The aim of this study was to determine the effects of different agricultural treatments and plant communities on the diversity of ammonia oxidizer populations in soil. Denaturing gradient gel electrophoresis (DGGE), coupled with specific oligonucleotide probing, was used to analyze 16S rRNA genes of ammonia oxidizers belonging to the ␤ subgroup of the division Proteobacteria by use of DNA extracted from cultivated, successional, and native deciduous forest soils. Community profiles of the different soil types were compared with nitrification rates and most-probable-number (MPN) counts. Despite significant variation in measured nitrification rates among communities, there were no differences in the DGGE banding profiles of DNAs extracted from these soils. DGGE profiles of DNA extracted from samples of MPN incubations, cultivated at a range of ammonia concentrations, showed the presence of bands not amplified from directly extracted DNA. Nitrosomonas-like bands were seen in the MPN DNA but were not detected in the DNA extracted directly from soils. These bands were detected in some samples taken from MPN incubations carried out with medium containing 1,000 g of NH 4 ؉ -N ml ؊1 , to the exclusion of bands detected in the native DNA. Cell concentrations of ammonia oxidizers determined by MPN counts were between 10-and 100-fold lower than those determined by competitive PCR (cPCR). Although no differences were seen in ammonia oxidizer MPN counts from the different soil treatments, cPCR revealed higher numbers in fertilized soils. The use of a combination of traditional and molecular methods to investigate the activities and compositions of ammonia oxidizers in soil demonstrates differences in fine-scale compositions among treatments that may be associated with changes in population size and function.

The mean time for 50% germination at 20 8C of 12 Indian wheat (Triticum aestivum) cultivars was nearly halved, from 51 h to 27 h, by soaking seed in water for 8 h prior to sowing. A delay of 24 h without further soaking, intended to simulate postponement of sowing, reduced the time saved by priming to 16%. Priming had no effect on ®nal germination percentage. These results were used in the design of 275 on-farm, farmer-managed, participatory trials of seed priming in wheat during the 1997±98 and 1998±99 rabi (post-monsoon) seasons.In forty-one trials in tribal areas of Bihar and West Bengal states of India, seed priming gave a 13% grain yield advantage for farmers growing wheat in marginal areas with low levels of agricultural inputs. Mean bene®ts from seed priming of wheat in nine trials in Chitwan, Nepal were 17%. In high potential areas of Gujarat, India, 205 trials had higher rates of input use. Yield bene®t from priming in these trials averaged only 5% but constituted an extra 200 kg ha 71 grain at little or no cost. In 20 trials on marginal land, with slightly saline irrigation water in Ahmadwala, Pakistan, an average yield increase of 36% was obtained using seed primed with a 0.2% gypsum solution. Collaborating farmers reported that priming wheat seed overnight resulted in faster, more complete emergence, more vigorous early growth, better tillering, earlier owering, larger ears, earlier maturity and higher yields. In addition, many farmers also reported that foliage in primed plots was a darker shade of green than that in non-primed plots, suggesting that primed plants may have been using nitrogen more ef®ciently.Seed priming was popular with farmers, most of whom reported that they would prime wheat seed the following year. A survey in Gujarat in 1998±99 of 63 farmers who had tested priming in 1997±98 showed that, while 65% had primed some of their own seed, none had primed more than 50 kg, suggesting that there were practical dif®culties in priming larger volumes of seed.introdution Wheat (Triticum aestivum) is grown widely in South Asia in the rabi (post-monsoon season) after the harvest of kharif (rainy season) crops (Hobbs and Morris, 1996).

The effects of several factors on the estimation of Verticillium dahliae in soil by the wet-sieving method were studied. The following factors were important for maximising recovery: the removal of soil particles of < 20 nm size from suspensions before plating; the medium used for plating; the amount of sieved soil inoculated to plates; the length of time of incubating plates; and the method of incubating soil on plates. There was no short-term effect of air-drying soil before analysis. Using sodium hexametaphosphate to aid soil dispersion, treating soi) suspensions with sodium hypochlorite. or making suspensions from different amounts of soil had no consistent effect on recovery. Excessive sample-to-sample variability in the results of some experiments was attributed to non-random distribution of fungus propagules in soil, or to the difficulty of standardizing the sieving part of the analysis, or both. Wet-sieving was generally more effective in detecting I'. dahliae and gave higher counts than a sucroseflotation method. Bait methods with eggplants or antirrhinums proved ineffective for estimating V. dahliae in naturally infested soil.

The incidence of wilt was recorded in runner and fruiting crops of 13 strawberry cultivars at 72 locations in southern England in 1989 and 1990, and soil samples from the sites were analysed for Verticillium dahliae. Linear regressions of wilt incidence on inoculum concentration in soil for runner crops of the susceptible cv. Elsanta in both years were significant whilst that for runner crops of the susceptible cv. Hapil in 1989 approached significance; the regression for cv. Elsanta fruiting crops in 1990 was not significant. The inclusion of sand content of soil in the regression model improved the fit for the cv. Hapil data but not for the cv. Elsanta data; neither clay nor silt content of soil significantly improved the fit of the models for any data set. There were insufficient data in either year for regression analysis for other cultivars, but the levels of wilt generally corresponded with the degree of soil infestation and broadly reflected known field resistance. The data were used to estimate an inoculum concentration which corresponds to 5% wilt incidence (IC5) for cv. Elsanta. It is suggested that this could be used as a yardstick for determining the risk of unacceptable levels of wilt in susceptible cultivars on the basis of pre‐planting soil analysis.  For the 44 sites where the cropping history over the 15 years prior to soil analysis was available there was no clear association between any crop and soil infestation levels at or above the IC5. However, V.  dahliae was more common at sites with a history of vegetatively propagated crops than at sites which had only supported crops grown from true seed.

Spatio-temporal development of brown rot (Monilinia fructigena) on apple and pear was monitored in an apple (cv. Cox) orchard and a pear orchard of several cultivars over several years. Disease on individual trees was recorded weekly from July to harvest, individual fruits with brown rot were tagged but not removed and rot-origin identified. On apple cv. Cox and pear (cvs Conference and Comice), all primary rot arose from infection via wounds caused by insects, birds and growth cracks. Birds were the most important wounding agents on pear in the field. Secondary (fruit-to-fruit contact) rot was considerably less than primary rot, especially for pear. Incidence of disease (percentage of fruits with brown rot) increased gradually from late July up to harvest; the final disease incidence varied with seasons and cultivars, ranging from 1 to 11%. For pear, Comice had greater incidence than Conference. Significant aggregation of diseased fruits among trees was detected for assessment dates when the overall incidence of disease was greater than 0´5%. On Cox and Conference, significant correlation of disease incidence between adjacent trees or trees separated by one or more trees (i.e. spatial lag measured as units of distance between adjacent trees) was detected, but there was no clear relationship between the correlation, the distance or time. For Comice, there was consistent and significant positive correlation of brown rot incidence over 3 years. It is speculated that behavioural characteristics of wounding agents may have played an important role in influencing the spatio-temporal dynamics of brown rot on apple and pear.

Rural Kenyan households have different aspirations and income portfolio strategies, including agricultural intensification and income diversification. This article reports on a study that interviewed 624 households to explore rural aspirations and derive lessons for agricultural technology development and transfer. Though few households specialised in farming, many households self-identified as farmers and aspired to increase their agricultural income. Despite the prevalence of agricultural aspirations, few aspired for their children to have a future in farming. Combining aspirations with potential to invest, the article provides suggestions for targeting agricultural interventions. We need to start listening better to those people we call "farmers" to develop and offer innovations that meet their realities.

In sub-Saharan Africa, rural households are the focus of many development efforts and the transformation of smallholder agriculture is one entry point for this process. Understanding farming households’ technology choices remains one of the most critical aspects of agricultural research in rural areas. However, many technologies that are known to be effective and potentially highly beneficial have remained widely unused. One reason is that predicting farmers’ decisions concerning agricultural technologies using conventional economic theories is flawed. In this article, we suggest that human aspirations have a much greater influence on technology choices than hitherto believed. We further argue that a better understanding of aspirations will improve the targeting of technology development by researchers. We propose distributed ethnography to empirically test the influence of human aspirations on technology choice. From such insight, we anticipate better research priority setting as well as more effective rural development strategies in general.

A method with the combined advantages of soil particle washing, selective inhibitors, and an indicator substrate was developed to isolate saprophytic basidiomycetes from soil. Organic particles were washed from soil and plated on a medium containing lignin, guaiacol, and benomyl, which reduced mold growth and allowed detection of basidiomycetes producing laccase or peroxidase. The 64 soil samples yielded 67 basidiomycete isolates, representing 51 groups on the basis of morphology and physiology. This method should facilitate investigations into the biodiversity of soil basidiomycetes and yield organisms that are useful in bioremediation of soils contaminated with pesticides or other recalcitrant aromatic compounds.