Minimal Growth Temperature of Pasteuria penetrans 1

Pasteuria penetrans is an obligate, mycelial, and endospore-forming bacterial parasite of Meloidogyne spp. with promise for the management of root-knot nematodes. Our objective was to use regression analysis of developmental time (days) to various temperatures to determine the minimal temperature for growth and development of P. penetrans in Meloidogyne spp. The data set for regression originated from a previously published report. The data fit well to hyperbolic equations. For various developmental stages of P. penetrans, the minimal growth temperature ranged from 16.7 °C to 17.8 °C and averaged 17.2 °C. Key wards: bacterium, biological control, degree-day, developmental threshold, endospore, Meloidogyne spp. , minimM growth temperature, Pasteuria penetrans, root-knot nematode, temperature. Pasteuria penetrans (Thorne) Sayre & Starr is an obligate, mycelial, and endosporeforming bacterial parasite of Meloidogyne spp. that has shown potential as a biological control agent against root-knot nematodes (Chela et al., 1996; Dickson et al., 1994). Future successful use of the organism depends on our ability to manipulate its development. Pasteuria penetrans has not been grown on artificial media (Bishop and Ellar, 1991). Currently, the parasite must be reared on Meloidogyne spp. , which, in turn, must be reared on susceptible plants (Sharma and Stirling, 1991) or in a nematode-root explant system (Verdejo andJaffee, 1988). The former method, using potted tomato plants in a greenhouse or growth chamber, is widely used for production of endospores of P. penetrans. Several factors have been shown to affect the development of P. penetrans in such culture. Ammonium nitrate is capable of slowing the development of P. penetrans (Z. X. Chen and D.W. Dickson, unpubl.), and some chemicals, such as chloropicrin and methyl bromide, prevent development but do not prevent attachment (Freitas, 1997). However, the most important factor affecting development may be temperature (Hatz and Dickson, 1992; Serracin et al., 1997). Bacteria have a characteristic optimal Received for publication 3 February 1997. a Florida Agricultural Experiment Station Journal Series No. R-05582. Supported in part by Southern Region IPM Grant No. 93-34103-8396. 2 Graduate Research Associate, and 3 Professor, Entomology and Nematology Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL, 32611O620. E-mail: dwd@gnv.ifas. ufl.edu growth temperature at which they exhibit their highest growth and reproduct ion rates, a minimal growth temperature below which they are metabolically inactive and do not demonstrate growth, and an upper temperature limit beyond which they ~fail to grow (Atlas and Bartha, 1993). Both the optimal growth temperature and the ranges of temperatures that microorganisms can tolerate determine their distribution and ecological significance (Atlas and Bartha, 1993). The production of endospores increases with temperatures above 20 °C, and an optimum temperature for growth has been reported as 35 °C (Hatz and Dickson, 1992). The objective of this study was to provide further information on the temperature requirements of a Florida isolate of P. penetrans by determining the minimal growth temperature for its development. MATERIALS AND METHODS Data source: All data were derived from a publication by Hatz and Dickson (1992). The development of P. penetrans in the nematode pseudocoelom was categorized into nine stages as follows: A) early vegetative stage, B) later stage, C) mycelial branches, D) fragmentation, E) sporangial development, F) sporangium size increasing, G) endospore development, H) sporangia separation, and I) mature sporangium. The developmental time (days) for each stage at various temperatures was reported. Stages A, C, D, F, H, and I were selected for this study because they are the most definitive growth stages.