An in vitro co-culture system for rapid differential response to Fusarium oxysporum f. sp. vasinfectum race 4 in three cotton cultivars.

Fusarium oxysporum f. sp. vasinfectum race 4 (FOV4) is a devastating fungus pathogen that causes Fusarium wilt in both domesticated cotton species, Gossypium hirsutum (Upland) and G. barbadense (Pima). Greenhouse and field-based pathogenicity assays can be a challenge due to non-uniform inoculum levels, the presence of endophytes, and varying environmental factors. Therefore, an in vitro co-culture system was designed to support the growth of both domesticated cotton species and FOV4 using an inert polyphenolic foam substrate with a liquid medium. A Fusarium wilt-susceptible Pima cotton cultivar, G. barbadense 'GB1031', a highly resistant Pima cotton cultivar, G. barbadense 'DP348RF', and a susceptible Upland cotton cultivar, G. hirsutum 'TM-1', were evaluated for 30 days during co-culture with FOV4 in this foam-based system. Thirty days after inoculation, disease symptoms were more severe in both the susceptible cultivars, which displayed higher percentages of foliar damage, and greater plant mortality, than observed in 'DP348RF', the resistant Pima cotton cultivar. This foam-based in vitro system may be useful for screening cotton germplasm for resistance to a variety of fungus pathogens and to facilitate the study of biotic interactions in domesticated cotton species under controlled environmental conditions.