Effects of Wetness Duration and Grain Development Stages on Sorghum Grain Mold Infection

Abstract

Grain mold caused by a complex of fungi is an economically important disease of sorghum worldwide. Little is known about the epidemiology of sorghum grain mold, which is essential for its management. Studies were conducted to quantify the effects of wetness duration on grain mold development under controlled conditions at ICRISAT. Six major sorghum grain mold fungi determined from previous field experiments,Curvularia lunata, Cladosporium oxysporum, Bipolaris australiensis, Fusarium moniliforme, F. pallidoroseum, and Phoma sorghina, were used. Panicles of a pot-grown mold-susceptible sorghum line, IS 10513, were spray inoculated with each fungus at five growth stages: flowering (F), milk (M), soft dough (S), hard dough (H), and physiological maturity (P), and were incubated in dew chambers for 0,16, 24, 40, 48, and 72 h. Then, the plants were placed on greenhouse benches at 25 ± 1°C to allow grain mold infection to develop. Eight days after treatments, grains from F, M, and S stages were plated onto potato dextrose agar, while those from H and P stages were incubated in blotter paper humid chambers at 28 ± 1°C. Fungal colonization of grains were scored after 7 days. Results indicated a significant (P < 0.01) correlation between wetness duration and grain mold development at different stages of inoculation. Generally, with increasing wetness duration, there was an increase in grain infection by all six fungi. However, infection frequency varied among fungi and grain development stages, indicating that individual fungi might have different windows for maximum infection during the grain development stages. In many regions of the world where sorghum (Sorghum bicolor (L.) Moench) is produced, grain mold is a serious disease that reduces grain quality and utilization. The term "grain mold" is used to describe the diseased appearance of sorghum grain resulting from infection by one or more parasitic fungal species (21). Grain mold is most commonly caused by Fusarium moniliforme J. Sheld. and Curvularia lunata (Wakk.) Boedjin, although many other fungal species are also associated with the mold complex (9,16). It is a major biotic constraint to sorghum improvement and production worldwide, especially when grain development coincides with wet and warm weather conditions (10). It is estimated that annual economic losses in Asia and Africa as a result of grain mold are in excess of US $130 million (13). In some cases, yield losses can reach 100% in highly susceptible cultivars (12). Apart from yield reduction, grain mold also reduces seed quality, with effects ranging from cosmetic deterioration of the pericarp to substantial deterioration of the endosperm and embryo with reduction in acceptability by food and feed processors (17). In addition to reducing the nutritional value, fungi that cause grain mold in sorghum may also produce mycotoxins (7), thus limiting the use of sorghum grain as food and feed (16). Molded sorghum grain fetches lower market prices and therefore affects the income of sorghum farmers (2).Ce...

Occurrence of filamentous fungi in maize destined for human consumption in South Africa

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Inoculation strategies to assess biological interactions betweenFusariumandAlternariaspecies infecting sorghum

“…Direct application of fungal conidia to sorghum flowers and developing grain would appear to mimic natural infection (Navi et al 2005). Sorghum grain mold is likely caused by a species complex that may include Curvularia lunata, members of the F. moniliforme complex, Alternaria spp., Bipolaris spp., Cladosporium spp., or Phoma spp.…”

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Evaluation of A1, A2, A3, A4(M), A4(G) and A4(VZM) cytoplasms in iso-nuclear backgrounds for grain mold resistance

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