Rukhsana Bajwa

New report of Alternaria alternata causing leaf spot of Aloe vera in Pakistan

Abstract A leaf spot disease was observed on Aloe vera plants as small, circular to oval dark brown necrotic sunken spots on the leaves. Infected tissues collected from different sites in diseased fields were cultured on malt extract agar medium, and the pathogen was identified as Alternaria alternata on the basis of morphological and cultural characteristics. The fungus produced effuse, olivaceous black colonies with dark olive-green margins, and abundant branched septate, golden brown mycelium. The conidiophores were branched, straight, golden-brown, smooth-walled, measuring up to 60 μm long by 3 μm wide with one conidial scar. The conidia were obpyriform, golden-brown, smooth-walled, produced in long branched chains, with a short pale beak. Pathogenicity tests conducted on healthy potted aloe plants in a glasshouse showed typical leaf spot symptoms after four to seven days. This is the first report of a leaf spot disease of A. vera in Pakistan.

Screening of Sunflower Varieties for Their Herbicidal Potential Against Common Weeds of Wheat

ABSTRACT Sunflower is a putative source of bioactive allelochemicals, especially phenolics and terpenoids. Because qualitative and quantitative variation is well documented in sunflower types, we screened three commercially grown varieties of sunflower (Hybrid Supper-25, Gulshan-98 and Hybrid Suncross-42) through aqueous extract bioassays against five selected weeds of wheat (i.e., Chenopodium album, Rumex dentatus, Coronopus didymus, Phalaris minor, and Medicago polymorpha). Sunflower proved to be a potential source of allelochemicals as natural herbicides for weed management of selected weeds. The allelopathic effect was found to be dosage dependant, as it gradually increased as the concentration use from 30% to 50%. The lower concentrations of 10% and 20% showed stimulatory effects or insignificant weed reduction. C. album and R. dentatus were found to be the most sensitive to various treatments. The studies were extended to pot trials to determine the ecological significance of the laboratory findings.

Sunflower phytochemicals adversely affect wheat yield.

Various researchers have reported the weedicidal potential of sunflower when used as incorporation, mulch or aqueous extract without noticing its effect on crop. This study was planned to investigate the harmful effects of sunflower phytochemicals on wheat varieties. Early laboratory experiments were performed on four wheat varieties, i.e. Inqlab-91, Punjab-96, Pasban-90 and Uqab-2000. The aqueous extract of three sunflower varieties tested against wheat varieties significantly decreased biomass of wheat seedlings, especially at concentrations of 40% and 50%. However, wheat variety Punjab-96 resisted the most, which was selected for further trials. This detrimental effect was also noticed in pot trials, the extent of which varied with the age of the wheat seedlings and number of sprays. Three early sprays with one week intervals showed maximum losses to the crop plant. The study suggests the use of sunflower extracts for the management of weeds that emerge 3–4 weeks after wheat seedlings. However, the study discourages the use of sunflower mulch or incorporation in wheat fields for weed management.

Isolation of bioactive allelochemicals from sunflower (variety Suncross-42) through fractionation-guided bioassays.

Plants are rich source of biologically active allelochemicals. However, natural product discovery is not an easy task. Many problems encountered during this laborious practice can be overcome through the modification of preliminary trials. Bioassay-directed isolation of active plant compounds can increase efficiency by eliminating many of the problems encountered. This strategy avoids unnecessary compounds, concentrating on potential components and thus reducing the cost and time required. In this study, a crude aqueous extract of sunflower leaves was fractionated through high performance liquid chromatography. The isolated fractions were checked against Chenopodium album and Rumex dentatus. The fraction found active against two selected weeds was re-fractionated, and the active components were checked for their composition. Thin layer chromatography isolated a range of phenolics, whereas the presence of bioactive terpenoids was confirmed through mass spectroscopy and nuclear magnetic resonance spectroscopy.

Response of arbuscular mycorrhizal mungbean plants to ambient air pollution

The experiments were conducted in open top chamber system installed at the University of the Punjab, Quaid-e-Azam Campus, Lahore, Pakistan. The mungbean (Vigna radiata (L.) Wilczek var.M28) seeds were sown in earthen pots and were kept in filtered air, unfiltered air and ambient air. The ozone concentration was monitored daily during 1000hrs till 1600 h. The data for light intensity and relative humidity was also regularly collected. The sets of plants growing in FA chambers (without ozone and dust particles) responded well as regards growth and yields are concerned. Unfiltered air reduced the number of nodules, their biomass and nitroginase activity in mungbean plants. The present study documents that the species of mycorrhizal fungi sensitive to tropospheric ozone failed to reproduce in ambient air and unfiltered air chambers (without dust particles). Out of a total of 24 species, eighteen species belonged to the genus Glomus, two each to Sclerocystis, to Acaulospora and one each to Gigaspora and Scutellospora. The total number of species was variable during the growth phase. The total number of species reduced in soil of UFA chambers with the passage of time. Species richness reduced to almost half in UFA plants as compared to FA plants. Species of the Genus Glomus were highly abundant species at various harvests in all air treatments. Amongst most abundantly recovered Glomus species were G. fasciculatum, G. mosseae, G. aggregatum, G. caledonicum, G. deserticola, G. geosporum, and G. monosporum. The pattern of abundance kept on varying at various harvests for different air and mycorrhizal treatments. In the case of plants of UFA treatment, only two species of Glomus were abundant namely G. fasciculatum and G. geosporum. Species of Acaulospora and Gigaspora in particular and Scutellospora and Sclerocystis in general were sensitive to polluted air.

Effect of Effective Microorganism Application on Crop Growth, Yield, and Nutrition in Vigna radiata (L.) Wilczek in Different Soil Amendment Systems

A pot experiment was conducted in heat-sterilized soil to evaluate the effect of effective microorganism (EM) application on growth, yield, and nutrient uptake in Vigna radiata (L.) Wilczek var. NIAB Mung 98 in different soil amendment systems. Pot soil was amended with farmyard manure (FYM), Trifolium alexanrinum L. crop residues (TCR), and half (½NPK) and recommended dose (NPK) of chemical fertilizers. The EM application significantly enhanced shoot and root biomass in TCR-amended soil. However, grain yield was significantly enhanced in FYM, TCR, and NPK amendments by 24%, 15%, and 84%, respectively, as a result of EM application. Effect of EM application on nutrient uptake was variable with respect to soil amendment and plant growth stage. In general, EM application enhanced plant nitrogen (N), phosphorus (P), and potassium (K) nutrition in organic amendments while its effect was either negative or insignificant in chemical fertilizer amendments. Effects of EM application on plant nutrient uptake were more pronounced at maturity than at flowering stage.

Comparative tolerance of different rice varieties to sunflower phytotoxicity

The present study was conducted to investigate the phytotixic effects of aqueous extracts of dry and fresh leaf, stem and inflorescence of sunflower (Helianthus annuus L.) var. Hysun 33 against germination and early seedling growth of four varieties of rice, namely Basmati Pak, Basmati Supper, Basmati 385 and IRRI-fine. Extracts of all the three parts of sunflower showed toxicity against germination and seedling growth of different rice varieties. Leaf extract exhibited the highest toxicity against germination followed by root and stem extracts, respectively. With respect to seed germination, rice varieties Basmati 385 and IRRI Fine were more resistant against various types of sunflower extracts while Basmati Pak was found to be the most susceptible one. None of the extract exhibited any significant effect on shoot length of Basmati supper and IRRI Fine. Root growth in Basmati 385 showed the most susceptible response to sunflower extracts toxicity followed by Basmati supper and Basmati Pak, respectively. Results of the present study suggest that rice variety IRRI Fine is the most tolerant to sunflower phytotoxicity followed by Basmati supper and thus may be suitable for cultivation under sunflower allelopathic stress. Basmati 385 showed highly tolerant germination behaviour and can be sown for raising of rice nursery under allelopathic stress of sunflower.

Mutagenesis and genetic characterisation of amylolytic Aspergillus niger

Aspergillus niger FCBP-198 was genetically modified for its ability to reveal extra cellular α-amylase enzyme activity. From 76 efficient mutants isolated after ultraviolet (UV) irradiation, An-UV-5.6 was selected as the most efficient UV mutant, with 76.41 units mL−1 of α-amylase activity compared to wild (34.45 units mL−1). In case of ethyl methane sulphonate (EMS), among 242 survivors, 74 were assayed quantitatively and An-Ch-4.7 was found to be the most competent, as it exhibited a three-fold increase in α-amylase activity (89.38 units mL−1) than the parental strain. Genetic relationships of the mutants of A. niger FCBP-198 were analysed with a randomly amplified polymorphic DNA–polymerase chain reaction (RAPD–PCR). Results obtained from the comparison between genotypes of A. niger FCBP-198 showed differences in the sizes and numbers of amplified fragments per primer for each isolate. The dendrogram showed that genotypes An-Ch-4.7 and An-Ch-4.2 were distinctly classified into one category, while the isolates An-UV-5.6, An-UV-5.1 and A. niger FCBP-198 have the nearest genetic relationship. The five isolates from A. niger FCBP-198 genotypes shared an average of 65% bands.

Alpha-amylase production by toxigenic fungi

This study is concerned with the screening of Alternaria alternata (Fr.) Keissler and Alternaria tenuissima (Kunze ex Pers.) Wilts strains for the biosynthesis of α-amylases. Nine strains of A. alternata and three strains of A. tenuissima were grown on enzyme production medium (EPM) and potato dextrose agar (PDA) using three pH levels (4.5–6.5); then the selected strains, able to produce bigger zones of starch hydrolysis on solid media, were subjected the testing of their amylolytic efficacy in liquid medium. In primary screening, the amylolytic activity of all the strains was tolerant to a wide range of initial culture pH values (4.5–6.5). Of all the cultures tested, A. alternata strains FCBP-100 and FCBP-385, and A. tenuissima strains FCBP-183 and FCBP-252 exhibited the maximum potential in terms of starch hydrolysis at pH 4.5 on EPM, and hence were selected for further studies. In secondary screening, the optimum pH of fermentation medium was adjusted to 4.5 using 0.05 M citrate buffer for the estimation of amylolytic enzyme activities. At 48 h incubation, the maximum α-amylase activity (31.8 units mL−1) was discerned by A. tenuissima strain FCBP-252.

Molecular characterisation of UV and chemically induced mutants of Trichoderma reesei FCBP-364

Cellulases are a highly diverse group of enzymes whose function is crucial to the healthy functioning of the biosphere, since more than half of all biomass on the planet consists of their substrate, cellulose. Trials were conducted to study the effect of mutagenesis by ultraviolet (UV) irradiation (5–40 min) and ethyl methane sulphonate (EMS) treatment (50–300 µg mL−1) to obtain hyperactive cellulase enzyme producers. Putative mutants of Trichoderma reesei FCBP-364 were selected on the basis of their bigger hydrolysing zone formation and compared to the parental strains quantitatively. UV- and EMS-treated putative mutants of the test strains exhibited a 1.5–2-fold enhancement in enzymatic activity over the parental strain. The profile of genetic variability among native and mutant derivatives was scrutinised through random amplification of polymorphic DNA-polymerase chain reaction (RAPD-PCR). The scanned amplicons confirmed the modification in genetic make up which might be the cause of the stir up in the enzyme activity.