Determination of Resistance to Phytophthora infestans on Potato Plants in Field, Laboratory and Greenhouse Conditions

Abstract

An experiment was conducted to determine the host resistance of potato against Phytophthora infestans for twenty-five potato genotypes in 2010 and 2011 at Khumaltar, Lalitpur, Nepal using four assays: three for foliage resistance (field, whole-plant and detached leaf) and one for tuber resistance (tuber slice). An isolate of P. infestans collected from Lalitpur (LPR-1) was used for inoculation at a concentration of 3 x 10 3 sporangia ml -1 in all assays. Infected foliage area in the field and whole-plant assays, lesion size on detached leaves, and colony growth on tuber slice were all individually converted to 0-9 interval scale for susceptibility. Field assessment, considering the most robust measure of resistance, was used as benchmark for comparing the other assays. Sixteen of the genotypes had very little disease in the field (scale value <1) indicating they were probably expressing race-specific resistance, which has historically been short lived. Susceptibility levels measured in the whole-pant assay were highly correlated (r = 0.90) with converted field scale values, although the correlation was lower for the detached leaf assay (r = 0.63) and least for tuber-slice assay (r = 0.46). Low correlation in the detached leaf assay was assumed to represent lower resolution of the single-cycle assay. Low correlation in the tuber assay may have also reflected genetic differences as foliage and tuber blight resistance are not always correlated. Genotypes with extreme resistance in the field were frequently identified as having partial resistance in the other assays, which could mistakenly be interpreted as more durable field resistance. The consequences for selecting durable resistance are discussed.

REACTION OF POTATO CULTIVARS AND CLONES TO Phytophthora infestans

“…The detached leaflet method was moderately correlated with the field test, for disease severity. According to Sharma et al (2013), a moderate correlation of resistance of potato genotypes to P. infestans was also found between the detached leaflet and field trial assays. However, in this study, genotypes with high resistance in the field were identified as having a lower level of resistance in the leaflet test when it was inoculated with the more aggressive isolate, suggesting caution in the results of the detached leaflet test.…”

Greater aggressiveness in the 2_A1 lineage of Phytophthora infestans may partially explain its rapid displacement of the US‐1 lineage in east Africa

“…This study did not fully reflect the conditions of whole tuber infections because the standard tuber slice technique was used, which did not include initial infection through the tuber skin. However, both techniques have been reported to successfully separate resistant from susceptible potato varieties (Sharma et al ., ). Despite the lack of statistical relationship between foliar and tuber blight, the current tuber slice assay analysis did reveal variations in aggressiveness of the isolates, and it is noteworthy that the least aggressive isolates in the detached leaf assays had minimal colony sizes on the tuber slices.…”

“…The assay was adapted from the method described by Sharma et al (2013). Medium-sized potato tubers of cvs Kachpot-1 and Sarpo Mira without any visual symptoms of infection of P. infestans or other disease were harvested from the screenhousegrown plants in Uganda and used for this assay.…”

“…The procedure was to use a detached leaf assay experiment adapted from Knapova & Gisi (2002) that involved placing inoculum on the abaxial leaflet surface, followed by incubation under favourable conditions for pathogen infection, development and establishment. Equally, a tuber slice assay adapted with slight modifications from Sharma et al (2013) was used.…”

Ketahanan Lapangan Klon-Klon Kentang Hasil Persilangan terhadap Penyakit Busuk Daun

“…Kuhl et al (2007) juga melaporkan bahwa gen Rb dapat menciptakan ketahanan penyakit busuk daun pada kultivar kentang yang rentan. Percobaan lapangan diperlukan untuk membuktikan efektivitas gen Rb karena karakterisasi molekuler serta pengujian di tingkat laboratorium dan rumah kaca tidak menjamin munculnya fenotipe tahan di kondisi lapangan (Sharma et al 2013, Kuhl et al 2007 Perakitan varietas tahan terhadap penyakit busuk daun menjadi salah satu tujuan penting dalam pemuliaan kentang, akan tetapi seringkali klon unggul yang tahan penyakit busuk daun tidak mendapat penerimaan pasar dan konsumen, sehubungan dengan morfologi umbi. Morfologi umbi menjadi pertimbangan tersendiri oleh konsumen, termasuk untuk kepentingan industri olahan.…”