can be risky, often resulting in plants emerging during a period of drought. On the other hand, late sowing Peanut (Arachis hypogaea L.) yield in Ghana is limited by variable may increase risk of water deficit at critical pod-filling rainfall, low soil fertility, pests and diseases, and poor crop management. Field experiments were conducted during the 1997 and 1998 stages of the crop if the season is short. Yield losses seasons at the Savanna Agricultural Research Station in Ghana to from diseases such as early leafspot (Cercospora araevaluate the CROPGRO-peanut model for its ability to simulate chidicola), late leafspot (Cercosporidum personatum), growth, yield, and soil water balance of a peanut crop and to quantify rosette virus, and rust (Puccinia arachidis Speg.) are yield losses caused by biotic and abiotic factors. Two peanut cultivars, also prevalent because peanut farmers in West Africa Chinese which matures in 90 d, and F-Mix which matures in 120 d, do not use disease control measures. The soils of the were grown rainfed on an Alfisol soil at three sowing dates between region generally have low fertility and low water-hold-May and August in 1997 and at four dates in 1998. Soil water and ing capacity, both contributing to lower yields. crop growth were measured during the season and compared with Identifying major yield-limiting factors and approcrop model simulations to determine yield-limiting factors relative to priate agronomic management practices for increasing potential yield. Growth and yield were highest for the early sowing dates and decreased progressively with later sowing, a trend attributed peanut production through field experimentation may to leaf diseases. After incorporating functions for percentage leaf involve many years of data collection on which to make defoliation and percentage diseased leaf area, the model accurately meaningful deductions. This is time consuming and exsimulated soil water content fluctuations, crop growth, and yield of pensive. In recent years, crop models have increasingly cultivars for the sowing dates and seasons. Simulated yield losses been used to support breeding research, field agronomic caused by water deficits were small (averaging 5-10%) for early sowadvice, and even decision support for agricultural policy ing dates (late May to mid-July) and increased with later sowing dates formulation (Boote et al., 1996). Crop models can also (20 and 70% for third and fourth sowings). Yield losses due to diseases be used to determine potential yields for a site based and pests were simulated as a percentage of potential yield under on the weather conditions and soil water-holding charwater-limited environments and averaged 40%, also increasing with acteristics of the site, and then a systems approach can later sowing dates. Using 13 yr of weather data, simulated yields were reduced 10 to 20% by water deficit for the two earlier (normal) sowing be taken to determine causes of, and possible remedies dates, but more for the later sowing dates, while additional yield ...

Summary. -Although a wide range of policies to conserve the environment in the forest zones of southern Ghana exists on paper, in practice most are only applied in the commercially-valuable timber reserves. Environmental policies have little impact on those living in the forest margins since they are only sporadically applied, if at all. Indeed, even accepted community norms for resource use tend to be set aside when their application would interfere with key occupations. Livelihoods, however, depend heavily on natural resources, so conservation is necessary. The dilemma is to devise policies that are effective. Some decentralization of policy-making might improve matters, but care will be needed to avoid pitfalls.

The productivity of cowpea (Vigna unguiculata (L.) Walp.] can be reduced substantially by hot weather during flowering. Inheritance and heritability of tolerance to heat during reproductive development were studied to develop efficient methods for breeding improved cultivars. Heat tolerant (‘Prima’ and TVu 4552) and heat sensitive (Barnbey 23, ‘Magnolia’ and 7964) cowpea genotypes were chosen for studies of heat tolerance during pod set under hot long days. Parental genotypes, F1, F2 and backcross progenies were evaluated under field conditions in the Imperial Valley of California during the summers of 1987 and 1988, and heat‐tolerant and heat‐sensitive F2's were selected in 1987 and evaluated as F3 families in 1988. Average daily minimum and maximum air temperatures were 24 and 43 °C, respectively, and the photoperiod decreased from 14 h 31 min to 13 h 20 min during flowering. Individual plants were scored for average number of pods per peduncle and plants with ≥ 1.5 (the mean of the value for the most tolerant parent and the average value for the sensitive parents) were classified as heat tolerant. Analyses of pods per peduncle and proportions of tolerant plants for F1, F2, and backcross populations indicated that heat tolerance is conferred by a single dominant gene in both Prima and TVu 4552. Narrow‐sense heritability obtained from variance components was 0.26. Comparison of pods per peduncle of F2 plants with their F3 families from crosses between heat‐tolerant and heat‐sensitive parents gave a realized heritability of 0.27. The low values for heritability were due to large environmental effects on pods per peduncle. Incorporating heat tolerance during pod set into other genetic backgrounds will require family selection in advanced generations to ensure that the trait is fixed, and, to partially overcome selection difficulties caused by environmentally induced variation.

This paper considers the process of Participatory Varietal Selection (PVS) and presents approaches and ideas based on PVS activities conducted on upland rice throughout Ghana between 1997 and 2003. In particular the role of informal seed systems in PVS is investigated and implications for PVS design are identiWed. PVS programmes were conducted in two main agroecological zones, Forest and Savannah, with 1,578 and 1,143 mm of annual rainfall, respectively, and between 40 and 100 varieties tested at each site. In the Savannah zone IR12979-24-1 was oYcially released and in the Forest zone IDSA 85 was widely accepted by farmers. Two surveys were conducted in an area of the Forest zone to study mechanisms of spread. Here small amounts (1-2 kg) of seed of selected varieties had been given to 94 farmers. In 2002, 37% of 2,289 farmers in communities surveyed had already grown a PVS variety and had obtained seed via informal mechanisms from other farmers, i.e. through gift, exchange or purchase. A modiWed approach for PVS is presented which enables important issues identiWed in the paper to be accommodated. These issues include: utilising existing seed spread mechanisms; facilitating formal release of acceptable varieties; assessing post-harvest traits, and; the need for PVS to be an ongoing and sustainable process.

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