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Cultivar 2, on the other hand, managed to
maintain its yield irrespective of the dis-
ease severity observed at dent stage, which
was as high as 60%. As however mentioned,
the hybrid in general had a lower yield
potential, which points to the ‘yield penalty’
that is speculated to be associated with the
incorporation of resistance into crops.
Although the findings discussed here only
represent one-year data, a number of im-
portant aspects were again emphasised by
the study.
Early infections will result in greater disease
losses. As observed during our 2016/2017
trials, the early planting were slow to develop
disease, most probably due to the climate
not being ideal for disease development.
The two susceptible cultivars (Cultivar 1
and Cultivar 3) at this point had very similar
yield losses (0,32% and 0,39% per 1% in-
crease in disease severity). With the second
planting date, the disease was already es-
tablished very early, resulting in Cultivar 1
having a higher rate of yield loss compared
to Cultivar 3.
Cultivar 2, initially included as a resistant
variety, ended up having a disease sever-
ity of close to 60% at dent stage of the first
planting, yet not suffering any significant
yield losses.
From this observation two things must be
highlighted. The first is that applying fun-
gicide on this cultivar did not significantly
increase the yield, even when compared to
the plots where the cultivar suffered almost
60% disease severity.
The second aspect is, however, that even
though it had resistance, the eventual yield
obtained was still lower compared to that
of the other two cultivars which were se-
verely susceptible.
Producers are welcome to
contact Dr Maryke Craven at
018 299 6100 with any further
questions.
Graan SA/Sasol photo competition
67
September 2017
Letsels op weerstandbiedende basters is
geneig om kleiner te wees en minder te
sporuleer.
Foto 2
toon ‘n tipiese noordelike mielie-
blaarskroeiweerstandsletsel wat op weer-
standbiedende basters voorkom. Die
siekte versprei nie so vinnig nie en skade
aan die blare is ook minder. Dit is egter
belangrik dat die produsent moet verstaan
dat die weerstand wat ‘n spesifieke baster
teen noordelike mielieblaarskroei het, kan
verskil tussen verskillende omgewings
– afhangende van watter noordelike mie-
lieblaarskroeiras dominant in die spesifieke
omgewing is.
Dit is raadsaam om uit te vind in watter
omgewing die betrokke baster aanvanklik
vir weerstand teen noordelike mielieblaar-
skroei geëvalueer is. Produsente word
aangeraai om verskillende weerstandbie-
dende basters aan te plant om sodoende
die risiko verder te verminder.
Voortdurende monitering van die mielie-
baster vanaf blom (veral by aanplantings
onder besproeiing), is steeds krities al
word daar van weerstandbiedende basters
gebruik gemaak. Sodoende kan die pro-
dusent nie onverhoeds betrap word nie.
Gedurende die 2016/2017-seisoen is 30 ultra-
kort mieliebasters in Potchefstroom ge-
evalueer. Die doel van hierdie proef was om
die mieliebasters te toets vir hul vatbaar-
heid vir noordelike mielieblaarskroei sodat
daar bepaal kon word hoe die verskillende
basters presteer onder die infeksiedruk
van noordelike mielieblaarskroeirasse wat
spesifiek in die Potchefstroom-omgewing
voorgekom het.
Omdat lokaliteit en seisoen ‘n rol kan
speel in die voorkoms van noordelike mie-
lieblaarskroei, het ons die siektegraad
wat gedurende die afgelope seisoen by
Potchefstroom waargeneem is, vergelyk
met die siektegraad wat waargeneem is
gedurende 2014/2015 tydens die evalu-
ering van LNR-kultivarevaluasieproewe by
Potchefstroom en Grootpan, onderskeide-
lik (
Grafiek 1
).
‘n Aantal nuwe kultivars wat nie deel
was van die groep wat tydens die
2014/2015-seisoen geëvalueer is nie, is
ook gedurende 2016/2017 ingesluit. By
Potchefstroom is daar oor die algemeen
soortgelyke infeksievlakke oor die twee
seisoene waargeneem, met enkele kultivars
wat gedurende die 2016/2017-seisoen
hoër infeksievlakke ervaar het as met die
2014/2015-seisoen.
Produsente kan hierdie inligting as riglyn
gebruik wanneer hulle met die onder-
skeie saadverteenwoordigers gesels en
besluite neem oor watter basters hulle die
komende seisoen wil plant. Deur kennis
te dra van die baster se vatbaarheid vir
noordelike mielieblaarskroei, sal produ-
sente meer ingeligte besluite kan neem
rakende siektebeheerprogramme vir die
komende seisoen.
Produsente is welkom om die outeurs van
die artikel te kontak by 018
299 6100 met enige verdere
vrae in hierdie verband.
Noordelike mielieblaarskroei-infeksievlakke
Yield loss associated with northern corn leaf blight