1. Catherall, Rep. Welsh Pl. Breed. Stn, 1967: 120, 1968.
2. Huth, Phytopath. Z. 62: 300, 1968.
3. Serjeant, Rep. Rothamsted exp. Stn, 1962: 112, 1963.
4. Serjeant, Pl. Path. 13: 23, 1964.
5. Serjeant, Ann. appl. Biol. 59: 31, 1967.
6. Smith, Pl. Path. 1: 118, 1952.
7. Upstone, Ann. appl. Biol. 64: 49, 1969.