Abstract
Seed-borne fungi in 69 sunflower cultivars were evaluated which comprised 52 confectionery and 17 oilseed types. Seed coats were placed on both NP-10 (Nonylphenol Ethoxylate based surfacant −10) and potato dextrose agar (PDA) media to culture fungi. The rate of contamination among the different varieties was calculated by counting seed coats with fungal colonies. The rate of contamination in the confectionary group (88%) was significantly (p ≤ 0.05) higher than in the oilseed group (71%). Of the 52 confectionery varieties, the dominant fungi recovered were Verticillium dahliae along with Alternaria spp., Fusarium spp., and Rhizopus spp., whereas the oilseed type varieties were contaminated with only V. dahliae. Molecular identification of fungal species via BLAST (Basic Alignment Search Tool) was performed on fungal sequences obtained from PCR (Polymerase Chain Reaction) analysis. The results included five Alternaria spp. that included Alternaria tenuissima, Alternaria alternata, Alternaria helianthiinficiens, Alternaria longipes, and Alternaria tamaricis, three Fusarium spp. such as Fusarium oxysporum, Fusarium incarnatum, and Fusarium proliferatum, and V. dahliae and Cladosporium cladosporioides. These were identified from pure fungal cultures recovered from seed coats. To efficiently control seed-borne fungi, four broad spectrum fungicides (carbendazim, triadimefon, caprio F-500, and flusilazole) were screened against V. dahliae isolate Gn3, which was isolated from a diseased LD 5009 sunflower plant. Flusilazole was selected based on its low half-maximal effective concentration value (EC50), 78.7 µg/mL. Seeds of diseased LD 5009 plants obtained from two different locations treated with formulated flusilazole fungicide at optimum parameters showed a significant (p ≤ 0.05) increase in seed germination and a decrease in contamination rate from 98% to less than 10%. The results affirmed that confectionery cultivars are much more susceptible to fungal contamination than oilseeds, and also that seed pretreatment is a suitable way to prevent the spread of soil- and seed-borne fungi in sunflower production.
Highlights
Sunflower (Helianthus annuus L.) is one of the top oilseed crops grown for their edible oil
The results affirmed that confectionery cultivars are much more susceptible to fungal contamination than oilseeds, and that seed pretreatment is a suitable way to prevent the spread of soil- and seed-borne fungi in sunflower production
We have found that sunflower seed coat is one of the major tissues where soil and seed-borne fungi inocula aggregate, aiding in the rapid and long-distance spread of diseases aside from the use of farm tools in multiple farms
Summary
Sunflower (Helianthus annuus L.) is one of the top oilseed crops grown for their edible oil. A number of soil- and seed-borne fungal pathogens and other phytopathogenic microorganisms negatively affect the sunflower cultivation and seed production. Pathogens 2020, 9, 29 causing huge economic losses of sunflower production [3,4]. Fusarium spp. and Verticillium spp. infect plant roots and expand via the vascular system causing severe leaf wilting, stunted plant growth, and vascular discoloration [5]. Due to the high economic value of sunflower seeds, poor irrigation system, and salty and alkali soil conditions, successive cropping is the main farming system in this region. This causes a gradual increase in pathogen inoculum in the soil, soil-borne diseases such as sunflower verticillium wilt (SVW) and sunflower fusarium wilt (SFW)
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