Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/2000
Publication Date: 8/20/2000
Citation: MASANGKAY, R.F., PAULITZ, T.C., HALLETT, S.G., WATSON, A.K. CHARACTERIZATION OF SPORULATION OF ALTERNARIA ALTERNATA F. SP. SPHENOCLEAE.. BIOCONTROL SCIENCE AND TECHNOLOGY. 10: 385-397. 2000. Interpretive Summary: Alternaria alternata f. sp sphenocleae was developed as a mycoherbicide against gooseweed (Sphenoclea zeylanica), a major weed in rice paddies. This paper looks at cultural conditions (nutrition, temperature, light conditions, and moisture) in order to optimize spore production for use as inoculum.
Technical Abstract: Studies were conducted on agar media to characterize the factors for the optimization of sporulation of Alternaria alternata f. sp. sphenocleae, a fungal pathogen being evaluated as a biological control agent for Sphenoclea zeylanica (gooseweed). A. alternata f. sp. sphenocleae conidiation was affected by nutrition, temperature, light conditions, and moisture. On all agar media tested, except for half-strength potato dextrose agar (½ PDA) and V-8 juice agar (VJA), exposure to different light conditions did not have any significant effect on conidia production. However, when comparing ½ PDA and VJA, sporulation under constant near-ultraviolet (NUV) light at 28oC increased markedly on VJA, but decreased substantially on ½ PDA. This trend, however, was opposite under dark conditions since ½ PDA produced the greatest number of conidia whereas a 75% reduction in conidia production occurred on VJA in the dark. On all the standard agar media evaluated, the most virulent conidia were obtained on ½ PDA at 28oC under constant NUV incubated for 4 weeks. Sporulation of A. alternata f. sp. sphenocleae using the sporulation medium (S-medium) technique was rapid. Conidia were produced within 24 h and continuous sporulation was still observed until 120 h. The best primary agar media for conidia production were PDA, ½ PDA and VJA, while water agar was the poorest. Conidia production was optimized with the addition of 20 g l-1 of calcium carbonate (CaCO3) and the addition of 2 ml of sterile distilled water on the medium. The most virulent conidia were produced when the primary agar was ½ PDA, the CaCO3 concentration was 20 g l-1, and the cultures were incubated at 18oC in the dark. Conidiophore induction occurred on nutrient rich media and was stimulated by NUV, while formation of conidia proceeded in darkness after nutrients were depleted under warm dry or cool moist conditions. Culture media, growth conditions, and CaCO3 affected the inoculum potential of A. alternata f. sp. sphenocleae conidia.