Diagnosis and Control of <i>Harpophora maydis</i>, the Cause of Late Wilt in Maize

Abstract

Late wilt, a severe vascular disease of maize caused by the fungus Harpophora maydis, is characterized by relatively rapid wilting of maize plants, before tasseling and until shortly before maturity. In Israel, the disease becomes a major problem in recent years. The pathogen currently controlled using varieties of maize has reduced sensitivity. In earlier work, we modified a molecular method for use as a diagnostic tool to evaluate the disease progress in field infested plants. Several fungicides suppressed H. maydis in vitro and in a detached root pathogenicity assay. Seedling pathogenicity assay enables us to identified H. maydis DNA in the host root and stem tissues 18 days after sowing in both susceptible and tolerant maize plants. Although the infested plants exhibited no wilt symptoms, their roots were significantly shorter in length. This seedling assay was used to demonstrate the suppressive effect of the fungicide Flutriafol on H. maydis virulence. The method of assaying the pathogen in a series of trials starting in a plate assay, followed by a detached root and resulting in a seedlings pathogenicity assay, using molecular and morphological approaches could be generalized to other plant pathogens.

Plant growth hormones suppress the development of Harpophora maydis, the cause of late wilt in maize

“…The morphological and microscopic characteristics of the pathogen were identical to those of previously described strains found in Egypt and India (Payak et al 1970;Samra et al 1963). Final confirmation was achieved by PCR-based DNA analysis (Degani and Cernica 2014;Drori et al 2012). All isolates were grown on potato dextrose agar (PDA) (Difco, Detroit, MI, USA) at 28±1°C in complete darkness.…”

“…Here, we conducted a first in vitro examination of the influence of the plant hormones on H. maydis under controlled conditions. We used a DNA-sequence-based approach (Degani and Cernica 2014;Drori et al 2012) along with traditional morphological methods to conduct a controlled inspection of the influence of major plant hormones on H. maydis colonies growth rate, spore germination, and on its ability to infect maize detached roots and field plants.…”

Methods for Studying Magnaporthiopsis maydis, the Maize Late Wilt Causal Agent

“…First wilt symptoms appear near the flowering stage (from the R1 silking to the R2 blister stages), approximately 50-60 days after seeding [23] close to the male flowering stage. With disease progression, the lower stem dries out (particularly at the internodes) and has a shrunken and hollow appearance, with dark yellow to brownish macerated pith and brownish-black vascular bundles [24]. Late wilt is often associated with infection by secondary invaders, causing the stem symptoms to become more severe [25,26].…”

“…Spreading is through the movement of infested soil, crop residue [31], or seed-borne inoculum [32]. Lately, the former reports on potential secondary plant hosts were confirmed for M. maydis, Lupinus termis (lupine) [33], and cotton [22], and new hosts-watermelon and Setaria viridis (common name green foxtail)-were introduced [34].Some agricultural [30,35], biological [11,[36][37][38], and chemical controls [10,24,39,40] were able to reduce the pathogen's impact on commercial production. A combined treatment of fungicide seed coating and drip irrigation was recently demonstrated to be a cost-effective and powerful treatment to protect sensitive maize hybrids, even in heavily infested soils [28].…”

“…Later, a specific real-time PCR (qPCR) method was developed for the same purpose [10]. These molecular methods, together with symptoms evaluation methods, were used to study the effect of selected fungicides on the pathogen in a series of trials that would gradually increase the investment in time and work without wasting efforts if the treatment had not successfully passed the early steps.The series of experiments was started in a Petri dish plate assay, followed by an in vitro seed assay (seed inoculation in an Erlenmeyer flask), a detached root assay, a seedling pathogenicity assay (sprouts up to the age of six weeks) in a growth chamber, potted plant evaluation over a full growth period (from seed to seed) in a greenhouse, and eventually a field assay [10,24]. The preliminary steps, up to the greenhouse trial, should be addressed in a critical manner, but they have several advantages.…”