Aggrey Nyende

Differential effects of various African nightshade species on the fecundity and movement of Tetranychus evansi (Acari: Tetranychidae)

The tomato red spider mite Tetranychus evansi Baker & Pritchard is a serious pest of solanaceous plants worldwide. Management of this oligophagous pest in African nightshades has been a challenge to smallholder African farmers due to its high reproductive rate and rapid development of resistance to synthetic pesticides. The aim of the present study was to determine the influence of leaf trichomes on T. evansi by comparing its fecundity and movement on the leaf surfaces of five African nightshade species, namely Solanum sarrachoides Sendter, S. villosum Miller, S. tarderemotum Bitter, S. americanum Miller and S. scabrum Miller. Data were recorded in the laboratory at 23 ± 1°C, 50–70% relative humidity and a 12 h light:12 h dark photoperiod for the effect of trichome type and density of the abaxial leaf surface on mite fecundity. Distances travelled by mites on the leaf surface from the edge of a thumbtack pin inserted on the leaf were also recorded. Different trichomes, glandular and non-glandular types, were identified. There was a significant negative correlation of fecundity and distance walked by mites with the density of glandular trichomes. Significantly fewer eggs were laid on S. sarrachoides in comparison with the other Solanum species. The distance walked by mites was also significantly shorter in this species, indicating that higher densities of glandular trichomes interfere with mite movements. These results suggest that African nightshade genotypes differ in their levels of resistance to T. evansi, which is partially associated with differences in trichome types and their densities.

Yield Selection within Coffea arabica cv. Ruiru 11

Aims: This study was aimed at identifying high yielding Ruiru 11 sibs in varying growing conditions. The study also intended to measure the extent to which cherry yields of Ruiru 11 are affected by the environment. Study Design: Randomized Complete Block Design with three replications. Place and Duration of Study: The study was conducted in three different agro-ecological zones in Kenya namely Mariene in Meru County, Kisii near Kisii town in Kisii county and Koru in Kericho County between November 2008 and September 2011. Methodology: Thirty four (34) Ruiru 11 sibs, all of which are resistant to Coffee Berry Disease and Coffee Leaf Rust, were evaluated in this study alongside two entries of SL28, a cultivar susceptible to the two diseases. One entry of SL28 was sprayed with copper fungicides to control, while the other SL28 entry was not sprayed with any fungicides. Planted at a spacing of 2m by 2m, each entry had 12 trees per plot per rep, giving a total of 1296 plants per experiment per site. Cherry yield recording was done during the peak harvesting period of May to July at Mariene and July to September at Koru and Kisii. The data was subjected to Analysis of Variance (ANOVA) using XLSTAT version 2012 statistical software and effects declared significant at 5% level. Results: Significant (P = .05) yield differences among Ruiru 11 sibs were obtained in all Research Article American Journal of Experimental Agriculture, 3(1): 76-88, 2013 77 years of evaluation at Koru but only in 2011 at Kisii and Mariene. There was a greater discrimination between sibs at Koru, followed by Kisii and then Mariene. Year effect was highly significant (P < .001) and equally distinguished in all sites but year x sib interactions were significant (P = .05) only at Kisii. Combined analysis for all environmental combinations showed highly significant (P < .001) differences between sibs, environments and their interaction. Environments made a greater contribution (42.6%) to the variation compared to sibs (7%). The interaction term also made a significant contribution (18.7%). The best sibs per site and those adapted to contrasting environments were identified. Conclusion: The expression of high yield variation among Ruiru 11 sibs is a sign of high potential of intra-selection within the cultivar for yield improvement. Identified sibs can be recommended to farmers and also exploited in future breeding programmes for improvement of Ruiru 11 productivity and agronomic adaptability. The occurrence of significant sib by environment (G x E) interactions was an indication that the best improvement strategy should be a multi-site selection.