الفهرس 
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Abstract
Maize (Zea mays L.) considered one of the most important cereal crops in Egypt. Maize constitutes up to 75% of the total requirements. The annual area devoted to maize cultivars in Egypt, is about 1.8 million feddans in 2001. Average yield per feddan is about 24.6 ardabs with total national production of grains of about 6.1 million tons (ton =7ardabs). The common smut disease [Ustilago maydis] is widespread and endemic on maize. The losses due to disease are usually slight, but may be severe locally on susceptible varieties, especially in areas with warm and somewhat dry climates. The present investigation aimed to studying some aspects related to such disease. Results obtained can be summarized in the following:
1.Germination of Ustilago maydis teliospores was greatly varied among tested isolates. It was ranged between 41.6% in Sids isolate [Beni-Sueif] to 19.4% in isolate of Sakha [Kafr El-Sheikh].
2.Both teliospores and sporidiospores were able to infect maize plants under greenhouse conditions. Inoculation with sporidiospores produces higher disease than teliospores.
3.The tested isolates were significantly varied in disease incidence (30.0-90.0%) and disease severity (19.0-56.0%). Among the 6 tested isolates of U. maydis, the isolate obtained from Sids (Beni-Sueif) was the most virulent while the isolate from Sakha (Kafr El-Sheikh) was the less.
124 Summary
4.The corn-meal agar medium, whatever, was the
best medium for growth of the fungus followed by Richard’s agar medium. Whereas, Czapek’s agar was the
least favorable one. Abundant teliospores were formed on both corn-meal agar and Richard’s media. PDA,
Carrot dextrose and Ustilago-medium came next. Whereas, the fungus never produced teliospores on
Czapek’s agar.
5.Growth dry weight was increased in general by prolonging the incubation period from 10 to 20 days. However, an obvious decline was happened on potato dextrose broth, potato dextrose yeast broth, and cornmeal broth.
6.Th fungus Ustilago maydis could grew and sporulate and its teliospores could germinate at a wide range of temperature (16-35°C). The maximum values of fungal growth and germination of teliospores were produced at 30°C followed by 28°C.
7.Both fungal growth and germination of teliospores were dramatically lower under constant adjusted levels (90-100%) of relative humidity when compared with humidity conditions of control treatments (uncontrolled R.H.). No fungal growth and no germination of teliospores were occurred at relative humidity less than 80%.
125 Summary
8.Germination of teliospores was negatively affected by prolongation of storage period. Germination was sharply decreased one month after storage at room temperature from 41.6% [October 1998] to 13.3% [November 1998]. It was completely stopped in the cooler months (December and January) then be resumed and increased gradually till it reached the maximum in warmer months of 1999 (May, June, July, August, and September). Similar trend but lower values were noticed in 2000. No germination occurred at all during
2001.
9.The teliospores germination was negatively and significantly affected by root exudates of some tested plants. The root exudates of garlic, onion, sugar beet, and faba bean caused the highest reduction in teliospores germination [97.5-90.9%], while those of lentil, oat, and lupine reduced it by 85.3-69.1%. The root exudates of clover ”G.1 Sewa”, chickpea, and wheat produced the lowest significant suppressive effect [33.1-22.8%]. On the other hand, root exudates of barley, clover ”Misqawy”, and maize had no significant suppressive effect on teliospore germination when compared with germination in free water.
10.Compared with initial germination of U maydis teliospores, cultivation of garlic, sugar beet, and oat as maize-preceding winter crops caused the highest decreases in teliospores germination, respectively. The lowest reduction in
126 Summary
germination was associated with teliospores buried in fallow irrigated soil (15.8%), soils cultivated with chickpea (14.2%), wheat (12.8%), fallow non-irrigated soil (3.4%), and soil cultivated with clover ”Misqawy” (3.0%) without significant differences in between.
11.The hypodermic injection method was the most efficient for inducing common smut infection. Injection with sporidiospores was more infective than teliospores. The DROP method was far less effective while leaf inoculation and soil infestation were ineffective, failing to produce any symptoms on the maize plants.
12.Eucalyptus, cinnamon, and peppermint oils inhibited fungal growth completely at 750 ppm while clove and anise oils only do this at 500 ppm. Applying the same oils at same conc. as spray either 48 hrs before or after pathogen inoculation reduced disease incidence significantly but to less extent than simultaneous injection method. In the field trials, average grain yield/plant due to the above mentioned oil treatments was comparable to the yield of healthy untreated plants and significantly higher than the yield of control (oil non-treated) plants. Simultaneously injection with both suspension of U. maydis sporidia and peppermint or eucalyptus oils at 750 and 1500 ppm or cinnamon oil at 1500 ppm caused the greatest reduction in disease incidence [0.0-3.6%] compared with 44.1-61.2% in control untreated plants
127 Summary
that were injected only with spore suspension. The average grain yield/plant due these treatments [302.0-345.1 g/plant] was comparable to the yield of healthy untreated plants [316.5-343.9 g/plant] and significantly higher than the yield of control plants [143.8-161.2 g/plant].
13.The screened maize accessions exhibited considerable variations in their reaction against artificial infection with common smut disease under greenhouse conditions. The three way hybrids TWC-Baraka followed by the TWC-322 and the SC-129 exhibited the lowest level of disease indices. On the other hand, the highest limits of disease indices were recorded on Giza-2 and Boushi (open pollinated local varieties), TWC.320, TWC.324, TWC.321 (three way crosses), and DC Dahab (double cross) accessions.
14.Under stress of both artificial and natural infection, the ear infection sowed destructive effect on grain yield particularly if smut gall was occurred above the ear.