Temperature-Dependent Development of Pasteuria penetrans in Meloidogyne arenaria

Abstract

Pasteuria penetrans is a promising biological control agent of plant-parasitic nematodes. This study was conducted to determine effects of temperature on the bacterium's development in Meloidogyne arenaria. Developmental stages of P. penetrans were viewed with a compound microscope and verified with scanning electron microscopy within each nematode at 100 accumulated degree-day intervals by tracking accumulated degree-days at three temperatures (21, 28, and 35ºC). Five predominant developmental stages of P. penetrans were identified with light microscopy: endospore germination, vegetative growth, differentiation, sporulation, and maturation. Mature endospores were detected at 28, 35, and 90 calendar days at 35, 28, and 21ºC, respectively. The number of accumulated degree-days required for P. penetrans to reach a specific developmental stage was different for each temperature. Differences were observed in the development of P. penetrans at 21, 28, and 35ºC based on regression values fitted for data from 100 to 600 accumulated degree-days. A linear response was observed between 100 to 600 accumulated degree-days; however, after 600 accumulated degree-days the rate of development of P. penetrans leveled off at 21 and 28ºC, whereas at 35ºC the rate decreased. Results suggest that accumulated degree-days may be useful only in predicting early-developmental stages of P. penetrans. Key wards: bacterium, biological control, degree-days, development, endospore, life cycle, Meloidogyne arenaria, Pasteuria penetrans, root-knot nematode, scanning electron microscopy, temperature.