Sukhada Mohandas

Parthenium pollen induced feeding by Zygogramma bicolorata (Coleoptera: Chrysomelidae) on sunflower (Helianthus annuus) (Compositae)

Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae) of Mexican origin, introduced for biological control trials against the weed Parthenium hysterophorus (Compositae), was found to feed on the tender leaves of the related plant sunflower ( Helianthus annuus Linnaeus) at a few places in Kolar district in Karnataka State, India. The insects in these populations exhibited variability in feeding response to sunflower under laboratory and field conditions. The sesqueterpene lactone parthenin, specific to P. hysterophorus , was found to induce feeding by the adults of Z. bicolorata on treated sunflower leaves within six hours, as compared to 4–7 days on untreated leaves. Further investigations resulted in the novel finding that dusting of parthenium pollen, or smearing its extract which contains parthenin, on sunflower leaves also induced feeding responses in adults. Parthenium pollen was detected on sunflower leaves growing in close proximity to the weed stand, suggesting that this could be one of the factors influencing variability in the feeding behaviour of Z. bicolorata .

Effect of VAM inoculation on plant growth, nutrient level and root phosphatase activity in papaya (Carica papaya cv. Coorg Honey Dew)

Papaya (Carica papaya cv. Coorg Honey Dew) plants inoculated with the VA mycorrhizal fungiGlomus mossae andG. fasciculatum in sterilized nursery soil showed improved plant height, dry matter as well as P, N and Zn concentrations with no or low levels of phosphorus application. There was an enhanced alkaline and acid phosphatase activity on the root surface and also in the enzyme extract of the root of papaya

Field response of tomato (Lycopersicon esculentum Mill ‘Pusa Ruby’) to inoculation with a VA mycorrhizal fungusGlomus fasiculatum and withAzotobacter vinelandii

SummaryThe response of tomato (Lycopersicon esculentum Mill) to inoculation with the vasicular arbuscular mycorrhizal (VAM) fungusGlomus fasiculatum andAzotobacter vinelandii singly and in combination was tested in the field. It was found thatG. fasiculatum as well asA. vinelandii significantly increased leaf area, shoot dry weight, nitrogen content phosphorus content and yield in respect to uninoculated control. While, VAM fungal treatment alone could bring about substantial increase in growth, nitrogen content, phosphorus content and yield, its combination withA. vinelandii produced additional effects on leaf area, shoot dry weight, phosphorus content and yield.

Evaluation of arbuscular mycorrhiza and other biocontrol agents in managing Fusarium oxysporum f. sp. Cubense infection in banana cv. Neypoovan

Abstract Panama wilt of banana caused by Fusarium oxysporum f. sp. cubense (race 1) is a serious disease devastating the important cultivar Neypoovan (syn Elakki Bale AB) in southern India. Chemical control methods are not very effective in controlling the disease. The objective of this study was to evaluate biocontrol agents (BCAs) under controlled and field conditions for their efficacy against the pathogen and to detect and quantify the reduction in FOC population. Arbuscular mycorrhizal (AM) fungi, Trichoderma harzianum and Pseudomonas fluorescens were inoculated at the time of planting in single, dual and tripartite combinations allowing colonization up to 0, 45 and 90 days. Plants were challenged thereafter with 50 g of FOC inoculum multiplied on sorghum grains containing 1.5×106 cfu g−1. Uninoculated plants and those inoculated with pathogen only were controls. Plant growth parameters were measured and structural modifications in the roots were studied. FOC populations in the roots were determined by ELISA every month and final yield was recorded. At the end of 7 months, plants pre-inoculated with BCAs i.e., G. mosseae+T. harzianum and challenged with Fusarium under field conditions could sustain 61 and 70% improvement in plant height and girth, respectively, and 75% in bunch weight over plants not precolonised with BCAs but challenged with FOC which finally succumbed to the disease. ELISA study revealed Fusarium population was reduced to 0.58 OD in 7 months in G. mosseae and T. harzianum treatment compared to a level of 1.9 OD in Fusarium alone treated plants. Beneficial effect of BCAs may be due to the over all protection provided by them by causing physical modifications in the cell wall, growth promotion and through induction of disease resistance.

Nitrogen fixation in tomato (Lycopersicon esculentum mill Pusa Ruby)

Nitrogen fixation (acetylene reduction) was found in intact tomato (Lycopersicon esculentum Mill ‘Pusa Ruby’) plants in the field, in pots and also in aseptic cultures. The unsterilized as well as sterilized rhizoplane and phylloplane of the plant when assayed separately also responded to the test. From root bits of tomato sterilized upto 20 minutes with 0.1% mercuric chloride, growth of the bacterium from the interior of the root into the medium was observed thereby indicating their presence within the endorhizosphere. Phase contrast and electron microscopic studies of the root system of tomato revealed the presence of bacterial colonies in the epidermis, cortex and vascular bundles. Bacterial numbers in the endosphere, of root and leaf were 30×104 and 12×104, respectively, per gram fresh weight of tissue. The bacteria were predominantly rod-shaped 1.4–4.8×0.9–1.95 μm in 24-h-old cultures, pleomorphic, polar or bipolary flagellated having β-hydroxy butyrate granules. The bacterium has been identified as a new species of Azospirillum.

Glomus mosseae associated bacteria and their influence on stimulation of mycorrhizal colonization, sporulation, and growth promotion in guava (Psidium guajava L.) seedlings

Arbuscular mycorrhiza (AM) associated bacteria were isolated from G. mosseae spores from different guava cropping systems in southern India. Seven bacteria were isolated and evaluated for their performance in stimulation of AM fungal colonization and spore proliferation in the roots of guava seedlings. Of the seven isolates, four G. mosseae associated bacterial isolates were selected based on their efficiency in stimulation of AM root colonization and spore production. They were identified as Pseudomonas putida (HM590706), Pseudomonas aeruginosa (HM590705), Brevibacillus sp. (HM590700), and Bacillus subtilis (HM590703) by polymerase chain reaction amplification of 16S rRNA. Ability of the four isolates to produce indole acetic acid and GA3 was analysed by high performance liquid chromatography and their P and Zn solubilization potential was assessed in vitro. Of these isolates, P. putida was selected for further studies for growth promotion attributes and ability to stimulate AM fungal colonization and spore proliferation in guava seedlings. Further evaluation indicated that application of G. mosseae along with P. putida produced significantly higher leaf, stem, shoot, and root dry masses, total biomass, and total leaf area than other treatments followed by G. mosseae and P. putida alone. Application of G. mosseae with P. putida significantly increased the contents of leaf chlorophyll, phenol, and total glomalin, acid and alkaline phosphatase activities, AM fungal colonization, and spore population in the rhizosphere of guava seedlings compared with either G. mosseae or P. putida alone. The results obtained show that combined inoculation of G. mosseae with its associated bacterium, P. putida, significantly improved AM fungal colonization and spore proliferation in addition to enhancement of the growth promotion in guava seedlings. These findings have a significant impact for the raising of guava seedling root stocks for commercial multiplication.

Effect of presowing seed treatment with molybdenum and cobalt on growth, nitrogen and yield in bean (Phaseolus vulgaris L.)

SummaryBean (Phaseolus vulgaris L. Cv. ‘Burpees Stringless’) seeds were subjected to two cycles of presowing soaking and drying treatments with sodium molybdate and cobalt nitrite at 1 and 5 ppm concentrations used separately and also in combination. Sodium molybdate 2 ppm and cobalt nitrite 1 ppm used singly proved better than the remaining treatments with respect to nodulation, dry matter, nitrogen and yield. Combined treatment with sodium molybdate and cobalt nitrite did not produce additive effect on any parameter studied compared to their usage alone.

Effect of mycorrhiza-associated bacteria on enhancing colonization and sporulation of Glomus mosseae and growth promotion in sapota (Manilkara achras (Mill) Forsberg) seedlings

Satisfactory establishment of sapota is one of the major challenges in India due to poor seedling growth in the nursery. A study was undertaken on co-inoculation of sapota (Manilkara achras (Mill) Forsberg) seedlings with mycorrhiza fungus (Glomus mosseae) and mycorrhiza-associated bacteria (MAB) to establish healthy sapota seedlings under nursery conditions. Based on the survey from different sapota cropping systems in India, four bacteria were isolated from G. mosseae spores and identified as Brevibacillus parabrevis (HM590702), Pseudomonas putida (HM590707), B. choshinensis (HM590701) and Providencia rettgeri (HM590704) by polymerase chain reaction amplification of 16S rRNA. These four bacterial isolates were chosen because of their growth-promoting attributes; phytohormones, siderophore and hydrogen cyanide production; antifungal and enzyme activity; and phosphorus and zinc solubilization, and were evaluated with G. mosseae for growth promotion and mycorrhizal development in sapota seedlings. Among these isolates, application of P. putida with G. mosseae significantly increased seedling height, fresh and dry shoot and root weight, total biomass, total leaf area and mycorrhizal colonization compared with other bacterial isolates. The present study findings clearly demonstrated that healthy sapota seedlings can be established by co-inoculation with mycorrhiza fungus and MAB, and these findings have a large impact on establishment of sapota seedlings and germplasm maintenance.

Field response of papaya (Carica papaya L. cv. Coorg Honey Dew) to inoculation with arbuscular mycorrhizal fungi at different levels of phosphorus

Summary Papaya (Carica papaya L.) cv. Coorg Honey Dew is one of the most popular cultivars grown in Southern India, but it requires high doses of inorganic phosphorus (P) fertilisation for growth. Arbuscular mycorrhizal fungi (AMF) are known to improve plant growth and nutrient uptake, especially the uptake of P and micronutrients. As papaya plants respond well to high levels of P, inoculation with AMF was studied to see if AMF could fulfill the requirement for P in plants grown under field conditions. Papaya seedlings (n = 36 per AMF) were colonised separately, in polybags, for 45 d by two species of AMF, Glomus mosseae and G. fasciculatum. Seedlings were then transplanted to the field, with uninoculated seedlings as controls, in a replicated randomised block design. Three levels of P were applied [50, 75, or 100% of the recommended dose (240 g plant–1 year–1) of P fertiliser, as super-phosphate]. Plants were studied for root colonisation by AMF, for growth parameters, and for leaf nutrient contents (especially, P, Zn, and Cu). Acidic and alkaline phosphatase activities in the roots of AMF-colonised plants were recorded as these enzymes are involved in the mobilisation of P. The yields of plants up to 18 months-old, and fruit quality, measured by total soluble solids contents (TSSC) and β-carotene contents, were recorded. AMF-inoculated plants performed better than uninoculated control plants at all levels of P applied. G. mosseae was more effective at improving plant growth, fruit yield, and P and Zn contents than G. fasciculatum at the 75% and 50% P-levels. Cu contents increased at all P-levels in G. fasciculatum-colonised plants. Total soluble solids contents showed marginal improvements at the 75% P level with both fungi. β-carotene contents increased significantly in G. mosseae-colonised plants at the 50% and 75% P-levels, and in G. fasciculatum-colonised plants at the 75% P-level. The feasibility of applying on-farm produced AMF inoculum to improve papaya cultivation and to save 25% of the P applied during papaya cultivation is discussed.

Somatic Embryogenesis as a Tool in Genetic Transformation

Bananas and plantains are the most important staple food crop in the world. The production of banana is hampered by various stresses. Genetic transformation has become an important potential tool in developing improved banana with desired agronomic traits, which is highly difficult to achieve through conventional breeding. To be successful, genetic engineering technique requires reliable, efficient in vitro regeneration protocol through tissue culture. Plant regeneration through somatic embryogenesis has become an important tool due to high proliferation potential, minimal genetic instability, and single-cell origin which in turn reduces the formation of chimera. However, banana is highly recalcitrant toward the development of somatic embryogenesis. Considerable progress has been achieved in the regeneration of banana through somatic embryogenesis, but there are still many factors to overcome. In present review key factors such as age of the explant, genotype, and plant growth regulators affecting the induction and regeneration of plants by embryogenic callus are discussed. This review also provides special focus on methods being applied in plant transformation through somatic embryogenesis, different factors which affect somatic embryogenesis, and various strategies to improve the transformation efficiency using somatic embryogenesis.