Assessing the Incidences of Late Blight Disease on Irish Potato Varieties in Kisii County, Kenya

Background: Late Blight Disease, caused by the fungal pathogen, Phytophthora infestans, is a major constraint of Irish potato production in Kenya. The disease can destroy a crop, causing up to 100% yield loss. Small scale holder farmers in Kisii County continuously grow Irish potato that is susceptible to P. infestans which require a number of fungicides sprays. The study was formulated out of the realization that Irish potato plays a major role in food security and contributes to poverty alleviation. Also, the commonly used protectant fungicides for the crop are expensive, hazardous and are not effective against Phytophthora infestans.

Aim: To assess the incidences of late blight disease on Irish potato varieties in Kisii County, Kenya.

Study Design: The Irish potato farms were selected randomly following a line transect. Twenty nine stops at every ten kilometres were made, three potato farms around every stop were inspected for the presence of late blight infected Irish potato varieties. A total of eighty seven farms were inspected for the presence of late blight. Five late blight infected leaves from each farm were collected for examination in the laboratory.

Methodology: A random sampling method was used to collect late blight infected Irish potato plants from various farms along the transect routes. P. infestans were isolated, cultured on a potato dextrose agar and identified by microscopic techniques at National Agricultural Research Laboratories and Kenya Agricultural research and Livestock Organisation Kisii. An inoculum prepared was standardized to 1x107 sporangia/ml concentration using haemocytometer. Pathogenicity test was done on health Irish potato plants to confirm the pathogenicity nature of the Phytophthora infestans. The data collected was subjected to analysis of variance using GENSTAT directive version 12.0 and chi-square.

Place and Duration of the Study: Sampling was carried out in the month of April, May and June 2015 during the long rain season in Kisii County, Kenya.

Results: Late blight disease was found to be rampant in all the 87 farms inspected in the County. Late blight effect differed significantly at P<.001 among the Irish potato varieties assessed. There was no significant different among the farms inspected and this indicated that all farms visited were infected with late blight the same way. Along the transect routes six Irish potato varieties were identified notably Mang’ere (55.6%), Nyayo (17.2%), Tigoni (3.4%), Asante (3.4%), Shangi (10.3%) and Purple gold (10.3%).

Conclusion: Late blight disease remains a serious threat to Irish potato production causing significant yield and economic losses to farmers. The diversity of Phytophthora infestans in the region calls for the most sustainable approach for reducing late blight problem significantly and this would enable the farmers to get good yields from their Irish potato crop.