Virulence of Puccinia helianthi on Differential Sunflower Genotypes in South Africa. O. Los, Glen Agricultural Development Institute, Glen 9360, South Africa. Z. A. Pretorius and F. J. Kloppers, Department of Plant Pathology, University of the Orange Free State, Bloemfontein 9300, South Africa and Z. van der Linde, Glen Agricultural Development Institute, Glen 9360, South Africa. Plant Dis. 79:859. Accepted for publication 5 June 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0859C.
Sunflower rust caused by Puccinia helianthi Schwein. occurs annually in most sunflower (Helianthus annuus L.)–growing areas of South Africa. Although the disease has been known in South Africa since 1944, and has often caused significant losses, physiological specialization within the local population of P. helianthi has not been determined. To study variation in virulence in P. helianthi, a survey was undertaken in the main sunflower-producing areas of South Africa during 1992 to 1994. Rust-infected leaves were obtained from volunteer sunflower plants, experimental plots, or commercial fields at 27 geographically different localities. From each collection two single-pustule isolates were established and increased in isolation on the susceptible genotype S37-388. Isolates were inoculated separately onto 3-week-old seedlings of the differential sunflower lines S37-388, HA-R1, HA-R2, HA-R3, HA-R4, HA-R5, P386, PhRR3, 18.104.22.168 (69), CM29-3-1-3-2-1 (CM29-3), and S37-388RR. Seed of these lines were provided by J. Kochman, (Toowoomba, Australia). Inoculated seedlings were incubated in a dew chamber for 16 h before being transferred to a greenhouse at 18 to 250C. Infection types (ITs) were scored according to the description of Rashid (1) 12 to 14 days after inoculation. During 1992 to 1993, only one pathotype (UVPhel), virulent to lines 69, S37-388, and S37-388RR, was detected. ITs produced by isolates of UVPhel on the resistant lines HA RI, HA-R3, HA-R4, HA-R5, and P386 ranged between 0 and 2. IT 2 on P386 was often associated with chlorosis. HA-R2 and PhRR3 were highly resistant (fleck [;] IT) to all UVPhel isolates, whereas isolates on CM29-3 produced ITs to 1. The same pathotype predominated during 1993 to 1994. Two isolates collected near Bothaville in the Free State province were avirulent only to HA-R2 (IT ), CM29-3 (IT V), and PhRR3 (IT ). These isolates belong to pathotype UVPhe2. In artificial inoculations using one isolate from each pathotype, no symptoms were produced on Xanthium spinosum L. or X. strumarium L., a genus previ ously reported as a host for P. helianthi. Knowledge of the occurrence and distribution of P. helianthi pathotypes, and the availability of these pathotypes for screening purposes, should assist local sunflower breeders in developing rust-resistant germ plasm.Reference: (1) K. Y. Rashid. Can. J. Plant Pathol. 13:356, 1991.