Evaluating Azoxystrobin Seed Coating Against Maize Late Wilt Disease Using a Sensitive qPCR-Based Method.

Harpophora maydis, a phytopathogenic fungus, causes late wilt, a severe vascular maize disease characterized by relatively rapid wilting of maize plants near fertilization. The disease is currently controlled using resistant varieties. Here, we evaluated seed coating efficiency with azoxystrobin against H. maydis in a series of in vitro and in vivo trials. A real-time polymerase chain reaction (qPCR)-based method was developed and proved to be a sensitive, accurate tool for monitoring H. maydis DNA inside infected seeds, sprouts, and tissues of mature plants. In the early growth stages, the chemical coating drastically reduced the pathogen DNA prevalence in host tissues and minimized the suppressing effect on the plants' biomass and development. In an infested field, the qPCR assay identified the pathogen 20 days after seeding, up to a month before conventional PCR detection. In the resistant fodder maize cultivar 32D99, which showed only minor disease symptoms, the seed coating blocked fungal progression and increased cob and plant weight by 39 and 60%, respectively. Nevertheless, this treatment was unable to protect a sensitive maize hybrid, cultivar Prelude, at the disease wilting breakout (60 days after sowing). These results encourage further examination of azoxystrobin and other fungicides in the field using the qPCR detection method to evaluate their efficiency.

Effective chemical protection against the maize late wilt causal agent, Harpophora maydis, in the field.

Late wilt, a disease severely affecting maize fields throughout Israel, is characterized by relatively rapid wilting of maize plants before tasseling and until shortly before maturity. The disease's causal agent is the fungus Harpophora maydis, a soil-borne and seed-borne pathogen, which is currently controlled using reduced sensitivity maize cultivars. In a former study, we showed that Azoxystrobin (AS) injected into a drip irrigation line assigned for each row can suppress H. maydis in the field and that AS seed coating can provide an additional layer of protection. In the present study, we examine a more cost-effective protective treatment using this fungicide with Difenoconazole mixture (AS+DC), or Fluazinam, or Fluopyram and Trifloxystrobin mixture, or Prothioconazole and Tebuconazole mixture in combined treatment of seed coating and a drip irrigation line for two coupling rows. A recently developed Real-Time PCR method revealed that protecting the plants using AS+DC seed coating alone managed to delay pathogen DNA spread in the maize tissues, in the early stages of the growth season (up to the age of 50 days from sowing), but was less effective in protecting the crops later. AS+DC seed coating combined with drip irrigation using AS+DC was the most successful treatment, and in the double-row cultivation, it reduced fungal DNA in the host tissues to near zero levels. This treatment minimized the development of wilt symptoms by 41% and recovered cob yield by a factor of 1.6 (to the level common in healthy fields). Moreover, the yield classified as A class (cob weight of more than 250 g) increased from 58% to 75% in this treatment. This successful treatment against H. maydis in Israel can now be applied in vast areas to protect sensitive maize cultivars against maize late wilt disease.