Genetic analysis of maize streak virus disease resistance on tropical maize.
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Date
2021
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Abstract
Maize streak virus (MSV) disease, transmitted by leafhoppers (Cicadulina mbila) is a major
contributing factor to low maize yields in Africa. The disease threatens maize production in
Zimbabwe, thus the importance of breeding Zimbabwe maize varieties that carry resistance to
this disease. Cimmyt has developed inbred lines, good for other traits, for example, high
general combining ability (GCA) effects for grain yield performance, but susceptible to MSV
hence efforts are being made in CIMMYT to introduce MSV resistance genes from MSV
resistant donor lines known to be good for important traits, especially yield, but bad for MSV
resistance.
This study was designed to assess newly developed tropical maize inbred lines with complete
resistance to MSV and to compare disease progression between the MSV susceptible and
resistant inbred lines artificially infect plants with virulent leafhoppers. Breeders usually cross
two resistant parents to exploit the potential contribution of beneficial resistance alleles
originating from them to generate transgressive segregation that can lead the development of
new maize inbred lines with much higher levels of resistance to MSVD and desirable
agronomic traits. Twelve inbred lines from CIMMYT were evaluated to determine their level
of resistance. Genotype effects on MSV scores were significant from week 1-6 as well as for
the average (p < 0.05). Significant effects on MSV scores were also observed on each week
interval, except for week 4. Broad-sense heritability (H2) estimates for MSV scores was high
(<50%) on each week interval as well as for the average MSV score. Genotypic effects showed
to be more important than the environmental variances on each week MSV recordings were
taken.
This study showed that inbred line CML536 was highly resistant confirming previous
observations made with artificial infection in Zimbabwe. Candidate lines CL1210634 and
CL1210635 showed complete resistance to MSV meaning they may share the same major gene
Msv1 with CML539 and CML536 check inbred. The data we obtained provide quantification
of conclusions of visual observations: (a) some varieties bred for resistance are less affected by
MSD than others, even when infected at the same stage; (b) early infection is more damaging
than late infection, but resistant varieties differ in their response, and; (c) varieties carrying no
resistance can be little damaged if infected late.
In order to avoid the over-dependence on Msv1, further studies should be carried out to identify
a second gene for MSD resistance to compliment Msv1 gene in conferring enhanced and
durable resistance to MSD. Enhanced resistance through additional phenotypic selection will
also help prevent possible breakdown of Msv1.
Description
Masters Degree. University of KwaZulu-Natal, Pietermaritzburg.