Reproduction of root knot nematode (Meloidogyne incognita) on Bt cotton expressing Cry1Ac and Cry2Ab2 protein

Objective: The sedentary endoparasite Meloidogyne incognita is an important plant parasitic nematode that infects cotton causing significant yield losses. The objective of this study was to evaluate reproduction of M. incognita in Bt cotton (06Z604D), isoline (99M03) and HART 89M (local non-Bt cotton cultivar) under greenhouse conditions.Methods and results: Plant height, number of squares/bolls, fresh shoot and root weight were determined before root knot nematode (RKN) screening at 90 and 180 days after planting (DAP). Galling severity, egg mass index, number of juveniles and the presence of Bt protein in roots and soil were also determined. The ELISA detected Bt protein in soil and roots of Bt cotton but not in HART 89M and isoline plant tissues and soil. Reaction of Bt cotton and isoline to M. incognita was different with the transgenic cotton being more susceptible to RKN. HART 89M was more resistant to RKN infection compared with the isoline.Conclusion and application of findings: The study has demonstrated that Bt cotton (06Z604D) is susceptible to M. Incognita. The results indicate the importance of integrating nematode management practices such as the use of organic amendments and nematicides with other cultural practices in future Kenyan Bt cotton agroecosystems.Keywords: Bacillus thuringiensis, Biosafety, root knot nematode, cotto

Characterization of Kenyan sweet potato genotypes for SPVD resistance and high dry matter content using simple sequence repeat markers

Simple sequence repeat (SSR) markers were used to characterize Kenyan sweet potato genotypes for resistance to the sweet potato virus disease (SPVD) and high dry matter content. Eighty nine (89)genotypes with a mean symptom severity score of between 1 and 1.5 were selected following graft inoculation with SPVD-infected scions and characterized using 6 SSR primers. The 6 SSR primer pairshad an average polymorphic information content (PIC) of 0.47. The average number of alleles within the 89 genotypes across the 6 loci was 13.52. Cluster analyses revealed a 50% variation among the 89genotypes. The dendrogram did not reveal any unique clustering of the genotypes according to dry matter content and reaction to SPVD. The genetic differences among the SPVD resistant genotypes andthose with high dry matter revealed by the distinct groups suggest a significant genetic variability and the presence of different sources of resistance to SPVD and high dry matter. This characterization willgive valuable information for breeders and serve as a baseline for efficient development of new cultivars resistant to SPVD and containing high dry matter