2.8.24
OCCURRENCE OF POTATO EARLY BLIGHT ALTERNARIA SOLANI AND A. ALTERNATA ON POTATO AND NITROGEN FERTILIZATION

W CZAJKA1, B CWALINAl, Z CIECKO2, Z GRONOWICZ3

1Department of Plant Protection, 2Department of Environmental Chemistry, and 3Department of Crop Production, Oisztyn University of Agriculture and Technology, 10-720 Oisztyn-Kortowo, Poland

Background and objectives
The application of mineral fertilizers, as well as organic manuring, has an important role in potato production. The highest increase of tuber yield results from nitrogen application [1,2]. However, high rates of mineral nitrogen and the lack of maintaining a rational proportion among mineral nutrients may adversely affect health status of the crop [3]. The intensity of an occurrence of potato early blight depends upon several factors, including the weather. The aim of our studies was to determine the effect of nitrogen fertilization on an intensity of occurrence of potato early blight during growth period.

Materials and methods
Our studies were based on a 2-year field trial which was conducted at Experimental Station in Tomaszkowo owned by Oisztyn University of Agriculture and Technology (north-eastern Poland). Three Polish potato cultivars (Ania, Mila and Dunajec) were grown. Farmyard manure was spread in the rate of 25 ;t/ha. Nitrogen was applied at three experimental rates: 0.60, 90 and 120 ;kg N/ha. Plots had an area of 54 ;m2. Potatoes were planted in rows spaced at 62 ;cm and 40 ;cm between plants. A total of 115 tubers were planted per plot and tubers were harvested from 100 plants. The experiment used a randomized block design in four replications. During growing period an intensity of occurrence of potato early blight was estimated using nine-point scale. For chemical analysis, 25 plants per plot were taken at random.

Results and conclusions
The symptoms of potato early blight (Alternaria solani and A. ;alternata) were detected on potato leaves at the end of July in 1996 and 1997. At first, on the lowest leaves, dark brownish spots were visible with typical patterns of concentric rings. Increase in disease caused withering and, consequently, early death of crop foliage. In 1996, which was characterized by low precipitation the development of the disease was inhibited and never exceeded 14%. A wet summer in 1997 favoured disease development, especially on foliage of the cultivars Mila and Ania (38%). Observations made in the second half of August revealed more intense infection in the plots fertilized with the highest nitrogen rate (120 ;kg N/ha). In conclusion; the intensity of occurrence of potato early blight was related to nitrogen fertilization and the weather, and different nitrogen rates (0, 60 90 and 120 ;kg N/ha) significantly affected the intensity of potato early blight. Higher nitrogen rates favoured disease development.

References
1. Czajka W, 1990. Rocz. Nauk. Roin. ser. E, 20(1/2), pp. 31-39.
2. Wyszkowski M, 1996. Acta Acad. Agricult. Tech. Oist. Agricultura 63, 115-127.
3. Wojciechowska-Kot H, Czajka W, Wiwart M, 1987. Acta Acad. Agricult. Tech. Oist. Agricultura 44, 191-204.