PREVALENCE AND SEVERITY OF BACTERIAL SOFT ROT IN COMMONLY GROWN POTATO VARIETIES IN NYANGA DISTRICT, ZIMBABWE

Abstract

Potato (Solanum tuberosum L.) 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 greenhouse, in storage at 10 o C and at room temperature on soft rot inoculated and un-inoculated potato tubers. The experiments were conducted on five locally available varieties in Zimbabwe. Tubers were screened for soft rot infection using counts and weights of infected tubers and BP1 showed significant difference (p<0.05) in terms of soft rot infestation on counted tubers. The field experiment treatments of Amethyst, Mnandi, BP1, Montclare and Jasper were laid in Randomized Complete Block Design (RCBD). The Area under Disease Progress Curve (AUDPC) for potato late blight recorded was highest for BP1 (10.04%) and least for Jasper (6.81%). Amethyst and BP1 varieties recorded the highest (5.0%) incidence for tuber soft rot. The greenhouse pot experiment had five soft rot inoculated and un-inoculated potato tubers and treatments were laid in Complete Random Design (CRD). Percentage emergence for inoculated pots dropped by more than 75% relative to the un-inoculated plot for BP1, Montclare and Mnandi varieties. Amethyst recorded a 100% drop in germination for the inoculated plots. Mnandi had the highest (41.37%) proportion of tubers from small and below grade. On the other hand, variety BP1 had the highest (80.01%) proportion of tubers from medium size and above. Tuber yield was highest for Jasper (34.01t/ha). 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 varieties and have reliable seed sources.