EFFECT OF ELEVATED CO2 ON INFECTION OF THREE FOLIAR DISEASES IN OILSEED BRASSICA JUNCEA
P. Mathur, E. Sharma, S.D. Singh, A.K. Bhatnagar, V.P. Singh, R. Kapoor
The present investigation was carried out in a free-air CO2 enrichment (FACE) facility to assess the effect of elevated CO2 on the incidence and severity of three foliar diseases of Brassica juncea cv. Pusa Tarak. Exposure of plants to elevated concentration of CO2 (550 ppm) revealed lower incidence and severity of Alternaria blight caused by Alternaria brassicae and downy mildew caused by Hyaloperonospora brassicae, while white rust infection caused by Albugo candida increased. Leaves of mustard plants grown under elevated CO2 had a higher amount of epicuticular wax which, together with higher concentration of total phenols and phenylalanine ammonia lyase activity, may have increased the ability of mustard plants to resist infection by A. brassicae and H. brassicae. Mustard plants grown under elevated CO2 showed a decrease in stomatal density and pore size, and consequently also in stomatal conductance. This might explain the decrease in disease index of downy mildew caused by the stomata-invading pathogen H. brassicae. There was no change in leaf protein concentration, whereas sugars were three times as concentrated in plants grown under high vs. ambient CO2. There was an increase in the concentration of total glucosinolates (GSs) under FACE in plants grown under elevated CO2, but a decrease in their diversity. Namely, the aliphatic GS gluconapin was more abundant in plants grown under high CO2, while three out of eight different GSs found in the leaves of plants grown under ambient CO2 could not be detected. Higher sugar availability and lower GSs diversity may account for the higher incidence and severity of white rust caused by the obligate biotroph A. candida.