EFFECT OF PLANT GROWTH REGULATORS ON MORPHO-PHYSIOLOGICAL, BIOPHYSICAL AND ANATOMICAL CHARACTERS IN COTTON Thesis submitted to the University of Agricultural Sciences, Dharwad in partial fulfillment of the requirements for the Degree of DOCTOR OF PHILOSOPHY in CROP PHYSIOLOGY By PRAKASH KOLER DEPARTMENT OF CROP PHYSIOLOGY COLLEGE OF AGRICULTURE, DHARWAD UNIVERSITY OF AGRICULTURAL SCIENCES, DHARWAD – 580 005 SEPTEMBER, 2008 ADVISORY COMMITTEE DHARWAD (B.C.PATIL) SEPTEMBER,2008 (CHAIRMAN) Approved by : Chairman :__________________________ (B. C. PATIL) Members : 1. ______________________ (M. B. CHETTI) 2._______________________ (A. S. NALINI PRABHAKAR) 3._______________________ (I. S. KATAGERI) 4._______________________ (S. M. HIREMATH) CONTENTS Sl. No. Chapter Particulars Page No. I. INTRODUCTION II. REVIEW OF LITERATURE III. MATERIAL AND METHODS IV. EXPERIMENTAL RESULTS V SUMMARY VI. DISCUSSION VII. REFERENCES LIST OF TABLES Table Title No. 1. Physical and chemical properties of the soil of experimental field 2. Weather data of Agricultural Research Station, Dharwad Farm for the year 2005-06; 2006-07 and the average of past 25 years 3. Treatment details of the experiment 4. Effect of plant growth regulators on plant height (cm) at different growth stages in cotton 5. Effect of plant growth regulators on number of leaves per plant at different growth stages in cotton 6. Effect of plant growth regulators on leaf length (cm) and leaf width (cm) at different growth stages in cotton 7. Effect of plant growth regulators on number of monpodia, sympodia, nodes and internodal length in cotton 7a. Effect of plant growth regulators on number of fruiting bodies at different growth stages in cotton 8. Effect of plant growth regulators on phenological characters in cotton 9. Effect of plant growth regulators on leaf dry weight (g plant-1) at different growth stages in cotton 10. Effect of plant growth regulators on stem dry weight (g plant-1) at different growth stages in cotton 11. Effect of plant growth regulators on dry weight of reproductive parts (g plant-1) at different growth stages in cotton 12. Effect of plant growth regulators on total dry weight (g plant-1) at different growth stages in cotton 13. Effect of plant growth regulators on absolute growth rate (g day-1) at different growth stages in cotton 14. Effect of plant growth regulators on crop growth rate (g m2day-1) at different growth stages in cotton 15. Effect of plant growth regulators on relative growth rate (g g-1 day-1) at different growth stages in cotton Contd….. Table Title No. 16. Effect of plant growth regulators on net assimilation rate (g-1 dm-2 day-1) at different growth stages in cotton 17. Effect of plant growth regulators on leaf area (dm2 plant-1) at different growth stages in cotton 18. Effect of plant growth regulators on leaf area index at different growth stages in cotton 19. Effect of plant growth regulators on leaf area duration (days) at different growth stages in cotton 20. Effect of plant growth regulators on specific leaf weight (mg dm-2) at different growth stages in cotton 21. Effect of plant growth regulators on chlorophyll ‘a’ content (mg g-1 fresh weight) at different growth stages in cotton 22. Effect of plant growth regulators on chlorophyll ‘b’ content (mg g-1 fresh weight) at different growth stages in cotton 23. Effect of plant growth regulators on total chlorophyll content (mg g-1 fresh weight) at different growth stages in cotton 24. Effect of plant growth regulators on nitrate reductase activity (µg NO g- 2 1 fresh weight) at different growth stages in cotton 25. Effect of plant growth regulators on membrane integrity (dS/m) at different growth stages in cotton 26. Effect of plant growth regulators on yield and yield components in cotton 27. Effect of plant growth regulators on fibre quality parameters in hybrid cotton 28. Correlation co-efficient values of yield with growth and yield components in cotton hybirds as influeced by PGRS (Pooled) 29. Effect of PGRS’s and spacing on yield and yield components, LAI, TDM and biophysical characters in hybrid cotton (RAHB-87) 30. Effect of growth regulators on economics of interspecific cotton hybrid (DHB-290) LIST OF FIGURES Figure Title No. 1. Weather data of ARS, Dharwad Farm, Dharwad (Karnataka) 2. Plan of layout of the experiment 3. Effect of foliar spray of PGRs on number of fruiting bodies in cotton hybrids 4. Effect of plant growth regulators on plant height (cm) at different growth stages in cotton 5. Effect of plant growth regulators on number of sympodia and number of nodes in cotton 6. Effect of plant growth regulators on total dry weight (g/plant) at different growth stages in cotton 7. Effect of plant growth regulators on leaf area index at different growth stages in cotton 8. Effect of plant growth regulators on leaf area duration (days) at different growth stages in cotton 9. Effect of plant growth regulators on specific leaf weight (mg/dm ) at different growth stages in cotton 2 10. Effect of plant growth regulators on total chlorophyll content (mg/g fresh weight) at different growth stages in cotton 11. Effect of plant growth regulators on nitrate reductase activity (µg NO /g fresh weight) at different growth stages in cotton 2 12. Effect of plant growth regulators on yield and yield components in cotton 13. Effect of plant growth regulators on fibre quality parameters in hybrid cotton LIST OF PLATES Plate Title No. 1. Morphological view of growth regulators treated plants 2. Morphological view of comparison of growth retardants sprayed at one stage (90 DAS) and at two stages (70 + 90 DAS) 3. Morphological view of comparison of growth promoters and growth retardants treated plants 4. Morphological view of leaves treated with plant growth regulators 5. Anatomical view (40x) of plant growth regulator treated leaves 6. Anatomical view (10x) of plant growth regulator treated leaves I. INTRODUCTION Cotton is one of the most important fibre crops playing a key role in the economic and social affairs of the world providing basic input to the textile industry. It is the oldest among the commercial crops of the world and is regarded as white gold. Cotton is grown chiefly for its fibre used in the manufacturing of cloth. Presently, India is the second largest producer of cotton in the world having the largest acreage. In India, cotton occupies five per cent of the total cultivated area, which is ¼th of the world’s area under this crop. Cotton is grown in India from 80 - 32.50 latitude and 700 - 800E longitude with an elevation ranging from 0 - 950 m. It is cultivated in areas where the average annual rainfall ranges from 250 - 1500 mm and widely varying soil conditions in terms of colour, texture, depth and nutrient status. In India, cotton is cultivated in an area of 9.53 million hectares with a production of 31.0 million bales of seed cotton (170 kg/bale) during 2007 - 08 (Anon, 2008). The average productivity of cotton in India is 599 kg lint per hectare, which is low when compared to world average (733 kg lint/ha). In Karnataka, the area under cotton during 2000 AD was over 6.0 lakh ha with average productivity of 220 kg per ha, which is again low compared to Indian average. Severe pest incidence, delayed sowing due to late release of water in the command areas, increased cost of cultivation, unpredictable yields, lower returns on high investments, etc. are the major reasons of lower productivity. Cotton productivity in India is low due to the fact that more than 65 per cent of the cotton area is under rainfed condition, low fertilizer consumption and low fertilizer user efficiency. In addition, India has about 28 per cent of area under desi cotton (G. herbaceum and G. arboreum) which are intrinsically low yielders due to the genetic and physiological constraints like long duration, shedding of plant parts, leaf reddening, bad opening of bolls and are grown in areas of high biotic and abiotic stresses. Cotton under the conditions of high rainfall or irrigation produces excessive vegetative growth resulting in mutual shading and shedding of reproductive parts, thereby reducing the yield. The desire to optimize plant growth, while maximizing yield led to the use of interest in PGRs. In the past two decades many new plant growth regulators have been developed and tested under field conditions. Cotton is a sub tropical, perennial plant with indeterminate growth habit. Vegetative and reproductive growth occurs simultaneously where vegetative growth is necessary to support reproductive growth. The growth habits of these varieties/hybrids combined with high availability of nutrients, timely rainfall or irrigation and delayed fruit retention can encourage excessive vegetative growth. Excessive vegetative growth leads to severe production problems like fruit abortion, delayed maturity, boll rot and harvest difficulties. The physiological efficiency of a plant can be improved by prolonging photosynthesis, reducing photorespiration, better partitioning of photo assimilates, improving mineral ions uptake and stimulating nitrogen metabolism. All these processes are inter-linked through several interactions and influence growth and productivity. Plant growth regulators have been found to influence these processes in one way or the other. Plant growth regulators are substances when added in small amounts modify the growth of plant usually by stimulating or inhibiting part of the natural growth regulation. They are considered as new generation of agrochemicals after fertilizers, pesticides and herbicides. Plant growth regulators are capable of increasing yield by 100-200 per cent under laboratory conditions, 10 - 15 per cent in the field conditions (Kiran Kumar, 2001). Plant growth regulators like promoters, inhibitors or retardants play a key role in internal control mechanism of plant growth by interacting with key metabolic processes such as nucleic acid and protein synthesis. The most commonly used growth regulator in cotton is mepiquat chloride, which is an inhibitor of gibberlic acid. This curtails excessive vegetative growth and increases the yield. Plant growth regulators are shown to change leaf resistance by altering stomatal aperture, the rate of photosynthesis could be manipulated through this technology. IAA, GA, kinetin, phenolics and aliphatic alcohols are reported to increase and stimulate the rate of photosynthesis. In several species, the application of growth retardants is shown to stimulate photosynthesis by increasing LAI, delaying leaf senescence, increasing the functional duration of the leaf or delaying degradation of chlorophyll which has improved source-sink relationship. Cotton plant has a natural mechanism to prevent excessive vegetative growth with higher nitrogen levels, soil moisture, temperature and fruit loss by insect, disease and nematodes. In many cases, these factors are not well balanced and growth regulators are needed to maintain proper plant size and to synchronize boll set and to regulate maturity. Additionally, indeterminate varieties also require plant growth regulators to shift cotton from vegetative to reproductive growth. Mepiquat chloride is an anti-gibberelin that inhibits cell expansion but not cell division. Its spray directs carbohydrates into reproductive organs and hence used to control plant growth. It is available in different trade names that include pix, mepex, pixplus, pix ultra and others. Pix, which is a growth retardant when applied as foliar spray reduces the vegetative growth, leaves become coarse and dark green in colour (Cothren and Osterhuis, 1993; Brigg, 1980; York, 1983 and Edmisten, 2000). With the above background, the present investigation was carried out with the following objectives. 1. To know the effect of plant growth regulators on leaf anatomy and morphological characters of cotton. 2. To know the effect of plant growth regulators on biophysical and phenological characters of cotton. 3. To know the effect of plant growth regulators on membrane integrity and nitrate reductase activity of cotton. 4. To know the effect of plant growth regulators on yield and yield components of cotton. II. REVIEW OF LITERATURE The role of plant growth regulators (PGR’s) on various physiological and bio-chemical processes of plants is well known, which enables a rapid change in the phenotype of the plant with one season to achieve desirable results. Plant growth regulators are known to affect right from seed germination to senescence by enhancing the growth (growth promoters) reducing the plant height (growth retardants), altered flowering, fruit set, seed development, fruit ripening and yield. Cotton often produces more vegetative growth than is needed for maximum boll production and yield especially when climatic conditions favour vegetative growth, thereby directing the photo-assimilates towards the vegetative growth rather than reproductive growth. However, in the recent past, different workers have emphasized the use of various growth regulating chemicals for the control of vegetative growth in cotton. This chapter emphasizes the recent work on plant growth regulators in cotton and their effect on morphological, physiological, bio-chemical parameters and yield attributes. 2.1 EFFECT OF PGR’s ON MORPHOLOGICAL CHARACTERS 2.1.1 Plant height Plant height and number of branches are influenced by interaction between the environmental conditions and genetic make up of the plant. Dastur and Prakash (1954) observed that foliar application of NAA @ 40 ppm increased the plant height. Thomas (1964) reported that plants characteristically produce dark foliage and develop short stem internodes, hence the term dwarfing chemicals to this class of growth retardants. Later, they observed reduction in elongation of main stem, fruiting branches and flowering. Annapan and Aaron (1969) reported that NAA increased the plant height when sprayed at 60 and 75 DAS in cotton. Chokhey Singh et al. (1970) indicated an increase in plant height by increase in sympodial branches and number of bolls per plant. Plant height had strong correlation with number of branches and days to first flower. Zur et al. (1970) found that application of CCC @ 50 and 100 g ai ha-1 at square initiation stage reduced the plant height significantly. Application of CCC at 0.2 kg ha-1 before flowering provided temporary check on the vegetative growth and reduced plant height (Singh and Singh, 1970). Gidnavar (1979) found that the application of CCC decreased the height of cotton plant. Misra and Malik (1980) observed a reduction in height of plant with increasing concentration of CCC. Walter et al. (1980) reported that the application of dimethyl piperidinium chloride (DPC) @ 1500 ppm at first bloom stage in cotton reduced the plant height by 28 per cent. Mulder et al. (1981) reported that spraying of mepiquat chloride at an early reproductive stage in cotton reduced the plant height. Varela and Yellejo (1982) reported that the application of DPC (25, 50, 70 g/ha) twice at 60 days after sowing and 15 days later resulted in the reduction of plant height in cotton. Virk et al. (1984) reported that increased cycocel concentration reduced plant height in cotton. Azab et al. (1987) reported that the application of cycocel at square initiation or at flowering stage reduced the plant height in cotton. Sheshadri (1989) concluded that the application of CCC to cotton decreased average plant height and internodal length. Kapagate et al. (1989) reported that GA (500 ppm) was most effective in increasing plant height followed by NAA (1000 ppm) in cotton cv. Branil 1007. Vyakaranahal et al. (1989) reported that the influence of fertilizer dosage and five sprays (at 90,100,110, 120 and 130 days after of sowing) of NAA (10 ppm) to female parent of Varalaxmi cotton hybrid helped to restructure the plant by decreasing vertical growth and enhancing the lateral growth with significant increase in monopodial and sympodial branches. Ansari et al. (1989) reported that yield per plant correlated with plant height and boll number, but not with number of monopodial branches. James (1991) reported that pix reduced plant size and enhanced earliness. Pix partially inhibits one of the enzymes that is involved in GA biosynthesis, produce fewer fruiting branches, shorter plant, shorter internodes and higher per cent of fruit set by the application of pix (453.6 g ha-1) at early blooming stage (Charles Stichler, 1991). Boquet and Coco (1993) opined that MC can be used to manage the vegetative development of cotton plants to offset the effect of excessive irrigation or N 2