Identification of potato genotypes resistant to, occurrence of latent infection and races of Pseudomonas solabacearum in Uganda

Studies were conducted for three seasons to screen 26 potato genotypes for resistance to bacterial wilt, study the occurence of latent infection in potato seed tubers and common weeds on hihland Uganda; and characterise isolates of the bacterium in terms of races. Bacterial wilt is incited by pseudomonas solanacearum (synony. Burkholderia solanacearum, Ralstonia solanacearum). This write up has adopted the old name of the pathogen, i.e., P. solanacearum. Infested plots were used for screening the 26 genotypes. To ensure no disease escape, the same plots were used for 3 consecutive seasons. In addition, inoculum level was increased by planting tomatoes (cv Marglobe) between the seasons. All the 26 genotypes succumbed to bacterial wilt, but disease incidence and severity varied with location and potato genotype. Low levels of becterial wilt appeared in highlands (Kachwekano), but severe bacterial wilt was recorded in the two land locations (Kabanyolo and Kawanda). Based on lowland locational severity means, genetypes Rosita, 720144, Cruza and 382575.5 were considered resistant, while 387201.7, 388572.6, 388572.2, Kisoro, 390016.1 and 388580.18A were moderately resistant. The most susceptible genotypes were Kabale, Rutuke, 388576.10, 382171.10, and 381406.7 which recorded 100% wilt and no yields. Occurrence of latent I fections in potato seed tubers with and without storage, and in weeds form potato and fallow fields were tested using the incubation and Kelmans media techniques. Potatoes form the highland were latently infected. Hence potato sedd tubers should be tested for bacterial latant infection before sale to farmers. Storing and incubation of potatoes increased detection of latent infection as bacterial ooze, but didn’t improve detection using Kelman’s media. Typical virulent colonies of P. solanacearum were obtained form herbaceous weeds from both potato fields and fallow plots. Oxalis Latifolia, Amaranthus sp., Rummex abyssinicum, Spergula arvensis, Ageratum conyzoides, Galinsonga perviflora, Tagetes minuta, Leucas martinicensis, Erigeron floribundus, Bidens pilosa, Stellaria sennii and polygonum napalense were infected. However, no bacteria colonies were isolated form grass weeds. Thus, herbaceous weeds probably play a significant role in the survival of P.solanacearum, wheat, could ne included in rotation management of this disease in Uganda. Isolates of pseudomonas solanacearum from lowland and highland Uganda were classified into races. Isolates from the highland area belonged to race 3 and those from the lowland areas were all race 1. Two isolates from highlands did not fit into race 3 or race 1.