Isolation of bioagents was carried out from rhizoplane of healthy onion plants,
70 and 120 days after transplanting from different governorates, i.e. El-Behera; EI-
Sharkia; Beni-Swif and El-Menia. Only 21 isolates from the obtained 331 isolates have
prevented sclerotial formation of Sc/emtiurn cepivorum on NYDA medium. The
inhibition zones of mycelial growth of S. cepivorum after 14 days were 13, 9, 7, 4 and
2 ml for isolates Pseudomonas flourescens; Bacillus llcheniformis 10014; Bacillus
licheniformls 6011; 7012 and Chaetomium globosum respectively. Most of
treatments of potting medium, with bacterial isolates soon after onion seeds sewing,
increased the percentage of onion seed germination. The highest increase 195 °/o
was achieved by isolates B. licheniformis 6011 and B. amylo/iquefac/ens 109. The
promising biocontrol agents that had promotion toward onion seed germination and
plant growth were tested in greenhouse for their potential control of onion white rot. At
50 or 100 scierotia/ Kg potting medium, the best reduction in dead plants was
achieved by treatment with P. flourescens, B. licheniformis 6011. T. harzianum, B.
amyloliquefaciens 109, C. globosum or Paenibacll/us polymyxa 9014. Clear
significant increase in plant height was occurred by treatment with P. flourescens
followed by B. licheniformis 6011, C. globosum, B. amo/iquefaciens 109,
Trichoderma harzianum and Paenibaci/lus polymyxa 9014. However, in field
experiment all applications were highly effective in reducing the percentage of dead
onion plants due to white rot infection till the end of growing season (4.5 months from
transplanting), The isolates, P. flourescens, B. llchenlformis 6011, B.
amo/iquefaciens 109 or T. harzianum isolates were the most effective on disease
control in the field. Significant increase in bulb yield was recorded with all tested
isolates especially those of bacteria.
Keywords: Biological control, Onion, White rot, Sclerotium cepivorum, Pseudomonas
flourescens, Bacillus licheniformis, B. amyloliquefaciens, Trichoderma
harzianum, Chaetomium globosum