Contents - Faperta

176 Biotechnological Approaches for Pest Management and Ecological Sustainability
48.4, and 58.7% of the total phenotypic variation in four populations, respectively
[MoSCSSS-High (selection for high RPR), MoSCSSS-Low (selection for low RPR), MoSQB-
Low (selection for low stalk crushing strength), and inbred lines Mo47 and B73] (Flint-Garcia,
McMullen, and Darrah, 2003). One chromosomal region contained a QTL in all four populations,
while two QTLs were common among three of the four populations, and fi ve QTLs
in two populations. Candidate genes that overlap QTL confi dence intervals include those
involved in lignin synthesis, the phenylpropanoid pathway, and the timing of vegetative
phase change are linked to resistance to European corn borer, O. nubilalis. QTLs have been
identifi ed for RPR and second generation O. nubilalis resistance (Flint-Garcia et al., 2003).
Phenotypic recurrent selection increases the frequency of resistance alleles over cycles
of selection. Phenotypic selection for both high and low RPR was more effective than MAS
in two populations, while MAS was more effective than phenotypic selection in another
population. The MAS was more effective in selecting for increased susceptibility, but not
in increasing resistance to damage by O. nubilalis.
QTL linked to maysin production (a glycosyl fl avone that controls antibiosis to H. zea
larvae) have been identifi ed (Guo et al., 2001). Butron et al. (2001) identifi ed two major QTLs
for synthesis of maysin and related compounds, the already known pl, on the short arm of
chromosome 1, and a novel one in the interval csu1066-umc176 on genomic region 2C-2L.
A QTL for husk tightness was located near p1. The functional allele for p1 and the favorable
allele for husk tightness were in repulsion linkage. In a marker-assisted selection
program for increasing resistance to corn earworm, H. zea markers for silk antibiotic synthesis
should be accompanied by markers for husk tightness. The maize chromosome 1
locus p1, which activates transcription of parts of the fl avonoid pathway, explains 58% of
the variance for maysin content (Byrne et al., 1996). A second QTL on chromosome 9, which
is dominant for low maysin levels and interacts with p1, is rem (recessive enhancer of maysin)
I. When a functional p1 allele is present, reml nearly doubles the maysin concentration.
The p1 locus is highly signifi cant in explaining the variation for both H. zea larval weight
reduction and increased silk maysin concentration (Byrne et al., 1997). Additional loci on
chromosomes 1 and 9 also explain signifi cant variation for H. zea larval weight and maysin
concentration. Both maysin and apimaysin are closely related glycosyl fl avones. A QTL for
maysin on maize chromosome 9 (rem1) explained 55% of the variance for maysin synthesis,
while the QTL for apimaysin from the pr1 region of chromosome 5, explained 64% of
the variance for apimaysin synthesis (Lee et al., 1998). Neither QTL affects the other, indicating
that synthesis of maysin and apimaysin occurs independently. However, rem1
accounted for only 14.1% of the H. zea antibiosis and pr1 accounted for 14.7% of the antibiosis,
suggesting that other antibiotic compounds may contribute to H. zea antibiosis in
maize. Chlorogenic acid, a maize phenylpropanoid metabolite with an adjacent hydroxyl
ring structure similar to maysin, has also been implicated in H. zea resistance (Duffey and
Stout, 1996). Bushman et al. (2002) detected a QTL in maize silks corresponding to the
p1 locus that increases both chlorogenic acid and total fl avone content. Chlorogenic
acid accumulation is probably due to the pI induction of chlorogenic acid synthesis, and
induction of fl avonoid genes to increase phenylpropanoid pathway substrate availability
(Bushman et al., 2002).
Sorghum
QTL analyses have been used to document resistance in sorghum to the greenbug,
S. graminum (Agrama et al., 2002; Katsar et al., 2002). Several QTLs in linkage groups of