The Division of Plant Physiology and Biochemistry came into being since inception of the institute during 1968. During the initial years of the institute Plant physiology and Biochemistry was one of the largest divisions having laboratories on tissue culture, molecular biology, pesticide residue and food microbiology in addition to the existing laboratories. Later these laboratories were merged with other divisions. The division was earlier headed by Dr. Raja Rao, Dr. Doreswamy, Dr. Selvaraj, Dr. Awasthi and Dr. G.S.R. Murti, Dr. S.Shivashankar and presently being headed by Dr K.S.Shivashankara.
- To undertake basic and applied research on physiological and biochemical aspects of horticultural crops with particular reference to physiology of growth, development, yield and quality.
- To assess the impact of climate change on crop productivity and quality.
SALIENT RESEARCH ACHIEVEMENTS
Physiology of growth and development
- In okra, fruits on middle nodes are strong sinks for photo-assimilates. Seeds from these nodes had higher germination percentage.
- In capsicum fruit, first flowering node acts as the major sink up to 20 days which later becomes a weak sink as neighbouring fruits compete for assimilates. Night temperature plays an important role in plant growth and fruit set in capsicum.
- In Alphonso mango, fruit bud differentiation is found to occur during November to December under Bangalore conditions.
- Hormonal imbalance marked by reduction in IAA, free cytokinins- DHZR and ZR and polyamines coupled with an increase in ABA and ethylene are associated with high incidence of fruitlet drop in mango during early phase of fruit development.
- Night temperatures greater than 17 °C during the flower induction period (October to December) is detrimental to flowering in mango. The effects of high night temperature on flowering were accentuated by rainfall during September – December. Temperature of around 15 °C is vital for inducing floral bud morphogenesis.
- Leaf water potential, ABA and phenols are negatively related to seedling vigour of polyembrynic mango cultivars. p-Hydroxybenozoic acid followed by cinnamic acid and vanillic acid are major phenolic acids in the leaves of polyembryonic cultivars, and their levels were negatively related to seedling vigour.
- The growth inhibitory responses of paclobutrazol is due to reduction in the xylem sap yield, radial width of xylem, stomatal density, stomatal conductance and leaf IAA levels concomitant with increases in leaf water potential, ABA, phenols, chlorophyll, polyamines, cytokinins-t-ZR and DHZR.
Crop responses to abiotic stresses
a) Water stress
- In okra, genotype BO-1 having short plant stature is found to perform better under water stress.
- In onion, the genotypes with small bulb size and erect leaf orientation (eg. MS-11 and MS-39) are found to perform better under water stress conditions.
- Based on the cell membrane stability test, chilli genotypes, G-4, CM-334, VN-2 and EG-12 are classified as water stress tolerant and these are included in the breeding programme on water stress tolerance in chilli. The critical level of stress for seed germination in chilli varied from -0.4MPa to -0.6MPa.
- Following the changes in morpho-physiological characters, hormonal content and yield attributes, cvs. Contender in French bean, Arka Ajit in peas and Arka Kalyan in onion are characterized as water stress tolerant to cultivars.
b) High temperature stress
- In capsicum, cvs. Arka Gaurav, Indra and Sweet ban showed better performance under high temperature. High levels of IAA, cytokinin-ZR and polyamines-spermidine and spermine in the reproductive parts are found important attributes of high temperature tolerance in cv. Arka Gaurav. The induction of 70 and 90 KDa Hsps is also related to high temperature tolerance in capsicum cultivars.
- The high temperature induced abscission of floral organs in capsicum is related to an increase in the levels of ethylene and its precursor ACC, ABA and a decline in IAA and cytokinins in the flower buds and open flowers.
- Grape rootstocks endowed with higher ABA, glycine betaine and polyamines-spermine and spermidine are found to accumulate less Na+ content. These rootstocks maintained low Na:K ratio, high osmotic potential, good root growth and high root:shoot dry mass ratio under salinity conditions.
- The salinity tolerant grape rootstocks showed greater induction in the activities of SOD, catalase and peroxidase, and accumulation in 11, 42.7, 66.4, 70.1 and 89.4 KDa proteins under salinity conditions.
- The grape rootstock, 110R is found to be relatively salinity tolerant rootstock.
- The soil application of mixture of VAM (Glomus species) + bacterial consortium is found improve the salinity tolerance of Dogridge rootstock by improving root:shoot ratio and root K:Na ratio, and inducing accumulation of polyamines and ABA.
- Under alkaline soils, the better performance of mango rootstocks, Kurukan and 13-1 is due to higher water use efficiency and induction in sugar and ABA accumulation in the roots. Analyses of root sugars is found to have potential to serve as biochemical marker for discriminating rootstocks for alkalinity tolerance.
Crop responses to biotic stresses
a) Fungal diseases
- In chilli, the anthracnose resistant cv. AR-24 had significantly higher polygalacturonase inhibitor protein (PGIP) activity in maturing fruits as compared to susceptible cv. Byadgi.
- In rose, foliar application of KH2PO4 led to enhanced activities of peroxidase and polyphenol oxidase (PPO) enzymes as compared to control. Higher activities of antioxidant enzymes were maintained up to a period of 15 days. The level of jasmonic acid in KH2PO4 treated leaves of rose increased steeply by 10.3 times as compared to control.
- Volatile compounds, namely, caryophyllene oxide, limonene, linalool and 1-hexanol identified in the volatile fraction are found to be responsible for insect repellant action of neem cake.
- The resistance mechanism of chayote to melon fly infestation is due to antibiosis mediated by the production of reactive oxygen species and not due to antixenosis.
- Allelopathic weed management improved the soil physical, chemical, and biological parameters. Rotation of crops with the medicinal legume cover crops, Mucuna utilis and Dolichos with other vegetable crops is found to be effective in reducing the population of the noxious weed Cyperus.
- The following herbicides are recommended for management of weeds in various horticultural crops :
Recommended herbicides and their dosages in vegetable crops
Recommended herbicides and their dosages in fruit crops
Recommended herbicides and their dosages in ornamental crops
Physiological disorders of fruit crops
a) Identification of the cause of spongy tissue formation in Alphonso mango
- The cause of spongy tissue formation in Alphonso mango was identified for the first time in the world. Physiological and biochemical studies have firmly established that the disorder is caused due to the premature onset of germination-associated events in the seed during fruit maturation on the tree/ postharvest ripening stages. Radiotracer studies using tritiated water confirmed the increased mobilization of water from mesocarp to seed during spongy tissue formation. Preharvest application of GA3 to fruits during fruit development phase resulted in an increase of seed amylase activity, fruit respiratory rate and a proportionate increase of the incidence of spongy tissue while paclobutrazol application reduced the seed amylase activity, fruit respiration and spongy tissue incidence further confirming the fact that the formation of spongy tissue in Alphonso mango is influenced by the activity of seed.
- Studies conducted on stone weevil affected fruits of Alphonso mango clearly established the decisive role played by the seed in the formation of spongy tissue.
- An eco-friendly formulation is developed and tested in farmers’ fields in the Konkan region for the successful control of the disorder.
b) Aril Browning in Pomegranate
- The causative factor of aril browning in pomegranate has been identified. Hormonal studies on developing fruits have confirmed the role of seed in initiating the disorder. Preharvest application of plant growth regulators could reduce the incidence of aril browning significantly.
c) Chilling injury in mango
- Fatty acid desaturation is more in Dashehari and Alphonso compared to Banganapalli, indicating that Dashehari may tolerate low temperature better than other varieties.
Nutritive value of fruits and vegetables
a) Antioxidant capacity of fruits and vegetables
- In tomato, dark red types with high total carotenoids, lycopene and total phenols showed high antioxidant and radical scavenging capacities. Wild varieties recorded high ascorbic acids.
- Dark red small onions have very high antioxidant capacity due to higher anthocyanins and flavonoids. White onions possessed lowest antioxidant capacity.
- Frying in oil is found to be better method for retaining the antioxidant capacity of cauliflowers followed by microwave cooking and boiling in water. Genotypic variability is observed in the antioxidant capacity, oxalates and nitrates. In carrot, variation in antioxidant capacity is related to the total phenols and carotene contents.
- The high antioxidant capacity in cv. Pusa Navrang fresh fruits is found to be due to high anthocyanins. Black grapes have higher antioxidant values than green grapes. Seeds and peel contribute relatively more to the high antioxidant activity in grapes.
- Mulberry fruits show higher antioxidant and radical scavenging ability when compared to other fruits like pomegranate, mango, grapes and papaya mainly due high anthocyanin content. Jamun fruits have high antioxidant capacity due to anthocyanins and total phenols. Aonla fruits shows very high antioxidant capacity due to their high phenols and vitamin C contents.
- Cultivar Alphonso possesses higher vitamin A, vitamin C, antioxidant and radical scavenging abilities compared to Totapuri, Banganapalli, Fazli, Dashehari, Langra and Suvarnarekha. Mango kernel is found to have very high antioxidant capacity mainly due to higher polyphenols. This can be commercially exploited for food additives for enhancing antioxidant values.
- An eco-friendly formulation was developed and tested in farmers’ fields in the Konkan region for the successful control of the spongy tissue disorder in Alphonso mango
- Processes for the extraction of volatiles of neem cake using hydro-distillation procedure and enrichment of inert carriers is developed.
- Release of volatiles in cropped area at regular intervals through inert carriers is highly effective in repelling diamond back moth of cabbage and other insect pests of horticultural crops. A patent has been filed on the process for use of neem volatiles to repel insects. As the process is based on plant based organic extract, which is effective, economical and eco-friendly, it can be used in organic agriculture.
- Spraying 10% urea as defoliation treatment in annona enhances sprouting of sub-petiolar buds any time of the year, and subsequent production of shoots for round the year grafting.
- Management of crop yield under stress
- A commercial formulation of PCPA ‑Tomatotone at 100 ppm concentration is found to be effective in improving the fruit set in tomato under high temperature conditions.
- Antitranspirant (Kaolin) application at 30 or 50 days after planting improved the bulb yield in onion. Osmoprotectant, glycinebetaine treatment to seeds (2.5 and 5%) followed by foliar spray is effective in increasing the yield in onion under water stress conditions.
- Application of antitranspirant (PME, 8 HQ or kaolin) to tomato plants at flowering and fruiting stages improved the yield under rainfed condition.
- Seed priming with BA (10 mg/l) in French beans is effective in improving the germination under osmotic stress conditions.
- Treatment of French bean plants with epibrassinosteroid (5µM) at reproductive phase is found to improve root nodulation, seed yield and pod yield under water stress.
- Tomato plants grafted on wild species is found to perform better under water stress.
- A simple and sensitive HPLC procedure for the quantification of osmo-protectant, glycine betaine was worked out.
- Immuno-electrophoresis procedure for identification and characterization of heat shock proteins was standardized, which may be being used to identify genotypes tolerant to heat stress.
Principal Scientist & Head
Division of Plant Physiology & Biochemistry
IIHR, Hessaraghatta Lake Post
Bangalore – 560 089.