The relationship between the chemical structure of s-triazines and fungitoxicity to Sclerotium rolfsii

Thirty eight substituted s-triazine and three dialkyl biguanide analogs were tested for their effects on mycelial growth and the formation of sclerotia by Sclerotium rolfsii. None of the chemicals were fungicidal to the organism at a test concentration of 100 μg/ml in potato dextrose agar. One of the chemicals, ipazine, was highly fungistatic, and 11 others demonstrated a significant but lower degree of activity against mycelial growth. The formation of sclerotia was completely inhibited in the presence of only one s-triazine, 2-amino-4-chloro-6-n-propylamino-s-triazine. Eight other s-triazines were as active as atrazine, the standard test chemical, in inhibiting the formation of sclerotia, and 10 more of the s-triazines were significantly effective but at a lower level of activity than atrazine. N1,N5-bis(ethyl)biguanide was the only chemical which caused a significant increase in the number of sclerotia formed. No absolute correlation was observed between biological activity and chemical structure although in certain instances there was an apparent correlation between toxicity and the overall electron withdrawing character of the non-alkylamino substituent on the s-triazine ring, or to the steric effects caused by the configuration of the alkylamino substituents. Only those chemicals which were highly active as herbicides were significantly effective in inhibiting mycelial growth and sclerotia formation; however, not all of the herbicidally active compounds were effective in this regard.