Sorghum Seed Fungal Community and Their Association with Grain Mold Severity, Seed Weight, and Germination Rate

Grain mold, considered the most important disease of sorghum, is associated with several fungal genera. The disease reduces both yield and quality. In this study, over 300 sorghum seed samples collected from Texas, Florida, and Georgia were evaluated for grain mold severity, seed weight, germination rate, and seed fungal community. Grain mold severity of the seed samples, except for those collected from Cameron, Texas, were rated 3 or higher, indicating that these sorghum lines were moderately susceptible under naturally-infected field conditions during the 2016 and 2017 growing seasons. Seed weight across surveyed locations ranged from 1.1 g to 4.0g for samples collected in Texas during the same period. Percent germination rates for samples collected in Texas ranged from 59.6% to 86.7%. Sorghum samples collected from Florida and Georgia exhibited moderately susceptible response to grain mold infection. Mean seed weight was 1.9 g for samples collected from Florida, while in Georgia, mean seed weight was 2.3 g. Germination rate was low for samples collected from Florida and Georgia. Mycological analysis of sorghum seed samples collected from farmers' fields in Central and South Texas during the 2016 and 2017 growing seasons showed Alternaria species as the most frequently isolated fungal genus, accounting for 40% and 42 % in 2016 and 2017, followed by Fusarium incarnatum, F. acuminatum, F. equiseti, & F. semitectum Complex. In Florida and Georgia, Fusarium incarnatum, F. acuminatum, F. equiseti, & F. semitectum Complex was the most frequently recovered fungal species, accounting for 77% and 72% of the total. genera/species isolated from seed samples. Other fungal species, including Curvularia lunata, Bipolaris sp., Colletotrichum sublineola, F. verticillioides, Penicillium sp., Aspergillus flavus, F. thapsinum, F. oxysporum, F. sporotrichioides, F. graminearum, F. proliferatum, and Aspergillus niger were also isolated from sorghum seeds in various frequencies. In conclusion, the presence of large number of fungal genera associated with grain deterioration and their effect on other traits, makes management of this disease complex challenging. To identify grain mold resistant sources in a region, using the most dominant species in that region to screen the sorghum germplasm is recommended.