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Plantwise Technical Factsheet

head smut of maize (Sphacelotheca reiliana)

Host plants / species affected
Andropogon (beardgrass)
Sorghum bicolor (sorghum)
Zea mays (maize)
Zea mays subsp. mays (sweetcorn)
Zea mays subsp. mexicana (teosinte)
List of symptoms/signs
Inflorescence  -  abnormal leaves (phyllody)
Inflorescence  -  black fungal spores
Inflorescence  -  discoloration panicle
Inflorescence  -  twisting and distortion
Leaves  -  abnormal colours
Leaves  -  abnormal forms
Leaves  -  fungal growth
Seeds  -  empty grains
Seeds  -  galls
Seeds  -  rot
Stems  -  mould growth on lesion
Whole plant  -  dwarfing
Symptoms
On maize, sporulation by S. reiliana may occur in tassels, in ears and occasionally in leaves of infected corn plants. Tassel infection may be confined to individual spikelets and result in anomalous, shoot-like growth, or the entire tassel may proliferate and form bizarre leafy structures. Ears of infected corn plants may be smutted or they may be aborted, with rudimentary leaf buds in place of normal ears. In some plants, the tassels remain healthy while sori form in the ears, but most frequently, sori develop only in tassels and the ears are aborted. Sori often form at both sites on the same plant (Halisky, 1963).

Sporulation in the ears may be independent of tassel sori, whereas terminally smutted plants usually bore either smutted or aborted ears. Plants with smutted tassels were severely dwarfed, often to less than one half of the normal plant height (Halisky, 1963).

Height reduction of up to 64 sweetcorn varieties by S. reiliana was measured in four field studies using seed furrow inoculation. Infected plants were consistently stunted whether sori occurred on the ears only or on ears and tassels. There was a significant relationship between height and infection of individual plants (Wang and Wang, 1989).

Chlorotic spots containing hyphae developed on the fourth or fifth emerged leaf of S. reiliana-infected maize seedlings. Analysis of data in multidimensional contingency tables showed that symptomatic seedlings are likely to produce sori in inflorescences (Matyac and Kommedahl, 1985).

On sorghum, S. reiliana produces a smooth-walled sorus as large as 8-10 x 2.5-3.0 cm, which replaces the inflorescence. This sorus, or smut body, is composed of millions of ustilospores when mature. Symptoms include the formation of a sorus which completely replaces the inflorescence and dwarfing of the plant to the appearance of partially smutted inflorescence on tillers. Intermediate symptoms include variations in sori, partially smutted, sterile head, sterile, and sterile-leafy heads. Following spore release from a smutted plant, the development of leafy shoots in the inflorescence area is common. Symptom variation in sorghum may be related to the extent of host meristematic differentiation at the time of colonization by the pathogen. Small smut sori develop infrequently on leaves of infected plants (Frederiksen, 1977).
Prevention and control
Cultural Control and Sanitary Methods

The survival of ustiloospores of S. reiliana in soil for several years has prompted the recommendation for deep ploughing, destruction of infected plants and crop rotation as control practices (Mazhara, 1978; Saf'yanov et al., 1980). In Russia, growing barley for 2 years after continuous maize greatly reduced infection by S. reiliana (Kozhevnikova, 1975).

In the Ukraine, S. reiliana infection of maize tended to decrease with application of potassium fertilizer and to increase with nitrogen, compared with unfertilized controls (Danilevskii et al., 1973). In Minnesota, applications of urea, ammonium sulphate and triple superphosphate significantly reduced the frequency of disease in maize field plots, whereas the addition of calcium nitrate caused slight but non-significant increases (Matyac and Kommedahl, 1985).

Frequent irrigation (total 15-20 cm of water) for 18-21 days after planting reduced incidence of S. reiliana on maize. Infection increased with planting depth. Large seeds produced fewer infected plants than did small seeds (Saf'yanov et al., 1980).

Planting date had no effect on disease severity in maize variety testing trials in the USA (Stromberg et al., 1984), Romania (Dracea, 1970) and China (Xu et al., 1982). There was no difference in the frequency of smutted maize plants when seed was planted at depths of 2.5 or 8 cm (Matyac and Kommedahl, 1985).

Host-Plant Resistance

Many common maize hybrids and inbreds express considerable degrees of resistance to S. reiliana (Frederiksen, 1977). In resistance trials in 1981 and 1982, 56% of 238 maize inbreds and hybrids had at least 5% smutted plants. Of 168 elite hybrids, 113 were resistant or moderately so (Stromberg et al., 1984). Resistance is considered to be dominant or partially dominant (Frederiksen, 1977; Akhtar-Ali and Baggett, 1990). In China, results of a 6 x 6 diallele cross of inbred lines with different degrees of resistance to S. reiliana var. zeae indicated that resistance was mainly controlled by additive genes. The lines differed significantly in general combining ability for resistance (Cao et al., 1986). Eleven quantitative trait loci (QTLs) have been identified and mapped to eight maize chromosomes; they showed mostly additive or partial dominant gene action (Lubberstedt et al., 1999). Lu and Brewbaker (1999) found evidence for a single major gene (spr1) on maize chromosome 1 that conferred resistance to head smut.

Resistance to head smut in in-bred maize lines has been linked to peroxidase activity in coleoptile tissues of infected plants (Zhao et al., 1996).

Resistant lines exist for sorghum (Miller, 1984; Wang et al., 1996). Despite changes in race profiles, no unusual erosion of host plant resistance has occurred (Omer and Frederiksen, 1992). The quantitative pattern of inheritance of resistance in sorghum appeared to be controlled by additive genes resulting in significant variation among cultivars, lines or their hybrids. Broad and narrow-sense heritability were 65.5 and 57.6%, respectively. General and specific combining ability variances were 95.1 and 4.9%, respectively (Cao et al., 1988).

Considerable attention has been paid to developing artificial inoculation systems to screen for resistance. In one study natural resting spores of S. reiliana, embedded in moist soil and overwintered under room conditions, were used for inoculating sorghum in Shanxi, China, between 1979 and 1983. Soil inoculation with the spores from the previous year gave a higher rate of infection than that with spores after a 2-year resting period, and no disease occurred in plants inoculated with spores kept for 4 years. Early sown plants were much more susceptible than the late sown ones (Yao and Wang, 1984b). In Russia, methods for evaluating resistance in maize included incorporation of a 2% suspension of teliospores at 3 ml/hole at sowing and the mechanical incorporation of 1% teliospores into soil using a special sowing unit (Yurku et al., 1997).

Chemical Control

Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:

Biological Control

Application of organic amendments with low carbon : nitrogen ratios reduced inoculum density in microplots after 0.5, 1, 1.5 and 2 years, but did not significantly affect the survival of ustilospores, either in microplots after 3 years or in the controlled environment (Matyac and Kommedahl, 1986).

Three species of Coleoptera (a species of Phalacrus near P. obscurus, a species of Brachytarsus [Anthribus] and Lystronychus coeruleus) found to be feeding on S. reiliana on Sudan grass have been suggested as potential biological control agents (Pruett and Colque, 1984).

Seed treatment of maize with new strains of phosphorobacterin decreased the incidence of S. reiliana and markedly increased populations of Bacillus megaterium, from which the biologically active strains 89 and 1049 were isolated (Gevers, 1975).
Impact
Losses from S. reiliana in maize and sorghum are generally minor, but individual fields may lose 30-50% of yield (Frederiksen et al., 1976; Kruger, 1962; Lynch, 1980; Simpson, 1966; Yak and Wang, 1984a). The disease is more severe on sweetcorn than field corn. Head smut occurred in 1980-83 in only four counties in Minnesota. In resistance trials in 1981 and 1982, 56% of 238 maize inbreds and hybrids had at least 5% smutted plants (Stromberg et al., 1984). Incidence ranged from 0-22% (average 2.9%) in a New Zealand survey (Jacks and Graham, 1955). Yield losses up to 80.4% have been reported in Romania (Tusa et al., 1981). In China, head smut incidence on sorghum has been recorded up to 70% in continuous cropping plots (Yao and Wang, 1984a). In Brazil it has been estimated that every 1% increase in the incidence of head smut results in 100kg/ha lost yield (Pacheco and Dittrich, 1999).
Related treatment support
Plantwise Factsheets for Farmers
Montenegro Coca, D.; CABI, 2012, English language
Montenegro Coca, D.; CABI, 2012, Spanish language
 
Pest Management Decision Guides
CABI; CABI, 2017, Spanish language
CABI; CABI, 2017, Portuguese language
CABI; CABI, 2016, French language
CABI; CABI, 2017, English language
Kiritai, S.; Kagai, K.; Ngigi, B.; Mulaa, M.; CABI, 2013, English language
 
External factsheets
PANNAR Seed Factsheets, PANNAR Seed (Pty) Ltd, 2009, English language
CIMMYT Plant Pest and Disease Factsheets, Centro Internacional de Mejoramiento de Maiz y Trigo (CIMMYT) (International Maize and Wheat Improvement Center), English language
PANNAR Seed Factsheets, Pannar Seed (Pty) Ltd, 2009, English language
University of California IPM Pest Management Guidelines, University of California, 2006, English language
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