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Articles by F. Azam
Total Records ( 26 ) for F. Azam
  F. Azam , M.H. Sajjad , A. Lodhi and R.M. Qureshi
  Experiments were conducted under greenhouse conditions to study I) the dynamics over time of mineral N, mineralizable N and humus N during decomposition in soil of leguminous and non-leguminous plant material and ii) the impact of these changes on growth and N nutrition of wheat fertilized with 15N-labelled ammonium sulphate. Finely ground straw of wheat, maize and sesbania was allowed to decompose in soil for 0, 2, 4 and 8 weeks. Sub-samples of soil were analyzed for the content of mineral N, mineralizable N and humus N. The bulk soil was sown to wheat and the plants harvested at maturity. Nitrogen as 15N-labelled ammonium sulphate was applied in two split doses of 40 and 60 mg kg-1 soil. Accumulation of mineral N in soil during 8 weeks of residue decomposition was found to depend on the chemistry of plant residues, more mineral N being released in soil amended with plant residues with narrow C/N ratio i.e., maize and sesbania. These residues also contributed more to humus N and maintained a higher content of potentially mineralizable N. Wheat straw not only caused a net immobilization of N during 8 weeks of aerobic incubation but a substantially higher loss of NO3¯+NO2¯ -N during subsequent incubation under submerged conditions. The loss of NO3¯+NO2¯ -N was more where residues were given less time for decomposition. Plant residues applied immediately before sowing wheat or those allowed shorter period of decomposition had a negative effect on plant growth. Of the three residue types, wheat straw caused a higher reduction in plant growth. This was attributed mainly to significantly reduced availability to plants of soil-N, while uptake of fertilizer N was affected almost similarly by the three types of residues. Residues of maize and sesbania had a positive effect on grain yield and total biomass of wheat. As a whole, ca 30% of the fertilizer N applied was taken up by the plants and >40% was unaccounted in the soil-plant system, fertilizer N remaining in soil being <30% of the applied. Relatively higher proportion of the applied N remained in amended than unamended soil after crop harvest.
  F. Azam
  Studies conducted under controlled laboratory conditions using 14C showed a reduction in the rate of decomposition of plant residues with increased chemical complexity of the material; glucose being the most rapidly decomposed and least transformed into humic compounds. Lignin carbon was the most recalcitrant, but up to 50% was transformed into stable humus fractions. Rate and extent of immobilization and remineralization of N decreased with increased complexity of the plant residues/components; maximum being observed for glucose and minimum for lignins. Immobilization and remineralization turnover of N was used to determine dynamics of microbial biomass as well as to test assumptions used for its quantification with chloroform fumigation method. Chloroform fumigation was found to cause a substantial increase in the extractability and mineralization of non-biomass N. Quality of plant residues had a significant bearing on mineralization of N and its interaction with native soil N. Residues with narrow C/N ratio and high content of labile C had a positive effect on release of N from soil organic matter and its availability to crop plants. A substantial and real added nitrogen interaction was observed following application of fertilizer N (more for NH4 than NO3) and leguminous plant residues. In plant experiments, the interaction was exhibited by a substantial increase in root biomass especially under salinity stress. Higher amounts of N were released from leguminous plant residues in the presence of NH4 than NO3. Residues from cereal crops like rice and wheat had a negative effect on the plant availability of N from soil organic matter rather than from applied fertilizer. Studies under field conditions compared leguminous and non-leguminous crops for biomass accumulation and grain yield. When used as a green manuring crop, maize had an effect similar to recommended dose of fertilizer. Green manuring of cereal crop residues like wheat, avena and barley also had a positive effect on yield of wheat.
  F. Azam
  Application of fertilizer N to soil or to the soil-plant system often leads to enhanced mineralization and plant availability of N. By using 15N isotope methodology, it has been found that the extra N comes from soil organic matter as a result of interaction of the added N. This phenomenon is termed "priming" action or added nitrogen interaction (ANI) and may be apparent or real and positive or negative. Apparent ANI is supposedly caused by pool substitution, while real ANI results from changes in the processes that move N into or out of a given pool. Although ANI is generally positive, negative ANIs may arise from processes like net immobilization, denitrification and NO3- leaching. Occurrence of ANI has implications to the determination of fertilizer use efficiency as well as to the fate of fertilizer and soil N. Hence, an understanding of the occurrence of ANI and the mechanisms involved is necessary to devise strategies for improved fertilizer management practices.
  F. Azam , M. Ashraf , A. Lodhi and A. Gulnaz
  A microplot field experiment was conducted to study the effect of irradiated and unirradiated sewage sludge on dry matter yield and N uptake of wheat. Sewage sludge was applied at rates equivalent to 120, 180, and 240 kg N ha–1, either with or without 15N-labelled (NH4)2SO4-N at 20 kg ha–1. In addition, one control (no treatment) and a treatment receiving 120 kg N ha–1 as 15N-labelled (NH4)2SO4 was also included in the experiment. Wheat was grown to maturity and the plots were then sown to Sesbania aculeata (a green manuring legume). A highly positive effect of sewage sludge, whether irradiated or unirradiated on dry matter yield and N uptake. Sewage sludge not only served as an additional source of plant available N but it helped conserve fertilizer N leading to its increased uptake by plants. The beneficial effect of sludge was more pronounced in the presence of fertilizer N and the effect increased with the rate of application. The effects seemed to persist after harvesting wheat as suggested by higher dry matter yield and N yield of Sesbania. However, the analyses of physico-chemical and biological properties of the soil after harvesting wheat indicated that probably the applied sewage sludge decomposed quite rapidly and thus did not add much to the soil organic matter content and other properties. Nevertheless, N content of the soil showed some improvement although not very consistent with the rate of application.
  T. Mahmood , R. Ali , F. Azam and K. A. Malik
  Study was conducted on the role of nitrogen (N), applied either alone or in combination with phosphorus (P), in composting of kallar grass [Leptochloa fusca (L.) Kunth] with particular emphasis on carbon (C) and N conservation during composting. Nitrogen was added as ammonium sulphate and P as single superphosphate. Addition of N alone, though accelerated the composing rate, it did not conserve C and N during composting. However, application of P along with optimum level of N accelerated the composting rate, stimulated the substrate transformation into humic acid, and decreased the N loss. The results erriphasized the need of phosphorus amendment along with nitrogen to conserve C and N during composting of kallar grass.
  A. Lodhi , N.N. Malik , T. Mahmood and F. Azam
  Laboratory incubation experiments were conducted to study the response of bacterial and fungal population, soil microbial biomass, urease, amylase, invertase and cellulase to Baythroid applied at 0, 0.4, 0.8, 1.6, 3.2 and 6.4 pg g–1 soil (on an active ingredient basis). Generally, a positive effect on bacterial and fungal population was observed. 'Bacterial population increased from 13 to an average of 25 after 5 days of incubation of soil samples treated with different levels of Baythroid. Baythroid did not have a significant effect on fungal population, which was quite low after 5 days of incubation. After 15 days of incubation, however, Baythroid caused a substantial increase in fungal population although no consistent trends were observed with the rate of application.
Carbon dioxide evolution from soil was almost unaffected by Baythroid except at the lowest and the highest levels of addition, where a negative and a positive effect, respectively, was obvious. Cumulative losses of CO2-C increased by 38% at the highest level of Baythroid. The microbial biomass C varied between 138 and 147 pg CO2-C g–1 soil in differently treated soils, a substantially positive effect of Baythroid was observed only at the highest rate of addition, while at lower levels a positive but non-significant effect was observed. Amylase activity increased by a maximum of 91.5% at Baythroid level of 1.6 μg g–1. At 6.4 μg g–1 soil Baythroid, however, the activity was reduced by 47.9%. Invertase activity also increased by 110.9% at 1.6 μg Baythroid g–1 soil followed by a decrease of 40.3% at the highest level tested. Cellulase activity was not much affected, although an increase of 18.5% was observed at 1.6 pg g–1 soil Baythroid. At the highest level of Baythroid, however, cellulase activity was reduced by 25.9%. Response of urease was almost similar to that of other enzymes. However, maximum increase of 40.9% was achieved at 0.8 pg g–1 soil Baythroid, while the decrease (9.1%) at higher levels of Baythroid was less pronounced as compared to that for other enzymes. All the four enzymes showed a positive relationship in their response to different rates of Baythroid.
  F. Azam and A. Lodhi
  Interactive effect of inorganic fertilizer and sewage sludge on nitrogen nutrition and growth of wheat was studied. Nitrogen was applied as 15N-labelled (NH4)2SO4 at 0, 50 , 150, and 300 mg pot–1 in all possible combinations with 0, 16, 24, 32, and 64 g pot–1sewage sludge (SS). Fertilizer N had no significant effect on the dry weight of roots. The above-ground plant components responded positively to the application of both fertilizer N and SS. The positive effect increased with the rate of application. In absence of SS, grain yield increased from 4.8 g pot–1 in the control to 10.6 g pot–1 at the highest level of fertilizer N. Likewise, the increase in grain yield due to different treatments ranged between 97 and 233% as compared to 23.3 and 82.5% recorded for straw component. The trends in N content of different plant components were fairly similar to those observed for dry matter yield and a significant correlation was observed between two parameters. Combination of both treatments at highest rate resulted in 127% increase in the total N yield of the plants. The contribution of N fertilizer to the total N content of the whole plant and its components remained fairly low and ranged between 11 and 45% in different treatments. The percent fertilizer N uptake (%FNU) varied from 22.6% at the highest level of application in the absence of sludge to 79.4% at the lowest level of application and in the presence of highest amount of SS. Fertilizer N uptake increased with the amount of SS; the extent of increase being more at the lower level of fertilizer N. Application of SS significantly improved the amount of unlabeled N determined in plants, with maximum effect being observed at the highest level of application. A part of this increase was due to N uptake from SS itself, while a substantial amount could be derived from the soil organic matter.
  S. Farooq and F. Azam
  This paper describes the concept of agricultural biodiversity and its importance in present and future food security. Some facts and figures are being presented in order to apprise the reader about the state of agricultural biodiversity in this country and elsewhere. The term agricultural biodiversity has been elaborated at length with special reference to the type of biodiversity available in Pakistan. The importance of biodiversity has been discussed in relation to its role in value addition to commercial crops in the form of resistance against pests and diseases. Its contribution, to human foodstuff, removal of genetic vulnerability and food security has also been discussed in detail. How agro-biodiversity has been utilized in crop production programmes and how rapidly it is being eroded, has also been described. Emphasis has been made on the conservation (both in situ and ex situ) of sites rich in agro-biodiversity along with its characterization and utilization in order to enhance its present status and to create new biodiversity to meet the future demand of crop improvement especially for tolerance to abiotic stresses.
  F. Azam and S. Farooq
  Form (NH4 or NO3) and availability of N has significant implications to the functioning and sustainability of agroecosystems. Most of the fertilizer nitrogen (N) applied to agricultural soils is in the form of NH4 or NH4-forming fertilizers. This form of N is rapidly oxidized to NO3 by nitrifying microorganisms leading to significant losses of N through NO3-leaching and denitrification. Both denitrification and NO3-leaching have environmental implications and economic concerns. Strategies have therefore been sought to regulate the process of nitrification leading to its complete or partial inhibition. Indeed, climax ecosystems are developed in such a way that the process of nitrification is already fairly inhibited. This paper presents an overview on: I) the process of nitrification, ii) microorganisms involved, iii) the implications of nitrification and nitrification inhibition to ecosystem functioning and finally iv) the methods to inhibit nitrification.
  M.H. Sajjad , F. Azam and A. Lodhi
  Laboratory and greenhouse experiments were conducted to study the changes in mineral N, humus N and plant available N during following decomposition of plant residues (wheat straw, maize straw and sesbania straw) for different time periods. Accumulation of mineral N in soil was found to depend on the chemistry of plant residues, more mineral N being released in soil amended with plant residues with narrow C/N ratio i.e., maize and sesbania. These residues also contributed more to humus N and maintained a higher content of potentially mineralizable N. Wheat straw not only caused a net immobilization of N during 8 weeks of aerobic but a substantially higher loss of NO3 +NO2 -N during anaerobic incubation. The loss of N under these conditions appeared to depend on the length of time the residues were allowed to decompose in the soil, more losses being recorded for residues at early stages of decomposition. Undecomposed or partially decomposed plant residues had a negative effect on plant (wheat) growth; the effect was positively related to N uptake by plants. The negative effect was eliminated by increasing the time of residue decomposition to 8 weeks at which point maize and sesbania had a positive effect on grain yield and total biomass of wheat. Since N availability could be the main yield determining factor, sufficient time for residue decomposition will be required to achieve net N mineralization and thus improved plant growth especially for plant residues with a wide C/N ratio. However, the N released during aerobic incubation (or during land preparation prior to planting) may indeed be lost at first irrigation from the soil-plant system depending upon the content of easily oxidizable organic C.
  F. Azam and S. Farooq
  Atmospheric concentration of CO2 has increased significantly over the past few decades and so have the concerns about the greenhouse effect and global warming. One of the extensively explored aspects is the response of ecosystem components in terms of performance and productivity. A host of information thus generated suggests a positive effect of elevated CO2 on functioning of plants from seed germination through maturation vis-a-vis rhizospheric microbial functions. Amazingly, most (if not all) of the researches deal with plant responses to CO2 at levels twice that of ambient with a view that fossil fuel burning and increased agricultural activity are adding substantially to the atmospheric CO2 . As such, hardly any attention has been paid to the contribution of soil respiration (includes that of microbes and plant roots) to CO2 concentration within the soil matrix as well as above the soil surface. This study presents an analysis of the available literature to demonstrate that by default the plant communities are already functioning at elevated levels of CO2 . Any further increase due to human intervention (especially fossil fuel burning) may not have a significant effect on plant functions and productivity. Hence the potential dangers of elevated CO2 resulting from fossil fuel burning should not be considered as alleviated through increased plant productivity.
  F. Azam and C. Mueller
  Laboratory incubation experiments were conducted to study the effect of 3,4-dimethylpyrazole phosphate (DMPP) on I) nitrification, ii) N mineralization potential of the soil, iii) immobilization-remineralization of N and iv) respiratory activity of the soil as well as N2O emissions. The inhibitor was applied at 0.35 to 17.5 mg kg-1 soil in different experiments and the incubation carried out at 25°C for variable lengths of time depending upon the nature of experiment. As expected, the process of nitrification slowed down in the presence of DMPP, rate of nitrification being slower at higher levels of the inhibitor. Measurable quantities of NO2- were found only during the first 3 days of incubation with DMPP having a negligible effect. Potentially mineralizable N showed a small but significant increase in the presence of DMPP i.e., an average of 11 and 9 mg kg-1 NH4+-N accumulating in treated and untreated soil samples, respectively, during the first week of incubation. As expected, only 10% of the NO3--N present initially was recovered after one week and ca 5% at the end of 2nd week of incubation suggesting significant losses, DMPP had a negligible effect on disappearance of NO3-. Immobilization of NH4+-N and NO3--N in glucose amended soil was significantly retarded by DMPP, the effect being more at higher than recommended concentrations. Immobilization of NO3--N was retarded more than that of NH4+-N suggesting that the immobilization of two forms of N was affected differently by DMPP. Net accumulation of mineral N (remineralization) was slower in DMPP-treated soil. The flux of N2O and respiratory activity (loss of CO2 and consumption of O2) decreased in the presence of DMPP.
  F. Azam and S. Farooq
  Over the past few decades, global warming vis-a-vis elevated CO2 and other greenhouse gases (GHGs) has remained an issue of concern for researchers, environmentalists and policy makers. Fossil fuels have been blamed for most of the rise in atmospheric CO2 over the recent past in spite of the fact that water vapour (WV) is the predominant greenhouse gas (atmospheric concentration of 1-2% i.e., 27-54 times that of CO2 and >95% contribution to greenhouse effect) and mostly of natural origin. Incidentally, most if not all, statistics on GHGs overlooks WV creating the impression of human intervention (anthropogenic) as the dominant contributor to global warming. Similarly, role of evapotranspiration (ET) from the vegetated land in elevating the atmospheric concentration of WV is almost completely overlooked. According to highly conservative estimates ET from agricultural lands is responsible for adding >22x1012 t year-1 to the total atmospheric water of 30-60x012 t. These are astonishing high contributions to atmospheric WV that need to be considered when assessing anthropogenic (agricultural activity is certainly an anthropogenic activity) aspects of global warming. This review takes an account of these factors ultimately suggesting that i) ET is capable of raising the atmospheric WV concentration significantly and ii) evolution and introduction of crop types more efficient in water use may help resolve the problem.
  M. Ashraf , O. Berge , F. Azam and T. Heulin
  This study was conducted to isolate and identify the EPS-producing bacteria associated with the roots of three wheat lines grown in saline and non-saline soils. Results indicated the presence of various EPS-producing bacterial genera in unplanted saline and non-saline soil, rhizosphere and rhizoplane of the three wheat fines. Bacillus sp. were more variable in unplanted saline than non-saline soil. In contrast to uniform distribution of Bacillus sp. in unplanted soils, other EPS-producing bacterial genera isolated from rhizosphere and rhizoplane were more numerous and diversified. Frequent occurrence of Microbacterium sp. in the soil and rhizosphere of the plants invoke the desire for more research work to explore the role of this bacterium in the saline environment.
  A. Lodhi , N.N. Malik and F. Azam
  A field lysimeter experiment was conducted to study the uptake by plants, dissipation and movement in soil of 14C-cyfluthrin (active ingredient of Baythroid, an insecticide produced by Bayer, Germany). Cotton and wheat plants were grown in succession to study the uptake of 14C. The chemical was worked well into the soil supporting the growth of a healthy cotton plant. The plant harvested at maturity contained 0.376 percent of the applied 14C; a major portion (ca 65 percent of the total) of the 14C being located in the stem portion. Wheat plants grown after cotton contained 0.11 percent of the initially applied 14C.
Dissipation of 14C from the soil-plant system was fairly rapid and after 9 weeks (during growth of cotton), ca 50 percent of the applied 14C was unaccounted. Subsequent losses were slower and during the remaining study period of 29 weeks, a further decrease of only 10 percent of the applied 14C occurred. Wheat growth and organic amendment caused a decrease in the loss of 14C from the soil-plant system. At all sampling intervals, a greater proportion of 14C was restricted to the top 0-10 cm layer and the amount consistently decreased with depth. In general, >80 percent of the 14C determined in soil at different sampling intervals was present in forms non-extractable with methanol.
  A. Lodhi , N.N. Malik and F. Azam
  A greenhouse experiment was conducted to study the uptake and metabolism in cotton leaves of 14C-labelled cyfluthrin, (C22H18Cl2FNO3, active ingredient of Baythroid insecticide). The labelled chemical was sprayed onto the selected portions of leaves which were subsequently studied for the movement (using autoradiography) and recovery of 14C (using extraction, purification procedures). Autoradiography showed a fairly rapid movement of 14C in the leaf tissues through vascular tissues. Movement was more efficient when application was made on the mid-rib region. Dissipation of 14C was also fast and even after 2 days, >60 percent of it was unaccounted. Subsequently, however, the losses were slow and amounted to 70.6 percent after 35 days. Thin layer chromatography/co-chromatography of organic extracts followed by linear scanning revealed that >60 percent of the 14C was still present as parent compound. Partial hydrolysis of cyfluthrin was found to be the main process involved in degradation that resulted in two major degradation products or metabolites.
  F. Azam and S. Farooq
  One of the dramatic observations on response of plants to elevated CO2 is their enhanced tolerance to stresses like light, temperature, salinity and nutrients. High temperatures and light intensity (like that in Pakistan) have generally a depressing effect on growth of plants, especially those having C3 photosynthetic system. These plants have a lower optimum temperature for photosynthesis that is raised at elevated CO2 thereby protecting the plants from being over-heated. In addition, the photorespiratory activities of C3 plants at higher temperatures are curtailed in the presence of high CO2 concentrations, thereby helping the plants conserve C and energy. Low as well as high light intensities are reported to limit photosynthesis at ambient concentrations of CO2, while elevated CO2 levels have a mitigating effect. Elevated CO2 levels allow plants to live under light conditions insufficient to meet photosynthetic requirements, while under high light intensities photorespiratory activities are curtailed. Similarly, positive effect of elevated CO2 on plant performance under conditions of limited water availability (e.g., because of soil salinity, drought) has consistently been reported. It is believed that the on-going rise in air`s CO2 content will protect trees from debilitating water stress. The water stress may not necessarily be that of drought, excessive irrigation may have negative effect as well and is reported to be mitigated by elevated CO2. Plants growing under soil salinity stress have also been reported to benefit from elevated CO2. The benefit is reported to be derived from the availability of more solutes for osmoregulation by reducing the transpirational intake of salts or by improving RUBISCO activity. In C4 plants, elevated CO2 helps overcome the leakiness induced by salt stress. In addition, positive effect of elevated CO2 on root proliferation and root-induced microbiological and biochemical changes may help plants withstand salinity stress. One of the reasons for a more positive effect of elevated CO2 on plants under growth limiting conditions is the enhanced root proliferation. Thus at low level of N availability that would generally limit plant growth, elevated CO2 helps plants extract more N from soil by exploring a greater soil volume and stimulation of photosynthetic rates. This paper gives an overview of the available information on the subject vis-à-vis agroclimatic conditions prevailing in Pakistan.
  F. Azam
  Nitrogen is the most common nutrient element, limiting crop production. Introduction and use of chemical N fertilizers has therefore led to a significant increase in crop yields. A major proportion of the nitrogenous fertilizers used in agriculture is applied to staple cereals like rice, wheat and maize. However, because of inherent economical and environmental implications of fertilizer N use, efforts have consistently been made to induce/enhance biological nitrogen fixation in cereals. Induction of nodulation has therefore been the main target of researchers over the past few years. This paper presents an evaluation of the achievements and prospects of nodulation in cereals (with particular reference to wheat and rice) as a means to decrease their dependence on fertilizer N.
  M.H. Sajjad , A. Lodhi and F. Azam
  An incubation experiment was conducted under laboratory conditions to study the changes in some soil enzymes during the decomposition of plant residues. Soil samples amended with powdered plant material of wheat, maize and sesbania were incubated for 8 weeks at moisture content of 60% of the maximum water holding capacity and 22-26°C for 8 weeks. At 0, 2, 4 and 8 weeks of incubation, portions of soil were analyzed for total C and activity of different enzymes. Maximum dehydrogenase and invertase activity was observed for sesbania and minimum in unamended soil, however there was no consistent trends with incubation intervals. Cellulase activity was not affected strongly by organic amendments, however it increased with time in amended than unamended soils. The differences between different treatments were non significant for urease.
  S. Farooq and F. Azam
  Plant breeding is a combination of principles and methods of changing the genetic constitution of a plant to make it more suitable for human needs. Conventional plant breeding has evolved with the passage of time from simple seed saving of the best harvest to the selection of seeds according to the laws of Mendel. With the advent of morphological and biochemical markers, the selection process has hastened and the scope of conventional plant breeding increased many folds during the recent years. However, the process that actually revolutionized the plant breeding in the 20th century was the realization that there exist a widespread polymorphism in natural populations, the degree of which can be assessed by sequencing or making restriction maps: an application of new tools of molecular biology. The first and the foremost molecular markers system i.e., restriction fragment length polymorphism (RFLP) was developed in early 1980. These are co-dominant markers and are available in unlimited number. Another breakthrough was the emergence of polymerase chain reaction (PCR) in 1990. With this technology, a new generation of DNA markers such as randomly amplified polymorphic DNA (RAPDs), sequence characterized amplified regions (SCARs), sequence tagged sites (STS), single polymorphic amplification test (SPLAT), variable number of tendom repeats (VNTRs), amplified fragment length polymorphism (AFLP), DNA amplification fingerprinting (DFA), single strand conformational polymorphism (SSCP), single nucleotide polymorphism (SNPs), micro-satellites or short tandem repeats (STRs), cDNA, DNA micro arrays and rDNA-ITS were introduced into the modern plant breeding systems. The concept of DNA based markers has increased our ability many folds, to follow minute regions of chromosome through opportunities such as map based cloning and Marker-assisted Plant (MAP) Breeding. In MAP breeding, the new ideas and concepts have been introduced which need to be understood thoroughly, before applying these ideas in practical breeding programmes particular in country like Pakistan where application of molecular biological approaches are still in its infancy. In order to achieve this objective, efforts were made to write a series of review articles in which concept of MAP breeding is being described thoroughly yet in a simple way so that student and researchers can build their understanding of plant molecular breeding and application of DNA based markers for the genetic dissection of qualitative and quantitative traits. In the present paper, concepts of MAP breeding and the type and characteristics of DNA markers is presented so that choice of the marker(s) can be made rational and for the defined purposes.
  S. Farooq and F. Azam
  This paper describes some of the pre-requisites for applying molecular markers in plant breeding or crop improvement programmes. This includes, possible answers to some of the very pertinent questions regarding marker-assisted plant breeding. For example, I) how an effective marker system is to be selected, ii) how, when and where these expensive technologies can be used efficiently and iii) what particular problem would be solved just by using a particular marker system. The most commonly used marker systems including restriction fragment length polymorphism (RFLP), amplified fragment length polymorphism (AFLP), micro-satellite or simple sequence repeat (SSR) and random amplified polymorphic DNAs (RAPDs) have been described in detail. The advantages and disadvantages (if any) of these marker systems and their practical utilization in different areas of crop improvement programmes have been discussed. Different methods of integrating molecular markers in conventional plant breeding programmes have also been described in greater detail with special reference to varietal identification and germplasm characterization, marker-assisted selection for qualitative and quantitative traits and abiotic stress tolerance. It is suggested that in all these cases, cost-effective application of markers can best be achieved through collaboration with those who excel in this technology. This collaboration is also necessary in order to integrate the systems and technologies to deliver the product in minimum possible time and with minimum extra input/investment in terms of operational expenses.
  S. Farooq and F. Azam
  Some of the empirical results obtained through the use of RFLP, AFLP, SSR and RAPD markers in the areas of DNA fingerprinting, measurement of genetic distance and heterosis, marker-assisted selections and abiotic stress tolerance are being described. Various difficulties that a user can encounter during the ontogeny of marker`s application have also been discussed. Marker mediated varietal fingerprinting and germplasm characterization appeared most common and most pervasive application with AFLP and SSR markers. Being cost effective, easy to handle and devoid of any radioisotope requirement, SSR markers are considered as the most suitable and reliable system for DNA fingerprinting. Capturing heterosis appeared most difficult with very little success due to lack of a facile marker system that could unconditionally identify the heterotic groups, population and progenies. Marker-assisted selections for qualitative traits appeared most successful after DNA fingerprinting while for quantitative characters, major disease resistance genes and genes controlling QTL for abiotic stress tolerance, the success is limited. It is anticipated that application of markers will remain restricted in these areas till the allele-specific markers are available and the cost of marker analysis is reduced significantly.
  F. Azam , S. Farooq and A. Lodhi
  Microbial biomass is a small but labile component of soil organic matter and plays an important role in cycling and other nutrient elements. Because of its importance in the functioning of different ecosystems, synthesis/dynamics of microbial biomass and its role in plant nutrition under different ecosystem conditions has assumed greater significance. In the same perspective, developing quick and convenient methods of determination have been of immense research interest for the least few decades. As a result significant improvements have thus far been made although no single method is devoid of snags. This paper presents I) a critical evaluation of methods to determine microbial biomass and ii) a review on the formation/dynamics of microbial biomass and its role in plant nutrition. Since carbon © and nitrogen (N) are the major elements, special attention has been given to these while discussing microbial biomass.
  S. Farooq and F. Azam
  Plant breeding in its primitive form is being practiced since the transition of human being from hunter/gatherers to settled agriculturist, approximately 10,000 thousand years ago. Without knowing genetics and its principal, it was used genetics to modify crops and their products. The selection of plants with best characteristics as source of next year seeds quickly resulted into domestication of crops that were distinct from their wild relative. Genetic modification (GM) has emerged against this historic background of breeding and selection and is thus, the extension of existing techniques and not something, which is unprecedented. In present paper, efforts have been made to review situation (s) that are responsible for the origin of genetically modified (transgenic) approaches to be used for crop improvement. The outcome of these approaches and the credibility of the resultant products along with their impact and significance on crop productivity in particular have also been reviewed. Impact of GM technology on the poor farmers in the developing countries with special reference to their needs and resources has been discussed in detail. The current status of genetically modified crops in the developed countries and also in the developing countries willing to adopt this technology albeit slowly has also been described along with their fears and concerns in order to provide the readers the choice to select this technology or otherwise according to their own needs and resources. The paper also provides information on the genetically modified products that can have significant impact in improving nutritional status of food generally consumed by millions of people living in the hart land of poverty that is South Asia and Sub-Saharan Africa.
  F. Azam and S. Farooq
  Symbiotic nitrogen fixation by legumes is the major natural process of adding nitrogen into the biosphere amounting to about 35 million tons annually. The process of nitrogen addition to the ecosystems and its further fate is such as to pose minimum threat to environmental cleanliness relative to N used as chemical fertilizers. Therefore, it has been of great interest not only to understand the basics of nitrogen fixation process but also to quantify the amount of N added to a system under different conditions. This is important in order to quickly screen the available germplasm for its potential of biological N2 fixation and to devise strategies for further improving the process under different ecological conditions. A critical evaluation of some common methods of studying N2 fixation in legumes is presented.
  F. Azam , F. Aziz , S. Farooq and A. Lodhi
  A greenhouse experiment was conducted to assess the chamber effect on growth and nitrogen fixation in Sesbania aculeata (L.) at two levels each of soil salinity (electrical conductivity 4.65 and 7.23 dS m-1) and moisture (15 and 25%, v/w). The plants were grown either in the open or placed in an open-top polyethylene chamber and harvested 6 weeks after seed sowing. Salinization of soil led to a decrease, while higher moisture caused an increase, in different growth attributes of the plants. Growth reduction due to salt stress was less than that due to low moisture stress. Plants kept in the open-top polyethylene chamber showed better growth than those placed outside (in the open); all the parameters studied were better in the chamber. Chamber effect measured as Biomass Enhancement Ratio (BER) averaged 1.22 for different salinity and moisture treatments. However, root biomass of plants grown in the chamber was less than those grown in the open. Negative effect of salinity and low moisture was mitigated to a significant extent under chamber conditions. The analysis of root and shoot material for total N and 15N showed significant amounts of N2 being fixed as measured by isotopic dilution technique. Significantly higher amounts of N were fixed at 25 than 15% soil moisture; soil salinity had a depressing effect on the amount of N2 fixed. The contribution of biologically-fixed N (Ndfa) to the total N content of shoot and root portions was 23-62% and 21-52%, respectively, under different growth conditions. Contribution of Ndfa decreased with salinity but was more at 25% than 15% soil moisture.
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