Reaction Of Maize Germplasm To Common Foliar Diseases And Variability Of Maize Streak Virus Isolates
Abstract
Maize is an important food crop that is grown in most regions of Kenya and it is
consumed in various forms by over 80% of the population. Among the biotic constraints,
foliar diseases cause heavy yield losses thus compromising food security in the country.
This study was undertaken to determine the major foliar diseases infecting maize in
different agro-ecological zones in Kenya and assess the reaction of various germplasm to
these diseases. Isolates of Maize streak virus (MSV), a causal agent of one of the main
maize diseases in the country was also characterized using molecular techniques.
A survey was conducted to determine the occurrence, incidence, severity and distribution
of different diseases infecting the crop in different agro-ecological zones in Kiambu,
Embu and Nakuru counties. The study focused on six diseases which were northern leaf
blight (Exserohilum turcicum), common rust (Puccinia sorghi), maize streak disease
(Maize streak virus, MSV), gray leaf spot (Cercospora zea maydis, (GLS), head smut
(Sphacelotheca reiliana) and common smut (Ustilago maydis). Twenty maize varieties
were also evaluated for their reaction to the different maize diseases in a field experiment
at University of Nairobi Kabete Campus. During the survey, maize leaves with maize
streak disease (MSD) symptoms were collected to study the variability of MSV.
Degenerate primers for Geminiviruses were used to amplify C1/C2 regions of different
isolates of MSV. Polymerase chain reaction (PCR) products were sequenced and
nucleotides used to compare the Kenyan isolates within themselves and with other
sequences from the GenBank.
Northern leaf blight, common rust and maize streak disease were found to be the three
most prevalent and severe diseases in the different agro-ecological zones of the three
counties. The same diseases were recorded in all the genotypes in the field evaluation.
More efforts are therefore needed to manage the three diseases. Gray leaf spot, head and
common smuts were also present, but were not widely distributed and had low incidence
and severity both in the survey and field evaluations. These diseases should however not
be ignored as their status may change with changes in climatic conditions.
The Kenyan isolates were highly similar to one another with 99 to 100% nucleotide and
95 to 100% amino acid sequence similarities. They were also closely related to others
from the rest of the world with 98 to 100% nucleotide and 94 to 100% amino acid
sequence similarities. They all belonged to the MSV-A strain, the main subtype infecting
maize. The high percent sequence similarities indicate low variability within the
sequenced C1/C2 region of the virus. This information is important to breeders since low
virus diversity indicates that maize genotypes showing resistance to MSV may have
wider areas where they can be grown without risk of infection by different virus strains.
Citation
Degree of Master of Science in Crop Protection,2014Publisher
University Of Nairobi