model identified essential features of desirable plant type to assure grain yield of 3.0 t/ha (against <1.2 t/ha average).

The potential for plant physiology to contribute to agriculture in India can be seen as a matrix with increased production or decreased inputs on the axis defining objectives, and improved agronomy or improved genotypes on the other axis defining how the objectives can be met. Improved agronomy to increase and stabilize production, and to conserve natural resources, requires a better understanding of how plants interact with their environments, in the air,in the water, and perhaps especially in the soil. Some of the recent and striking genotypes improvements in rices have been based in part on physiological principles, e.g. both short stems and large flag leaves can increase the quantity of assimilates allocated to grain production. But many other possibilities remain to be explored ; submergence tolerance to make use under flash floods, water-logged tolerance to combat with higher level of water depth, higher photosynthesis especially under low light to overcome the production barrier particularly in eastern India or development of cultivation technology to reduce the cost of cultivation which is useful for resource poor farmers and at the same time the agriculture is being competitive with international markets.

Realising the importance of rice physiology in variety improvement programmes, for sustained, and higher rice yields especially under stress conditions, the Indian Council of Agricultural Research upgraded the section of Plant Physiology (initiated in June 1960) into a full fledged division during 4th five year plan in the year 1972. The main emphasis on the research of the division is to identify physiologically elite donors/varieties for specific stress situations and assess the characters associated with such varieties so as to suggest appropriate morpho-physiological parameters for field selection of desirable plant types to specific ecological conditions.

Studies on drought tolerance

Tolerance to drought, in general , is associated with 1) higher germination in polyethylene glycol, 2) less statolith starch disintegration in root and low destruction of chlorophyll, 3) tillering in quick succession before onset of drought, 4) fast recovery on re-watering, 5) more root length (> 25 cm), 6) higher leaf moisture content, greater accumulation of sugars in stem predominantly in the non-reducing form, and 7) more proline during and at recovery phase.

Donors for drought tolerance : Mtu 17, Lalnakanda 41,

Ch 45, Dular, W 691, AC 511, Dhangora, Blackgora, Kalakeri, Surjamukhi and Selumpikit,Rasi, C 22, CR 113-84-2, CR 143-2-2, TNAU 6464, TN1 x T 65, Annada.

Studies on salt tolerance

A simple laboratory technique for identification of salt tolerant types was also worked out making use of the fact that the salt tolerant varieties absorbed less salts than the susceptible types.

The donors identified for salt tolerance were Getu, Dasal, SR 26B, Leelavati, IR 8, Kalarata, Damodar and T(N)1 x T 65.

Studies on water-logged tolerance

Tolerance to water-logging,in general, is associated with 1) fast early tiller development, 2) liberation of more oxygen from the root, 3) moderate pectin-methyl-esterase activity in the culm with optimum air space and less susceptibility to lodging , 4) greater chlorophyll especially chlorophyll `b' and higher photosynthetic rate of the top leaves above water level and 5) more grain number/ panicle, less spikelet sterility and higher harvest index.

Donors for water-logged conditions: T 1237, Mtu 16, Monoharsali, NC 1281, IR 5, CR 70-91, TN1 x T 65, CRM 10-4622, Intan, CN 540 (Suresh), IET 5638, IET 6206, C 4045, Hatipanjari, CRRI accession no. 2386,1922 and 1020, Panidhan, CR 383-10.

Studies on submergence tolerance

Crop submergence at any growth stage limits rice productivity in eastern India. Considering the large dimension of the problem big efforts were made to develop the strategies to withstand the adverse effects of submergence to enhance productivity.

Mechanism of submergence tolerance : Tolerance to submergence, in general, is associated with 1) elongation of leaf sheath, culm and leaf or combinaton of these factors,2) higher oxygen liberation by roots,4) higher amylase and acid phosphatase activity of stem, 5) greater pre-submergence stored carbohydrate ,and 6) high specific leaf weight and maintenance of greater chlorophyll content during submergence.

Strategic Technology for submergence prone area

As pre-submergence carbohydrate level determines submergence tolerance, a new cultivation technology was developed on the basis of it.

a. Seed selection : use of high density grain ( more than 1.20 sp.g.)

b. Preparation of seed bed : less seedling density with nitrogen application less than 15 kg/ha.

c. Transplanting : Use of sturdy and vigorous seedlings (0.8-1.0 g as fresh weight/seedling).

d. Fertilizer application : application of less nitrogen (15 kg/ha) and more phosphorus (60 kg/ha) as basal.

Donors for submergence tolerance : FuKoku ,T 1808, Hatipanjari, CR 383-10, Sarubhujini, T 300,B 24-92, T 535.

Studies on low light stress

Lower incidence of solar radiation coupled with fluctuating light intensity due to overcast sky during wet season is one of the major constraints for rice production in eastern India. To assess the effects of these adverse factors on different rice cultivars, intensive investigations were carried out under simulated conditions of low light with varying level of solar radiations.

Mechanism of adaptibility to low light : 1)Under low light, chlorophyll b increases with reduction in chl a/b ratio, 2) maintenance of higher photosynthetic activity and absorption of optimum nitrogen content, 3) slower senescence with lower respiration and higher carbohydrate translocation from shoot to the developing grains

High specific leaf weight at flowering under normal light condition is significantly associated with biomass or grain yield at harvest under low light, suggesting its usefulness as a preliminary selection criteria for low light adapted variety. Further, a critical value of leaf area ratio 80 cm2/g found to be ideal ceiling under light stress situations to assure yield of 2 t/ha or more.

Varieties adapted to low light : Swarnaprabha, Ptb 10, Hamsa, T 90, Mahsuri, Pallavi, Vijaya, NC 1281, Vajram & Hybrid IR 54752A/Vajram, 29A/Vajram, Archana, Prakash, Karikalan, Padma, IET 355, IET 721,CS 725, Monoharsali, IET 12238, 12537, 12563, 12564, and 12785.

PRODUCTION PHYSIOLOGY

The programme was reoriented in mid sixties with special emphasis on production physiology. Impetus was given on varietal improvement programme.

Studies on transplanted rice

The dry matter production after flowering directly contributes to grain yield under optimum conditions in dry season(DS). However, during wet season (WS) due to climatic constraints like low light and high night temperatures, the contribution of reserve carbohydrates becomes substantial for grain filling and yield.

The sink components like spikelet and grain number/m2 are associated with dry matter production at reproductive (r=0.56**) and ripening (r=0.79**) stages, respectively.

Yield is linearly related with panicle number/m2 (350-400 panicles/m2) but this relation fails at higher population density.

For growth of each spikelet the optimum source is 2.5 cm2 leaf area and 14 mg of stem weight at flowering stage, especially for early varieties like Ratna or Pallavi.

Major constraints for productivity in wet season are low grain number/panicle in early, high spikelet sterility in medium, and low panicle number in late duration varieties.

Besides efficient grain filling, high density grain(%) is also a desirable trait. High density grain varieties are characterised by higher rate of translocation of photosynthates to panicle, higher phosphorylase and nitrate reductase activity in shoot, greater mobilisation of N and rapid accumulation of starch in the developing grain.

Studies on photosynthesis

Leaf thickness (SLW), leaf vein frequency, stomatal conductance, leaf N percentage and leaf protein showed high association with Photosynthetic rate while leaf area and yield had a tendency for negative association.

Varieties with high Photosynthetic rate concomitantly recorded high respiration including photo-respiration, exception cvs.Ratna.

Maximum translocation of 14C assimilates to panicle was evident at 2 weeks after flowering. Assimilates produced during milk stage contributed 75% of total carbohydrates in grain. Varieties with high Pn are not necessrily efficient in translocation.

Donors for high photosynthesis: C 3383, CR 110-174, Pallavi, Kalinga I & II, Saket-4, CO 41, Ratna, Ptb 10, Swarnaprabha, IET 734, Jayanti, Sona, Vijaya, Indira, Jagannath, Asd 5, Mtu 15, Mahsuri, SR 26B, GEB 24, Mtu 16, Latisail, CR 1014, Sigadis,Club, Tainan 3 M, Brittle culm, Saturn striata, CR 125-12-30, CR 143-2-2, Sita, Indrasail,IR 54752A/Vajram, IR 62829A/Vajram, Anamica, IR 58, IR 9761-19-1, Vajram, IR 19806-8-1-3-2.

Cultivars with low photorespiration : B 76, Adt 27, Tkm 6, IR 8 , Ratna, Pankaj, Vijaya.

BASIC STUDIES ON PHYSIOOGICAL ASPECTS

Senescence in rice

The senescence of rice leaves in general may not be a simple function of chronological leaf age during grain filling period.During post flowering leaf senescence increased and a gradual accumulation of ethylene in leaf impaired the functional activity. In general, the Japaonica x Indica hybrids exhibit slower senescence than the derivatives from DgWg dwarfing gene source.

Seed germination/dormancy

Seed dormancy is a desirable character, especially with early types grown during the monsoon season.Many early types with moderate to high dormancy were identified e.g. Adt 19, adt 413, W 371, N 136, Mtu 17, IR 9, IR 5 etc. However, for immediate multiplication or sowing of seed , simple methods for breaking dormancy of seed were identified viz. heat treatment of seed at 42oC for 5-7 days or soaking seeds in dilute nitric acid for 24-36 hrs helped in breaking dormancy. The viability of rice seed can be maintained even for 10 years by keeping in a desiccator with calcium chloride.

Photoperiodism

Rice in general is a short day (SD) plant. Treatments of 30 d old seedlings for 8 hrs short day (8 am to 4 pm) for 20 days was optimum. In wild species response was evident in O. officinalis than in O. perennis. Tetraploids are more sensitive to short days than diploids. Foliar spray of NAA (10 ppm) hastened flower emergence even under non inductive photoperiods indicating that after floral initiation the emergence of panicle is mostly hormonal in nature.

Mineral nutrition:

Nutrio-physiological studies have indicated that the shy tillering varieties, Ptb 10 and Chianung 242, showed lower N and P concentrations than the high tillering types CB.II and T(N) 1. The lack of response to nitrogen in wet season was associated with low light and high temperature leading to high leaf weight ratio (LWR) at flowering of more than 25% which was found to be the threshold value for N response.

Development of Methodology : Chloropyll estimation :

A less complicated easy procedure to extract chlorophyll from rice leaves has been standardised. Incubating fresh leaf tissues (100 mg/25 ml) in acetone at 4oC in dark for 27 hours gave better result than the traditional grinding and centrifuging procedures or by using any other solvents.

Physiological studies on scented/long slender quality rice

Productivity of long slender rice either scented or non-scented is low in eastern India. The plant characters associated with such lower production are identified:

1) Non-synchronous tiller formation

2) Degeneration of spikelets

3) Higher percentage of sterility specially in early and medium duration varieties. "Dubraj", a medium slender scented variety showed minimum (<10%) sterility percentage.

4) Low head rice recovery; Highly significant positive association was observed between high density grain and head rice recovery in long slender rice.

Crop Modeling:

System Analysis and Simulation Modeling work started in the year 1986 after an exposure on the subject at CABO, The Netherlands, which continued since then under a collaborative banner known as SARP.

1)Crop Growth Modeling for Low Light Stress situations.

The macros model L1D.CSM was taken as the base model. Various physiological process oriented functions as appropriate to wet season of eastern India, were incorporated to simulate dynamics of crop growth more realistically. The model identified essential features of desirable plant type to assure grain yield of 3.0 t/ha (against <1.2t/ha average).

# plant height 1-1.15 m

# tiller number per hill 5-6 (15x10 cm spacing)

# grain number per panicle 125-135

# Max.photosynthetic rate 35-40 kgCO2/ha/h

# Initial solar energy utilisation efficiency 0.4-0.45 [kg CO2/ha/h]/[J/m2/s]

# maintenance respiration 0.03-0.05 g CO2/g dry matter per day at 30oC

# specific leaf weight not more than 350 kg/ha

# light extinction coefficient 0.7

2)Crop growth model for water deficit situations.

A simulation model was developed for economy in use of irrigation water under water deficit situations. Normal crop growth is a function of radiation use efficiency and cumulative PAR but under defined stress situation, the model switches over to calculate crop growth rate through transpiration efficiency and rate of transpiration. The leaf senescence index is introduced to give a feedback for remobilisation of carbohydrate and subsequent partitioning. Water balance on three layer soil profile is incorporated to precisely monitor soil-plant interaction and water uptake.

The model can advise the timing and amount of water needed for irrigation depending on the demand by the plant.

3)Simulation of population dynamics of BPH.

The model simulates two to three generations of the insect depending on the development rate based on physiological timings. It takes into account two forms of the insect, egg stage and efcundity, nymaphal stage and mortality, immigration and emigration and finaly the predator feeding dynamics to give a ralistic yet dynamic population growth rate of BPH - Nilaparvat lugens. It can forecast imminent epidemic situations and corresponding damage on host depending on the actual meteorological parameters of the locality.