Research on identification and the characteristics of fungus Phytopythium cucurbitacearum causing root rot disease of orange tree in Ha Giang

Abstract

This research identification and the characteristics of fungus Phytopythium cucurbitacearum causing the root rot disease and degradation of orange in Ha Giang, where soil and orange root samples were collected from 3 orange-growing districts in Ha Giang province (Vi Xuyen, Quang Binh and Bac Quang). Research results showed that P. cucurbitacearum has a spherical, ovate, elliptical, amorphous spore capsule with a distinct knob, 21.2 - 68.5 μm in length and 18.6 - 37.25 μm in width, with a pore size of 3.2 - 5.6 μm. P. cucurbitacearum grown on CA medium showed the best growth, after 7 days of culture on petri dishes, the diameter of 90.00 mm was achieved; the next one is the V8 environment, the size of 75.67 mm was reached; PA and CMA medium yielded the size of the fungus of 65.50 and 67.33 mm, respectively; PDA medium had the slowest growth of the fungus with a size of 43.33 mm. The most favorable temperature for the growth of P. cucurbitacearum is from 20ºC - 30ºC; after 3 days, the mycelium had grown covering the plates with a diameter of 90 mm at 30ºC; at temperature thresholds of 20ºC and 25ºC on the third day, the sizes were 67.33 and 81.50 mm, respectively, and the plates were fully grown on the fourth day; The temperature range of 20ºC - 30ºC provides the most suitable condition for the growth of P. cucurbitacearum causing root rot on citrus.