VIEW ARTICLE

Heat-Induced Ultrastructural Changes in Germinating Spores of Rhizopus stolonifer and Monilinia fructicola. James E. Baker, Research Plant Physiologist, ARS, USDA, MQ, Pioneering Research Laboratory for Postharvest Physiology and Horticultural Crops Research Branch, Plant Industry Station, Beltsville, Maryland 20705; Wilson L. Smith, Jr., Research Plant Pathologist, ARS, USDA, MQ, Pioneering Research Laboratory for Postharvest Physiology and Horticultural Crops Research Branch, Plant Industry Station, Beltsville, Maryland 20705. Phytopathology 60:869-874. Accepted for publication 18 December 1969. DOI: 10.1094/Phyto-60-869.

Germinating sporangiospores of Rhizopus stolonifer showed striking ultrastructural changes after exposure to nutrient broth at 52 C for a period of 2.5 min. Nuclei were either disrupted or very granular and disorganized. Mitochondria were distorted or disrupted. The ribosomes, normally distributed rather uniformly throughout the cytoplasm, tended to aggregate. The plasmalemma, while appearing relatively intact, was frequently withdrawn from the spore wall. Effects of heat-treatment on the ultrastructure of germinating conidiospores of Monilinia fructicola were qualitatively similar, but not as extreme as the effects described for the Rhizopus spore. Globular-shaped bodies were observed in some unheated Rhizopus sporangiospores during early stages of germination. These bodies consisted of regularly-spaced granules about 50-60 å in diam.