Effect of Temperature on Apothecial Longevity and Ascospore Discharge by Apothecia of Monilinia vaccinii-corymbosi

Abstract

Pseudosclerotia of Monilinia vaccinii-corymbosi with apothecial initials were collected from blueberry (Vaccinium corymbosi cv. Jersey) fields in Grand Junction, MI, in the spring of 2002 and 2003 and monitored during apothecial development and maturation. Apothecia with cup openings as small as 1.2 mm in diameter were able to discharge ascospores. The number of ascospores discharged increased exponentially as the diameter of the cup opening increased, before leveling off at a cup diameter of about 6 mm. Cytological studies showed that ascospore discharge correlated well with the stage of development of asci and ascospores in the apothecium. The effect of temperature on the longevity of apothecia was studied at 10, 15, 20, and 25°C. Initial ascospore discharge was greater for apothecia incubated at higher temperatures (20 and 25°C). However, total discharge was greater in apothecia incubated at lower temperatures (10 and 15°C), as they persisted longer than those incubated at 20 and 25°C. Incubating apothecia at freezing temperatures (-2, -4, -6, and -8°C) for 1 h resulted in a 50 to 98% reduction in the number of ascospores discharged compared with before freezing. However, apothecia incubated down to -6°C were able to recover their ability to discharge ascospores by 2 days after the freezing treatment. Ascospores discharged from apothecia after freezing at -2°C for 1 h remained viable. However, the germination ability of ascospores from apothecia frozen at -4, -6, and -8°C decreased with decreasing temperature such that only 10% of ascospores from apothecia frozen at -8°C germinated successfully. The information obtained in this study may be useful in the development of scouting and management strategies for the control of mummy berry disease.