Enumeration of ice nucleation active bacteria and severity of frost injury (embun upas) on potato in Wonosobo, Dieng Plateau

Abstract

The altitude of the Dieng plateau is between 1,500-2,500 meters above sea level (m ASL), with an average temperature of 14°C. During the dry season, the temperature in this area becomes very cold that reaches -2°C, therefore frost injury may occur in potato, which is often referred to as embun upas (frozen dew). Frost injury causes the production of potatoes in Dieng to decline. Frost injury in plants is characterized by spots symptom, which can be brown, yellow, or black on leaves surface with the chlorotic ring that surrounds them. The phenomenon of frost injury is thought to be related to the activity of ice formation by the Ice Nucleation Active (INA) bacteria and triggered by cold temperatures (-2°C). This study aimed to determine the number of INA bacteria and its correlation with frost injury spots on potato leaves and to discover the class of INA bacteria based on ice formation temperature. The sampling of the potato leaves used purposive sampling method. Leaves showed frost injury symptom with different severity were taken from a different altitude of ± 2,000 m ASL (Dieng Wetan village) and ± 2,500 m ASL (Sembungan village). Bacterial isolation was done by spread plate method on Nutrient Agar supplemented with 2.5% glycerol. The activity of ice nucleation was determined using tube nucleation method. Estimation of INA bacteria number was done by multiple-tube nucleation method 3.3.3. Correlation between the number of INA bacteria and percentages of frost injury spots was analyzed using SPSS bivariate. The results showed that the highest INA bacteria number i.e. >2.75 × 104 was found on scale 3 of leave spots while the lowest value of 7.25 × 103 on scale 1. Correlation between the populations of INA bacteria with the scale of frost injury spots showed 0.844. The correlation values ranging from 0.80 to 1.00 indicating a strong association between the INA bacterial number and the scale of frost injury spots of potato leaves. Based on the ice forming temperatures, INA bacteria were classified into three classes, i.e., class A that can freeze water at temperatures of -2 to -4°C, class B -5 to -7°C and freezing point of class C below -8°C.