Biological control of the grapevine diseases ‘grey mold’ and ‘powdery mildew’ by <i>Bacillus</i> <span style="mso-bidi-font-family:"Times New Roman"; mso-fareast-language:FR" lang="EN-US">B27 and B29 strains<span style="mso-bidi-font-style:italic"> </span></span>

109-115<span style="mso-ansi-language:EN-US; mso-fareast-language:FR" lang="EN-US">Uncinula necator and Botrytis cinerea are the most destructive pathogens of the grapevine in Tunisia and elsewhere. We used <span style="mso-ansi-language:EN-US;mso-fareast-language: FR" lang="EN-US">two strains of Bacillus subtilis group, B27 and B29 to control powdery mildew and the grey mold disease of the grapevine. Green house experiments showed that B29 and B27 strains of the bacteria efficiently reduced the severity of powdery mildew up to 50% and 60%, respectively. Further, they decreased Botrytis cinerea development on grape leaf by 77% and 99%, respectively. The mode of action has been shown to be chitinolytic. These two bacteria showed significant production of total proteins discharged into the culture medium. Determination of some chitinolytic enzymes revealed the involvement of N-acetyl glucosaminidase (Nagase), the chitin-1,4-chitobiosidase (Biase) and endochitinase in degrading the mycelium of B. cinerea. </span

Manganese Deficiency is Associated with Histological Changes in Date Palm Fronds Showing Brittle Leaf Disease Symptoms

Several diseases, pests and physiological disorders threat date palm life. Among them, Brittle leaf disease or, in French, Maladie des feuilles cassantes (MFC) is a lethal disease that has acquired alarming proportions since the 1960s, when it was first observed in southern Tunisia. Up to now no causal agent has been found. Previous studies have reported that brittle fronds are deficient in manganese but the mechanisms involved in symptom expression have not yet been identified. In this study, an anatomical investigation was carried out in order to identify the deleterious effect of MFC on the development and structure of palm fronds. Results showed that in old healthy fronds the major tissue is schlerenchyma, which is characterized by very thick lignified cell walls and is often associated with conducting tissue. Indeed, large vessels are surrounded by schlerenchyma fibers that are strongly lignified when compared with those of young fronds. Diseased young fronds have almost the same shape as the healthy young fronds. Nevertheless, in old diseased fronds MFC induces important structural changes. Xylem and phloem vessels are larger, taking more space through the fibers that are smaller in number and size, and tighter. The larger diameter of the lumen and the lower thickness of the fibers present in the fronds in advanced disease stages, decreases the lignin content of cells walls, leading to an increased frond friability, which gives &quot;the brittle leaf disease&quot; its name