First Report of Pythium paroecandrum on Lupinus havardii.

ABSTRACT

Lupinus havardii Wats. (Big Bend Bluebonnet), a plant native to Texas, has been tested extensively for greenhouse production as a cutflower crop (1). Disease symptoms were observed on L. havardii plants grown in Las Cruces, NM, during two consecutive years. Plants were grown in Metro Mix 200 and watered by an automatic irrigation system every 3 days. During the growing season, which extended from September through February, 6% of mature plants (10-week-old plants) became chlorotic, wilted, and died. The first symptoms were observed during December 1998, when greenhouse temperatures were from 10 to 13°C. During the rest of the growing season, from February to July, only one plant became diseased, during May 1999, and the plant died within 1 week after greenhouse temperatures reached 20 to 25°C. Diseased plants were examined, and root, crown, and stem rot were found. Pythium paroecandrum Drechs. (2) was isolated routinely from infected tissues. Koch's postulates were fulfilled after plants were inoculated with oospores and mycelia of P. paroecandrum. Inoculum was applied next to the crown of 6-week-old plants in the form of water-agar plugs and a suspension that contained P. paroecandrum oospores and mycelia. Plants were maintained at 20 to 25°C. After 10 days, symptoms were similar to those previously observed, and the pathogen was reisolated from necrotic lesions observed on stems and crowns. Disease developed slower on 6-week-old plants (inoculated) than on 10-week-old plants (naturally infected). This is the first report of P. paroecandrum on L. havardii. References (1) W. A. Mackay and T. D. Davis. HortScience 33348, 1998. (2) A. J. Van der Plaats-Niterink. Monograph of the genus Pythium. Studies Mycol. 211, 1981.