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.

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.

Late wilt, a destructive vascular disease of maize caused by the fungus Magnaporthiopsis maydis, is characterized by relatively fast wilting of maize plants closely before the physiological maturity stage. Previously, traditional microbiology-based methods have been used to isolate the pathogen and to characterize its traits. More recently, several molecular methods have been developed, enabling accurate and sensitive examination of the pathogen spread within the host. Here, we review the methods developed in the past 10 years in Israel, which include new or modified microbial and molecular techniques to identify, monitor, and study M. maydis in controlled environments and in the field. The assays inspected are exemplified with new findings and include microbial isolation methods, microscopic and PCR or qPCR identification, spore germination evaluation, root pathogenicity assay, M. maydis hyphae or filtrate effects on grain germination and sprout development, and a field assay. These diagnostic protocols enable rapid and reliable detection and identification of the pathogen in plants and seeds and studying the pathogenesis of M. maydis in susceptible and relatively resistant maize cultivars in a contaminated field. Moreover, these techniques are important for studying the population structure, and for future development of new strategies to restrict the disease's outburst and spread.The fungus reproduces asexually, and no perfect stage has been identified [5]. To date, late wilt has been reported in about 10 countries, with significant economic losses in Egypt [6], India [7], Spain and Portugal [8], and Israel [9]. In Israel, the sweet maize growth area covered about 2800 ha and yielded almost 57,000 metric tons of grains (data from the Israel Organization of Crops and Vegetables, 2017). Late wilt is considered to be the most destructive disease in maize-growing areas in this country, with up to 100% infection and total yield loss reported in some fields [10]. In Egypt, the cultivated maize area covered about 880,000 ha and yielded almost 7.2 million metric tons of grains [11], with a degree of loss that may reach up to 80% in infested fields [12]. The Egyptian, Indian, and Hungarian isolates of M. maydis differ in morphology, pathogenicity, and route of infection [13]. For example, in Egypt, four clonal lineages of M. maydis isolates show diversity in amplification fragment length polymorphism (AFLP), colonization ability, and virulence on maize [14][15][16][17][18]. In Spain and southern Portugal, 14 isolates of M. maydis were analyzed by inoculating maize-susceptible cultivars [19]. One of the isolates was more aggressive, caused significant weight reductions of both roots and above-ground parts.Late wilt disease is characterized by relatively burst-wilting symptoms of maize plants, typically two weeks after the R1 fertilization growth stage (70 days after sowing) at the R3 growth stage (corn development described by [20]). The pathogen can negatively affect seedling emergence and cause seedling root necrosis...

Fungal pathogens are a significant threat to crops worldwide. The soil fungus, Magnaporthiopsis maydis, severely affects sensitive maize hybrids by causing the rapid wilting of plants at the maturity stage. Similarly, the soil fungus, Macrophomina phaseolina, develops in a variety of host plants, which leads to rot and plant mortality. The presence of both pathogens together in diseased cotton plants in Israel suggests possible interactions between them. Here, these relationships were tested in a series of experiments accompanied by real-time PCR tracking in maize and cotton. Despite the fact that neither of the pathogens was superior in a growth plate confrontation assay, their co-inoculum had a significant influence under field conditions. In maize sprouts and fully matured plants, infection by both pathogens (compared to inoculation with each of them alone) led to lesser amounts of M. maydis DNA but to increased amounts of M. phaseolina DNA levels. These results were obtained under a restricted water regime, while optimal water irrigation led to less pronounced differences. In water-stressed cotton sprouts, infection with both pathogens led to an increase in DNA amounts of each of the pathogens. Whereas the M. maydis DNA levels in the double infection remain high at the end of the season, a reduction in the amount of M. phaseolina DNA was observed. The double infection caused an increase in growth parameters in maize and cotton and decreased levels of dehydration in maize plants accompanied by an increase in yield production. Dehydration symptoms were minor in cotton under an optimal water supply. However, under a restricted water regime, the double infection abolished the harmful effect of M. phaseolina on the plants’ development and yield. These findings are the first report of interactions between these two pathogens in maize and cotton, and they encourage expanding the study to additional plant hosts and examining the potential involvement of other pathogens.