GENETICS AND HISTOLOGY OF SLOW LEAF-RUSTING RESISTANCE IN WHEAT
Abstract
Inheritance of latent period of Puccinia recondita on wheat was studied by making corsses between slow-rusting and fast-rusting cultivars and inoculating plants in the greenhouse. Analyses of F(,3) families and backcrosses for Morocco?SW 72469-6 and L574-1/ Suwon 92 showed that long latent period in slow-rusting wheats SW 72469-6 and L475-1 is conditioned by two recessive genes with equal effects and an equal egree of dominance. Latent period and uredinium size were ngatively correlated. Long latent periods in CI 10745 and Milyang 8-6 are conditioned by two recessive genes with equal effect. Long latent period is controlled by one or two recessive genes in P65113B6, and by three recessive genes in CI 13227 and P6028A2. Seven slow-rusting wheat cultivars were intercrossed to determine whether these cultivars possess unique genes for a long latent period. Seven out of the eight crosses showed transgreesive segregation. Witin some transgressively segregating F(,2) populations, some plants had latent periods as short as in the fast-rusting cultivar Morocco and others longer than in the slow-rusting cultivar CI 13227. These results indicate that most of the genes conditioning long latent period in these seven cultivars differ from each other and very long latent periods could be obtained by making crosses among alow leaf-rusting wheats. Histology of P. recondita infection on eleven wheat cultivars was studied from spore germination to uredinia formation to investigate the interactions between the host and the parasite and to determine whether long latent period and small uredinia are due to reduced mycelial growth in leaf tissue. Six sequential flag leaf samples (24-216 hr after inoculation) treated with an optical brightener (Uvitex BOPT) were observed with a fluorescence miroscope. Percentages of urediniospore germination, germinated urediniospores forming appressoria, and appressoria forming substomatal vesicles were the same for fast-rusting (Morocco, Suwon 92, Monon, and '72482), intermediate slow-rusting (SW 210), slow-rusting (Suwon 85, SW 72469, P6028A2, CI 13227, and L574-1), as well as hypersensitive resistant (P68130) cultivars. However, the colonies were smaller and bad fewer haustorial mother cells in slow-rusting wheats than in fast-rusting wheats. Although the colony growth ates of P. recondita on fast-rusting and slow-rusting cultivars were different, uredinial bed formation on both groups of cultivars began when the average colony size was 0.12 to 0.14 mm('2). The longer time required for colonies to reach this incipient stage of sporulation on slow-rusting cultivars would explain their long latent period.
Degree
Ph.D.
Subject Area
Plant pathology
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