MSc

The study entitled “Influence of CO2 enrichment and associated high temperature on reproductive physiology of tomato (Solanum lycopersicum L.)”, was undertaken with the objective to study the effect of CO2 enrichment and associated high temperature on flowering and fruiting in tomato and their improvement through growth regulators and nutrient applications and through temperature induction response technique. The experiments were conducted using the Open Top Chamber (OTC) facility at the Department of Plant Physiology, College of Agriculture, Vellayani during 2017-2019.

The first part of Experiment I was designed for the standardization of Temperature Induction Response Technique (TIRT) for two popular varieties of tomato namely Vellayani Vijay and Anagha by identifying lethal and induction temperatures. Five day old tomato seedlings grown in petri plates were exposed to different temperatures (35-50 0C) for different durations (1h to 2h). The temperatures of 48oC for 2 h and 38oC (1h)- 43 oC (1h)- 48 oC (2h) proved to be the lethal and induction temperatures respectively for both the varieties based on the recovery responses.

In the second part of Experiment I growth performance of temperature induced seedlings of variety Vellayani Vijay was evaluated under elevated CO2 (500 ppm) and ambient conditions. The experiment was laid out in CRD with four replications. Growth parameters like plant height, number of branches and number of leaves were not significantly affected by temperature induction but significantly higher value was recorded in the case of specific leaf area (283.50 cm2 g-1) compared to control (261.83 cm2 g-1). Among the physiological and biochemical parameters, temperature induction resulted in significantly higher values for total chlorophyll content (1.74 mg g-1), total carbohydrate (36.71 mg g-1), photosynthetic rate (22.13 µmol CO2 m-2 sec-1), water use efficiency (4.98 mmol CO2 mol-1 H2O), chlorophyll fluorescence (Fv/Fm) (0.82), relative water content (92.20 %), superoxide dismutase (0.21 activity g-1min-1), chlorophyll stability index (145.97 %) and proline content (1.32 µM g-1 tissue) compared to plants without induction.

In the second experiment, flowering and fruiting in tomato under elevated CO2 environment, as influenced by growth regulators and nutrient applications, were evaluated. The experiment was laid out in CRD with eight treatments and three replications. The treatments comprised of 50 ppm NAA (T1), 50 ppm Salicylic acid (T2), 50 ppm Boron (B) (T3), 50 ppm Boron (B) + 50 ppm Zinc (Zn) (T4), as foliar spray (at 40,55 and 75 DAS), nutrient application of POP 125% N: 100% P: 100% K (T5), POP 125% N: 125% P: 125% K (T6), a control (water spray) (T7) and an absolute control (T8).
Plant height, number of branches, number of leaves and specific leaf area were found to increase significantly under elevated CO2 condition. Among the treatments, T3 recorded taller plants (85.33 cm). However number of branches (5.50), number of leaves (46.67) were significantly higher in T5. T6 recorded significantly higher value (347.99 cm2 g-1) for specific leaf area.
All the physiological and biochemical parameters except transpiration rate and total soluble protein content showed significantly higher values inside OTC. T3 significantly higher values for chlorophyll content (1.55 mg g-1) and chlorophyll stability index (124.88 %) among treatments. T5 recorded highest values for photosynthetic rate (21.62 µmol CO2 m-2 sec-1) and water use efficiency (4.67 mmol CO2 mol-2 H2O). T6 resulted in significantly higher values for chlorophyll fluorescence (0.75), relative water content (96.87 %), superoxide dismutase (0.23 activity g-1 min-1) and peroxidase (44.43 unit min-1 g-1) compared to control.
Flowering was delayed under elevated CO2 condition. There was an increase in total number of flower clusters inside OTC. However a significant reduction in pollen viability (82.35 %) was noticed under elevated CO2 conditions. T3 resulted in a higher pollen viability (30.28 %) and fruit setting percentage (38.52 %) compared to control under elevated CO2 condition. Days to fruiting was found to be delayed inside OTC. T7 and T4 significantly increased the fruit weight. T5 resulted in less fruit drop leading to increased number of fruits.
Yield per plant was significantly higher for T5 (190.85 g plant-1), T6 (155.21 g plant-1) and T3 (148.29 g plant-1) compared to control (61.83 g plant-1). Under elevated CO2 condition, T5, T4and T3 were found to increase the yield per plant. T3, T1 and T6 resulted in an increase in the lycopene content, thus improving quality of the fruit.
In the present study, CO2 enrichment was found to have a deleterious influence on flowering and fruiting in tomato mainly due to reduced pollen viability and floral deformities. TIRT was proved to improve photosynthetic efficiency and stress tolerance mechanism. Foliar spray with 50 ppm B + 50 ppm Zn at 40, 55 and 75 DAS and addition of 25% extra nitrogen than recommended dose in equal splits were found to improve yield and quality to a great extent. This was achieved through improvement in pollen viability, fruit set and individual fruit weight and also through a reduction in fruit drop. These treatments can be exploited further, individually or in combination, in any crop management programme for tomato under increasing CO2 and associated high temperature conditions. The study also highlights a need for reassessment of critical nutrient requirements for individual crops in the changing global climatic scenario.