|Kousik, Chandrasekar - Shaker|
|PARADA, C - North Carolina State University|
|QUESADA-OCAMPO, L - North Carolina State University|
Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/17/2015
Publication Date: 5/6/2015
Publication URL: http://doi:10.1094/PHP-BR-15-0005
Citation: Kousik, C.S., Parada, C., Quesada-Ocampo, L. 2015. First report of phytophthora fruit rot on bitter gourd (Mormodica charantia) and sponge gourd (Luffa cylindrica) caused by phytophthora capsici. Plant Health Progress. 16:93-94.
Interpretive Summary: Luffa sponge (smooth gourd) and bitter gourds (bitter melon) are specialty vegetables in the cucumber family (known as Cucurbitaceae) that are cultivated in the United States on a small scale for select markets. Luffa gourds are also grown for the sponge obtained from dried fruit for personal hygiene and skin care. During September of 2014, 19 days of rainfall produced over 27 cm of rain that resulted in the rot of over 50% of the fruit of bitter gourd and over 25 % on sponge gourd in a field in Charleston, SC. The microbe causing the fruit rot was identified using microscopy and molecular tools. Prior to this study, it was not known if this microbe, known as Phytophthora capsici, could cause fruit rot of bitter gourd. Knowledge of the microbe causing the rot will be useful to suggest appropriate strategies to growers and extension agents to help manage the rot in areas where the gourds are grown for select markets.
Technical Abstract: Luffa sponge (smooth gourd) and bitter gourds (bitter melon) are specialty cucurbit vegetables cultivated in the United States (US) on a small scale for select markets. Luffa gourds are also grown for the sponge obtained from dried fruit for personal hygiene and skin care. These two cucurbits produce vines and are generally grown on a trellis to allow the fruit to grow straight, but some growers have eliminated the trellis and use raised beds to lower production costs. As a part of a project to monitor powdery mildew pathotypes present in South Carolina, we have been growing various cucurbits including: pumpkin, squash, melon, bitter gourd, squash, and ridge gourds for the past 5 years on raised plastic mulched beds. During September of 2014, 19 days of rainfall produced over 27 cm of rain that resulted in the rot of over 50% of the fruit of bitter gourd variety ‘Bitter Green Long’ and over 25 % on sponge gourd variety ‘Harita’ in a field with no history of fruit rot. The rotting fruits were in contact with the soil in most cases. Earlier reports from the US have indicated that Luffa fruit touching or close to the ground can rot, however, the causal organism is generally not specified. Microscopic examination of rotting fruit revealed presence of abundant oomycete sporangia. The pathogen was isolated on V8 Juice agar amended with antibiotics and identified as Phytophthora capsici based on sporangia morphology and amplification of the ITS region using specific polymerase chain reaction (PCR) primers. Further confirmation of the pathogen as P. capsici was done by PCR amplification and sequencing of 12 specific regions using four isolates from bitter gourd and three from sponge gourd. We observed 100% similarity to known P. capsici sequences in the National Center of Biotechnology Information (NCBI) data base for the following regions: Cox1 (reference sequence: AB688175.1), Cox2 (JN618617.1), Nad1 (DQ361203.1), Nad5 (HQ726266.1), ß-tubulin (HQ389125.1 & EU080406.1), EF1 (HQ388948.1), Enolase (KF305195.1), HSP090 (HQ725985.1), TigA (HQ388987.1), Ura3 (HQ389053.1 and EF617414.1), ITS5 (KM369965.1), and ITS6 (KM496492.1 and KM369965.1). The sequences for these regions have been submitted to the NCBI data base. Four isolates collected from bitter gourd belonged to P. capsici A2 mating type. Both A1 and A2 mating types were isolated from sponge gourd fruit. Fruits of bitter gourd and sponge gourd were surface sterilized and arranged randomly in four replications with five fruits per replication in a humid chamber. Fruits were inoculated with agar plugs (7 mm) from actively growing colonies of P. capsici isolated from the respective rotting fruit as described previously. Five days after inoculation fruit rot identical to what was observed in the field developed on both cucurbits. Phytophthora capsici was re-isolated from edges of rotting lesions of inoculated fruit. The experiments were repeated with similar results. Sixty-five percent of 4-wk old bitter gourd and 100% of squash (Cucurbita pepo; susceptible variety, Early Prolific Straight Neck) seedlings succumbed to crown rot when inoculated with P. capsici (5 ml, 104 zoospores ml-1/seedling) isolated from the fruit. Crown rot was not observed on sponge gourd seedlings that were similarly inoculated. Phytophthora capsici has been reported to infect crops belonging to 27 families including several members of Cucurbitaceae. However, P. capsici has not been reported on bitter gourd before. Similarly P. capsici has not been reported on sponge gourd in the U.S. However, it was isolated from a rotting fruit from the market in Asia. Several fungicides that are effective in managing Phytophthora fruit rot of watermelon are also labelled for application on Mormodica spp. and edible gourds. In fields with a history of P. capsici these gourds may need to be sprayed,