การแพร่ระบาดของไส้เดือนฝอยศัตรูพืชในแปลงข้าวจังหวัดปทุมธานีและการตอบสนองเชิงป้องกันของข้าว (Oryza sativa L.) ต่อไส้เดือนฝอยรากปม Meloidogyne graminicola

Abstract

Rice (Oryza sativa L.) is a vital economic crop of Thailand; both for exportation and household consumption. In central plain of Thailand, Pathum Thani province has been recorded as one of the most important places for rice cultivation, with rice cultivation area about 55% of the total area and rice production up to 0.2 million tons per year. High population densities of the plant-parasitic nematodes appearance leading to yield loss of rice. Therefore, the objectives of this study were (1) to identify species of predominant plant-parasitic nematodes and their distribution in Pathum Thani's rice fields, and (2) to evaluate the defensive response of rice against M. graminicola infestation. Forty-two soil and rice root samples were collected from seven districts of Pathum Thani province including Nong Suca, Thanyaburi, Lam Luk Ka, Khong Luang, Meung, Sam Khok and Lat Lum kaeo. Consequently, plant-parasitic nematodes were extracted, counted and identified by morphological and molecular characters by using specific primers. The result showed that the predominant plant-parasitic nematodes highly found in all rice fields were Hirschmanniella sp. (96.54%) and Meloidogyne sp. (3.22%). The morphological characters of Hirschmanniella sp., body length ranged from 1,639. 2,329 um, stylet length was 24-27 um and an obvious mucron at the end of terminus. Likewise, molecular identification based on PCR technique by using D2A/D3B and rDNA2DNA1.58s were 98 % similarity with H. mucronata from Cambodia's population. For morphological identification of root-knot nematodes, body and stylet lengths of second stage juveniles were 427-501 um and 13.1-15.7 pm, respectively and the tail character was conoid, male body length was 1,060-1,734 μm, stylet length was 18-22 μm, tail character was bluntly rounded, the perineal patterns of the root-knot nematodes were generally oval shaped without lateral lines and smoothly cuticular matched with M. graminicola. Molecular identification based on PCR technique with three different primer sets including rDNA2/1.58s, CF/1108 and SCAR-MgFW/SCAR-MgRev showed DNA fragments with size of 490, 520 and 650 bp, respectively. Phylogenetic tree based on 188-ITS1-5.88 genes illustrated that the root-knot nematodes found in this study were M. graminicola with 97% similarity to the population of root-knot nematodes from rice fields of Madagascar. Therefore, the predominant plant-parasitic nematodes found in Pathum's Thani rice fields were H. mucronata and M. graminicola. Six rice cultivars including Khao Dawk Mali 105 (KDML105), Pathum Thani 1 (PT1), San-Pah-Tawng 1 (SPT1), Rice Department No. 6 (RD6), Rice Department No. 43 (RD43), and Rice Department No.57 (RD57) were evaluated for their resistance levels to M. graminicola (RKN). The result showed that RD6 proved to be the most response against root-knot nematodes among six rice cultivars, with lowest number of gall index. However, gall numbers and number of nematodes inside rice roots at 14 days were not significant difference with SPT1 and PTI cultivars, respectively. Likewise, defense-related enzymes of RD6 cultivar including phenylalanine ammonia lyase, peroxidase and polyphenol oxidase significantly increased during 2 and 3 days after nematode inoculation (nematode infection periods). On the other hand, the enzyme activities in KDMI.105 (susceptible cultivar) were not significantly different between RKN inoculation and un-inoculation during 1-4 days after nematode inoculation. This study illustrated that RD6 was the most response against M. graminicola among evaluated six rice cultivars.