Physiological studies on the defence reaction of potato plant to the infection by Phytophthora infestans

Abstract

In the previous reports17, 18, 19), it was shown that in the Phytophthora infestans infected tuber tissue of resistant potato varieties, remarkable increase in respiration, water soluble protein, starch, and polyphenol compounds content occurred at an early stage of infection (15-20hrs. after inoculation), while in susceptibles no such a remarkable increase took place, and it was concluded that the resistance of potato tuber to P. infestans accompanies the activation of metabolism in the infected tissue. In the present paper studies on the physiological changes in the potato tuber tissue, and the susceptibility to P. infestans under the influence of ethanol narcosis, are reported.Tuber of highly resistant seedling “41089-8” was cut in halves; one half was immersed in 10% ethanol for 10 minutes, and the other half was immersed in water. After washing for a short time, tubers in each plot were divided into two groups, then the cut surface of tuber of one group was inoculated by zoospore suspension of P. infestans (common strain H1) and that of the other group was left noninoculated. Twenty or 44 hours after inoculation, blockets of tissue were stamped out of the tuber at a right angle to the cut surface by means of a cork borer having a diameter of 2cm. Superficial layer of these blockets was then worked up into slices 0.45mm thick with microtome. After washing the slices in running water, the O2 uptake and the CO2 output were determined by means of Warburg's “direct method”. Slices were also used for determination of water soluble protein-N, total water soluble-N, and polyphenol compounds content.Results obtained are shown in Tables 1, 2, 3 and 4. Twenty hours after treatment, the respiratory rate in the non-anaesthetized tissue both inoculated and non-inoculated, was remarkably accelerated, while in the ethanol-treated tissue of potato tuber such a remarkable increase in respiration was not observed in either inoculated or noninoculated tubers. The RQ value of ethanol-treated tissue of cut surface was lowered slightly in comparison with that of non-anaestized tissue (Table 5). Accompanying the inhibition of respiratory increase, the amounts of water soluble protein and polyphenol content in the ethanol-treaded cut surface of potato tuber were less than those of non-treated tissue 20hrs. after treatment. When non-anaesthetized cut surface of potato tuber was infected by P. infestans, rate of increase in respiration, water soluble protein and polyphenol content was greater in the infected tissue than in the non-infected one. In the ethanol-treated tissue, however, increase in such physiological reactions induced by infection of P. infestans was not so great as that in non-narcotized tissue (shown in Table 4). It was. stated in the previous report that the changes in hyphal substance in inoculated tissue may be negligible in comparison with the physiological changes in host tissue within the period of about 20hrs. On the contrary, 44hrs after inoculation, the content of hyphal substance in the infected tissue may play an important role in the changes of chemical compounds contained in the tissue. Forty-four hours after inoculation, moreover, the content of polyphenol compounds decreases in infected resistant tissue, possibly due to the deposition of the compounds in collapsed cells (Table 3).Above described results show that the excited metabolism in tissue of resistant potato tuber induced by P. infestans may be inhibited by the pre-infectional ethanol narcosis. It may be possible to presume that such an inhibition of metabolic acceleration may result in the reduction of resistance of interspecific hybrids to the infection by common strain of P. infestans.