Developing Maize (Zea Mays) Populations Resistant To Stem Borers For Southeastern Nigeria.

ABSTRACT

Development of maize populations resistant to stem borers depends largely on the

existence of useful genes or alleles, which can combine to confer resistance to progenies.

Such genes are often available in areas of stress, having been responsible for the survival

of such crops over the years. Pink stem borer, Sesamia calamistis (Hampson, Noctuidae)

and sugarcane borer, Eldana saccharina (Walker, Pyralidae) are endemic in southeastern

Nigeria. Damages caused by the larvae of these moths are more prevalent during the

second planting season (August-November). Genetic diversity for a range of agronomic

and resistance attributes within 209 local maize collections from southeastern Nigeria and

3 improved check varieties were investigated in field trials in randomised complete block

design (RCBD) with two replications across three environments. Data collected from the

evaluations were subjected to both uni- and multivariate statistics. Furthermore, four traits

namely, leaf feeding, ear damage, shoot breakage and yield were used from across three

environments to construct a selection index. The multivariate analysis on the plant

attributes, using canonical discriminant analysis, revealed the agronomic and borer

damage parameters that contributed significantly to the total variation observed in

different environments. Out of the four canonical discriminant functions obtained, two

had significant (P=0.05) eigenvalues accounting for over 98 % of the total variation. The

first canonical function was mainly associated with yield while the second was associated

with the borer damage attributes. Rank summation index (RSI) used to rank the entries

for resistance to stem borers identified 11 genotypes representing top 5 % of the total as

resistant. In the second experiment the 11 genotypes and their hybrids, made in a diallel

fashion were evaluated for agronomic and borer damage attributes in seven environments

in RCBD with three replications. Data collected were subjected to analysis of variance

and those found significant (P=0.05) were further subjected to diallel analysis using

Griffing’s method 2 model 1 for fixed effects. Significant GCA and SCA effects were

obtained for most of the traits studied in the various environments and in the pooled

environment thus indicating that additive and non-additive gene effects were involved in

the expressions of the traits studied. However, in a few cases, only GCA or SCA was

important thus indicating the relative importance of the genetic component of the

variance. The assessment of the agronomic and borer damage attributes of the parents and

the crosses indicate that the variety crosses were not superior to the parents in most of the

traits. The significant differences observed between the parents and the crosses for dead

heart and leaf feeding damage parameters is suggestive of the occurrence of exploitable

heterosis for the development of genotypes that are resistant to stem borer attack.

Genotypes SE NG-33, SE NG-65 and TZBR Syn W had high negative GCA values for

dead heart while SE NG-62, SE NG-148, TZBR Syn W and TZBR ELD 3 C2 had the

high negative GCA values for leaf feeding damage. For ear damage, SE NG-65, SE NG-

67, SE NG-119, SE NG-148 and AMA TZBR-W-C1 had high negative GCA estimates.

Genotypes SE NG-33, SE NG-62, SE NG-65, SE NG-77, SE NG-106 and SE NG-119

had the highest positive GCA effects for grain yield. The nine genotypes selected formed

two heterotic pools: Group A comprised SE NG-33, SE NG-77, SE NG-106, SE NG-148

and TZBR Syn W while Group B included SE NG-62, SE NG-119, AMA TZBR-W-C1

and TZBR ELD 3 C2. Average yield of the grouped genotypes crossed in all possible

combinations was 1.06 t ha-1 showing 5 % yield increase. Furthermore, the best five

yielding crosses namely; SE NG-33 x TZBR ELD 3 C2, SE NG-62 x SE NG-77, SE NG-

62 x SE NG-106, SE NG-106 x TZBR ELD 3 C2 and TZBR Syn W x TZBR ELD 3 C2,

selected may be used as population crosses or in the formation of composite varieties.