Kaushal K. Upreti

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.

Role of Plant Growth Regulators in Abiotic Stress Tolerance

Endogenous plant growth regulators play an important role in regulating plant responses to abiotic stress by sensitizing growth and developmental processes. While the physiological and molecular mechanisms linked to the role of ABA and cytokinins in stress tolerance are well explained, there is growing interest to elucidate the associations of auxins, ethylene, gibberellins, brassinosteroids, and polyamines in stress tolerance mechanism and also on possible cross talk mechanism among different growth regulators during stress tolerance acquisition. Identification and characterization of the gene regulating synthesis of different endogenous growth regulators and recent progresses on hormonal signaling, mutant research, and physiological actions have provided scope for manipulating their biosynthetic pathways for developing transgenic crop plants with enhanced abiotic stress tolerance. Researches have also provided some leads in exploiting the potential of growth regulators in enhancing the resistance to abiotic stresses of crops.

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.

Morpho-Physiological Responses of Grape Rootstock ‘Dogridge’ to Arbuscular Mycorrhizal Fungi Inoculation Under Salinity Stress

ABSTRACT Effects of arbuscular mycorrhizal fungi (AMF) alone or in combination with bacterial consortium (AMF+BC) inoculation prior to induced salinity (NaCl @ 150 or 250 mM) were studied on root growth; plant biomass; leaf area; Na+ and K+ contents; leaf water potential (Ψw); osmotic potential (Ψπ); photosynthesis rate (Pn); and contents of chlorophyll, phytohormones, and polyamines in the grape rootstock ‘Dogridge’, popular among Indian vine growers. AMF inoculation in the NaCl untreated rootstocks plants increased root growth, root and shoot biomass, and leaf area and improved leaf Ψw, Ψπ, Pn, and chlorophyll content, and also countered the stress-induced decline in the NaCl treated plants. The abscisic acid (ABA), cytokinins, and polyamine-spermidine and spermine contents in the leaves of NaCl untreated or treated were significantly increased by the AMF inoculation. Among the treatments, AMF with BC was relatively more effective than AMF alone with respect to changes in above morpho-physiological characters. The results depicted that AMF (AMF alone or AMF+BC) inoculation significantly improved salinity tolerance of grape rootstock and tolerance is induced by improvements in plant water balance, K+:Na+ ratio, and Pn, besides distinct accumulations in ABA and polyamines-spermine and spermidine. The above findings have potential in suggesting the AMF usefulness in improving the efficacy of ‘Dogridge’ rootstock in grape cultivation under salt affected soils.

Studies on Changes in Carbohydrate Metabolism in Regular Bearing and “Off” Season Bearing Cultivars of Mango (Mangifera indica L.) During Flowering

Studies were conducted at Indian Institute of Horticultural Research, Bangalore, India, to compare the role of carbohydrate and its metabolizing enzymes in “off” season bearing cultivar Royal Special and regular bearing cultivar Totapuri during the time of flowering. Totapuri is a regular bearing cultivar mainly used for processing and has high yielding potential. “Off” seasonal cropping in mango is the unique feature of mango cultivar Royal Special which contributes to “off” season mango production under South Indian conditions. During the bud swelling stage, the maximum reducing sugars contents were recorded while higher chlorophyll a and b values were recorded during bud break stage in ‘Royal Special’ as compared to ‘Totapuri’. Higher acid invertase activity was recorded during emergence of panicles, and increased amylase activity was observed during pre-swelling stage in ‘Royal Special’. Sucrose and its metabolizing enzymatic activities increased during flowering, indicating their decisive role in the flowering process in the case of both cultivars of mango.

Harmonious Phenological Data: A Basic Need for Understanding the Impact of Climate Change on Mango

Uniformly collated phenological data set is the most important requirement for developing climate change impact models for mango. Consistently collected phenological records directly indicate the effect of change in climatic parameters by depicting shifts in phenological events. Recording of consistent data pertaining to phenophases as a function of time serves as critical input for working out integrated interaction of interannual variability, spatial differences and climate variability impacts. In general, uniform qualitative data recording is difficult in mango due to variations in plant growth and development under diverse climatic fluxes occurring in subtropical to tropical regions. Major observed effects of climate change on mango include early or delayed flowering, multiple reproductive flushes, variations in fruit maturity, abnormal fruit set and transformation of reproductive buds into vegetative ones. These critical phenophase-dependent events require supporting quantitative data representing behaviour of sufficient number of shoots within a tree for objective analysis of factors influencing them. For monitoring the phenophase dynamics, use of extended BBCH (Biologische Bundesanstalt, Bundessortenamt und Chemische Industrie) scale developed for mango helps in monitoring the phenology by employing uniform methodology over same or different locations with the description of each phenophase in mango as distinctly classified by adopting numerical code. A manual to elucidate the methodology for general users has been developed with the help of pictorial representation of phenophases along with corresponding scores, analysis, depiction of results and interpretation for uniform data recording, and this can be downloaded from http://offseasonmango.cishlko.org/phenology.pdf.