Herbicides Impact on the Growth of Alternaria alternata and Morphological Variation in Spores under in vitro Condition

: Herbicides impact was assessed against phytopathogenic fungi Alternaria alternata using different concentrations on the colony growth, spores structure, spores germination and elongation of germ tube. At the 5000 ppm concentration growth of A. alternata was completely restricted but some growth was found in fluchloralin and benthiocarb treated samples at the same concentration. At low concentration (10 ppm) stimulation in growth was occurred in 2,4-D treated Petri plates. Herbicides were found to promote abnormalities in the spores structures at higher concentration. Spores of A. alternata growing on untreated PDA had mean length 27.5 um width 9.5 um; number of horizontal septa 5.0 and vertical septa were 3.0 and 2.0 respectively. At 5000 ppm concentration in 2,4-D treated medium sporulation was prohibited and colour of colony became white. Herbicides also changed the spore structure. In 2,4-D treated cultures mean length of spore decreased by 3.27 um and mean width increased by 1.80 um. Number of horizontal septa also decreased but number of vertical septa was not affected. In case of benthiocarb, spore length decreased considerably while no marked change in width was found. In fluchloralin mean length of spore was 17.12 um and mean width 12.65um. In benthiocarb and fluchloralin treated culture the mean number of horizontal septa were 1.0 and no vertical septa was observed. Percentage germination of spores and growth of germ tube was also affected by the herbicides and inhibitory effect was corresponding to the concentration of herbicides.