Abstract:
Maize underpins food security in South Africa. An annual production of more than 10 million tons is a
combination of the output of large-scale commercial farms plus an estimated 250 000 ha cultivated by
smallholder farmers. Maize leaves are a rich source of nutrients for fungal pathogens. Farmers must limit
leaf blighting by fungi to prevent sugars captured by photosynthesis being ‘stolen’ instead of filling the
grain. This study aimed to fill the knowledge gap on the prevalence and impact of fungal foliar diseases
in local smallholder maize fields. A survey with 1124 plant observations from diverse maize hybrids
was conducted over three seasons from 2015 to 2017 in five farming communities in KwaZulu-Natal
Province (Hlanganani, Ntabamhlophe, KwaNxamalala) and Eastern Cape Province (Bizana, Tabankulu).
Northern leaf blight (NLB), common rust, Phaeosphaeria leaf spot, and grey leaf spot had overall disease
incidences of 75%, 77%, 68% and 56%, respectively, indicating high disease pressure in smallholder
farming environments. NLB had the highest disease severity (LSD test, p<0.05). A yield trial focused on
NLB in KwaZulu-Natal showed that this disease reduced yields in the three most susceptible maize hybrids
by 36%, 71% and 72%, respectively. Eighteen other hybrids in this trial did not show significant yield
reductions due to NLB, which illustrates the progress made by local maize breeders in disease resistance
breeding. This work highlights the risk to smallholder farmers of planting disease-susceptible varieties,
and makes recommendations on how to exploit the advances of hybrid maize disease resistance breeding
to develop farmer-preferred varieties for smallholder production.
SIGNIFICANCE :
• Northern leaf blight, grey leaf spot, Phaeosphaeria leaf spot and common rust diseases were widespread
in KwaZulu-Natal and Eastern Cape smallholder maize fields where fungicides were not applied.
• NLB was the most severe maize leaf disease overall.
• NLB caused maize leaf blighting, which reduced grain yields by 36–72% in susceptible maize hybrids.
• Maize resistance breeding has produced locally adapted hybrids that do not have significant yield losses
under NLB disease pressure.
