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Title: Reaction of Phytophthora fruit rot resistant germplasm lines to a broad range of Phytophthora capsici isolates from across the United States of America

item Kousik, Chandrasekar - Shaker
item Ikerd, Jennifer

Submitted to: Proceedings of the International Oomycete Conference
Publication Type: Abstract Only
Publication Acceptance Date: 12/1/2015
Publication Date: 12/8/2015
Citation: Kousik, C.S., Ikerd, J.L. 2015. Reaction of Phytophthora fruit rot resistant germplasm lines to a broad range of Phytophthora capsici isolates from across the United States of America. Proceedings of the International Oomycete Conference. pp 22.

Interpretive Summary: N/A

Technical Abstract: Phytophthora fruit rot limits watermelon production in most states in the Southeastern US (FL, GA, SC, NC and VA). It has also become a serious problem in recent years in northern states (IN, MD, DE). About 50% of the US watermelons are grown in the southeastern states where environmental conditions favorable for development of fruit rot are very common. The disease has caused serious yield losses to growers before and after harvest of the crop, resulting in loss of revenue especially in GA and NC. Identifying solutions to manage Phytophthora fruit rot has been considered a high priority by the National Watermelon Association (NWA) for the past few years (2013-2015). Previous research conducted in NC, SC and GA helped identify several effective fungicides (Revus, Presidio, Zampro) to manage Phytophthora fruit rot of watermelon. However, the prevalence of resistance to chemicals such as Ridomil and Ranman has been well documented for P. capsici in the US. Therefore it is necessary that we continue to identify new fungicides and develop rotation schemes and strategies to manage this serious production limiting factor for watermelon growers. Experiments to evaluate the effect of fungicide rotations on development of Phytophthora fruit rot of watermelon were conducted in Phytophthora capsici infested fields at three locations in southeastern US (North Carolina, South Carolina and Georgia) in 2014 and at two locations in 2015 (SC, GA). The mini seedless cultivar ‘Wonder’ was used in these trials. The seeded cultivar ‘Mickey Lee’ which is also susceptible to fruit rot was used as the pollenizer. Five weekly application of fungicides were made at all locations. The following fungicide rotations were evaluated: 1) Actigard/K-Phite/Revus/Presidio/Zampro; 2) Forum/Presidio/Phosphite/ Ranman+Ridomil/ Revus; 3) Actigard/Ranman+Ridomil/Presidio/ V10208/ Orondis (also known as OXTP or QGU-42); 4) Forum/K-Phite / Presidio /Zampro/Ranman; 5) Zampro with Orondis (QGU-42); 6) MELCAST based Spray of most effective fungicides in rotation (Presidio, Ranman+Ridomil, Revus, Zampro, Orondis). 7) Ridomil Gold (standard treatment); and 8) Non-treated control. Significant fruit rot was observed in the non-treated control plots in 2014 and 2015 across all three locations (Mean=68%). All the fungicide rotation schemes significantly reduced Phytophthora fruit rot compared to non-treated check at all three locations. Ridomil Gold was not as effective in SC due to presence of insensitive strains of P. capsici. However, it performed similar to other rotation schemes in NC and GA in 2015. Overall the rotation scheme of Zampro alternated with Orondis (also known as OXTP or QGU-42) was very effective across three locations. Revus (Mandipropamid) alternated with Presidio (Fluopicolide) was similarly effective in SC. Use of MELCAST helped reduce one spray in SC in 2014 but not in NC or GA. In 2015, MELCAST reduced one spray application in GA and SC and reduction in fruit rot was similar to other rotations. Application of Actigard or K-Phite during the early stages of fruit development may be useful for managing Phytophthora fruit rot followed by other fungicides. Though many fungicides are available for using in rotations schemes to manage Phytophthora fruit rot of watermelon, under very heavy rainy conditions and serious pathogen pressure the fungicides still may not be able to offer adequate protection.