IDENTIFICATION OF Phytophthora AND Phytopythium SPECIES ISOLATED ON DISEASED SAMPLES AND RHIZOSPHERE SOILS OF NAM ROI POMELO IN MY HOA COMMUNE, BINH MINH TOWN, VINH LONG PROVINCE

Abstract

The study was aimed to identify Phytophthora and Phytopythium species present in disease samples (leaves and fruits) and from the rhizosphere soil of Nam Roi pomelo in My Hoa commune, Binh Minh town, Vinh Long province. Based on morphological characteristics on V8 medium, 18 out of 73 Phytophthora and Phytopythium isolates were selected to represent subsequent experiments. The experiment evaluating pathogenicity on Nam Roi pomelo leaves was arranged in a completely randomized design with one factor, 4 replications, and 18 treatments, with each treatment being one Phytophthora or Phytopythium isolate. Morphological characteristics and sizes of sporangia, chlamydospores and sporangial proliferation of the 18 representative Phytophthora and Phytopythium isolates were recorded. DNA of the 18 representative Phytophthora and Phytopythium isolates was PCR-amplified using the ITS1/ITS4 primer pair; subsequently, PCR products with a clear, bright band were sequenced; the sequencing products were processed using Finch TV software (version 1.4.0), compared with reference sequences (BLAST) on NCBI for species identification and a phylogenetic tree was constructed using MEGA software (version 11.0.14). The results showed that all 18 representative isolates caused disease on Nam Roi pomelo leaves after 5 days of inoculation with varying degrees of severity, depending on the virulence of each isolate. Based on morphological characteristics and PCR-sequencing results, the 18 representative isolates were divided into 5 Groups: Group 1 included 10 isolates: PP7, PP8, PP9, PP13, PP17, PP18, PP22, PP23, PP27, and PP28, belonging to the species Phytophthora virginiana; group 2 included 5 isolates: PP1, PP2, PP3, PP4, PP5, belonging to the species Phytophthora parvispora; group 3 included 1 isolate, PP21, belonging to the species Phytophthora prodigiosa; group 4 included 1 isolate, PP11, belonging to the species Phytophthora citrophthora; group 5 included 1 isolate, PP12, belonging to the species Phytopythium helicoides.