BIOLOGICAL, MOLECULAR CHARACTERIZATION AND CONTROL OF Spiroplasma citri THE CAUSAL OF CITRUS STUBBORN DISEASE ON LIME TREES IN EGYPT

Abstract

Lime (Citrus aurantiifolia) is considered one of the main fruit crop in Egypt, which is considered the twelfth largest limes/lemons producer in the world. Lime trees are subjected to invasion by several fungal, bacterial, viral and virus-like diseases. In recent years, lime/lemon trees have been seriously affected by citrus stubborn disease (CSD) caused by a prokaryotic pathogen Spiroplasma citri.

In Egypt, CSD is a very serious disease in most lime growing regions and dramatically decreased lime yields in the last three years. In Egypt, Spiroplasma citri the causal organism of Citrus Stubborn Disease (CSD) has been considered as a major threat and devastating for lime/lemon plants either grown as trees in the fields or as seedlings in the greenhouses. Many complains were received from several citrus producers about the large yield loss and degeneration of lime trees leading to the remarkable and unusual raise in lime price in the Egyptian markets during the years 2018-2019 and 2019-2020. For these reasons this study was carried out.

The obtained results can be summarized in the following points:

1. Different limes (Citrus aurantiifolia (Christm.) Swingle), lemons (Citrus limon L. Osbeck) and volkamer lemons (Citrus volkameriana Tan & Pasq.) samples showed symptoms suspected to be caused by citrus stubborn disease (CSD) were collected. Samples were collected from eight Egyptian governorates; Ismailia, Damietta, Faiyoum,

Giza (Al Mansouria, and Kirdasah), Cairo (Maadi and Cairo University, Faculty of Agriculture experimental station), Luxor (Al-Odeisat), Qalyubia (Benha University, Faculty of Agriculture experimental station and Tersa) and Beheira. Spiroplasma citri was isolated from all samples of young leaves, flowers, fruits and seeds showing typical symptoms of disease. The isolates were coded as EL 1, EL 2, EL 3, EL 4, EL K, EL G, EL Be-Fl, EL Be-F, EL Be-L, EL Lux, EL M, EL I, EL B, EL T-F, EL T-L and EL T-S.