Comparing decentralized participatory breeding with on-station conventional sorghum breeding in Nicaragua: I. Agronomic performance

Few studies have assessed the effective gains achieved by collaborative decentralized participatory breeding, in terms of yield and other agronomic traits, in comparison with centralized conventional breeding using the same breeding schemes. Our study concerned an experience of participatory improvement of tortillero sorghum for low-input cropping systems in northern Nicaragua. It set out to compare the effect of two breeding schemes simultaneously managed on-station and on-farm. Two synthetic populations were used as sources of genetic variability. The study was designed to distinguish between three “selection modes”: farmers’ selection on-farm (FoF), breeder’ selection on-station (BoS) and breeder's selection on-farm (BoF). After two selection cycles, we found that FoF selection reduced phenotypic variability as much as BoS selection. In general, BoS selection produced higher-yielding lines under the target on-farm conditions. But FoF selection was more effective in promoting lines with higher values for an index of agronomic suitability (IAS), expressing a better balance between earliness, plant height, grain size and yield. Such genotypes might cope more easily with local environmental constraints and farmers’ preferences. BoF selection did not prove to be effective for either yield or IAS. This research shows the need for close collaboration between farmers and breeders as well as complementarities between the selection phases managed on-farm and on-station, to make breeding for difficult environments fully efficient.     

Levels of organochlorine pesticides in soils and rye plant tissues in a field study

The organochlorine pesticides are lipophilic and persistent and tend to accumulate in soils and growing plants. The contamination of growing plants occurs by adhesion of volatile substances from the air to the plant surface and by the migration of contaminants through xylem in inner ascendant transport. Persistent organochlorine pesticides (HCB, alpha,gamma-HCH, pp'DDE, op'DDT, pp'DDT) levels were determined in soils and rye plants. The aims of the study were the monitoring of organochlorine pesticide concentrations and the comparison of these levels among soil, rye straw, and rye grains. Fifty soil samples and 50 rye plant (50 straw and 50 grains) samples were taken. The GLC-ECD chromatographic results indicated the following contamination levels distributed among soil, straw, and grains: HCB (0.7-1.2-0.7 microg.kg(-1)), alpha-HCH (0.6-3.4-1.2 microg.kg(-1)), gamma-HCH (1.8-27.3-4.4 microg.kg(-1)), Sigma-HCH (2.5-30.7-5.6 microg.kg(-1)), pp'DDE (1.0-7.8-5.5 microg.kg(-1)), op'DDT (16.1-20.4-17.0 microg.kg(-1)), pp'DDT (38.0-41.7-49.6 microg.kg(-1)), and Sigma-DDT (54.2-63.2-72.1 microg.kg(-1)). The study verified the presence of organochlorine pesticides in the Mexican agricultural environment and their migration from soil to the growing rye plants. However, DDT has been banned since 1999 for sanitary reasons, and Lindane is applied only in some cases as a seed dresser. The determined organochlorine pesticide levels in rye plants are low, at residual levels that are below Codex Alimentarius Commission maximum residue limits.     

Ecological aspects of four species of ticks found on cattle in Salta, northwest Argentina

The seasonal activity of Amblyomma cajennense, Amblyomma neumanni, Amblyomma parvum and Boophilus microplus on cattle was studied in a ranch located in the northern part of the phytogeographical district of the Chaco Serrano where the habitat had suffered minimal human disturbance. The female ticks on one side of 10-25 cows were counted at intervals of 20-50 days from 29 October 1985 to 5 November 1986. The percentage of cattle parasitized with larvae and nymphs of Amblyomma was recorded, along with the proportion corresponding to the different species. Collection of ticks from the ground cover vegetation in areas with and without forest was performed using the dragging technique. B. microplus was found all year round; peaks of abundance were observed in May (55 females per cow/2) and November 1986 (71 females per cow/2). The peak in November was unexpected and possibly due to a higher stocking rate around watering places and poor nutrition at the end of the dry season. A. cajennense appears to produce a generation a year. Larvae were more abundant from June to August, nymphs from August to November and females from November (34 per cow/2) to January (15 per cow/2). A. neumanni showed a cycle corresponding to a generation every 3 years regulated via diapause that involves, at least, all the summer months. The peak of abundance for larvae, nymphs and females occurred in late autumn-early winter. The highest number of females (44 per cow/2) was recorded in June.(ABSTRACT TRUNCATED AT 250 WORDS)