Om P. Dhawan

ENHANCING THE PRODUCTIVITY OF SECONDARY METABOLITES VIA INDUCED POLYPLOIDY: A REVIEW

SummaryArtificial polyploidy generally enhances the vigour of determinate plant parts and may be favourable where vegetative organs and biomass constitute the economic product. Giving suitable examples, it is shown that genomic multiplication can confer enhanced production and/or qualitative improvement in the biochemical profile of secondary metabolites. Allopolyploidisation can bring about natural complementation of biosynthetic pathways to harness the useful metabolites. A plea is made to utilise the induced polyploidy approach as a rapid means to attain enhanced production of secondary metabolites: pharmaceuticals, aroma chemicals, etc. The necessary prerequisites that may be needed for achieving genetic stability and reproductive success of the induced polyploids are outlined.

Screening and evaluation of agronomically useful somaclonal variations in Japanese mint (Mentha arvensis L.)

SummaryA procedure has been standardized for high frequency plant regeneration response from nodal explant cultures of Mentha arvensis Linn. var. piperascens Holmes. Murashige and Skoogs medium supplemented with IAA or NAA (0.5–2.0 mgl−1) alone, supported axillary shoot elongation while BAP (2.0–3.0 mgl−1) alongwith IAA (1.0 mgl−1) supported multiple shoot production. In vitro-derived shoots readily developed roots when cultured on NAA (1.0 mgl−1) fortified MS medium. Regenerated plantlets were successfully transferred to glasshouse (90–95% survival rate) and ultimately to the field. Among 280 plants transferred to the field a wide range of variation was observed for various agronomic traits i.e. plant height (32.0–92.0 cm), leaf-stem weight ratio (0.53–2.32), herb yield (105.0–870.0 g), oil content (0.32–1.10%) and oil yield (0.66–5.22 ml/plant). In addition, variations were also recorded for four major constituents of the essential oil i.e. menthol (65.2–94.77%), menthone (1.40–20.89%), isomenthone (0.96–5.14%) and menthyl acetate (0.75–8.52%). A positive correlation is found for oil yield with plant height and herb yield, whereas a negative correlation exists between herb yield and oil content. Based on the initial agronomic assessments on individual plant basis, 27 somaclones were selected and further evaluated in a replicated plant to row trial with parent plant CIMAP/Hy-77 as standard check. Somaclones Sc 59 and Sc 179, selected on the basis of higher herb yield in the initial screening, recorded 55.8% and 64.3% increase in oil yield over the control, respectively. Somaclones Sc 93, Sc 114, Sc 121 and Sc 124 that were selected for their better oil content exhibited 47.2%, 50.6%, 57.5% and 48.2% increase in oil yield over the parent variety, respectively. The performance of these clones in evaluation trials is discussed in relation to the possibility of genetic improvement of mints through somaclonal breeding.

Downy mildew resistance in opium poppy: resistance sources, inheritance pattern, genetic variability and strategies for crop improvement

Downy mildew (DM) caused by Peronospora arborescens is the most destructive disease of opium poppy which assumes considerable importance in India and other poppy growing countries. The present study was aimed at identification and evaluation of stable resistance sources of DM in opium poppy. Furthermore, genetic variability and inheritance pattern of DM resistance has also been studied which can help in making strategy for crop improvement. Evaluation of 35 selected germplasm accessions of opium poppy under glasshouse and field conditions during the three consecutive years (2004–2005 to 2006–2007) resulted in identification of two genotypes (I-14 and Pps-1) as highly resistant and stable sources for DM resistance. Genetic studies of DM resistance revealed polygenic control with the dominance of susceptibility over resistance. Significant reciprocal differences were found largely due to maternal transmission of DM resistance indicating the involvement of cytoplasmic genes in addition to nuclear control. Analysis of genetic variability and selection parameters indicated predominance of additive effects for DM resistance and other yield contributing traits. Multivariate analysis resulted in classification of 35 selected accessions into 11 different clusters revealing very high level of diversity among the genotypes. Cluster analysis suggested that hybridization program involving genotypes from cluster V (which included highly resistant genotypes Pps-1 and I-14) and cluster IX (which included highly susceptible Jawahar-16 having good economically important traits like seed yield) could be expected to give best recombinants for improvement in terms of DM resistance and high seed and straw yield in opium poppy. Analysis of selection parameters like heritability and genetic advance also suggested that simple selection methods will be effective in stabilizing resistance traits following hybridization with high yielding genotypes.

Genetic parameters and correlations of collar rot resistance with important biochemical and yield traits in opium poppy (Papaver somniferum L.)

Collar rot, caused byRhizoctonia solani Kühn, is one of the most severe fungal diseases of opium poppy. In this study, heritability, genetic advance and correlation for 10 agronomic, 1 physiological, 3 biochemical and 1 chemical traits with disease severity index (DSI) for collar rot were assessed in 35 accessions of opium poppy. Most of the economically important characters, like seed and capsule straw yield per plant, oil and protein content of seeds, peroxidase activity in leaves, morphine content of capsule straw and DSI for collar rot showed high heritability as well as genetic advance. Highly significant negative correlation between DSI and seed yield clearly shows that as the disease progresses in plants, seed yield declines, chiefly due to premature death of infected plants aswell as low seed and capsule setting in the survived population of susceptible plants. Similarly, a highly significant negative correlation between peroxidase activity and DSI indicated that marker-assisted selection of disease-resistant plants based on high peroxidase activity would be effective and survived susceptible plants could be removed from the population to stop further spread.

Recessive Loci Pps-1 and OM Differentially Regulate PISTILLATA-1 and APETALA3-1 Expression for Sepal and Petal Development in Papaver somniferum

The involvement of PISTILLATA (PI) and APETALA (AP) transcription factors in the development of floral organs has previously been elucidated but little is known about their upstream regulation. In this investigation, two novel mutants generated in Papaver somniferum were analyzed - one with partially petaloid sepals and another having sepaloid petals. Progeny from reciprocal crosses of respective mutant parent genotypes showed a good fit to the monogenic Mendelian inheritance model, indicating that the mutant traits are likely controlled by the single, recessive nuclear genes named “Pps-1” and “OM” in the partially petaloid sepal and sepaloid petal phenotypes, respectively. Both paralogs of PISTILLATA (PapsPI-1 and PapsPI-3) were obtained from the sepals and petals of P. somniferum. Ectopic expression of PapsPI-1 in tobacco resulted in a partially petaloid sepal phenotype at a low frequency. Upregulation of PapsPI-1 and PapsAP3-1 in the petal and the petal part of partially petaloid sepal mutant and down-regulation of the same in sepaloid petal mutant indicates a differential pattern of regulation for flowering-related genes in various whorls. Similarly, it was found that the recessive mutation OM in sepaloid petal mutant downregulates PapsPI-1 and PapsAP3-1 transcripts. The recessive nature of the mutations was confirmed by the segregation ratios obtained in this analysis.

Detection of DNA polymorphism in Papaver somniferum genotypes differing in straw morphinan alkaloid content

Abstract Thirty‐two distinct accessions of Papaver somniferum were screened for morphinan alkaloid content in the straw. The combined content of major morphinan alkaloids (morphine+codeine+thebaine) was found to vary in the range 0.2260–0.0683%. Two genotypes each, were selected as prototypes for low [I‐48 (0.0683%) and I‐344 (0.0878%)] and high [Pps‐1 (0.2260%) and N‐3 (0.2074%)] morphinan alkaloid content for studying DNA polymorphism. RAPD analysis of these four genotypes using 80 primers could not detect the polymorphism. However, AFLP analysis of these genotypes with 12 EcoRI/MseI primer pairs could distinctly group the high‐ and low‐morphinan alkaloid genotypes separately. Furthermore, 50 AFLP fragments, specific to high‐straw morphinan alkaloid genotypes (Pps‐1 and N‐3) and 28 DNA fragments specific to low‐straw morphinan alkaloid genotypes (I‐48 and I‐344) could be identified. This investigation is the first report on the polymorphism identified in the genotypes differing in their straw morphinan alkaloid content. This DNA polymorphism could be exploited for defining chemotypes at an early seedling stage in poppy breeding programmes.

AFLP studies on downy-mildew-resistant and downy-mildew-susceptible genotypes of opium poppy

Downy mildew (DM) caused by Peronospora arborescens, is a serious disease in opium poppy (Papaver somniferum), which has a world-wide spread. The establishment of DM-resistant cultivars appears to be a sustainable way to control the disease. In this paper, we present the results of a study aimed at the identification of amplified fragment length polymorphism (AFLP) markers for DM-resistance in opium poppy. Three opium poppy genotypes (inbred over about 10 years): Pps-1 (DM-resistant), Jawahar-16 (DM-susceptible) and H-9 (DM-susceptible) were crossed in a diallel manner and the F1 progeny along with the parents were subjected to AFLP analysis of chloroplast (cp) and nuclear DNA with seven and nine EcoRI / MseI primer combinations, respectively. cpDNA AFLP analysis identified 24 Pps-1 (DM-resistant)-specific unique fragments that were found to be maternally inherited in both the crosses, Pps-1 × Jawahar-16 and Pps-1 × H-9. In the case of nuclear DNA AFLP analysis, it was found that 17 fragments inherited from Pps-1 were common to the reciprocal crosses of both (i) Pps-1 and Jawahar-16 as well as (ii) Pps-1 and H-9. This is the first molecular investigation on the identification of polymorphism between DM-resistant and DM-susceptible opium poppy genotypes and development of DM-resistant opium poppy genotype-specific AFLP markers. These AFLP markers could be used in future genetic studies for analysis of linkage to the downy mildew resistance trait.

Relationship of downy mildew resistance with yield related traits helpful for achieving reliable selection criteria in opium poppy (Papaver somniferum L.)

Present study aims to understand the nature and degree of relationships between different morphometric and yield influencing traits using correlation and path coefficient analysis in medicinally important plant opium poppy. Genotypic and phenotypic correlation coefficients analysis showed significant negative correlation between downy mildew disease severity Index (DSI) and seed and straw yield. Furthermore, path analysis showed direct and positive effect of capsule diameter and number of capsule/plant to straw yield. In contrast, DSI had highest direct and negative contribution to straw yield. These results support effectiveness of selections for high seed and straw yield together with downey mildew-resistance in development of effective selection criteria for crop improvement.