SOME FACTORS AFFECTING THE DEVELOPMENT AND BIOCONTROL OF COTTON SEEDLING DISEASE

The effects of temperature and cultivar on disease development in cott on were investigated in addition to the duration of susceptibility to infection and the timing of infection by Pythium ultimum and Rhizocton ia solani. Symptom development was also monitored. Disease was more se vere at day/night temperature regimes of 20/15, 25/20, and 30/25 degre es C than at 35/30 degrees C. Disease development differed significant ly between cotton cvv. Deltapine 90 and Siokra 1-4 at 30/25 degrees C and 35/30 degrees C. In glasshouse trials in field soil, both R. solan i and P. ultimum were isolated from seeds as early as 2 h after inocul ation, although most seeds were not infected with P. ultimum until 10 h after inoculation and with R. solani until 24 h after inoculation. I ncreasing the duration of exposure to inoculum increased the number of seeds infected and reduced the number of plants surviving. Seedlings were resistant to P. ultimum infection by 14 days after sowing but wer e not resistant to infection by R. solani until 28 days after sowing.