MSc

Plant growth is influenced by both the quality and intensity of light. The transmittance of light by different shade nets are unique. Hence the spectral quality of light vary under each coloured net. Different wave length of light influence specific physiological process. In this context, the study entitled “Spectral management for improving photosynthetic efficiency in polyhouse cultivation of vegetables” was conducted at the Dept of Plant Physiology, College of Agriculture, Vellayani and at Pothencode, Thiruvananthapuram during 2014- 2016. The main objective was to study the morphological and physiological responses of vegetables, viz. tomato, salad cucumber, capsicum and yard long bean exposed to spectral modification through different colored shade nets. A survey was conducted in 20 polyhouse units in Thiruvananthapuram district to know the adoption of shade nets by the farmers practicing polyhouse cultivation. The experiment was done in a polyhouse of dimension 500m2, which was divided into five parts on an east-west direction roofed with two photoselective and two neutral shade nets of four different optical properties and one part without any shade net. The light interception by shade nets were analysed using spectro radiometer at University of Agricultural Science, Bangalore. The green net reduced 59.9%, white net reduced 55.14% and red net reduced 41.05% of red light compared to open. Four different crops, viz. salad cucumber, yardlong bean, capsicum and tomato were grown under these shade nets. Weather parameters such as Photosynthetically Active Radiation (PAR), global radiation and temperature were recorded but didnot show much variation. The pollen viability was not altered by spectral variation. Earliness to flowering, fruiting and fruit maturity was observed in open condition for salad cucumber and capsicum.
The number of leaves at first flowering was higher in white net for salad cucumber and yardlong bean while it was higher in red net for capsicum and tomato. Specific Leaf Area was significantly higher under red net for salad cucumber (979.52cm2g-1), capsicum (564.21cm2g-1) and tomato (631.18 cm2g-1). The same trend was followed in case of photosynthetic rate also. The internode elongation was found to be minimum in open condition for all the four crops. The leaf anatomy of salad cucumber grown under white net showed higher vascular thickness.

Setting percentage was higher in white and green shade nets for salad cucumber (85.40%) and yardlong bean (89.35%) respectively where as red net was suitable for capsicum (80.99%) and tomato (81.80%). Higher shoot weight and root weight were observed under white shade net for tomato. Root shoot ratio and total dry matter content was higher in capsicum grown under red shade net. Transpiration rate of yardlong bean and tomato plants grown under green shade net was higher while higher transpiration rate of salad cucumber and capsicum was observed under white shade net. The pigment composition of salad cucumber was higher under black shade net. Abaxial stomatal frequency in all the four crops was higher in open condition. Total soluble protein content of tomato and salad cucumber at flowering stage was higher under red shade net. Higher carbohydrate content was observed under open condition in case of yardlong bean, capsicum and tomato. Phenol content increased in tomato plant grown under white shade net. There was no significant variation in IAA. Higher crude protein was observed in yardlong bean grown under white shade net while the crude fibre was higher under open condition. Ascorbic acid was higher in capsicum grown under open condition while for tomato it was under white shade net. Spectral modifications through shade nets altered morphological and physiological responses of salad cucumber, yardlong bean, capsicum and tomato. Varietal suitability was observed in different shade nets. Photosynthetic efficiency was also influenced by shade nets and reflected in the yield of selected crops. Red net was suitable for capsicum and tomato while white net was ideal for salald cucumber and green for yardlong bean.