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Disease Note

Abstract:

Maize (Zea mays) is the second most cultivated grain crop in Ecuador, with growing significance as a source of fodder and food. During the rainy season (November and December) of 2018 and 2019, a disease of maize that was not previously observed in Ecuador was found at commercial fields of variety Misqui Sara, at four parishes of canton Quito (Tumbaco, Pifo, Puembo, and Checa), Pichincha Province. At tassel initiation, infected plants displayed symptoms of localized chlorotic streaks on leaves that expanded with time, and around a month later turned necrotic. Severely affected plants wilted and died. Symptoms appeared in lower leaves first and were later observed in upper leaves as the disease progressed. Disease incidence was between 20 and 30% in the affected plantations, with around 30% of infected plants wilting and dying, resulting in 20 to 25% yield losses. Upper leaves from 10 symptomatic plants, five from Puembo and five from Checa, were collected randomly. Two 0.5-cm2 pieces of leaf from each plant were excised from the margins of the necrotic lesions, surface sterilized, and macerated in 9 ml of sterile peptone water. The 10− 3 dilutions were plated onto nutrient agar and incubated at 28 C for 24 h. Yellow, mucoid colonies were isolated on nutrient agar. Three isolates from Puembo and two from Checa were selected for testing Koch, s postulates and further biochemical and molecular characterization. Isolates were gramnegative rods, oxidase negative, catalase, indol and citrate positive. Fragments of the 16S, gyrB, and rpoB loci were amplified and sequenced using the 27F/1492R (Lane 1991), UP-1/UP-2r (Yamamoto …