NUCLEAR-CYTOPLASMIC INTERACTIONS IN WHEAT RESISTANCE TO FUNGAL PATHOGENS .7. EFFECTS OF ALIEN CYTOPLASMS IN PLANT ONTOGENY UPON INFECTION BY A VIRULENT BROWN RUST CLONE

The modifying effect of cytoplasms of wild cereal species on quantitat ive resistance of common wheat to a virulent clone of brown rust was s tudied during host plant ontogeny. Mean spore-forming ability (MSFA) p er cm2 of leaf surface was estimated for the first and flag leaves of 34 alloplasmatic lines with the genome of Penjamo 62 variety. The sign ificant effect of alien cytoplasms on MSFA at early and late stages of ontogeny was revealed using ANOVA. For seedlings and grown plants of alloplasmatic lines, the contribution of the cytoplasmic factor was 23 .51% and 17.35%, respectively. At an early stage of ontogeny, 10 alien cytoplasms (six fertile and four sterile) increased MSFA as compared to the stock euplasmatic variety Penjamo 62. Only fertile cytoplasms o f the species Triticum haynaltricum and Haynaldia villosa inhibited MS FA. At the earing stage, this parameter increased on a background of f ive fertile and six sterile cytoplasms and decreased in the case of cy toplasms from Agropyron glaucum and H. villosa. For five alloplasmatic lines, a similarity of cytoplasmic influence at both stages of ontoge ny, which consisted of promotion of fungus growth in relation to eupla smatic control, was demonstrated. Only one cytoplasm derived from H. v illosa decreased MSFA irrespective of the developmental stage of plant s. Comparison of spore-forming ability for the first and flag leaves r evealed a general trend toward an increase of quantitative resistance at the stage of earing. The variability observed in the majority of ca ses, of the modifying influence of cytoplasm in ontogeny, may be attri buted to a different regulatory effect on the expression of resistance polygenes or genes controlling constitutive characters of natural res istance.