Rice Root-Associated Endophytic Microbiome in Correspondence To Different Levels of Salinity At Indian Sundarban Areas

The present study attempted to analyse rice root endogenous microbial diversity and their relationship with soil salinity and physicochemical factors in the salt stressed region of Sundarbans, India using amplicon metagenomics approaches. Our investigation indicates, the unique microbiome at slightly acidic nutrient enriched non-saline zone characterized by microbial genera that reported either having plant growth promotion (Flavobacterium, Novosphingobium and Kocuria) or biocontrol abilities (Leptotrichia) whereas high ionic alkaline saline stressed zone dominated with either salt-tolerant microbes or less characterized endophytes (Arcobacter and Vogesella). The number of genera represented by significantly abundant OTUs was higher at the non-saline zone compared to that of the saline stressed zone probably due to higher nutrient concentrations and the absence of abiotic stress factors including salinity. Physicochemical parameters like nitrogen, phosphorus and potassium were found significantly positively correlated with Muribaculaceae highly enriched at the non-saline zone. However, relative dissolved oxygen was found significantly negatively correlated with Rikenellaceae and Desulfovibrionaceae, enriched in the non-saline soil. This study gives a well resolved picture of microbial community composition impacted by salinity and other rhizospheric soil factors.

Nursery Management of Two Major Below-Ground Feeding Plant Pests: Root Mealybug, Rhizoecus sp. and Rice Root Aphid, Rhopalosiphum rufiabdominalis (Sasaki) (Hemiptera: Pseudococcidae and Aphididae)

Root mealybug (Rhizoecus sp.) and rice root aphid (Rhopalosiphum rufibdominalis) are below-ground feeding insects that are difficult to control and have become major pests as production of their host plants has grown. Field trials were designed to investigate the impact new insecticides and biopesticides have on root mealybugs and rice root aphids. In our first three trials, we investigated the effects of biopesticides, entomopathogenic nematodes or fungi on reflexed stonecrop (Sedum rupestre) and stonecrop (S. montanum) against root mealybug. We found that flupyradifurone (Altus), flonicamid (Aria), chlorantraniliprole (Acelepryn), pymetrozine (Endeavor), Beauveria bassiana (Mycotrol), Chromobacterium subtsugae (Grandevo), Burkholderia spp. strain A396 (Venerate), cyantraniliprole (Mainspring) and Steinernema carpocapsae (Millenium) significantly reduced root mealybug populations compared to nontreated controls when applied as drenches in a curative manner. In our fourth trial, we evaluated biopesticides and Beauveria bassiana, on rice root aphid feeding on common rush (Juncus effusus) roots. Results showed pymetrozine significantly reduced populations as early as 14 days after treatment and continued to reduce their population throughout the remainder of the trial. However, chlorantraniliprole, cyantraniliprole, Beauveria bassiana, M-306 and MBI-203 did not significantly reduce rice root aphid populations until 28 days after initial application. Predator activity on root balls of Juncus effusus plants was also noted during the trials and may provide an integrated pest management (IPM) approach in controlling populations. Index words: reflexed stonecrop, Sedum rupestre L, stonecrop, Sedum montanum Song. & Perr, common rush, Juncus effuses L, Beauveria bassiana, Mycotrol, Steinernema carpocapsae, Millenium, reduced-risk pesticides, Chromobacterium subtsugae (Grandevo), flupyradifurone, Altus, flonicamid, Aria, chlorantraniliprole, Acelepryn, pymetrozine, Endeavor, Burkholderia spp. strain A396, Venerate, cyantraniliprole, Mainspring, M-306, MBI-203. Chemicals used in this study: flupyradifurone (Altus); flonicamid (Aria); chlorantraniliprole (Acelepryn); cyantraniliprole (Mainspring); pyrometrozine (Endeavor); Burkholderia spp. strain 396 (Venerate); Chromobacterium subtsugae (Grandevo); Beauveria bassiana (Mycotrol); AMBI-203 WDG – 30% Chromobacterium subtsugae strain PRAA4-1T cells and spent fermentation media. EPA registration number 84059-27; MBI-206 EP – 94.46% Heat-killed Burkholderia spp. strain A396 cells and spent fermentation media. EPA registration number 84059-14; MBI-203 SC2 – 98% Chromobacterium subtsugae strain PRAA4-1T cells and spent fermentation media. Experimental; MBI-306 SC1 - 94.46% non-viable Burkholderia spp. strain A396 cells and spent fermentation media. Experimental. Species used in this study: Root mealybug, Rhizoecus sp; Rice root aphid, Rhopalosiphum rufiabdominalis (Sasaki); reflexed stonecrop, Sedum rupestre; stonecrop, Sedum montanum; common rush, Juncus effusus.

Incidence and Characterization of Rice Root Nematodes, Hirschmanniella mucronata, from Rice Fields in Pathum Thani Province, Thailand

The rice root nematodes, Hirschmanniella oryzae and H. mucronata, are serious and widespread threats to global rice production, especially in tropical and subtropical zones. Reliable and efficient identification of these nematodes is vital to nematode control and management. In this current study, 36 soil or rice root samples were collected from rice fields located in Pathum Thani province and used for nematode extraction. The results demonstrated that Hirschmanniella sp. was found in all paddy fields, especially in Muang District, where RD47 rice cultivars were grown at soil pH of 5.9. Molecular identification based on the analysis of 28S rRNA and 18S-ITS1-1.58S genes revealed 98 – 99 % similarity to H. mucronata, and its phylogenetic trees were grouped with H. mucronata from Cambodia and Philippines. Likewise, the morphometric characterization revealed remarkable features of H. mucronata with long body (1,639 - 2,329 µm), long stylet (24 - 27 µm) and an obvious mucron at the end of terminus. Therefore, the main rice root nematode species found in Pathum Thani’s rice fields were H. mucronata. HIGHLIGHTS The rice root nematodes, Hirschmanniella, are presented the predominant plant-parasitic nematodes in rice cultivated areas of Pathum Thani province, Thailand Population densities of Hirschmanniella are encountered in rice roots than in soil, especially in RD47 rice cultivars grown in Muang District Both of morphological and molecular characterization illustrating the species of rice root nematodes were mucronate This is a first description on the molecular characterization of mucronata from rice fields in Thailand GRAPHICAL ABSTRACT

Supraoptimal Brassinosteroid Levels Inhibit Root Growth by Reducing Root Meristem and Cell Elongation in Rice

Root growth depends on cell proliferation and cell elongation at the root meristem, which are controlled by plant hormones and nutrient availability. As a foraging strategy, rice (Oryza sativa L.) grows longer roots when nitrogen (N) is scarce. However, how the plant steroid hormone brassinosteroid (BR) regulates rice root meristem development and responses to N deficiency remains unclear. Here, we show that BR has a negative effect on meristem size and a dose-dependent effect on cell elongation in roots of rice seedlings treated with exogenous BR (24-epicastasterone, ECS) and the BR biosynthesis inhibitor propiconazole (PPZ). A genome-wide transcriptome analysis identified 4110 and 3076 differentially expressed genes in response to ECS and PPZ treatments, respectively. The gene ontology (GO) analysis shows that terms related to cell proliferation and cell elongation were enriched among the ECS-repressed genes. Furthermore, microscopic analysis of ECS- and PPZ-treated roots grown under N-sufficient and N-deficient conditions demonstrates that exogenous BR or PPZ application could not enhance N deficiency-mediated root elongation promotion as the treatments could not promote root meristem size and cell elongation simultaneously. Our study demonstrates that optimal levels of BR in the rice root meristem are crucial for optimal root growth and the foraging response to N deficiency.