| The worldwide distribution of Sclerotinia sclerotiorum is facilitated by the production of sclerotia capable of surviving adverse environmental conditions. However, the role of freezing as a regulator of germination in S. sclerotiorum is not well understood and past literature is in conflict with observations in natural environments. This study assessed the effects of freezing on carpogenic germination (CG), myceliogenic germination (MG), and cell damage of sclerotia in in vitro and in vivo conditions, and subsequent changes in susceptibility of sclerotia to parasitism by Coniothyrium minitans . Freezing at -12°C for 28 days did not reduce CG of either of two isolates tested in sterile conditions, even with cell damage and MG as high as 75% and 50%, respectively. Isolate 274 was more susceptible to freezing damage than isolate ZQ 35-10, and CG was hastened in isolate 274 when cell damage ranged from 12-75%. However, the freeze-damaged isolate 274 was also more susceptible to parasitism by C. minitans and antagonism in natural soils relative to unfrozen sclerotia, whereas frozen sclerotia of isolate ZQ 35-10 were not more susceptible. Furthermore, a comparison between contrasting field environments suggested that soils can differ in their effects on both CG of damaged sclerotia and the effectiveness of C. minitans as a biological control. These results have implications for understanding the variable survival of sclerotia of S. sclerotiorum and the variable efficacy of C. minitans. Variability among freezing studies is discussed and a new framework is presented for understanding the relationships among cell damage, MG, and CG in frozen sclerotia of S. sclerotiorum. |
