Physiology and ecophysiology

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As discussed, Cymbopogon has a photosynthetic machinery that allows the plant to perform high rates of carbon assimilation and, at the same time, save water. In species that produce essential oil, the biogenesis of terpenoids relies on photosynthetic carbon dioxide reduction on the one hand and availability of water and nutrients, on the other. For this reason several studies have been conducted in order to assess which nutrients and at what conditions were required for an optimal production of both biomass and essential oils. In this section, we will discuss the most important Cymbopogon species in terms of yield of biomass and essential oil production as related to nutrition. Furthermore, when available, references to biotechnological applications will be also reported.

1.5.1 Cymbopogon martinii

Water requirement, productivity, and water use efficiency of palmarosa (C. martinii) were studied under different levels of irrigation (0.1, 0.3, 0.5, 0.7, 0.9, 1.1, 1.3, and 1.5 IW:CPE ratio). Growth, herb, and essential oil yield increased significantly up to 0.5 IW:CPE ratio. At 0.5 IW:CPE ratio palmarosa produced 47.3 t ha-1 yr-1 of fresh herb and 227.3 kg ha-1 yr-1 of essential oil. Further increase in irrigation levels caused an adverse effect on growth and yield of palmarosa. Irrigation levels did not affect the quality of oil in terms of its geraniol and geranyl acetate contents. Water requirement of palmarosa was worked out to be 89.1 cm. The highest water use efficiency of 2.97 kg ha-1 cm-1 oil was recorded at 0.1 IW:CPE ratio, at 0.5 IW:CPE ratio (optimum) it was 2.55 kg ha-1 cm-1 oil. Irrigation scheduled at 0.5 IW:CPE ratio gave the highest net return of Rs 51 963 ha-1 yr-1 (Singh et al. 1997). In C. martinii the application of 160 kg N/ha per year produced the highest amount of biomass and essential oil, and increased the net profit and NPK uptake by the crop (Rao et al. 1988); furthermore, dressing of 40 kg K/ha enhanced the yield of biomass by 13.6% and 6.5% and that of oil by 12.9% and 6.1%, compared with 20 and 80 kg K/ha, respectively (Singh et al. 1992). In the same species, harvesting the crop at early seeding (112-115 days after planting) gave 25% more herbage and 51% more oil yield over harvesting vegetative stage, while the oil so produced had higher content (90.1%) geraniol (Maheshwari et al. 1992). Highest dry-matter yield, essential oil yield, and maximum net return of palmarosa were recorded by applying Azotobacter at 2 kg/ha together with 20 kg N + 20 kg P/ha under rainfed condition in a shallow black soil (Maheshwari et al. 1998). Intercropping of blackgram-blackgram or sorghum fodder-ratoon with palmarosa gave additional yields of 660 kg/ha seed and 16.6 t/ha fodder, respectively, compared with the sole crop of palmarosa (Rao et al. 1994). Moreover, sowing of pigeon pea in alternate rows parallel to palmarosa proved most efficient and economic, as it provided higher economic returns, bonus income, and monetary advantage, and the oil content and quality in terms of total geraniols of palmarosa were not adversely affected by adoption of intercropping (Maheshwari et al. 1995). However, in palmarosa-pigeon pea intercropping systems, competition exists mainly for light rather than for nutrients and moisture, possibly because the two crop components acquire their nutrients and moisture from different soil layers (Singh et al. 1998). Concerning essential oil production of palmarosa, changes in fresh weight, dry weight, chlorophyll, and essential oil content and its major constituents, such as geraniol and geranyl acetate, were examined for both racemes and spathe at various stages of spikelet development (Dubey et al. 2000). The essential oil content was maximal at the unopened spikelets stage and decreased significantly thereafter. At unopened spikelets stage, the proportion of geranyl acetate (58.6%) in the raceme oil was relatively greater compared with geraniol (37.2%), whereas the spathe oil contained more geraniol (61.9%) compared with geranyl acetate (33.4%). The relative percentage of geranyl acetate in both the oils, however, decreased significantly with development, and this is accompanied by a corresponding increase in the percentage of geraniol. Analysis of the volatile constituents from racemes and spathes (from mature spikelets) and seeds by capillary GC indicated 28 minor constituents besides the major constituent geraniol. (E)-Nerolidol was detected for the first time in an essential oil from this species. The geraniol content predominated in the seed oil, whereas the geranyl acetate content was higher in the raceme oil (Dubey et al. 2000).

Biotechnology is a powerful and consolidated technique for understanding plant growth and development as well as for improving biomass and yield of crops. Callus could be induced from nodal explant of mature tillering plant of C. martinii in different basal media supplemented with 2,4-dichlorophenoxy acetic acid (2,4-D) and kinetin (Kin). Shoot bud was regenerated from such calli in MS and B5 basal media modified with various combinations of phytohormones, vitamins, and amino acids. Root formation was induced either in white basal medium or half-strength MS or B5 media containing naphthalene acetic acid (NAA) or indole-3-butyric acid (IBA). High survival percentage of regenerated plants in soil was obtained after acclimatization in normal environment (Baruah and Bordoloi 1991). A detailed characterization of chromosomal status was carried out in callus, somatic embryos, and regenerants derived from in vitro cultured nodal and inflorescence explants of C. martinii (2n = 20). Both the callus lines revealed considerable ploidy variations (tet-raploids to octoploids and hyperoctoploids), and the degree of polyploidization increased with the culture age. Frequencies of various polyploid cells were significantly higher in nodal callus lines (3.6% to 46.3%) than the inflorescence callus lines (1.9% to 23.6%) when analyzed over 520 days of culture. Somatic embryos derived from both the callus lines retained a predominantly diploid chromosome status throughout (99.0% to 93.1%). Root tip analysis of about 70 regenerants randomly taken from cultures of various ages (days 20 to 520) revealed only diploid chromosome numbers (2n = 20) implying a strong relative stability of diploidy among the regenerants (Patnaik et al. 1996). Chromosome counts of cells in suspensions, calli, and somatic embryos derived from cultures of different ages revealed the presence of diploids, tetraploids, and octaploids (Patnaik et al. 1997). Sodium chloride tolerant callus lines of C. martinii were obtained by exposing the callus to increasing concentrations of NaCl (0-350 mM) in the MS medium. The tolerant lines grew better than the sensitive wild-type lines in all concentrations of NaCl tested up to 300 mM. Callus survival and growth were completely inhibited, resulting in tissue browning and subsequent death at 350 mM NaCl. The selected lines retained their salt tolerance after 3-4 subcultures on salt-free medium, indicating the stability of the induced salt tolerance. The growth behavior, the Na+, K+, and proline contents of the selected callus lines were characterized and compared with those of the NaCl-sensitive lines. The Na+ levels increased sharply, while the K+ level declined continuously with the corresponding increase in external NaCl concentrations in both lines, but the NaCl-tolerant callus lines always maintained higher Na+ and K+ levels than that of the sensitive lines. The NaCl-selected callus line accumulated high levels of proline under salt stress. The degree of NaCl tolerance of the selected lines was in negative correlation with the K+/Na+ ratio and in positive correlation with proline accumulation (Patnaik and Debata 1997a). The embryogenic potential of NaCl-tolerant callus selected even at 300 mM could be improved significantly by the incorporation of gibberellic acid (GA(3)) and abscisic acid (ABA), in the medium where, with 2 mg/L of GA(3) and 1 mg/L of ABA, the highest rates of embryogenesis (44.5%, 28.8%, and 18.6%) were achieved against 17.5%, 8.2%, and 1.8% on medium devoid of GA(3), and ABA at 50%, 150%, and 250 mM of NaCl, respectively (Patnaik and Debata 1997b). Finally, plants regenerated from cell suspension cultures of palmarosa were analyzed for somaclonal variation in five clonal generations. A wide range of variation in important quantitative traits, for example, plant yield, height, tiller number, oil content and qualitative changes in essential oil constituents geraniol, geranyl acetate, geranyl formate, and linalool, were observed among the 120 somaclones screened. Eight somaclones were selected on the basis of high herb and oil yield over the donor line and high geraniol content in the oil. Based on performance in the field trials, three superior lines were selected, and maintained for five clonal generations. The superior lines exhibited a reasonable degree of stability in the traits selected (Patnaik et al. 1999).

Palmarosa was also found to be associated with a vesicular-arbuscular mycorrhizal (VAM) fungus, Glomus aggregatum. Glasshouse experiments showed that inoculation of palmarosa with G. aggregatum caused a twofold and threefold biomass production as compared to nonmycorrhizal plants. These findings indicate the potential use of VAM-fungi for improving the production of this essential oil-bearing plant (Gupta and Janardhanan 1991). Furthermore, when the interactive effects of phosphate solubilizing bacteria, N-2 or fixing bacteria, and arbuscular mycorrhizal fungi (AMF) were studied in a low phosphate alkaline soil amended with a tricalcium insoluble source of inorganic phosphate on the growth of C. martinii. The rhizobacteria behaved as a "mycorrhiza helper" and enhanced root colonization by G. aggregatum in presence of tricalcium phosphate at the rate of 200 mg kg-1 soil (P1 level) (Ratti et al. 2001).

A dramatic increase in PEP carboxylase activity and oil biosynthesis was observed under drought conditions in C. martinii (Sangwan et al. 1993). The physiological and biochemical basis of drought tolerance in C. martinii has been elucidated on the basis of growth and metabolic responses (Fatima et al. 2002).

1.5.2 Cymbopogon flexuosus

Cymbopogon flexuosus (also known as lemongrass) is a perennial, multicut aromatic grass that yields an essential oil used in perfumery and pharmaceutical industries and vitamin A. It has a long initial lag phase. The growth and herbage and oil production of C. flexuosus in response to different levels of irrigation water (IW) 0.1, 0.3, 0.5, 0.7, 0.9, 1.1, 1.3, and 1.5 times cumulative pan evaporation CPE evaluated on deep sandy soils showed that an increment in the level of irrigation increased the plant height up to 0.7 IW:CPE ratio. However, the response of irrigation levels on tiller production of lemongrass differed with the season of harvest. Oil content had an inverse relationship with the levels of irrigation, whereas significantly higher herb and essential oil yields were recorded at 0.7 IW:CPE ratio, irrespective of season of harvest (Singh et al. 2000). Application of nitrogen (0, 50, 100, and 150 kg N ha-1 yr-1) and phosphorus to C. flexuosus crops maintained the fertility of the soil, while potassium depletion was noticed (Singh 2001). When the effects of phosphorus (at 0, 17.75, and 35.50 kg ha-1 yr-1), potassium (at 0, 33.2, 66.4, and 99.6 kg ha-1 yr-1) and nitrogen (at 100 and 200 kg ha-1 yr-1) and potassium (at 0, 33.2 and 66.4 kg ha-1 yr-1) were studied on herbage and oil yield of C. flexuosus, it was found that plants produced significantly higher herbage and oil yields compared with controls (Singh et al. 2005; Singh and Shivaraj 1999). Spraying of iron-complexed additives on C. flexuosus increased iron translocation and the dry-matter production. Application of iron chelates and salts increased the vegetative herb yield, and oil and citral content. While maximum geraniol and less citral were obtained in the chlorotic plants, Fe recovered plants possessed more citral and less geraniol. The maximum recovery of total chlorophyll and nitrate reductase activity were recorded in the crop when Fe-EDTA chelates were sprayed at 22.4 ppm (Misra and Khan 1992). In C. flexuosus, a closer plant spacing of 45 x 45 cm resulted in higher herb and oil yields compared to wider spacing of 60 x 60 cm. Application of 150 kg N ha-1 yr-1 resulted in higher herb and oil yields. Higher nitrogen applications also increased the plant height and number of tillers per clump. The oil content and quality were not influenced by spacing and nitrogen levels (Singh et al. 1996b).

As for C. martinii, intercropping of C. flexuosus with the food legumes such as blackgram (Vigna mungo (L) Hepper), cowpea (Vigna unguiculata (L) Walp), or soybean (Glycine max (L) Merr.) prompted extra yields over and above that of pure cultures, without affecting the oil yield (Singh and Shivaraj 1998).

The influence of different foliar applications of the triacontanol (Tria.)-based plant growth regulator Miraculan on growth, CO2 exchange, and essential oil accumulation in C. flexuosus showed increased rates in plant height, tillers per plant, biomass yield, accumulation of essential oil, net CO2, and exchange and transpiration compared to the untreated control, but the number of leaves per tiller remained unaffected. Application of Miraculan also increased micronutrient uptake and total chlorophyll and citral content but decreased chlorophyll a/b ratio and stomatal resistance. Increase in shoot biomass, photosynthesis, and chlorophyll were significantly correlated with essential oil content (Misra and Srivastava 1991). Only young and rapidly expanding C. flexuosus leaves were found to have the capacity to synthesize and accumulate essential oil and citral. The pattern of the ratio of the label incorporated in citral to that in geraniol, during leaf ontogeny, evinced parallelism with the geraniol dehydrogenase activity. The elevated levels of glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, NADP+-malic enzyme, and NADP+-isocitrate dehydrogenase coincided with the period of active essential oil biogenesis accompanying early leaf growth (Singh et al. 1990). Thus, there is an active involvement of oxidative pathways in essential oil biosynthesis. The time-course (12 h light followed by 12 h dark) monitoring of the C-14 radioactivity in starch and essential oil, after exposure of the immature (15 days after emergence) leaf to (CO)-C-14, revealed a progressive loss of label from starch and a parallel increase in radioactivity in essential oil. Thus, there was indication of a possible degradation of transitory starch serving as the source of carbon precursor for essential oil (monoterpene) biogenesis in the tissue (Singh et al. 1991).

Biotechnological applications revealed that C. flexuosus plants derived from somatic embryoids were more uniform in all the characteristics examined when compared with the field performance of plants raised through slips by standard propagation procedures (Nayak et al. 1996).

A fungal endophyte, Balansia sclerotica (Pat.) Hohn., has been found to establish a perennial association with the commercially grown East Indian C. flexuosus cv. Kerala local (syn. = OD-19). Endophyte-infected plants produced 195% more shoot biomass and 185% more essential oil than the endophyte-free control plants when grown experimentally under glasshouse conditions. The essential oil extracted from the endophyte-infected plants is qualitatively identical with that of endophyte-free plants and is free of toxic ergot alkaloids. Thus, B. sclerotica-infected East Indian C. flexuosus has potential for agricultural exploitation (Ahmad et al. 2001).

1.5.3 Cymbopogon winterianus

Java citronella (C. winterianus) is a perennial, multiharvest aromatic grass, the shoot biomass of which, on steam distillation, yields an essential oil extensively used in fragrance and flavor industries. Fresh C. winterianus (Java citronella) herbage and essential oil yields were significantly influenced by application of N up to 200 kg ha-1 yr-1, while tissue N concentration and N uptake increased only to 150 kg N ha-1. The oil yields with neem cake-coated urea (urea granules coated with neem cake) and urea super granules were 22 and 9% higher over that with prilled urea, and urea supergranules were significantly increased up to 200 kg N ha-1 while with neem cake-coated urea, response was observed only to 150 kg N ha-1! Estimated recovery of N during two years from neem cake-coated urea, urea supergranules, and prilled urea were 38%, 31%, and 21%, respectively (Singh and Singh 1992). The interaction between N doses and nitrification inhibitors was also significant. Nitrification inhibitors performed better at the highest N dose (450 kg N ha-1 yr-1), and the increase in the essential oil yields was to an extent of 27.3% to 34.6% when compared with "N alone" treatment. The nitrification inhibitors also increased the apparent N recoveries by citronella considerably. The oil content in the herb and its quality were not affected by the treatments. The nitrification inhibitors increased citronella yields and improved N economy (Puttanna et al. 2001). In Java citronella significant positive correlations were observed between fresh matter, citronellol content, dry and fresh matter yields, and total essential oil content (Omisra and Srivastava 1994). When the effect of depth (25, 37.5, and 50 mm) and methods (ridge and furrow, and broad bed and furrow method) of irrigation acid nitrogen levels (0, 200, and 400 kg N ha-1 yr-1) were studied on herb and oil yields of Java citronella, highest herb and oil yields were achieved with the application of 400 kg N, maintaining 25 mm depth of irrigation, while the content and quality of oil were not affected either by irrigation or nitrogen (Singh et al. 1996a).

Among food legumes, greengram (Vigna radiata (L.) Wilez.), and among vegetables, clusterbean (Cyamopsis psoraloides D. C., syn. Cyamopsis tetragonoloba (L.) Taub.), tomato (Lycopersicon esculentum Mill.) and lady's finger (Abelmoschus esculentus Moench.) as intercrops of C. win-terianus did not decrease its biomass and essential oil yield and produced bonus yields of these crops over and above that of Java citronella. Maximum monetary returns were recorded by Java citronella intercropped with tomato or greengram. However, Java citronella intercropped with redgram (Cajanus cajan (L.) Millsp.), horsegram (Macrotyloma uniflorum (Lam.) Verd, syn. Dolichos biflorus Roxb.), and brinjal (Solanum melongena L.) suffered significant biomass and essential oil yield reductions. Horsegram proved to be the most competitive intercrop, producing least yields and minimum monetary returns (Rao 2000).

Changes in the utilization pattern of primary substrate, viz. [U-C-14] acetate, (CO^-C-14 and [U-C-14] saccharose, and the contents of C-14 fixation products in photosynthetic metabolites (sugars, amino acids, and organic acids) were determined in Fe-deficient Java citronella in relation to the essential oil accumulation. An overall decrease in photosynthetic efficiency of the Fe-deficient plants as evidenced by lower levels of incorporation into the sugar fraction and essential oil after (CO2)-C-14 had been supplied was observed. When acetate and saccharose were fed to the Fe-deficient plants, despite a higher incorporation of label into sugars, amino acids, and organic acids, there was a lower incorporation of these metabolites into essential oils than in control plants. Thus, the availability of precursors and the translocation to a site of synthesis/accumulation, severely affected by Fe deficiency, is equally important for the essential oil biosynthesis in citro-nella (Srivastava et al. 1998). Lal and coworkers (2001) observed that improvement of oil quality with high citronellal content and low elemol content in Java citronella is believed to be achievable, although some compromise will have to be made in oil yield.

Nutrient acquisition and growth of Java citronella was also studied in a P-deficient sandy soil to determine the effects of mycorrhizal symbiosis and soil compaction. When a pasteurized sandy loam soil was inoculated either with rhizosphere microorganisms excluding VAM fungi (nonmycor-rhizal) or with the VAM fungus, Glomus intraradices Schenck and Smith (mycorrhizal) and supplied with 0, 50, or 100 mg P kg-1 soil, G. intraradices was found to substantially increase root and shoot biomass, root length, nutrient (P, Zn, and Cu) uptake per unit root length, and nutrient concentrations in the plant, compared to inoculation with rhizosphere microorganisms when the soil was at the low bulk density and not amended with P. Little or no plant response to the VAM fungus was observed when the soil was supplied with 50 or 100 mg P kg-1 soil and/or compacted to the highest bulk density. At higher soil compaction and P supply, the VAM fungus significantly reduced root length. Nonmycorrhizal plants at higher soil compaction produced relatively thinner roots and had higher concentrations and uptake of P, Zn, and Cu than at lower soil compaction, particularly under conditions of P deficiency (Kothari and Singh 1996).

Pythium aphanidermatum was the predominant fungus recovered from the roots of Java citro-nella showing lethal yellowing in the northern part of India. Roots of infected plants showed marked discoloration, and the cortical region was completely disintegrated and sloughed from the vascular tissue. Diseased plants were chlorotic and stunted. Rotting was often found to spread from roots to stem, leading to severe chlorosis and death of the infected plants. The pathogenicity of the fungus was established. The disease is a potential constraint to citronella cultivation in nonarid climates where the crop is irrigated extensively (Alam et al. 1992). Another disease affecting commercial plantations of Java citronella is a collar rot and wilt disease. The causal organism was identified as Fusarium moniliforme, anamorph of Gibberella fujikuroi. Isolates of the pathogen differed in their pathogenicity on the host plant under glasshouse conditions. Differences were also observed in growth rates, pigment production, and sporulation between isolates (Alam et al. 1994).

1.5.4 Other Cymbopogon Species

Application of graded levels of lime up to 10 t/ha on acid soil (pH 4.2) raised the pH up to 6.7. It increased the dry herbage of C. khasianus linearly. Increase of soil pH decreased N, P, K, Fe, and Zn contents in dry herbage significantly but increased the Ca and Mg contents. Liming showed a positive effect on the uptake of N, P, K, and Ca. However, Fe and Mg declined beyond lime levels of 23 and 5.0 t, respectively. Uptake of Zn was found fluctuating. Oil content (2.00%-2.07%; DWB) and geraniol (80.2%-81.0%) in the oil were unaffected by the lime treatments (Choudhury and

Bordoloi 1992). Experiments were also conducted to measure the rate of C. caesius litter decomposition and to identify fungal flora associated with the litter during different stages of decomposition in a tropical grassland. Rate of litter decomposition was several times higher than in temperate grasslands. Buried litter decayed more rapidly, and this rate was not influenced by climatic conditions. In contrast, surface litter recorded a lower decomposition rate, which was dependent on temporal (seasonal) fluctuations. Total nitrogen, available phosphorus, and potassium contents of the stem litter decreased during the initial stages of incubation.

Thirty-five species of fungi were isolated from the litter during the different stages of litter degradation. Most belonged to Hyphomycetes, which are active decomposers (Senthilkumar et al. 1992). C. nardus var. confertiflorus and C. pendulus were grown under mild and moderate water stress for 45 and 90 d to investigate the impact of in situ drought stress on plants in terms of relative water content, psi, concentration of proline, activities of PEP carboxylase and geraniol dehydroge-nase, and geraniol and citral biogenesis. The results revealed that the species exhibited differential responses under mild and moderate stress treatments. In general, plant growth was reduced considerably, while the level of essential oils was maintained or enhanced.

Significant induction in catalytic activity of PEP carboxylase under water stress was one of the consistent metabolic responses of the aromatic grasses. The major oil constituents, geraniol and citral, increased substantially in both the species. Activity of geraniol dehydrogenase was also modulated under moisture stress. The responses varied depending upon the level and duration of moisture stress. The observations have been analyzed in terms of possible relevance of some of these responses to their drought stress adaptability/tolerance (Singhsangwan et al. 1994). In vitro plants of C. citratus were established, starting from shoot apices derived from plants cultivated under field conditions. The effect of the immersion frequency (two, four, and six immersions per day) on the production of biomass in temporary immersion systems (TIS) of 1 L capacity was studied. The highest multiplication coefficient (12.3) was obtained when six immersions per day were used. The maximum values of fresh weight (FW; 62.2 and 66.2 g) were obtained with a frequency of four and six immersions per day, respectively. However, the values for dry weight (DW; 6.4 g) and height (8.97 cm) were greater in the treatment with four immersions per day. The TIS used in this work for the production of lemongrass biomass may offer the possibility of manipulating the culture parameters, which can influence the production of biomass and the accumulation of secondary metabolites. We describe for the first time the in vitro production of Cymbopogon citratus biomass in TIS. In vitro regeneration of C. polyneuros was obtained through callus culture using leaf base, node, and root as explants. Callus was induced from different explants with 2-5 mg/L alpha-naphthalene acetic acid (NAA) and 1-2 mg/L kinetin in Murashige and Skoog's (MS) basal medium. High frequency shoots were noticed from leaf-base callus supplemented with 3.5 mg/L 6-benzylaminopurine (BA), l-arginine, adenine, and a low level of NAA (0.2 mg/L). About 80-85 shoot buds were obtained from ca. 200 mg of callus per culture. The individual shoots produced root in the presence of 0.5-3 mg/L indole 3-butyric acid or its potassium salt.

Regenerated plants were cytologically and phenotypically stable. Regenerants were transplanted into soil and subsequently transferred to the field (Das 1999). C. nardus could be propagated via tissue culture using axillary buds as explants. The aseptic bud explants obtained using double sterilization methods produced stunted abnormal multiple shoots when they were cultured on Murashige and Skoog (MS) medium supplemented with 1.0 mg L-1 or 2.0 mg L-1 benzyladenine (BA). Stunted shoots that cultured on MS + 1.0 mg L-1 RA + 1.0 mg L-1 N-6-isopentenyl-adenine (2iP) could induce elongation of shoots from about 60% of the stunted shoots. Normal multiple shoots could be induced at the highest (19.7 shoots per bud) from the bud explants within 6 weeks when cultured on proliferation medium consisted of MS supplemented with 0.3 mg L-1 BA and 0.1 mg L-1 indole-3-butyric acid (IBA). The separated individual shoot produced roots when transferred to basic MS solid medium. The essential oils that were contained in the mature plants namely citro-nellal, geraniol, and citronellol, were also found in the in vitro C. nardus plantlets. Citronellal was the main essential oil component in the matured plants, while geraniol was the main component in the in vitro plantlets (Chan et al. 2005). The occurrence, mode of infection, and the extent of damage caused by Psilocybe kashmeriensis sp. nov. Abraham on oil grass C. jawarancusa in Kashmir valley is discussed herein. A brief description of the new agaric species is also offered (Abraham 1995). Dormant vegetative slips of jamrosa (C. nardus var. confertiflorus x C. jwarancusa) were subjected to various doses of gamma rays. Plants raised from them were screened with a view to isolate improved clones of the crop. Five mutant clones isolated exhibited variation in quality/quantity of essential oil. These changes in oil characters were attributed to microlevel mutations induced by gamma rays (Kak et al. 2000).

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