Different chemical changes were observed in the root and bulb tissues of three conventional onion cultivars (cvs.) Shandaweel-1 (resistant) and Giza-6 (tolerant) and Giza-20 (susceptible) under artificial infection with pink root rot (Pyrenochaeta terestris). The Changes in phenols, sugars and individual free amino acid contents were assayed after 30, 60 and 90 days form transplanting in infested soil under glasshouse conditions at 27 °C +2.
At early stage of the disease (after 30 days), the healthy root tissues of the resistant transplants contained higher amount of phenols than those determined in the toler¬ant and susceptible cvs. Infection increased the phenolic compounds of all cvs. but with different levels. Noticeable further amounts of such phenolic substances were assayed in the susceptible tissues particularly after 90 days from inoculation, whereas niglicable decrease was observed in both tolerant and resistant cvs.
With regard to the sugar contents, it was concluded that the total soluble sugars particularly non-reducing were greatly increased in the bulbs of susceptible transplants after 30 days, such increase was not found in root tissues. Limited increase was determined in the reducing sugars of the roots due to infection, however a reduction in non-reducing was detected in the bulb tissues of both tolerant and resistant cvs. With the disease development, gradual decrease in the total soluble sugars were assayed in either resistant or tolerant cvs. whereas noticeable decrease was observed in the susceptible diseased tissues after 60 days but a remarkable increase was occurred after 90 days.
Total free amino acids in the whole diseased transplants of the susceptible cv. was lowered by infection after 30 days from inoculation. Similar decrease was observed in the resistant cv., however reverse reaction was recorded in the tolerant cv.. All amino acid groups in the susceptible cv., were decreased in the root tissues and increased in its bulb tissues. Only the sulphorlc and hydroxylic groups were increased in the root and bulb tissues of the resistant cv., non-polar alephatic and amino groups were decreased in its both tissues, whereas aromatic, emino and basic groups were decreased in its roots (particularly aromatic group) and were increased in its bulb tissues.
After 90 days, the total amino acids in the whole dis¬eased transplants were remarkably increased in the suscep¬tible cv., slightly increased in the resistant cv., and clearly decreased in the tolone. In the susceptible cv., sulphoric and hydroxylic groups were increased in it- roots and bulbs, amino group was decreased in both tissues meanwhile non-polar alephatic, aromatic, amino and basic groups were decreased in its roots and increased in its bulbs. The inoculated transplants of the resistant cv. showed higher concentrations of sulphoric and amino groups in its roots and bulbs meanwhile hydroxylic; and aromatic groups were decreased in its roots and Increased in its bulbs, however non-polar alephatic, amino and basic groups were obviously decreased In its root and bulb tissues. |
