THE COMBINING ABILITY OF SINGLE CROSSES AND THEIR REACTION TO MAIZE LETHAL NECROSIS VIRUS.

Abstract

Maize is a key staple crop that is grown in most regions of Kenya and it is consumed in various forms by 80% of the population. Among the biotic constraints, maize lethal necrosis disease causes heavy yield losses thus compromising food security in the country. In 2011, Maize lethal Necrosis came about as a destructive disease in Kenya and many parts of Sub-Saharan Africa. MLN was discovered to be as a result of a dependent interaction between Maize Chlorotic Mottle Virus and Sugarcane Chlorotic Mottle Virus. MLND affects maize plants at all developmental phases from seedling to maturity. Although MLN has been extensively studied, it is still a persistent menace in many parts of Africa due to various hindrances in developing maize varieties that are tolerant to MLND which includes: assembling of germplasm that is resistant to the disease from various sources, using few sources that are resistant and association of the genotype and location. The trial focused on 120 single cross hybrids set up in an incomplete block design in the two sites. The single crosses were sourced from CIMMYT and KALRO formed through crossing resistant and susceptible inbred lines. Diallel crosses are used to investigate the gene action controlling grain yield. Data collection was on the basis MLN disease score, grain yield, days to pollen shed, days to silking, moisture content, plant height and ear height. The data was analyzed using GENSTAT statistical package (5th edition). Generally, the study was able to show that MLN is still a major problem in Kenya with rising incidences and intensity in maize fields of farmers. MLN resistance levels in varieties that are grown locally need to be boosted. Severity scores for the single crosses were variable indicating the existing and potentially useful germplasm for improving MLN resistance in breeding programs. The study identified lines SC-MLN15-56 in Naivasha and lines SC-MLN-15-3 and SC-MLN-15-23 which had disease severity scores of ≤ 3.0 which could be further improved to be used in disseminating resistant gene varieties that are susceptible to MLN. When analysis of variance for diallel cross was exploited both GCA and SCA were highly significant showing that grain yield is as a result of both additive and non-additive effects. GCA effects revealed CML498 as an ideal combiner for most characters and cross combinations involving CML498 as one of its parents recorded desirable SCA effects. Estimates of SCA showed cross CML395×CML505 as the most desirable cross which could be further improved in hybridization programs for developing hybrids that are efficient and MLN resistant. These would be given out as recommendations to program that mainly deal with development of hybrids that are resistant to MLN.