Effect of Host Resistance on Foliar Late Blight Severity, Disease Development and Progress on Selected Irish Potato Varieties in Kenya

Abstract

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 fungicide sprays. This 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 late blight disease are expensive, hazardous and are not effective against P. infestans. Aim: To evaluate the effect of host resistance to foliar late blight severity, disease development and progress on selected potato varieties under field and glasshouse conditions in Kisii County, Kenya. Study Design: Nine potato varieties (Tigoni, Meru red, Kenya mpya, Sherekea, Shangi, Purple gold, Asante, Mang’ere and Nyayo) were grown in the field and glasshouse following a randomized complete block design.  Place and Duration of the Study: This research was carried out in Kisii County, Kenya between January 2015 and September 2015. Methodology: Late blight infected Irish potato leaves were collected from the field. Field symptoms of late blight were used to identify the diseased leaves. In the laboratory isolation and identification was done using culture and microscopic techniques. Phytophthora infestans inoculum was prepared using pure culture, standardized to 1x107 sporangia/ml concentration using haemocytometer. Pathogenicity test was done to confirm pathogenicity of the pathogen. Ten millimetres of the inoculum was sprayed on each healthy potato plant. Disease development and progress was monitored, and the area under disease progress curve was used to score the severity of late blight progress on various potato varieties. The relative area under disease progress curve was also used to compare data from different experimental plots. Data collected was analysed by analysis of variance using GENSTAT directive Version 12.0. Treatment means were separated using significant difference test at P<.001. Results: Irish potato varieties from various experimental plots showed varied reaction to 1x107 sporangia/ml concentration P. infestans inoculum in both the field and glasshouse. Late blight severity differed significantly among various Irish potato varieties. The results showed that Sherekea had better tolerance of 7.0 (0.003) in the glasshouse and 468.0 (0.223) in the field to late blight. Mang’ere showed high susceptibility of 630.0 (0.3) in the glasshouse and 2093.0 (0.997) in the field to late blight. The major finding was that Sherekea can yield despite being infected by late blight disease. Conclusion: Late blight disease remains a serious threat to Irish potato production causing significant yield and economic losses to farmers. It is suggested that growing Sherekea variety could significantly reduce late blight yield losses.