Scions of lemon and orange were grafted on sweet orange rootstocks, Citrus sinensis Osbeck “Bessie” grown in fumigated sandy loam. After the plants were well established, half of their number were inoculated with Phytophthora parasitica Dastur and P. citrophthora (Sm. and Sm.) Leonian. Oxygen supply to the root soil environment was controlled by having sealed containers in which oxygen concentrations over the soil surface could be reduced from atmospheric oxygen (20.93 percent) by mixing nitrogen with air. Total dry weights of leaves, stems, and roots were significantly reduced by the presence of Phytophthora spp. while only dry weight of roots was significantly reduced due to low oxygen supply. Even though the dry weight of the lemon tops was greater than that of orange the vigor of the top had no effect on root growth or root rot due to Phytophthora spp.
Plants in infested soil had leaves with significantly lower concentrations of P, Ca, Mn, and Fe and significantly higher concentrations of K, Na, and Cl than those from plants grown in noninfested soil. However, supplying oxygen to the root zone at concentrations less than that in air significantly reduced concentrations of N, P, K, Ca, Mg, B, and Fe in leaves. Concentrations of K, Mg, Na, Cl, Zn, and Mn in roots were decreased in the presence of Phytophthora spp., while concentrations of N, P, K, Mg, Na, and Cl in roots were decreased by low oxygen supply. There were significantly higher concentrations of N, K, Ca, Na, Cl, and B in leaves of orange than in leaves of lemon, while in roots of orange there were significantly lower concentrations of Mg, Zn, Mn, and Fe than in lemon roots.