Relative abundance and molecular characterization of stem borers and evaluation of maize genotypes (Zea mays L.) for resistance in Nigeria

AJIBOYE, TIMOTHY OLUWAFEMI (2018)

Thesis

Stemborers constitute a major constraints to cereals production generally and specifically to maize production in Nigeria due to yield and economic losses. Nevertheless there is still dearth of information relative abundance of stemborers, intraspecific differences between stemborers, and genotypes that are resistant to stemborers. The specific objectives of this study therefore were to: (i) determine the relative abundance of stemborers in different locations; (ii) characterize for the purpose of proper identification of the various stemborers collected in Nigeria and (iii) (ii) to evaluate different maize genotypes for their resistance to stemborers. Sixty maize germplasms including land races and improved varieties were screened at Ibadan, Mokwa, Kontagora, Kabba and Abuja to identify stemborer resistant genotypes. The experimental design usedwas Randomised Complete Block Design .Agronomic and entomological data were collected and analysed with Statistical analysis system(SAS). Survey of farmers‘ fields was carried out in Oyo, Ekiti, Osun, Ondo, Kwara and Ogun to determine relative abundance of stemborers in different locations. Collected stemborers were reared to adult stage. DNA was extracted and amplified using primers (CP1, TRs, Tser, 16SAA, 16SBB, LP01 and LP02). This was followed by Sanger dideoxy sequencing.Bioinformatic tools were employed to analyse DNA nucleotides sequences from the resulting electrophoreogram. The findings of the study were: (i) The survey results reveal that stemborer infestation was lowest in Oyo (9.4%) and highest in Ogun (50%). The other states were Ekiti (36%), Osun (38%), Ondo (42%), Kwara (44%), Ogun (50%) (ii) The stemborers identified were Chilo orichalcociliellus (Strand), Eldana sacharina (Walker), Sesamia calamistis (Hampson), and Longhorn beetles (subfamily Lamiinae; family Cerambycidae). (iii)Based on stem tunneling, deadhearts, stemborer leaf feeding, husk cover, lodging, field weight and yield, none of the evaluated maize varieties was absolutely resistant. Those found tolerant were TZM 1327, TZM 112, Aflatoxin Syn W5, ACR 06 TZL Comp 4C4, PVA Syn 11F2, PVA Syn 9F2, PVA Syn19F2 and PVA Syn 3F2. (iv) Molecular characterization of the identified stemborers were similar to those found in Kenya with average sequence divergence among conspecific individuals averaging 3.3% in the mitochondrial cytochrome c oxidase II (COX II), while two were also similar to those found in Zimbabwe with intraspecific divergence at COX II averaging 3.0%. (v) The findings that the evaluated germplasm showed varying degree of tolerance is an indication that many of them can be used in further breeding program aimed at developing complete/ total stemborer resistant varieties. Artificial screening using only one stem borer type in screen house may not produce truly stemborer resistant maize varieties. The resistant lines produced under this condition may break down in the presence of stemborer complex in the field. The use of resistant varieties is the most promising control measure in reducing yield loses caused by stem borers for resource constrained farmers and may be enhanced by cultural practices.