Screening Maize Germplasm for Resistance to Sugarcane Mosaic Virus

Abstract

The first report of Maize lethal necrosis (MLN) in Kenya was in 2011 in Bomet County. The disease quickly spread to nearby counties causing devastating damage to maize crop yield. The causative agents of MLN are two viruses MCMV and SCMV. The study’s objectives were i) to identify germplasm with resistance to SCMV and ii) to identify the mode of gene action associated with tolerance to the virus. To achieve objective one, 42 parental maize genotypes were planted in a screen house of the Faculty of Agriculture, University of Nairobi, in a completely randomized design to identify the ones with resistance to SCMV using the CIMMYT SCMV disease severity scale. Analysis of variance (ANOVA) tests were conducted on disease severity, disease incidence and Area under disease curve progression (AUDPC) scores using GENSTAT statistical software and showed significant differences among the genotypes for all the parameters. The genotype means were separated using least significant differences (LSD) at 0.05 significance level. Four genotypes had no symptoms of SCMV and 27 genotypes had a score of between 2 to 2.8 and were therefore classified as resistant or tolerant to SCMV, respectively. The rest had a score of 3 and above, and classified as highly susceptible. The resistant/tolerant genotypes are valuable sources of resistance to SCMV and could be employed in development of MLN resistant maize varieties. To achieve objective two, 448 maize genotypes consisting of 60 parents and 388 F1s were planted in the short rains season of 2016 and were self-pollinated and each cob harvested singly to give F2 population. Two populations namely 384 (parents UON-2015-50 × UON-2015-115) and 385 (parents UON-2015-50 × UON-2015-117) with the common parent 50 previously identified as resistant in MLN screening were selected for further genetic analysis studies. For genetic studies, xii 150 seeds of each F2 derived families were planted in the screen house in plastic pots and artificially inoculated with SCMV and evaluated for disease symptoms for 6 weeks using the CIMMYT SCMV disease severity scale and then categorized as either resistant or susceptible for based on the F2 generation. Resistant plants had a disease score of 2 and below and susceptible plants had a score of 3 and above. Chi-square goodness-of-fit test was then conducted to find conformity to various genetic ratios. The results of this study showed conformity to the 15:1 ratio which means the resistance to SCMV in these crosses could be controlled by major genes with complementary epistatic effects. These parents could be exploited in developing maize hybrids with resistance to SCMV, and therefore contribute towards management of MLN disease.