Environmental Factors Influencing Safflower Screening for Resistance to Phytophthora cryptogea. A. D. Heritage, Research Scientist, CSIRO, Centre for Irrigation Research, Private Mail Bag, Griffith, NSW 2680, Australia. E. K. S. Harrigan, Senior Technical Officer, CSIRO, Centre for Irrigation Research, Private Mail Bag, Griffith, NSW 2680, Australia. Plant Dis. 68:767-769. Accepted for publication 24 February 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-767.

Sand texture influenced infection of safflower seedlings by zoospores of Phytophthora cryptogea. In fine sand, an inoculum of 10⁷ zoospores was required to uniformly infect trays of safflower seedlings, but when coarser sand was used, 2 × 10⁶ zoospores were sufficient. Withholding water from seedlings to induce wilt symptoms before inoculation improved the reliability of glasshouse screening. Breeding lines resistant to infection as 10-day-old seedlings also expressed resistance when tested after 90 days in pot experiments. Selected breeding lines were screened in a field disease nursery. When sown on ridges, some safflower lines reacted differently from those sown on the flat for border check irrigation. Ponding of water in border check irrigation for as little as 2 hr led to successful infection provided air temperatures exceeded 35 C. Some breeding lines expressed field resistance but failed to show resistance under glasshouse conditions. One breeding line showed little or no infection in both field and glasshouse screenings.