Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: January 5, 2004
Publication Date: May 25, 2004
Citation: Bell, A.A., Medrano, E.G., Jones, M.A. 2004. Frequency and pathogenicity of microorganisms associated with cotton seed rot in South Carolina. In: Proceedings of the Beltwide Cotton Conferences, January 5-9, 2004, San Antonio, Texas. 2004 CDROM. Interpretive Summary: During the past four years (2001-2004), a seed rot of cotton has occurred extensively (5-40% of the bolls) in the southeastern states of the USA Cotton Belt. Various isolation and inoculation techniques were used to identify pathogens associated with the seed discoloration in cotton bolls that otherwise appeared healthy. Five fungal species and three bacterial species obtained from affected bolls, were shown to cause a similar seed rot when introduced through puncture wounds similar to those caused by stink bugs and plant bugs. No infection occurred without wounds. The most prevalent pathogens were two species of Pantoea, a bacterial pathogen. The results indicate that pathogens introduced and possibly transmitted by bugs are responsible for cotton seed rot.
Technical Abstract: More than 50% of bolls from 'Acala Maxxa' cotton grown at the Pee Dee Research Station in South Carolina showed internal discoloration and rot of seed without external symptoms on the boll. Various isolation and inoculation techniques were used to identify pathogenic fungi and bacteria associated with seed discoloration. The number of pathogenic fungal isolates obtained asceptically from ca. 60 bolls were: Phoma exigua, 20; Verticillium nigrescens, 13; Alternaria alternata, 7; Fusarium semitectum, 1; and Curvularia lunata, 1. The number of pathogenic bacterial isolates obtained from 20 seeds, each from different bolls, were: Pantoea agglomerans, 10; a bacterium putatively identified as Pantoea stewartii, 4; and Agrobacterium tumefaciens, 2. Each of these pathogens, when introduced through puncture wounds (28 gauge needle), caused seed rot similar to that found in young and middle-aged bolls in the field. None of these pathogens infected bolls through intact or scratched sutures, nectaries, bracts, or calyxes or through punctured peduncles. The same pathogens caused spotting of fiber, tight locks, or completely macerated and discolored locks depending on the age of bolls at infection. The seed rot in Acala apparently was due to a large variety of pathogens taking advantage of boll wounds that disrupted the endocarp, such as wounds caused by Lygus bugs or boll weevils.