CHARACTERIZATION OF RESISTANCE OF SPINACH TO WHITE RUST (ALBUGO-OCCIDENTALIS) AND DOWNY MILDEW (PERONOSPORA-FARINOSA F SP SPINACIAE)

Resistance of spinach to white rust (Albugo occidentalis) and races 3 and 4 of downy mildew (Peronospora farinosa f. sp. spinaciae) was quan tified on several cultivars and breeding lines in separate field inocu lation experiments. Several cultivars and breeding lines from the Arka nsas breeding program had undergone repeated field selections for whit e rust resistance (Fall Green, Ozarka II, FA88-310, FA88-354, and FA86 -70) while others had not (Grandstand, St. Helens, and Hybrid 424). Re sistance to both diseases was quantified by measuring disease incidenc e and severity at regular intervals 7-32 days after inoculation. The l atent periods and the area under the disease progress curve (AUDPC) al so were compared. Overall, the cultivars and breeding lines that had u ndergone selection for white rust resistance had significantly higher levels of field resistance to both white rust and races 3 and 4 of dow ny mildew relative to the other cultivars tested. Two cultivars (Fall Green and Ozarka II) and three breeding lines (FA88-354 and FA88-310 o r FA86-70) had significantly lower disease incidences and severity rat ings to white rust and race 4 of downy mildew on most sampling dates t han did St. Helens, Hybrid 424, and Grandstand. The AUDPC for Fall Gre en, Ozarka II, FA88-354, and FA88-310 or FA86-70 also was significantl y lower than that of St. Helens, Hybrid 424, and Grandstand for white rust and race 4 of downy mildew. Fall Green, Ozarka II, and FA88-354 h ad significantly lower disease incidences and severity ratings than di d Grandstand in the race 3 downy mildew tests. The AUDPC for Fall Gree n, Ozarka II, and FA88-354 also was significantly lower than that of G randstand in the race 3 downy mildew tests. The estimated latent perio ds were generally 1-4 days longer for Fall Green, Ozarka II, FA88-354, and FA88-310 or FA86-70 in the white rust and race 3 tests compared w ith the other cultivars tested. The latent periods for the race 4 test s could not be accurately estimated. Several of the cultivars and bree ding lines have measurable levels of field resistance to both white ru st and races 3 and 4 of downy mildew and can be used to help manage th ese economically important diseases of spinach.