Rust of sunflower (Helianthus annuus L.) caused by Puccinia helianthi Schwein. is a major sunflower disease in Mozambique where local ecotypes, from Peredovik and Record selections, and South African commercial varieties were all susceptible to race 4, which was prevalent among isolates collected from 1996 to 1997 (1). Disease surveys carried out in southern Mozambique (Maputo) from August until September 2002 revealed an increase in the incidence and severity of sunflower rust compared to previous investigations on the same varieties. Rust symptoms, observed in all fields, appeared on the last leaf pairs of plants at the 5.1 growth stage. Disease severity (percentage of leaf area infected) (2) ranged from 20 to 60%, but the disease did not cause noticeable yield loss because rust infection started near the end of the season. Argentine and African commercial varieties and some experimental Mozambican selections from sunflower accessions of different origin were the most severely affected. Two rust samples were collected from infected leaves, stored at 5°C, and increased on the universal suscept (S-37-388). Race identification of both isolates was determined on three sets of nine differential lines (three lines per each set): S-37-388, CM 90 RR, MC 29; P-386, HA-R1, HA-R2; and HA-R3, HA-R4, HA-R5 using the triplet coding system (3). The 2-week-old seedlings (four per 10-cm pot) of each differential line (four pots per line) were inoculated on the upper surface of the first pair of true leaves. Inoculated seedlings were covered with plastic bags, placed in a growth chamber without light for 18 to 22 h, and then transferred to a greenhouse under alternate day/night temperatures of 22/18 ± 2°C, 60 to 70% relative humidity, and 12 h of light (180 μE·m-2·s-1) per day. The inoculation test was repeated twice. Assessment of host differential reactions, 14 days after inoculation, was based on five categories of sunflower reaction to rust (4). Both isolates were identified as race 314 and to our knowledge, this is the first report of this race in Mozambique. Since P. helianthi completes its life cycle annually, the occurrence of new races is expected. The opportunity for new races to occur is particularly high and severe in Mozambique where all sunflower varieties grown as summer (January to June) and winter (August to December) crops are susceptible.
References: (1) P. M. Vicente and A. Zazzerini. Helia 20:25, 1997. (2) T. J. Gulya et al. NDSU Extension Serv. PP-998, 1990. (3) T. J. Gulya and S. Masirevic. FAO Eur. Res. Network on Sunflower. Bucarest, Romania, 31, 1995. (4) S. M. Yang. Ann. Phytopathol. Soc. Jpn. 52:248, 1986.
