POTENTIAL USE OF ALTERNATIVE BIOCONTROL FOR SOYBEAN RUST

Soybean rust is a polycyclic foliar disease with high destructive power caused by the obligate biotrophic fungus Phakopsora Pachyrhizi. Rust management is carried out mostly by the use of fungicides. However, the development of fungicide resistant races has made the control of the disease increasingly difficult. In addition, there has been increasing concern about the use of chemical fungicides in the field due to environmental contamination. In this way, scientific community could search for alternative products to promote a biological and less aggressive rust control. In recent unpublished studies, we noticed the presence of Penicillium sp. colonizing rust lesions in soybean leaves. The observed fungus grower forming a structure that seems to hinder rust sporulation. Thus, we decided to evaluate its effects on the development of Phakopsora pachyrhizi. The commercial bio-fertilizer Microgeo, which is recommended as a potential phytopathogen control was also evaluated as a biocontrol compared to Penicillium sp. A total of 60 leaves of the susceptible cultivar CD219-RR were desinfected and cultivated in 1% ágar on petri dishes. Detached leaves were submitted to the following treatments: (1) – bio-fertilizer spray and after 24 hours inoculation with P. pachyrhizi, (2) - P. pachyrhizi inoculation and after 24 hours bio-fertilizer application; (3) - Inoculation of Penicillium sp and after 24 hours inoculation with P. pachyrhizi; (4) - Inoculation of P. pachyrhizi and after 24 hours inoculation of Penicillium sp.; (5) - Inoculation of Penicillium sp. and after 24 hours inoculation of P. pachyrhizi and after another 24 hours bio-fertilizer spray; (6) - Inoculation of P. pachyrhizi and after 24 hours distilled water spray. In conclusion, the use of Penicillium sp. was effective in controlling the disease when used as a preventive treatment, reducing in 42.6% the number of lesions after 21 days of treatment and delaying the appearance of sporulation in soybean leaves in relation to other treatments. However, there was no difference in the latency period between treatments, which suggests that Penicillium would be acting in the initial stages of Phakopsora pachyrhizi development. In this sense, we evaluated the inhibitory potential of inoculants with different concentrations of Penicillium spores on the germination of Phakopsora pachyrhizi urediospores in 1% agar dishes and observed a reduction in germination of 60.5% what supports its action during the initial developmental stages. In summary, our early results indicate that Penicillium can be effective as a preventive treatment for soybean rust.