Introgression of Maize Lethal Necrosis Resistance Quantitative Trait Loci Into Susceptible Maize Populations and Validation of the Resistance Under Field Conditions in Naivasha, Kenya

Abstract

Maize lethal necrosis (MLN), resulting from co-infection by maize chlorotic mottle virus (MCMV) and sugarcane mosaic virus (SCMV) can cause up to 100% yield losses in maize in Africa under serious disease conditions. Maize improvement through conventional backcross (BC) takes many generations but can significantly be shortened when molecular tools are utilized in the breeding process. We used a donor parent (KS23-6) to transfer quantitative trait loci (QTL) for resistance to MLN into nine adapted but MLN susceptible lines. Nurseries were established in Kiboko, Kenya during 2015–2017 seasons and BC3F2 progeny were developed using marker assisted backcrossing (MABC) approach. Six single nucleotide polymorphism (SNP) markers linked to QTL for resistance to MLN were used to genotype 2,400 BC3F2 lines using Kompetitive Allele Specific PCR (KASP) platform. We detected that two of the six QTL had major effects for resistance to MLN under artificial inoculation field conditions in 56 candidate BC3F2 lines. To confirm whether these two QTL are reproducible under different field conditions, the 56 BC3F2 lines including their parents were evaluated in replicated trials for two seasons under artificial MLN inoculations in Naivasha, Kenya in 2018. Strong association of genotype with phenotype was detected. Consequently, 19 superior BC3F2 lines with favorable alleles and showing improved levels of resistance to MLN under artificial field inoculation were identified. These elite lines represent superior genetic resources for improvement of maize hybrids for resistance to MLN. However, 20 BC3F2 lines were fixed for both KASP markers but were susceptible to MLN under field conditions, which could suggest weak linkage between the KASP markers and target genes. The validated two major QTL can be utilized to speed up the breeding process but additional loci need to be identified between the KASP markers and the resistance genes to strengthen the linkage.

Genetic engineering and genome editing technologies as catalyst for Africa’s food security: the case of plant biotechnology in Nigeria

“…An example of biotic stress that has caused significant yield loss in the country in recent time is Maize Lethal Necrosis (MLN), a viral disease that has caused between 23%–100% yield loss, estimated to be 180 million USD ( Redinbaugh and Stewart, 2018 ). Conventional method for breeding high yielding maize varieties that are resistant to MLN is preferred over the use of pollution-prone method involving spraying of the MLN vector (Aphids and Thrips) ( Awata et al, 2021 ). However, introgression of MLN resistant genes into susceptible varieties through backcrossing will take years to develop and may still suffer yield penalty as a result.…”

Discovery and Validation of a Recessively Inherited Major-Effect QTL Conferring Resistance to Maize Lethal Necrosis (MLN) Disease

“…On the other hand, having single gene or QTL-based resistance is always risk of losing it quickly at any given point of time especially after introgression of the QTL to many elite lines. To avoid such scenario, it suggested to combine the QTL (qMLN6-157) with other MLN resistant, dominantly inherited major-effect QTL from chromosome 3 (region of 130-140 Mb) and chromosome 6 (region of 5-20 Mb; Gowda et al, 2015Gowda et al, , 2018Sitonik et al, 2019;Nyaga et al, 2020;Awata et al, 2020;Awata et al, 2021).…”

“…The detailed protocol for MLN artificial inoculation was explained in earlier publications (Gowda et al, 2015(Gowda et al, , 2018Nyaga et al, 2020;Awata et al, 2020;Awata et al, 2021). In brief, artificial inoculation of the materials in all the field trials was done following the standard protocols developed by CIMMYT, as below.…”

Transcriptomic and Functional Analyses Reveal the Different Roles of Vitamins C, E, and K in Regulating Viral Infections in Maize

“…However, the genetic basis of maize plant tolerance/resistance to MCMV/MLN is poorly understood [2]. Numerous QTLs associated with resistance to MLN across maize chromosomes in multiple mapping populations have been identified, while no maize inbred lines show significant resistance to MLN [2,9,10]. Moreover, several studies have been conducted to elucidate how maize responds to MCMV/MLN infection [11][12][13][14].…”