Advanced Research Journal of Microbiology  ISSN:1718-3499  Vol. 5 (6), pp. 276-284. August, 2018.  © Advanced Scholars Journals 

Full length Research paper

Growth Characterisitics And Pathogenecity Of Indigenous Beauveria Bassiana Isolates  Against The Nyambene Tea Weevil(Sphrigodes Mixtous) In Kenya

^*1Evelyn Cheramgoi, ²Samuel Muluka, ¹Irene Cherono  ³ Robert Nyukuri and ²Jackline Chepkemoi

¹Crop Improvement Programme, Integrated Pest and Disease Management (IPDM)Section, Tea Research Foundation of Kenya(TRFK), P.O. Box 820-20200, Kericho

² Department of Medical and Applied Sciences Rift Valley Technical Training Institute,P.O. Box 244 ,30100, Eldoret

³Department of Biological Sciences, School of Science, University of Eldoret, P.O. Box 1125, Eldoret, Kenya.

Correspondence Author’s Email: [email protected]

Accepted 3 June, 2018

Abstract

22 Local isolates of Beauveria bassiana were characterised on their radial growth, sporulation, germination and assayed for insecticidal activities against adult Nyambene tea weevils.  The isolates were coded according to the different places they were isolated from. They include Bb Ke 1-5 recently isolated from Kericho County, TRFK Timbilil Tea Fields and isolates Bb Ke 6a and Bb Ke 6b isolated in 2006 from within Kericho County, TRFK Timbilil tea Estate Fields, Bb Gi7 series which were isolated from soils and assorted weevils from Giciaro farm in Nyambene, Meru County, Bb Ch 8 and Bb Ch c(1-5) isolated from Chepkoilel soils in Eldoret, Uasin Gishu County and Bb Mu 9 series which was isolated from Mununga, Kirinyaga County. The growth characteristics were determined by measuring the radial diameter in mm for seven days of the isolates growing on Potato Dextrose Agar (PDA), sporulation was determined after 2 weeks using a Neubauerheamacy to meter under a light microscope (40X) and germination of conidia after 16hrs of inoculation on freshly prepared PDA plates. A few representatives of the isolates were chosen to determine their efficacy against the Nyambene weevils (Sphrigodes mixtous) by dipping in conidia concentration of 10⁵, 10⁴and 10³. The radial growth, germination and sporulation varied in the different isolates. Bb Ke 4 (51mm) and Bb Ke 5(31.33mm) exhibited higher radial growth, Bb Ch c4 (17216.70) had high sporulation whereas Bb Ke 6a (75.67%), Bb Ch c3 (70%) and Bb Ch c4 (68%) showed high number of germinating conidia. Other isolates exhibited slow growth rates i.e. isolates Bb Gi 7f (8.33mm), Bb Gi 7c (8.67mm), Bb Gi 7a (9mm) and Bb Ke 3 (9.33mm). Isolates Bb Ke 5 (925), Bb Ke 4 (1058.3), Bb Gi 7d (1375), Bb Ke 1Bb Ke 1(1800) and Bb Ke 2(1483.30) showed low sporulation. Low number of germinating conidia was seen in Bb Ke 1 (13.67%), Bb Gi 7f (19%), Bb Ke 3 (20%), Bb Ch 8b (30.67%) and Bb Ke 4 (24.33%) isolates. Isolate Bb Gi 7a showed higher insecticidal activity against the tea weevils compared to the other few selected isolates.   High negative correlation was noted between some variables like radial growth and spore count. A positive correlation between the cfu and germinating conidial count was noted as well as between spore count and germinating conidia.

Key words: Beauveria bassiana, radial, germination, sporulation, efficacy, tea, Sphrigodes mixtous, isolates, spore, microscope.