An Assessment of Potato (Solanum tuberosum L.) Varietal Tolerance to Bacterial Soft Rot (Pectobacterium caratovorum subsp. carotovorum) Disease

Abstract

Potato production in Zimbabwe is an important element of the Agricultural Production sector. The local industry is however affected by low yields due to soft rot disease (Pectobacterium carotororum subsp carotovorum) and poor quality produce. The main thrust of this study was to come up with recommendations that would increase potato production through improved knowledge of cultivar choices according to ranked performance in terms of soft rot infestations. Four experiments were conducted, in the field; in the greenhouse, in storage at 100C and at room temperature on soft rot inoculated and uninoculated potato tubers. The experiments were carried out on five locally available varieties in Zimbabwe. Seeds were screened for soft rot infection using counts and weights of infected tubers and BP1 showed significant difference (p<0.05) interms of soft rot infestation on counted tubers. The field experiment treatments of Amethyst, Mnandi, BP1, Montclare and Jasper were laid in Randomised Complete Block Design (RCBD). Germination percentages for planted varieties were recorded and Jasper had 70.3%, Amethyst had 56.7%, Mnandi had 57.7%, BP1 had the lowest percentage of 50.7% and Montclare had 55.5%. On the Area under Disease Progress Curve (AUDPC) for potato blight BP1 was significantly different (p<0.05) from other varieties as it was most infected by early blight. For disease scores, incidence of soft rot on harvested tubers BP1 and Amethyst displayed significant difference (P<0.05) as they were more susceptible to the disease. The greenhouse pot experiment had five soft rot inoculated and uninoculated potato tubers and treatments were laid in Complete Random Design (CRD). Percentage emergence for inoculated pots was below 50% for all varieties except for Diamond which was less suceptible to soft rot and had 83.3% germination. Emergence was above 83% in uninoculated pots across all varieties. For Amethyst a significant difference (p<0.05) was observed as there was zero emergence for soft rot inoculated pots. In the storage experiment, three tubers per variety of the five cultivars were placed in a polythene bag and replicated 3 times. The soft rot inoculated tubers were stored at 100C and at room temperature an uninoculated treatment was included as the control. Weekly weight (g) reading were collected and the weights showed significant differences (p<0.05) as soft rot infestation was more at room temperature in the first week than at 100C for BP1 and Mnandi varieties. Soft rot was expressed in week four and five at 100C and a significant difference (p>0.05) was observed. Specific gravity of soft rot inoculated and uninoculated tubers at room temperature indicated more weight reduction and a significant difference (p<0.05) was indicated on Amethyst and Montclare varieties than specific gravity weight at 100C which showed no weight reduction hence there were significant difference (p>0.05) amongst varieties. Tubers were graded after harvesting and BP1 had the largest tuber size 31.1% and Amethyst at 8.82% .The least susceptible varieties to soft rot disease were Diamond and Montclare. BP1 variety showed the most susceptibility in storage. This study shows that BP1 variety rank in the potato seed certification industry needs to be revised according to soft rot tolerance to update previous ranks of the cultivar; farmers are advised to adopt new cultivars and have reliable seed sources.