ABSTRACT
Phytophthora nicotianae is a devastating root and stem pathogen of tobacco (Nicotiana tabacum) in South Africa. Growers strive to control the resulting disease, known as black shank, with metalaxyl treatments and resistant cultivars. The aim of this study was to consider whether development of metalaxyl resistance in P. nicotianae has contributed to poor disease control and if recently developed cultivars with high levels of resistance require metalaxyl for effective control. One hundred and thirty-two isolates of P. nicotianae were screened for sensitivity to metalaxyl. P. nicotianae isolates from most tobacco farms were metalaxyl sensitive. Growth of most isolates was inhibited completely at 1.0 µg a.i./ml. However, isolates from the MKTV tobacco producing area showed EC50 values ranging from 1.02 µg a.i./ml to 3.57 µg a.i./ml. Twenty-one tobacco cultivars were planted and treated with and without metalaxyl in two different growing seasons to evaluate their resistance to P. nicotianae and the value of using metalaxyl. Hicks was the most susceptible cultivar. Vuma/3/46, LK30/40/60-1, and LK33/60 exhibited the greatest resistance to P. nicotianae. Use of metalaxyl in combination with moderately resistant cultivars such as NC60 × TL33 and LK10/80/60 effectively reduced black shank in the field. Resistant cultivars were healthy and no significant difference between metalaxyl treated and untreated plants was observed.
ABSTRACT
Pachypodium namaquanum (Nyley ex Harb.) Welw., an unusual arborescent stem succulent from the succulent karoo of the arid Richtersveld in north-western South Africa and adjacent Namibia, is characterized by a striking curvature of the terminal 20-60 cm of the trunk toward the north. This orientation displays the single terminal whorl of drought-deciduous leaves with their flat surface angled at a mean inclination of 55° from horizontal. Inclination of 50-60° was found in 65% of individuals sampled, and 85% were inclined between 45 and 65°. Northward azimuth was also quite regular, but varied slightly between populations. The fixed leaf orientation in P. namaquanum maximizes radiation absorption during the winter months when leaves are present. Leaves normally form in early fall (April) and abscise early in spring (October). Growing season conditions in the Richtersveld are relatively mild, with mean maximum temperature dropping only to 21.6°C in July, the coldest month of the year. Frosts are rare. By the fixed orientation of its leaf whorl, P. namaquanum is able to maintain nearly twice the midwinter radiation absorptance that it would have with horizontal orientation. Over an annual cycle the angled leaves receive more radiation than would horizontal leaves for each of the 6 months in which they are present on the plant. This increased winter irradiance is hypothesized to singificantly increase net primary production by concentrating growth activities in winter months and allowing the species to remain dormant during the hyperarid conditions of the hot summer months. Midwinter flowering from apical buds in P. namaquanum may also be aided by its stem orientation. The evolution of this characteristic pattern of winter growth phenology and nodding stem orientation may have come about because of low but relatively regular autumn precipitation and moderate winter temperatures. Slow and regular growth of P. namaquanum leads to long lifespans which may reach 300 years or more.
ABSTRACT
OBJECTIVE: To assess the validity of extrapolation from sentinel data by comparing the HIV-1 prevalence of various sentinel groups with that of the general population in Mwanza Region, Tanzania. METHODS: In a population survey, 4161 individuals were selected in a stratified random cluster sample. Sentinel groups (all in the age group 15-54 years) included blood donors (n = 1090); patients examined at district hospitals for the presence of malaria parasites (n = 1488), anaemia (n = 1339), or syphilis (n = 33); and antenatal clinic attenders (n = 1193). The HIV-1 serostatus of individuals selected from the population survey was tested using enzyme-linked immunosorbent assay (ELISA) and Western blot; 51% of the blood donors were tested using HIVCHEK, and all others using ELISA. HIV-1 prevalence was standardized for age, sex, and urban/non-urban location. RESULTS: HIV-1 prevalence (standardized by age, sex, and residence) in Mwanza Region was 4.0% (3.0% in non-urban areas and 11.3% in town). The standardized HIV-1 prevalences in the sentinel groups were: blood donors, 4.5%; patients with fever, 11.6%; patients with anaemia, 8.9%; urban sexually transmitted disease patients, 27.1%; urban antenatal clinic attenders, 11.8%. The crude prevalence in blood donors was 6.0%. CONCLUSION: Blood donors who are related to blood recipients appear to be a representative sentinel group in this region, provided that data are standardized for age, sex, and urban/non-urban location. Patients with fever and antenatal clinic attenders may reflect trends, but data from patients with fever markedly overestimate, and data from antenatal clinic attenders underestimate, population HIV-1 prevalence. Because self-selection of blood donors may become more pronounced, this comparison should be repeated later or elsewhere, should the opportunity arise.
PIP: When full-scale surveys of HIV-1 prevalence are not possible, sentinel surveillance is conducted at specific sites with specific population groups. In this study, 2 sentinel groups have been monitored since 1989 in the Mwanza region on the shores of Lake Victoria in Tanzania. The groups included blood donors in all hospitals of the region an prenatal clinic attenders in Mwanza Municipality. Also considered specifically for this study were outpatients from all 6 district hospitals (including 2 roadside hospitals) who had given blood samples. Population survey data on HIV prevalence between August 1990 and February 1991 were available for reference use. The sample included 1090 blood donors aged 15-54 years, 800 outpatients from district hospitals, and 1193 pregnant women attending a prenatal clinic. Blood donors (49%) were tested with enzyme immunosorbent assay (ELISA). Outpatients provided capillary blood samples collected on filter paper, of which 4605 samples were further tested with ELISA. 1866 were excluded because of age, inadequate samples, or missing data. The results of the comparison of HIV prevalence in the sentinel group and in the population survey showed that in both groups HIV-1 infection was more common in women, particularly those 15-34 years old, than in men, who were particularly affected in the 25-44 year old group. Blood donors, who were mostly male and related to the recipient, showed a crude HIV-1 prevalence of 6% (65 out of 1090). Rates were standardized, and standardized prevalence ratios were calculated. In the general population in both surveys, prevalence was 4.5%. Men had a higher prevalence in non-urban areas. Among outpatients with fever who gave blood for anemia, the crude prevalence was 9% (115 out of 1339). Prevalence was higher in the sentinel group. Of the 33 sexually transmitted diseases outpatients screened for syphilis, 33% (11) were seropositive. Prenatal clinic attenders had a HIV-prevalence of 12% (138 out of 1193).
