Abstract:
The degree of virulence of different isolates of Verticillium dahliae (V08sn-1, Anyang and V07df2) was evaluated using pathogen and pathogen free approaches on upland cotton. Direct use of pathogen in the soil classified isolates into highly virulent (V08sn-1), moderate virulent (Anyang) and less virulent (V07df2) with disease index of 65, 40 and 27 on the basis of leaf necrosis and vascular browning. For pathogen free approach, toxins from these isolates were prepared and their protein contents were quantified. Results revealed highest level of soluble protein in V08sn-1 (78 mg/L) followed by Anyang (55 mg/L) and V07df2 (43 mg/L). Similarly, addition of toxin (10 µg/mL) on germinating cotton seeds inhibited radical length in order of V08sn-1(62 %) > Anyang (33%) > V07df2 (17%). Besides, the addition of same quantity of toxin on detached cotton leaves produced marked symptoms of chlorosis/necrosis which was more severe in V08sn-1 and
followed by Anyang and V07df2. Moreover, dipping of leaf petiole in Vd toxin of Anyang isolate resulted in leaf wilting in contrast to the leaf dipped in equivalent amount of glucose solution (55 mg/L) which demonstrated that elicitor component of Vd toxin is protein in nature. The results of Vd toxin experiment were consistent with the soil inoculation experiment using V. dahliae but the onset of diseased symptoms was quicker in former than later. These findings suggest that utilization of Vd toxin can be an environmental friendly and robust approach for plant breeders to accelerate the process of breeding new resistant lines.
