AUTHOR=Alwahshi Khawla J. , Purayil Gouthaman P. , Saeed Esam Eldin , Abufarajallah Haneen A. , Aldhaheri Shama J. , AbuQamar Synan F. , El-Tarabily Khaled A. 

TITLE=The 1-aminocyclopropane-1-carboxylic acid deaminase-producing Streptomyces violaceoruber UAE1 can provide protection from sudden decline syndrome on date palm

JOURNAL=Frontiers in Plant Science

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.904166

DOI=10.3389/fpls.2022.904166

ISSN=1664-462X

ABSTRACT=<p>In the United Arab Emirates (UAE), sudden decline syndrome (SDS) is one of the major fungal diseases caused by <italic>Fusarium solani</italic> affecting date palm plantations. To minimize the impact of the causal agent of SDS on date palm, native actinobacterial strains isolated from rhizosphere soils of healthy date palm plants were characterized according to their antifungal activities against <italic>F. solani</italic> DSM 106836 (<italic>Fs</italic>). Based on their <italic>in vitro</italic> abilities, two promising biocontrol agents (BCAs), namely <italic>Streptomyces tendae</italic> UAE1 (<italic>St</italic>) and<italic>Streptomyces violaceoruber</italic> UAE1 (<italic>Sv</italic>), were selected for the production of antifungal compounds and cell wall degrading enzymes (CWDEs), albeit their variations in synthesizing 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase (ACCD). Although both isolates showed antagonism when applied 7 days before the pathogen in the greenhouse experiments, the ACCD-producing <italic>Sv</italic> was relatively superior in its efficacy against SDS over the non-ACCD-producing <italic>St</italic>. This was evident from the symptoms of SDS in diseased date palm seedlings which were greatly reduced by <italic>Sv</italic> compared to <italic>St</italic>. On a scale of 5.0, the estimated disease severity indices in <italic>Fs</italic>-diseased seedlings were significantly (<italic>P</italic> &lt; 0.05) reduced from 4.8 to 1.5 and 0.5 by <italic>St</italic> and <italic>Sv</italic>, respectively. Thus, the number of conidia of <italic>Fs</italic> recovered from plants pre-treated with both BCAs was comparable, but significantly (<italic>P</italic> &lt; 0.05) reduced compared to plants without any BCA treatment. In addition, a significant (<italic>P</italic> &lt; 0.05) decrease in ACC levels of both the root and shoot tissues was detected in<italic>Sv</italic> + <italic>Fs</italic> seedlings to almost similar levels of healthy seedlings. However, <italic>in planta</italic> ACC levels highly increased in seedlings grown in soils infested with the pathogen alone or amended with <italic>St</italic> prior to <italic>F. solani</italic> infestation (<italic>St</italic> + <italic>Fs</italic>). This suggests a major role of ACCD production in relieving the stress of date palm seedlings infected with <italic>F. solani</italic>, thus supporting the integrated preventive disease management programs against this pathogen. This is the first report of effective rhizosphere actinobacterial BCAs to provide protection against SDS on date palm, and to help increase agricultural productivity in a more sustainable manner in the UAE and the other arid regions.</p>