First Report of the Rust Fungus Olivea scitula on Vitex doniana in Zambia.

Vitex doniana Sweet (Verbenaceae) is a semideciduous tree that occurs throughtout Africa from Senegal to the Sudan and in Somalia, Angola, Botswana, South Africa, and most provinces of Zambia. Wood from V. doniana is used in construction, making boxes and furniture; jam and wine are made from the vitamin-rich fruits; the leaves provide cattle feed; and other plant parts are used in traditional medicines. The tree itself is a favorite for hanging bark beehives. In September 2004, leaves of V. doniana trees (20 km southeast of Lusaka) were found bearing brown uredinia, which were subsequently identified as the rust fungus, Olivea scitula Syd. The following description is based on the Zambian material that has slightly smaller spores than those of the original published description (2). Uredinia were hypophyllous, brown, round, at first scattered irregularly in the interveinal areas, then coalescing to form a continuous erumpent covering on the base, margin, or middle of the leaflet. Urediniospores were yellow brown, verrucose, globose, triangular or oval, 20 to 25 × 20 µm, with densely filled oil globules, and the wall 2 to 2.5 µm thick. Paraphyses were peripheral, incurved, basally united, and 50 to 75 × 5 to 6.25 µm. The pathogen has been reported previously from Sierra Leone, Uganda, and Nigeria (1). To our knowledge, this is the first report of Olivea spp. in Zambia and the first report of O. scitula from Central Africa. References: (1) D. F. Farr et al. Fungal Databases. Systematic Botany and Mycology Laboratory, On-line publication. ARS, USDA, 2004. (2) A. H. Sydow. Ann. Mycol. 35:251, 1937.

Incidence and severity of frogeye leaf spot and associated yield losses in soybeans in agroecological zone II of Zambia.

The incidence and severity of frogeye leaf spot of soybean (Glycine max (L.) Merr.) was studied in agroecological region II of Zambia during the 1997/98 crop growing season. A survey was conducted on farmers' fields on SCSI Kaleya, Magoye and Hernon-147 cultivars. Disease incidence and severity was assessed by monitoring disease increments at two weeks interval (beginning of January to April) from nine fields, three from each province. Soybean cultivars were evaluated for yield losses resulting from frogeye leaf spot. Field plots of each cultivar were either sprayed twice with benomyl (benlate) or not sprayed at all. The results showed that the incidence of frogeye leaf spot was highest in Southern province (5.1), followed by Lusaka province (4.9) while Central province had the lowest disease incidence (1.8). Values for area under disease progress curve (AUDPC) were significantly greater (P < 0.05) for Lusaka and Southern provinces than for Central province. Yields in benomyl protected plots ranged from 1444 kg ha-1 to 2320 kg ha-1 and were significantly different among the cultivars. Average yields of non protected plants were reduced by 30.5% for Kaleya, 35.6% for Hernon-147 and 37.2% for SCS1. Incidence and severity increased with time and varied depending on weather parameters and susceptibility of cultivars to the disease. Yield losses due to frogeye leaf spot occurred through a reduction in seed size. Differences in weather conditions and amount of inocula are believed to contribute to the observed variation in incidence and severity of the disease at different locations.

First Reports of Soilborne wheat mosaic virus and Wheat spindle streak mosaic virus in Africa.

During 1997 and 1998, virus symptoms similar to those of Soilborne wheat mosaic virus (SBWMV) and Wheat spindle streak mosaic virus (WSSMV) were observed on nine wheat cultivars (Triticum aestivum cvs. Deka, Gamtoos, Lorie II, MM2, Nata, Nkwazi, P7, Scepter, and Scan) in the Central, Copper-Belt, Lusaka, and Southern provinces of Zambia. Symptoms were observed between June and August on wheat, which in Zambia is an irrigated crop grown during the cooler months (May to August). In fields suspected to be infected with SBWMV, irregularly distributed, circular patches of severely stunted sparse plants were observed. Because of these symptoms, the syndrome is described in Zambia as the "crater disease." Infection was more common on light to medium sandy-loam clay soils, and affected patches were particularly common along the field edges and in poorly drained areas. Such waterlogged conditions are conducive to the multiplication and spread of Polymyxa graminis, the protist vector of SBWMV (1). Affected plants initially showed chlorotic streaks on all leaves, which became uniformly yellow and eventually necrotic. The roots of these plants were slightly swollen and enlarged and are likened to "Rastafarian pleats" locally. In fields suspected to be infected with WSSMV, symptomatic plants were observed in the border rows of affected fields. Chlorotic streaks and mosaics were observed on the leaves of affected plants, and the tips of these leaves were also frequently twisted. Using double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA), SBWMV and WSSMV were positively identified in symptomatic plants. In total, 81 plants from the four provinces were tested, and 72 and 37% were infected with SBWMV and WSSMV, respectively. Identification was confirmed by DAS-ELISA using antisera from W. Huth (BBA-Braunschweig, Germany) and C. Rubies-Autonell (Bologna University, Italy) for SBWMV and using antisera from W. Huth (BBA-Braunschweig, Germany) and G. Bergstrom (Cornell University, New York) for WSSMV. Further confirmation of the identity of the two viruses was provided by the reaction of 12 indicator species (Chenopodium amaranticolor, C. quinoa, C. hybridum, Digitaria milanjiana, Eleusine indica, Oryza sativa (cv. IITA 212), Panicum maximum, Rottboellia cochinchinensis, Setaria verticillata, Sorghum bicolor(cv. Sima), S. halepense, and Triticum aestivum (cvs. Lucal, Kwale, Lorie II, Nkanga, 128, and GV 4-12) in mechanical transmission studies using infected leaf sap. This is the first report of SBWMV and WSSMV not only in Zambia but also Africa. The area of wheat grown in Zambia has risen in the past several years to approximately 18,000 ha per annum. However, annual wheat yield (60,000 tons) has not risen to match this increase. The effect of SBWMV and WSSMV on yield in Zambia has not yet been measured, but both viruses cause serious losses in other countries (1-3) and the severity of the symptoms suggests that significant yield reductions are likely. Furthermore, no Zambian wheat cultivars are known to be resistant to either virus. Generally, wheat production fails to meet demand in the country and therefore further yield losses due to virus infection could be disastrous. References: (1) M. K. Brakke. CMI/AAB Desc. of Plant Viruses 77, 1971. (2) J. T. Slykhuis. Phytopathology 60:319, 1970. (3) V. Vallega and C. Rubies-Autonell. Plant Dis. 69:64, 1985.

Rare symptoms and conidial variation in Septoria lycopersici in Zambia.

Surveys during the rainy season of 1996 showed that Septoria lycopersici developed two different types of leaf spots on tomatoes grown in kitchen gardens at the University of Zambia Campus and in nearby gardens. The two types of spots could be easily distinguished on the basis of their external morphology. One type, designated as T1, began as dark brown spots of less than 1 mm diameter. Upon increase in size, the spots differentiated into a dark brown outer ring and a grey centre, reaching a maximum diameter of 5 mm. Spots of this type are common and have been described in reports on Septoria leaf spot disease. A second type of spot found in our survey was designated as T2. This Septoria spot was greyish brown with several concentric rings of shrunken leaf tissue. The type T2 spots were larger and did not differentiate into two parts as in T1. The T2 spot diameter was 4-12 mm. The conidia showed differences in curvature, and significantly length, between T1 and T2. The study has shown that S. lycopersici in Zambia is variable.