1.3.24
AN INFECTION OF POTATO SPROUTS BY PHYTOPHTHORA INFESTANS

Z WEBER1 and P LIU 2

1University of Agriculture, Dobrowskiego 159, 60-594 Poznan, Poland; 2Guangxi Agricultural University, Guangxi, China

Background and objectives
Leaf and tuber responses to Phytophthora infestans are well known. However, the pathogen can also infect the potato sprouts, particularly when grown from infected tubers. The infected sprouts can be destroyed or, if they emerge, are small and weak. Infected sprouts often serve as a source of infection for the neighbouring plants. Sprout infection may be very important from an epidemiological point of view. The objective of this work was laboratory assessment of the sprout susceptibility of 52 potato cultivars to 10 races of Phytophthora infestans.

Materials and methods
Ten single-zoospore isolates (A-2 mating type) of P. infestans were used for sprout inoculation. Races of the isolates were determined using the potato leaflets of Black's genotypes [1]. 52 potato cultivars from the Research Centre for Cultivar Testing in Stupia Wielka, Poland, were used. Sprouts of 2-3 cm (50 cultivars) and 5-6 cm length (36 cultivars) produced on the tubers in dark storage in the spring of 1997 were used. Inoculation was done by putting 5-mm disks of rye medium [2] overgrown with the particular race of P. infestans on the middle part of the sprout. Inoculated, sprouted tubers were kept in plastic bags with wet filter paper, in darkness at 18-20C. Sprout infection was assessed on the 7th day after inoculation. Both sporulation of the pathogen and brown discoloration of the sprouts were determined

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Results and conclusions
Each of 10 isolates represented other races: 2.3, 3.4, 3.4.7, 3.7.10, 1.2.3.7, 1.3.7.10, 1.3.4.7.10, 2.3.4.7.11, 3.4.7.10.11, 1.3.4.7.10.11. The most pathogenic races to 2-3-cm and 5-6-cm sprouts were, respectivel,y races 0.1.3.4.7.9 and 0.1.3.4.7.10.11. The percentage of sprouts with pathogen sporulation was usually positively correlated with the volume of discoloured sprouts. The least susceptible appeared to be sprouts of the following potato cultivars: Aster, Glada, Ania, Anielka, Beata, Klepa, Meduza, Omulew, Vistula, Bzura, and the very susceptible ones: Kariena, Kolia, Mors and Arkadia

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References
1.Shattock RC, Janssen BD, Whitbread R, Shaw DS, 1977. Annals of Applied Biology 86, 249-260.
2.Caten CE, Jinks JL, 1968. Canadian Journal of Botany 46, 329-348.