J Mycol Pl Pathol, Vol. 39, No.3, 2009 458 Influence of Photoperiod on Growth and Mycoherbicidal Potential of Alternaria alternata, a Biocontrol Agent of Waterhyacinth Puja Ray, Sushilkumar and Akhilesh Kumar Pandey National Research Centre for Weed Science, Maharajpur, Adhartal, Jabalpur- 482004, Madhya Pradesh, India; 1 Mycological Research Laboratory, Department of Biological Science, R.D. University, Jabalpur-482001, Madhya Pradesh, India; e-mail: puja.ray@gmail.com Abstract Light exhibits a profound influence on the physiology of several fungi. The effect of light on growth, sporulation and toxin production of Alternaria alternata was studied in three light regimes, 12 h of alternate light and darkness, 24 h of continuous darkness and 24 h of continuous light. Maximum growth was obtained under the conditions of total darkness followed by 12 h of alternate dark and light period and the least growth was in 24 h of continuous light. Maximum sporulation was obtained under total darkness and the least was under continuous light. Maximum phytotoxicity was caused by toxin produced at 12 h of alternate dark and light period. Key words: Alternaria alternata, mycoherbicide, sporulation, toxin, waterhyacinth, toxin Citation: Ray P, Sushilkumar and Pandey AK. 2009. Influence of photoperiod on growth and mycoherbicidal potential of Alternaria alternata, a biocontrol agent of waterhyacinth. J Mycol Pl Pathol 39(3):458-461. Alternaria alternata (Fr.) Keissler is a common saprophytic fungus. It has been reported as potential biocontrol agent of waterhyacinth, Eichhornia crassipes (Mohanbabu et al 2003; Aneja and Singh 1989; Nagraj and Ponnappa 1970). The disease symptoms caused by the fungi on the weed appear as small, oval lesions on lamina and petiole. Concentric rings are often surrounded by yellow halo. These spots become irregular in shape with age. Several such lesions may coalesce to cover large areas leading to death of the plant. Several physico-chemical factors are known to have a profound influence on fungal physiology. A detailed knowledge about the disease development and weed mortality is an important pre-requisite for the development of mycoherbicide. Light exerts an important effect upon cellular metabolites through changes in chemical environment (Prasad and Kapoor 1975). The growth of only a few fungi is affected by light. At a high light intensity, growth of certain fungi may be inhibited while several others may actually require light for initiation and maturation of reproductive bodies (Deacon 2006). Although the effect of light on sporulation of Alternaria spp. is well documented (Prasad and Dutt 1974; Tan 1978), very little information is available in relation to the effect of light on toxin production by the fungus. An investigation was made to observe the effect of light on growth, sporulation and toxin production by A. alternata. Materials and Methods Source of isolate. Indigenous strain of A. alternata was isolated from infected leaves of waterhyacinth collected from water bodies of Jabalpur, India. A 7 day old stock culture of A. alternata grown on PDA was used as basal culture. As sporulation in A. alternata was absent in liquid media (Tebeest 1996; Singh et al 2001; Ray et al 2007), spores were obtained from solid media and the toxic filtrate was obtained from 21 d old metabolized broth. Effect of light on growth and sporulation of A. alternata. Radial growth and sporulation of A. alternata was studied in Petri-plates containing 20 ml of sterilized Richard’s agar medium adjusted to pH 5. In Petri plate, five mm disc of the fungus was inoculated using sterilized cork borer and incubated in BOD at 25 C. The inoculated Petri plates were exposed to three light conditions viz, 12 h of alternate light and darkness, 24 h of continuous darkness and 24 h of continuous light during a day. Light was provided with the help of white fluorescent tube light (four Phillips TL 40 W/33, 1000 lux) and continuous darkness was maintained by wrapping the Petri plates with black paper. For alternate light and darkness, the plates were kept in BOD incubator with adjusted photoperiod. Radial growth of A. alternata was recorded in inoculated Petri- plates after 3, 5 and 7 d of incubation and sporulation was recorded after 21 d using haemocytometer.