Exclusion of solar UV components improves growth and performance of Amaranthus tricolor varieties

• Intraspecific variation exists in Amaranthus tricolor varieties to ambient UV sensitivity.
• Exclusion of solar UV improves growth and performance of A. tricolor varieties.
• Ambient UV detrimental to photosynthesis.
• First report of enhancement of CA/PEPcase in higher plants after solar UV exclusion.

A field experiment was conducted to study the influence of exclusion of solar UV components on the growth responses, gas exchange rates, chlorophyll fluorescence, pigmentation, carboxylation enzymes and foliage yield of four Amaranthus tricolor varieties; Arka arunima, Arka suguna, Pusa lalchaulai and Pusa kiran. The plants were grown in specially designed UV exclusion chambers, wrapped with filters that excluded UV-B (<315 nm), UV-A/B (<400 nm) or transmitted ambient UV or lacked filters. Plants grown under ambient UV radiation (280–400 nm) were compared with those grown without UV-B or UV-A/B. The results indicated increased plant height, leaf weight ratio, specific leaf weight and foliage yield in all the four varieties of A. tricolor grown without UV-B and UV-A/B compared with those grown under ambient UV. Exclusion of UV significantly increased the total chlorophyll while Chl a/b ratio decreased. The efficiency of PS II (Fv/Fm), rate of photosynthesis and stomatal conductance significantly enhanced along with a remarkable increase in Carbonic anhydrase, PEP carboxylase and total soluble proteins. Thus UV excluded plants have higher reducing power and increased CO2 fixation and decreased UV-B absorbing compounds, channelling the additional fixation of carbon towards the improvement of yield in A. tricolor varieties. The response for UV exclusion was higher in variety Arka arunima and Arka suguna compared with Pusa kiran and Pusa lalchaulai. UV sensitivity of the A. tricolor varieties was in the following sequence – Pusa lalchaulai > Pusa kiran > Arka suguna > Arka arunima. Thus Arka arunima and Arka suguna were most sensitive and Pusa lalchaulai and Pusa kiran the least sensitive varieties to ambient level of UV. The least sensitive varieties may be used in the development of UV-B tolerance mechanisms and also developing new varieties tolerant to higher levels of UV-B in future attempts in plant breeding programmes.