General Commission of Scientific Agricultural Research-
Faculty of Agriculture- Damascus University-
Results of field survey to assess the prevalence of common smut on maize conducted during 2004 growing season showed that disease spread average incidence (DSA) was variable according to Syrian governorates (11 governorates).
The highest DSA was found in AL-Reqqa gov. (13.95%), and the lowest DSA was recorded in Latakia gov. (1.7%). The mean percentages of infected plants ranged between 1.7 (Latakia gov.) and 11.6% (Damascus countryside gov.), whereas the percentages of infected ears were 1.3 in Hama gov. and 6.7% in Aleppo gov. Infection levels of ears were variable according to governorates and within the same governorate, the highest infection percentages (more than 55% of grain in ear were infected) were found in ears collected from Aleppo, Edlib, Die razor, Damascus countryside and Latakia govs. (60-70%), and the lowest infection percentage was recorded in Tartous gov. (10.5%).
The percentages of direct yield loss of maize plants in Syria ranged between 1.3% and 6.7%, while the main percentage of yield loss was 4.4%. A signifiacant correlation was found between DSA in surveyed governorates of percentages of infected plants and ears. Germination of teliospores of U. maydis was better in solid media than in liquid media. In comparison with other media, the PDA medium was superior in its promotional effect on teliospore germination after 8 or 24 hours of incubation.
No teliospores germination was observed on soil media, whereas potato sucrose peptone (PSP) liquid medium was the best for propagation of fungus sporidia. In comparison with glucose, sucrose and maltose, the dextrose was the most suitable sugar for propagation of U. maydis sporidia, when added to liquid potato medium and the differences were significant. 4-6C were more effective to save teliospore viability where 82% of teliospores were viable after 6 months of storage, meanwhile the viability was very low (3.4%) when teliospores were stored at 32 ±4C. Treatment of stem Injection with fungal sporidia suspension was significantly superior in comparison with other treatments in disease occurrence on corn seedling and disease index (DI) was 87% followed by dropping in upper whorl leaves treatment (50%), where (DI) in spraying treatment of whole plant was 43%.
The pathogenicity levels of U. maydis isolates (20 isolates) collected from different cultivars and geographic areas against maize seedlings (Guta 82 cv.) were variable in some cases, the highest pathogenicity level was recorded in fungal isolates collected from Damascus countryside gov., meanwhile the lowest pathogenicity was found in isolates collected from Al-Reqqa and Edlib govs. Five corn cultivars were evaluated against U. maydis under natural and artificial infection conditions. All adult plants of tested cultivars were infected under natural inoculation conditions with different levels, The DI ranged from 2.7 to 15.2%. The Guta 1 cv. was the most susceptible to disease under artificial infection conditions, where Basel 1cv. was less susceptible when plants were in adult plant stage. DI differences were not significant in most of tested cultivars in seedling stage.
No signifiacant correlation was found between DSA of corn plants in surveyed governorates and daily air temperature average and relative humidity of air during 2004 growing season. Contribution of different factors is essential for the epidemic status of the disease to take place, such as: presence of pathogenic fungus inoculum in soil, cultivation of susceptible corn cultivars, beside the presence of suitable environmental conditions: temperature, humidity, rainfall, in addition to the application of some agricultural practices like removing of lower leaves, sprinkler irrigation, increase of planting density and leaving of crop residues.