3 COMPONENTS OF SLOW LEAF-RUSTING AT DIFFERENT GROWTH STAGES IN WHEAT

Latent period, pustule size and number of pustules/cm2 of leaf area of 2 slow-rusting [''Suwon 85'' and ''Purdue 6028A2-9-6-1'', (''P6028'')] and 2 fast-rusting (''Monon'' and ''Suwon 92'') [Triticum aestivum] cultivars were compared in greenhouse and field inoculations with Puccinia recondita f. sp. tritici. The appearance of pustules was protracted on ''Suwon 85'' and ''P6028'' compared to ''Suwon 92'' and ''Monon''. The latent period for ''Suwon 85'' and ''P6028'' was longer by a factor of 1.2-1.8 compared to that of ''Suwon 92'' and ''Monon''. Pustule size on the 2 slow-rusting cultivars was 4/10-6/10 of that on the 2 fast-rusting cultivars. Pustule size was largest on the flag leaf compared to that on the 1st and 2nd leaves below the flag leaf for all cultivars. Latent period was longest and pustule size was most restricted on plants of ''Suwon 85'' and ''P6028'' which were inoculated in the boot stage compared to when plants were inoculated at 6 other plant growth stages. ''Suwon 85'' consistently developed fewer pustules/cm2 of leaf area than ''Suwon 92'', ''Monon'' or ''P6028'' in greenhouse experiments. Leaf rust severity was less and pustule size was smaller in the field for the 2 slow-rusting cultivars than for ''Suwon 92'' and ''Monon''.