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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Sustainable Agricultural Systems Laboratory » Research » Publications at this Location » Publication #321063
Title: Factors associated with Leguminous Green Manure Incorporation and Fusarium wilt suppression in watermelon

Author
item HIMMELSTEIN, JENNIFER - University Of Maryland
item Maul, Jude
item BALCI, YALMAZ - University Of Maryland
item EVERTS, KATE - University Of Maryland

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/28/2015
Publication Date: 5/5/2016
Citation: Himmelstein, J., Maul, J.E., Balci, Y., Everts, K.L. 2016. Factors associated with Leguminous Green Manure Incorporation and Fusarium wilt suppression in watermelon. Plant Disease 100 (9). Scientific Societies: 1910-20. doi:10.1094/PDIS-08-15-0956-RE.

Interpretive Summary: Watermelon represents a vital part of the eastern seaboard agricultural landscape from Georgia to the Delmarva Peninsula. As market preference has shifted from seeded to seedless varieties, growers have had to rely on watermelon varieties that lack the Fusarium wilt resistance they were accustomed to with the hybrid seeded varieties. Farmers on the Eastern Shore of Maryland and Delaware observed what appeared to be disease suppression of Fusarium wilt on watermelon following a legume cover crop (Hairy Vetch and Crimson Clover), and communicated these observations to our research team at field days and farmer meetings. We designed research plots to emulate the field conditions farmers were experiencing and tested their field observations in replicated plots at various locations around Maryland and the Delmarva Peninsula. We found that winter annual leguminous cover crops such as Hairy Vetch and Crimson Clover, grown over the preceding winter, suppressed Fusarium wilt on watermelon. We tested cover crop pre-treatments under conditions in which we inoculated the root systems of the watermelon with Fusarium wilt and still found that the legume cover crops suppressed the occurrence of disease. These results showed that crop rotations that include leguminous cover crops such as Hairy Vetch and Crimson Clover can suppress Fusarium wilt. This information can be used by scientists working on developing cover crops as sustainable multi-functional tools for farmers nation wide.

Technical Abstract: A fall planted Vicia villosa cover crop incorporated in spring as a green manure can suppress Fusarium wilt [Fusarium oxysporum f. sp. niveum (FON)] of watermelon in Maryland and Delaware. Experiments were conducted to determine whether the mechanism of this suppression was general or specific, and to evaluate the efficacy of the biocontrol Actinovate. General suppression was examined in the field by assessing the effects of cover crop green manures (V. villosa, Trifolium incarnatum, Secale cereale, and Brassica juncea) on soil respiration, presence of F. oxysporum spp., and arbuscular mycorrhizal (AM) colonization of watermelon. Cover crop treatments V. villosa, T. incarnatum, and S. cereale, and no cover crop were evaluated both alone and in combination with Actinovate in the greenhouse. Additionally, in vitro experiments were conducted to measure the effects of cover crop leachate on the mycelial growth rates of FON, Trichoderma harzianum, and on Streptomyces lydicus. Soil microbial respiration was significantly elevated in V. villosa and T. incarnatum treatments, both preceding and following green manure incorporation, and was significantly, negatively correlated with Fusarium wilt, suggesting that microbial activity was higher under the legumes, which has been suggested as a mechanism for general suppression. Parallel to this, in vitro growth rates of FON and T. harzanium on V. villosa leachate amended media were 66% and 213% greater, respectively, than on non-amended plates. The Fusarium oxysporum spp. population (not differentiated into races), significantly increased in V. villosa amended field plots. Additionally, the percentage of watermelon roots colonized by AM following V. villosa and T. incarnatum green manures was significantly higher than in watermelon following bare ground (58% and 44% higher, respectively). In greenhouse trials where cover crops were amended to soil, Actinovate did not consistently reduce Fusarium wilt. ur results suggest that both general and specific disease suppression play a role in reducing Fusarium wilt on watermelon.