THE ROLE OF ICE NUCLEATION ACTIVE BACTERIA IN FROST DAMAGE TO EARLY SOWN Solanum tuberosum var. JERSEY ROYAL

Abstract

The present study indicated that S. tuberosum var. Jersey Royal could supercool to temperatures as low as -6ºC during in-vitro frost tests, whereas in the field freezing occurred at immediate sub-zero temperatures (between 0 and -1ºC). The microbial flora upon the early. sown S. tuberosum var. Jersey Royal did not contain INA bacterial species active at warm sub-zero temperatures. Plants inoculated with a strain of Ps. syringae (84:27) containing type 1 active nuclei readily froze at -2 to -3ºC. Applications of leaf surface water applied to plants during in-vitro frost tests resulted in nucleation temperatures comparable to those measured in the field. Applications of leaf surface water initiated freezing in whole plants during in-vitro frost tests at temperatures warmer than those caused by Ps. syringae (84:27). Thus field frost kill and ice nucleation in the presence of leaf surface water occurred at temperatures warmer than type 1 INA bacterial nucleation temperatures. Exogenous foliar applications of ethylene glycol applied in the presence of leaf surface water led to enhanced supercooling and frost avoidance during in-vitro frost tests and during field frost events. It was concluded that modifying the formation and freezing of leaf surface water would be more likely to provide a frost control strategy applicable to the field crop than frost control through manipulation of phylloplane microorganisms.